U.S. patent application number 16/336873 was filed with the patent office on 2019-08-15 for integrated membrane solar fuel production assembly.
The applicant listed for this patent is HYPERSOLAR, INC., UNIVERSITY OF IOWA RESEARCH FOUNDATION. Invention is credited to Wei CHENG, Syed Mubeen Jawahar HUSSAINI, Joun LEE, Timothy YOUNG.
Application Number | 20190249313 16/336873 |
Document ID | / |
Family ID | 60022219 |
Filed Date | 2019-08-15 |
United States Patent
Application |
20190249313 |
Kind Code |
A1 |
LEE; Joun ; et al. |
August 15, 2019 |
INTEGRATED MEMBRANE SOLAR FUEL PRODUCTION ASSEMBLY
Abstract
A solar fuel production assembly comprises a separation
structure including an ion conducting membrane structurally
integrated with one or more solar fuel production units that absorb
solar energy to drive one or more redox reactions. A reduction
half-reaction occurs on a first side of the separation structure to
produce one or more reduction products and an associated oxidation
half-reaction occurs on an opposite second side of the separation
structure to produce one or more oxidation products. The one or
more reduction products are collectable from the first side and the
one or more oxidation products are collectable from the second side
of the separation structure. The ion conducting membrane provides
facile transport of ions to reduce ion transfer ohmic losses
associated with the one or more redox reactions, and also provides
for separation of the one or more reduction products from the one
or more oxidation products.
Inventors: |
LEE; Joun; (Iowa City,
IA) ; HUSSAINI; Syed Mubeen Jawahar; (Iowa City,
IA) ; CHENG; Wei; (Iowa City, IA) ; YOUNG;
Timothy; (Iowa City, IA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UNIVERSITY OF IOWA RESEARCH FOUNDATION
HYPERSOLAR, INC. |
Iowa City
SANTA BARBARA |
IA
CA |
US
US |
|
|
Family ID: |
60022219 |
Appl. No.: |
16/336873 |
Filed: |
September 26, 2017 |
PCT Filed: |
September 26, 2017 |
PCT NO: |
PCT/US2017/053408 |
371 Date: |
March 26, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62399747 |
Sep 26, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02P 20/133 20151101;
C25B 1/003 20130101; C25B 1/10 20130101; Y02E 70/10 20130101; Y02E
60/366 20130101; C25B 9/10 20130101; Y02P 20/134 20151101 |
International
Class: |
C25B 1/00 20060101
C25B001/00; C25B 1/10 20060101 C25B001/10; C25B 9/10 20060101
C25B009/10 |
Claims
1. A solar fuel production assembly, comprising: a separation
structure including one or more ion-conducting membranes
structurally integrated with one or more solar fuel production
units; wherein the one or more solar fuel production units absorb
solar energy to drive one or more redox reactions, with a reduction
half-reaction occurring on a first side of the separation structure
to produce one or more reduction products associated with the
reduction half-reaction and an associated oxidation half-reaction
occurring on a second side of the separation structure opposite
from the first side to produce one or more oxidation products
associated with the associated oxidation half-reaction, wherein the
one or more reduction products are collectable from the first side
and the one or more oxidation products are collectable from the
second side, and wherein the one or more ion-conducting membranes
provides facile transport of ions to reduce ion transfer ohmic
losses associated with the one or more redox reactions, and also
provides for separation of the one or more reduction products from
the one or more oxidation products.
2. An assembly according to claim 1, wherein the separation
structure comprises a perforated solar fuel production unit having
holes, wherein each hole is covered or filled by one of the one or
more ion-conducting membranes.
3. An assembly according to claim 2, wherein the solar fuel
production unit is perforated using at least one of: a chemical
etching process, a vapor etching process, or a mechanical
perforation process.
4. An assembly according to claim 1, wherein the separation
structure comprises a perforated ion-conducting membrane having one
or more separated solar fuel production units embedded into
respective perforations of the perforated ion-conducting
membrane.
5. An assembly according to claim 1, wherein the one or more solar
fuel production units includes a multi-junction photosynthetically
active heterostructure comprising: a continuous sheet-like material
forming or supporting a protective structure having a plurality of
cavities defining electrically insulating partitions; a plurality
of independent light absorbing units, each including one or more
types or regions of n-type or p-type semiconductor material, with
each independent light absorbing unit being disposed entirely
within one of the plurality of cavities of the protective structure
such that the protective structure partially covers and protects
the semiconductor material of each independent light absorbing unit
from corrosion and such that each independent light absorbing unit
is separated from and independent of other light absorbing units of
the multi-junction photosynthetically active heterostructure; one
or more cathodes coupled to the independent light absorbing units;
and one or more anodes coupled to the independent light absorbing
units and being isolated from the one or more cathodes so that each
independent light absorbing unit is autonomous from other light
absorbing units.
6. An assembly according to claim 1, wherein the one or more solar
fuel production units comprise a thin film monolithic or
multi-junction tandem solar cell coated with protective coating to
prevent chemical and electrochemical corrosion and capped with
oxidation and reduction electrocatalyst.
7. An assembly according to claim 1, wherein each of the one or
more ion-conducting membranes is an anion exchange membrane or a
cation exchange membrane.
8. A method for generation of fuel using solar power, the method
comprising: providing or receiving a solar fuel production assembly
comprising; a separation structure including one or more
ion-conducting membranes structurally integrated with one or more
solar fuel production units; wherein the one or more solar fuel
production units absorb solar energy to drive one or more redox
reactions, with a reduction half-reaction occurring on a first side
of the separation structure to produce one or more reduction
products associated with the reduction half-reaction and an
associated oxidation half-reaction occurring on a second side of
the separation structure opposite from the first side to produce
one or more oxidation products associated with the associated
oxidation half-reaction, wherein the one or more reduction products
are collectable from the first side and the one or more oxidation
products are collectable from the second side, and wherein the one
or more ion-conducting membranes provides facile transport of ions
to reduce ion transfer ohmic losses associated with the one or more
redox reactions, and also provides for separation of the one or
more reduction products from the one or more oxidation products;
providing an electrolyte to the first side and the second side of
the separation structure; submitting the solar fuel production
assembly to solar radiation to enable the solar radiation to drive
the one or more redox reactions to generate the one or more
reduction reaction products and the one or more oxidation reaction
products; and collecting at least one of the one or more reduction
reaction products and the one or more oxidation reaction
products.
9. A method according to claim 8, wherein the electrolyte comprises
water.
10. A method according to claim 8, wherein the electrolyte
comprises at least one of: wastewater, seawater, and brine
water.
11. A method according to claim 8, wherein the one or more redox
reactions comprise water electrolysis, wherein the one or more
reduction products comprise hydrogen gas, and the one or more
oxidation products comprise oxygen gas.
12. A method according to claim 8, wherein the separation structure
comprises a perforated solar fuel production unit having holes,
wherein each hole is covered or filled by one of the one or more
ion-conducting membranes.
13. A method according to claim 12, wherein the solar fuel
production unit is perforated using at least one of: a chemical
etching process, a vapor etching process, or a mechanical
perforation process.
14. A method according to claim 8, wherein the separation structure
comprises a perforated ion-conducting membrane having one or more
separated solar fuel production units embedded into respective
perforations of the perforated ion-conducting membrane.
15. A method according to claim 8, wherein the one or more solar
fuel production units includes a multi-junction photosynthetically
active heterostructure comprising: a continuous sheet-like material
forming or supporting a protective structure having a plurality of
cavities defining electrically insulating partitions; a plurality
of independent light absorbing units, each including one or more
types or regions of n-type or p-type semiconductor material, with
each independent light absorbing unit being disposed entirely
within one of the plurality of cavities of the protective structure
such that the protective structure partially covers and protects
the semiconductor material of each independent light absorbing unit
from corrosion and such that each independent light absorbing unit
is separated from and independent of other light absorbing units of
the multi-junction photosynthetically active heterostructure; one
or more cathodes coupled to the independent light absorbing units;
one or more anodes coupled to the independent light absorbing units
and being isolated from the one or more cathodes so that each
independent light absorbing unit is autonomous from other light
absorbing units; wherein each anode and cathode is capped with an
oxidation and reduction electrocatalyst; and a hydrogen permeable
layer covering the one or more cathodes.
16. A method according to claim 8, wherein the one or more solar
fuel production units comprise a thin film monolithic or
multi-junction tandem solar cell coated with protective coating to
prevent chemical and electrochemical corrosion and capped with
oxidation and reduction electrocatalyst.
17. (canceled)
18. An assembly according to claim 4, wherein at least one of the
separated solar fuel production units is perforated and has at
least one hole, the at least one hole being covered or filled by an
ion-conducting membrane.
19. An assembly according to claim 5, wherein each anode and
cathode is capped with an oxidation and reduction
electrocatalyst.
20. An assembly according to claim 5, further comprising a hydrogen
permeable layer covering the one or more cathodes.
21. A method according to claim 14, wherein at least one of the
separated solar fuel production units is perforated and has at
least one hole, the at least one hole being covered or filled by an
ion-conducting membrane.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority to U.S.
Provisional Application Ser. No. 62/399,747, filed on Sep. 26,
2016, entitled "INTEGRATED MEMBRANE SOLAR FUEL PRODUCTION
ASSEMBLY," which application is incorporated by reference herein in
its entirety.
BACKGROUND
[0002] There is great interest in renewable energy generation in
order to replace conventional fossil fuels. This includes utilizing
solar, wind, and biomass for producing fuels. Solar energy is
particularly interesting because it is a fundamental renewable
energy source that theoretically can be used to continuously,
noiselessly, and passively generate fuels once the infrastructure
to produce fuel from solar energy has been developed.
[0003] Conventionally, photovoltaic devices have been used to
convert solar energy to another form of energy to electrical
energy. Photovoltaic devices include one or more semiconductor
materials that are capable of capturing photons from solar
irradiation and converting at least a portion of their energy into
electrical energy. For solar fuel production, the electrical energy
generated from the solar energy is used to drive chemical reactions
on a catalyst surface, where the catalyst of interest is either
placed in a separate electrolyzer device or integrated with the
photovoltaic assembly.
SUMMARY
[0004] In an example, the present disclosure describes a solar fuel
production assembly comprising a separation structure including an
ion-conducting membrane structurally integrated with one or more
solar fuel production units. The one or more solar fuel production
units absorb solar energy to drive one or more redox reactions,
such as one or more reduction half-reactions occurring on a first
side of the separation structure to produce one or more reduction
products associated with the reduction half-reaction and one or
more associated oxidation half-reactions occurring on a second side
of the separation structure opposite from the first side to produce
one or more oxidation products associated with the associated
oxidation half-reaction. The one or more reduction products are
collectable from the first side of the separation structure and the
one or more oxidation products are collectable from the second side
of the separation structure. The ion-conducting membrane provides
facile transport of ions to reduce ion transfer ohmic losses
associated with the one or more redox reactions, and also provides
for separation of the one or more reduction products from the one
or more oxidation products.
[0005] In some examples, the one or more solar fuel production
units of the solar production assembly each include a
multi-junction photosynthetically active heterostructure that
includes a continuous sheet-like material forming or supporting a
protective structure having a plurality of cavities defining
electrically insulating partitions, a plurality of independent
light absorbing units, each including one or more types or regions
of n-type or p-type semiconductor material, with each independent
light absorbing unit being disposed entirely within one of the
plurality of cavities of the protective structure such that the
protective structure partially covers and protects the
semiconductor material of each independent light absorbing unit
from corrosion and such that each independent light absorbing unit
is separated from and independent of other light absorbing units of
the multi-junction photosynthetically active heterostructure, one
or more cathodes electrically coupled to the independent light
absorbing units, one or more anodes electrically coupled to the
independent light absorbing units and electrically isolated from
the one or more cathodes so that each independent light absorbing
unit is autonomous from other light absorbing units, and a hydrogen
permeable layer covering the one or more cathodes, wherein each
anode and cathode is capped with an oxidation and reduction
electrocatalyst
BRIEF DESCRIPTION OF THE FIGURES
[0006] In order to describe the manner in which the advantages and
features of the assemblies and methods described herein can be
obtained. A more particular description of the subject matter
briefly described above will be rendered by reference to specific
embodiments thereof, which are illustrated in the appended
drawings. Understanding that these drawings depict only exemplary
embodiments and are not therefore to be considered as limiting of
the scope of the inventions described herein, the subject matter
will be described and explained with additional specificity and
detail through the use of the accompanying drawings in which:
[0007] FIG. 1 is an exploded perspective view of an example solar
fuel production assembly including a subassembly comprising one or
more ion-exchange membranes integrated with one or more solar fuel
production units that convert energy from light to electrical
energy sufficient to electrolytically convert water molecules to
hydrogen gas and oxygen gas, in accordance with various embodiments
of the present disclosure.
[0008] FIG. 2 is a cross-sectional side view of the example solar
fuel production assembly of FIG. 1, in accordance with various
embodiments of the present disclosure.
[0009] FIG. 3 is a front view of another example of a solar fuel
production assembly including an integrated ion-exchange membrane
and fuel production unit subassembly, similar to the example fuel
production assembly shown in FIGS. 1 and 2, in accordance with
various embodiments of the present disclosure.
[0010] FIG. 4 is a cross-sectional view of the example solar fuel
production assembly of FIG. 3, taken along section 4-4 in FIG. 3,
in accordance with various embodiments of the present
disclosure.
[0011] FIG. 5 is a photograph of an example integrated ion-exchange
membrane and fuel production unit subassembly that can be used in
either of the example solar fuel production assemblies of FIGS.
1-4. FIG. 5 shows the integrated subassembly during operation, with
gas bubbles being generated at an interface between the solar fuel
production unit and an electrolyte, in accordance with various
embodiments of the present disclosure.
[0012] FIG. 6 is a front view of another example of an integrated
ion-exchange membrane and solar fuel production unit subassembly
that can be used in either of the solar fuel production assemblies
of FIGS. 1-4, in accordance with various embodiments of the present
disclosure.
[0013] FIG. 7 is another example of an integrated subassembly
ion-exchange membrane and solar fuel production unit subassembly
that can be used in either of the solar fuel production assemblies
of FIGS. 1-4, in accordance with various embodiments of the present
disclosure.
[0014] FIG. 8 is another example of an integrated subassembly
ion-exchange membrane and solar fuel production unit subassembly
that can be used in either of the solar fuel production assemblies
of FIGS. 1-4, in accordance with various embodiments of the present
disclosure.
[0015] FIG. 9 is a front view of another example another example of
a solar fuel production assembly that includes another example of
an integrated ion-exchange membrane and fuel production unit
subassembly, in accordance with various embodiments of the present
disclosure.
[0016] FIG. 10 is a cross-sectional side view of the example solar
fuel production assembly shown in FIG. 9, taken along section 10-10
in FIG. 9, in accordance with various embodiments of the present
disclosure.
[0017] FIG. 11 is a bar graph of the solar-to-hydrogen conversion
efficiency of a solid solar cell and a perforated solar cell, as
compared in EXAMPLE 1.
[0018] FIG. 12 is a Bode impedance log-log plot of electrochemical
impedance spectroscopy measured on the solid solar cell of EXAMPLE
1.
DETAILED DESCRIPTION
[0019] Using solar energy to drive the electrolysis of water has
become an increased area of research. Electrolysis of water
involves the use of electrical energy to split water molecules into
hydrogen gas (H.sub.2) and oxygen gas (O.sub.2), according to
overall hydrolysis reaction [1].
2 H.sub.2O.sub.(l).fwdarw.2 H.sub.2(g)+O.sub.2(g) [1]
[0020] As will be appreciated by those of skill in the art, the
electrolysis of reaction [1] is made up of two half reactions--an
oxidation half reaction and a reduction half reaction. The
oxidation half reaction occurs at the anode and produces one or
more oxidation products, such as oxygen gas (O.sub.2) and hydrogen
ions (H.sup.+). The reduction half reaction occurs at the cathode
and produces one or more reduction products, such as hydrogen gas
(H.sub.2) and hydroxide ions (OH.sup.-). The H.sub.2 gas can be
used as a clean fuel source, while the O.sub.2 gas co-product can
be collected for further industrial use or simply discarded as a
clean byproduct of the reaction. The overall water hydrolysis
reaction [1] has a standard potential of -1.23 V, meaning that at
standard temperature and pressure, reaction [1] theoretically
requires an applied potential difference of 1.23 V to drive the
endothermic decomposition for every two water molecules (as in the
overall hydrolysis reaction [1]). However, in practical
application, water electrolysis requires an additional potential
difference, commonly referred to as "overpotential," to overcome
various limitations, such as activation barriers and system
inefficiencies.
[0021] One common example of such a limitation in solar-powered
electrolysis is ohmic losses related to the hindrance of ion
diffusion that drives reaction [1] between an anode region and a
cathode region of the solar fuel cell. For instance, to maintain
reaction [1] in the forward direction toward the H.sub.2 and
O.sub.2 co-products and minimize required overpotentials, oxidation
products (i.e., H.sup.+ ions) formed at the anode are transported
through an electrolyte to the cathode (e.g., where H.sup.+ ions can
be reduced to form the H.sub.2 gas co-product) and/or reduction
products (i.e., OH.sup.- ions) formed at the cathode are
transported through the electrolyte to the anode (e.g., where the
OH.sup.- ions can be oxidized to form the O.sub.2 gas co-product or
water). In some instances, limits on ion transport cause a
counteracting ion concentration overpotential that limits the
effectiveness of the solar fuel cell and of the process that uses
the fuel cell to generate H.sub.2 fuel.
[0022] Another common limitation on solar-powered electrolysis is
inefficiency caused by undesirable recombination of oxidation and
reduction products, i.e., reaction of H.sup.+ ions and OH.sup.-
ions back into water molecules, reducing the overall efficiency of
the process as well as the yield of the solar-derived fuel sought
to be produced. In addition, in some examples, the solar-powered
fuel cell can produce products or co-products that can produce an
undesirable effect. For example, in water splitting applications,
the H.sub.2 and O.sub.2 co-products can form a flammable or even
explosive mixture that can pose a safety hazard.
[0023] The subject matter present disclosure is not limited to
embodiments that solve any disadvantages or that operate only in
environments described herein. Rather, the preceding information
has been provided to illustrate an exemplary technology area where
some of the embodiments and methods described herein can be
practiced.
[0024] Certain embodiments described herein are directed to
effective and efficient solar fuel production units for use in a
solar-powered fuel production process. In particular, some
embodiments described herein can be particularly effective when
used in the electrolysis of water for the efficient generation of
H.sub.2 fuel. One or more of the embodiments described herein are
configured to separate reduction products and oxidation products in
order to beneficially enhance fuel production efficiency. One or
more of the embodiments described herein are configured to provide
for efficient ion transport and for reduced ohmic losses associated
with ion transport compared to other known systems and methods for
H.sub.2 fuel generation via solar-powered electrolysis of
water.
[0025] In some embodiments, a solar fuel production assembly
includes a reduction compartment separated from an oxidation
compartment by a planar ion exchange membrane. The ion exchange
membrane includes a plurality of embedded solar fuel production
units distributed across the ion exchange medium so as to provide a
surface area having a mixture of ion exchange functionality and
solar radiation capture functionality.
[0026] FIGS. 1 and 2 show conceptual schematic views an exemplary
embodiment of a solar fuel production assembly 10 (also referred to
hereinafter as "the fuel production assembly 10" or simply as "the
assembly 10"). FIG. 1 is an exploded perspective view of the
assembly 10, while FIG. 2 is a cross-sectional side view of the
fuel production assembly 10. As shown, an ion-exchange membrane 12
(also referred to simply as "the membrane 12") is embedded with a
plurality of solar fuel production units 14 (also referred to as
"fuel production units 14") to form an integrated membrane and fuel
production unit subassembly 16, which will be referred to
hereinafter as the "integrated subassembly 16" for brevity.
[0027] The integrated subassembly 16 is positionable within a
housing to form the fuel production assembly 10. In the embodiment
shown in FIGS. 1 and 2, the housing comprises two or more housing
sections 18A, 18B (collectively referred to as "the housing
sections 18" or simply as "the housing 18") that are coupled
together onto or around the integrated subassembly 16. The housing
18, when assembled (i.e., when the housing sections 18A, 18B are
coupled together), forms a housing chamber 20 in which at least a
portion of the integrated subassembly 16 is positioned. In
particular, the fuel production units 14 of the integrated
subassembly 16 are positioned within the housing chamber 20. As
mentioned above and described in more detail below, an electrolyte
is also placed into the housing chamber 20 to provide a medium in
which ions (i.e., H.sup.+ and OH.sup.- ions) can be formed and
through which the ions can be transported.
[0028] The housing 18 also includes at least one solar face 24A,
24B (collectively referred to as "the solar faces 24" or "the solar
face 24") that is able to transmit, or at least partially transmit,
light (such as solar energy) that is irradiated onto the solar fuel
production assembly 10 into the main housing chamber 20. Light
transmitted through the one or more solar faces 24A, 24B can then
irradiate onto the fuel production units 14 so that at least a
portion of the photons in the light can be captured by the fuel
production units 14 for conversion to fuel (i.e., H.sub.2 fuel), as
described in more detail below. In the embodiment shown in FIGS. 1
and 2, the housing 18 includes a first solar face 24A that is part
of a first housing section 18A and a second solar face 24B that is
part of a second housing section 24B. In the embodiment shown, each
solar face 24A, 24B forms a major portion of the surface area of
that particular housing section 18A, 18B so that a large proportion
of the light that is irradiated onto the solar fuel production
assembly 10 can pass into the housing chamber 20 where, at least
theoretically, it can be captured and converted by the fuel
production units 14. Each of the one or more solar faces 24 can be
made from any material that is able to transmit a substantial
portion of light that is emitted onto the solar face 24 including,
but not limited to, glass or polymers that are transparent,
substantially transparent, or semi-transparent to light, and in
particular to solar energy.
[0029] In some embodiments, the ion-exchange membrane 12 acts to
divide the housing chamber 20 into two sub-chambers 26 and 28 (best
seen in FIG. 2), which are also referred to herein as compartments
26 and 28. As described in more detail below, in some embodiments,
the fuel production units 14 of the integrated subassembly 16 can
be configured so that a first side of each fuel production unit 14
is positioned to be exposed to the first compartment 26 and will
produce one or more reduction products 30 (i.e., H.sub.2 gas and
OH.sup.- ions formed via a water electrolysis reduction half
reaction). In these embodiments, the fuel production units 14 can
be further configured so that a second side of each fuel production
unit 14 is positioned to be exposed to the second compartment 28
and will produce one or more oxidation products 32 (i.e., O.sub.2
gas and H.sup.+ ions via a water electrolysis oxidation half
reaction). In other words, in such embodiments, the first side and
second side of each fuel production unit 14 are configured to be
the cathode and the anode, respectively. For this reason, in some
embodiments the first compartment 26 will be referred to as "the
reduction compartment 26" (i.e., because it is where the reduction
half reaction occurs and the one or more reduction products 30 are
produced) and the second compartment 28 will be referred to as "the
oxidation compartment 28" (i.e., because it is where the oxidation
half reaction occurs and the one or more oxidation products 32 are
produced). However, those of skill in the art will appreciate that
the configuration of the fuel production units 14 can be reversed
from that which is shown in FIG. 2, i.e., such that the first
compartment 26 is where the one or more oxidation products 32 are
produced and the second compartment 28 is where the one or more
reduction products 30 are produced, without varying from the scope
of the present disclosure. In some examples, the ion-exchange
membrane 12 is configured to allow for the transport of ions
produced by one or both of the reduction half reaction (such as
OH.sup.- ions) and the oxidation half reaction (such as H.sup.-
ions). In some examples, the ion exchange membrane 12 is configured
in particular to allow H.sup.+ ions to be transported from the
oxidation compartment 28 to the reduction compartment 28 such that
the H.sup.+ ions may be reduced to produce H.sub.2 gas as a product
gas. In such cases, the membrane 12 may be referred to as an
"H.sup.+ transport membrane" or a "proton transport membrane."
[0030] In the embodiment best seen in FIG. 1, the ion-exchange
membrane 12 maintains spacing between adjacent fuel production
units 14 such that there is sufficient membrane surface area for
ion exchange between the reduction compartment 26 on one side of
the ion-exchange membrane 12 and the oxidation compartment 28 on
the opposite side of the membrane 12. In the embodiment shown in
FIG. 1, the fuel production units 14 are integrated with the
ion-exchange membrane 12 in a grid pattern, i.e., with a specified
number of rows and a specified number of columns of the production
units 14 (eight (8) rows and two (2) columns in the embodiment
shown in FIG. 1, with only four (4) of the rows shown in the
cross-sectional view of FIG. 2). The grid-like arrangement of the
illustrated embodiment for the integrated subassembly 16 enables
facile transport of ions across the membrane 12, which in turn can
reduce or minimize the distance through which the ions must travel
in order to complete the "circuit" of the electrolysis half
reactions, and thereby reduce or minimize ohmic losses related to
ion transport.
[0031] The embodiment illustrated in FIG. 2 also shows that the
housing 18 and the ion-exchange membrane 12 separately maintains
the one or more reduction products 30 and the one or more oxidation
products 32 within their respective compartments 26 and 28,
preventing easy mixing and recombination of the reaction products
30, 32. For example, in some embodiments, the reduction products 30
formed in the reduction compartment 26 include H.sub.2 gas, and the
oxidation products 32 formed in the oxidation compartment 28
include O.sub.2 gas. The ion exchange membrane 12, while allowing
transport of ions from one compartment to another (such as OH.sup.-
ions from the reduction compartment 26 to the oxidation compartment
28 or H.sup.+ ions from the oxidation compartment 28 to the
reduction compartment 26), prevents the passage of H.sub.2 gas from
the reduction compartment 26 to the oxidation compartment 28 and of
O.sub.2 gas from the oxidation compartment 28 to the reduction
compartment 26.
[0032] In an embodiment, shown in FIGS. 1 and 2, each compartment
26, 28 includes a separate gas outlet, i.e., a first gas outlet 34
from the reduction compartment 26 and a separate second gas outlet
36 from the oxidation compartment 30, where each separate gas
product may be extracted. In some embodiments, the first gas outlet
34 provides for the removal of H.sub.2 fuel gas 38 from the
reduction compartment 26, such that the outlet 34 will also be
referred to as the "reduction outlet 34" or the "H.sub.2 outlet
34." In some embodiments, the second gas outlet 36 provides for the
removal of O.sub.2 co-product gas 40 from the oxidation compartment
28 such that the outlet 36 will also be referred to as the
"oxidation outlet 36" "O.sub.2 outlet 36." Beneficially, the
gaseous co-products are separated throughout operation of the fuel
production assembly 10, preventing or minimizing co-product loss
through recombination, which can also be potentially dangerous, as
in the case of H.sub.2 and O.sub.2 recombination.
[0033] The integrated membrane solar fuel production assembly 10
illustrated in FIG. 1 beneficially enables separation of the one or
more reduction products 30 and the one or more oxidation products
32 formed during operation as they are produced within the separate
compartments 26, 28 of the assembly 10. In water splitting
applications, where the primary reduction product 30 is H.sub.2
fuel gas 38 and the primary oxidation product 32 is O.sub.2 gas 40,
the illustrated embodiment beneficially maintains separation of the
generated H.sub.2 fuel gas 38 and the O.sub.2 co-product gas 38 on
opposite sides of the membrane 12 in the reduction compartment 26
and in the oxidation compartment 28, respectively. Not only does
this separation advantageously prevent recombination of the
co-products and associated production losses, but the separation
also keeps the product gases 38, 40 from mixing and forming a
dangerous mixture with high explosion hazard. In contrast to other
monolithic solar devices not configured for such a separation of
co-products, the illustrated embodiment of the fuel production
assembly 10 is both more effective and safer.
[0034] In addition, the illustrated embodiment of the fuel
production assembly 10 is able to achieve this beneficial
separation without introducing high ohmic losses. The configuration
of the assembly 10, which combines an ion exchange membrane 12 with
interspersed solar fuel production units 14, beneficially enables
the separate compartments 26, 28 to be functionally separate with
respect to the produced co-products 30, 32, yet close in physical
proximity with relatively limited ion transport distances. This is
in contrast to other solar devices that separate the co-products,
which require longer distances for ion transport and therefore
higher ohmic losses. In short, the illustrated embodiment of the
fuel production assembly 10 is capable of achieving efficient and
safe separation of products with minimum loss of efficiencies.
[0035] The fuel production assembly 10 also includes one or more
liquid inlets 42, 44 for the introduction of water or electrolyte,
or both, to the compartments 26, 28. In the embodiment shown in
FIGS. 1 and 2, there is a separate and dedicated liquid inlet 42,
44 for each separate compartment 26, 28, i.e., a first liquid inlet
42 that feeds into the reduction compartment 26 and a separate
second liquid inlet 44 that feeds into the oxidation compartment
28. In some embodiments, the liquid inlets 42, 44 are for feeding
the electrolyte solution into the compartments 26, 28. Because the
electrolyte solution that is fed into the reduction compartment 26
(shown as solution 46 in FIG. 2) contacts the cathode side of the
fuel production units 14, electrolyte solution is typically
referred to as "catholyte solution" or simply "catholyte" (as is
typical with electrolyte that contacts the cathode in an
electrolysis cell). Similarly, because the electrolyte solution
that is added into the oxidation compartment 28 (shown as solution
38 in FIG. 2) contacts the anode side of the fuel production units
14, it is typically referred to as the "anolyte solution" or simply
"anolyte" (as is typical with electrolyte that contacts the anode
in an electrolysis cell).
[0036] In some embodiments, the catholyte added to the reduction
compartment 26 is substantially the same or even identical to the
anolyte added to the oxidation compartment 28. Alternatively, the
catholyte and anolyte can be selected as different electrolyte
solutions, depending on the specifications for each compartment 26,
28 within the fuel production assembly 10. Exemplary electrolyte
sources that may be utilized as catholyte and/or anolyte include,
but are not limited to: wastewater (e.g., organic, nitrate,
phosphorous, and/or sulfur rich wastewater); seawater or other
brines; fresh water; carbonated water; other water source
(typically, a low quality or wastewater source), or combinations
thereof.
[0037] In the example embodiment shown in FIGS. 1 and 2, a portion
of the ion-exchange membrane 12, such as a periphery, is clamped
between the housing sections 18A, 18B to secure the integrated
subassembly 16 within the solar fuel production assembly 10. In
some embodiments, however, one or more fasteners or fastening
mechanisms can be used to secure the housing sections 18A, 18B
together. FIGS. 3 and 4 show an alternative example embodiment of a
fuel production assembly 50 where a set of fastening mechanism 52
are used to secure a first housing section 54A to a second housing
section 54B. In the example embodiment shown in FIGS. 3 and 4, the
fastening mechanisms 52 comprise sets of bolts and corresponding
wing nuts shown, although other mechanical fasteners and fastening
mechanism could be used. The housing sections 54A, 54B and their
corresponding solar faces 56A, 56B of the fuel production assembly
50 shown in FIGS. 3 and 4 are similar to the housing sections 18A,
18B and the solar faces 24A, 24B of the fuel production assembly 10
of FIGS. 1 and 2, except that the housing sections 54A, 54B and the
solar faces 56A, 56B are slightly modified to accommodate one or
more structures of the fastening mechanisms 52 (e.g., holes or
other openings through the solar faces 56A, 56B and the housing
sections 54A, 54B to accommodate the bolts of the example fastening
mechanisms 52). Similarly, the ion-exchange membrane 58 of the
example fuel production assembly 50 of FIGS. 3 and 4 is similar to
the ion-exchange membrane 12 of the fuel production assembly 10 of
FIGS. 1 and 2, except that the ion-exchange membrane 58 has also
been modified to accommodate
[0038] In some embodiments, the fastening mechanisms 52 can also
act to couple the ion-exchange membrane of the assembly to its
housing, rather than only relying on clamping the ion-exchange
membrane 12 between the housing sections 18A, 18B. For example, the
ion-exchange membrane 58 of the example fuel production assembly 50
of FIGS. 3 and 4 is similar to the ion-exchange membrane 12 of the
fuel production assembly 10 of FIGS. 1 and 2, except that the
ion-exchange membrane 58 has also been modified to accommodate the
fastening mechanisms 52 (i.e., with openings in the ion-exchange
membrane 58 that accommodate bolts of the fastening mechanisms
52).
[0039] Other than these modifications to accommodate the fastening
mechanisms 52, the housing sections 54A, 54B, the solar faces 56A,
56B, and the ion-exchange membrane 58, can be substantially similar
or identical to the housing sections 18A, 18B, the solar faces 24A,
24B, and the ion-exchange membrane 12, respectively, of the
assembly 10 described herein with respect to FIGS. 1 and 2. Those
of skill in the art will appreciate, therefore, that descriptions
in other parts of the present disclosure of details regarding the
housing sections 18A, 18B, the solar faces 24A, 24B, and the
membrane 12 in other parts of this disclosure can apply to the
housing sections 54A, 54B, the solar faces 56A, 56B, and the
membrane 58 of the assembly 50 of FIGS. 3 and 4 even if those other
parts of the present disclosure do not refer to reference numbers
54A, 54B, 56A, 56B, or 58. Other components of the example fuel
production assembly 50 of FIGS. 3 and 4--such as the fuel
production units 14, the first and second compartments 26 and 28
(also referred to herein as the reduction compartment 26 and the
oxidation compartment 28), the first and second gas outlets 34 and
36 (also referred to herein as the H.sub.2 gas outlet 34 and the
O.sub.2 gas outlet 36), and the one or more liquid inlets 42,
44--are substantially similar or even identical to those described
above with respect to the assembly 10 of FIGS. 1 and 2, and as such
the same reference numbers are used to indicate these
components.
[0040] Although most of the examples described herein describe
oxidation and reduction products in the context of electrolysis of
water, it will be understood that other reduction and/or oxidation
products may additionally or alternatively be generated using one
or more of the described embodiments of the assembly 10 or assembly
50, or for any of the other assemblies described herein. In some
examples, the one or more solar fuel production units 14 that are
integrated with an ion-exchange membrane 12, 58 to form an
integrated subassembly 16 may be utilized to generate, as reduction
products, ammonia, formic acid, methanol, methane, oxalic acid,
metals, sodium hydroxide, formaldehyde, carbon monoxide, ethylene
glycol, nitrogen, and phosphorus. In some examples, the one or more
integrated membrane solar fuel production units 14 may be utilized
to generate, as oxidation products, chlorine, bromine, hydrogen
peroxide, oxygen, fluorine, iodine, metal oxides, and sulfides.
Those having skill in the art will understand that a variety of
combinations of reduction products and oxidation products may be
produced according to selected process inputs (e.g., the
composition of the reactant or reactants fed to the assembly 10, 50
via the one or more feed inlets 42, 44) and operational
configurations.
[0041] The plurality of solar fuel production units 14 may be
formed as any suitable photosensitizer capable of capturing light
energy and transferring electrons to the side of the unit facing
the reduction/cathodic compartment 36 so that reduction half
reactions can occur. In some embodiments, the solar fuel production
units 14 also include one or more suitable electrocatalysts and/or
protective layers. Examples of protective layer may include, for
example, any suitable electrically insulating material, including,
but not limited to A1203, SiO.sub.2, ZrO, AlF.sub.3, and TiF.sub.2,
ZnO, TiO.sub.2, or combinations thereof.
[0042] In some examples, an electrocatalyst layer on the side of
the fuel production units 14 that act as the cathode side (i.e.,
that are exposed to the reduction compartment 36) may include, for
example, conductors including, but not limited to: noble metals,
including platinum group metals such as platinum (Pt) or precious
metals including gold (Au); transition metals; transition metal
oxides (e.g. NiO); metal carbides (e.g., WC); metal sulfides (e.g.
MoS.sub.2); electrically-conducting carbon containing materials,
such as graphite, graphene, and carbon nanotubes; or combinations
thereof. In some examples, an electrocatalyst layer on the side of
the fuel production units 14 that act as the anode (i.e., that are
exposed to the oxidation compartment 28) may include, for example,
conductors including, but not limited to: metals; metal oxides; and
mixtures of, metals including Ru, Ag, V, W, Fe, Ni, Pt, Pd, Ir, Cr,
Mn, Cu, Ti, and metal sulfides (e.g., MoS.sub.2); electrical
conducting carbon containing materials such as graphite, graphene,
and carbon nanotubes; and combinations thereof
[0043] A semiconductor absorber portion of each of the solar fuel
production units 14 can include one or more types of semiconductor
materials (e.g., p-type and/or n-type) to form one or more p-n
junctions or one or more Schottky junctions, as is known in the art
of photovoltaic devices.
[0044] Examples of suitable p-type semiconductor materials include
at least one of, but are not limited to, intrinsic or p-doped SnS,
ZnS, CdS, CdSe, CdTe, Cu.sub.2S, WS.sub.2, Cu.sub.xO,
Cu.sub.2ZnSnS.sub.4, CuIn.sub.xGa.sub.1-xSe.sub.2, GaN, InP, SiC,
and others selected from the classes of doped (p-type) or undoped
i) elemental semiconductors including Si, and Ge, or ii) compound
semiconductors including, but not limited to: metal sulfides;
selenides; arsenides; nitrides; antinomides; phosphides; oxides;
tellurides; and their mixtures containing respectively, sulfur (S),
selenium (Se), arsenic (As), antimony (Sb), nitrogen (N), oxygen
(O), tellurium (Te), and/or phosphorus (P) as one or more
electronegative element(s) (designated as "A"), and one or more
metals (designated as "M") of the form M.sub.nA.sub.x where M is
one or a combination of elements including but not limited to Cu,
Ga, Ge, Si, Zn, Sn, W, In, Ni, Fe, Mo, Bi, Sb, Mg.
[0045] Examples of suitable n-type semiconductor materials include
at least one of, but are not limited to, intrinsic or n-doped InS,
CdTe, CdS, CdSe, CdTe, Cu.sub.2S, WS.sub.2, Cu.sub.xO,
Cu.sub.2ZnSnS.sub.4, CuIn.sub.xGa.sub.1-xSe.sub.2, GaN, InP, SiC,
and others selected from the classes of doped (n-type) or undoped
i) elemental semiconductors including Si, and Ge, or ii) compound
semiconductors including, metal sulfides, selenides, arsenides,
nitrides, antinomides, phosphides, oxides, tellurides, and their
mixtures containing respectively, sulfur (S), selenium (Se),
arsenic (As), antimony (Sb), nitrogen (N), oxygen (O), tellurium
(Te), and/or phosphorus (P) as one or more electronegative
element(s) ("A"), and one or more metals ("M"), of the form
M.sub.nA.sub.x where M is one or a combination of elements
including but not limited to Cu, Ga, Ge, Si, Zn, Sn, W, In, Ni, Fe,
Mo, Bi, Sb, Mg.
[0046] The ion-exchange membranes described herein, such as the
membrane 12 or membrane 58, may be formed, for example, at least
partly from one or more of the following: polyethylene oxide,
polyacrylonitrile, fluorinated polymers functionalized with
sulphonic acid moieties (such as Nafion.TM.), polyethylene oxide,
polyacrylonitrile, poly(ethylene-co-tetrafluoroethylene),
poly(hexafluoropropylene-co-tetrafluoroethylene),
poly(epichlorhydrinally glycidyl ether), poly(ether imide),
poly(ethersulfone) cardo, poly(2,6-dimethyl-1,4-phenylene oxide),
polysulfone, or polyethersulfone, associated with a plurality of
cationic species (e.g., quaternary ammonium groups, phosphonium
groups, etc.), ceramic membranes coated with appropriate functional
groups, and combinations thereof. However, the ion-transport
membranes described herein for use in solar fuel production
assemblies are not limited to only these materials, but rather any
material currently known or yet to be discovered that can provide
desired transport properties for one or more specified ions and/or
desired barrier properties with respect to one or more other
reactants or products in the assembly 10, 50 can be used to form
the membrane 12, 58.
[0047] FIG. 5 is a photograph showing a close-up view of the
cathode side (i.e., the side that is exposed to the reduction
compartment 26 of an example integrated subassembly 16 including an
ion-exchange membrane 12 integrated with a plurality of solar fuel
production units 14 assembly. The photograph in FIG. 5 was taken
during operation of the fuel production assembly 10, as can be seen
by the formation of gas bubbles 60 at an interface between the
solar fuel production units 14 and an electrolyte (e.g., H.sub.2
fuel gas bubbles forming at an interface between the fuel
production units 14 and the catholyte).
[0048] FIGS. 6-8 illustrate additional examples of integrated
subassemblies 70, 80, and 90 comprising one or more ion-exchange
membranes integrated with one or more solar fuel production units.
FIG. 6 shows an example of an integrated subassembly 70 with a fuel
production device in the form of a sheet-like structure 74, which
may comprise a single relatively large fuel production device or
may include a plurality of separate fuel production units. A
plurality of holes 76 are formed in the sheet-like fuel production
device 74, and an ion-exchange membrane 72 fills or spans across
each of the holes 74 so that the final integrated subassembly 70
comprises a relatively large sheet-like fuel production structure
74 that support a plurality of smaller integrated ion-exchanged
membranes 72. In an example, the integrated subassembly 70 can be
manufactured by perforating a fuel production structure or device
to form the holes 74 in the sheet-like fuel production device 72,
such as via vapor and/or chemical etching, and then back-filling
the holes 74 with an ion exchange membrane material to form the
ion-exchange membranes 76. The example integrated subassembly 70
shown in FIG. 6 is in contrast to the integrated subassembly 16
shown in FIGS. 1 and 2, which was formed from a relatively large
ion-exchange membrane 12 onto or into which a plurality of smaller
fuel production units 14 have been integrated.
[0049] FIG. 7 shows another example construction of an integrated
subassembly 80 where an arrangement of fuel production devices 84
are mounted within or on a relatively large ion-exchange membrane
82, which is similar or identical to the integrated subassembly 16
shown in FIGS. 1 and 2. In an example, the integrated subassembly
80 shown in FIG. 7 can be made by physically perforating the
membrane 82 and adhering the fuel production devices 84 in place
using a suitable adhesive, such as a suitable epoxy, or otherwise
coupling the fuel production devices 84 to the membrane 82.
[0050] FIG. 8 illustrates another example of an integrated
subassembly 90 that provides dual functionality of both
ion-exchange and solar fuel production. The example integrated
subassembly 90 includes a relatively large ion-exchange membrane 92
onto which is embedded or otherwise integrated a plurality of
smaller solar fuel production devices 94. Moreover, one or more,
and in some examples all of, the solar fuel production devices 94
are also perforated to form one or more smaller holes 96 through
specified portions of the solar fuel production device 94 and the
one or more holes 96 of the solar fuel production devices 94 are
filled with an ion-exchange membrane material to form small
supplemental ion-exchange membranes 98 through one or more of the
fuel production devices 94. The combination of the large supporting
ion-exchange membrane 92 and the small supplemental ion-exchange
membranes 98 beneficially distribute and intermix the different
functions of the ion-exchange membranes 92, 98 and the solar fuel
production devices 94 across the surface area of the integrated
subassembly 90.
[0051] In some examples, smaller individual fuel production units
or devices may be structurally integrated within or on a
corresponding larger ion-exchange membrane, as is the case with the
fuel production units 14 in the membrane 12 in FIGS. 1 and 2 or the
fuel production units 84 in the membrane 82 in FIG. 7. In some
examples, smaller individual membranes can be structurally
integrated within or on a corresponding fuel production structure,
as is the case with the smaller membranes 72 filled into holes 76
in the sheet-like fuel production device 74 in FIG. 6. In yet other
examples, an integrated subassembly can include a combination of
smaller fuel production devices structurally integrated into or on
a larger support ion-exchange membrane and smaller individual
membrane structures can be structural integrated into the fuel
production devices, as is the case with the fuel production devices
94 that are integrated into the larger support ion-support membrane
92 and that include the smaller supplemental membranes 98
integrated into the fuel production devices 94 in FIG. 8. Membrane
sections can be structurally integrated into corresponding solar
fuel production devices or units, or vice versa, using any suitable
coupling structure, including, but not limited to: one or more
chemical adhesives (e.g., acrylic adhesives, epoxies, silicones,
and/or other chemical-resistant polymers); one or more thermally
activated adhesives; one or more mechanical fastening mechanisms,
or combinations thereof.
[0052] FIGS. 9 and 10 show various views of another example
embodiment of a solar fuel production assembly 100 (also referred
to hereinafter as "the fuel production assembly 100" or simply as
"the assembly 100"). Many of the general structural components of
the assembly 100 are substantially similar or even identical to
those of the fuel production assembly 10 of FIGS. 1 and 2 or the
fuel production assembly 50 of FIGS. 3 and 4. Therefore, when
possible, the same component names are used for the components of
the assembly 100 as are used for the components of the assembly 10
and the assembly 50. For example, the example assembly 100 shown in
FIGS. 9 and 10 includes a housing formed from one or more housing
sections, such as the pair of housing sections 102A, 102B (best
seen in FIG. 10). In the example shown in FIGS. 9 and 10, the
housing sections 102A, 102B are coupled together with one or more
fastening mechanisms 104, such as the wing nuts and corresponding
bolts shown in FIGS. 9 and 10. In some embodiments, the one or more
fastening mechanisms 104 clamp the housing sections 102A, 102B
together to form the overall housing.
[0053] The assembled housing (i.e., comprised of the assembled and
coupled together housing sections 102A, 102B) defines a housing
chamber 106 within the housing 102A, 102B. A subassembly 108 is at
least partially housed within the housing chamber 106, wherein the
subassembly 108 comprises a relatively large sheet-like solar fuel
production structure 110 (referred to hereinafter as "the solar
fuel production sheet 110" or simply "the fuel production sheet
110") and a plurality of ion-exchange membranes 112 that are
integrated into the fuel production sheet 110. In the examples
shown in FIGS. 9 and 10, a plurality of holes 114 are formed in the
fuel production sheet 110, and each hole 114 are filled with an
ion-exchanging material to form an ion-exchange membrane 112 in
each hole 114.
[0054] The fuel production sheet 110 and the membranes 112 divide
the housing chamber 106 into a pair of compartments 116, 118.
Similar to the compartments 26 and 28 described above with respect
to the fuel production assembly 10, the compartments 116 and 118
can act as a reduction compartment 116 where a reduction
half-reaction occurs (i.e., where H.sup.+ ions are reduced to form
an H.sub.2 fuel gas) and as an oxidation compartment 118 where an
oxidation half-reaction occurs (i.e., where water molecules are
oxidized to produce H.sup.+ ions and an O.sub.2 co-product gas). As
is also described above, gas products (such as the H.sub.2 fuel gas
and the O.sub.2 co-product gas) can be withdrawn from the
compartments 116, 118 via gas outlets 120, 122, such as a reduction
outlet 120 for reduction product gases (such as H.sub.2 fuel gas)
and an oxidation outlet 120 for oxidation product gases (such as
O.sub.2 co-product gas). the half reactions that occur in the
compartments 116, 118 can be carried out in one or more electrolyte
solutions (i.e., an anolyte and a catholyte), which in turn can be
fed to the compartments 116, 118 via one or more inlets 124, 126,
such as a catholyte inlet 124 for feeding catholyte to the
reduction compartment 116 and an anolyte inlet 126 for feeding
anolyte to the oxidation compartment 118.
[0055] In an example, the fuel production sheet 110 is a
specialized structure that has found to be particular advantageous
in electrolytically splitting water molecules via the conversion of
solar energy. In these examples, the specialized structure
comprises a plurality of multi-junction photosynthetically active
heterostructure (PAH) units 130 (shown in the magnified inset of
FIG. 10), which are also referred to simply as "PAH units 130," or
"light-absorbing units 130," or "light absorbing and converting
units 130." Similarly, the fuel production sheet 110 will also be
referred to hereinafter as "the PAH fuel production sheet 110" or
"the PAH sheet." In some examples, the PAH sheet 110 and the PAH
units 130 formed therein advantageously provide for efficient light
absorption and conversion to energy that can drive the oxidation
and reduction half reactions of the fuel production assembly
100.
[0056] In an example, the PAH fuel production sheet 110 is formed
from a continuous sheet-like material that provides a support
structure for the light-absorbing and fuel producing structures of
the PAH units 130. In some examples, the sheet-like material of the
fuel production sheet 110 forms or supports a protective structure
that is porous with a plurality of small-scale pores or cavities
132 (which are, in some example micro-scale or even nano-scale
cavities). The pores or cavities 132 are defined by a plurality of
partitions 134, as shown in the magnified inset of FIG. 10. In the
example shown, the holes 114 in the PAH sheet 110 where the
ion-exchange membrane 112 is placed are also defined by partitions
134 and the membrane 112 is coupled to the partition 134.
[0057] In the example shown, a PAH unit 130 is formed in each of
the cavities 132 formed in the PAH sheet 110. As summarized below,
the PAH units 130 are small-scale devices (and in some examples
micro-scale devices or even nano-scale devices) that are configured
to absorb photons from light radiation (and particularly from solar
radiation) and to convert at least a portion of the energy from the
absorbed photons to a form that can drive the electrolysis of water
molecules in the compartments 116 and 118. In an example, at least
a portion of each partition 134 acts to electrically insulate each
cavity 132 from adjacent cavities 132, which in turn acts to
electrically insulate the PAH unit 130 formed in each cavity from
adjacent PAH units 130. In this way, each light-absorbing PAH unit
130 is separated from and independent of the other light absorbing
PAH units 130 in the PAH sheet 110.
[0058] In some embodiments, each PAH unit 130 is made from a
plurality of vertically stacked nanostructured semiconductors
(n-type or p-type) of the same or different materials with the same
or different thicknesses. In some embodiments, the PAH units 130
are electrically isolated from each other and are capped with
appropriate oxidation and reduction electrocatalyst, described in
more detail below. In an example, each of the PAH units 130 include
one or more types or regions of n-type or p-type semiconductor
material, or both, which in turn provides for the light-absorbing
and converting functionality of the PAH unit 130. In the example
shown, each PAH unit 130 includes a p-type semiconductor region 136
and an n-type semiconductor region 138, which are also referred to
as the "p-type region 136" and the "n-type region 138" or simply as
"the p-region 136 and "the n-region 138," respectively. A
non-limiting list of examples of n-type semiconductor materials and
p-type semiconductor materials that can be used to form the p-type
region 136 and the n-type region 138, respectively, is provided
above. When the p-type region 136 and the n-type region 138 are in
electrical contact without one another, they form a p-n junction
140. As will be appreciated by those of skill in the art, a p-n
junction (such as the junction 140) can allow for the conversion of
at least a portion of the energy from photons that are irradiated
onto the semiconductor structures 136, 138 to electrical energy,
which in turn can drive the electrolysis half reactions in
compartments 116 and 118, described above.
[0059] In the example shown, the p-type region 136 is positioned so
that it is closer to the reduction compartment 116 while the n-type
region 138 is positioned so that is closer to the oxidation
compartment 118. In examples of water electrolysis, those of skill
in the art will appreciate that the p-type region 136 is associated
with the cathode side of the reduction and oxidation half reactions
such that the p-type region 136 is associated with the reduction
half reaction that produces H.sub.2 gas in the reduction
compartment 116. Similarly, those of skill in the art will
appreciate that the n-type region 138 is associated with the anode
side such that the n-type region 138 is associated with the
oxidation half reaction that produces O.sub.2 gas in the oxidation
compartment 118.
[0060] In the example shown in FIG. 10, each PAH unit 130 includes
one or both of a first catalyst layer 142 that at least partially
caps the p-type region 136 and a second catalyst layer 144 that at
least partially caps the n-type region 138. The first catalyst
layer 142 can include a first catalyst material that is
particularly adapted to promoting reduction half reactions (also
referred to as "the reduction promoting catalyst layer 142"). The
second catalyst layer 144 can include a second catalyst material
that is particularly adapted to promoting oxidation half reactions
(also referred to as "the oxidation promoting catalyst layer 144").
In examples where the PAH units 130 and the PAH sheet 110 are
configured for water hydrolysis, the reduction promoting catalyst
layer 142 can comprise a catalyst that promotes the production of
H.sub.2 gas such that the first catalyst layer 142 will also be
referred to as "the hydrogen evolving catalyst layer 142."
Similarly, in water hydrolysis applications the oxidation promoting
catalyst layer 144 can comprise a catalyst that promotes the
formation of O.sub.2 gas such that the second catalyst layer 144
will also be referred to as "the oxygen evolving catalyst layer
144." In some examples, a hydrogen permeable layer can also be
deposited over the cathode side of the PAH units 130.
[0061] The relative sizes of the structures of the PAH sheet 110
and the membrane 112 (i.e., of the small-scale light-absorbing and
converting units 130 formed in the cavities 116) are not
necessarily drawn to scale in FIG. 10. Rather, as noted above, in
some examples the light-absorbing units 130 can be nano-scale
structures, such as nanowire-shaped structures, that substantially
a large proportion of the surface area of the PAH sheet 110.
[0062] In some examples, each PAH unit 130 is disposed entirely or
substantially entirely within one of the cavities 132 so that the
supporting structure of the PAH sheet 110 at least partially covers
and protects the semiconductor material (
[0063] Additional details of PAH units such as the PAH units 130
and the overall sheet-like structure in which they are
incorporated, such as in the PAH sheet 110, are described in: U.S.
patent application Ser. No. 13/676,901, filed on Nov. 14, 2012,
which published as U.S. Patent Application Publication No.
2017/0141258 A1 on May 18, 2017, and issued as U.S. Pat. No.
9,593,053 B1 on Mar. 14, 2017; U.S. patent application Ser. No.
14/426,594, filed on Sep. 3, 2013, which published as U.S. Patent
Application Publication No. 2015/0303540 A1 on Oct. 22, 2015; and
U.S. patent application Ser. No. 14/659,243, filed on Mar. 16,
2015, which published as U.S. Patent Application Publication No.
2016/0076154 A1 on Mar. 17, 2016, the disclosures of which are
incorporated herein by reference in their entireties. Additional
examples of materials and components that may be utilized to form
one or more structures or components of the solar fuel production
assemblies and solar fuel production units described herein may be
found in: U.S. patent application Ser. No. 10/454,009, filed on
Jun. 3, 2003, which published as U.S. Patent Application
Publication No. 2003/0233940 A1 on Dec. 25, 2003 and issued as U.S.
Pat. No. 7,144,444 B2 on Dec. 5, 2006; U.S. patent application Ser.
No. 14/111,673, filed on Apr. 12, 2012, which published as U.S.
Patent Application Publication No. 2014/0127093 A1 on May 8, 2014
and issued as U.S. Pat. No. 9,186,621 B2 on Nov. 17, 2015; and U.S.
patent application Ser. No. 12/576,066, filed on Oct. 8, 2009,
which published as U.S. Patent Application Publication No.
2010/0133111 A1 on Jun. 3, 2010, the disclosures of which are
incorporated by reference herein in their entireties.
EXAMPLE 1
[0064] In order to provide those of skill in the art with a better
understanding of the subject matter of the present disclosure, the
following non-limiting example is provided. This EXAMPLE
demonstrates the improvement of ion transport in the integrated
membrane solar fuel production assembly that can be achieved using
the systems and methods described in the present disclosure.
[0065] A solar fuel production assembly with triple junction
monolithic silicon solar cell structure with perforations (such as
the example solar fuel production structure 74 with holes 76 for an
ion-exchange membrane 72, as shown in FIG. 6) was prepared, along
with a comparable solar production triple junction monolithic
silicon solar cell structure that is not perforated, to test
H.sub.2 production efficiency and ohmic losses across the solar
cells. The porosity of the perforated assembly was 16.8%. Platinum
H.sub.2 evolution catalyst was e-beam deposited on the cathode side
of the solar cells for H.sub.2 evolution and transparent
Co/Ni-based oxygen evolution catalyst was electrochemically
deposited on the anode side of the solar cells.
[0066] Light simulating solar light was illuminated onto both the
perforated solar cell structure and the solid, non-perforated solar
cell structure using a solar lamp. An O.sub.2 evolution reaction
was observed on the anode side and a H.sub.2 evolution reaction was
observed on the cathode side for both solar cell structures. Ohmic
losses across both solar cell structures was measured using
electrochemical impedance spectroscopy (Multi-channel
multi-potentiostat/galvanostat/frequency response analyzer,
Bio-Logic, VSP-300) and H.sub.2 product analysis (Gas
Chromatograph, SRI 8610c). FIG. 11 shows the solar-to-hydrogen
conversion efficiency of the solid, non-perforated solar cell
structure (represented by data bar 200) and the perforated solar
cell structure (represented by data bar 210), as analyzed by gas
chromatography (Gas Chromatograph, SRI 8610c). The
solar-to-hydrogen efficiency of the perforated cell solar cell
structure resulted in about 38% more hydrogen production than the
comparable solid, non-perforated solar cell structure.
[0067] FIG. 12 is a Bode impedance log-log plot of the
electrochemical impedance spectroscopy measurement on the solid,
non-perforated solar cell structure (data series 300) and the
porous solar cell structure (data series 310) to compare the ion
transport efficiencies of the perforated solar cell structure to
that of the solid, non-perforated solar cell structure. The Bode
impedance log-log plot shows substantially lower cell resistance
for the porous solar cell structure compared to the solid,
non-perforated solar cell structure in the low-frequency regime,
e.g., at frequencies below 10 Hz, particularly for frequencies at
or below about 7.5 Hz, still more particularly at frequencies at or
below about 5 Hz, and even more particularly at frequencies at or
below about 1 Hz.
[0068] The present invention may be embodied in other forms,
without departing from its spirit or essential characteristics. The
described embodiments are to be considered in all respects only as
illustrative and not restrictive. The scope of the invention is,
therefore, indicated by the appended claims rather than by the
foregoing description. All changes which come within the meaning
and range of equivalency of the claims are to be embraced within
their scope.
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