U.S. patent application number 14/191824 was filed with the patent office on 2014-09-04 for electrochemical cell.
This patent application is currently assigned to COMPUR MONITORS GMBH & CO. KG. The applicant listed for this patent is COMPUR MONITORS GMBH & CO. KG. Invention is credited to Christopher Frey.
Application Number | 20140246309 14/191824 |
Document ID | / |
Family ID | 50490610 |
Filed Date | 2014-09-04 |
United States Patent
Application |
20140246309 |
Kind Code |
A1 |
Frey; Christopher |
September 4, 2014 |
ELECTROCHEMICAL CELL
Abstract
An electrochemical cell is described, which provides a reliable
gas generation even under unfavorable environmental conditions and
with significant changes in temperature and environment.
Furthermore the cell has a long life time. The electrolyte of this
electrochemical cell comprises at least one ionic liquid containing
thiocyanate ions for the generation of hydrogen cyanide gas.
Preferred substances for the composition of the electrolyte and for
the provision of thiocyanate ions in the electrolyte are
specified.
Inventors: |
Frey; Christopher;
(Ingolstadt, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
COMPUR MONITORS GMBH & CO. KG |
Munchen |
|
DE |
|
|
Assignee: |
COMPUR MONITORS GMBH & CO.
KG
Munchen
DE
|
Family ID: |
50490610 |
Appl. No.: |
14/191824 |
Filed: |
February 27, 2014 |
Current U.S.
Class: |
204/278 ;
204/242 |
Current CPC
Class: |
C25B 9/06 20130101; C25B
1/22 20130101; C25B 1/00 20130101 |
Class at
Publication: |
204/278 ;
204/242 |
International
Class: |
C25B 9/06 20060101
C25B009/06; C25B 1/22 20060101 C25B001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2013 |
DE |
10 2013 003 559.7 |
Claims
1. An electrochemical cell (1) having an electrolyte (4), a
generator electrode (5) and a counter electrode (3), wherein the
electrolyte (4) comprises at least one ionic liquid and contains
thiocyanate ions for generating hydrogen cyanide gas.
2. An electrochemical cell (1) according to claim 1, wherein the
electrolyte (4) comprises a mixture of at least two ionic fluids
preferably from the group of 1-butyl-3-methylimidazolium
trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium
trifluoromethanesulfonate and 1-ethyl-3-methylimidazolium
thiocyanate.
3. An electrochemical cell (1) according to claim 1, wherein the
gas generating substance is a thiocyanate salt.
4. An electrochemical cell (1) according to claim 3, wherein the
thiocyanate salt is at least one of the group of NaSCN, KSCN,
LiSCN, NH.sub.4SCN, NBu.sub.4SCN.
5. An electrochemical cell (1) according to claim 1, wherein the
generator electrode (5) consists of a noble metal, preferably of
one of the group of gold, rhodium, iridium, palladium and
platinum.
6. An electrochemical cell (1) according to claim 5, wherein the
generator electrode (5) is a noble metal wire mesh and preferably a
platinum wire mesh.
7. An electrochemical cell (1) according to claim 5, wherein the
generator electrode (5) is a PTFE gas diffusion membrane coated on
one side with a noble metal.
8. An electrochemical cell (1) according to claim 1, wherein it is
sealed to the outside by a PTFE gas diffusion membrane (7), which
is permeable to the generated hydrogen cyanide gas.
9. An electrochemical cell (1) according to claim 1, wherein the
ionic liquid (4) is provided in a housing or container (2)
comprising glass fiber layers.
10. An electrochemical cell (1) according to claim 1, wherein the
counter electrode (3) essentially consists of platinum.
11. An electrochemical cell (1) according to claim 10, wherein the
counter electrode (2) is a PTFE coated with platinum.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an electrochemical cell for
generating hydrogen cyanide gas using a generator electrode and a
counter electrode.
BACKGROUND OF THE INVENTION
[0002] Electrochemical cells for generating test gases for gas
analysis devices are known, e.g. from German patent specification
26 21 677, for various gases, but not for hydrogen cyanide gas.
[0003] From document Z. Tocksteinova, F. Opekar, "The
Electrochemical Generation of Small Amounts of Hydrogen Cyanide",
Talanta, 1986, vol. 33, no. 8, pages 688-690 a method for
generating hydrogen cyanide gas using an electrochemical cell is
known, wherein hydrogen cyanide gas is generated by oxidation of
thiocyanate ions. The gas is generated via controlled oxidation of
thiocyanate in aqueous solution according to reaction
SCN.sup.-+4 H.sub.2O.fwdarw.6 e.sup.-+SO.sub.4.sup.2-+HCN+7
H.sup.+
[0004] A platinum electrode completely submerged in an aqueous
electrolyte is flushed by nitrogen, so as to transport the
generated hydrogen cyanide gas outward.
[0005] Besides the fact that the use of such a gas generator is
only possible under laboratory conditions, this gas generator is
unfavorable in particular due to the electrolyte which is an
aqueous solution. Thus in practical applications for example
climatic influences will cause loss of electrolyte, which does not
allow for a reliable generation of hydrogen cyanide gas in
controllable and constant amounts or might even cause a complete
functional failure of such a generator.
SUMMARY OF THE INVENTION
[0006] Thus it is an object of the invention to provide an
electrochemical cell which makes a reliable hydrogen cyanide gas
generation with a long life possible even under unfavorable and
substantially changing environmental conditions, such as
significant changes in temperature and environment.
[0007] According to the invention the object is accomplished by an
electrochemical cell of the type mentioned above, wherein the
electrolyte comprises at least one ionic liquid and includes
thiocyanate ions for generating hydrogen cyanide gas.
[0008] Due to its high electrochemical stability with respect to
oxidation and reduction, the use of ionic liquids makes it possible
to provide electrochemical cells for generating hydrogen cyanide
gas, e.g. to check gas analysing devices, whereby the
electrochemical cells generate stable amounts of hydrogen cyanide
gas without failing over a long life time and also at changing
temperatures and environmental conditions. The use of ionic liquid
as electrolyte makes it possible to have long storage periods for
such gas generators without impacting their function in later
use.
[0009] According to a preferred embodiment of the invention, the
electrolyte comprises a mixture of at least two ionic liquids, thus
allowing to easily select and set the melting point and water
absorption capacity of the electrolyte by an appropriate choice of
ionic liquids and/or their appropriate mixing ratio. The
electrolyte preferably comprises at least one ionic liquid of the
group of 1-butyl-3-methylimidazoliurn trifluoromethanesulfonate
(hereinafter abbreviated as BMIM OTf), 1-ethyl-3-methylimidazolium
trifluoromethanesulfonate (hereinafter abbreviated as EMIM OTf) and
1-ethyl-3-methylimidazolium thiocyanate (hereinafter abbreviated as
EMIM SCN). These ionic liquids have been found to be particularly
advantageous especially in view of the setting and adjusting
options with respect to melting point and water absorption. In
particular, the use of the mentioned ionic liquids and optionally
of further additional substances results in reductions in the
electroyte's melting point, which allows operation until far below
the melting points of the individual ionic liquids and thus within
the operating temperature range of the electrochemical cell, such
as between -30.degree. C. and +60.degree. C.
[0010] Thiocyanate salt is preferably used as gas generating
substance, and it is particularly advantageous to select it from
the group NaSCN, KSCN, LiSCN, NH.sub.4SCN, NBu.sub.4SCN. However,
thiocyanate can also be itself the anion of an ionic liquid.
[0011] It is particularly advantageous to have at least one noble
metal as generator electrode, in particular one of the group of
gold, rhodium, iridium, palladium or platinum, wherein platinum is
particularly advantageous. The generator electrode is preferably
formed as a platinum wire mesh or as a polytetrafluorethylene (in
the following abbreviated as PTFE) gas diffusion membrane coated
with the noble metal.
[0012] The container for the ionic liquid in the electrochemical
cell is sealed to the outside by a PTFE gas diffusion membrane,
which is permeable for the generated hydrogen cyanide gas. The
generated hydrogen cyanide gas is discharged to the outside via
this PTFE gas diffusion membrane.
[0013] It is advantageous to provide layers of glass fiber between
the generator electrode and the counter electrode, the glass fiber
being impregnated with the ionic liquid or with a mixture of ionic
liquids, whereby these liquids comprise thiocyanate ions.
[0014] The counter electrode is preferably a PTFE support which is
coated with platinum or platinum black, which is preferably
porous.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present invention and preferred embodiments will be
discussed below further with reference to the single drawing
schematically showing an electrochemical cell according to the
present invention.
[0016] An electrochemical cell 1 comprises a cell housing or
container 2 at its bottom side above of which a counter electrode 3
is disposed on which ionic liquid 4 is provided. A generator
electrode 5 is disposed on the side of the ionic liquid opposing
the counter electrode 3. The generator electrode 5 acting as an
anode and the counter electrode 3 acting as a cathode are connected
to a constant current source 6.
[0017] On the outer side of generator electrode 5, which is formed
for example as a wire mesh or as a gas diffusion membrane, another
gas diffusion membrane is possibly provided, through which the
generated hydrogen cyanide by diffusion passes out of the cell to
the outside. The gas diffusion membrane 7 is additionally
stabilized by a PTFE support grid 8.
[0018] The interior of the cell housing 2 containing the ionic
liquid 4 preferably comprises glass fiber layers impregnated with
ionic liquid containing thiocyanate ions.
[0019] The ionic liquid is selected in particular with regard of
the melting point and the water absorbing capacity. BMIM OTf, EMIM
OTf and EMIM SCN are of particular advantage. The ionic liquids can
be used as a basis for the cell's electrolyte, either in its pure
forms or as mixtures. It is preferred to have a proportion of 30-25
vol % of EMIM SCN in the mixture with EMIM OTf or BMIM OTf.
Typically 0.2-0.4 mol/l lithium thiocyanate, potassium thiocyanate,
sodium thiocyanate, ammonium thiocyanate or tetrabutylammonium
thiocyanate are added to BMIM OTf. A proportion of 5-20% H.sub.2O
is required as a reactant in all cases. It is also used to optimize
the solubility of thiocyanate salts and the reaction products.
[0020] Current densities of the current provided by the constant
power source 6 and flowing through ionic electrolyte 4 are
typically between 0.3 1.5 mA/cm.sup.3. The generated hydrogen
cyanide gas passes through the PTFE gas diffusion membrane 7 by
diffusion out of the cell to the outside. For a performance test of
hydrogen cyanide detectors a generator electrode area of preferably
3.8 cm.sup.2 and an operating current of about 2 mA with a power-on
time of 30 s is advantageous, in order to generate hydrogen cyanide
concentrations greater than 20 ppm in front of the outlet opening
of the cell.
[0021] In the present embodiment the generator electrode consists
of a platinum wire mesh or a coating of noble metal and preferably
of platinum on the inner side of PTFE gas diffusion membrane 7. The
counter electrode is a 0.25 mm PTFE gore membrane coated with
platinum black. The electrochemical cell operates galvanostatically
with current densities preferably between 0.5 and 1.5 mA/cm.sup.2.
With a generator electrode having a diameter of 20 mm the optimum
operating current is 2 to 3 mA.
[0022] The invention has been described with reference to preferred
embodiments. However, a person skilled in the art is capable of
further embodiments or modifications without departing from the
scope of the invention.
* * * * *