Electrode for electrochemical cells and composition thereof

Abstract

An electrode for use in an electrochemical cell, especially a zinc-bromine flow battery or a hydrogen/bromine flow battery, and methods for manufacturing and using the electrode is provided. The electrode has a metal substrate and a catalytic coating applied onto the substrate wherein the catalytic coating has a Ru-rich mixture of ruthenium and having 70-80 mol % Ru, 1-5 mol % Pt and 17-25 mol % Ir. The catalytic coating composition exhibits a surprisingly high voltage efficiency and operating lifetime despite its relatively low Ir/Ru and Pt/Ru ratios. The underlying metal substrate is for example a porous Ti layer or a layer with titanium suboxides Ti.sub.xO.sub.y.

Claims

1. Electrode for use in electrochemical cells comprising: a metal substrate; and a catalytic coating comprising a mixture of noble metals or oxides thereof, wherein said mixture comprises 70-80% ruthenium, 17-25% iridium and 1-5% platinum in mole percentage referred to the elements.

2. The electrode according to claim 1, wherein the loading of ruthenium, iridium and platinum is 5 to 30 g/m.sup.2 referred to the sum of the elements.

3. The electrode according to claim 1, wherein said metal substrate consists of a titanium material.

4. The electrode according to claim 3 further comprising an intermediate layer containing titanium material applied between said metal substrate and said catalytic coating.

5. The electrode according to claim 4, wherein said titanium material comprises titanium suboxides according to the formula Ti.sub.xO.sub.y, wherein x is in the range of 2 to 10 and y is in the range of 3 to 19.

6. The electrode according to claim 1, wherein said substrate has an average porosity of 40% to 60%.

7. Method for the production of an electrode according to claim 1 comprising the following sequential steps: applying a precursor solution comprising a mixture of ruthenium, iridium and platinum compounds in one or more coats over said metal substrate; drying said metal substrate after each coating at a temperature of 80 C. to 150 C.; and thermally treating said dried metal substrate at a temperature of 350 C. to 600 C.

8. The method according to claim 7, wherein the precursor solution is applied to said metal substrate in 3 to 8 coats.

9. Process for energy storage comprising the following steps: circulating a zinc bromide solution within at least one electrochemical cell; and performing the electrolysis of said solution within said electrochemical cell; said electrochemical cell being equipped with at least one electrode comprising a metal substrate and a catalytic coating comprising a mixture of noble metals or oxides thereof, wherein said mixture comprises 60-85% ruthenium, 0-25% iridium and 1-15% platinum in mole percentage referred to the elements, wherein said electrode alternately evolves and reduces bromine.

10. The process according to claim 9 further comprising the execution of a periodic electric charge and discharge cycle on said electrochemical cell by means of an external electric circuit.

11. Flow battery comprising at least one electrode according to claim 1.

12. Flow battery comprising at least one electrode which alternately evolves and reduces bromine comprising a metal substrate and a catalytic coating comprising a mixture of noble metals or oxides thereof, wherein said mixture comprises 60-85% ruthenium, 0-25% iridium and 1-15% platinum in mole percentage referred to the elements, wherein said flow battery is a zinc/bromine flow battery, a hydrogen/bromine flow battery or an organic redox species/bromine flow battery.

Description

EXAMPLE 1

(1) A coating solution was prepared by dissolving the following compounds in 17 ml of 0.1 M HCl and 1 ml of t-octylphenoxypolyethoxyethanol solution, commercialized by Dow Chemicals under the trade name Triton X-100:

(2) 0.641 g RuCl.sub.3.xH.sub.2O;

(3) 0.395 g H.sub.2IrCl.sub.6.xH.sub.2O;

(4) 0.038 g H.sub.2PtCl.sub.6.xH.sub.2O.

(5) This solution was coated by brush onto a 2.0 mm thick porous titanium substrate (4 cm.sup.2 shadow area), with average pore volume equal to 50%, mounted in a titanium sheet frame. The sample was dried at 110 C. for 10 minutes and then baked at 470 C. for 10 minutes. A total of three coats were applied to provide a coating of RuO.sub.2, IrO.sub.2 and Pt with a nominal composition of 75% Ru, 23% Ir and 2% Pt by mole percentage. The coated sample was placed in an electrochemical cell opposite a titanium sheet electrode. An electrolyte composed of ZnBr.sub.2, ZnCl.sub.2, Br.sub.2 and Methyl Ethyl Pyrrolidinium Bromide (MEP) was circulated through the cell with a pump. The electrolyte was maintained at a temperature of 40-45 C. A current of 200 mA was applied to the cell for 10 minutes to evolve bromine and plate zinc on the Ti sheet electrode. The cell was then placed at open circuit for 30 seconds and then discharged at 532 mA until the zinc was fully removed. The cell voltage was monitored during the test. The measured voltage efficiency was 79%. The short term stability has been assessed by performing 50 charge/discharge cycles and monitoring the cell voltage; after each run the voltage efficiency remained above 99.0% of the initial efficiency. The long term stability has been assessed by performing 5000 charge/discharge cycles and monitoring the cell voltage; the voltage efficiency has shown to remain above 95.0% of the initial efficiency during the whole experiment.

EXAMPLE 2

(6) A coating solution is prepared by dissolving the following compounds in 17 ml of 0.1 M HCl and 1 ml of octylphenoxypolyethoxyethanol solution, commercialized by Dow Chemicals under the trade name Triton X-100:

(7) 0.7815 g RuCl.sub.3.xH.sub.2O;

(8) 0.30489 g H.sub.2PtCl.sub.6.xH.sub.2O

(9) This solution was coated by brush onto a 2.0 mm thick porous titanium substrate (4 cm.sup.2 shadow area) mounted in a titanium sheet frame. The sample was dried at 110 C. for 10 minutes and then baked at 470 C. for 10 minutes. A total of four coats were applied to provide a coating of RuO.sub.2 and Pt with a nominal composition of 85% Ru and 15% Pt in mole percentage referred to the elements. The coated sample was placed in an electrochemical cell opposite a titanium sheet electrode. An electrolytic solution composed of ZnBr.sub.2, ZnCl.sub.2, Br.sub.2 with MEP complexing agent was circulated through the cell with a pump. The electrolyte was maintained at a temperature of 40-45 C. A current of 200 mA was applied to the cell for 10 minutes to evolve bromine and plate zinc on the titanium sheet electrode. The cell was then placed at open circuit for 30 seconds and then discharged at 532 mA until the zinc was fully removed. The cell voltage is monitored during the test. The resulting voltage efficiency was found to be 78.5%. The short term stability has been assessed by performing 50 charge/discharge cycles and monitoring the cell voltage; after each run the voltage efficiency was found to be above 99.0% of the initial efficiency. The long term stability was assessed by performing 4500 charge/discharge cycles and monitoring the cell voltage; the voltage efficiency remained above 95.0% of the initial voltage efficiency during the whole experiment.

COUNTER EXAMPLE 1

(10) A coating solution was prepared by dissolving the following compounds in 17 ml of 0.1 M HCl and 1 ml of octylphenoxypolyethoxyethanol solution, commercialized by Dow Chemicals under the trade name Triton X-100:

(11) RuCl.sub.3: 0.641195 g

(12) H.sub.2IrCl.sub.6:0.429062 g

(13) This solution was coated by brush onto a 2.0 mm thick porous titanium substrate (4 cm.sup.2 shadow area) mounted in a titanium sheet frame. The sample was dried at 110 C. for 10 minutes and then baked at 470 C. for 10 minutes. A total of four coats were applied to provide a coating of RuO.sub.2 and Pt with a nominal composition of 75% Ru and 25% Ir in mole percentage referred to the elements. The coated sample was placed in an electrochemical cell opposite a titanium sheet electrode. An electrolytic solution composed of ZnBr.sub.2, ZnCl.sub.2, Br.sub.2 with MEP complexing agent was circulated through the cell with a pump. The electrolyte was maintained at a temperature of 40-45 C. A current of 200 mA was applied to the cell for 10 minutes to evolve bromine and plate zinc on the titanium sheet electrode. The cell was then placed at open circuit for 30 seconds and then discharged at 532 mA until the zinc was fully removed. The cell voltage is monitored during the test. The resulting voltage efficiency was found to be 71%. The short term stability has been assessed by performing 50 charge/discharge cycles and monitoring the cell voltage; after each run the voltage efficiency was found to be above 99.0% of the initial efficiency. The long term stability was assessed by performing 4500 charge/discharge cycles and monitoring the cell voltage; the voltage efficiency remained above 95.0% of the initial voltage efficiency during the whole experiment.

(14) The previous description shall not be intended as limiting the invention, which may be used according to different embodiments without departing from the scopes thereof, and whose extent is solely defined by the appended claims.

(15) Throughout the description and claims of the present application, the term comprise and variations thereof such as comprising and comprises are not intended to exclude the presence of other elements, components or additional process steps.

(16) The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention before the priority date of each claim of this application.