WO2012095862A2

WO2012095862A2 - An electrode for a fuel cell

Info

Publication number: WO2012095862A2
Application number: PCT/IN2012/000017
Authority: WO
Inventors: Alkesh AHIRE; Nawal Kishor MAL; Rajiv Kumar
Original assignee: Tata Chemicals Limited
Priority date: 2011-01-11
Filing date: 2012-01-05
Publication date: 2012-07-19
Also published as: WO2012095862A3

Abstract

An electrode for a fuel cell is disclosed. The electrode comprises of a gas diffusion layer having an electrode catalyst layer coated thereon. The electrode catalyst layer comprises of a carbon supported catalyst. The carbon supported catalyst comprises of carbon supported platinum nanoparticles having at least one mercapto alkyl acid selected from the group comprising of mercatopropyl sulfonic acid, mercapto propionic acid and mercapto succinic acid, attached thereon.

Description

AN ELECTRODE FOR A FUEL CELL

The disclosure generally relates to an electrode for a fuel cell. More particularly, the disclosure relates to an electrode comprising a gas diffusion layer having a catalyst layer coated thereon.

BACKGROUND

Fuel cells are power generation systems that convert chemical energy into electrical energy by oxidation of fuel. Fuel cells have a higher efficiency compared to internal combustion engines and are environment friendly. Therefore, fuel cells have become the focus of attention for researchers as an alternative energy source for fossil fuels.

One type of electrochemical fuel cell is the polymer electrolyte membrane (PEM) fuel cell, which employs a membrane electrode assembly (MEA) comprising of a proton conductive membrane which has cathode catalyst layer on one side and anode catalyst layer on the other side, sandwiched between two gas diffusion layers. Gas diffusion layers serve as current collectors that allow ready access of the fuel and oxidant to anode and cathode catalyst surfaces, respectively.

It is well known in prior art that anode and cathode catalyst layers comprise of carbon as electron conductor from current collectors to the catalyst layer, platinum (zero) as catalyst to convert hydrogen into proton and nafion as proton conductor. Nafion is a sulfonated tetrafluroethylene based fluropolymer-copolymer and is commonly used as proton conductor in fuel cell technology. However, nafion and Platinum being expensive, make the fuel cells expensive. As a consequence, a lot of research is being carried out to devise cost effective fuel cells. Further, nafion also reduces the resiliency of the catalyst layer in the fuel cells; hence there is a need for efficient and cost effective fuel cells which can eliminate/reduce the use of nafion in the electrode catalyst layer. Another drawback of the conventional fuel cells is that the efficiency of fuel cells decreases at low temperatures due to the decrease in catalytic activity of the catalyst layer. Thus, there is also a need to devise a catalyst layer which is cost effective and is also operable even at low temperatures.

SUMMARY

A membrane electrode assembly for a fuel cell is also disclosed. The membrane electrode assembly comprises of a cathode and an anode disposed on both surfaces of an electrolyte membrane. The anode and the cathode comprising the electrode as disclosed.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1: Polarization curve (V-I) and power density curve (P-I) of 0.10 milligrams Pt/Cm² loading on anode electrode catalyst measured using single cell.

Figure 2: Polarization curve (V-I) and power density curve (P-I) of 0.15 milligrams Pt/Cm² loading on anode electrode catalyst measured using single cell. DETAILED DESCRIPTION

To promote an understanding of the principles of the invention, reference will be made to the embodiment illustrated in the drawing and specific language will be used to describe the same. It will nevertheless be understood that no limitation of scope of the invention is thereby intended, such alterations and further modifications in the described method and such further applications of the principles of the inventions as illustrated therein being contemplated as would normally occur to one skilled in art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

The present disclosure generally relates to an electrode for a fuel cell. More particularly, the present disclosure relates to an electrode for a fuel cell comprising a gas diffusion layer having an electrode catalyst layer coated thereon, wherein the electrode catalyst layer comprises of a carbon supported catalyst. The said carbon supported catalyst comprises of carbon supported platinum nanoparticles having at least one mercapto alkyl acid selected from the group consisting of mercatopropyl sulfonic acid(MPSA), mercapto propionic acid (MP A) and mercapto succinic acid(MSA), attached thereon. By way of a specific example, the carbon supported catalyst comprises of carbon supported platinum nanoparticles having mercatopropyl sulfonic acid, attached thereon (C/Pt np MPSA). The carbon supported catalyst disclosed above provides: carbon for transport of electrons from the current collector through the gas diffusion layer to the electrode catalyst layer; platinum nanoparticles for breakdown of hydrogen to proton, and anionic component of the mercapto alkyl acid for transportation of protons from the membrane to the electrode catalyst layer. Thus, electrode catalyst layer disclosed herein eliminates the use of nation in the electrode catalyst layer as used in conventional fuel cells.

In accordance with an embodiment, the carbon supported catalyst comprises of carbon supported platinum nanoparticles having at least one mercapto alkyl acid selected from the group consisting of mercatopropyl sulfonic acid, mercapto propionic acid and mercapto succinic acid and at least one alkyl thiol selected from the group consisting of hexane thiol (HT), octane thiol (OT), decane thiol(DT) and dodecane thiol (DDT), attached thereon. By way of a specific example, the carbon supported catalyst comprises of carbon supported platinum nanoparticles having mercatopropyl sulfonic acid and hexane thiol (C/Pt np MPSA - HT), attached thereon.

The carbon supported catalyst disclosed above provides: carbon for transporting electrons from the current collector through the gas diffusion layer to the electrode catalyst layer; platinum nanoparticles for breakdown of hydrogen to proton; anionic component of the mercapto alkyl acid for transportation of protons from the membrane to the electrode catalyst layer and hydrophobic alkyl group of alkyl thiol for preventing crystallization of water over the electrode catalyst layer at low temperatures. Thus, the electrode catalyst layer comprising the carbon supported catalyst disclosed herein, eliminates the use of nafion and exhibits effective catalysis even at low temperatures. Furthermore, mercapto alkyl caid and the alkyl thiol facilitates the immbolization of the platinum nanoparticles on the carbon support.

In accordance with an aspect the carbon support is selected from graphite, carbon black, activated carbon, carbon nanotubes etc. In accordance with an aspect, in the carbon supported catalyst the platinum nanoparticles are attached to mercaptan/thiol (-SH) group of alkyl thiol and mercapto alkyl acid.

In accordance with an embodiment, the electrode catalyst layer further comprises of a binder to facilitate the immbilization of the carbon supported catalyst on the gas diffusion layer. The binder is an organic polymer including but not limited to polytetrafluoroethylene (PTFE), polyvinylidenefluoride-hexafluoropropene (PVDF-HFP), polyvinyl fluoride (PVF), polyvinylidenefluoride (PVDF), polychlorotrifluoroethylene (PCTEF), tetrafluoroethylene thylene (ETFE) and nation.

In accordance with an aspect, platinum compnses 0.05 -5 milligrams/cm of the electrode catalyst layer.

In accordance with an aspect, the particle size of the platinum nanoparticles is in the range of 1-1000 nm and is preferably in the range of 2 to 20 nanometers.

In accordance with an aspect, the gas diffusion layer is made of a conductive porous substrate including but not limited to carbon cloth, carbon paper, carbon felt or Teflon sheet.

The present disclosure further relates to a membrane electrode assembly for a fuel cell. The said membrane electrode assembly comprises of a pair of electrodes sandwiching an electrolyte membrane. Each electrode comprises of a gas diffusion layer having an electrode catalyst layer coated thereon. The electrode catalyst layer comprises of the carbon supported catalyst disclosed above.

In accordance with an aspect, the electrode catalyst layer of the electrode is in direct contact with the electrolyte membrane.

In accordance with an aspect, the fuel cell is a Proton exchange Membrane Fuel Cell. The present disclosure also provides a method of preparing the carbon supported catalyst comprising carbon supported platinum nanoparticles having at least one mercapto alkyl acid selected from the group consisting of mercatopropyl sulfonic acid, mercapto propionic acid and mercapto succinic acid, attached thereon. The said method comprises of dispersing Vulcan carbon in water followed by the addition of a mercapto alkyl acid selected from the group consisting of mercatopropyl sulfonic acid, mercapto propionic acid and mercapto succinic acid and a platinum precursor to above dispersion to obtain a first solution. A reducing agent is then added to the first solution over a predetermined time period and preferably at the rate of 1 millilitre/minute, followed by stirring for 20 minutes to obtain a second solution. The second solution is then heated to a temperature that facilitates the formation of carbon supported platinum nanoparticles having the mercapto alkyl acid, attached thereon. The carbon supported catalyst is then filtered and washed with distilled water several times followed by drying preferably at 30 °C for 16 hours.

By way of a specific example, a method of preparing carbon supported catalyst comprising carbon supported platinum nanoparticles having mercapto propyl sulfonic acid attached thereon, is disclosed. The said method comprises of first preparing a dispersion of Vulcan carbon in water by adding 150 milligrams of Vulcan carbon in 50 millilitres distilled water at once, followed by stirring for 20 minutes to get it well dispersed at 0 °C. 92.53 milligrams of mercapto propylsulfonic acid (MPSA) (99%, 0.514 mmol) is then added to the above dispersion followed by stirring for 30 minutes at 0 °C and adding of 253 milligrams of K₂PtCl₆ (99%, 0.514 mmol) followed by stirring for 30 minutes to obtain the first solution. 71 milligrams of NaBH₄ (98%, 1.84 mmol) is dissolved in 25 millilitres distilled water and added to the first solution at the rate of 1 millilitre/minute, followed by stirring for 20 minutes to obtain the second solution. Finally, the second solution is heated at 60 °C under stirring for 1 hour. The carbon supported catalyst thus obtained was filtered and washed with distilled water several times followed by drying at 30 °C for 16 hours.

The present disclosure further provides a method of preparing the carbon supported catalyst comprising carbon supported platinum nanoparticles having at least one mercapto alkyl acid selected from the group consisting of mercatopropyl sulfonic acid, mercapto propionic acid and mercapto succinic acid and at least one alkyl thiol selected from the group consisting of hexane thiol, octane thiol, decane thiol and dodecane thiol, attached thereon. The said method comprises of preparing a dispersion of Vulcan carbon in water followed by the addition of a mercapto alkyl acid selected from the group consisting of mercatopropyl sulfonic acid, mercapto propionic acid and mercapto succinic acid; at least one alkyl thiol selected from the group consisting of hexane thiol, octane thiol, decane thiol and dodecane thiol and a platinum precursor to the said dispersion to obtain a first solution. A reducing agent is then added to the first solution over a predetermined time period and preferably at the rate of 1 millilitre/minute, followed by stirring for 20 minutes to obtain a second solution. The second solution is then heated to a temperature that facilitates the formation of carbon supported platinum nanoparticles having the mercapto alkyl acid and the alkyl thiol, attached thereon. The carbon supported catalyst is then filtered and washed with distilled water several times followed by drying preferably 30 °C for 16 hours.

By way of a specific example, a method of preparing carbon supported catalyst comprising carbon supported platinum nanoparticles having mercapto propyl sulfonic acid and octane thiol, attached thereon, is disclosed. The said method comprises of first preparing a dispersion of Vulcan carbon in water by adding 150 milligrams of Vulcan carbon in 50 millilitres distilled water at once, followed by stirring for 20 minutes to get it well dispersed at 0 °C. 92.53 milligrams of mercapto propylsulfonic acid (MPSA) (99%, 0.514 mmol) is then added to the above dispersion followed by stirring for 30 minutes at 0 °C and adding of 253 milligrams of K₂PtCl₆ (99%, 0.514 mmol) and 45.2 microlitres of Octane thiol (98%, 0.257 mmol; in 10 millilitres of ethanol) followed by stirring for 30 minutes to obtain the first solution. 71 milligrams of NaBH* (98%, 1.84 mmol) is dissolved in 25 millilitres distilled water and added to the first solution at the rate of 1 millilitres/minute, followed by stirring for 20 minutes to obtain the second solution. Finally, the second solution is heated at 60 °C under stirring for 1 hour. The carbon supported catalyst thus obtained was filtered and washed with distilled water several times followed by drying at 30 °C for 16 hours.

The present disclosure further provides a method for preparing the above disclosed electrode for a fuel cell. The said process comprises of mixing the carbon supported catalyst with an alcohol. The mixture thus obtained is coated on the gas diffusion layer followed by drying at a temperature that facilitates coating of the carbon supported catalyst on the gas diffusion layer.

The alcohol may be selected from the group comprising of methanol, ethanol, propanol, butanol, isobutanol and is preferably isopropanol.

A binder may be added to the solution to further facilitate the immobilization of the carbon supported catalyst on the gas diffusion layer. The binder may be any organic polymer including but not limited to polytetrafluoroethylene (PTFE), polyvinylidenefluoride- hexafluoropropene (PVDF-HFP), polyvinyl fluoride (PVF), polyvinylidenefluoride (PVDF), polychlorotrifluoroethylene (PCTEF), tetrafluoroethylene thylene (ETFE) and nation. The following examples of preparing the electrode are exemplary and should not be understood to be in any way limiting.

Example 1:

22 milligrams of C/Pt -MPS A np is mixed with 267 microlitres of water and 333 microlitres of 2-propanol under stirring for 15 minutes at 28 °C. The mixture thus obtained is coated on the gas diffusion layer followed by drying overnight at room temperature. This dried coated gas diffusion layer is used as an anode in hydrogen fuel cell. The power density observed is 330 milliwatt per centimeter square with the Pt loading of < 0.10 mg/cm . Similarly, other coating mixtures are prepared using C/Pt -MSA np and C/Pt- MPA np in place of C/Pt -MPS A np.

Example 2:

22 milligrams of C/Pt -MPSA np is mixed with 267 microlitres of water and 333 microlitres of 2-propanol. 4.4 milligrams of polyvinylidenefluoride-hexafluoropropene (PVDF-HFP) dissolved in 5 milligrams of dimethylformamide (DMF) is added to the above said mixture under stirring for 15 minutes. This mixture is then coated on the gas diffusion layer of 25 centimeter square in area. Coated gas diffusion layer is dried overnight at room temperature. This dried coated substrate is used as an anode and cathode in hydrogen fuel cell. The power density observed is 280 milliwatt per centimeter square. Similarly, other coating mixtures are prepared by using C/Pt-MSA np and C/Pt- MPA np instead of C/Pt- MPSA np.

Example 3:

22 milligrams of C/Pt-MPSA np is mixed with 150 microlitres of water and 150 microlitres of 2-propanol. 7.33 milligrams of polytetrafluoroethylene (PTFE, 60% aq.) is then added to above said mixture under stirring for 15 minutes. The mixture is then coated on the gas diffusion layer of 25 centimeter square in area. Coated substrate is dried overnight at room temperature. This dried coated gas diffusion layer is used as an anode and cathode in hydrogen fuel cell. The power density observed is 230 milliwatt per centimeter square. Similarly, other coating mixtures are prepared using C/Pt-MSA np and C/Pt-MPA np instead of C/Pt-MPSA np.

Example 4:

22 milligrams of C/Pt-MPSA np is mixed with 7.33 milligrams of polytetrafluoroethylene (PTFE, 60% aq.) under stirring for 15 minutes. The mixture thus obtained is coated on the carbon cloth of 25 centimeter square in area. Coated carbon cloth is dried overnight at room temperature. This dried coated carbon cloth is used as an anode and cathode in hydrogen fuel cell. . Similarly, other coating mixtures are prepared using C/Pt-MSA np and C/Pt-MPA np instead of C/Pt-MPSA np.

Example 5:

22 milligrams of C/Pt MPSA np is mixed with 267 microlitres of water and 333 microlitres of 2-propanol. 36.67 milligrams of Nafion (20% aq.-alcohol) is then added to the above mixture under stirring for 15 minutes. The mixture thus obtained is coated on the gas diffusion layer of 25 centimeter square in area. Coated gas diffusion layer is dried overnight at room temperature. This dried coated gas diffusion layer is used as an anode and cathode in hydrogen fuel cell. Another batch is prepared with the same composition and coated on the substrate of 10 centimeter square in area, followed by drying at room temperature. In another batch, 10, 15, 20 and 25 milligrams of Nafion solution (20% aq.- alcohol) is used in place of 36.67 milligrams of Nafion. The power density observed was observed in the range of 200-360 milliwatt per centimeter square. Similarly, other coating mixtures are prepared using C/Pt-MSA np and C/Pt-MPA np instead of C/Pt-MPSA np. Example 6:

22 milligrams of C/Pt-MPSA np is mixed with 267 microlitres of water and 333 microlitres of 2-propanol under stirring for 15 minutes at 28 °C. The mixture thus obtained is coated on the gas diffusion layer of 25 centimeter square in area. Coated gas diffusion layer is dried overnight at room temperature. This dried coated gas diffusion layer is used as an anode and cathode in hydrogen fuel cell. Similarly, other coating mixtures are prepared using C/Pt-MSA np and C/Pt-MPA np instead of C/Pt-MPSA np.

Example 7:

22 milligrams of C/Pt-MPSA-np is mixed with 267 microlitres of water and 333 microlitres of 2-propanol under stirring for 15 minutes at 28 °C. The mixture thus obtained is coated on the gas diffusion layer of 150 centimeter square in area. Coated gas diffusion layer is dried overnight at 28 °C. The loading of Platinum is around 0.10-0.15 milligrams/cm². This dried coated gas diffusion layer is used as an anode and cathode in hydrogen fuel cell. Figure 1 shows the Polarization curve (V-I) and power density curve (P-I) measured by loading of 0.10 milligrams Pt/cm2 on anode using single cell. The maximum power density obtained was 90.28 milliwatt per centimeter square. Similarly, other coating mixtures are prepared using C/Pt-MSA np and C/Pt-MPA np instead of C/Pt-MPSA np. Figure 2 shows the power density curve (P-I) measured by loading 0.15 milligrams Pt cm2 on anode using single cell at 44°C.

SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW

An electrode for a fuel cell comprising a gas diffusion layer having an electrode catalyst layer coated thereon, wherein the electrode catalyst layer comprises of a carbon supported catalyst, the carbon supported catalyst comprising carbon supported platinum nanoparticles having at least one mercapto alkyl acid selected from the group comprising of mercatopropyl sulfonic acid, mercapto propionic acid and mercapto succinic acid, attached thereon.

Such electrode(s), wherein the carbon supported catalyst further comprises at least one alkyl thiol selected from the group comprising of hexane thiol, octane thiol, decane thiol and dodecane thiol attached to the platinum nanoparticles.

Such electrode(s), wherein the electrode catalyst layer further comprises a binder. Such electrode(s), wherein the binder is selected from the group comprising of polytetrafluoroethylene, polyvinylidenefluoride-hexafluoropropene, polyvinyl fluoride, polyvinylidenefluoride, polychlorotrifluoroethylene, tetrafluoroethylene thylene and Nafion.

Such electrode(s), wherein the gas diffusion layer is selected from the group comprising of carbon cloth, carbon paper, carbon felt and teflon sheet.

Such electrode(s), wherein platinum comprises 0.05 -5 milligrams/cm² of the electrode catalyst layer.

A membrane electrode assembly for a fuel cell comprising a cathode and an anode disposed on both surfaces of an electrolyte membrane, the anode and cathode comprising the electrode as disclosed.

INDUSTRIAL APPLICABILITY

The electrode for a fuel cell described above is cost effective and highly efficient. The said electrode can be used in fuel cell technology and other electrolysis applications. The use of afore-described electron catalyst layer eliminates the use of nafion as proton conductor and makes fuel cells more economical.

Claims

WE CLAIM:

1. An electrode for a fuel cell comprising:

a gas diffusion layer having an electrode catalyst layer coated thereon, wherein the electrode catalyst layer comprises of a carbon supported catalyst, the carbon supported catalyst comprising carbon supported platinum nanoparticles having at least one mercapto alkyl acid selected from the group comprising of mercatopropyl sulfonic acid, mercapto propionic acid and mercapto succinic acid, attached thereon.

2. An electrode for a fuel cell as claimed in claim 1 wherein the carbon supported catalyst further comprises at least one alkyl thiol selected from the group comprising of hexane thiol, octane thiol, decane thiol and dodecane thiol attached to the platinum nanoparticles.

3. An electrode for a fuel cell as claimed in claim 1 or 2 wherein the electrode catalyst layer further comprises a binder.

4. An electrode for a fuel cell as claimed in claim 3 wherein the binder is selected from the group comprising of polytetrafluoroethylene, polyvinylidenefluoride- hexafluoropropene, polyvinyl fluoride, polyvinylidenefluoride, polychlorotrifluoroethylene, tetrafluoroethylene thylene and Nation.

5. An electrode for a fuel cell as claimed in claim 1 or 2 wherein the gas diffusion layer is selected from the group comprising of carbon cloth, carbon paper, carbon felt and teflon sheet.

6. An electrode for a fuel cell as claimed in claim 1 or 2 wherein platinum comprises 0.05 -5 milligrams/cm of the electrode catalyst layer.

7. A membrane electrode assembly for a fuel cell comprising:

a cathode and an anode disposed on both surfaces of an electrolyte membrane, the anode and cathode comprising the electrode according to any of claims 1 to 6.