Formulation of an active layer having improved performances

Abstract

An active layer for a proton-exchange membrane fuel cell (PEMFC) including at least two perfluorosulfonate ionomers.

Claims

1. An active layer for a proton-exchange membrane fuel cell (PEMFC) comprising a catalyst and a mixture of at least a first perfluorosulfonate ionomer and a second perfluorosulfonate ionomer, the first perfluorosulfonate ionomer having a first dangling chain, the first perfluorosulfonate ionomer having the following structure: ##STR00009##  wherein k is an integer, the second perfluorosulfonate ionomer having a second dangling chain, and wherein the second dangling chain is shorter than the first dangling chain.

2. The active layer for a proton-exchange membrane fuel cell (PEMFC) of claim 1, wherein the second perfluorosulfonate ionomer has the following structure: ##STR00010##  wherein k is an integer.

3. The active layer for a proton-exchange membrane fuel cell (PEMFC) of claim 1, wherein the relative concentration of the first ionomer is in the range from 50 to 80% by weight of a combined amount of the first ionomer and the second ionomer as dry matter, and wherein the relative concentration of the second ionomer is in the range from 20% to 50% by weight of said dry matter.

4. The active layer for a proton-exchange membrane fuel cell (PEMFC) of claim 3, wherein the relative concentration of the first ionomer is in the range from 60 to 70% by weight of a combined amount of the first ionomer and the second ionomer as dry matter, and wherein the relative concentration of the second ionomer is in the range from 30 to 40% by weight of said dry matter.

5. The active layer for a proton-exchange membrane fuel cell (PEMFC) of claim 1, wherein the catalyst comprises platinum nanoparticles on a carbonaceous support.

6. A membrane-electrode assembly (MEA), wherein at least one of an anode of the MEA and a cathode of the MEA comprises an active layer as recited in claim 1.

7. The membrane-electrode assembly (MEA) of claim 6, wherein a membrane of the MEA is made of one of the first and second perfluorosulfonate ionomers.

8. A proton-exchange membrane fuel cell (PEMFC) comprising the membrane-electrode assembly (MEA) of claim 6.

9. A proton-exchange membrane fuel cell (PEMFC) comprising the membrane-electrode assembly (MEA) of claim 7.

10. A proton-exchange membrane fuel cell (PEMFC)-type fuel cell comprising an active layer as recited in claim 1.

11. A membrane-electrode assembly (MEA), wherein a cathode of the MEA comprises an active layer as recited in claim 1.

12. A membrane-electrode assembly (MEA) as recited in claim 6, wherein the anode of the MEA is made of one of the first and second perfluorosulfonate ionomers.

13. A membrane-electrode assembly (MEA) as recited in claim 6, wherein a membrane of the MEA is made of the first perfluorosulfonate ionomer.

14. A membrane-electrode assembly (MEA) as recited in claim 6, wherein the anode of the MEA is made of the first perfluorosulfonate ionomer.

15. A catalytic ink for the forming of an active layer, the catalytic ink comprising; a mixture of at least a first perfluorosulfonate ionomer and a second perfluorosulfonate ionomer, the first perfluorosulfonate ionomer having a first dangling chain, the first perfluorosulfonate ionomer having the following structure: ##STR00011##  wherein k is an integer, the second perfluorosulfonate ionomer having a second dangling chain, and wherein the second dangling chain is shorter than the first dangling chain.

16. The catalytic ink of claim 15, wherein the catalytic ink further comprises a catalyst.

17. The catalytic ink of claim 16, wherein the catalyst comprises platinum nanoparticles on a carbonaceous support.

18. The catalytic ink of claim 16, wherein the catalytic ink further comprises a solvent or carrier fluid.

19. The catalytic ink of claim 17, wherein the catalytic ink further comprises a solvent or carrier fluid.

20. An active layer for a proton-exchange membrane fuel cell (PEMFC) comprising a catalyst and a mixture of at least a first perfluorosulfonate ionomer and a second perfluorosulfonate ionomer, the first perfluorosulfonate ionomer having a first dangling chain, the second perfluorosulfonate ionomer having a second dangling chain, wherein the second dangling chain is shorter than the first dangling chain, the second perfluorosulfonate ionomer having the following structure: ##STR00012##  wherein k is an integer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing features and advantages will now be discussed in the following non-limiting description of a specific embodiment, in relation with the accompanying drawings, among which:

(2) FIG. 1 shows the diagram of the operating principle of a PEMFC-type fuel cell.

(3) FIG. 2 shows the structure of the dangling chains of perfluorosulfonate ionomers (on the left-hand side, Nafion®, on the right-hand side, Aquivion®).

(4) FIG. 3 compares the performances of a device according to the invention (mixture of Aquivion® and Nafion®) and of prior art devices (Aquivion® or Nafion® alone).

EMBODIMENTS OF THE INVENTION

(5) I/Forming of the Devices:

(6) The forming of the MEA (Membrane-Electrode Assembly) is carried out in three steps: the first step comprises preparing the catalytic ink, comprising the ionomer(s) and the catalyst on a carbonaceous support, in a solvent. the second step is the manufacturing of the electrode by deposition of the ink on the diffusion layer, according to a method described hereafter. the last manufacturing step is the assembly of two electrodes (cathode and anode) with, in the middle, a membrane generally made of the same polymer as one of the ionomers present in the active layer.

(7) a/Device According to the Invention:

(8) According to the invention, the composition of the anode differs from that of the cathode. The following percentages should be understood by mass, in the dry catalytic layer:

(9) The anode is made of 75% of catalyst (containing 50% of carbon and 50% of platinum) and of 25% of ionomer.

(10) The cathode is generally made of 75% of the same catalyst, of 18% of the first ionomer, preferably Nafion® and of 7% of the second ionomer, preferably Aquivion®.

(11) The membrane is a Nafion®-type membrane.

(12) A water-based catalytic ink is prepared to obtain these concentrations. According to the manufacturing method, the dry extract varies from 1% to 20%. A thermal treatment enables to dry the deposited ink.

(13) The assembly of the anode and of the cathode, with a membrane in the middle, provides the MEA. It takes place in a press, according to temperature, pressure, and duration conditions variable according to the membrane used.

(14) The MEA thus obtained, having a 25-cm.sup.2 surface area, is assembled in a single cell to test the performances. The single cell is fitted with monopolar plates allowing the incoming of gases, with current collection plates, and with clamping plates.

(15) The structure of the used Nafion® (supplied by Dupont) and Aquivion® (supplied by Solvay) is illustrated in FIG. 2.

(16) b/Prior Art Devices (Nafion® Alone or Aquivion® Alone):

(17) The manufacturing protocol of a MEA containing a single ionomer is the same as hereabove. The only difference is the cathode manufacturing. The latter is made of the same materials as the anode, that is, 75% of catalyst, and 25% of ionomer.

(18) II/Performances of the Devices:

(19) The performances of the devices are studied in conditions close to those recommended for an automotive use.

(20) The operating temperature is 80° C. The relative humidity varies from 50% to 80%. The gas pressure is 1.5 bar.

(21) The test starts with a measurement of the rest potential. A current is then imposed, from 0 to 2 A/cm.sup.2, and the potential is measured. The result is a voltage-vs.-current curve representative of the cell performances.

(22) The results are shown in FIG. 3. In the cell operating conditions, the mixture of Nafion® (70% concentration) and Aquivion® (30% concentration) enables to exceed the performances of Nafion® alone.