Modeling of Transient State Carbon Corrosion for PEMFC Electrodes

The degradation of carbon on PEMFC electrodes has been reported as carbon corrosion recently [1-4]. These carbon corrosion phenomena are fatal problems for the PEMFC commercialization because of the short life time. The developments of catalyst materials, cell designs and the management of operation condition are important to solve these problems. Generally speaking, the carbon corrosion requires high overpotential in PEMFC because of slow kinetic properties, though the carbon might start to be oxidized even at 0.2 V (vs. RHE) based on thermodynamics. In steady PEMFC operations, the carbon materials on both electrodes are rarely exposed to such high potential. But, in transient conditions, the carbon materials on electrodes are often exposed to such conditions. Some cases are predicted: (a) start up, (b) after shut down, (c) partial hydrogen starvation [3] and so on. In every case, it is predicted that the hydrogen deficiency or hydrogen and oxygen co-existence on anode electrode will cause a large enough overpotential between the solution and the cathode metal to oxidize the carbon supports on the cathode electrode. At start up, first the anode gas channel is filled with air, hydrogen flows into cell from anode inlet (Figure 1). Then hydrogen gas diffused into anode catalyst layer with time dependence. In this model, carbon oxidation occurred on the part of the cathode electrode that is opposite the part of anode electrode exposed to air. Figure 2 shows the result of the solution potential in membrane (b) and carbon corrosion current on cathode electrode (a) at PEMFC start up condition at an arbitrary moment. The solution potential distribution drastically changed at the 0 50 100 150 200 ca rb on c or ro si on cu rr en t d en si ty / m A /c m 2 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 -0 .11 -0 .1 0 -0 .0 9 -0 .0 8 -0 .0 7 -0 .0 6 -0 .0 5 -0 .0 4 -.03 -.02 .01 0 50 100 150 200 di st an ce fr om a no de / um