ABSTRACT
This chapter describes the different mechanisms causing decay in electrocatalyst surface area and activity at the PEMFC cathode and anode. In operational automotive PEMFC systems, load cycles and start-stop events will be common occurrences, leading to higher voltages and Pt dissolution/sintering, particularly at the cathode. The effect of these voltage transients is first discussed in the context of Pt/C electrocatalyst materials, then extended to Pt alloys and more novel structures such as core-shell electrocatalysts. Decay of cathode and anode electrocatalysts is considered; however, corrosion of catalyst supports is the subject of a separate chapter. The effects of varying the accelerated test conditions used, for example, RDE or MEA, steady state or cycles, and the potential limits, relative humidity and temperature used, are all shown to play a significant role in electrocatalyst decay at both anode and cathode electrodes. Conventional alloy materials, such as PtCo cathodes,
show short-term benefit of higher mass activity and surface area stability over commercial Pt/C electrocatalysts but fall short of the durability required when tested under real automotive drive cycles. Likewise, conventional anode alloys PtRu/PtMo show stability issues under start-stop cycles, but anode cost/metal loading reduction using Pt/C materials is limited by their intolerance to fuel impurities. Novel structures such as core-shell electrocatalysts provide exciting opportunities for precious metal thrifting and cost reduction, but demonstration of their stability to operational voltage cycles within MEAs is still in progress.
