Catalyst and catalyst‐support durability

Automotive duty cycles impose multiple mechanisms for the loss of kinetic activity of oxygen-reduction catalysts for proton-exchange membrane fuel cells. Load cycling causes dissolution of Pt into the electrolyte, leading to the growth of larger Pt particles with lower specific surface area and to the permanent loss of Pt into the ionomer phase, where it is no longer active. An increase in the activity per surface Pt atom during cycling partially compensates for the former, but not the latter, loss mechanism. Higher initial activities can be achieved with Pt-alloy catalysts, but these may bring additional loss mechanisms into play. Corrosion of the carbon support can decrease both the kinetic activity of the catalyst and the ability of the fuel cell to sustain high current densities. The rates of carbon corrosion depend strongly on both the type of carbon used and the fuel cell operating conditions, but all types of carbon seem to exhibit significant fuel cell performance loss after ∼10% of the carbon is consumed. Noncarbon supports give promise of improved durability under severe conditions, but their practical use will require improved control over bulk physical properties, surface chemistry, and pore structure. Keywords: electrocatalyst; oxygen reduction activity; catalyst support; durability; particle size growth; carbon corrosion; Pt dissolution; voltage cycling; place exchange; noncarbon support