Proton
exchange membrane fuel cells (PEMFCs) are a promising
zero-emission
power source for heavy-duty vehicles (HDVs). However, long-term durability
of up to 25,000 h is challenging because current carbon support, catalyst,
membrane, and ionomer developed for traditional light-duty vehicles
cannot meet the stringent requirement. Therefore, understanding catalyst
degradation mechanisms under the HDV condition is crucial for rationally
designing highly active and durable platinum group metal (PGM) catalysts
for high-performance membrane electrode assemblies (MEAs). Herein,
we report a PGM catalyst consisting of platinum nanoparticles with
a high content (40 wt %) on atomic-metal-site (e.g., MnN4)-rich carbon support. MEAs with the Pt (40 wt %)/Mn–N–C
cathode catalyst achieved significantly enhanced performance and durability,
generating 1.41 A cm–2 at 0.7 V under HDV conditions
(0.25 mgPt cm–2 and 250 kPaabs pressure) and retaining 1.20 A cm–2 after an extended
and accelerated stress test up to 150,000 voltage cycles. Electron
microscopy studies indicate that most fine Pt nanoparticles are retained
on or/and in the carbon support covered with the ionomer throughout
the catalyst layer at the end of life. During the long-term stability
test, the observed electrochemical active surface area reduction and
performance loss primarily result from Pt depletion in the catalyst
layer due to Pt dissolution and redeposition at the interface of the
cathode and membrane. The first-principle density functional theory
calculations further reveal a support entrapment effect of the Mn–N–C,
in which the MnN4 site can specifically adsorb the Pt atom
and further retard the Pt dissolution and migration, therefore enhancing
long-term MEA durability.