Development of efficient electrocatalysts usually relies on half-cell electrochemical tests for rapid material screening, which however are not always consistent with the associated full cell evaluation. This study designs a tensile-strained Pd anode and reveals that with a lower apparent activity toward the hydrogen oxidation reaction as compared to the unstrained one, it exhibits a surprisingly high activity in proton exchange membrane fuel cells (PEMFCs). With an ultralow Pd loading of 4.5 µg cm-2 , the tensile-strained Pd achieves a maximum power density of 1048 mW cm-2 , indicating a 30-fold improvement in power efficiency than that of commercial Pd/C, nearly four times of that of the unstrained one. This discrepancy can be ascribed to the hydrogen-rich surface in the H2 atmosphere of PEMFCs owing to the accelerated hydrogen "spill-over" in the tensile-strained Pd with a standout hydrogen storage property.
Keywords: hydrogen oxidation reaction; hydrogen “spill-over;” Pd; proton exchange membrane fuel cells; tensile strain.
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