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Platinum metal (PtM, M=Ni, Fe, Co) alloys catalysts show high oxygen reduction reaction (ORR) activity due to their well‐known strain and ligand effects. However, these PtM alloys usually suffer from a deficient ORR durability in acidic environment as the alloyed metal is prone to be dissolved due to its high electronegativity. Herein, we report a new class of PtMn alloy nanodendrite catalyst with low‐electronegativity Mn‐contraction for boosting the oxygen reduction durability of fuel cells. The moderate strain in PtMn, induced by Mn contraction, yields optimal oxygen reduction activity at 0.53 A mg−1 at 0.9 V versus reversible hydrogen electrode (RHE). Most importantly, we show that relative to well‐known high‐electronegativity Ni‐based Pt alloy counterpart, the PtMn nanodendrite catalyst experiences less transition metals' dissolution in acidic solution and achieves an outstanding mass activity retention of 96 % after 10,000 degradation cycles. Density functional theory calculation reveals that PtMn alloys are thermodynamically more stable than PtNi alloys in terms of formation enthalpy and cohesive energy. The PtMn nanodendrite‐based membrane electrode assembly delivers an outstanding peak power density of 1.36 W cm−2 at a low Pt loading and high‐performance retention over 50 h operations at 0.6 V in H2‐O2 hydrogen fuel cells. [ABSTRACT FROM AUTHOR]

Pt poisoning by phosphate in high temperature proton exchange membrane fuel cells (HT‐PEMFC) leads to loadings up to 1 mgPt cm−2 per electrode of costly materials. While cheaper Fe−N−C catalysts are unaffected by phosphate deactivation and contribute to the catalysis of the oxygen reduction reaction, their volumetric activity is substantially lower. In this study, the effect of Pt‐loading reduced hybrid cathodes for HT‐PEMFC is investigated using commercial Celtec®‐P‐based assembling. A promising effect of Fe−N−C incorporation in terms of acid attraction and activity retention is found. A longer activation (230 h, 0.3 A cm−2) for the hybrid membrane electrode assembly (MEA) is necessary, due to the slower acid distribution within Fe−N−Cs. This study shows the potential of Pt‐content reduction by up to 25 % compared to standard MEA using hybrid electrodes. Moreover, important insights for future strategies of cell activation are revealed for these hybrid MEAs. [ABSTRACT FROM AUTHOR]