Carbon-Supported Pt-Rich Cr-Mn-Fe-Co-Ni-Pt Nanoparticles for Enhanced Oxygen Reduction Reaction

Abstract

In this work, a fast moving bed pyrolysis method was used for the synthesis of multimetal catalyst nanoparticles, which have higher ORR activity and durability than those of the Pt–C catalyst synthesized by the same method and a commercial Pt–C catalyst. Carbon-supported multimetal catalyst nanoparticles (Cr₁₀Mn₁₀Fe₁₀Co₁₀Ni₁₀Pt₅₀) were synthesized, and the Pt fraction increased from 55 to 66 at% by acid washing. Structural characterization revealed that multimetal catalysts consist of well-dispersed nanoparticles, whose diffraction patterns were assigned to an L1₀-type ordered intermetallic structure rather than to the disordered fcc structure characteristic of the conventional CrMnFeCoNi Cantor alloy. The mass and specific activities (MA, SA) of both catalysts in 0.1 M HClO₄ at 0.9 V vs RHE are approximately three times higher than those for commercial Pt–C, reaching 780 A g_Pt^–1 and 17 A m_Pt^–2, respectively. The activity enhancement reflects a genuine increase in intrinsic site activity rather than a surface area effect. After 10,000 potential cycles, the multimetal catalysts retained 84–87% of their initial electrochemically active surface area (ECSA), compared with 66% for commercial Pt–C. Although the multimetal catalysts showed lower relative retention of MA and SA than commercial Pt–C, their higher initial activities resulted in substantially higher absolute ORR activities after cycling. Degradation analysis indicated selective dissolution of 3d metals during potential cycling and possible Pt redeposition, reinforcing the formation of a Pt-rich near-surface region, which contributes to higher retention of the ECSA of these catalysts. This performance arises from the combination of an ordered L1₀ intermetallic structure, a Pt-rich near-surface region, and a chemically complex subsurface, enabling high intrinsic ORR activity while mitigating the loss of electrochemically accessible Pt surface area.