Mechanism of L12-Pt3Co intermetallic compounds in fuel cells modulated by oxygen functional groups on the surface of carbon supports

Abstract

Phase transformation of disordered solid solution alloys to ordered intermetallic compounds via high-temperature annealing typically results in significant nanocrystal sintering, hindering practical applications in proton exchange membrane fuel cells (PEMFCs). Despite the potential significance of intermetallic compounds, the strategic modulation of surface oxygen content on carbon supports to optimize intermetallic compounds for fuel cell applications remains inadequately explored. This study systematically investigates the influence of oxygen functional groups on the carbon support surfaces on both intermetallic compound particle size formation and performance in PEMFCs. Comparative analysis of two pre-treatments shows that carbon supports with low surface oxygen content (EC-H₂/Ar) facilitate the formation of smaller Pt₃Co particles (6.02 ± 0.10 nm). Notably, Pt₃Co/EC-H₂/Ar showed exceptional stability in the Rotating Disc Electrode (RDE) test, manifesting merely 14 mV decay in half-wave potential after 5000 ADT cycles. Meanwhile, it also achieved a peak power density of 0.78 W/cm² at 1.60 A/cm² in H₂-air single cell tests and a minimum loss of 12.2 % of peak power density was demonstrated after 5000 accelerated stress test (AST) cycles compared Pt₃Co/original and Pt₃Co/HNO₃. Density-functional theory (DFT) calculations reveal that the ordered Pt₃Co lattice effectively modulates the d-band center, thereby attenuating the adsorption of oxygen-containing intermediates and reducing the reaction barrier for the ORR process. Furthermore, the carbon surface with about 2.5 % oxygen exhibits enhanced metal-support interactions, significantly alleviates the dissolution of surface Pt atoms. significantly improving the anti-dissolution ability of surface Pt atoms. Such surface modification strategy of carbon supports effectively suppresses the sintering of intermetallic compounds while simultaneously establishing a viable pathway for their practical implementation in fuel cell applications.