Polarisation Effects at Metal/Support Interfaces Transcend Reactivity Constraints in Oxygen Electrocatalysis

Platinum-based catalysts are widely used for the Oxygen Reduction Reaction (ORR) in fuel cells, metal-air batteries, and electrolyzers due to their excellent electrocatalytic activity and stability. However, platinum's high cost and scarcity have led to extensive efforts in alloying platinum with other transition metals and nano-structuring the Pt surface. Experimentally synthesizable, rationally designed, supported metal films on various earth-abundant carbides and nitrides have the potential to exceed the theoretical maximum for ORR and achieve high activity and stability with low Pt usage. In this study, we selected (111) surfaces of nonmagnetic 2D and 3D metal carbides and nitrides (TiC, TiN, VC, VN, CrN, NiC, NiN, MoC, MoN, and WC), and adsorbed mono- and bilayers of Pt, Ag, and Au epitaxially and as moire patterns. We assessed the thermodynamic and electrochemical stability of 200+ films and evaluated their ORR catalytic activity through a limiting potential analysis using the computational hydrogen electrode model. The OOH* vs OH* scaling relation deviates from the bond order conservation slope of 1 (seen across unsupported metals, alloys, and single-atom catalysts). This deviation in slope results in the ORR limiting potential volcano peak shifting upward by >0.15 V, relative to the unsupported metal catalysts. These deviations in slopes are attributed to modulations in the metal film's reactivity by electronic metal-support interaction (EMSI) and strain. The computational analysis explains the superior stability and performance of experimentally validated Pt/TiWC catalysts. Furthermore, we identify at least 10 heterostructures with higher limiting potentials than Pt (111), including Pt/CrC with the highest at 0.93 V. We perform a detailed electronic structure analysis on these heterostructures to rationalize their increased limiting potentials relative to Pt (111) and qualitatively explain these deviations in scaling slopes from bond order conservation rules. Tuning the reactivity of the metal film via its interaction with the underlying support opens a wide material space for designing high-performance ORR catalysts with reduced precious metal loading.