Electrical Junction at the Substrate-Fe₃O₄ Nanoparticle Interface Governs Oxygen Evolution Reaction Activity

The oxygen evolution reaction (OER) can be fundamentally considered as a process in which an electrocatalyst converts electrical energy to chemical energy. In nanoparticle-based OER devices, current flows through complex substrate-particle and interparticle junctions before delivering the energy at the catalyst-electrolyte interface. Performance optimization requires the right combination of the metallic substrate and semiconducting catalyst. We demonstrate that the performance of Fe₃O₄ nanoparticles is strongly influenced by the principle of energy matching at the substrate-catalyst interface. Using substrates with distinct work functions, we show that the Ohmic junctions, formed between Fe₃O₄ and low work function metals (Cu, Ni), exhibit significantly lower overpotentials and Tafel slopes than Schottky junctions formed with high work function materials (glassy carbon (GC), Pt, and Au). Furthermore, we tune the GC and Fe₃O₄ nanoparticle interface from Schottky to Ohmic by introducing a Ni₂P buffer layer. Our findings highlight the importance of interfacial engineering for designing efficient water electrolysis devices.