Rational Lattice Engineering of Spinel Co_xRh_3-xO₄ Solid Solution Expediting Oxygen Evolution Reaction

Electrochemical water splitting holds great promise as a viable method to produce a sustainable hydrogen fuel. Spinel crystal structure (AB₂O₄) is regarded as a promising electrocatalyst for the anodic oxygen evolution reaction (OER) of water electrolysis. Fine-tuning of metal cations’ composition at the tetrahedral (A) and octahedral (B) sites within the well-defined spinel structure plays a critical role in determining the electroactivities for electrochemical reactions, including the OER. Herein, we report the rational incorporation of rhodium ions into the B sites of the spinel lattice of Co₃O₄ to form the Co_xRh_3-xO₄ solid solution via an ecofriendly acid-base reaction between metal (Co, Rh) chlorides and NaOH in an aqueous solution, followed by the thermal annealing process. Among the Co_xRh_3-xO₄ series, Co_1.47Rh_1.53O₄ nanoparticles represented superior OER catalytic performances in alkaline conditions, verified by the lowest onset potential, small Tafel slope, and excellent long-term stability. The combination of experimental data with theoretical simulations suggests that the moderate d-band center (ϵ_d) energy levels are responsible for the enhanced activity by tuning the adsorption and desorption strengths of oxygen-containing intermediates, such as *OH, *O, and *OOH species. Our findings introduce a straightforward and environmentally friendly synthetic methodology for a single phase of spinel Co_1.47Rh_1.53O₄ nanoparticles, resulting in a rational lattice structure that can be applied as an effective OER catalyst electrode.