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 CoxRh3–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 CoxRh3–xO4 series, Co1.47Rh1.53O4 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 (εd) 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 Co1.47Rh1.53O4 nanoparticles, resulting in a rational lattice structure that can be applied as an effective OER catalyst electrode.