Chromium Promotes Phase Transformation to Active Oxyhydroxide for Efficient Oxygen Evolution

The oxygen evolution reaction (OER) is crucial for renewable energy technologies like metal–air batteries and water splitting. However, it suffers from sluggish kinetics, necessitating a high-activity and stable catalyst. In this study, we used Density Functional Theory (DFT) calculations to demonstrate that Cr doping favors the phase transition of metal (Fe, Co, Ni) hydroxide to the active phase oxyhydroxide. We synthesized FeCoNiCr hydroxide using an aqueous sol–gel method, ensuring that the four elements Fe, Co, Ni, and Cr are uniformly distributed at the atomic level. As an OER catalyst, FeCoNiCr hydroxide exhibits a very low overpotential of 224 mV in alkaline media, which is 52 mV lower than that of FeCoNi hydroxide, placing it among the best nonprecious metal catalysts reported so far. Additionally, it demonstrates long-term catalytic stability of 150 h. An assembled Zn-Air battery with FeCoNiCr hydroxides was cycled stably for 160 h with a low discharge/charge voltage difference of 0.70 V. DFT calculations and microkinetic modeling demonstrated that Cr doping significantly optimized the adsorption energies of OER intermediates at the Ni and Co sites, thereby enhancing overall OER activity. Bader charge calculations further revealed that Ni and Co in the catalysts consistently maintained a +3 valence throughout the OER process, which is beneficial for OER catalysis.