Chromium Promotes\nPhase Transformation to Active Oxyhydroxide\nfor Efficient Oxygen Evolution

The oxygen evolution reaction (OER) is crucial for renewable\nenergy\ntechnologies like metal–air batteries and water splitting.\nHowever, it suffers from sluggish kinetics, necessitating a high-activity\nand stable catalyst. In this study, we used Density Functional Theory\n(DFT) calculations to demonstrate that Cr doping favors the phase\ntransition of metal (Fe, Co, Ni) hydroxide to the active phase oxyhydroxide.\nWe synthesized FeCoNiCr hydroxide using an aqueous sol–gel\nmethod, ensuring that the four elements Fe, Co, Ni, and Cr are uniformly\ndistributed at the atomic level. As an OER catalyst, FeCoNiCr hydroxide\nexhibits a very low overpotential of 224 mV in alkaline media, which\nis 52 mV lower than that of FeCoNi hydroxide, placing it among the\nbest nonprecious metal catalysts reported so far. Additionally, it\ndemonstrates long-term catalytic stability of 150 h. An assembled\nZn-Air battery with FeCoNiCr hydroxides was cycled stably for 160\nh with a low discharge/charge voltage difference of 0.70 V. DFT calculations\nand microkinetic modeling demonstrated that Cr doping significantly\noptimized the adsorption energies of OER intermediates at the Ni and\nCo sites, thereby enhancing overall OER activity. Bader charge calculations\nfurther revealed that Ni and Co in the catalysts consistently maintained\na +3 valence throughout the OER process, which is beneficial for OER\ncatalysis.