Catalyst development for the efficient direction of electrocatalytic water splitting with much less overpotential is crucial for meeting large-scale hydrogen generation. Being highly abundant and cost-effective, 3d transition-metal-based catalysts show promising activities in alkaline conditions. In this work, bimetallic nickel−cobalt carbonate hydroxide hydrate (NiCo-CHH) was prepared by a co-precipitation method with varying molar ratios of Ni/Co of 0.5:1, 1:1, and 1.5:1, which were analyzed for oxygen evolution reaction (OER) study in both alkaline (1 M KOH) and near-neutral (1 M NaHCO 3 ) media. For OER in 1 M KOH, NiCoCHH 1:1 required overpotential of just 238 mV at 10 mA cm −2 current density compared to other ratios of 0.5:1 and 1.5:1, which required 290 and 308 mV, respectively. Similarly, in 1 M NaHCO 3 , NiCoCHH 1:1 required an overpotential of 623 mV to reach 10 mA cm −2 . A post-OER study confirmed the formation of NiOOH during OER. The observed faradaic efficiency was nearly 95.21% for the NiCoCHH 1:1 catalyst. A two-electrode setup with NiCoCHH 1:1∥Pt required just 312 mV as an overpotential at 10 mA cm −2 . These kinds of comparative studies can be used in other 3d transition-metal-based catalysts for OER in the future.

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