Interfacial Engineering of MgCo₂O₄@Ni(OH)₂ Heterostructures for Efficient Alkaline Water Oxidation

Developing highly active, durable, and earth-abundant electrocatalysts is essential for advancing sustainable hydrogen production through electrochemical water oxidation. Herein, a hierarchical MgCo₂O₄@Ni(OH)₂ heterostructure was constructed by electrodepositing Ni(OH)₂ nanosheets onto MgCo₂O₄ nanorods and investigated as an electrocatalyst for alkaline water splitting. The intimate contact between the MgCo₂O₄ nanorod and Ni(OH)₂ nanosheet creates a hierarchical architecture with abundant accessible surface sites and favorable pathways for electrolyte penetration and charge transport. Among the prepared electrodes, MCO@Ni(OH)₂-2 exhibited the best OER performance, requiring an overpotential of 348 mV to achieve 10 mA cm^-2 with a Tafel slope of 70.2 mV dec^-1. The optimized electrode also showed a low charge-transfer resistance of 2.7 Ω, indicating favorable interfacial charge transport. Its hierarchical architecture provides a highly accessible electrochemical surface, shortened ion-diffusion pathways, and efficient electrolyte penetration, thereby promoting the adsorption and transformation of reaction intermediates. The enhanced performance is attributed to the optimized Ni(OH)₂ nanosheet coverage, increased electrochemically active surface area, and synergistic interaction between the MgCo₂O₄ nanorod and Ni(OH)₂. Furthermore, the electrode retained substantial electrocatalytic activity during prolonged cycling and continuous operation under alkaline conditions. These results demonstrate that engineering hierarchical oxide/hydroxide interfaces offers an effective approach for developing efficient transition-metal-based electrocatalysts for sustainable water splitting.