In Situ Transformation of Metal–Organic Frameworks into Hollow Nickel–Cobalt Double Hydroxide Arrays for Efficient Water Oxidation

Developing earth-abundant electrocatalysts for efficient oxygen evolution reaction (OER) is of paramount significance for electrochemical water splitting. Herein, an efficient in situ etching-deposition growth strategy is employed to transform pristine two-dimensional (2D) Co-metal-organic frameworks into hollow Ni/Co double hydroxide arrays (denoted as Ni/Co-DH), which not only yields a larger surface area and exposes more active sites but also decreases the activation energy to the OER. With structural and compositional benefits, the Ni/Co-DH exhibits high performance with an overpotential of 229 mV at 10 mA cm-2 and exceptional long-term stability of over 90 h in 1 M KOH medium for OER, comparable to most non-noble oxygen evolution catalysts reported so far. In addition, a two-electrode Ni/Co-DH∥Pt/C electrolyzer also requires a considerably low voltage of 1.58 V at 10 mA cm-2 for overall water splitting. This study affords a rational strategy to develop water-alkali electrolyzers with great complexity for large-scale water-splitting systems.