Overall Water-Splitting Electrocatalysts Based on 2D CoNi-Metal-Organic Frameworks and Its Derivative

Efficient electrocatalysts composed of non-precious elements are central to the development of overall water-splitting system. Herein, it is demonstrated that 2D CoNi-metal-organic framework (CoNi-MOF) array grown directly on a Cu substrate is a highly efficient and stable electrocatalyst for oxygen evolution reaction with a low overpotential (265 mV at 10 mA cm⁻²) in alkaline medium. With the combination of in situ conducting atomic force microscopy and two-point conductivity measurements, it is revealed that the electron transfer is facilitated along the Z-axis better than the other directions, which can lead to an enhanced catalytic activity. In addition, a simple annealing treatment converts this 2D CoNi-MOF to a hybrid nanoplate array of metallic nitrides on an amorphous carbon network, which catalyzes the hydrogen evolution reaction with a compatible overpotential of 120 mV (at 10 mA cm⁻²) and excellent stability. The overall water splitting using these 2D CoNi-MOF-based catalysts shows a 99% Faradaic efficiency at 1.64 V, suggesting a promising pathway forward for the commercial realization of complete water-splitting systems.