In situ controllable construction of Ni@NiO Schottky heterojunctions for electrocatalytic hydrogen evolution

Abstract

NiO is widely recognized as a prospective electrocatalyst for the hydrogen evolution reaction (HER) due to its abundant reserves and superior electrocatalytic performance. However, there exists a substantial gap between its HER catalytic activity and practical application. In this research, we present a straightforward in situ partial reduction methodology via vacuum annealing to synthesize Ni@NiO Schottky heterojunctions upon carbon fiber paper (CFP). The successful formation of the heterojunctions was confirmed using Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Herein, the CFP serves two roles: (a) acting as the substrate to support the nanosheet array structure and (b) reducing NiO to Ni at high temperatures. By adjusting the vacuum annealing temperature, the proportion of Ni to NiO within the Ni@NiO Schottky heterojunction can be regulated in a wide range, thus regulating the HER activity of the samples. When the vacuum annealing temperature is 600 °C, the Ni@NiO heterojunction sample exhibits outstanding HER performance with an overpotential of 172 mV at 10 mA cm⁻², which decreases the energy consumption by 66% relative to the pure NiO sample. The in situ construction of Ni@NiO Schottky heterojunctions by such partial reduction methodology via vacuum annealing significantly enhances the HER performance of NiO with good stability, making it a promising candidate for hydrogen evolution electrocatalysts. This research also provides a method to improve the activity of other HER catalysts.