Improving electrocatalytic hydrogen evolution reaction with NiO2/Ni2O3 heterostructures synthesized by laser spraying

Efficient, stable, low costs and environmentally friendly electrocatalysts are crucial for hydrogen evolution reactions. Multi-dimensional porous coatings containing NiO2/Ni2O3 heterostructures were fabricated by laser spraying through regulating spray distance. The surface morphology, oxygen content and microstructures of the coatings were characterized. The electrochemical performance of the coatings was evaluated and the density functional theory (DFT) calculations were employed to explore the electrocatalytic mechanism. The results indicate that increasing the spray distance benefited the formation of multi-dimensional porous coatings. The bonding mechanism of the coatings involved metallurgical bonding and mechanical interlocking. The oxygen content of the coatings increased as the spraying distance increased, and the NiO2/Ni2O3 heterostructure was found due to the rapid solidification of the melted particles. Specifically, the catalytic electrode with the NiO2/ Ni2O3 heterostructure exhibited better performance. The charge density difference from DFT calculations indicates electron transfer at the interface of the NiO2/Ni2O3 heterostructure. Furthermore, the NiO2/Ni2O3 heterostructure exhibited higher density of states and lower Gibbs free energy compared to the individual NiO2 and Ni2O3 structures, which benefited the enhancement of hydrogen adsorption and reaction rates. This work provides a new technology for hydrogen production catalysts with the advantages of porous structures, low costs and simple operation.