Efficient Alkaline Hydrogen Evolution Reaction Using Superaerophobic Ni Nanoarrays with Accelerated H2 Bubble Release

Abstract

Water electrolysis for producing green hydrogen is of central importance in the hydrogen economy to meet the global mission of carbon neutrality. Hydrogen evolution reaction (HER) under alkaline conditions has many advantages in cost and stability over acidic HER, but it requires high overpotential due to sluggish reaction kinetics. Pt-based materials are still considered the benchmark for HER catalysts, however, their high cost is the major hurdle for large-scale applications, motivating tremendous efforts to find earth-abundant catalytic materials as alternatives.In addition to catalytic materials, the formation and release of H2 bubbles on the surface of catalysts should be considered when designing efficient catalysts, as this significantly affects catalytic performance. Adhered H2 bubbles on the catalyst surface can cause reduced active surface sites, blockage of ion pathways, and destruction of catalyst film by inducing a large stretch force. Despite the adverse effects of H2 bubbles adhering to catalyst’s surface on the performance of water electrolysis, the mechanisms by which H2 bubbles are effectively released during the alkaline HER remain elusive.In this study, we conducted a systematic investigation on the effect of nanoscale surface morphologies on H2 bubble release behaviors and HER performance by employing earth-abundant Ni catalysts consisting of an array of Ni nanorods (NRs) with controlled surface porosities. Both aerophobicity and hydrophilicity of the catalyst’s surface vary according to the surface porosity of catalysts. The Ni catalyst with the highest porosity of ~52% exhibits superaerophobic nature as well as the best HER performance among the Ni catalysts. It was found that the Ni catalyst’s superaerophobicity combined with the effective open pore channels enables the accelerated release of H2 bubbles from the surface, leading to a significant improvement in geometric activities, particularly at high current densities, as well as intrinsic activities including both specific and mass activities. It was also demonstrated that the superaerophobicity enabled by highly porous Ni NRs can be combined with Pt and Cr having optimal binding abilities to further optimize electrocatalytic performance. Our work can help to elucidate the fundamental and practical design rules for efficient alkaline HER catalysts consisting of earth-abundant elements.