Role of diffusivity in hydrogen evolution reaction

The hydrogen binding strength on a catalyst is known to be an important factor in electrochemical hydrogen evolution. Although much effort has been exerted to improve the binding strength to exploit precious-metal-free catalysts, their performance is still inferior to that of platinum. Based on first-principles calculations, here we investigate the role of a different physical property, namely, the diffusivity, in hydrogen evolution reaction. On typical catalytic metal surfaces, the diffusivity of hydrogen is high, and the binding strength is the dominant controlling factor. In contrast, the diffusion barrier on the surfaces or edges of two-dimensional catalytic materials such as MoS₂ is found to be inversely proportional to the binding strength. This relatively large diffusion barrier may serve as another important factor on such surfaces. Moreover, the charge density wave of a catalytic surface can also significantly modulate the diffusion barrier. These findings provide important insights into how to design efficient catalysts for enhanced hydrogen evolution reaction.