Water electrolysis for hydrogen harvesting has become a research hotspot in both academia and industry due to its low carbon emissions, high energy efficiency, and high purity, which offer significant advantages over the majority of hydrogen production technologies. Thereinto, the electrocatalytic hydrogen reaction （HER） is at the core, which aways involves a multi-step hydrogen transfer process and multiple active sites working together. However, catalytic correlations between those active sites and potential hydrogen spillover effects involved are often overlooked. In this paper, we first review the hydrogen evolving properties and reaction mechanisms in electrocatalytic systems such as transition metal oxides, phosphides, and sulfides. By combining traditional theories of thermal catalysis, active sites involved in hydrogen spillover are then conceptually summarized into both the primary and secondary active sites, elucidating their catalytic relevance and functional differences. This paper will not only provide a design concept for the creation of efficient and inexpensive electrocatalysts for hydrogen evolution, but also serve as a useful reference for further studies of hydrogen transfer behaviors in other hydrogen-involved electrocatalytic reactions.

Contents

1 Introduction

2 Electrocatalyst for hydrogen spillover

2.1 Metal oxide

2.2 Metal phosphide

2.3 Metal sulfides

3 Conclusion and outlook