Electronic structure engineering of transition metal dichalcogenides for boosting hydrogen energy conversion electrocatalysts

Electrocatalytic water splitting for hydrogen production is an appealing strategy to reduce carbon emissions and generate renewable fuels. This promising process, however, is limited by its sluggish reaction kinetics and high-cost catalysts. The two- dimensional (2D) transition metal dichalcogenides (TMDCs) have presented great potential as electrocatalytic materials due to their tunable bandgaps, abundant defective active sites, and good chemical stability. Consequently, phase engineering, defect engineering and interface engineering have been adopted to manipulate the electronic structure of TMDCs for boosting their exceptional catalytic performance. Particularly, it is essential to clarify the local structure of catalytically active sites of TMDCs and their structural evolution in catalytic reactions, using atomic resolution electron microscopy and the booming in situ technologies, which is beneficial for exploring the underlying reaction mechanism. In this review, the growth regulation, characterization, particularly atomic configurations of active sites in TMDCs were summarized. The significant role of electron microscopy for the understanding of the growth mechanism, the controlled synthesis and functional optimization of 2D TMDCs are discussed. This review will shed lights on the design and synthesis of novel electrocatalysts with high performance, as well as prompt the application of advanced electron microscopy in the research of materials science.