Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets

Molybdenum disulfide (MoS₂) is a promising nonprecious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding of the factors that impact its catalytic activity hinders further design and enhancement of MoS₂-based electrocatalysts. Here, by using novel porous (holey) metallic 1T phase MoS₂ nanosheets synthesized by a liquid-ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity toward HER from five representative MoS₂ nanosheet samples, including 2H and 1T phase, porous 2H and 1T phase, and sulfur-compensated porous 2H phase. Superior HER catalytic activity was achieved in the porous 1T phase MoS₂ nanosheets that have even more edges and S-vacancies than conventional 1T phase MoS₂. A comparative study revealed that the phase serves as the key role in determining the HER performance, as 1T phase MoS₂ always outperforms the corresponding 2H phase MoS₂ samples, and that both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS₂ samples. Then, using combined defect characterization techniques of electron spin resonance spectroscopy and positron annihilation lifetime spectroscopy to quantify the S-vacancies, the contributions of each factor were individually elucidated. This study presents new insights and opens up new avenues for designing electrocatalysts based on MoS₂ or other layered materials with enhanced HER performance.