Hierarchically nanostructured MoS2 with rich in-plane edges as a high-performance electrocatalyst for the hydrogen evolution reaction

Abstract

As a low-cost and earth-abundant electrocatalyst for the hydrogen evolution reaction (HER), molybdenum sulfide (MoS₂) is recognized as a two dimensional material composed of catalytically active edges and an inert basal plane. Thus, optimizing simultaneously the hierarchical nanostructure and active site density could substantially improve its HER activity but it is not an effortless strategy to do so. Herein, we report for the first time a facile and controllable synthesis for engineering hierarchically nanostructured MoS₂ nanosheets with rich in-plane edges (IE-MoS₂ NSs). The IE-MoS₂ NSs feature HER-oriented nanostructures with a tiny size, few-layer, expanded interlayer spacing and an unconventional in-plane-edge structure where separated MoS₂ nanoflakes stand on the basal plane of nanosheets. Defects (Mo species with multiple chemical states and oxygen heteroatoms) were identified and they were proposed to be responsible for stabilizing the highly active MoS₂ nanoflakes, forming the unique in-plane edges. IE-MoS₂ NSs exhibit surprisingly high HER activity with a low onset potential of −87 mV and a Tafel slope of 41 mV per decade, exceeding other nanostructured MoS₂ materials in this work and surpass almost all documented MoS₂-based electrocatalysts. The surging activity has been discussed in detail, showing that the in-plane-edge nanostructure boosts the number of catalytic sites and promotes the intrinsic activity of each site at the same time, facilitating the catalytic process for H₂ evolution.