Defective Molybdenum Sulfide for Catalysis

Electrochemical energy conversion and storage driven by renewable energy sources such as solar and wind are drawing ever-increasing interest due to their critical roles in sustainable development. Advances in these applications rely on highly active and cost-effective electrocatalysts to accelerate the sluggish kinetics of the electrochemical reactions involved. A substantial amount of such electrocatalysts have been exploited recently thanks to the advances in material science and continuous breakthroughs in engineering tools. In particular, molybdenum sulfide (MoS_x) furnishes a classic platform for study of catalysis fundamentals as well as exploration of new applications in hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), CO₂ reduction reaction (CO₂RR), polysulfide conversion reaction (metal-sulfur batteries), <i>etc</i>. Recent studies of MoS_x have focused on activating its inert part [<i>e.g.</i>, basal plan of two-dimensional (2D) molybdenum disulfide (MoS₂)] by tailoring its electronic structure through defect engineering. In this talk, I will recap recent theoretical and experimental advances in the use of defective MoS_x for various electrocatalytic applications with a highlight of our own progress. I will start with a brief description of the structure and basic electrocatalytic applications of 2D MoS₂ with 2H, 1T, and 3R crystalline phases. Then, I will discuss the employment of defective MoS₂, which is a model system thanks to its atomically isolated structure, as the electrocatalyst for the popular HER. Next, I will detail the recent development in defect-enhanced non-2D MoS_x-based (<i>i.e.</i>, amorphous and cluster structures) HER catalysts. For HER applications, I highlight the combination of theoretical and experimental tools for rational design of defects and understanding of the detailed reaction mechanisms. Lastly, I will briefly discuss the applications of defective MoS_x as catalysts for emerging application such as NRR, CO₂RR, metal-sulfur batteries, and metal-oxygen/air batteries, with a particular emphasis on the synergy built on defects for performance breakthroughs.