Chemisorption Can Reverse Defect–Defect Interaction on Heterogeneous Catalyst Surfaces

Atomic-level understanding of roles of defect–defect interaction in the bonding of adsorbates on surfaces is critical for tailoring catalysts atom-by-atom and designing new catalysts. Here, from first-principles calculations, we propose a microscopic mechanism for the role of sulfur vacancy–vacancy interaction in hydrogen bonding on surfaces of MoS2, a nonprecious two-dimensional catalyst for hydrogen evolution reaction. We find that before hydrogen adsorption the interaction of a sulfur vacancy with others is repulsive, originating from the antibonding-like coupling of occupied in-gap vacancy states. When the sulfur vacancy is adsorbed by a hydrogen atom, its interaction with other unadsorbed sulfur vacancies becomes attractive, which can be attributed to the decoupling of repulsive vacancy–vacancy interactions and the occupying of bonding-like coupling states between the in-gap vacancy states that are unoccupied before hydrogen adsorption. This repulsive-to-attractive reverse of vacancy–vacancy interaction reduces the hydrogen adsorption energy and explains why the hydrogen adsorption energy decreases with increasing sulfur vacancy concentration. The emerging picture enables a more general discussion of local defect effects on the adsorption of various adsorbates at different surfaces, providing guidance to improve catalytic performance through defect engineering.对表面吸附质键合过程中缺陷-缺陷相互作用的原子级认知，是实现原子级精准定制催化剂与设计新型催化剂的关键所在。本研究通过第一性原理计算，针对用于析氢反应（hydrogen evolution reaction）的非贵金属二维催化剂二硫化钼（MoS₂）的表面氢键合过程，提出了硫空位-空位相互作用的微观机制。研究发现，在氢吸附发生前，硫空位与其他空位的相互作用呈排斥性，其起源于占据的带隙内空位态的类反键耦合。当硫空位被氢原子吸附后，其与未被吸附的其他硫空位的相互作用转变为吸引性，这一现象可归因于排斥性空位-空位相互作用的解耦，以及氢吸附前未占据的带隙内空位态之间形成的类成键耦合态被占据。这种空位-空位相互作用从排斥到吸引的反转，降低了氢吸附能，并解释了氢吸附能随硫空位浓度升高而降低的原因。该研究图景为探讨不同表面上各类吸附质吸附的局部缺陷效应提供了更普适的分析思路，可为通过缺陷工程优化催化性能提供理论指导。