The spontaneous formation of surface electron accumulation (SEA) was observed in synthesized molybdenum diselenide (MoSe₂) layered crystals with two-hexagonal (2H) structure. An anomalously high electron concentration at the surface up to 10¹⁹ cm^-3 is several orders of magnitude higher than that (3.6 × 10¹² cm^-3) of the inner bulk. The SEA is found to be generated easily by mechanical exfoliation and room temperature deselenization. Se-vacancies have been confirmed to be the major source resulting in SEA and n-type conductivity, and also the active sites for electrochemical catalysis in MoSe₂. Noted that the SEA conjugated with the Se-vacancy-related surface defects enhances the electrochemical hydrogen evolution reaction (HER) activity substantially. The optimized HER efficiency with an overpotential at 0.17 V and Tafel slope at 60 mV/dec of the basal plane of 2H-MoSe₂ was achieved by the nitrogen plasma treatment, which has outperformed several nanostructures, thin films, and hybrid counterparts. This study reveals the intriguing surface-dominant electronic property and its effect on the HER enhancement of the basal plane, which is crucial for development of a stable, low-cost and highly efficient catalyst using 2H-MoSe₂.

在具有两个六边形（2H）结构的合成二硒化钼（MoSe ₂）层状晶体中观察到表面电子累积（SEA）的自发形成。高达10 ¹⁹ cm ^-3的表面异常高的电子浓度比内部体积的电子浓度高（3.6×10 ¹² cm ^-3）高几个数量级。发现通过机械剥离和室温去硒化很容易产生SEA。硒空位已被证实是导致SEA和n型电导率的主要来源，并且也是MoSe _2中电化学催化的活性位点。注意，与硒空位相关的表面缺陷共轭的SEA大大增强了电化学放氢反应（HER）的活性。通过氮等离子体处理，可以实现最佳的HER效率（在0.17 V的过电势和2h-MoSe ₂的基面的60 mV / dec的Tafel斜率），其性能优于几种纳米结构，薄膜和杂化结构。这项研究揭示了有趣的表面主导电子性质及其对基面HER增强的影响，这对于使用2H-MoSe ₂开发稳定，低成本和高效的催化剂至关重要。