Sulfur-Functionalized MXenes Nanosheets for Efficient Electrocatalytic Hydrogen Evolution

Two-dimensional MXenes are emerging as promising materials for electrocatalysts owing to their layered structure, metallic conductivity, and abundant catalytically active basal planes. However, achieving coordinated regulation of both reactivity and the number of active sites through modulation of surface groups remains challenging, which hinders further optimization of the electrocatalytic performance of MXene. Herein, sulfur-functionalized MXene with enhanced HER catalytic activity was achieved through a convenient one-step sulfurization strategy. During the sulfidation process, the surface fluorine atoms of MXene were partially replaced by sulfur atoms, providing enhanced electrocatalytic activity and high stability. The strategy was applied for various MXenes: Mo4/3C, W4/3C, and Nb1.33C, and particularly, S–Mo4/3C delivers a low overpotential, 210 mV for a current density of 10 mA cm–2, with a Tafel slope of 67 mV dec–1, and possesses excellent HER stability with negligible attenuation of the current density after 120 h. In situ Raman spectroscopy shows that sulfur atoms serve as active sites for the hydrogen evolution, confirmed by the appearance of a Raman peak at 2542 cm–1 which is ascribed to the S–H stretching vibration of Mo–S–H moieties. This work promotes further efforts in exploration of efficient catalysts within the large MXene materials family, as well as exploiting their potential toward more versatile applications.