Ultrathin MXene nanosheets with rich fluorine termination groups realizing efficient electrocatalytic hydrogen evolution

Exploring efficient noble-metal-free electrocatalysts for hydrogen evolution reaction (HER) is of great importance to solve the energy crisis. The family of two-dimension transition metal carbides, MXenes, has received a small amount of research, including the reactivity and number of active sites, relative to their extraordinary potential as electrocatalysts for HER. Herein, a model of atomically-thin Ti2CTx (where T-x denotes the surface termination groups; -F, -O, -OH) nanosheets with the rich surface fluorine termination groups is put forward to achieve synergistic regulations of both reactivity and number of active sites. Theoretical calculations and electrochemical tests show that the rich surface F terminations can promote the proton adsorption kinetics and reduce the charge-transfer resistance of the Ti2CTx nanosheets, leading to the increased reactivity of active sites and favorable electrode kinetics. Besides, the ultrathin thickness of the Ti2CTx nanosheets offers high-density active sites for HER. As expected, the rich F-terminated Ti2CTx nanosheets exhibit a small onset overpotential of 75 mV and a large exchange current density of 0.41 mA cm(-2). Our discovery adds to the growing potential of MXene-based materials for application in hydrogen evolution reaction.