(Invited) Tunable Chemistry of 2D Carbide Mxenes for Hydrogen Evolution Reaction

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) are a large family of earth-abundant materials with more than forty compositions synthesized since 2011, such as Ti 2 CT x , Mo 2 CT x , Nb 2 CT x , Ti 3 C 2 T x , Mo 2 TiC 2 T x , and Mo 2 Ti 2 C 3 T x . MXenes have emerged as promising candidates for catalytic energy storage and conversion because their 2D surfaces are electrochemically active combined with MXenes’ hydrophilicity, high electrical conductivity, and affinity to bond to molecules and nanomaterials to form hybrid structures. MXenes electrochemical properties can be tuned by the control of multiple variables: in the MXene formula of M n +1 X n T x , the transition metals (M) can be any of the groups 4, 5, 6 of the periodic table or their combination, X can be carbon, nitrogen, or a solid solution of both, surface terminations (T x ) can be any of the group 16 and 17, and the ‘ n’ (MXene 2D flake thicknesses) can be 1 to 4. In this talk, we will discuss the control of MXene transition metals, their thicknesses, and surfaces to tune their electrocatalytic behavior. Specifically, we present a systematic study of 20 different MXenes, including novel compositions such as W 2 TiC 2 T x and Mo 2 Nb 2 C 3 T x and high-entropy MXenes, and discuss how we achieve low overpotential for hydron evolution reaction (as low as ~160 mV).