Theory-Driven Synthesis of Tungsten Titanium Carbide MXene for Hydrogen Evolution Electrocatalysis

Tungsten (W) based-MXenes are of particular interest as they are predicted to have overpotentials close to Pt-based catalysts in hydrogen evolution reaction (HER), making them candidates for a more sustainable clean energy application. However, the incorporation of W into the MXene structure has proven difficult due to the calculated instability of its hypothetical precursor M_n+1AX_n phases (W₂AC and W₃AC₂). In this study, we present the theory-driven synthesis of a tungsten titanium carbide, W₂TiC₂T_x, derived from a modified covalently bonded nanolaminated double transition metal carbide ternary carbide (W,Ti)₄C_4-y precursor. We confirm the atomistic out-of-plane ordering of W and Ti, using density functional theory, Rietveld refinement, and electron microscopy methods. Our results indicate the importance of W and Ti ordering and defects in the successful synthesis of W₂TiC₂T_x. Additionally, the W-rich basal plane endows W₂TiC₂T_xMXene with a remarkable electrocatalytic HER performance with the lowest HER overpotential (~144 mV at 10 mA/cm²) for a MXene under acidic conditions over other W_1.33CT_x MXenes (~320 mV) and Mo₂CT_x MXenes (~190 mV). In this direction, more efforts on the continuous exploration of W-containing MXenes with low overpotentials are noteworthy toward the clean energy applications due to their highly active basal plane.