(V_1-yMo_y)₂CT_x MXene Nanosheets as Electrocatalysts for Hydrogen Evolution

MAX phases are a large and growing family of transition metal-based ternary carbides and (carbo)nitrides, that have also attracted significant attention as precursors for a class of two-dimensional materials referred to as MXenes. The ability to partially substitute elements on the M-, A-, and X-sites of the layered crystal structure has expanded MAX phases to over 340 members known to date. They can be exfoliated to form single- and few-layer MXene sheets by removal of the A-element while maintaining the M- and X-elements of the precursor MAX phase. MXenes are extremely interesting materials with properties that are, among other factors, dependent on their chemical composition and offer a wide array of potential applications, for example for energy conversion. Here, we synthesize hitherto unknown solid solution MAX phases, (V_1-yMo_y)₂AlC (y = 0.0-0.5) and exfoliate all compounds with varying V/Mo ratios into the respective MXenes by hydrothermal treatment with in situ-formed hydrofluoric acid. The delaminated MXenes can be utilized for electrocatalytic reactions, here demonstrated for the hydrogen evolution reaction (HER). As the Mo content within the MXenes increases, electrocatalytic activity for HER improves, peaking at an overpotential of 394 mV at 10 mA cm^-2 and a Tafel slope of 129 mV dec^-1 for (V_0.5Mo_0.5)₂CT_x