2D/2D Heterojunction of Cobalt-Iron Selenide Nanolamellas/MXene for Enhanced Electrocatalytic Hydrogen Evolution

Electrochemical water splitting is considered to be a green and flexible strategy for the mass production of hydrogen fuel, while the high cost and insufficent activity of current cathode catalysts severely suffocate the widespread thriving of hydrogen economy. Herein, we present a bottom-up assembly strategy to the controllable construction of 2D/2D heterojunctions built from cobalt-iron selenide nanolamellas and Ti₃C₂T_x MXene nanosheets. This unique architectural design gives the resulting Co_yFe_1-ySe₂/Ti₃C₂T_x catalysts a series of interesting structural advantages, such as 2D/2D heterostructure, large active surface areas, modulated electronic structure, uniform Co_yFe_1-ySe₂ dispersion, and good electron conductivity, thereby leading to strong synergistic coupling effects. As a consequence, the optimized Co_0.7Fe_0.3Se₂/Ti₃C₂T_x electrocatalyst with an appropriate Co/Fe ratio possesses unusual hydrogen evolution properties in terms of a low overpotential of 69 mV at 10 mA cm⁻², a small Tafel slope of 51 mV dec⁻¹ and reliable long-term durability, which are more competitive than those of bare Ti₃C₂T_x, FeSe₂ and CoSe catalysts.