Defective Nb₂C MXene anchored Cu sites enhancing photocatalytic CO₂ reduction to ethanol

In photocatalytic CO₂ reduction, switching the product selectivity from C₁ to C₂ products remains a major challenge as it requires the efficient formation of carbon-carbon (C-C) bonds. This work addresses this challenge by synthesizing defective NbC_0.67 MXene to anchor Cu atoms (CuM) at different densities via a surface redox reaction, followed by wet deposition onto titanium dioxide (P25). The optimized 10% CuM/P25 catalyst demonstrated a remarkable ethanol yield of 76.3 μmol g^-1 h^-1 with 99.9% selectivity in an aqueous electrolyte, whereas bare MXene-coated P25 is reluctant to produce ethanol. The high performance arises from two synergistic roles of the MXene: its large specific surface area and abundant Nb cation vacancies stabilize Cu⁺ active sites, while its semi-metallic nature leads to the formation of a Schottky junction with P25 which significantly enhances charge-transfer kinetics to drive the multi-electron reduction of CO₂ to ethanol. In situ DRIFTS experiments confirm that the Cu⁺ sites effectively promote the dimerization of *CO intermediates, thereby initiating the critical C-C coupling pathway. Notably, the catalyst maintains stable ethanol production over three consecutive cycles without structural degradation or Cu site agglomeration. This study provides a durable design strategy for selective CO₂-to-ethanol photocatalysis.