Ballistic electron pumping: constructing Mo2C MXene ohmic junctions to boost charge transfer for hydrogen production

Interfacial charge recombination remains the fundamental bottleneck in semiconductor photocatalysis. Herein, this study presents a transformative strategy to construct an extremely low-barrier ohmic interface between 0D Zn0.7Cd0.3S quantum dots (ZCSQ) and 2D Mo2C MXene (MC) nanosheets. The work function disparity between MC and ZCSQ induces a spontaneous electron accumulation layer at the interface. This extremely low-barrier conduit enables ballistic-like electron extraction, as evidenced by a dramatic reduction in charge transfer resistance and photoluminescence quenching. In situ irradiation XPS and transient photocurrent analysis confirmed the unidirectional electron overflow from the conduction band of ZCSQ to the Mo2C metal reservoir. Furthermore, MXene enhances the hydrophilicity of ZCSQ (with a contact angle of 13°), enabling the catalyst to reduce the interfacial mass transfer resistance; moreover, density functional theory (DFT) calculations indicate that the Gibbs free energy of hydrogen adsorption on the surface (ΔGH* = −0.92 eV) is favorable for hydrogen atom adsorption. Both factors explain the efficient production of hydrogen on MC. Consequently, the MZQ composite achieves an extraordinary photocatalytic hydrogen evolution rate with exceptional stability. This work elaborates on how to design efficient charge transfer pathways to enhance the efficiency of photocatalytic hydrogen production through MXene-based ohmic contacts.