Oxygen Vacancies Promote Formaldehyde Base-Free Reforming into Hydrogen over Cu Doping-Induced Cu–Cu_<i>x</i>Zn_1<i>–x</i>O Heterointerfaces

Element doping is a viable strategy to regulate the metal-support interface for enhancing the catalytic performance of supported metal catalysts. Herein, Cu/ZnO:Cu-<i>T</i>H catalysts are prepared by immobilizing Cu nanoparticles (NPs) on ZnO nanorods featuring an adjustable oxygen vacancy, in which partial Cu atoms at the Cu-ZnO interface are incorporated into the ZnO lattice to form Cu_<i>x</i>Zn_1-<i>x</i>O species. Such Cu atom doping induces the creation of distinctive Cu-Cu_<i>x</i>Zn_1-<i>x</i>O interface sites and optimizes electron transfer from ZnO to Cu NPs, thereby achieving intermediate activation and ultimately endowing the catalyst with superior performance in reforming alkali-free formaldehyde (HCHO) into hydrogen at low temperatures. The Cu-Cu_<i>x</i>Zn_1-<i>x</i>O interface sites serve as pivotal centers for HCHO reforming, where the Cu sites and Cu_<i>x</i>Zn_1-<i>x</i>O sites selectively engage in the cleavage of C-H bonds in HCHO and O-H bonds in H₂O, respectively. Meanwhile, the presence of oxygen vacancies bolsters the Cu-Cu_<i>x</i>Zn_1-<i>x</i>O sites in enhancing the adsorption of HCHO and H₂O, further improving the activity. The Cu/ZnO:Cu-450H catalyst, distinguished by abundant Cu-Cu_<i>x</i>Zn_1-<i>x</i>O sites and a high concentration of oxygen vacancies, demonstrates optimal activity with TOF values of 16.9 and 72.4 h^-1 under anaerobic and aerobic conditions, respectively, which are 8.9 and 29.0 times higher than those of the Cu/ZnO-450N catalyst, which lacks doped Cu atoms and oxygen vacancies.