Oxygen VacanciesPromote Formaldehyde Base-Free Reforminginto 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.