Universal and scalable synthesis of ultrahigh-density single-atom libraries on metal oxides

Metal oxides have served as ideal catalyst supports since the early 20th century due to their strong structural stability and excellent redox properties. However, achieving ultrahigh-loading single-atom catalysts (UHL-SACs) on these oxides remains a significant challenge, due to aggregation resulting from the lattice confinement effect in conventional synthesis. Here, we report a universal and scalable plasma-microwave strategy for synthesizing UHL-SACs on diverse metal oxide supports. This approach effectively suppresses atomic segregation by leveraging plasma-induced metal/non-metal defects, followed by rapid microwave-assisted annealing for the instantaneous anchoring of atoms. UHL-SACs of 33 distinct metal elements, along with their multimetallic single-atom mixtures on metal oxides ranging from 1D to 3D architectures and from crystalline to amorphous structures, have been successfully synthesized. The achieved metal loadings reach up to 21.02 wt% for single metals and 27.69 wt% for multimetallic systems. Notably, the 5‑MPM/Fe2O3 photoanode delivers a remarkable photoelectrochemical oxygen evolution reaction current density of 5.7 mA cm-2 at 1.23 VRHE and maintains excellent long-term stability for 600 h, which represents the highest performance reported for a metal oxide‑based semiconductor. This work proposes a general guideline for the rational design of metal oxide-supported UHL-SACs and demonstrates the ready scalability of the strategy to kilogram-scale production.