Flow Pyrolysis Synthesis of Single-Atom Catalysts With Tunable Crumple and Electronic Structures for 2-Electron Oxygen Reduction.

Single-atom catalysts (SACs) are attractive due to their high metal utilization efficiency and intriguing properties. Developing a facile and general method to synthesize SACs with tunable geometric and electronic structure is critical for realizing their widespread application. Here we report a continuous-flow spray pyrolysis approach to SACs (including iron, cobalt, nickel, copper, and platinum) with control over the crumple structure of the graphene substrate and the electronic structure of the single-atom sites. Notably, the formation of single-atom sites and morphologic engineering of the substrate are simultaneously achieved within the single-step droplet-to-particle conversion process. Taking Co SACs for catalyzing the 2-electron oxygen reduction reaction (ORR) as a representative example, the Co moieties possess a deformed local geometric structure and electron deficiency that are dependent on the crumpling degree of the graphene substrate, leading to controllable ORR activity and selectivity. The optimal catalyst achieves an unprecedently high mass activity of 456 ± 4 A g-1 at 0.65 V, along with a high H2O2 selectivity of up to 97%. Furthermore, a flow-cell electrolyzer assembled with this catalyst demonstrates an averaged H2O2 productivity of 23.78 mol g-1 catalyst h-1, sustained over 120 h of operation.