Understanding the preparative chemistry of atomically dispersed nickel catalysts for achieving high-efficiency H 2 O 2 electrosynthesis.

Electrochemical hydrogen peroxide (H 2 O 2 ) production via two-electron oxygen reduction reaction (2e - ORR) has received increasing attention as it enables clean, sustainable, and on-site H 2 O 2 production. Mimicking the active site structure of H 2 O 2 production enzymes, such as nickel superoxide dismutase, is the most intuitive way to design efficient 2e - ORR electrocatalysts. However, Ni-based catalysts have thus far shown relatively low 2e - ORR activity. In this work, we present the design of high-performing, atomically dispersed Ni-based catalysts (Ni ADCs) for H 2 O 2 production through understanding the formation chemistry of the Ni-based active sites. The use of a precoordinated precursor and pyrolysis within a confined nanospace were found to be essential for generating active Ni-N x sites in high density and increasing carbon yields, respectively. A series of model catalysts prepared from coordinating solvents having different vapor pressures gave rise to Ni ADCs with controlled ratios of Ni-N x sites and Ni nanoparticles, which revealed that the Ni-N x sites have greater 2e - ORR activity. Another set of Ni ADCs identified the important role of the degree of distortion from the square planar structure in H 2 O 2 electrosynthesis activity. The optimized catalyst exhibited a record H 2 O 2 electrosynthesis mass activity with excellent H 2 O 2 selectivity.