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

Electrochemical hydrogen peroxide (HO) production two-electron oxygen reduction reaction (2e ORR) has received increasing attention as it enables clean, sustainable, and on-site HO production. Mimicking the active site structure of HO 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 HO 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 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 sites and Ni nanoparticles, which revealed that the Ni-N 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 HO electrosynthesis activity. The optimized catalyst exhibited a record HO electrosynthesis mass activity with excellent HO selectivity.