Abstract
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.