Sulfur-modulated isolated NiNx sites toward electrocatalytic hydrogen peroxide generation

Achieving hydrogen peroxide (H2O2) production through the electrocatalytic two-electron (2e−) oxygen reduction reaction (ORR) is a crucial alternative to the energy-intensive anthraquinone process. The competitive four-electron (4e−) ORR pathway, however, limits the selectivity to H2O2. Here, we report the rational design of isolated NiN3S moieties by introducing one sulfur atom into NiNx sites embedded in carbon supports. The sulfur-modified active sites yield a selectivity of nearly 90% for H2O2 generation. Density functional theory calculations indicate that incorporation of sulfur in Ni's coordination environment, together with oxidation of the active-site motif, weakens the adsorption energy of OOH∗. This weakening of adsorption strengths for a key reaction intermediate in the 2e− pathway increases selectivity toward H2O2. This work provides a promising approach to direct the selectivity of oxygen reduction by modulating the local structure of isolated metal sites.