Identification of the highly active Zn-N4 sites with pyrrole/pyridine-N synergistic coordination by dz2+s-band center for electrocatalytic H2O2 production

Abstract

Single metal atoms anchored on nitrogen-doped carbon materials (M-N4) have been identified as effective active sites for catalyzing the two-electron oxygen reduction reaction (2e-ORR). However, the relationship between the local atomic/electronic environments of the M-N4 sites (metal atoms coordinated with different types of N species) and their catalytic activity for 2e-ORR has rarely been elaborated clearly, which imposes significant ambiguity for the rational design of catalysts. Herein, guided by the comprehensive density-functional theory calculations and predictions, a series of Zn-N4 single-atom catalysts (SACs) are designed with pyrrole/pyridine-N (NPo/NPd) synergistic coordination and prepared by controlling the pyrolysis temperature (600, 700, and 800 °C). Among them, the dominated Zn-N4 configurations with rationally combined NPo/NPd coordination show *OOH adsorption strength close to the optimal value, much superior to those with mono N species. Thus, the as-prepared catalyst exhibits a high H2O2 selectivity of over 90% both in neutral and alkaline environments, with a superb H2O2 yield of up to 33.63 mol g−1 h−1 in an alkaline with flow cell. More importantly, a new descriptor, dz2+s band center, has been proposed, which is especially feasible for predicting the activity for metal types with fully occupied s and d orbitals. This work thus presents clear guidance for the rational design of highly active SACs toward ORR and provides a complement to the d-band theory for more accurately predicting the catalytic activity of the materials.