Boosting ORR performance by single atomic divacancy Zn–N3C–C8 sites on ultrathin N-doped carbon nanosheets

Abstract

Single-atom catalysts (SACs) show great promise to improve the performance of catalysis because of their spatially isolated single-atom sites with unique electronic properties. Herein, we construct single Zn atoms anchored on ultrathin two-dimensional (2D) N-doped carbon nanosheets (Zn–SAs/UNCNS) as an efficient electrocatalyst for oxygen reduction reaction (ORR). The microenvironment of Zn–SAs/UNCNS with super ORR intrinsic activity was identified as the divacancy Zn–N 3 C–C 8 by both experiments and theoretical simulations. Density functional theory (DFT) calculations reveal that the divacancy Zn–N 3 C–C 8 sites exhibit near-Fermi electronic states distinct from those of graphene-enclosed Zn–N 4 –C 10 and divacancy trans -Zn–N 2 C 2 –C 8 sites, which greatly facilitate the ORR process. Furthermore, compared with 3D architecture, the single atomic divacancy Zn–N 3 C–C 8 sites anchored on ultrathin 2D carbon nanosheets show more active site exposure and fast electron transport, which collectively boost the ORR performance, showing a high half-wave potential of 0.91 V versus reversible hydrogen electrode [RHE] and a super turnover frequency (4.99 e − site −1 s −1 ). • The coordination environment of the Zn single-atom catalyst is regulated • Zn–SAs/UNCNS with divacancy Zn–N 3 C–C 8 sites demonstrate high ORR performance • Zn–SAs/UNCNS delivers a maximum primary Zn–air battery power density of 282 mW cm −2 Zn–air batteries are promising next-generation energy-storage devices. A major challenge for further boosting the efficiency of Zn–air batteries is to develop highly efficient and low-cost oxygen reduction reaction (ORR) catalysts. Due to the complexity of screening catalysts, it is of great importance to discover the underlying principles to guide the rational design of cost-effective catalysts. In this work, we identify the coordination environment of the Zn single-atom catalyst with the best ORR performance. By changing the pyrolysis temperature, the relationship between the coordination environment of the Zn single-atom catalyst and ORR activity is discovered. Additionally, we demonstrate the support effect of ultrathin 2D carbon that promotes the active sites’ exposure and electron transport compared with the bulk one. The insights of the coordination environment-activity relationship obtained can guide the further development of efficient and earth-abundant single-atom catalysts for ORR. By anchoring atomically dispersed divacancy Zn–N 3 C–C 8 sites on ultrathin two-dimensional N-doped carbon nanosheets (Zn–SAs/UNCNS), the Zn–SAs/UNCNS exhibits an excellent four-electron oxygen reduction reaction performance with a high half-wave potential of 0.91 V versus RHE and a super turnover frequency (4.99 e − site −1 s −1 ) at 0.90 V (versus RHE).