Metal-organic framework-derived Co single atoms anchored on N-doped hierarchically porous carbon as a pH-universal ORR electrocatalyst for Zn-air batteries

Developing non-Pt-group-metal (non-PGM) electrocatalysts with excellent pH-universal catalytic activity offers bright prospects in the context of the electrochemical oxygen reduction reaction (ORR). Herein, we report a simple spatial-isolation strategy for the fabrication of atomic Co catalytic sites anchored on hierarchical porous N-doped carbon (Co-SAs/N-C/rGO) as a competitive candidate for ORR across a wide pH range. The resultant Co-SAs/N-C/rGO catalyst exhibits pH-universal ORR activity with half-wave potentials (E-1/2) of 0.84, 0.77, and 0.65 V vs. RHE in alkaline, acidic, and neutral media, respectively, which are comparable to the commercial Pt/C (0.85, 0.79, and 0.65 V vs. RHE, respectively). These superior ORR catalytic activities across a wide pH range are attributed to the combined effect of atomic active sites, a large specific surface area, and a hierarchical porous structure. As a demonstration, the homemade liquid Zn-air battery (ZAB) assembled with Co-SAs/N-C/rGO as the cathode catalyst displays an open-circuit voltage (OCV) of similar to 1.52 V and a discharging specific capacity of 671.94 mA h g(-1), outperforming those of the device with commercial Pt/C + RuO2 (1.49 V and 657.32 mA h g(-1), respectively). Notably, the corresponding flexible solid-state ZAB manifests state-of-the-art OCV, peak power density, foldability, and cycling stability. Based on density functional theory (DFT) calculations, the CoN4 configuration is the real catalytically active center for ORR. Besides, the introduction of the Co active center can lower the energy barrier of the rate-determining step (RDS). This work opens an avenue for the rational design of non-PGM electrocatalysts with pH-universal adaptability for energy storage and conversion.

Automated summary

A simple spatial-isolation strategy was developed to fabricate Cobalt catalysts anchored on N-doped carbon. The resulting catalyst showed pH-universal catalytic activity in acidic, neutral, and alkaline media, providing a new approach for the design of non-Pt-group-metal (non-PGM) electrocatalysts.