Highly dispersed La-O/N-C sites anchored in hierarchically porous nitrogen-doped carbon as bifunctional catalysts for high-performance rechargeable Zn-air batteries

Inexpensive, high-activity bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are imperative for the development of energy storage and conversion systems. A nitrogen-doped carbon material with a micro-meso-macroporous structure doped with La (LaPNC) containing La-O/N-C active sites is prepared using SiO2 particle templating of carbon and a metal node exchange strategy. The coordination environment of La sites stabilized by two oxygen and four nitrogen atoms (LaO2N4), is further verified by X-ray absorption spectroscopy. The ORR half-wave potential reaches 0.852 V, and the OER overpotential reaches 263 mV at 10 mA cm-2. The Zn-air battery, with LaPNC as the air cathode, has a maximum power density of 202 mW cm-2 and achieves stable charge-discharge for at least 100 h without a significant increase or decrease in the charge or discharge voltages, respectively. Density functional theory calculations suggest that LaO2N4 sites exhibit the lowest activation free energy and the most easily desorbed oxygen capacity. This study provides new insights into the design of efficient, durable bifunctional catalysts as alternatives to precious-metalbased catalysts.

Automated summary

In this study, a nitrogen-doped carbon material with a micro-meso-macroporous structure doped with La was prepared and its La-O/N-C active sites were confirmed by experimental results. The material exhibited low half-wave potential and overpotential for both ORR and OER reactions. A zinc-air battery with this material as the air cathode showed high power density and stable charge-discharge performance. Density functional theory calculations indicated that LaO2N4 sites had the lowest activation free energy and the most easily desorbed oxygen capacity. This study provides important insights for the design of efficient and durable alternatives to precious-metal-based catalysts.