Enhanced oxygen reduction activity and stability of double-layer nitrogen-doped carbon catalyst with abundant Fe-Co dual-atom sites

The synergistic effect between metal atoms gives dual-atom catalysts superior catalytic performance to single-atom catalysts. Herein, we report a ZIF-derived double-layer Fe-Co dual-atom catalyst (D-FeCo-DAs-N-C) for oxygen reduction reaction (ORR). The formation of N3-Fe-Co-N3 Fe-Co dual-atom structure was confirmed by X-ray absorption spectroscopy. A ZIF-derived Zn/Co bimetallic double-layer structure was used as a host, and the guest Fe3+ ions were encapsulated to the cavities by dual solvent method to form the ZIF-derived Zn/Co/Fe trimetallic double-layer structure. During the pyrolysis process, part of the Fe3+ ions were reduced by the generated carbon and combined with adjacent Co atoms to form Fe-Co dual-atom catalyst. The special double-layer structure provided abundant active sites and stable coordination environment for Fe-Co dual-atom sites. The density functional theory calculation shows that Fe-Co dual-atom sites promote the accumulation of electrons, and regulate the adsorption free energy of reaction intermediates, leading to higher limit potential. The D-FeCo-DAs-N-C exhibits excellent ORR performance (E1/2 =0.927 V) and extraordinary stability in alkaline media. The ORR chronoamperometry test showed that the current maintained 94.18% of the initial value after 100 h. The catalytic activity and stability of D-FeCo-DAs-N-C are higher than those of single-atom and single-layer catalysts synthesized as control samples. In addition, the practical zinc-air battery using D-FeCo-DAs-N-C as cathodic catalyst showed a maximum power density of 259 mW cm−2, a specific capacity of 814 W h kg−1 at 10 mA cm−2, and a stability of 400 cycles without detectable attenuation for 200 h. Furthermore, this catalyst also exhibits excellent performance in flexible zinc-air battery with a maximum power density of 140.3 mW cm−2 and excellent mechanical flexibility.