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 percent 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.