Transition metal (Co, Ni, Cu) 1-vinylimidazole templated borates as high-efficiency oxygen reduction catalysts for zinc-air battery.

The development of efficient and stable catalysts for the oxygen reduction reaction (ORR) is crucial for advancing zinc-air batteries (ZAB). Herein, three metal complex templated borates [Co(1-VIM)6]·[B5O6(OH)4]2 (1), [Ni(1-VIM)6]·[B5O6(OH)4]2 (2), and [Cu(1-VIM)5]·[B5O6(OH)4]2·1-VIM·H2O (3) are synthesized. Their crystal structures feature extensive networks of hydrogen bonds (H-Bs) and porous frameworks. The ordered borate framework provides spatial confinement that prevents severe aggregation during in situ metal nanocrystal formation and facilitates a nanoscale dispersion of metal active sites. After in situ pyrolysis of 1, a carbon-supported Co nanocrystal catalyst (1-Co-750) is produced and exhibits excellent ORR activity. The catalyst exhibits a half-wave potential (E1/2) of 0.85 V (vs. RHE) and excellent long-term stability in 0.1 m KOH. Moreover, ZAB assembled with 1-Co-750 attains a great specific capacity of 825.83 mAh g-1 and long-term cycling stability (800 h), outperforming the commercial Pt/C. This study has put forward new design concepts for highly efficient, cost-effective ORR catalysts and has promoted the practical application of borate materials in energy conversion.