Hetero-Diatomic CoN₄-NiN₄ Site Pairs with Long-Range Coupling as Efficient Bifunctional Catalyst for Rechargeable...

In this study, Co/Ni-NC catalyst with hetero-diatomic Co/Ni active sites dispersed on nitrogen-doped carbon matrix is synthesized via the controlled pyrolysis of ZIF-8 containing Co²⁺ and Ni²⁺ compounds. Experimental characterizations and theoretical calculations reveal that Co and Ni are atomically and uniformly dispersed in pairs of CoN₄-NiN₄ with an intersite distance ≈0.41 nm, and there is long-range d-d coupling between Co and Ni with more electron delocalization for higher bifunctional activity. Besides, the in situ grown carbon nanotubes at the edges of the catalyst particles allow high electronic conductivity for electrocatalysis process. Electrochemical evaluations demonstrate the superior ORR and OER bifunctionality of Co/Ni-NC catalyst with a narrow potential gap of only 0.691 V and long-term durability, significantly prevailing over the single-atom Co-NC and Ni-NC catalysts and the benchmark Pt/C and RuO₂ catalysts. Co/Ni-NC catalyzed Zn-air batteries achieve a high specific capacity of 771 mAh g^-1 and a long continuous operation period up to 340 h with a small voltage gap of ≈0.65 V, also much superior to Pt/C-RuO₂.