Boosting the bifunctional oxygen electrocatalytic performance of atomically dispersed Fe site via atomic Ni neighboring

•Atomically dispersed binary NiFe-NC with tunable Ni/Fe ratios were fabricated.•The NiFe-NC with an optimal Ni/Fe ratio of 66:34 contained rich Ni-Fe dual-site.•Dual-site mode of Ni-Fe was beneficial for more charge localized over Ni/Fe sites.•Ni66Fe34-NC showed excellent ORR, OER, and rechargeable Zn-air battery performance.•DFT and in-situ Raman studies suggested Fe in Ni-Fe dimer responded for ORR/OER.