Efficient bifunctional catalysts for oxygen evolution and reduction reactions (OERs/ORRs) are of great importance for sustainable and renewable clean energy, especially for metal–air batteries. Herein, we investigated β₁₂-borophene with double-hole sites capped with 3d transition metal atoms to explore its catalyst performance for hydrogen evolution reactions (HERs), OERs and ORRs. It was found that the borophene is a good platform for diatomic site catalysts (DASCs) due to their advantage of stability over the corresponding single-atom catalysts (SACs) or clusters. The HER performance of DASCs on β₁₂-BM was further improved compared to the SAC case. Furthermore, the supported FeNi DASC exhibited good catalytic performance for both OERs and ORRs, the overpotentials for which were 0.43 and 0.55 V, respectively, better than those of the corresponding supported Ni or Fe SAC due to synergistic effects. We herein propose a novel descriptor involving the Bader charges of coordinated atoms explicitly, behaving much better than the d-band center and integrated crystal orbital Hamilton population (-ICOHP) for DASCs. The synergistic effect of Fe–Ni pairs balanced the too strong binding of OH and further activated OH to achieve better catalytic performance. The results of this study can provide theoretical guidance for the design of efficient bifunctional electrocatalysts.