Orbital coupling of hetero-diatomic nickel-iron site for bifunctional electrocatalysis of CO reduction and oxygen evolution.

While inheriting the exceptional merits of single atom catalysts, diatomic site catalysts (DASCs) utilize two adjacent atomic metal species for their complementary functionalities and synergistic actions. Herein, a DASC consisting of nickel-iron hetero-diatomic pairs anchored on nitrogen-doped graphene is synthesized. It exhibits extraordinary electrocatalytic activities and stability for both CO reduction reaction (CORR) and oxygen evolution reaction (OER). Furthermore, the rechargeable Zn-CO battery equipped with such bifunctional catalyst shows high Faradaic efficiency and outstanding rechargeability. The in-depth experimental and theoretical analyses reveal the orbital coupling between the catalytic iron center and the adjacent nickel atom, which leads to alteration in orbital energy level, unique electronic states, higher oxidation state of iron, and weakened binding strength to the reaction intermediates, thus boosted CORR and OER performance. This work provides critical insights to rational design, working mechanism, and application of hetero-DASCs.