Discretizing Cobalt Spin–Orbitals through Tuning the Crystal Symmetry for Zinc–Air Batteries

Regulating the electron-spin state of metal active sites is a rarely cultivated topic for oxygen electrocatalysis. Here, a dual-ligand metal-organic framework (DM) is developed to endow Co sites with D_4h crystal symmetry, reconfiguring their orbital degeneracy and electron spin state. The discretized spin-orbital configuration offers the accelerated transformation of the O-related intermediate by accepting electrons via partial d-orbital occupation and mediation of the hydroxyl adsorption strength through electron donation to O p-orbitals. With this orbital flexibility, Co sites serve as "Lewis acid-base" pairs that hasten O redox of oxygen during Zn-air battery cycling, which is validated by operando X-ray absorption spectroscopy and theoretical modeling. Compared to counterparts with different crystal symmetries, Zn-air batteries using the DM electrocatalyst showcase reduced charge-discharge voltage gap and high round-trip energy efficiency at high areal capacity.