D-orbital Reconstruction Achieves Low Charge Overpotential in Li-oxygen Batteries

Abstract

Charge overpotential for oxygen evolution reaction is a crucial parameter for the energy conversion efficiency of lithium-oxygen (Li-O2) batteries. So far, the realization of low charge overpotential via catalyst design is a grand challenge in this field, which usually exceeds 0.25 V. Herein, we report an orbital reconstruction strategy to significantly decrease the charge overpotential to the low 0.11 V by employing PdCo nanosheet catalyst under a low-loading mass (0.3 mg/cm2) and capacity (0.3 mAh/cm2). Experimental and theoretical calculations demonstrate that the precise d-d orbital coupling (dxz-dxz, dyz-dyz and dz2-dz2) between the low-electronegativity Co and Pd leads to the reconstruction of Pd 4 d orbitals in PdCo nanosheets, thereby resulting in a downward shift of all the three active Pd 4 d orbitals (dz2, dxz and dyz) relative to that of Pd nanosheets. Furthermore, the highest energy level of the Pd 4dz2 orbital in PdCo is lower than the lowest energy levels of the Pd 4dxz and 4dyz orbitals in pure Pd, significantly decreasing the charge activation energy and achieving a highest energy conversion efficiency of 91%. This finding provides the orbital-level tuning into rational design of highly efficient electrocatalysts for Li-O2 batteries.