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

Charge overpotential for oxygen evolution reaction is a crucial parameter for the energy conversion efficiency of lithium-oxygen (Li-O 2 ) 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/cm 2 ) and capacity (0.3 mAh/cm 2 ). Experimental and theoretical calculations demonstrate that the precise d-d orbital coupling ( d xz - d xz , d yz - d yz and d z 2 - d z 2 ) 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 ( d z 2 , d xz and d yz ) relative to that of Pd nanosheets. Furthermore, the highest energy level of the Pd 4 d z 2 orbital in PdCo is lower than the lowest energy levels of the Pd 4 d xz and 4 d yz 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-O 2 batteries.