Cascaded orbital–oriented hybridization of intermetallic Pd 3 Pb boosts electrocatalysis of Li-O 2 battery

Abstract

Catalysts with a refined electronic structure are highly desirable for promoting the oxygen evolution reaction (OER) kinetics and reduce the charge overpotentials for lithium–oxygen (Li-O 2 ) batteries. However, bridging the orbital interactions inside the catalyst with external orbital coupling between catalysts and intermediates for reinforcing OER catalytic activities remains a grand challenge. Herein, we report a cascaded orbital–oriented hybridization, namely alloying hybridization in intermetallic Pd 3 Pb followed by intermolecular orbital hybridization between low-energy Pd atom and reaction intermediates, for greatly enhancing the OER electrocatalytic activity in Li-O 2 battery. The oriented orbital hybridization in two axes between Pb and Pd first lowers the d band energy level of Pd atoms in the intermetallic Pd 3 Pb; during the charging process, the low-lying 4d xz/yz and 4d z 2 orbital of the Pd further hybridizes with 2π* and 5σ orbitals of lithium superoxide (LiO 2 ) (key reaction intermediate), eventually leading to lower energy levels of antibonding and, thus, weakened orbital interaction toward LiO 2 . As a consequence, the cascaded orbital–oriented hybridization in intermetallic Pd 3 Pb considerably decreases the activation energy and accelerates the OER kinetics. The Pd 3 Pb-based Li-O 2 batteries exhibit a low OER overpotential of 0.45 V and superior cycle stability of 175 cycles at a fixed capacity of 1,000 mAh g −1 , which is among the best in the reported catalysts. The present work opens up a way for designing sophisticated Li-O 2 batteries at the orbital level.