Cascaded orbital-oriented hybridization of intermetallic Pd₃Pb boosts electrocatalysis of Li-O₂ 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-O₂) 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 Pd₃Pb followed by intermolecular orbital hybridization between low-energy Pd atom and reaction intermediates, for greatly enhancing the OER electrocatalytic activity in Li-O₂ 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 Pd₃Pb; during the charging process, the low-lying 4d_xz/yz and 4d_z² orbital of the Pd further hybridizes with 2π* and 5σ orbitals of lithium superoxide (LiO₂) (key reaction intermediate), eventually leading to lower energy levels of antibonding and, thus, weakened orbital interaction toward LiO₂. As a consequence, the cascaded orbital-oriented hybridization in intermetallic Pd₃Pb considerably decreases the activation energy and accelerates the OER kinetics. The Pd₃Pb-based Li-O₂ 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-O₂ batteries at the orbital level.