Defects in the catalyst are considered to be important for generating the active sites for electrocatalytic reactions, due to the changed distribution of the charge density. In this work, Li vacancy defects are purposely created in a series of one-dimensional (1D) porous multi-shell Li(NixCoyMnz)O2 hollow fibers by a facile electrochemical lithium ion (Li+) intercalation and extraction. The total Li vacancy concentrations are 0.52, 0.49, and 0.53 in one unit of delithiated Li(NixCoyMnz)O2 hollow fibers (De-Li(NixCoyMnz)O2) for De-Li(Ni0.20Co0.60Mn0.20)O2, De-Li(Ni0.33Co0.33Mn0.33)O2, De-Li(Ni0.65Co0.25Mn0.10)O2, respectively. When evaluated as oxygen electrocatalysts, the De-Li(Ni0.2Co0.6Mn0.2)O2 shows the best performance with onset potential of ~1.46 V vs. reversible hydrogen electrode (RHE) outperforming IrO2/C at 1 M KOH in OER and much improved onset potential of ~ 0.85 V vs. RHE than that of Li(Ni0.2Co0.6Mn0.2)O2 (~ 0.71 V vs. RHE) at 0.1 M KOH in ORR. Density functional theory (DFT) calculations for the sample before and after delithiation certified that the delithiated samples have a significantly improved carrier concentration and electronic conductivity in the Co-d orbitals near the sites of Li vacancies. This results in enhanced H2O (3.34 eV) and O2 (2.75 eV) adsorption energies and thus greatly reduces the OER-ORR potential difference (∆E) (0.17 V). A ZAB with the De-Li(Ni0.2Co0.6Mn0.2)O2 as the air cathode was also assembled, which shows high efficiency and long-term stability. At a constant current rate of 5 mA cm-2, the final charge and discharge potential is ~ 1.97 V and ~ 1.23 V after 441 h.
- lithium vacancy
- Bifunctional oxygen electrocatalysts
- Li(NixCoyMnz)O2 hollow fiber
- Metal-air battery