Oxygen Vacancies Boost δ-Bi₂O₃ as a High-Performance Electrode for Rechargeable Aqueous Batteries

Metal oxides as electrode materials are of great potential for rechargeable aqueous batteries. However, they suffer from inferior cycle stability and rate capability because of poor electronic and ionic conductivities. Herein, taking vertically orientated Bi₂O₃ nanoflakes on Ti substrates as examples, we find that the δ-Bi₂O₃ electrode with plenty of positively charged oxygen defects show remarkably higher specific capacity (264 mA h g^-1) and far superior rate capability than that of α-Bi₂O₃ with less oxygen vacancies. Through pinpointing the existence form and the role of oxygen vacancies within the electrochemical processes, we demonstrate that oxygen vacancies in δ-Bi₂O₃ can not only promote electrical conductivity but also serve as central entrepots collecting OH^- groups via electrostatic force effect, which has boosted the oxidation reaction and enhanced the electrochemical properties. Our work merits an excellent Bi₂O₃ negative electrode material via giving full play to the role of oxygen vacancies in electrochemical energy storage.