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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 Bi 2 O 3 nanoflakes on Ti substrates as examples, we find that the δ-Bi 2 O 3 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-Bi 2 O 3 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-Bi 2 O 3 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 Bi 2 O 3 negative electrode material via giving full play to the role of oxygen vacancies in electrochemical energy storage.

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