Oxygen-vacancy abundant alpha bismuth oxide with enhanced cycle stability for high-energy hybrid supercapacitor electrodes.

BiO is an outstanding electrode material due to its high theoretical specific capacity. Hence, the synthesis of δ-BiO materials with high oxygen-vacancy contents could improve their electrochemical performances but causes easy conversion to α-BiO with low oxygen-vacancy contents, leading to poor cycling stability and limited practical applications. To overcome these problems, an effective strategy for constructing high oxygen vacancies α-BiO on activated carbon fiber paper (ACFP) is developed in this study. To this end, ACFP/Bi(OH) is first synthesized by the solvothermal method and then converted to ACFP/α-BiO by in situ electrochemical activation. The proposed innovative electrochemical method quickly and easily introduces oxygen vacancies while preserving the three-dimensional structure, thereby promoting the charge transfer and ions diffusion in ACFP/α-BiO. Consequently, the specific capacity of ACFP/α-BiO reaches 906C g at 1 A g, and the capacity retention remains above 70% after 3000 cycles, a value higher than that of δ-BiO (45%). Furthermore, the hybrid supercapacitor device assembled by ACFP/α-BiO delivers a maximum energy density of 114.9 Wh kg at 900 W kg and outstanding cycle stability with 73.56 % retention after 5500 cycles. In sum, the proposed ACFP/α-BiO with high performance and good stability looks promising for use as bismuth-based anode materials in supercapacitors and aqueous batteries.