Oxygen vacancy-rich WO3 heterophase structure: A trade-off between surface-limited pseudocapacitance and intercalation-limited behaviour

Abstract Intercalation-pseudocapacitance materials are attracting increasing interest as promising electrodes for use in high-capacitance supercapacitors. However, these materials typically exhibit unsatisfactory rate performances due to their relatively slow cation-insertion process. Under high mass loading, their rate performances are even further degraded. Herein is presented our fabrication of an oxygen vacancy-rich h-WO3/ort-WO3·0.33H2O heterophase structure (HOHS) by a facile hydrothermal synthesis. The HOHS has a split-level nanotubes-on-nanoplates morphology and its formation and energy-storage mechanisms are discussed in detail. The HOHS exhibits a collaborative charge-storage mechanism involving surface redox and proton intercalation, and the capacitance contribution associated with the proton intercalation can be regulated over a wide range. By achieving a trade-off between the surface-limited pseudocapacitance and intercalation-limited behaviours and regulating its morphology, the HOHS electrode with an ultra-high mass loading of 10.8 mg cm−2 delivers a high areal capacitance of 2552 mF cm−2 at 1 mA cm−2 and excellent long-term stability. More importantly, the rate performance of the HOHS (78% capacitance retention at 20 mA cm−2 in comparison to 1 mA cm−2) is better than those reported for WO3-based materials. This strategy opens avenues for the fundamental study of the regulation of the energy storage mechanism and the achievement of a trade-off between the capacitance and rate capability in high-mass-loading electrodes.