Understanding self-photorechargeability of WO₃ for H₂ generation without light illumination

This work presents insight into the self-photorechargeability of WO ₃, whereby the intercalation of positive alkali cations is accompanied by the simultaneous storage of photo-excited electrons. The cyclic voltammetry studies verify the photo-assisted intercalation and de-intercalation of Na⁺ and K⁺ from the flower structured WO₃. A storage capacity of up to 0.722 C cm^-2 can be achieved in a saturated (0.68 M) K₂SO₄ electrolyte solution. However, the best photo recharge-discharge stability of the electrode are observed at a lower (0.1 M) cation concentration. At high electrolyte concentrations, the intercalated cations are firmly trapped, as indicated by the structural modifications observed in Raman analysis, resulting in much less photocharging and discharging abilities in subsequent cycles. The study also shows that the stored electrons can be successfully used to generate H₂ with 100 % faradaic efficiency in the absence of light.