pH‐Driven Trade‐Offs in V ₂ O ₅ Nanobelt Supercapacitors: Insights for Long‐Term Stability

Vanadium pentoxide (V ₂ O ₅ ) is a promising pseudocapacitive material for aqueous supercapacitors; however, the influence of pH of electrolyte on its charge storage mechanism and stability remains unclear. Here, we systematically investigate performance of V ₂ O ₅ nanobelts in 1 M LiCl electrolyte with pH adjusted to 2.5, 4.5, 5.5, 8 and 9. Electrochemical results indicate that at near‐neutral pH (5.5), highest specific capacitance (425 F/g at 0.5 A/g) and superior rate capability are obtained, suggesting enhanced surface‐controlled pseudocapacitive kinetics. In contrast, a mildly acidic electrolyte (pH 4.5) provides higher cycling stability (~99% retention after 250 cycles). Significant drift in pH of the electrolyte is observed under strongly acidic and alkaline conditions, with all systems converging towards a mildly acidic range (~5‐6) after electrochemical testing, indicating proton/hydroxide‐consuming side reactions outside the stability window of V ₂ O ₅ . These results demonstrate that electrolyte pH governs a critical trade‐off between electrochemical activity and structural durability. Optimising proton activity within a mildly acidic window enables balanced ion participation and improved long‐term performance. This study provides insights into pH‐regulated charge storage and offers practical guidance for electrolyte engineering in vanadium oxide‐based aqueous supercapacitors.