Unveiling the role of electrolyte to promote enhanced proton storage stability in WO3 for energy storage

In the present work, we systematically investigate the phenomenon of electrochemical proton storage in WO3 and subsequently demonstrate a strategy for enhancing the cycle life for proton storage. It was carried out in three different electrolytes medium based on H3PO4, H2SO4 and HCl. It was found that although H3PO4 can promote better cycling stability and high rate capability than HCl and H2SO4, there still persists an issue in achieving large number of charge/discharge cycles. The typical proton storage capacitance of WO3 in 3.75 M H3PO4 is estimated to be around 288–346 F g−1 at a current rate of 0.5 A g−1 over 30 cycles. The cycling stability could, however, be significantly improved by the utilization of gel electrolyte which is basically a mixture of H3PO4 and polyvinyl alcohol (PVA) of different concentrations. For example, the estimated proton storage capacitance is around 287 F g−1 in 3.75 M H3PO4-PVA gel electrolyte (1:8 wt %) over 100 cycles at a current density of 0.5 A g−1. On the basis of the improved proton storage stability in the gel electrolyte, the electrochemical performance of a proton storage full cell with WO3 and V10O24.12H2O as electrodes is also illustrated. Another important revelation is the drastic reduction of the self-discharge rate of the full cell in the gel electrolyte in comparison to pristine aqueous medium electrolyte.