Oxygen vacancies on the surface of HxWO3−y for enhanced charge storage

The dominant role of surface oxygen vacancies (OVs) in improving energy storage is underscored by comparing the OV-mediated charge storage performance of surface and bulk defective HxWO3−y with that of WO3 and bulk defective e-HxWO3−y. It shows that surface OVs are key hot spots for faradaic reactions in HxWO3−y, which promotes the formation of certain W5+ and W4+ during the reduction process.