Oxygen vacancies on the surface of HxWO3−y for enhanced charge storageElectronic supplementary information (ESI) available: Experimental details, structure refinements and electrochemical data. See DOI: 10.1039/c8ta00981c

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 H x WO 3− y with that of WO 3 and bulk defective e-H x WO 3− y . It shows that surface OVs are key hot spots for faradaic reactions in H x WO 3− y , which promotes the formation of certain W 5+ and W 4+ during the reduction process. 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 H x WO 3− y with that of WO 3 and bulk defective e-H x WO 3− y .