The present study elaborates facile approach to generate active sites in cashew nut shaped silica (SiO2). These active sites are attributed to the high concentration of oxygen vacancies and bimodal mesoporosity in silica owing to etching and calcination treatment. In the etched calcined silica (ECS), mesopores act as buffered spaces, whereas, OVs provide high carrier/donor density (3 x 10(24) cm(-3)). High density of carriers/donor reduces the distance between active sites (2.5 nm) further enhancing the rate of electron transfer. Consequent to the unique combination of OVs and bimodal mesoporosity, ECS exhibits high electrochemically accessible surface area (3170 m(2) g(-1)) and excellent charge storage in ECS parallel to ECS cell (similar to 337 F g(-1) at 1 A g(-1)). In addition, the symmetric cell (ECS parallel to ECS) delivers maximum energy density of 46.86 Wh Kg(-1) at power density of 537.59 W kg(-1) with respectable capacitance retention (111% after 10,000 cycles). Remarkably, the solid state flexible device unveiled energy density of 2.16 Wh Kg(-1) at 166.05 W kg(-1) even under the bent state retaining 165% of its capacitance up till 3000 cycles. This work essentially highlights the synergism between mesoporosity and oxygen vacancies on the charge storage characteristics of silica. (C) 2018 Elsevier Ltd. All rights reserved.