Recent advances in off-grid electrochemical capacitors

Requirement of autonomous energy storage systems has been increasing in today's world. Off-grid energy storage systems are the forthcoming potential devices due to their noteworthy advances of negligible unwanted energy losses, off-grid operation, light-weight, small in-size, and so forth. Electrochemical capacitors known as supercapacitors (SCs) show unique energy storage performance in terms of high power density, rapid charge/discharge characteristic and long cycling life, thereby they have been finding a special research attention in the scientific community. This article highlights recent developments of off-grid SCs - which are classified into mechanically rechargeable SCs, optically rechargeable SCs and thermally rechargeable SCs. The details working mechanisms along with their performances of these systems were discussed. In addition, this article covers recently developed some of the advanced integrated off-grid systems including integrated SCs with solar cells and nanogenerators, for simultaneous harvesting optical and mechanical energies for charge storage. Finally, the research outlooks and possible research pathways of these off-grid systems are addressed that requires for continuous powering the modern autonomous electronic systems.