Photo-rechargeable Zinc-Ion Capacitors using V2O5-Activated Carbon Electrodes

Electrochemical energy storage devices that can harvest energy from the environment and store it are increasingly important to address energy poverty in developing parts of the world as well as powering off-grid autonomous devices. Currently, batteries or supercapacitors connected to solar cells are used for these applications, but these frequently suffer from voltage mismatches and inefficiencies in the device packaging. This paper presents an optically and electrochemically active electrode for photo-rechargeable zinc-ion capacitors using vanadium oxide nanofibers. These rely on photoexcited charge carrier separation to charge the capacitors without any external photovoltaic or electrical devices. We found that silver nanowires are better than carbon-based conductive additives as they support photoexcited hole transport and provide light scattering centers that enhance visible light absorption. The proposed capacitors show a ∼63% capacity increase under illumination, photorecharge in 30 min, and ∼99% capacity retention over 4000 cycles.