Photo-rechargeable battery with an energetically aligned beetroot Dye/Cl-Graphene quantum dots/MoO3 nanorods composite

A stand-alone, low-cost non-aqueous photo-rechargeable zinc ion battery configuration is presented. The photo-battery integrates the functions of energy conversion and storage in a single device thus minimizing space and material requirements as well as cost. The cell is based on a photocathode with TiO2 and MoO3-nanorods (NRs) as the storage layers, with additional roles of electron transport layer and photosensitizer for TiO2 and MoO3 respectively. Photoactive beetroot (BT) dye and Cl-doped graphene quantum dots (GQDs) were also incorporated therein to yield the TiO2/BT/Cl-GQDs/MoO3-NRs composite photocathode for broad spectral utilization. Under irradiance, the BT dye, Cl-GQDs and MoO3 undergo electron-hole separation, channel the electrons to the external circuit via TiO2 through aligned energy levels and simultaneously charge the battery to ∼1 V, without the application of any external bias or current. The photo-charging and discharge capacities of the photo-battery: TiO2/BT/Cl-GQDs/MoO3-NRs/Zn2+/Zn-AC in the biased mode under an applied current density of 21 mA g−1 and under 1 sun irradiance (100 mW cm−2, AM 1.5 G) are 104 mAh g−1 and 240 mAh g−1 respectively. The photo-charging capacity under 1 sun irradiance in the unbiased mode is ∼75 mAh g−1. A Zn-activated carbon composite (derived from lemon pieces) as the anode electro-catalyzes the reduction of Zn2+ during photo-charging, leading to a power conversion efficiency of 4.03 % under one sun illumination. This has a cycle life of 200 cycles and offers a constant photocurrent of 8.3 mA cm−2 with a hold time of more than 100 s under irradiance which can easily charge any small electronic device. It is an economically viable configuration with huge technological potential for possible commercialization.