2, Department of chemistry, University of Bologna, Bologna, , Italy
With the increase in energy demand and the booming environmental crisis, the use of renewable energy sources, such as the Sun, has become an urgent matter in our daily life. Within this context, developing efficient, stable, low-cost and environmentally friendly solutions integrating solar energy harvesting and energy storage (batteries and supercaps) is a key challenge. Among electrochemical energy storage solutions, aqueous rechargeable batteries are particularly interesting since, in principle, they are safe and do not make use of critical elements .
Melanin is a bio-pigment found in various classes of mammals, fishes, and different species of plants. This organic bio-pigment features unique physiochemical properties such as UV-Vis-near IR absorption, redox activity (hydroquinone-semiquinone-quinone couples), metal chelation and ionic-electronic hybrid electrical conduction . The photoredox properties of melanin combined to its capability to reversibly bind cations opens the door to explore this intriguing quinone-based material as electrode for solar batteries .
Here we report on the use of melanin on carbon quantum dots (CQD)-based current collectors. CQDs offer high surface area to the redox active melanin and facilitate the electron transport to the back contact. Cyclic voltammetry and galvanostatic charge/discharge cycles were employed to evaluate the storage performance of the melanin-electrode materials at different pH conditions and chemical composition of the electrolyte (e.g. including cations such as H+, Na+, K+, Mg2+), under simulated solar light. We observed that the redox state of the melanin-based electrodes affects its photoresponse. Our work constitutes a relevant contribution towards (photo)electrodes for sustainable, aqueous, rechargeable solar batteries.
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