Light-enhanced Electrochemical Energy Storage of Synthetic Melanin on Conductive Glass Substrates
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.463
Light-enhanced Electrochemical Energy Storage of Synthetic Melanin on Conductive Glass Substrates Authors: Ri Xu1, Abdelaziz Gouda1, Maria Federica Caso2, Francesca Soavi3 and Clara Santato*1 1
Department of Engineering Physics, Polytechnique Montréal, C.P. 6079, Succ. Centre-ville, Montréal, QC, H3C 3A7, Canada 2
Nanofaber Spin-Off at ENEA, Casaccia Research Centre, Via Anguillarese 301, Roma, 00123, Italy
3 Dipartimento di Chimica “Giacomo Ciamician”, Alma Mater Studiorum Università di Bologna, Via Selmi, 2, 40126 Bologna, Italy
*Correspondence and requests for materials should be addressed to C.S. (e-mail: [email protected])
ABSTRACT Eumelanin is a redox active, quinone-based biopigment, featuring a broad band absorption in the UV-Vis region. The combination of the redox and optical properties makes eumelanin an interesting candidate to explore light-assisted storage technologies. Electrodes of melanin on indium tin oxide (ITO) current collectors were investigated for their morphological and voltammetric characteristics in aqueous electrolytes. Under solar light, we observed that the capacity and the capacitance of the melanin electrodes significantly increase with respect to the dark conditions (by 63% and 73%, respectively).
INTRODUCTION In order to face possible energy shortages caused by the increasing world population, it is relevant to develop sustainable and efficient solar energy storage technologies, combining the solar energy conversion and electrochemical energy storage functions [1]– [4].
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Scheme 1. Hydroquinone (H2Q), semiquinone (SQ) and quinone (Q) redox forms of the building blocks of eumelanin: 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA). R is –H in DHI whereas R is the – COOH group in DHICA. The quinone imine form (QI) is the tautomer of Q.
Nature is resourceful of environmentally benign and redox active materials, e.g. organic quinone-based species that can be assembled into energy storage devices [5]–[17]. Eumelanin is a quinone-based biopigment ubiquitous in flora and fauna. It has interesting physicochemical features, such as UV-Vis absorption, photoconductivity, hydrationdependent electrical conductivity, metal binding affinity (chelation) [18]–[20]. In eumelanin, different redox states coexist in the two building blocks 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole carboxylic acid (DHICA) making up the biopigment (Scheme 1). Eumelanin-based electrodes have been employed in energy storage devices, such as supercapacitors and batteries. Photovoltaic cells including eumelanin have been reported in the literature [7], [21]–[24]. The broad band optical absorption of eumelanin can be explained by chemical disorder (co-existing chromopho
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