Two-Dimensional Covalent Organic Framework Photoanode for High Capacity Solar Battery

To mitigate our reliance on fossil fuels and facilitate energy transition, efficient conversion and storage of ubiquitous solar energy is a key strategy. Despite significant research progress in photovoltaics, energy storage in decentralized batteries requires the decoupling of energy conversion and storage, which causes major energy loss and higher cost. Seamless integration of a photoconversion system and an energy storage system in a single device can effectively store the excess energy. Materials that can demonstrate light harvesting, effective charge carrier separation for long-term charge storage, and on-demand charge retrieval as electrical energy, would be the most suitable choice. Such properties have been demonstrated in graphene-, carbon-nitride-, polyoxometalate-, and metal organic frameworks- based materials; however, the charge storage capacity remains uncompetitive. Driven by the need for earth-abundant and sustainable materials for solar energy storage, covalent organic frameworks (COFs) have emerged as a new generation of molecularly defined semiconductors with tunable optoelectronic properties. Herein, the rational integration of an electron reservoir in a polyimide two-dimensional COF unlocks the unique combination of light harvesting and electrical energy storage. When used as an aqueous solar battery anode, the COF demonstrated a capacity of ~40 mAh g -1 operating as a pseudocapacitor, which stores charge as long-lived radical anions for days. With photo-electrochemical measurements in conjunction with detailed spectroscopic studies and theoretical support, we attempt to unravel the mechanism of long-term charge stabilization. Furthermore, on-demand release of long-lived electrons with a suitable co-catalyst unlocks the prospects of dark photocatalysis, which will be investigated in the future. References: F. Podjaski, B. V. Lotsch, Adv. Energy Mater . 2021 , 11 , 2003049. V. W. Lau, D. Klose, H. Kasap, F. Podjaski, M-C. Pignié, E. Reisner, G. Jeschke, B. V. Lotsch, Angew. Chem. Int. Ed . 2017 , 56 , 510 –514. S. Amthor, S. Knoll, M. Heiland, L. Zedler, C. Li, D. Nauroozi, W. Tobaschus, A. K. Mengele, M. Anjass, U. S. Schubert, B. Dietzek-Ivanšić, S. Rau, C. Streb, Nat. Chem . 2022 , 14 , 321−327. M. Stanley, F. Sixt, J. Warnan, Adv. Mater . 2023 , 35 , 2207280.