An all-iron photo-assisted redox-flow battery

The integration of solar energy into redox-flow batteries (RFBs) has recently attracted considerable attention as a promising strategy for sustainable energy storage. However, most early efforts have simply combined conventional photovoltaic cells with flow batteries, without achieving true functional coupling or synergistic operation between the two systems. This limitation is especially pronounced in high-voltage RFBs, where the photovoltaic component must deliver equally high photovoltages, often leading to complicated configurations and elevated fabrication costs. In this study, we present a simple and cost-effective approach by developing an all-iron photo-assisted redox-flow battery (PARFB) that integrates an iron oxide photoanode with K 4 [Fe(CN) 6 ]/K 3 [Fe(CN) 6 ] and FeTiPA(II)/FeTiPA(III) as the redox couples. By optimizing the interfacial charge-transfer kinetics at the electrode level, the system achieves a 15% reduction in charging energy, an output voltage of ~1.20 V, and a solar-to-output energy conversion efficiency of 0.1%, which is comparable to previously reported hematite-based photoelectrode systems. This work offers a viable and scalable strategy for coupling solar energy harvesting with redox-flow battery technologies, particularly for systems requiring high operational voltages.