Integrating Cu ₂ O and Fe ₂ O ₃ Dual Photoelectrodes Into a Solar Rechargeable Flow Battery

Solar rechargeable flow batteries (SRFBs), which integrate solar energy conversion with electrochemical energy storage, have attracted increasing attention in recent years. To date, the reported photoelectrode‐based SRFBs predominantly employ either a single photoanode or a photoanode coupled with a silicon‐based photocathode for battery charging. Although silicon possesses an optimal bandgap and outstanding light‐harvesting capability, its intrinsic instability in aqueous environments and severe interfacial charge recombination necessitate complex and precisely engineered device architectures, thereby fundamentally limiting its scalability and practical deployment. Consequently, metal‐oxide photoelectrodes emerge as more viable candidates for SRFB applications. Herein, we report for the first time an SRFB architecture incorporating a Cu 2 O photocathode in conjunction with an iron‐oxide photoanode and the Fe(BPMG) 2 (II)/Fe(BPMG) 2 (III) and Fe 2+ /Fe 3+ redox couples. Benefiting from rational photoelectrode and interface design, the Cu 2 O photocathode delivers an applied‐bias photon‐to‐current efficiency (ABPE) of up to 0.48%. As a result, the assembled SRFB achieves an output voltage of 0.62 V and a solar‐to‐output electricity efficiency of approximately 0.11%. This work demonstrates the feasibility of employing metal‐oxide photocathodes in SRFB systems and provides a new design paradigm for the development of advanced photocathodes toward fully solar‐driven flow battery technologies.