Solar redox flow batteries (SRFB) have received much attention as an alternative integrated technology for simultaneous conversion and storage of solar energy. Yet, the photocatalytic efficiency of semiconductor-based single photoelectrodes, such as hematite, remains low due to the trade-off between fast electron hole recombination and insufficient light utilization, as well as inferior reaction kinetics at the solid/liquid interface. Herein, we present an α-Fe2O3/CuxO p-n junction, coupled with a readily scalable nanostructure, that increases the electrochemically active sites and improves charge separation. Thanks to light-assisted scanning electrochemical microscopy (photo-SECM), we elucidate the morphology-dependent carrier transfer process involved in the photo-oxidation reaction at an α-Fe2O3 photoanode. The optimized nanostructure is then exploited in the α-Fe2O3/CuxO p-n junction, achieving an outstanding unbiased photocurrent density of 0.46 mA cm−2, solar-to-chemical (STC) efficiency over 0.35% and a stable photocharge-discharge cycling. The average solar-to-output energy efficiency (SOEE) for this unassisted α-Fe2O3-based SRFB system reaches 0.18%, comparable to previously reported DSSC-assisted hematite SRFBs. The use of earth-abundant materials and the compatibility with scalable nanostructuring and heterojunction preparation techniques offer promising opportunities for cost-effective device deployment in real-world applications.