  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
photoelectrode, 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
{\alpha}-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 a {\alpha}-Fe2O3 photoanode. The
optimized nanostructured is then exploited in the {\alpha}-Fe2O3/CuxO p-n
junction, achieving an outstanding unbiased photocurrent density of 0.46
mA/cm2, 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 {\alpha}-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.
