Solar bias enables cuprite deposition on ITO in a bioelectrochemical cell for copper recovery

Copper-bearing effluents from electronics manufacturing require recovery under mild aqueous conditions with minimal chemical inputs, yielding a reusable solid. A key challenge lies in controlling the recovered phase, which determines separability and downstream applications. In this study, a photovoltaic source (~1.25 V) was directly coupled to a bioanode-based two-chamber cell with an ITO cathode to treat a synthetic CuSO₄ solution (~1000 mg L^{− 1}) for seven days. Under solar assistance, the copper (Cu) concentration in the supernatant decreased to 670.6 ± 4.3 mg L^{− 1} (~33%), compared to 923.9 ± 2.2 mg L^{− 1} (~8%) open-circuit conditions. Post-run ITO cathodes exhibited interlocking and faceted plate-like crystallites. Energy dispersive X-ray analysis confirmed Cu-rich deposits with substantial oxygen (Cu ≈ 78 wt%, O ≈ 12.6 wt%). X-ray diffraction revealed reflections consistent with cuprite Cu₂O (Pn-3 m) in a cubic structure. These findings demonstrate phase-selective deposition of cuprite under moderate solar bias on oxide supports. Within this operating window, solar-assisted bioelectrochemical systems enable phase-directed copper recovery with minimal chemical addition. Moderate bias values favour Cu₂O, whereas higher bias promotes Cu⁰ formation.