Solar-Driven Hybrid Electrolysis System for CO ₂ Reduction and Off-Field H ₂ S Oxidation toward Formate and Sulfur Co-Generation

Solar-driven CO 2 conversion via photovoltaic-powered electrolysis offers a sustainable route for carbon utilization and renewable energy storage, yet its current output is still constrained by the low-value yield of the anodic reaction. Herein, we rationally designed a solar-compatible paired electrolysis system by coupling cathodic CO 2 reduction reaction (CO 2 RR) with anodic off-field H 2 S oxidation reaction (OFSOR) mediated by the I 3 − /I − redox couple, enabling synchronous production of high-value formate and elemental sulfur with significantly reduced energy input. An acid-tolerant Bi-based metal−organic framework (Bi-MOF) precursor was fabricated and underwent in situ structural reconstruction to form Bi 2 O 2 CO 3 as an active phase for CO 2 RR with a formate faradaic efficiency (FE) exceeding 90% over a wide current density range. In situ Raman spectroscopy confirmed the formation of key *HCOO − intermediates over the Bi 2 O 2 CO 3, accounting for the superior formate selectivity. By coupling with the carbon cloth anode, a two-electrode CO 2 RR-OFSOR electrolyzer was assembled, delivering a current density of 50 mA/cm 2 at a cell voltage of only 2.91 V and reducing cell voltage by 41% under the tested conditions as compared to the conventional CO 2 RR-OER configuration. Furthermore, a self-driven solar-powered photovoltaic-electrochemical device was established by directly powering the electrolyzer with commercial silicon photovoltaic cells, which steadily operates with formate FE above 90% and achieves a solar-to-chemical conversion efficiency of 4.6%. This work provides a promising and energy-efficient solar-driven integrated strategy for collaborative CO 2 conversion and H 2 S resource utilization, highlighting the potential of hybrid electrolysis systems in sustainable electrosynthesis.