A Stand-Alone Module for Solar-Driven H2 Production Coupled with Redox-Mediated Sulfide Remediation

Efficient electrochemical devices are required to convert electric power by intermittent renewable energy sources into a chemical form. The choice of combination in reduction–oxidation reactions can vary depending on the target, which provides different thermodynamics and kinetics. A promising approach for H2 production coupled with sulfide remediation is demonstrated to utilize the intermediate redox media. H2 is produced on the cathode, and soluble redox ions in a reduced form are oxidized on the anode. The ions are then transferred to a separate reactor to oxidize the sulfide ions via a homogeneous reaction, and the reduced redox ions are recirculated. A solar-driven redox photovoltaic-electrochemical (PV-EC) system is operated as a stand-alone module and is composed of Cu(In,Ga)(S,Se)2 (CIGS) PVs and EC cells in series and operated under natural solar irradiation. A unique EC cell is established in an aqueous-phase membraneless configuration at ambient temperature, and a cathode is decorated with a semipermeable CrOx-based nanomembrane. This allows for selective H2 evolution without causing Fe redox reduction. Remaining issues associated with the stability of the CrOx permselective layer on the cathode are also discussed, which are associated with the formation constant of a soluble metal complex in the presence of ligand counterions.