A Stand‐Alone Module for Solar‐Driven H 2 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 H 2 production coupled with sulfide remediation is demonstrated to utilize the intermediate redox media. H 2 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 CrO x ‐based nanomembrane. This allows for selective H 2 evolution without causing Fe redox reduction. Remaining issues associated with the stability of the CrO x 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.