Self-Driven Photoelectrochemical Splitting of H₂S for S and H₂ Recovery and Simultaneous Electricity Generation

A novel, facile self-driven photoelectrocatalytic (PEC) system was established for highly selective and efficient recovery of H₂S and simultaneous electricity production. The key ideas were the self-bias function between a WO₃ photoanode and a Si/PVC photocathode due to their mismatched Fermi levels and the special cyclic redox reaction mechanism of I^-/I₃^-. Under solar light, the system facilitated the separation of holes in the photoanode and electrons in the photocathode, which then generated electricity. Cyclic redox reactions were produced in the photoanode region as follows: I^- was transformed into I₃^- by photoholes or hydroxyl radicals, H₂S was oxidized to S by I₃^-, and I₃^- was then reduced to I^-. Meanwhile, H⁺ was efficiently converted to H₂ in the photocathode region. In the system, H₂S was uniquely oxidized to sulfur but not to polysulfide (S_x^n-) because of the mild oxidation capacity of I₃^-. High recovery rates for S and H₂ were obtained up to ∼1.04 mg h^-1 cm^-1 and ∼0.75 mL h^-1 cm^-1, respectively, suggesting that H₂S was completely converted into H₂ and S. In addition, the output power density of the system reached ∼0.11 mW cm^-2. The proposed PEC-H₂S system provides a self-sustaining, energy-saving method for simultaneous H₂S treatment and energy recovery.