Unassisted Photoelectrochemical HO Production with Glycerol Valorization Using α-FeO.

Photoelectrochemical (PEC) HO production via two-electron O reduction is promising for HO production without emitting CO. For PEC HO production, α-FeO is an ideal semiconductor owing to its earth abundance, superior stability in water, and an appropriate band gap for efficient solar light utilization. Moreover, its conduction band is suitable for O reduction to produce HO. However, a significant overpotential for water oxidation is required due to the poor surface properties of α-FeO. Thus, unassisted solar HO production is not yet possible. Herein, we demonstrate unassisted PEC HO production using α-FeO for the first time by applying glycerol oxidation, which requires less bias compared with water oxidation. We obtain maximum Faradaic efficiencies of 96.89 ± 0.6% and 100% for glycerol oxidation and HO production, respectively, with high stability for 25 h. Our results indicate that unassisted and stable PEC HO production is feasible with glycerol valorization using the α-FeO photoanode.