Transition Metal Coated Single Crystalline BiVO₄ Photoanode for Photoelectrochemical Chlorine Generation

Bismuth vanadate (BiVO₄) is an outstanding photoanode material for photoelectrochemical water splitting. In this work, a series of single crystalline BiVO₄ photoanodes are synthesized by pulsed laser deposition (PLD). Once coated with a thin layer of cobalt oxides (CoO<i>_x</i>) co-catalyst, also by PLD, the photoanodes support efficient photoelectrochemical generation of chlorine (Cl₂) from brine under simulated solar light. Activity of the chlorine generation reaction (ClER) is optimized when the thickness of CoO<i>_x</i> is about 3 nm, with the faradic efficiency of ClER exceeding 60%. Detailed studies show that the CoO<i>_x</i> co-catalyst layer is amorphous, uniform in thickness, and chemically robust. As such, the co-catalyst also effectively protects the underlaying BiVO₄ photoanodes against chlorine corrosion. The other metal oxides cocatalysts are also compared, detailed mechanism on how the cocatalyst layers influence the performance of BiVO₄ photoanode is revealed. This work provides insights on using artificial photosynthesis for by-products that carries significant economic value while avoiding the energetically expensive oxygen evolution reactions.