Durable bias-free solar Water-Splitting cell composed of n+p- Si/Nb2O5/NiPt photocathode and W:BiVO4/NiCo(O-OH)2 photoanode

Improving Photoelectrochemical Activity of a Silver Sulfide-Based Photoelectrode by Bismuth Doping for Hydrogen Evolution from Industrial Waste Water

“…Sustainable hydrogen (H 2 ) generation by means of photoelectrochemical (PEC) water splitting has stimulated tremendous research interest in view of its eco-friendliness, its cost-effectiveness, and more importantly, its great promise to cater for the burgeoning demand for H 2 as a powerful energy carrier in addition to an important feedstock for manufacturing a wide range of chemicals. − However, the reported solar-to-hydrogen efficiency for the PEC devices developed thus far is still well below the theoretical performance, which is primarily limited by the sluggish kinetics of the concomitant oxygen evolution reaction (OER). − Given that the evolved oxygen (O 2 ) is of little value and worse yet, its mixing with H 2 as an accidental result of gas crossover highly likely leads to a dangerous explosion hazard, an alternative oxidative reaction is thus required. − The present contribution has in this regard employed particularly a sulfide (S 2– )- and sulfite (SO 3 2– )-containing electrolyte, provided that their oxidation has been reported to be kinetically facile compared to OER. − As a result, the H 2 evolution rate is markedly promoted and more importantly, at the expense of S 2– and SO 3 2– , which are known to be the major pollutants and present in large quantities in the wastewater discharged from chemical and petroleum plants after the flue gas desulfurization process, leading to their environmental contamination in the meantime largely alleviated. − In addition to the aforementioned electrolyte engineering, the photoelectrode developed in this work has also been carefully designed in order to further accelerate the PEC H 2 evolution reaction (HER) by first using silver sulfide (Ag 2 S) as the light-absorbing material. Its ultrahigh absorption coefficient, which amounts to α ∼ 10 4 m –1 , and broadband light-harvesting ability, which benefits from its narrow band gap of merely E g ∼ 1.1 eV, allow Ag 2 S to take full advantage of incident light. − Moreover, Ag 2 S is further deposited on the zinc oxide nanorods (ZnO NRs), forming shell–core Ag 2 S/ZnO NRs, from which the photoexcited minority charge carriers migrate to the electrolyte along its radial direction.…”