Unprecedented solar water splitting of dendritic nanostructured Bi2O3 films by combined oxygen vacancy formation and Na2MoO4 doping

Abstract

We demonstrate the synergetic effect of Na2MoO4-doping and vacuum-annealing on dendritic nanostructured bismuth oxide (Bi2O3) thin films prepared by electrodeposition for visible-light-assisted photoelectrochemical (PEC) water oxidation. After evaluating various extents of Na2MoO4-doping as well as vacuum-annealing temperatures, it was evidenced that both Na2MoO4-doping and vacuum-annealing significantly improved the efficiency and PEC water oxidation performance. Compared to the undoped Bi2O3 photoanode, the optimized Na2MoO4-doped Bi2O3, after vacuum-annealing, resulted in more than 25-fold enhancement in the photoanodic current density to 1.06 mA/cm2 at 1.23 VRHE under AM1.5 G illumination. The PEC enhancement is credited mainly to the increased PEC surface active sites in the Na2MoO4-doped vacuum annealed sample. Confirmed by combined XPS and Mott-Schottky (M − S) analysis, vacuum annealing resulted in surface oxygen vacancies that can contribute to the photocatalytic activity. Besides, Na2MoO4-doping resulted in reduced dimensions of the dendritic structure, revealed by FE-SEM and XRD measurements, resulting in larger surface area and, therefore, larger surface/electrolyte contact. This dual strategy (metal doping + vacuum annealing) can be generalized to assemble photoanodes of other materials used for the production of solar fuels. Our results make a valuable step towards efficient Bi2O3/BiVO4 pn heterojunctions.