Extending the Absorption Limit of BiVO4 Photoanodes with Hydrogen Sulfide Treatment

Bismuth vanadate is a promising photoanode material for photoelectrochemical water splitting due to its relative stability, low cost, and nontoxic properties. However, its performance is limited by the large bandgap (E_g) of 2.4 eV, and the record photocurrent is already within 90% of its theoretical limit. Further photocurrent enhancement could only be obtained by increasing its optical absorption, for example, by reducing E_g. Herein, sulfur-incorporated bismuth vanadate (S-BiVO₄) thin films are synthesized via spray pyrolysis combined with post-treatment in hydrogen sulfide environment. Under optimal H₂S treatment conditions, sulfur can be incorporated successfully into the BiVO₄ lattice, without the formation of any secondary phases. The use of reactive H₂S, instead of solid sulfur powders, allows us to decrease the required annealing temperature and increase the kinetics for sulfur incorporation into BiVO₄. The E_g of the resulting S-BiVO₄ films is decreased by >200 meV (vs. pristine BiVO₄), which theoretically corresponds to a 20% increase in the theoretical photocurrent limit. Finally, the stability limitation of S-BiVO₄ is overcome by introducing pulsed-laser-deposited NiO_x protection layers. The modified S-BiVO₄/ NiO_x film exhibits higher photocurrent density with no reduction of photocurrent during the 9 h stability test with AM1.5 illumination.