Visible-Light-Active NiV₂O₆ Films for Photoelectrochemical Water Oxidation

NiV₂O₆ films were successfully fabricated and characterized as photoanodes for photoelectrochemical (PEC) water oxidation. The films were synthesized by vacuum codeposition of Ni and V followed by annealing in air. The resulting triclinic NiV₂O₆ films were n-type semiconductors with optical transitions at ∼2.1 eV (indirect) and 2.4 eV (direct). Photoelectrochemical testing in 1 M KOH showed a photoelectrochemical band gap of ∼2.4 eV and that ∼45% of the photocurrent came from light with λ > 420 nm. NiV₂O₆ electrodes showed quite stable photocurrent under bias in basic electrolyte, indicative of chemical stability against photocorrosion despite its relatively small band gap. The flat band potential of NiV₂O₆ was ∼0.6 V vs RHE, thus allowing photogenerated holes to oxidize water thermodynamically, and confirmed by oxygen evolution measurements (Faradaic efficiency ∼80%). Suitable oxygen evolution catalysts and n-type doping are suggested to improve the PEC performance of this material further. Regarding the search for inexpensive photoanodes capable of harvesting photons in the visible region of the solar spectrum, the availability of Ni and V makes NiV₂O₆ a promising anode material for photoelectrochemical use