Proceedings of nanoGe September Meeting 2017 (NFM17)
Publication date: 20th June 2016
The n-type semiconductor bismuth vanadate (BiVO4) has recently gained a lot of attention as photoanode material for visible-light induced water oxidation. Its absorption in the visible domain (band gap energy of 2.4 eV), its suitable band edge positions compared to the OER half reaction, its stability against photo-corrosion as well as its low cost, make BiVO4 one of the most interesting ternary oxide materials for light-induced oxygen evolution from water. One major drawback for BiVO4 is its poor bulk electronic conductivity; problem, which however can be overcome by doping as well as by improved structural design.
In contrast to well-known cation doping, we present a new approach of anion substitution in BiVO4 photoanodes. A new solid-vapor reaction method for the treatment of BiVO4 powder with HF(g) at ambient pressure and in inert gas atmosphere was developed to reproducibly substitute oxygen by fluorine. Obtained powder samples were characterized extensively by means of chemical and structural analysis as well as by electron microscopy. Using electrophoretic deposition and taking advantage of the low-temperature sintering of BiVO4, the as-synthesized powders were processed to photoanodes, allowing the (photo-)electrochemical characterization of F:BiVO4 regarding water oxidation compared to its pristine counterpart. Higher photocurrents were obtained for the fluorine-modified BiVO4 anode. Photocurrent transient analysis revealed that surface hole recombination is drastically reduced for the F:BiVO4 sample. Additionally, Mott-Schottky-type electrochemical impedance spectroscopy revealed the F:BiVO4 material to profit from a bigger amount of free charge carriers as well as from a cathodically shifted flat band potential.
Our results demonstrate the widely unapplied field of anion doping to be a viable tool to optimize photoanode properties with respect to photoelectrochemical water oxidation.
This work was funded by the DFG SPP1613 program.
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