Optimisation of Mo-modified BiVO4 photoabsorber sample preparation and the improvement of PEC performance with Ni/Fe LDH as oxygen evolution catalyst.

Joao Ricardo Coelho Junqueira, Ruhr-Universität Bochum, Bochum, Germany
Olga Krysiak, Ruhr-Universität Bochum, Bochum, Germany
Tim Bobrowski, Ruhr-Universität Bochum, Bochum, Germany
Ramona Gutkowski, Ruhr-Universität Bochum, Bochum, Germany
Wolfgang Schuhmann, Ruhr-Universität Bochum, Bochum, Germany

Photoelectrochemical (PEC) water splitting is one of the viable alternatives to mitigate the requirement on fossil fuels for energy applications. PEC cells are based on a semiconductor material capable of converting sunlight into useful electrons. Bismuth vanadate (BiVO4) is a possible candidate for being used because this material meets essential criteria, such as a band gap ~2.4 eV with its valence band providing sufficient overpotential for the oxygen evolution reaction (OER). It can be fabricated from inexpensive and environmental non-harmful chemicals. However BiVO4 has some drawbacks. Its semiconductor performance is limited by electron mobility within the bulk. This can be diminished upon addition of transition metals e.g. molybdenum and tuning the semiconductor film thickness. Moreover, the decoration of the material surface with oxygen evolution catalyst (OEC) can be used to decrease holes recombination at the surface and by this increase the OER kinetics. For the optimisation of Mo-modified BiVO4 sample preparation a spray-coating set-up was used. It is based on an airbrush pistol mounted on a robotic arm. Due to the combination of the spray-coating set-up with an in-house-written software a controlled amount of a precursor can be delivered to a substrate forming a homogeneous and reproducible film. Mo:BiVO4 photoanodes were prepared with different spray parameters and the result was samples with different layer thicknesses. The efficiency in dependence from the layer thickness of the samples were evaluated by means of incident photon-to-current efficiency and later assessed with SEM. The optimised sample was further modified with an increasing loading of Ni/Fe layered double hydroxide in order to tune the amount of the OER catalyst. High-throughput analysis performed by an optical scanning droplet cell revealed that the presence of the OEC increase significantly the measured photocurrent of the photoanode.

The authors are grateful to the financial support of the DFG within the framework of the SPP1613 (SCHU929/12-1 and 12-2). O. A. K. acknowledges financial support from the MAESTRO Grant UMO-2013/10/A/ST5/00245, awarded by NCN Poland.

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