Investigation of multinary vanadate thin film materials libraries for solar water splitting
Swati Kumari, Ruhr Universität Bochum, Bochum, GermanyJoão R. C. Junqueira, Ruhr Universität Bochum, Bochum, GermanyRamona Gutkowski, Ruhr Universität Bochum, Bochum, GermanyAleksander Kostka, Ruhr Universität Bochum, Bochum, GermanyKatharina Hengge, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, GermanyChristina Scheu, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, GermanyWolfgang Schuhmann, Ruhr Universität Bochum, Bochum, GermanyAlfred Ludwig, Ruhr Universität Bochum, Bochum, Germany
Photoelectrochemical (PEC) water splitting using semiconductor electrodes is a promising technology for generation of clean fuels.1 Multinary metal vanadate systems2 like Bi-V-O, Fe-V-O, Cu-V-O have attracted attention due to its low-cost fabrication, chemical stability and promising photoelectrocatalytic activity. The two metal vanadate systems of interest are Fe-V-O and Cu-V-O. Both ternary systems were fabricated using combinatorial reactive magnetron co sputtering covering a large compositional range, (Fe21-90V10-79)Ox and (Cu19-83V17-81)Ox, with subsequent annealing in air. The design of the materials libraries comprises a combination of composition and thickness gradients.3 High-throughput characterization methods were used to establish correlations between composition, crystallinity, thickness, optical properties, and photocurrent density.4 The Fe-V-O photoanodes showed three major crystalline phases throughout the composition gradients: Fe2V4O13, FeVO4 and Fe2O3. The photocurrent generation was increased with increasing crystallinity of the triclinic FeVO4 phase which corresponds to have ~2.04 eV indirect band gap energy. Therefore, material libraries with Fe content between 54 and 66 at.%, with FeVO4 as the prominent phase confirmed to be the most promising region for solar water splitting. For Cu-V-O photoanodes, high-throughput screening revealed presence of six different Cu vanadate phases throughout the composition gradients: CuV2O6, β-Cu2V2O7, α-Cu2V2O7, Cu3V2O8, Cu11V6O26, and Cu5V2O10. The photocurrent density was increased with change in crystal structure from CuV2O6-to-β-Cu2V2O7-to-α-Cu2V2O7-to-Cu3V2O8 and Cu11V6O26 (mixed phase region). The highest PEC activity was observed for composition (V39Cu61)Ox in the Cu3V2O8 and C11V6O26 mixed phase region with 321 nm thickness. Moreover, CuV2O6 (low-Cu region) and Cu5V2O10 (most Cu-rich region) phase regions are found to be the lowest photoelectrocatalytic active region in the materials libraries. All Cu vanadate phases have < 2 eV indirect band gap energy.
1. Van, D. K. R.; Grätzel, M. Springer New York Dordrecht Heidelberg London; 2012; pp 6-14.
2. Zhou, L.; Yan, Q.; Yu, J.; Jones, R. J. R.; Becerra-stasiewicz, N.; Suram, S. K.; Gregoire, J. M. Phys. Chem. Chem. Phys., 2016, 18, 9349–9352
3. Meyer, R.; Sliozberg, K.; Khare, C.; Schuhmann, W.; Ludwig, A. Chemsuschem, 2015, 8, 1279-1285.
4. Stein, H.; Jiao, S.; Ludwig, A. ASC Comb. Sci., 2017, 19, 1-8.