Investigation of Vanadate-Metal-Oxide Thin Film Systems for Solar Water Splitting

Swati Kumari^a, João R. C. Junqueira^b, Ramona Gutkowski^b, Aleksander Kostka^c, Katharina Hengge^d, Mona Nowak^a, Christina Scheu^d, Wolfgang Schuhmann^b^,^e, Alfred Ludwig^a^,^e

^aRuhr-Universität Bochum, Chair for MEMS Materials, Institute for Materials, Universitätsstraße, 150, Bochum, Germany

^bRuhr-Universität Bochum, Analytical Chemistry, Center for Electrochemical Sciences (CES), Universitätsstraße, 150, Bochum, Germany

^cRuhr-Universität Bochum, Center for Interface Dominated High-Performance Materials (ZGH), Universitätsstraße, 150, Bochum, Germany

^dMax Planck Institut für Eisenforschung GmbH, Dusseldorf

^eRuhr-Universität Bochum, Materials Research Department, Universitätsstraße, 150, Bochum, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting 2018 (NFM18)

S2 Light Driven Water Splitting

Torremolinos, Spain, 2018 October 22nd - 26th

Organizers: Wolfram Jaegermann and Bernhard Kaiser

Poster, Swati Kumari, 063
Publication date: 6th July 2018

Water splitting using photoelectrocatalytic materials is a challenging approach towards generation of clean fuel which can solve the energy and environmental issues^1,2. Vanadate-metal-oxides (V‑M-O, M: Fe, Cu) are of interest for photoelectrochemical water splitting (PEC)². Both ternary systems were fabricated using combinatorial reactive magnetron co-sputtering covering a large compositional range, (V_10-79Fe_21-90)O_x and (V_17‑81Cu_19‑83)O_x, with subsequent annealing in air. The design of the material libraries comprises a combination of composition and thickness gradient^4,5. High-throughput characterization techniques were used to establish correlations between composition, crystallinity, thickness and photocurrent density⁶. For V-Fe-O photoanodes, three different crystalline phases were observed throughout the composition gradient: Fe₂V₄O₁₃ towards low Fe content (11 to 42 at.%), FeVO₄ towards high Fe content (37 to 79 at.%) and Fe₂O₃ from low-Fe to Fe‑rich region (23 to 79 at.% Fe). 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, materials with Fe content between 54 and 66 at.%, with FeVO₄ as the prominent phase confirmed to be the most active region for solar water splitting. Films with Fe content > 66 at.% appear to suffer from surface recombination due to presence of dominant Fe₂O₃ over FeVO₄ phase. The second investigated photoanode system is V-Cu-O^7,8. Preliminary results reveal the presence of different crystalline structures throughout the composition space such as α-CuV₂O₆ (low Cu content), β‑Cu₂V₂O₇, α -Cu₂V₂O₇ (mid to Cu-rich region) and C₁₁V₆O₂₆(Cu-rich region). The highest PEC activity of ~73 µA/cm² at 1.23 V vs. RHE was observed for composition (V₃₉Cu₆₁)O_x with the C₁₁V₆O₂₆ phase which corresponds to have ~1.77 eV indirect band gap energy.

References:

1. Van, D. K. R.;Grätzel, M. Springer New York Dordrecht Heidelberg London; 2012; pp 6-14.

2. Grätzel, M. Nature, 2001, 414, 338-344

3. Yan, Q. et al. PNAS, 2017, 114, 3040-3043.

4. Meyer, R. et al. ChemSusChem, 2015, 8, 1279-1285

5. Stein, H. et al. ASC Comb. Sci., 2017, 19, 1-8.

6. Sliozberg, K et al. ChemSusChem, 2015, 8, 1270-1278.

7. Seabold, J. A. et al. Chem. Mater., 2015, 27, 1005-1013

8. Lumley, M. A. et al. Chem. Mater., 2017, 29, 9472-9479

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