Proceedings of nanoGe Fall Meeting 2018 (NFM18)
Publication date: 6th July 2018
Spinel ferrites (MFe2O4, M = divalent metals) are a diverse class of metal oxides which exhibits interesting magnetic, electrocatalytic and optical properties.1 The addition or substitution of Fe cations by transition metals affects the cation distribution, leading to significantly different electronic and magnetic properties. Such controlled tuning of the cation distribution or stoichiometric variation was effectively used in developing spinel ferrite based electrocatalysts2, gas sensors3, energy storage and converting devices4.
Here we report on stoichiometrically varied ferrite films (MxFe3-xO4, M = Zn, Co) prepared by electrochemical deposition which can potentially be used as photoanodes in solar water splitting cells following a previously reported protocol5. The influences of deposition time, potential and concentration of the metal ions on the structure, composition and photoelectrocatalytic activity of the electrodes were investigated6. The stoichiometry is controlled by fine tuning of the deposition potential and by adjusting the M/Fe ratio in the deposition bath.
Structural and morphological characterization was performed by transmission electron microscopy and x–ray diffraction. Raman spectroscopy was used to locally identify the phase compositions. The surface composition and the chemical state of the species were investigated by x-ray photoelectron spectroscopy which shows that the surface composition of the films is different from that of the bulk. Photoelectrochemical measurements show that the ferrites are n-type semiconductors with the onset and the magnitude of the photocurrent being strongly dependent on the M/Fe ratio. Photoelectrodes containing understoichiometric amount of zinc at the surface (Zn:Fe ratio = 0.25-0.40) exhibit the highest photocurrents. The enhanced photoresponse may be attributed to improved electronic conductivity or composite formation resulting efficient charge separation.
References
1. a) D.H. Taffa, R. Dillert, A.C. Ulpe, K.C. L. Bauerfeind, T. Bredow, D.W. Bahnemann, M. Wark, J. Photonics for Energy, 2016, 7, 012009; b) R. Dillert, D. H. Taffa, M. Wark, T. Bredow, D. W. Bahnemann, APL Mater. 2015, 3, 104001.
2. H. Zhu, S. Zhang, Y. Huang, L. Wu, S. Nano Lett. 2013, 13, 2947.
3. A. Sutka, K. A. Gross, Sens. Actuators B-Chem., 2016, 222, 95.
4. D. Kimmich, D. H. Taffa, C. Dosche, M. Wark, G. Wittstock; Electrochim. Acta, 2018, 259, 204
5. J. A. Switzer, R.V. Gudavarthy, E. A. Kulp, G. Mu, Z. He, A. J. Wessel, J. Am. Chem. Soc. 2010, 132, 1258.
6. S. Warfsmann, D. H. Taffa, M. Wark, J. Photochem. Photobiol. A: Chem. 2018, 362,49
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