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Marcus Einert1 André Bloesser1 Roland Marschall1

1, Justus-Liebig-University Giessen, Giessen, , Germany

Electrospinning is a well-known, simple and fast method to prepare polymer fibers with diameters of 100-500 nm and lengths up to several micrometers.[1] Since for many semiconductor materials the charge carrier diffusion length is a critical parameter restricting photocatalytic or photoelectrochemical performance, we use the electrospinning approach to prepare nanostructured metal oxide nanofibers.[2] Directly after electrospinning, such nanofibers still contain spinning polymer, after calcination crystalline metal oxide nanofibers with diameter of 100-200 nm can be prepared.[3] Using the electrospinning technique, it is also possible to prepare fibrous photoelectrodes directly onto conducting substrates in a one step process.[4,5]
Nanofibers of the (111)-layered perovskite materials Ba5Ta4O15 are built up from small single crystals, and are able to generate hydrogen without any co-catalyst in photocatalytic reformation of methanol. After photodeposition of Rh-Cr2O3 co-catalysts, the nanofibers show better activity in overall water splitting compared to sol–gel-derived powders.[3]
Hollow a-Fe2O3 nanofibers and core–shell-like a-Fe2O3/indium-tin oxide (ITO) nanofiber composites were utilized as a photoanode for solar water splitting, the latter showing a doubled photocurrent compared to the hollow fiber photoanodes. This can be most likely be attributed to fast interfacial charge carrier exchange between the highly conductive ITO nanoparticles and a-Fe2O3, thus inhibiting the recombination of the electron–hole pairs in the semiconductor by spatial separation.[4]
CuO photocathodes were directly prepared via electrospinning onto FTO, and calcination studies were performed to systematically characterize their crystallographic and structural evolution.[5] The higher the annealing temperature, the more developed are the crystalline domains of the nanofibers, which results in better conductivity and less defect sites serving as trap states for the photo-excited charge carriers. Hence, the CuO nanofiber photocathodes annealed at 800 °C showed the highest photoresponse and stability. No decrease in the photocurrent density after prolonged operation in aqueous electrolyte was observed.

References
[1] A. Greiner, J. H. Wendorff, Angew. Chem. Int. Ed. 2007, 46, 5670-5703.
[2] R. Ostermann, J. Cravillon, C. Weidmann, M. Wiebcke, B. M. Smarsly, Chem. Commun. 2011, 47, 442-444.
[3] N. C. Hildebrandt, J. Soldat, R. Marschall, Small 2015, 11, 2051–2057.
[4] M. Einert, R. Ostermann, T. Weller, S. Zellmer, G. Garnweitner, B. M. Smarsly, R. Marschall, J. Mater. Chem. A 2016, 4, 18444-18456.
[5] M. Einert, T. Weller, T. Leichtweiss, B. M. Smarsly, R. Marschall, Chem. Photo. Chem. 2017, 1, 326-340.

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