Scalable nanostructuring with combinatorial glancing angle deposition for improved photoanode performance

Aliaksandr Stepanovich^a, Robert Meyer^a, Helge Stein^a, Chinmay Khare^a, Pio. J. S Buenconsejo^a, Alfred Ludwig^a^,^c, Kirill Sliozberg^b, Wolfgang Schuhmann^b^,^c

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

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

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

Proceedings of International Conference on Light Driven Water Splitting Using Semiconductor Based Devices (SolarFuel15)

Illetes, Spain, 2015 March 11th - 13th

Organizers: Leslie Frotscher, Sixto Gimenez Julia, Wolfram Jaegermann and Bernhard Kaiser

Poster, Chinmay Khare, 022
Publication date: 15th December 2014

The combinatorial glancing angle sputter deposition (GLAD) approach was used to fabricate Ti-W-O and W-Fe-O thin film materials libraries (ML) consisting of columnar nanostructures. The combinatorial approach enables preparation and high-throughput characterization of large composition ranges of material systems having different microstructures with the aim of enhancing photoelectrochemical (PEC) performance. Increasing porosity and thus enhancing the effective surface area in contact with the electrolyte can lead to a shortening of charge carrier diffusion distances. Aiming on synthesizing highly porous nanostructures two approaches were developed. The first approach comprises of variation of sputtering conditions and deposition geometry to fabricate heterostructured WO₃-wedge/TiO₂-nanocolumnar layered films. As TiO₂ nanocolumns exhibit inter-column spaces that are filled with the electrolyte, the holes generated deep inside porous WO₃ nanostructures can readily react with the electrolyte. The maximum photocurrent density of 110 µA/cm² was observed at W_35.3Ti_64.7 on a ML, where TiO₂ and WO₃ layers exhibit thickness of ~ 600 nm and ~ 300 nm, respectively. The observed photocurrent density values are about two orders of magnitude higher than that of individual WO₃ layers and about two times higher than that of the reference individual TiO₂ layer. The second approach included utilization of as-deposited W_100-xFe_x (27 < x < 55 at. %) nanocolumnar ML as a precursor for dealloying. During dealloying atoms of the ‘less noble metal’ are selectively dissolved, while the ‘more noble metal’ atoms diffuse and aggregate to form clusters. Using this method various morphologies including nanoflake-, nanocactus- and nanoblade-like structures were developed. On the ML selective dissolution of Fe during dealloying led to formation of highly porous nanostructures with single crystal WO₃ nanoblades. XRD measurements revealed a monoclinic WO₃ structure, where Fe atoms exist at the substitutional sites in the crystal lattice. The measurement regions on the dealloyed ML with ≤ 2 at.% Fe exhibited the highest photocurrent density of 72 µA/cm². This is attributed to the suppressed recombination of electron-hole pairs within the porous film. The precursor composition was found to be an essential factor for obtaining porous Fe-doped WO₃ nanostructures, with improved photoconversion efficiency.

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