Discovering photocathode materials and hydrogen evolution catalysts by high-throughput experimentation
HElge Stein, Ruhr-Universität Bochum, Bochum, GermanyRamona Gutkowski, Ruhr-Univerisität Bochum, Bochum, GermanyKirill Sliozberg, Ruhr-Univerisität Bochum, Bochum, GermanyChinmay Khare, Ruhr-Univerisität Bochum, Bochum, GermanyWolfgang Schuhmann, Ruhr-Univerisität Bochum, Bochum, GermanyAlfred Ludwig, Ruhr-Univerisität Bochum, Bochum, Germany
Efficient photoelectrochemical water splitting materials are needed for a future hydrogen economy. In this contribution, we will present results from a combinatorial materials science workflow that aims at identifying new photocathode materials for solar water splitting. The talk will present recent findings from the materials systems Cu-Si-Ti-O  and Al-Cr-Fe-O . In the Al-Cr-Fe-O system Al:Cr2FeO4 was identified  as a new 1.5 eV bandgap absorber material with an outstanding photovoltage of 1 V and promising photocurrents. Recent results on the origin of this high photovoltage and routes to increase the photocurrent and to reduce photo generated charge carrier recombination will be addressed. Many p-type metal oxides suffer from photo corrosion during HER.
We choose Cu2O as a model material for stabilization studies , e.g. by alloying with third elements. From our study of the system Cu-Si-Ti-O , two new p-type materials based on Si:Cu3TiOx and Ti:CuSiO3 (Dioptase) were found to show promising photoelectrochemical properties and significantly better electrochemical stability compared to Cu2O. Without a co-catalyst, photocurrents of up to 430 µA/cm2 at 416 mV vs. RHE were observed under simulated AM1.5G irradiation in Si:Cu3TiOx. Finally, results from investigations of non-noble metal catalysts from the systems Co-Ni-Cu and Co-Ni-Fe for the hydrogen evolution reaction will be discussed.
 H. S. Stein, R. Gutkowski, A. Siegel, W. Schuhmann and A. Ludwig (2015), Ti-doped CuSiO3 as a promising material for the light induced hydrogen evolution reaction, Journal of Materials Chemistry A, 4, 3148-3152
 K. Sliozberg, H.S. Stein, C. Khare, B.A. Parkinson, A. Ludwig, W. Schuhmann (2015), Fe-Cr-Al containing oxide semiconductors as potential solar water splitting materials, Appl. Mater. Interfaces, 7, 4883-4889.
 H. S. Stein, D. Naujoks, D. Grochla, C. Khare, R. Gutkowski, S. Grützke, W.Schuhmann, A. Ludwig (2015), A structure zone diagram obtained by simultaneous deposition on a novel step heater: a case study for Cu2O thin films, Physica Status Solidi A, 212, 2798-2804