Publication date: 15th December 2014
Hydrogen production through photo-induced splitting of water is a promising avenue for sustainable energy economy, although no cost-effective photocatalytic system has been identified so far. It is believed that a successful search for a new and improved photocatalyst will be based on a molecular understanding of all elementary reaction steps in the photocatalytic water splitting. Concentrating on one of the most efficient electrocatalyst for the oxygen evolution reaction (OER), RuO2, we have investigated RuO2 layers on TiO2(110) single crystal substrates as model system. Though the band gap of TiO2 is certainly too large for application purposes, here it serves as absorber material to generate the charge carriers necessary for the electrocatalytic studies on the co-catalyst. Further, this heterojunction, which is often present when using passivation layers, has a well-defined morphology due to its pseudomorphic structure and is therefore best suited to combine theory and experiment. Combining surface science experiments and ab initio modelling we have investigated the morphology and the electronic structure of the RuO2-TiO2(110) heterostructures as well as the preferred surface composition that should be present under reaction conditions [1]. These investigations pave the way for in-depth studies on the mechanism of the OER on RuO2 surfaces, which might also be relevant for other water-splitting electrocatalysts.
Further, we report on the the electroless deposition of Au nanoparticles and submonolayer equivalents of Pt and/or Pd on p-type silicon, which has been studied with cyclic voltammetry (CV), angle-resolved X-ray photoelectron spectroscopy (AR-)XPS and tapping-mode atomic force microscopy (TM-AFM) [2]. The controlled variation of deposition parameters influences the semiconductor/metal interface and the corresponding (photo-)electrochemical behavior. The light-induced hydrogen evolution reaction (HER) serves as a model reaction for revealing the distinct changes in the electrode properties dependent on the plating procedure. Improved electrocatalytic activity is observed for Au particles on silicon when decorated with small amounts of Pt (Pd) by means of an additional electroless deposition step [3], were simultaneous deposition of Pt and Pd leads to the best performance. However, simultaneous deposition of Au and Pt (Pd) results in a complete loss of the photocathode characteristics, which could be related to the formation of an Pt/Au-silicide interlayer.
References
[1] K. S. Exner, J. Anton, T. Jacob, H. Over, Electrochim. Acta, 120, 460 (2014).
[2] M. Metzler, A. Thorwart, S. Zeller, T. Diemant, R. J. Behm, T. Jacob, Catal. Today, in press
[3] P. Schäfer, L. A. Kibler, Phys. Chem. Chem. Phys., 12, 15225-15230 (2010).
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