CHAPTER 7: Oxygen Evolution and Reduction Catalysts: Structural and Electronic Aspects of Transition Metal Based Compounds and Composites

Nature uses in photosynthesis transition metal complexes to evolve oxygen and hydrogen from water. In these processes the catalytic centers are separated from the light-capturing and absorbing co-factors in photosystem I and II of the thylakoid membrane. This chapter concentrates on transition metal chalcogenides acting as electrocatalysts in the oxygen evolution reaction (OER) as well as in the oxidation reduction reaction (ORR). In the first part of this chapter manganese oxides and calcium manganates are discussed with respect to their structural features and their electrochemical behavior in OER which is compared with the functionality of the Mn₃CaO₄MnO cluster in PS II. In the second part sulfur and selenium modified ruthenium catalysts are described to demonstrate how surface modified metal cores dramatically influence the catalytic behavior towards ORR and OER. In situ X-ray absorption spectroscopy (EXAFS and XANES) and in-system synchrotron radiation photoelectron spectroscopy (SR-XPS) are tools to investigate the electrochemical behavior of the catalysts at the electrode/electrolyte interface as a function of applied potential using an electrochemical half cell. At the end strategies will be discussed how these water splitting catalysts can be integrated in a solar light converting system (artificial leaf).