Screen Printed Metal Oxide Electrodes for Water Oxidation at neutral pH and its structure analysis by X-ray absorption spectroscopy

Lee Seung Y. ^a, I. Zaharieva^a, D. González-Flores^a

^aAlbert-Ludwigs-Universität Freiburg, Institut für Anorganische und Analytische Chemie, Albertstraße, 21, Freiburg im Breisgau, 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, Lee Seung Y. , 097
Publication date: 15th December 2014

The splitting of water to molecular oxygen is one of the fundamental reactions of the photosynthetic process. A μ-oxido-Mn4CaO5-cluster in Photosystem II (PSII), the oxygen-evolving-complex (OEC) is the enzymatic site. This led to the idea to develop manganese based catalysts for light-driven water oxidation catalysis(WOC), a key reaction to generate hydrogen, which may be a potential solar fuel of the future.[1] A mild screen-printing method was developed to coat conductive oxide surfaces (FTO) with µm-thick layers of pre-synthesised calcium manganese oxide (Ca-birnessite)[2] particles. After optimization steps concerning printing process and layer thickness, electrodes were obtained which can be used as corrosion-stable water-oxidizing anodes at pH7 yielding current densities of 1mA•cm-2 at an overpotential of less than 500mV. [3] Analyses of electrode coatings of optimal thickness (~10µm) indicated that composition, oxide phase and morphology of the synthetic Ca-birnessite particles are hardly affected by the screen-printing procedure. However,a more detailed analysis by X-ray absorption spectroscopy revealed small modifications of both Mn redox state and structure at the atomic level which could affect functional properties like proton conductivity. Furthermore, the versatile new screen-printing method was used for a comparative study of various transition metal oxides concerning electrochemical water oxidation at “artificial leafconditions” (neutral pH, fairly low η and i ), where a general activity ranking RuO2 > Co3O4~(Ca)MnOx~NiO was observed. Within the group of screened manganese oxides, Ca-birnessite performed better than “Mn-only materials” like Mn2O3or MnO2.

[1] N. Armaroli & V. Balzani, Energy for a Sustainable World, Wiley-VCH, Weinheim, 2011 [2] M. Wiechen, H.-M. Berends, Ph. Kurz, Dalton Trans, 2012, 41, 21. [3] S. Y. Lee, D. González-Flores, J. Ohms, T. Trost, H. Dau, I. Zaharieva, Ph. Kurz; ChemSusChem, 7, 3442 (2014)

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