Enhanced Ir-Ru-Ox Electro-Catalysts for Oxygen Evolution in Proton Exchange Membrane Water Electrolysis

Abstract

Interest in water electrolysis has recently increased with the large diffusion of renewable energy sources and the perspective to produce hydrogen with a very low environmental impact [1-2]. In this regard, hydrogen appears a promising energy carrier that can be produced by cost-effective electrolysis of water using renewable energy sources and it can be used to store energy in grid-balancing services. A challenging problem to the development of such process is the substantial energy loss associated with the oxygen evolution during electrochemical water splitting. High surface area nanostructured (2-10 nm) IrRu-oxide electro-catalysts can substantially reduce this loss allowing to achieve efficient hydrogen production. IrOx and Ir0.7Ru0.3Ox nanosized materials of similar crystallite size (mean size 5 nm) were prepared for application as oxygen evolution electro-catalysts in solid polymer membrane water electrolysers (PEMWEs). The physico-chemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) and X-ray-Photoelectron Spectroscopy (XPS). Particular efforts were addressed to tailor the crystallographic characteristics and the surface properties. The electrochemical properties were investigated in an electrolysis cell, based on Nafion 115 and 30% Pt/C as cathode catalyst, by using linear sweep voltammetry, electrochemical impedance spectroscopy and Tafel curves. The Ir0.7Ru0.3Ox-based electro-catalyst showed a performance of 3.2 A cm-2 at 1.85 V at 90°C which corresponds to a voltage gain of 0.1 V as compared to the IrOx catalyst at the same current density. A similar Tafel slope with a decrease of charge transfer resistance for IrRuOx compared to IrOx would indicate the same mechanism for these materials and higher intrinsic activity for the mixed oxide. The present study indicates that Ir0.7Ru0.3Oxcan be an excellent electro-catalyst for the oxygen evolution in PEM-based water electrolysis provided that structure, morphology and surface characteristics are properly tailored. Acknowledgements The authors acknowledge the financial support of the EU through the FCH JU Electrohypem Project. ‘‘The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2010-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement Electrohypem n 300081.’’ References Siracusano, S.; Van Dijk, N.; Payne-Johnson, E.; Baglio, V.; Aricò, A.S.; Applied Catalysis B: Environmental, 2015, 164:488. DOI:10.1016/j.apcatb.2014.09.005 Aricò, A.S., Siracusano, S., Briguglio, N., Baglio, V., Di Blasi, A., Antonucci, V. Journal of Applied Electrochemistry, 2013, 43:107. DOI: 10.1007/s10800-012-0490-5