Fine Tuning of the Oxygen Evolution Reaction Activity and Stability of Hydrous Iridium Oxides By Thermal Treatment
Authors: Geiger Simon , Kasian Olga , Cherevko Serhiy , Mayrhofer Karl J.J. 
Published: February 2020

In the future energy concept renewable wind and solar energy will play the dominating role. It is anticipated that due to the intermittent nature of power outcome from the renewable energy sources, there will be an energy surplus which can be efficiently stored. As an example hydrogen could be successfully produced by proton exchange membrane water electrolysis (PEM-WE). Alternatively carbon dioxide could be converted to a valuable product in an electrochemical reduction process. Up to now the oxygen evolution reaction (OER) will be the counter reaction for hydrogen evolution as well as CO2 reduction. Nowadays iridium is the main component of the anode catalyst in PEM-electrolysers since it shows the best performance in terms of activity and stability [1]. Due to the high price and scarcity of iridium, however, the goal for the near future is a better utilization and partial or complete replacement of this precious metal. Since no alternative with comparable performance is in the sight, current research efforts are directed towards increase in surface to mass ratio and specific activity of iridium catalysts. This can be achieved using nanoparticulated, highly porous materials [2]. Furthermore, introduction and leaching of a less noble metal [3] or tuning of the oxide structure, e.g. by varying calcination temperature should be considered [4, 5].                  

In this study a scanning flow cell (SFC) combined with an inductively coupled mass spectrometer (ICP-MS) is used to obtain synchronized time- and potential-resolved data on the OER-activity and dissolution of iridium electrodes [5, 6]. This should shed some light onto the stability of different kinds of iridium oxides used in literature by utilizing a model sputtered iridium film.

The examined materials are iridium (hydrous)-oxides prepared electrochemically and treated thermally in the temperature range of 100 – 600 °C. X-ray photoelectron spectroscopy (XPS) is used to correlate the electrochemical behaviour with the surface composition. The obtained information on the electrocatalytic activity and stability together with data on the electrodes physicochemical properties and their temperature dependence are used in the discussion of OER mechanism on iridium oxide electrodes.

References:

[1] D. Bessarabov, H. Wang, H. Li, N. Zaho, PEM Electrolysis for Hydrogen Production CRC Press, Boca Ranton, 2015.

[2] H.-S. Oh, H.N. Nong, T. Reier, M. Gliech, P. Strasser, Oxide-supported Ir nanodendrites with high activity and durability for the oxygen evolution reaction in acid PEM water electrolyzers, Chem. Sci., 6 (2015) 3321-3328.

[3] T. Reier, Z. Pawolek, S. Cherevko, M. Bruns, T. Jones, D. Teschner, S. Selve, A. Bergmann, H.N. Nong, R. Schlögl, K.J.J. Mayrhofer, P. Strasser, Molecular Insight in Structure and Activity of Highly Efficient, Low-Ir Ir-Ni Oxide Catalysts for Electrochemical Water Splitting (OER), J Am Chem Soc, 137 (2015) 13031-13040.

[4] M. Bernicke, E. Ortel, T. Reier, A. Bergmann, J. Ferreira de Araujo, P. Strasser, R. Kraehnert, Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: Structure-Activity Relationships, ChemSusChem, 8 (2015) 1908-1915.

[5] S. Cherevko, T. Reier, A.R. Zeradjanin, Z. Pawolek, P. Strasser, K.J.J. Mayrhofer, Stability of nanostructured iridium oxide electrocatalysts during oxygen evolution reaction in acidic environment, Electrochemistry Communications, 48 (2014) 81-85.

[6] S. Cherevko, S. Geiger, O. Kasian, N. Kulyk, J.-P. Grote, A. Savan, B.R. Shrestha, S. Merzlikin, B. Breitbach, A. Ludwig, K.J.J. Mayrhofer, Oxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stability, Catalysis Today, 262 (2016) 170-180.