Investigations on Oxygen Evolution Catalysts for PEM Electrolysis Cells

In recent years, electricity-driven hydrogen production by electrochemical splitting of water (water electrolysis) has received particular attention because of its potential applicability in decentralized energy storage concepts.  The electrolysis of water is nowadays mainly performed in alkaline or acidic electrolytes.  The acidic polymer electrolyte electrolysis cell (PEEC) has distinct advantages over the alkaline liquid electrolyte devices. PEECs can rapidly respond to changes in the power input and operate at a larger partial load range. Furthermore, high voltage efficiencies and the possibility to be operated at high pressures > 100 bar favor its use. Nevertheless, the anodic oxygen evolution reaction (OER) is catalytically demanding, showing high overpotentials. Additionally, the strongly oxidizing environment reduces the set of applicable materials to a few noble transition metal (mixed-) oxides. Transition metal oxides based on ruthenium and iridium constitute the state of the art catalysts for the OER performing with high catalytic activity and sufficient stability¹. The low availability of iridium raises its costs and new catalyst materials and/or surface morphologies have to be investigated to either replace or reduce the iridium content. For this purpose, a promising strategy is to develop catalyst materials as mixed oxides with non-noble substitutes and a high surface area. These new materials need to be characterized with respect to their performance and stability. Especially, at the high potentials which are needed to drive the oxygen evolution reaction, a thermodynamic instability of the catalysts lattice oxide anions may lead to an oxygen evolution from the lattice and concomitantly to an electrochemical corrosion of the material. Rotating ring-disc electrodes (RRDEs) enable the estimation of generated oxygen and thereby the determination of the catalysts current efficiency. Within this study the RRDE method will be applied to several promising OER catalysts to determine their current efficiencies. In addition, the materials stability with respect to its application in electrolysis cells facing intermittent power input will be investigated. 

Financial support of this project by CCEM (RENERG2), the Commission for Technology and Innovation (CTI) and the Swiss Competence Center for Energy Research (SCCER) Heat & Electricity Storage is gratefully acknowledged.

1.            Fabbri, E.; Habereder, A.; Waltar, K.; Kötz, R.; Schmidt, T. J., Developments and perspectives of oxide-based catalysts for the oxygen evolution reaction. Catalysis Science & Technology 2014, 4 (11), 3800-3821.

2.            Kötz, R.; Stucki, S., Stabilization of RuO₂ by IrO₂ for anodic oxygen evolution in acid media. Electrochimica acta1986, 31 (10), 1311-1316.