(Invited) From Atomic-Scale Understanding to Design of Advanced Electrocatalyst Materials

Abstract

Increasing concerns regarding the environmental impact of power generation and the reduction of carbon emissions have become a major motivation for the use of sustainable electrical power. In this perspective, renewable energy sources are expected to take up an important part of electric energy produced in the near future. Since renewable sources such as wind and solar are intermittent in nature, their increased installation will result in either excessive or insufficient power generation at times. A large variety of concepts for using this surplus power is currently under development.Acidic water electrolysis is an attractive environmentally-safe solution for the conversion and storage of excess electricity into hydrogen and oxygen. The large scale application of water electrolysis systems is currently hindered by low efficiency and instability of catalysts during long term operation [1]. This is especially crucial for the anodic oxygen evolution reaction (OER) which catalyzed by Iridium based alloys and oxides making the issues related to efficiency of catalyst utilization and durability even more critical. The development of catalyst materials with superior performance demands a deep understanding of the OER itself as well as electrocatalysts degradation mechanisms. Although a large number of possible OER mechanisms have been proposed [2], the topic remains a subject of intensive debates across the scientific literature, since the intermediates and their possible interrelations are in most cases unknown. Additional challenges in mechanistic studies are related to the changes in the composition of the catalyst and its degradation triggered by OER. Though the existence of experimental correlation between the structure, activity of OER catalyst and its dissolution was numerously reported and discussed [2,3], reports addressing all these aspects in one study are rare. This indicates that further research efforts are required to reveal reaction intermediates and products by means, for instance, of mass spectrometry at the atomic scale by atom probe tomography, that complement spectroscopic insight from synchrotron-based experiments, ideally in operando conditions.In this presentation, the main fundamental limitations that hinder the current understanding of the reactions mechanisms occurring in water electrolysis will be discussed. It will be stressed that only the combination of insights enables the establishing of reliable structure-function relationships in electrocatalyst materials. We present our approach to investigate complex processes in electrocatalysis with a combination of independent methods like online electrochemical mass spectrometry, atom probe tomography and synchrotron-based spectroscopy [4,5]. In particular, we discuss approaches to resolving the reaction mechanism on constantly evolving surfaces; present our recent results on the interplay between the nature of the active sites in Ir-based oxides and their stability towards the OER and establish structure–function relationships between the reactivity and the atomic-scale surface structure [5]. Finally, using the new insights gained in our recent studies [4-6], we discuss potential design strategy for Ir-based OER catalysts with high catalytic activity and long-term stable performance.[1] S. Cherevko et al., Catalysis Today 2016, 262, 170-180[2] T. Reier, H.N. Nong, D. Teschner, R. Schlögl, P. Strasser, Adv. Energy Mater. 2017, 7(1), 1601275.[3] O. Kasian, J.P. Grote, S. Geiger, S. Cherevko, K.J.J. Mayrhofer, Angew. Chem. Int. Ed. 2018, 57, 2488 –2491.[4] K. Schweinar, R.L. Nicholls, C.R. Rajamathi, P. Zeller, M. Amati, L. Gregoratti, D. Raabe, M. Greiner, B. Gault, O. Kasian, J. Mater. Chem. A 2020, 8(1), 388-400.[5] O. Kasian, S. Geiger, T. Li, J-P. Grote, K. Schweinar, S. Zhang, C. Scheu, D. Raabe, S. Cherevko, B. Gault, K. Mayrhofer, Energy Environ. Sci. 2019, 12(12), 3548-3555.[6] K. Schweinar, I. Mouton, B. Gault, O. Kasian, J. Phys. Chem. Lett. 2020, submitted.