(Invited) Water Adsorption on Transition Metal Oxide Pure IrO2, RuO2 and Alloy RuxIr1-XO2(110) Surfaces Investigated By Density Functional Theory

Abstract

RuO2 and IrO2 are the most used catalyst materials for water electrolysis in the anode electrode of the so-called polymer electrolyte membrane water electrolyzers (PEMWE), the former presents higher activity and the latter a higher resistance to corrosion. Therefore alloys, RuxIr1-xO2, have been proposed in order to enhance the stability of the anode electrode without affecting its activity. However, up to date, the origins of such an improvement are not elucidated. In this article, we propose to progress on that question by exploring the adsorption properties of one water molecule on model surfaces of RuO2(110), IrO2(110) and RuxIr1-xO2(110) from density functional theory (DFT) calculations. The manuscript details several initial structures of water molecule above the metal oxide surfaces. Energetics of adsorption of water on those oxide surfaces is presented and compared, as well as magnetic properties of these systems, an element which is rarely detailed in the corresponding literature. In particular, the role of the second metal in the alloy oxide surface on the adsorption properties is addressed by playing with the relative surface composition between Ru and Ir and alloying structure. For a substantial content of Ir in the surface of RuO2(110) (1D model), our DFT results show that the adsorption properties are similar to those on pure RuO2(110). This means that these particular mixed oxide surfaces should exhibit an equivalent activity than the one on pure RuO2(110), and in the same time, a larger resistance to corrosion due to the presence of Ir. This work is a prerequisite towards a systematic investigation of the adsorption of intermediate species for the oxygen evolution reaction (OER) on model surfaces of the aforementioned materials.