Development of ex-solution-applied perovskite oxides for versatile electrocatalysis in alkaline media

Abstract

Electrochemical water electrolysis has been pointed out as a promising way to turn energy from intermittent renewable sources like solar, wind, and geothermal energy into chemical energy (hydrogen). Among the various electrolysis systems, alkaline water electrolysis has been adopted at the industrial scale as the most advanced method for scalable, safe, and long-term H2 production. In that sense, the development of electrocatalysts to enhance the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) involved in alkaline water electrolysis has remained a continual objective in this field of research.

The most commonly used strategy to enhance catalytic activity is fabricating supported catalysts by evenly decorating nanocatalysts on the supporting material. However, the supported catalysts do not maintain their initial form and may deteriorate in many reasons under the actual driving environment. In general, four major factors can cause the deterioration of the electrocatalysts during alkaline electrochemical reactions. 1) coarsening of the supported nanocatalyst

4) redeposition of dissolved ions (Ostwald ripening)

Inspired by the above backgrounds, the ex-solution phenomenon is proposed as the main strategy to solve the stability issues in this study. Ex-solution, which is a facile method for synthesizing robust metal-support complex catalysts by a single heat treatment process, can spontaneously decorate fine and uniform nanocatalysts on the parental support. More importantly, the partially socketed geometry of the nanoparticles in the host oxide can induce an intimate interface between the exsolved particles and support, rendering the catalysts exceptionally resilient to agglomeration and physical detachment. However, this phenomenon has been mostly utilized for high-temperature electrochemical reactions so far, and even when applied in alkaline water electrolysis, its activity has not reached a sufficient level.

In this dissertation, I propose three different in-depth insights for applying the ex-solution phenomenon to versatile electrochemical reactions in alkaline media. First, it provides design guidelines for the selection of material composition and the engineering of ex-solution process parameters. Second, the core-shell geometry implemented through ex-solution offers new possibilities for stabilizing thermodynamically unstable substances, while synergistically enhancing their catalytic activities. Finally, a novel strategy was presented that can effectively utilize this phenomenon in commercial foam-type electrodes. Overall, our findings provide new perspectives on the material design for next-generation electrocatalysts and the proposed strategies can be possibly extended to various energy-related fields in the future.

2) physical detachment of catalyst from the support

3) dissolution of the catalyst into the corrosive electrolyte