PhD Defence Ellen Kiens | Multilayered Perovskite Oxides as Oxygen Evolution Catalysts

Multilayered Perovskite Oxides as Oxygen Evolution Catalysts

Ellen Kiens is a PhD student in the department Nano Electronic Materials. (Co)Promotors are prof.dr.ir. G. Koster; prof.dr. G. Mul; prof.dr. C. Baeumer and dr. B.T. Mei, from the faculty of Sciences & Technology (TNW)

Producing sustainable hydrogen through water electrolysis is considered an important step toward a future energy system based on renewable electricity. A major challenge in this process is the oxygen evolution reaction, which currently relies on catalysts that are either inefficient, unstable, or made from scarce materials. Perovskite oxides are promising alternatives because their electronic and structural properties can be precisely tuned.

This thesis investigates how the performance of these catalysts can be improved by engineering not only their surface, but also the layers hidden beneath it. Using epitaxial thin films with atomic-level precision, well-defined multilayer structures were designed to study how buried layers influence the electronic structure, surface chemistry, and stability of the active catalyst.

Advanced X-ray spectroscopy techniques, including operando measurements performed during the reaction itself, revealed that subsurface layers affect how the catalyst interacts with water and how it evolves under operating conditions. The work shows that interfaces between different oxide layers can affect catalytic activity, influence degradation pathways, and improve stability under more industrially relevant conditions such as elevated temperatures and concentrated electrolytes.

The results demonstrate that catalyst surfaces cannot be understood as isolated systems: buried layers actively participate in the reaction and dynamically evolve during operation. By combining model thin-film systems with advanced spectroscopy and electrochemistry, this research provides new insight into the fundamental behavior of perovskite catalysts and establishes multilayer design as a promising strategy for developing robust and efficient catalysts for sustainable hydrogen production.