Lecture

Van Marum Colloquium - Model Perovskite Oxide Electrocatalyst Surfaces

• Dr. Christoph Baeumer (UTwente)

Date

Friday 18 August 2023

Time

14:15 - 15:15

Location

Gorlaeus Building
Einsteinweg 55
2333 CC Leiden

Room

EM1.09

Abstract

Perovskite oxides are attractive electrocatalysts to catalyze the oxygen evolution reaction (OER) because they allow tuning electronic and atomic structure through compositional variations. This allows catalyst design based on so-called descriptors that relate materials properties to binding energies of reaction intermediates and therefore to catalytic activity. In this talk I will highlight recent developments in the exploration of the vast compositional space for earth-abundant perovskite oxide electrocatalysts and discuss the growing understanding of surface transformations during the reaction. In both cases, in situ or operando characterization with sufficient surface sensitivity are needed.

First, I will discuss how the multi-cation composition in so-called high entropy perovskite oxides (HEO) can maximize the catalytic activity. The HEO LaCr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2O_3-δ outperforms all of its parent compounds (single TM-site element in the LaTMO3 perovskite).[1] X-ray photoemission studies reveal a synergistic effect of simultaneous oxidation and reduction of different transition metal cations during adsorption of reaction intermediates. HEOs are thus found to be a highly attractive, earth-abundant new material class for high-activity OER electrocatalysts, possibly allowing OER activities beyond the theoretical scaling limits of mono- or bimetallic oxides.

Secondly, I will describe structural and chemical transformations of the outermost surface layer – i.e. the location of the active sites – during or preceding the electrocatalytic reaction.[2] Using the example of LaNiO₃ epitaxial thin films, we demonstrated that Ni-(001)-facets are approximately twice as active for the OER as the La-(001)-facets. Using a suite of ex situ, in situ and operando spectroscopy tools, we found that the reason for the activity-enhancement lies in a surface transformation of the Ni-rich perovskite surface towards a catalytically active Ni hydroxide-type surface, revealing the importance of phase transformations down to a single atomic layer.

References

1. Kante, M. V et al. A High-Entropy Oxide as High-Activity Electrocatalyst for Water Oxidation. ACS Nano 17, 5329–5339 (2023).
2. Baeumer, C. et al. Tuning electrochemically driven surface transformation in atomically flat LaNiO₃ thin films for enhanced water electrolysis. Nat Mater 20, 674–682 (2021).

Biography

Christoph Baeumer is an Assistant Professor at the University of Twente and guest scientist at Forschungszentrum Jülich.  Within the Inorganic Materials Science group at the UT, his Electrochemical Thin Films and Interfaces group focuses on operando characterization and fundamental structure-function relations in model electrocatalysts. He obtained his MSc in Materials Science from the University of Illinois, his PhD in Physics from RWTH Aachen University and Forschungszentrum Jülich (2016, mentors Regina Dittmann and Rainer Waser) and he was a Marie Skłodowska Curie Fellow at Stanford University (2018-2020 mentor William Chueh). He received several awards and personal grants, including the Helmholtz Doctoral Prize (2017) and the ERC Starting Grant (2022).