Green hydrogen, produced by water electrolysis from renewable electricity, is a highly recommended energy carrier in the energy transition. However, the oxygen evolution reaction (OER) on the anode suffers from sluggish kinetics, rendering the process inefficient. Thus, there is a strong need for efficient OER catalysts and to uncover their structure-property relationships for a predictable OER catalyst design. Furthermore, a sustainable material choice for catalysts is urgently needed due to the drastically increasing materials demand of the energy transition. Perovskites are promising catalysts to decrease the OER overpotentials. However, revealing the intrinsic catalytic activity independent of their large conductivity differences is a big challenge, and several electronic structure properties are discussed to determine their OER performance. In this thesis, the influence of the large conductivity differences is systematically disentangled from the intrinsic catalytic properties for the here investigated ABO3-δ (A = La, Sr, Ca; B = Mn, Fe, Co, Ni) perovskites based on a model catalyst approach of epitaxial thin films. The revealed intrinsic OER activity trend is then correlated to their electronic structure properties to uncover structure-property relationships for the OER. We found that the highly resistive ferrates have similar intrinsic OER activity compared to the highly conductive cobaltates and nickelates. Interestingly, the O 2p band center, as the energetic distance from the oxygen states in the valence band to the Fermi level, revealed a volcano-shaped OER activity trend. Hence, neither too high nor too low O 2p band center leads to a high OER activity, which may advance predictions of efficient catalysts based on the valence band electronic structure. Besides the catalytic efficiency, the perovskite oxide elemental diversity implies large sustainability differences often not considered in technical performance studies. However, determining sustainability parameters in early-stage research for those electrocatalysts is challenging, as final process and supply chains are not known at this stage. Therefore, this thesis determines sustainability parameters for the electrocatalysts in early-stage research to uncover material hotspots for the energy transition. For this, a process chain for the perovskite catalysts is projected, and their precursor materials are identified to evaluate their material criticality, economic, environmental, and social impact, in addition to their thin film OER activity. La0.6Sr0.4CoO3-δ is compared to the A- and B-site substituted La0.6Ca0.4FeO3-δ electrocatalyst as an exemplary case study. The exchange of Co to Fe and Sr to Ca results in a lower raw material criticality, lower economic, environmental, and social impact. However, the La-precursor has a high material criticality and environmental impact, which is a disadvantage for both perovskites. Together, the revelation of intrinsic properties of OER catalysts independent of their resistivity, the revelation of electronic structure-property relationships, as well as the evaluation of sustainability parameters enables one to identify efficient, and sustainable material compositions that can be feasible for the energy transition. Further feedback loops between electrocatalyst performance and sustainability evaluation in early-stage research can guide the path for holistic material design concepts from the onset.
Lisa Heymann (Wed,) studied this question.