Degradation-control of perovskite oxide OER catalysts under dynamic operation conditions via advanced operando characterization and orbital-d-band engineering

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Analysis and understanding of catalytic reactions under dynamic operation conditions are the major goals of the DFG-SPP2080 program. The present proposal deals with the catalysis of the oxygen evolution reaction (OER) upon water splitting in alkaline media. Green hydrogen production from water splitting (electrolysis) powered by intermittent renewable energy sources plays a crucial role for future energy storage and conversion devices, whereas long-term stability of the required catalysts is the major obstacle in the field. The central aim of our proposal is to understand electrochemical processes at the solid/liquid interface between the OER-catalyst and the electrolyte and to unravel the mechanism of long-term degradation under the applied dynamic load profile.Our approach involves perovskites as promising OER catalysts whereas orbital structure (i.e. transition metal 3d- O 2p hybrid orbitals) is a major descriptor for their catalytic activity and can be systematically modified by cation substitution. While the relation between orbital structure and activity is discussed in literature, the relation of orbital structure and long-term stability is not yet understood and will be subject to the present proposal. In previous work to this proposal we demonstrated, that the lifetime of perovskite-catalysts crucially depends on the history of the applied load profile. While dynamic operation conditions lead to bulk degradation, static conditions lead to a surface passivation. Besides load history, dynamic changes of the surface chemistry add additional complexity to understanding the long-term degradation behavior: It is anticipated that under dynamic OER conditions reversible (Oxy-)Hydroxide transformations take place on the perovskite surface enhancing degradation. To improve the OER catalysts, it is thus essential to understand the relation between orbital structure, surface chemistry and (electro)chemical degradation under dynamic (vs. static) operation. Therefore, a reproducible, controllable and tailored catalyst synthesis complemented by operando analysis of the active surface under dynamic operation with (electro)chemical, electronic and microscopic resolution is mandatory. In the present approach we will achieve this 1) by atomically-controlled catalyst epitaxy, 2) by systematic characterization of orbital structure and electrochemical performance and 3) by operando investigations of surface chemistry, morphology and orbital structure under dynamic operation conditions using correlative scanning probe techniques and synchrotron-based x-ray absorption spectroscopy.The comprehensive methodology and expertise of our consortium will enable us to unravel the relation between degradation and applied load history with atomistic precision, to derive systematic control over catalytic reactions and involved surface transformations, and to ultimately improve OER-catalyst performance by knowledge-based materials design via orbital engineering.