C04 - Atomic Scale Mechanisms of the Electrocatalytic Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is a 4-electron-4-proton process that can evolve via different reaction pathways. It is a key model reaction for proton coupled electron transfer (PCET) in electrochemical water oxidation. Despite a lot of progress, the mechanisms controlling the pathway of forming O2 out of 2 H2O molecules by removal of electrons and protons are not yet fully understood. Density functional theory (DFT) calculations assuming a single active site suggest reaction steps, which are typically based on a frozen surface approximation or idealized surfaces. This results in a so-called scaling relation, where the free enthalpies of different intermediate reaction steps are intimately connected to the binding energy of adsorbed oxygen species. Although many metal oxide electrocatalysts follow such a scaling law, several exceptions have been reported, showing a higher activity. Understanding such exceptions is of high importance, since this will provide a scientific basis to overcome present limitations of electrocatalytic water splitting due to high OER overpotentials. A scientific understanding of mechanisms breaking the scaling law requires the analysis of the real atomic and electronic electrolyte/catalyst interface structure in the active state as well as time-resolved studies of the interface dynamics, both in close connection with theoretical modelling, including reaction enthalpy as well as kinetic barriers. The goals of this joint project are thus
I) Studying the atomic structure and dynamics of an important model electrocatalyst with tunable OER via in-situ environmental transmission electron microscopy (ETEM) (atomic information) and ultrafast time-resolved in situ X-ray spectroscopy (electronic information).
II) Development of a theoretical understanding of the real interface dynamical state during PCET using molecular dynamics with an accurate DFT-based machine learning potential as a foundation for the determination of reaction mechanisms.
III) Using these experimental and theoretical insights as a foundation for establishing a new strategy for tuning the PCET reactivity and selectivity via a systematic modification of the catalyst surfaces, control of active sites, changing pH and combining electric and light-stimulus.
This finally aims at a systematic strategy for going beyond limiting scaling relations to realize highly active and stable electrocatalysts for PCET based water oxidation. As a model electrocatalyst, we select single crystalline ZnO surfaces with controlled 3d transition metal doping, because this system has already shown evidence for high activities, recently underpinned by theoretical studies