Prof. Dr. R. Kramer Campen
Experimentally probing the mechanism of the oxygen evolution and ethylene glycol oxidation reactions (OER and EGOR) on MxCo3-xO4 and LaCoO3 requires operando characterization of both the liquid and solid sides of the catalyst/electrolyte interface. B03 applies linear and non-linear optical spectroscopies to characterize catalyst oxidation state, catalyst surface phonon response and interfacial solute and solvent structure. By time-resolving these measurements following electrical perturbation in FP3 we will deconvolute the causal relationship of catalyst surface structure fluctuation and OER/EGOR activity as a function of catalyst composition. We will thus directly characterize the frustrated phase transition thought to underlie OER and EGOR activity and describe its dependence on catalyst and electrolyte composition.
The goal of B03 in FP3 is to collect time-resolved, operando, spectral observables of various doped and vacancy-rich Co-Spinels and LaCoO3. These observables, particularly the relative timing of solid and solution side change following potential perturbation, directly characterize the frustrated phase transition during catalytic activity and its control by bulk catalyst structure.
Figure: Probing EGOR intermediates operando on well-ordered Co3O4 thin films using VSFG (Vibrational Sum Frequency Generation). (A) Normalized ISFG spectra (gray lines, each spectrum by that recorded at 0.864 V vs. RHE) and the corresponding fitted spectra (colored lines) in the 1300–1650 cm-1 region. Fitting to a Lorentzian line shape model finds three resonances with center frequencies (damping constants) A1 = 1439(27), A2 = 1575(34) and A3 = 1652(55) cm-1. Prior literature suggests A3 is glycoaldehye, while A1 and A2 are the characteristic of glycolate, oxalate or formate[21]. (B) Potential dependence of the amplitudes (A1, A2, and A3). (C) CV within our spectroelectrochemical cell at 5 mV/sec.
B03: Linking Charge Carrier Dynamics and Liquid Phase Oxidation Catalysis in Spinel and Perovskite Oxides
A rational design of catalysts requires a detailed microscopic understanding of elementary kinetic processes occurring during catalytic reaction. Electrocatalysis of oxidation reactions demands the production of holes at the solid/liquid interface and a bulk phase that is sufficiently conductive to allow electrons to be extracted and employed in a reduction reaction at the electrochemical cell’s anode. Thermal oxidation catalysis needs the creation of nearby holes and electrons at the solid/liquid interface and low conductivity as the electron or hole should not diffuse apart. Viewed in this manner it is obvious that any mechanistic description of either type of catalysis requires the simultaneous description of charge carrier dynamics in the bulk catalyst and at the solid/liquid interface.
Our project goal is to identify the main kinetic bottlenecks of the activity in both, thermal and electrocatalysis, using in operando transient optical spectroscopy. During the first funding period the mutual relation between real structure and optical signatures has been elaborated. In this period, we will build on this foundation to characterize operando the dynamics of carriers in spinel and perovskite mixed oxides in bulk and at the solid/liquid interface and the chemical change they induce during thermal and electrocatalysis of water and 2-propanol oxidation. We will do so using transient absorption to characterize carrier dynamics in bulk, electronically resonant sum frequency generation and photoluminescence spectroscopy to characterize operando interfacial electronic structure and follow the resulting chemistry using vibrationally resonant sum frequency generation spectroscopy. In the electrocatalytic case we will additionally apply two photon photocurrent spectroscopies for extracting the optical response of particular sub-populations of holes. This suite of techniques will allow us to correlate optical observables of the entire journey from carrier creation to chemistry with steady-state reactivity induced by temperature or potential. Because charge generation – and thus chemistry – is stimulated optically, we will be able to follow changes in carrier population and chemical speciation at well-defined timescales ranging from seconds down to femtoseconds.
Both the OER and thermal 2-propanol oxidation require transferring electrons from bulk solution to charge separated states at the catalyst surface and either back to solution phase product species (thermal 2-propanol oxidation) or to the cathode (the OER). Project B03 considers these reactions on CoxFe3-xO4 spinels and LaCoxFe1-xO3 perovskites employing a suite of optical operando techniques: transient absorption, photoluminescence, Raman and several types of vibrationally and electronically resonant sum frequency generation spectroscopy. The combination of these methods enables the observation of every step in the electron's journey in real-time and thus provides a description of how elementary processes on timescales from femtoseconds to seconds influence catalyst activity.
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Last update: Aug 17, 2026
