Approach to electrochemical modulating differential extended X-ray absorption fine structure

The differential XAFS technique holds promise for detecting surface changes, which benefits many chemical applications. Phase-sensitive detection (PSD) analysis based on modulated excitation spectroscopy experiments is expected to obtain a high-quality difference spectrum, while the mathematical relationship and experiment parameters remain to be discussed. In this article, an approach to obtaining the difference spectrum from the PSD demodulated spectrum is described and its applicability in different experiment settings is discussed. The results indicate that the demodulated spectrum is almost equal to the difference spectrum when the modulating period is 20 times larger than the relaxation time constant. This approach was subsequently applied to an electrochemical modulation experiment and the demodulated spectrum was analyzed. A reversible lattice shrinking is observed via the fitting of demodulated spectra, which is proportional to the charge amount on the electrode. This approach could be used to quantitatively analyze the modulated excitation XAS data and holds promise for a wide range of electrochemical studies.

Structural dynamics in Ni–Fe catalysts during CO2 methanation – role of iron oxide clusters

Operando XAS coupled with MES supported by DFT unravel the highly dynamic nature of Ni–Fe catalysts during CO₂ methanation and beneficial formation of iron oxide clusters.

Investigation of periodically driven systems by x-ray absorption spectroscopy using asynchronous data collection mode

We report the development, testing, and demonstration of a setup for modulation excitation spectroscopy experiments at the Inner Shell Spectroscopy beamline of National Synchrotron Light Source - II. A computer algorithm and dedicated software were developed for asynchronous data processing and analysis. We demonstrate the reconstruction of X-ray absorption spectra for different time points within the modulation pulse using a model system. This setup and the software are intended for a broad range of functional materials which exhibit structural and/or electronic responses to the external stimulation, such as catalysts, energy and battery materials, and electromechanical devices.

An operando emission spectroscopy study of Pt/Al2O3 and Pt/CeO2/Al2O3

In situ time-resolved spectroscopic examination of catalysts based on well dispersed nanoparticles on metal oxides under transient conditions significantly facilitates the elucidation of reaction mechanisms. In this contribution, we demonstrate the level of structural information that can be obtained using high-energy resolution off-resonant spectroscopy (HEROS) to study 1.3 wt% Pt/Al₂O₃ and 1.3 wt% Pt/20 wt% CeO₂/Al₂O₃ catalysts subjected to redox pulsing. First, HEROS is compared with XANES in a temperature programmed reduction experiment to demonstrate the increased sensitivity and time resolution of HEROS. Second, modulation excitation spectroscopy is exploited by redox pulsing to enhance the sensitivity of HEROS to structural changes by the application of phase sensitive detection (PSD) to the time-resolved HEROS data set. The HEROS measurements were complemented by resonant X-ray emission (RXES) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy measurements performed under identical conditions and in a single reactor cell in order to probe different aspects of the catalyst materials under the selected experimental conditions.

Time-resolved operando studies of carbon supported Pd nanoparticles under hydrogenation reactions by X-ray diffraction and absorption

We present a comprehensive study of a 5 wt% Pd/C catalyst in various environments by using in situ and operando X-ray absorption and diffraction.

Chemical selectivity in structure determination by the time dependent analysis of in situ XRPD data: a clear view of Xe thermal behavior inside a MFI zeolite

PSD/PCA analysis of MED data allowed to enhance the chemical selectivity in X-ray powder diffraction and to obtain Xe substructure into MFI zeolite.