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Operando XAS and NAP-XPS investigation of CO oxidation on meso- and nanoscale CoO catalysts
摘要： In contrast to Co3O4, CoO has been much less studied for CO oxidation. Herein, the phase changes of commercial mesoscopic CoO (particle size ?1 μm) and nanosized CoO (20–50 nm particle size), the latter prepared by vacuum reduction of commercial Co3O4, were examined by operando X-ray absorption (XAS) and near-ambient pressure X-ray photoemission (NAP-XPS) spectroscopy during CO oxidation, as well as ex situ by transmission electron microscopy and di?raction (TEM/SAED). Commercial mesoscopic CoO exhibited CO oxidation activity at ?200 °C, but even up to 530 °C in pure O2 no substantial (bulk) oxidation was observed by operando XAS, likely due to the large grains and bulk nature of CoO. After pre-oxidation at 400 C, electron di?raction detected thin surface layers of Co3O4. This increased activity but the activity of nanosized Co3O4 of equal surface area was still not reached. For nanosized CoO (surface layers on vacuum-reduced Co3O4), operando NAP-XPS/XAS, acquired during CO oxidation, revealed oxidation of CoO to Co3O4 above 150 °C, yielding the activity of nanosized Co3O4. Evidently, the nanoscale CoO shell on a Co3O4 core with small grains more easily and more completely transformed to Co3O4 than mesoscopic (bulk) CoO with large grains. Our study demonstrates how ?exible and dynamic surfaces of cobalt oxide materials adjust to various reaction environments, which also depends on grain size and morphology (bulk vs. thin layers), illustrating the importance of operando techniques to determine active catalyst phases under reaction conditions.
关键词： CO oxidation,CoO,Co3O4,NAP-XPS,XAS,TEM,Operando
更新于2025-09-23 15:23:52
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Operando observation of chemical transformations of iridium oxide during photoelectrochemical water oxidation
摘要： Iridium oxide is one of the few catalysts capable of catalyzing the oxygen evolution reaction (OER) in both acidic and basic conditions. Understanding the mechanism of IrOx under realistic photoelectrochemical conditions is important for the development of integrated water splitting systems. Herein, we have developed a highly efficient OER photoanode in pH 1 aqueous solutions based on a sputtered IrOx film and a p+n-Si light absorber, interfaced with sputtered Au layer. Operando high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD XAS) was employed to monitor the oxidation state changes of IrOx during both electrochemical and photoelectrochemical (PEC) water oxidation reactions in pH 1 aqueous solutions. We observed a gradual increase of the average oxidation state of Ir with increasing anodic potential in the pre-catalytic region, followed by a reduction of Ir under O2 evolution conditions. Consistent results were obtained on dark anodes and illuminated photoanodes. However, when the thickness of IrO2 was increased to 2 and 3 nm, the spectral changes became much less pronounced and the reduction of Ir oxidation state after the OER onset was not observed. This is due to the lower surface to bulk ratio, where lattice oxygen sites in the bulk are not accessible for the formation of hydroxide. More generally, the operando method developed here can be extended to other materials, thereby providing a powerful tool for mechanism discovery and an enabling capability for catalyst design.
关键词： oxygen evolution reaction (OER),electrochemical and photoelectrochemical (PEC),high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD XAS),iridium oxide,Operando method
更新于2025-09-23 15:23:52
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Understanding the Sensing Mechanism of Rh2O3 loaded In2O3
摘要： The effect of Rh loading on CO sensing was studied for the case of In2O3. This was done by performing measurements with sensors based on loaded and unloaded materials that were performed at an operation temperature of 300 °C in the presence of low background oxygen concentration according to an experimental procedure that was demonstrated to help clarify the reception/transduction functions of loaded Semiconducting Metal Oxides (SMOX). The experimental investigation methods were DC resistance and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The results indicate that in the case of Rh2O3 loaded In2O3 the reaction primary takes place on the Rh2O3 cluster and the electrical properties of the In2O3 are controlled by the pinning of the SMOX Fermi-level to the one of the Rh2O3 cluster.
关键词： SMOX,surface chemistry,gas sensors,operando,Rh2O3 loading,DRIFTS,In2O3
更新于2025-09-23 15:23:52
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2D Material Membranes for Operando Atmospheric Pressure Photoelectron Spectroscopy
摘要： Probing the chemistry that occurs at catalyst interfaces under realistic process conditions is key to the rational design of better materials for industrial catalytic reactions. Ambient pressure X-ray photoelectron spectroscopy, has until recently been limited to pressures two orders of magnitude below atmosphere. However, the development of photoelectron transparent membranes based on two-dimensional materials that can maintain large pressure differences and yet have thicknesses approaching or even falling below the inelastic mean free path of photoelectrons, now allows the atmospheric pressure regime and above to be accessed. We introduce here the fundamental principles underlying this membrane-based approach to atmospheric pressure photoelectron spectroscopy, and in this context highlight some of the key design concepts and challenges in performing experiments with this technique. We discuss a number of recent proof-of-concept studies, and highlight the potential of the membrane-based approach for operando characterisation of catalyst interfaces under reaction conditions, as well as some current challenges and limitations in this area.
关键词： Atmospheric pressure,XPS,Operando spectroscopy,Graphene,Reaction cell
更新于2025-09-23 15:21:01
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In Situ Raman Spectroscopy on Silicon Nanowire Anodes Integrated in Lithium Ion Batteries
摘要： Rapid decay of silicon anodes during lithiation poses a significant challenge in application of silicon as an anode material in lithium ion batteries. In situ Raman spectroscopy is a powerful method to study the relationship between structural and electrochemical data during electrode cycling and to allow the observation of amorphous as well as liquid and transient species in a battery cell. Herein, we present in situ Raman spectroscopy on high capacity electrode using uncoated and carbon-coated silicon nanowires during first lithiation and delithiation cycle in an optimized lithium ion battery setup and complement the results with operando X-ray reflection diffraction measurements. During lithiation, we were able to detect a new Raman signal at 1859 cm?1 especially on uncoated silicon nanowires. The detailed in situ Raman measurement of the first lithiation/delithiation cycle allowed to differentiate between morphology changes of the electrode as well as interphase formation from electrolyte components.
关键词： silicon nanowires,lithium ion batteries,in situ Raman spectroscopy,operando XRD,solid electrolyte interphase
更新于2025-09-19 17:15:36
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On the Decomposition of Carbonate-Based Lithium-Ion Battery Electrolytes Studied Using Operando Infrared Spectroscopy
摘要： A novel infrared diagnostic for operando measurements of electrolyte decomposition is reported. The diagnostic was used to study the decomposition of LiPF6/EC/DEC electrolyte in LCO/graphite Li-ion cells. During formative cycles spectra revealed electrochemical reduction of the EC carbonyl group, which corresponded to simultaneous SEI formation on the graphite anode. This observation supplements current theories of EC decomposition during SEI formation. Operating LCO half-cells at voltages above 4.2 V caused permanent battery capacity loss but no observable electrolyte degradation, indicating the LCO electrode is degraded at high voltage. Infrared thermometry was used to measure the temperature of the electrolyte during heated tests. Operating cells at temperatures above 70°C resulted in SEI and electrolyte decomposition. Operando spectra collected during heating revealed EC ring-opening as the mechanism of thermal degradation, which resulted in permanent capacity loss. EC thermal decomposition was identical in all cells tested, indicating a homogeneous decomposition reaction independent of electrode material or potential. Thermal stability decreased with increased salt concentration indicating that decomposition is likely catalyzed by LiPF6 decomposition products. Thus, thermal decomposition is not caused by continued reduction reactions on the anode due to SEI failure, as EC reduction and EC thermal decomposition have different mechanisms.
关键词： SEI formation,operando infrared spectroscopy,thermal stability,lithium-ion batteries,electrolyte decomposition
更新于2025-09-19 17:15:36
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<i>Operando</i> observation of resistive switching in a resistive random-access memoryby laser-excited photoemission electron microscope
摘要： We developed a laser-excited photoemission electron microscope (Laser-PEEM) that enables us to perform a non-destructive operando observation for elucidating the changes in the physical properties of electronic devices. By utilizing the Laser-PEEM, the non-volatile resistance change in the resistive random-access memory (ReRAM) was clearly visualized, even though the resistance change occurred under the electrode of the ReRAM, thanks to the deep probing depth. The operando observation of the Laser-PEEM is very promising as an observation method for various kinds of devices because the observation simultaneously provides us with morphological and electrical properties in real time.
关键词： ReRAM,Laser-PEEM,operando observation,photoemission electron microscope,resistive switching
更新于2025-09-16 10:30:52
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Operando X-ray diffraction during laser 3D printing
摘要： Laser based additive manufacturing allows to build a designed shape layer-by-layer, offering versatility and flexibility to many metallurgical sectors. The fast cooling rates and repeated heat cycles depending on the laser and scanning parameters are not easily measurable with conventional methods. Thus, advanced predictive computational simulations, required to reduce trial and error lead time, are difficult to validate. A newly developed in operando X-ray diffraction device implemented at a synchrotron beamline, taking advantage of the high brilliance and the fast detectors available, brings the missing link with numerical methods. By performing operando experiments on Ti-6Al-4V with different printing parameters, the temporal evolution of the low and high temperature phases are followed, the heating and cooling rates are measured for the powder and the solid material; and the formation of residual stresses in the b phase is demonstrated. Moreover it is shown that the parameter that has the largest influence on the evolving microstructure is the scanning strategy, introducing a size effect related to the scanning length.
关键词： microstructure evolution,operando X-ray diffraction,scanning strategy,Laser based additive manufacturing,Ti-6Al-4V
更新于2025-09-12 10:27:22
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Operando UV-Raman study of the methanol to olefins reaction over SAPO-34: spatiotemporal evolution monitored by different reactor approaches
摘要： A molecular understanding of coke formation during the methanol to olefins (MTO) reaction is of great importance in order to adopt strategies that can improve the lifetime of the catalyst. UV-Raman has proven to be a valuable characterization tool, because of the favorable resonance conditions achieved towards key coke components, e.g. aromatic and olefinic compounds. Still, the applicability of UV-Raman in MTO is limited by the high risk of inducing sample damage under the exposure to the intense UV excitation laser. This drawback has been addressed by specific experimental setups, exploiting the concept of sample movement under the laser beam during the measurement, so that the laser-sample interaction is minimized by averaging over a wider sample surface. In this work, the impact of two different experimental setups, both relying on sample movement, are evaluated for the operando investigation of the MTO reaction over a SAPO-34. While in one case the whole catalytic bed is moved (fluidized bed), in the other case the sample is pressed into a pellet and rotated. Due to the peculiar spatial evolution of the reaction zone during MTO in a fixed-bed reactor, each method provides valuable information, but at very different spatiotemporal scales.
关键词： Raman,Zeolite,Methanol-to-hydrocarbons,Deactivation,Operando
更新于2025-09-10 09:29:36
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Planar Microstrip Ring Resonator Structure for Gas Sensing and Humidity Sensing Purposes
摘要： A planar microstrip ring resonator structure on alumina was developed. It was covered with a zeolite film. The device was successfully operated at around 8.5 GHz at room temperature as a humidity sensor. In the next step, an additional planar heater will be included on the reverse side of the resonator structure to allow for testing of gas sensitive materials under sensor conditions.
关键词： zeolite in operando spectroscopy,radio frequency gas sensing (RF),microwave sensors
更新于2025-09-09 09:28:46