Reactant Composition Research Articles

An operation strategy for mitigating the degradation of solid oxide electrolysis cells for syngas production

Three cells were tested under different conditions to mimic the situation with stacks arranged in gas flow series or parallel. The effects of reactant conversion ratio and inlet gas composition on the cell performance and durability were studied. The cells were operated under −1 A/cm2 at 800 °C for H2O + CO2 co-electrolysis. Flows were adjusted to realize the same overall production of syngas. Detailed electrochemical characterization was performed before, during and after the aging test and microstructural changes after aging were investigated. The results show that a gas-flow series arrangement is advantageous as it leads to reduced cell degradation: Reducing the H2O + CO2 conversion from 56% of a gas flow “parallel” case (Cell P) to 28% in the upstream of the series connected cells (Cell SU) and 39% in the downstream one (Cell SD) reduces the overall cell voltage degradation rate from 372 mV/kh for Cell P to140 mV/kh and 69 mV/kh for Cells SU and SD, respectively. This is tentatively ascribed to the “milder” overall conditions realized in the gas flow series case, where the average as well as maximum polarization (and local current density) is reduced relative to the parallel flow case.

Effect of Al Additions on the Microstructure and Mechanical Properties of the SHS Product of Ni-Al-TiO<sub>2 </sub>Mixtures

Intermetallics have attracted much interest in the high-temperature application. The Self-propagation High-temperature Synthesis (SHS) process offers an effective route to synthesize the intermetallic materials. However, an excessive composition of the SHS reactant can affect the structure and properties of the synthesized product. In this work, the SHS process was used to synthesize the mixture of Ni, Al, and TiO2 with different Al additions. The structure and properties of the product were characterized by SEM, EDS, and XRD tests. The mechanical properties of the product were evaluated by a Vickers microhardness test. The result shows that several intermetallic phases such as NiAl, TiNi, and TiAl were formed in the synthesized product. The formation of oxide appeared in the product due to the product reaction as well as the air environment. An increased Al addition resulted in decreased pores and increased hardness. The addition of 1.11 wt.% Al achieved the maximum hardness of the product. However, cracks were observed in the sample with the highest hardness. Excessive addition of Al decreased the hardness.

Kinetics of Intercluster Reactions between Atomically Precise Noble Metal Clusters [Ag25(DMBT)18]- and [Au25(PET)18]- in Room Temperature Solutions.

The kinetics of intercluster metal atom exchange reactions between solvated [Ag25(DMBT)18]- and [Au25(PET)18]- (DMBT and PET are 2,4-dimethylbenzenethiol and 2-phenylethanethiol, respectively, both C8H10S) were probed by electrospray ionization mass spectrometry and computer-based modeling. Anion mass spectra and collision induced dissociation (CID) measurements show that both cluster monomers and dimers are involved in the reactions. We have modeled the corresponding kinetics assuming a reaction mechanism in which metal atom exchange occurs through transient dimers. Our kinetic model contains three types of generic reactions: dimerization of monomers, metal atom exchange in the transient dimers, and dissociation of the dimers to monomers. There are correspondingly 377 discrete species connected by in total 1302 reactions (i.e., dimerization, dissociation and atom exchange reactions) leading to the entire series of monomeric and dimeric products [AgmAu25-m]- (m = 1-24) and [AgmAu50-m]2- (m = 0-50), respectively. The rate constants of the corresponding reactions were fitted to the experimental data, and good agreement was obtained with exchange rate constants which scale with the probability of finding a silver or gold atom in the respective monomeric subunit of the dimer, i.e., reflecting an entropic driving force for alloying. Allowing the dimerization rate constant to scale with increasing gold composition of the respective reactants improves the agreement further. The rate constants obtained are physically plausible, thus strongly supporting dimer-mediated metal atom exchange in this intercluster reaction system.

The Influence of the Compositions of Reactants on the Luminescence Intensity of Zn2SiO4: Mn Synthesized by Sol-Gel Method Using Hydrochloric Acid

The green emitting phosphor based on manganese activated zinc silicate was successfully synthesized by the sol – gel method using hydrochloric acid. The suitable molar ratio of the initial components is Zn(CH3COO)2: MnSO4: TEOS = 1.98: 0.02: 1 corresponding to the product formula Zn1.98Mn0,02SiO4. The suitable pH value for the gelation is 3, ratio of water phase: ethanol phase = 1:1 and the product when calcining the obtained gel at 10000C for 60 minutes has highest luminescence intensity. The synthesized phosphor consists of Zn2SiO4 with rhombohedral structure and emits a green light at the 525 nm wavelength when excited by the 325 nm UV radiation. The produced sample has spherical form with the particles size being 100 nm.

Catalytic consequences of the decoration of sodium and zinc atoms during CO2 hydrogenation to olefins over iron-based catalyst

This study unravels the effects of Na decoration and/or ZnO addition on the structures of Fe based catalysts, and the reaction pathways and the rate dependencies on both the composition of reactants and reaction temperature for CO2 hydrogenation to olefins, using kinetics and structure characterization by Raman spectroscopy, X-ray diffraction, and temperature-programmed CO reduction techniques. CO2 hydrogenation over Fe based catalysts occurs as a combination of the primary reverse water-gas-shift reaction to form CO and the subsequent CO hydrogenations to produce olefins and paraffins. Adding ZnO into Fe catalysts enhanced the rates of CO2 hydrogenation to all carbon containing products because ZnO facilitated the generation of iron carbide, as an active phase in Fe based catalysts, however, the relative rates among primary RWGS reactions, secondary CO hydrogenation to olefins and to paraffins were insensitive to the addition of Zn. Decoration of Na into Fe catalysts altered significantly the rate dependencies on both reactants and reaction temperature for olefins formation, which might be the results of the modification of the reducibility and surface identities of Fe catalysts by Na atoms, thus changed the rate ratios of paraffins and olefins. As results of decoration of Na and addition of Zn, the modified Fe based catalyst exhibits optimal performance for CO2 hydrogenation to olefins, which shows a CO2 conversion of 43 % with a selectivity of 54.1 % to high olefins, and a high olefins-to-paraffins ratio of 7.3.

Lean Operation of a Pulse Detonation Combustor by Fuel Stratification

Abstract Pressure gain combustion is a promising concept to substantially increase the thermal efficiency of gas turbines. One possible implementation that has been frequently investigated is pulse detonation combustors (PDCs), as they permit stable and reliable operation. At the same time, the need for part-load operation and low NOx emissions requires combustion concepts in the lean regime. However, realizing lean combustion is still very challenging in PDCs since the deflagration to detonation transition (DDT) is very sensitive to the reactant composition. This work investigates an approach to realize lean combustion in PDC by applying fuel stratification experimentally. The scope is to find the necessary increase of fuel concentration inside the predetonation chamber to provide reliable DDT with respect to the overall equivalence ratio. Emission measurements in the exhaust of the PDC allow for a quantification of the NOx emissions as a function of the injected fuel profile. A valveless PDC test rig is used, which contains a shock focusing geometry for detonation initiation and is ignited by a spark plug close to the upstream end wall. The subsequent expansion of the burned gas and interaction of the flame front with turbulence leads to the formation of a leading shock inside the predetonation chamber, which is then focused inside a converging-diverging geometry. The successful initiation of a detonation wave by shock focusing is very sensitive to the pressure ratio across the leading shock, which can be influenced by initial pressure, reactant composition and flow velocity. Results reveal that fuel stratification allows for reliable detonation initiation at a global equivalence ratio of φglob=0.65, whereas repeatable successful operation with nonstratified fuel injection is limited to φglob≥0.85.

Synthesis, parameters, properties and applications of responsive molecularly imprinted microgels: a review

Abstract Responsive molecularly imprinted microgels (MIGs) have gained a lot of interest due to their responsive specificity and selectivity for target compounds. Study on MIGs is rapidly increasing due to their quick responsive behavior in various stimuli like pH and temperature. MIGs show unique property of morphology control on in-situ synthesis of nanoparticles in response of variation in reactant concentration. Literature related to synthesis, parameters, characterization, applications and prospects of MIGs are critically reviewed here. Range of templates, monomers, initiators and crosslinkers are summarized for designing of desired MIGs. This review article describes effect of variation in reactants combination and composition on morphology, imprinting factor and percentage yield of MIGs. Hydrolysis of similar templates using MIGs is also described. Relation between percentage hydrolysis and hydrolysis time of targets at different temperatures and template:monomer ratio is also analyzed. Possible imprinting modes of ionic/non-ionic templates and its series are also generalized on the basis of previous literature. MIGs are investigated as efficient anchoring vehicles for adsorption, catalysis, bio-sensing, drug delivery, inhibition and detection.

Shedding Light on CO Oxidation Surface Chemistry on Single Pt Catalyst Nanoparticles Inside a Nanofluidic Model Pore.

Investigating a catalyst under relevant application conditions is experimentally challenging and parameters like reaction conditions in terms of temperature, pressure, and reactant mixing ratios, as well as catalyst design, may significantly impact the obtained experimental results. For Pt catalysts widely used for the oxidation of carbon monoxide, there is keen debate on the oxidation state of the surface at high temperatures and at/above atmospheric pressure, as well as on the most active surface state under these conditions. Here, we employ a nanoreactor in combination with single-particle plasmonic nanospectroscopy to investigate individual Pt catalyst nanoparticles localized inside a nanofluidic model pore during carbon monoxide oxidation at 2 bar in the 450–550 K temperature range. As a main finding, we demonstrate that our single-particle measurements effectively resolve a kinetic phase transition during the reaction and that each individual particle has a unique response. Based on spatially resolved measurements, we furthermore observe how reactant concentration gradients formed due to conversion inside the model pore give rise to position-dependent kinetic phase transitions of the individual particles. Finally, employing extensive electrodynamics simulations, we unravel the surface chemistry of the individual Pt nanoparticles as a function of reactant composition and find strongly temperature-dependent Pt-oxide formation and oxygen spillover to the SiO2 support as the main processes. These results therefore support the existence of a Pt surface oxide in the regime of high catalyst activity and demonstrate the possibility to use plasmonic nanospectroscopy in combination with nanofluidics as a tool for in situ studies of individual catalyst particles.

Nitrogen-Doped Carbons Derived from Imidazole-Based Cross-Linked Porous Organic Polymers.

Nitrogen-doped and heteroatom multi-doped carbon materials are considered excellent metal-free catalysts, superior catalyst supports for transition metal particles and single metal atoms (single-atom catalysts), as well as efficient sorbents for gas- and liquid-phase substances. Acid-catalyzed sol–gel polycondensation of hydroxybenzenes with heterocyclic aldehydes yields cross-linked thermosetting resins in the form of porous organic polymers (i.e., organic gels). Depending on the utilized hydroxybenzene (e.g., phenol, resorcinol, phloroglucinol, etc.) and heterocyclic aldehyde variety of heteroatom-doped organic polymers can be produced. Upon pyrolysis, highly porous and heteroatom-doped carbons are obtained. Herein, polycondensation of phloroglucinol with imidazole-2-carboxaldehyde (and other, similar heterocyclic aldehydes with two heteroatoms in the aromatic ring) is utilized to obtain porous, N-doped organic and carbon gels with N-content of up to 16.5 and 12 wt.%, respectively. Utilization of a heterocyclic aldehyde with two different heteroatoms yields dually-doped carbon materials. Upon pyrolysis, the porous polymers yield ultramicroporous N-doped and N,S co-doped carbons with specific surface areas of up to 800 m2g−1. The influence of the initial composition of reactants and the pyrolysis temperature on the structure and chemical composition of the final doped organic and carbon materials is studied in detail.

Crystal Facet Engineering of Copper-Based Metal–Organic Frameworks with Inorganic Modulators

Manipulating the exposed facets of metal-organic frameworks (MOFs) is of importance toward understanding their facet-dependent property in a variety of applications. Herein, we apply a novel inorganic competitive coordination strategy to control the growth orientation of copper-based MOFs (HKUST-1, MOF-14, and Cu-MOF-74) without sacrificing the pore accessibility and crystallinity. Through monitoring the reactant composition, we find that the competitive coordination induced by the added aluminium nitrate mainly affects the crystal growth stage rather than the nucleation stage. The kinetic study further reveals that Al3+ competes with Cu2+ to coordinate with ligands, restraining the growth rate of certain facets and resulting in the orientated growth of copper-based MOFs. Compared to the reduced pore accessibility of HKUST-1 crystals modulated by the organic modulation method, Al3+-modulated HKUST-1 displays a much larger surface area (>2200 m2/g) and more accessible Cu active sites. Hydroxylation of toluene was utilized as a model reaction to investigate the facet-catalytic activity for as-synthesized HKUST-1. The selectivity of the preferred product cresol increases with the morphology transformation of HKUST-1 from octahedron to cube.

Kinetic modeling of dynamic changing active sites in a Mars-van Krevelen type reaction: Ethylene oxychlorination on K-doped CuCl2/Al2O3

A kinetic model was developed by taking into account the dynamic nature of the active sites in Mars–van Krevelen type catalytic reactions to predict the evolution of the reactant and product composition in the gas phase and the CuCl2 concentration in the solid catalyst. The kinetic model at the steady-state of ethylene oxychlorination was obtained by combining transient experiments of the two half-reactions in the redox cycle, namely CuCl2 reduced to CuCl by ethylene and CuCl oxidation by oxygen on the K-promoted CuCl2/γ-Al2O3 catalyst. The dynamic transitions between CuCl2 and CuCl of the active sites during the reactions are also modeled, and the contributions of two active sites, namely Cu coordination numbers of 4 and 3 in CuCl2 were distinguished and included in the kinetic model. The kinetic models describe well the transient response of the reduction and oxidation steps as well as the reaction at the steady-state at different reaction conditions. Moreover, by combining the reactor modeling through a steady-state approach, the spatial-time resolved CuCl2 profile and the C2H4 reaction rate can be well predicted in comparison with the experimental results. The approach of both transient and steady-state kinetic modeling and simulation is supposed to have general relevance for a better understanding of Mars–van Krevelen type reactions.

Process evaluation of solvent‐free lipase‐catalyzed esterification schemes in the synthesis of structured triglycerides from oleic and palmitic acids

AbstractDifferent schemes in the production of structured triglycerides based on solvent‐free esterification of oleic acid and palmitic acid with glycerol were evaluated in terms of reactant conversion, product composition, and yield. Two‐step processes, with or without glycerol dosing, were compared with one‐step versions carried out at temperature conditions within 40°C–60°C to a final oleic acid/palmitic acid/glycerol ratio of 2:1:1, the stoichiometric ratio in 1,3‐dioleoyl‐2‐palmitoyl glycerol (OPO). Substantial amounts of C52 triglycerides, including OPO, were produced in all schemes at 34.98–39.55 wt.% of the total triglycerides and triglyceride yields of 50.10–56.56 wt.% based on the raw materials. The two‐step process with glycerol dosing at 60°C showed the highest palmitic acid incorporation at the sn‐2 position of 46.46%, but the same process carried out with a step increase in temperature from 40°C to 60°C gave the highest OPO yield at 19.30 wt.%. These results demonstrate the possibility of manipulating regioselectivity and triglyceride specificity by varying reactant feeding schemes without the use of solvents and sn‐1,3‐specific lipases common in conventional acidolysis‐based processes.

Synthesis of the Ti3SiC2 MAX Phase via Combustion in the TiO2–Mg–Si–C System

Technologically viable principles have been developed for the preparation of the MAX phase Ti3SiC2 by self-propagating high-temperature synthesis (SHS) with a reduction step, using titanium dioxide. We have studied the influence of synthesis conditions (starting-mixture composition and ratio of reactants) on the composition, structure, and particle size of the Ti3SiC2 powder. The results demonstrate that the addition of 10 to 20 wt % excess magnesium to the starting mixture leads to a decrease in the percentage of the TiSi2 and Ti5Si3 silicides in the Ti3SiC2 powder (from 8 to 5 wt %), with the smallest percentage of titanium carbide corresponding to a 10% excess of magnesium in the starting mixture. Raising the amount of silicon in the starting mixture by 10% leads to a decrease in the percentages of the TiSi2 and Ti5Si3 silicides and titanium carbide in the Ti3SiC2 powder. The addition of sodium chloride and magnesium perchlorate to the starting mixture has been shown to influence the percentages of the TiSi2 and Ti5Si3 silicides and TiC in the Ti3SiC2 powder. We have optimized conditions for the synthesis of powder containing 89.1 wt % Ti3SiC2. The powders prepared by SHS with a reduction step consist of agglomerates of layered particles ranging in size from 130 to 770 nm.

(Invited) Tailored Syngas Production Via High Temperature H2o-CO2 Co-Electrolysis

Solid oxide electrolysis cells (SOEC) operating at 600 – 850°C are used to split water using excess renewable or nuclear electrical energy and convert it to chemical energy which is stored in H2 and O2. SOECs can also be used as electrochemical reactors for the co-electrolysis of steam and carbon dioxide. The two reactants, typically waste products in an industrial plant, could be turned into syngas (CO+H2), a valuable and very commonly used reagent in the chemical industry. Syngas is subsequently used to produce synthetic fuels, olefins or other liquid hydrocarbons via Fischer-Tropsch synthesis or for methanol synthesis and hydroformylation.In this presentation we focus on CO2-H2O co-electrolysis, the simultaneous electrochemical reduction of carbon dioxide and steam, carried out on the porous Ni-based electrodes in high temperature SOECs. Experiments were conducted using multiple button cells. The rate of the electrochemical reactions was measured in the temperature range 700-850oC for varied reactant compositions: 10-98% CO2 and 5-50% H2O, also in the presence of some H2 and CO. Kinetics of electrochemical CO2 reduction were evaluated for different CO2/H2O ratios and compared to steam electrolysis. Product analysis was completed using gas chromatography. Long term electrochemical performance of multiple cells was recorded simultaneously for over 500 hours of continuous testing with occasional interruptions to obtain current-voltage characteristics and collect the impedance spectra. The ability to control H2 :CO ratios in generated syngas by varying the inlet H2O/CO2 ratios and cell potential was demonstrated. Thus, precise control of the H2 to CO ratios, a unique feature of electrochemical conversion can be used to optimize selectivity of the desired byproduct.

Metal-organic chemical vapour deposition of lanthana-doped ceria layers at low temperatures

Non-porous, amorphous and nanocrystalline CeO2–La2O3 layers were synthesized by means of MOCVD using Ce(tmhd)4 and La(tmhd)3 as reactants on tubular and planar quartz glass substrates. Different layers were synthesized in the temperature range 500–700 °C using various molar contents of La(tmhd)3, i.e. 10, 15, 26 and 50%, respectively. A mixture of Ar and air was used as a carrier gas. Air was also an oxygen source necessary for carbon oxidation (a solid by-product of reactant pyrolysis). Therefore, the layers should only contain Ce4+ ions. When the synthesis process was controlled by the surface reaction rate, there was no correlation between the chemical composition of reactants and that of the layers. Such a dependence was obtained when the synthesis process was controlled by mass diffusion to the substrate. In addition, it was observed that La3+ ion segregation can occur during layer synthesis between surface areas with lower and higher amounts of a crystalline phase. The molar percent of La2O3 in areas exhibiting less crystallization with smaller grains was higher than in locations with larger grains, because, in this case, intergranular boundary content was lower. X-ray analysis indicates that layers deposited at 500 °C were amorphous, although SEM images show numerous small nuclei of a crystalline phase. It seems that the crystalline phase content was not high enough to be identified by X-ray analysis. Layers deposited at 600 °C consisted of a solid solution of La2O3 dissolved in CeO2. From UV-VIS tests it follows that absorption is very strong up to a wavelength of approximately 320 nm.

Assessment of the electrochemical characteristics of a Polymer Electrolyte Membrane in a reference single fuel cell testing hardware

The design of a new testing hardware for Polymer Electrolyte Membrane (PEM) single cell is presented in this paper. It has been developed with the purpose to minimise the influence from the testing hardware itself on results of performance and durability tests. This has been achieved by exposing the tested Membrane Electrode Assembly (MEA) to as far as possible uniform distribution of temperature, pressure and reactant gases composition across the active area. The new hardware aims thus at providing a reference testing platform enabling the generation of accurate experimental results and better comparison among different laboratories. The performance of this new hardware has been compared with single-serpentine channel hardware, commonly used for PEM single cell testing. Evaluation of polarisation curve and electrochemical impedance spectroscopy experimental results show that it provides better quality results which are much less affected by accumulated liquid water, thus providing better information on MEA performance.

Synthesis and antiparkinsonian activity of nanocomposite of chitosan-tripolyphosphate-Mucuna pruriens L extract (CS-TPP-MP)

Mucuna pruriens L. (MP) has antiparkinsonian activity because it contains levodopa that acts as a dopamine precursor and plays a role to stimulate dopaminergic receptors in Parkinson's sufferers. The therapeutic efficacy of MP extract can be improved by using a nano drug carrier system, such as chitosan-tripolyphosphate (CS-TPP). This study aims to synthesize, characterize, and evaluate antiparkinsonian activity of chitosan-tripolyphosphate-MP extract (CS-TPP-MP) nanocomposite in mice. MP seed powder was extracted by maceration method using water-ethanol (1:1) by adding citric acid until it reached pH 3. The CS-TPP-MP nanocomposite was synthesized by using ionic gelation method with variations in reactant composition and reaction time. The CS-TPP-MP nanocomposite was characterized by Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX), X-Ray Diffraction (XRD) and Fourier-Transform Infrared (FTIR) Spectroscopy. Catalepsy test was performed to find the antiparkinsonian activity level of CS-TPP-MP nanocomposite at doses of 5, 10, 15, 20, and 25 mg/kg body weight. Based on the results of CS-TPP-MP synthesis, it was found that the reactant composition (CS-TPP:MP) of 1:3 with reaction time of 20 minutes produced the highest yield (14.21%.) SEM-EDX characterization showed that the morphology of CS-TPP-MP nanocomposite was predominantly spherical and the size was approximately 120-170 nm with a composition of C = 55.43%, O = 30.46%, N = 13.46%, P = 0.44%. XRD diffractogram showed that CS-TPP-MP nanocomposite has amorphous structure. FTIR analysis showed the appearance of absorption at wavelength of 1643.35 cm−1 which proved the interaction between the primary amine group of chitosan and the carbonyl group of EMP. Catalepsy test demonstrated that CS-TPP-MP nanocomposite at the doses of 5, 10, 15, 20, and 25 mg/kg body weight could reduce catalepsy symptoms in mice significantly, and the best dosage was 20 mg/kg body weight.

Tailored Syngas Production Via High Temperature H2o-CO2 Co-Electrolysis

Solid oxide electrolysis cells (SOEC) operating at 600 – 850°C are used to split water using excess renewable or nuclear electrical energy and convert it to chemical energy which is stored in H2 and O2. SOECs can also be used as electrochemical reactors for the co-electrolysis of steam and carbon dioxide. The two reactants, typically waste products in an industrial plant, could be turned into syngas (CO+H2), a valuable and very commonly used reagent in the chemical industry. Syngas is subsequently used to produce synthetic fuels, olefins or other liquid hydrocarbons via Fischer-Tropsch synthesis or for methanol synthesis and hydroformylation.In this presentation we focus on CO2-H2O co-electrolysis, the simultaneous electrochemical reduction of carbon dioxide and steam, carried out on the porous Ni-based electrodes in high temperature SOECs. Experiments were conducted using multiple button cells. The rate of the electrochemical reactions was measured in the temperature range 700-850oC for varied reactant compositions: 10-98% CO2 and 5-50% H2O, also in the presence of some H2 and CO. Kinetics of electrochemical CO2 reduction were evaluated for different CO2/H2O ratios and compared to steam electrolysis. Product analysis was completed using gas chromatography. Long term electrochemical performance of multiple cells was recorded simultaneously for over 500 hours of continuous testing with occasional interruptions to obtain current-voltage characteristics and collect the impedance spectra. The ability to control H2 :CO ratios in generated syngas by varying the inlet H2O/CO2 ratios and cell potential was demonstrated. Thus, precise control of the H2 to CO ratios, a unique feature of electrochemical conversion can be used to optimize selectivity of the desired byproduct.

Dry reforming of methane in a temperature-controlled dielectric barrier discharge reactor: disclosure of reactant effect

Plasma-assisted dry reforming of methane has attracted much research attention because this process simultaneously utilizes greenhouse, methane and carbon dioxide, to produce hydrogen-rich syngas at a relative low temperature. Although it is generally recognized that the gas composition of reactant has great effect on the methane conversion and products distribution, systematic studies that clarify the roles that electron-induced chemistry and thermochemistry play are needed for a full understanding of reactant effect. Here, we compared the reforming performance by varying the ratio of CO2/CH4 or O2/CH4 at the similar reduced field intensity (E/N) in a temperature-controlled dielectric barrier discharge reactor to elaborate the role of electron-induced chemistry and thermo-chemistry in the dry reforming process. By conducting optical emission spectrum measurement, the enrichment of O atoms was observed at the increased CO2/CH4 or O2/CH4 ratios. At T = 293 K, methane conversion was only dependent on the electron-induced chemistry regardless of the specific reactant gas composition. At a relative high temperature condition, however, thermochemistry could become pronounce when sufficient O atoms were added into the dry reforming process. In contrast, the chemical pathways to the products were overall controlled by the thermochemistry at the tested background temperatures. Due to the conversion of carbon-based products into the carbon dioxide, the conversion of carbon dioxide was influenced by the thermochemistry when the concentration of O atoms was high. Our findings may improve the understanding of reactant effect and the designs of plasma-reformer.

The effect of water vapor on surface oxygen exchange kinetics of thin film (La,Sr)(Co,Fe)O3-δ

Oxygen reduction and transport in electrochemical applications are strongly affected by the reactant gas composition, including impurities such as water. Understanding the relationship between oxygen reactivity and humidity is key for attaining stability and high efficiency of solid oxide fuel cells, which are especially attractive for transportation applications as low emission power generation devices. Both short- and long-term effects of moisture have previously been associated with use of ambient air. To better understand these effects, we study oxygen exchange kinetics at the cathode surface and the cathode/electrolyte interface using La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) epitaxial thin films as a model-surface system. In situ synchrotron X-ray techniques evaluate the oxygen reduction reaction (ORR) kinetics in response to environmental variables. The results suggest a clear enhancement of the ORR rate upon short term exposure of the perovskite-structured films to water. On the basis of these measurements, along with in situ X-ray characterization of Sr segregation and computational first-principles studies, we suggest a model for this increased ORR activity that may lead to further improvements by stabilizing active cathode surface configurations.