Fourier Transform Infrared Emission Spectroscopy Research Articles

Spatially Heterogeneous Chemistry Observed using NIRTI on SOFC Anodes

Carbon formation remains the primary degradation mechanism for solid oxide fuel cells (SOFCs) operating on carbonaceous fuels. The mechanisms for the remediation of carbon (C) induced degradation via electrochemical gasification and reforming using O2(g) and H2O(g) was studied using Near Infrared Thermal Imaging (NIRTI), Fourier Transform Infrared Emission Spectroscopy (FTIRES), chronoamperometry/chronopotentiometry (CA/CP), and mass spectrometry (MS). Carbon removal follows a stepwise mechanism, first oxidizing surface carbon to CO(g), and subsequently to CO2(g). CO(g) oxidation requires a catalytic surface to form CO2 which plays a key role in removing C via the reverse Boudouard chemistry. NIRTI reveals spatially heterogenous chemistry and suggests a specific role of surface oxygen species. These species form from dissociative adsorption and non-faradaic oxide flux through the electrolyte, as well as O2 transport limited processes occurring due to high O2 utilization. C removal from electrochemical oxidation and steam spatially homogeneous compared to O2, due in part to the respective active surface species, and their respective transport limitations. Under O2 C removal is appears incomplete, despite electrochemical results. These experiments clarify the mechanisms responsible for remediation of C on SOFC anodes and highlight the need of spatially resolved techniques to study SOFCs under operating conditions.

Comparison of Carbon Deposition and Removal from Ni-YSZ and Ni-BCZY Composites Using Operando Optical Methods

Solid oxide fuel cells (SOFCs) are attractive devices for power generation because they can operate with a variety of fuels, including H2, hydrocarbon fuels, biogas, and syngas. Conventional SOFC anode composites comprised of Ni-YSZ (YSZ = yttria-stabilized zirconia), however, suffer from performance degradation due to surface accumulation of carbon from hydrocarbon cracking. Alternative electrolyte materials such as yttria-doped barium cerate/zirconate mixtures (BCZY) offer the promise of reduced carbon formation over the Ni-BCZY electrode and lower operating temperatures by the conduction of protons instead of oxide ions. In this study, 50%-50% Ni-8YSZ and 50%-50% Ni-BCZY27 composites were exposed to CH4 in the absence and presence of either CO2 or H2O. The degree of carbon deposition and mechanism of carbon removal in the absence of fuel was estimated in the presence of steam using operando Fourier transform infrared emission spectroscopy (FTIRES) and near-infrared thermal imaging (NIRTI) at 750 °C. Upon exposure to each fuel condition, carbon removal using steam results in more CO2 + CO product formation from Ni-8YSZ implying more carbon formation on Ni-8YSZ compared to Ni-BCZY27. Carbon removal of cells exposed to CH4 alone indicate limited formation and fast depletion of CO over Ni-BCZY27; depletion of CO2, however, happens more slowly. Depletion of CO and CO2 in the Ni-8YSZ system happens more gradually suggesting the deposition of carbon over Ni-BCZY27 occurs less readily and its removal is more facile through gasification. Interestingly, the cracking of CH4 over Ni-8YSZ is accompanied by a larger degree of cooling compared to Ni-BCZY27 whereas both dry and wet reforming result in similar cooling over Ni-8YSZ and Ni-BCZY27. The results will be discussed in the context of recent work using operando spectroscopies to characterize CH4 fuel utilization in Ni-8YSZ based SOFCs in the absence and presence of various reformers.

Reactions of OH and OD radicals with ethanethiol and diethylsulfide: Branching ratio and vibrational energy disposal for the product water molecules

Reactions of OH and OD radicals with C 2 H 5 SH and (C 2 H 5 ) 2 S were studied by Fourier-transform infrared emission spectroscopy of the water product molecules from a fast-flow reactor. Vibrational excitation of the H 2 O, HOD and D 2 O product molecules was determined by computer modeling of the chemiluminescence spectra. Spectra of the abstraction of H-atom from the ethyl group (C-H) and sulfur atom (S-D) were separated using deuterated reactant, C 2 H 5 SD. The branching ratio was found to be 0.24 ± 0.05 (C-H):0.76 (S-D) both for OH and OD reactants. For the OH + C 2 H 5 SH reaction the branching fraction for the (C-H) channel of 0.25 ± 0.06 was obtained. Vibrational energy disposal for S-H abstraction is similar to that for the reaction with CH 3 SH, whereas abstraction from the ethyl group demonstrates higher bending excitation than abstraction from the methyl group of CH 3 SH. A similar trend was found for abstraction from the ethyl and methyl groups of (C 2 H 5 ) 2 S and CH 3 SCH 3 .

Roaming Dynamics and Conformational Memory in Photolysis of Formic Acid at 193\u2009nm Using Time-resolved Fourier-transform Infrared Emission Spectroscopy

In photodissociation of trans-formic acid (HCOOH) at 193 nm, we have observed two molecular channels of CO + H2O and CO2 + H2 by using 1 μs-resolved Fourier-transform infrared emission spectroscopy. With the aid of spectral simulation, the CO spectra are rotationally resolved for each vibrational state (v = 1–8). Each of the resulting vibrational and rotational population distributions is characteristic of two Boltzmann profiles with different temperatures, originating from either transition state pathway or OH-roaming to form the same CO + H2O products. The H2O roaming co-product is also spectrally simulated to understand the interplay with the CO product in the internal energy partitioning. Accordingly, this work has evaluated the internal energy disposal for the CO and H2O roaming products; especially the vibrational-state dependence of the roaming signature is reported for the first time. Further, given a 1 μs resolution, the temporal dependence of the CO/CO2 product ratio at v ≥ 1 rises from 3 to 10 of study, thereby characterizing the effect of conformational memory and well reconciling with the disputed results reported previously between absorption and emission methods.

Erratum: Time-resolved Fourier-transform infrared emission spectroscopy of Ag in the (1300–3600)−cm−1 region: Transitions involving f and g states and oscillator strengths [Phys. Rev. A 82 , 022502 (2010)

Received 11 August 2019DOI:https://doi.org/10.1103/PhysRevA.100.039902©2019 American Physical Society

In Situ Optical Studies of CO2 and Co-Electrolysis

The ability to understand the underlying mechanisms for electrolysis of CO2 and co-electrolysis of CO2 and steam has been hindered due to a lack of experimental methods that can probe intermediate species and materials directly during operation. Although there have been studies on using Ni-YSZ and ceria based cathodes for electrode materials in high temperature solid oxide electrolysis cells (SOECs), these have mainly utilized post-mortem and in situ electrochemical analyses. Here, we demonstrate an in situ duplex technique that combines near infrared thermal imaging (NIRTI) and Fourier-transform infrared emission spectroscopy (FTIRES) to monitor processes for electrolysis of CO2 and co-electrolysis on operating SOECs. The results are correlated with traditional electrochemical measurements to identify any polarization dependence on species during the course of reactions under a range of conditions. CO2 and co-electrolysis conditions are investigated on anode- and electrolyte-supported cells between 700 and 900 °C. NIRTI results indicate cooling on the anode surface during endothermic processes and heating during high loads due to joule heating. FTIRES indicates the first observation of a carbonate intermediate formed on a cathode during operation at normal SOEC working pressure and temperature. Diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) is used to confirm band assignments seen in situ for electrode materials. Ex situ mass spectrometry and exhaust gas FTIR absorption measurements are combined with in situ results to further characterize and quantify carbon monoxide and syn-gas production. These studies serve as benchmark data for better understanding the processes during CO2 electrolysis in real working conditions.

In Situ Optical Investigation of H2s Impact on Carbon Oxidation in Operating Solid Oxide Fuel Cells

While solid oxide fuel cells (SOFCs) promise efficient electricity production and high fuel flexibility, trace sulfur and chlorine constituents commonly found in desirable fuel sources such as syngas and biogas pose challenges. Sulfur poisoning is a well-established phenomenon that can lead to rapid loss of electrochemical performance in SOFCs that operate at high temperatures (650 – 800 °C). State-of-the-art Ni/YSZ (yttrium stabilized zirconia) anodes lose significant catalytic activity upon exposure to even ppm-levels of H2S, but details regarding how the catalyst degrades and the specific effects on electro-catalytic processes remain unclear. One approach to solving this shortcoming is to understand the degradation mechanisms through real time correlation of electrochemical performance with in situ, molecular specific observations. This current study uses infrared emission from the Ni/YSZ anode surface of an operating SOFC to simultaneously characterize 1) gas species using Fourier transform infrared emission spectroscopy (FTIRES) and 2) temperature changes using near infrared (NIR) thermal imaging. These data are collected with electrochemical potential when the SOFC is operated at 75% maximum current at 700 °C using CH4, with and without 170 ppm H2S added. In situ FTIRES measurements show that the CO2 oxidation product and the CO electrochemical intermediate are suppressed when cell potential deteriorates with H2S present. Simultaneous NIR thermal imaging measurements of surface temperatures show that cooling also reflects evolving processes at the anode. After each trial, electrochemical oxidation of deposited carbon showed that H2S also hindered carbon accumulation. These results together have begun to provide direct insight into how sulfur poisoning affects electrochemical processes in SOFCs through correlations of electrochemical potential, surface temperature changes, and gas species at the anode.

Branching Ratios and Vibrational Distributions in Water-Forming Reactions of OH and OD Radicals with Methylamines.

Reactions of OH and OD radicals with (CH3)3N, (CH3)2NH, and CH3NH2 were studied by Fourier transform infrared emission spectroscopy (FTIR) of the water product molecules from a fast-flow reactor at 298 K. The rate constants (4.4 ± 0.5) × 10(-11), (5.2 ± 0.8) × 10(-11), and (2.0 ± 0.4) × 10(-11) cm(3) molecule(-1) s(-1) were determined for OD + (CH3)3N, (CH3)2NH, and CH3NH2, respectively, by comparing the HOD emission intensities to the HOD intensity from the OD reaction with H2S. Abstraction from the nitrogen site competes with abstraction from the methyl group, as obtained from an analysis of the HOD and D2O emission intensities from the OD reactions with the deuterated reactants, (CD3)2NH and CD3NH2. After adjustment for the hydrogen-deuterium kinetic isotope effect, the product branching fractions of the hydrogen abstraction from the nitrogen for di- and monomethylamine were found to be 0.34 ± 0.04 and 0.26 ± 0.05, respectively. Vibrational distributions of the H2O, HOD, and D2O molecules are typical for direct hydrogen atom abstraction from polar molecules, even though activation energies are negative because of the formation of pre-transition-state complexes. Comparison is made to the reactions of hydroxyl radicals with ammonia and with other compounds with primary C-H bonds to discuss specific features of disposal of energy to water product.

(Invited) In Operando Optical Studies of Solid Oxide Electrochemical Cells

Solid oxide fuels cells (SOFCs) are promising devices for fuel flexible and efficient power generation. The high temperatures (>700 oC) required enable operation on hydrocarbon fuels but avoiding degradation by carbon deposition remains a challenge. In operando optical methods, including Raman and Fourier Transform infrared emission spectroscopy (FTIRES) and near infrared thermal imaging (NIRTI), have been developed to characterize and understand molecular and material processes in SOFCs in order to improve their performance and durability. Recent results include studies of SOFCs on methane operating under various reforming conditions. Dry reforming, using carbon dioxide, which is also simulated biogas, reveals a high degree of anode activity based on substantial cooling of the anode but also reduced carbon formation compared to unreformed methane. An intermediate amount of anode cooling and carbon formation is observed with steam reforming. Related studies have been carried out to assess the effectiveness of carbon removal by steam and carbon dioxide using a new, duplex method in which NIRTI and FTIRES are performed simultaneously. Also, NIRTI has been used in conjunction with near ambient pressure X-ray photoelectron spectroscopy (APXPS) to identify spatially resolved regions where the emission intensity changes are observed due to ceria reduction during water electrolysis. The results are consistent with the APXPS results and interpretation for the reaction. The observations also provide an example of emissivity rather than temperature changes observed with high temperature thermal imaging in solid oxide electrochemical cells.

ChemInform Abstract: Regulation of Nonadiabatic Processes in the Photolysis of Some Carbonyl Compounds

AbstractReview: 83 refs.

Rovibrationally Excited Molecules on the Verge of a Triple Breakdown: Molecular and Roaming Mechanisms in the Photodecomposition of Methyl Formate.

For the photodissociation of the simplest of esters, methyl formate HCOOCH3, the energy threshold for triple fragmentation into H, CH3O, and CO was measured by previous ion-imaging experiments at a sequence of wavelengths. The translational energy features of product CO in the ground vibrational level (υ = 0) and for selected rotational states were characterized. In this integrated experimental and theoretical approach (i) the focus is at a laser energy barely below that threshold; (ii) Fourier-transform infrared emission spectroscopy measurements probe the rovibrational energy deposition in CO(υ) for υ > 0 and the emergence of the roaming phenomenon; (iii) accompanying quantum chemical calculations describe the selective rupture of bonds; and (iv) molecular dynamics simulations of dissociation are performed, introducing an approach explicitly involving outcomes from paths originated nonadiabatically through conical intersections. Quantitative information on energy disposal is provided: we found extensive vibrational excitation of CO, while rotational bands are colder and bimodal, due to contributions from direct and roaming modes.

Regulation of nonadiabatic processes in the photolysis of some carbonyl compounds.

Carbonyl compounds studied are confined to acetyl halide (CH3COCl), acetyl cyanide (CH3COCN), acetyl sulfide (CH3COSH), acetaldehyde (CH3CHO), and methyl formate (HCOOCH3). They are asymmetrically substituted, but do not follow the well-known Norrish type I reactions. Each compound ejected in an effusive beam at about 300 K is commonly excited to the (1)(n, π*)CO lower state; that is, a nonbonding electron on O of the C[double bond, length as m-dash]O group is promoted to the antibonding orbital of π*CO. The photolysis experiments are conducted in the presence of Ar gas and the corresponding fragments are detected using time-resolved Fourier-transform Infrared (FTIR) emission spectroscopy. The enhancement of the collision-induced internal conversion or intersystem crossing facilitates the dissociation channels via highly vibrational states of the ground singlet (So) or triplet (T1) potential energy surfaces. In this manner, an alternative nonadiabatic channel is likely to open yielding different products, even if the diabatic coupling strength is strong between the excited state and the neighboring state. For instance, the photodissociation of CH3COCl at 248 nm produces HCl, CO, and CH2 fragments, in contrast to the supersonic jet experiments showing dominance of the Cl fragment eliminated from the excited state. If the diabatic coupling strength is weak, dissociation proceeds mainly through internal conversion, such as the cases of CH3COCN and CH3COSH. The photodissociation of CH3COCN at 308 nm has never been reported before, while for CH3COSH matrix-isolated photodissociation was conducted that shows a distinct spectral feature from the current FTIR method. The CH3CHO and HCOOCH3 molecules belong to the same type of carbonyl compounds, in which the molecular products, CO + CH4 and CO + CH3OH, are produced through both transition state and roaming pathways. Their products are characterized differently between molecular beam and current FTIR experiments. For instance, the photodissociation of HCOOCH3 at 248 nm yields CO with the vibrational state v ≥ 4, in contrast to the molecular beam experiments producing CO at v = 1. The photodissociation of CH3CHO at 308 nm intensifies a low energy component in the CH4 vibrational distribution, thus verifying the transition state pathway for the first time.

The effect of graphene oxide and its oxidized debris on the cure chemistry and interphase structure of epoxy nanocomposites

The influence of graphene oxide (GO) and its surface oxidized debris (OD) on the cure chemistry of an amine cured epoxy resin has been investigated by Fourier Transform Infrared Emission Spectroscopy (FT-IES) and Differential Scanning Calorimetry (DSC). Spectral analysis of IR radiation emitted at the cure temperature from thin films of diglycidyl ether of bisphenol A epoxy resin (DGEBA) and 4,4'-diaminodiphenylmethane (DDM) curing agent with and without GO allowed the cure kinetics of the interphase between the bulk resin and GO to be monitored in real time, by measuring both the consumption of primary (1°) amine and epoxy groups, formation of ether groups as well as computing the profiles for formation of secondary (2°) and tertiary (3°) amines. OD was isolated from as-produced GO (aGO) by a simple autoclave method to give OD-free autoclaved GO (acGO). It has been found that the presence of OD on the GO prevents active sites on GO surfaces fully catalysing and participating in the reaction of DGEBA with DDM, which results in slower reaction and a lower crosslink density of the three-dimensional networks in the aGO-resin interphase compared to the acGO-resin interphase. We also determined that OD itself promoted DGEBA homopolymerization. A DSC study further confirmed that the aGO nanocomposite exhibited lower Tg while acGO nanocomposite showed higher Tg compared to neat resin because of the difference in crosslink densities of the matrix around the different GOs.

Toward a Working Mechanism of Fuel Oxidation in SOFCs: In Situ Optical Studies of Simulated Biogas and Methane

Solid-oxide fuel cells (SOFCs) have potential as highly efficient, clean, and sustainable electricity sources. However, the current, limited state of understanding of the complex electrochemical processes that occur at the anode in these systems, particularly those that lead to anode carbon formation and degradation, are roadblocks to effective cell design and operation. A suite of noninvasive, in situ optical techniques has been developed to help identify these processes. Vibrational Raman spectroscopy, Fourier-transform infrared emission spectroscopy (FTIRES), and near-infrared thermal (NIR) imaging, along with electrochemical measurements, provide surface and gas-phase molecular-specific diagnostics with the requisite temporal, spatial, and thermal resolution to correlate in operando observations with model chemical mechanisms associated with oxidation and carbon formation on Ni-based, anode-supported cells. This present work expands upon earlier in operando studies to fully assess the performance of commercially available Ni-YSZ anode SOFCs from 700 to 800 °C and to provide a more comprehensive description of the anode chemistry involved. Methane and simulated biogas (BG) are used as fuel. Raman measurements show that carbon grows minimally only at the lower operational temperatures for BG; however under methane, carbon formation occurs at all temperatures. Subsequent electrochemical oxidation of deposited carbon revealed that carbon formation under both fuels varies differently as a function of temperature. FTIRES measurements show that COx constituents increase with cell polarization only under methane fuel; this effect changes with temperature. NIR imaging indicates that the Ni anode surface cools significantly when cells are operated at 800 °C relative to 700 °C under BG, and only minimal cooling is observed when operating with methane.

Optical Studies of Dry and Wet Reformed Methane on Solid Oxide Fuel Cell Anodes

The presently limited understanding of solid oxide fuel cell (SOFC) anode mechanisms is due to a lack of experimental techniques that can probe species and component materials directly during operation, or in operando. Previous investigations on the efficiency of Ni-YSZ-based electrode materials in different reforming conditions have been performed using post-mortem and in situ electrochemical analyses with little information on specific mechanisms that lead to fuel oxidation and cell degradation. An ensemble of non-invasive optical methods consisting of near infrared thermal imaging (NIRTI), Raman spectroscopy, and Fourier-transform infrared emission spectroscopy (FTIRES) is utilized to correlate the chemistry of fuel oxidation and carbon formation with traditional electrochemical measurements for methane and simulated biogas fuels in operating SOFCs. Different reforming conditions for methane including plain, wet (steam), and dry (carbon dioxide) are investigated on anode- and electrolyte-supported cells. NIRTI results demonstrate that cooling on the anode surface due to endothermic hydrocarbon cracking for dry reforming or simulated biogas is significantly greater than for unreformed methane on both types of cells. Raman and FTIRES both show that more carbon is deposited with methane than with biogas. The small amount of carbon formed is limited to lower temperatures with simulated biogas whereas carbon formation occurs to a great extent at all temperatures with methane. Exhaust gas analysis with ex situ FTIR absorption measurements and mass spectrometry are combined with in operando measurements to further characterize and quantify the species involved. These findings serve as benchmark data for a better understanding of the mechanisms responsible for performance and degradation of SOFCs.

Communication: photodissociation of CH3CHO at 308 nm: observation of H-roaming, CH3-roaming, and transition state pathways together along the ground state surface.

Following photodissociation of acetaldehyde (CH3CHO) at 308 nm, the CO(v = 1-4) fragment is acquired using time-resolved Fourier-transform infrared emission spectroscopy. The CO(v = 1) rotational distribution shows a bimodal feature; the low- and high-J components result from H-roaming around CH3CO core and CH3-roaming around CHO radical, respectively, in consistency with a recent assignment by Kable and co-workers (Lee et al., Chem. Sci. 5, 4633 (2014)). The H-roaming pathway disappears at the CO(v ≥ 2) states, because of insufficient available energy following bond-breaking of H + CH3CO. By analyzing the CH4 emission spectrum, we obtained a bimodal vibrational distribution; the low-energy component is ascribed to the transition state (TS) pathway, consistent with prediction by quasiclassical trajectory calculations, while the high-energy component results from H- and CH3-roamings. A branching fraction of H-roaming/CH3-roaming/TS contribution is evaluated to be (8% ± 3%)/(68% ± 10%)/(25% ± 5%), in which the TS pathway was observed for the first time. The three pathways proceed concomitantly along the electronic ground state surface.

Roaming as the dominant mechanism for molecular products in the photodissociation of large aliphatic aldehydes.

Photodissociation of isobutyraldehyde (C3H7CHO) at 248 nm is investigated using time-resolved Fourier-transform infrared emission spectroscopy to demonstrate the growing importance of the roaming pathway with increasing molecular size of aliphatic aldehydes. Each acquired CO rotational distribution from v = 1 to 4 is well characterized by a single Boltzmann rotational temperature from 637 to 750 K, corresponding to an average rotational energy of 5.9 ± 0.6 kJ mol(-1). The roaming signature that shows a small fraction of CO rotational energy disposal accompanied by a vibrationally hot C3H8 co-fragment is supported by theoretical prediction. The energy difference between the tight transition state (TS) and the roaming saddle point (SP) is found to be -27, 4, 15, 22, and 30 kJ mol(-1) for formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde, and 2,2-dimethyl propanal, respectively. The roaming SP is stabilized by a larger alkyl moiety. It is suggested that the roaming photodissociation rate of aldehydes increasingly exceeds those via the tight TS, resulting in the dominance of the CO + alkane products, as the size of aldehydes becomes larger. Along with formaldehyde, acetaldehyde, and propionaldehyde, in this work isobutyraldehyde is further demonstrated that this aldehyde family with special functional group is the first case in the organic compound to follow predominantly a roaming dissociation pathway, as the molecular size becomes larger.

Reaction dynamics of O(¹D) + HCOOD/DCOOH investigated with time-resolved Fourier-transform infrared emission spectroscopy.

We investigated the reaction dynamics of O((1)D) towards hydrogen atoms of two types in HCOOH. The reaction was initiated on irradiation of a flowing mixture of O3 and HCOOD or DCOOH at 248 nm. The relative vibration-rotational populations of OH and OD (1 ≦ v ≦ 4, J ≤ 15) states were determined from time-resolved IR emission recorded with a step-scan Fourier-transform spectrometer. In the reaction of O((1)D) + HCOOD, the rotational distribution of product OH is nearly Boltzmann, whereas that of OD is bimodal. The product ratio [OH]/[OD] is 0.16 ± 0.05. In the reaction of O((1)D) + DCOOH, the rotational distribution of product OH is bimodal, but the observed OD lines are too weak to provide reliable intensities. The three observed OH/OD channels agree with three major channels of production predicted with quantum-chemical calculations. In the case of O((1)D) + HCOOD, two intermediates HOC(O)OD and HC(O)OOD are produced in the initial C-H and O-D insertion, respectively. The former undergoes further decomposition of the newly formed OH or the original OD, whereas the latter produces OD via direct decomposition. Decomposition of HOC(O)OD produced OH and OD with similar vibrational excitation, indicating efficient intramolecular vibrational relaxation, IVR. Decomposition of HC(O)OOD produced OD with greater rotational excitation. The predicted [OH]/[OD] ratio is 0.20 for O((1)D) + HCOOD and 4.08 for O((1)D) + DCOOH; the former agrees satisfactorily with experiments. We also observed the v3 emission from the product CO2. This emission band is deconvoluted into two components corresponding to internal energies E = 317 and 96 kJ mol(-1) of CO2, predicted to be produced via direct dehydration of HOC(O)OH and secondary decomposition of HC(O)O that was produced via decomposition of HC(O)OOH, respectively.

Photodissociation of CH3CHO at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Verification of roaming and triple fragmentation

By using time-resolved Fourier-transform infrared emission spectroscopy, the HCO fragment dissociated from acetaldehyde (CH3CHO) at 248 nm is found to partially decompose to H and CO. The fragment yields are enhanced by the Ar addition that facilitates the collision-induced internal conversion. The channels to CH2CO + H2 and CH3CO + H are not detected significantly. The rotational population distribution of CO, after removing the Ar collision effect, shows a bimodal feature comprising both low- and high-rotational (J) components, sharing a fraction of 19% and 81%, respectively, for the vibrational state v = 1. The low-J component is ascribed to both roaming pathway and triple fragmentation. They are determined to have a branching ratio of <0.13 and >0.06, respectively, relative to the whole v = 1 population. The CO roaming is accompanied by a highly vibrational population of CH4 that yields a vibrational bimodality.

In situ optical studies of methane and simulated biogas oxidation on high temperature solid oxide fuel cell anodes

Novel integration of in situ near infrared (NIR) thermal imaging, vibrational Raman spectroscopy, and Fourier-transform infrared emission spectroscopy (FTIRES) coupled with traditional electrochemical measurements has been used to probe chemical and thermal properties of Ni-based, solid oxide fuel cell (SOFC) anodes operating with methane and simulated biogas fuel mixtures at 800 °C. Together, these three non-invasive optical techniques provide direct insight into the surface chemistry associated with device performance as a function of cell polarization. Specifically, data from these complementary methods measure with high spatial and temporal resolution thermal gradients and changes in material and gas phase composition in operando. NIR thermal images show that SOFC anodes operating with biogas undergo significant cooling (ΔT = -13 °C) relative to the same anodes operating with methane fuel (ΔT = -3 °C). This result is general regardless of cell polarization. Simultaneous Raman spectroscopic measurements are unable to detect carbon formation on anodes operating with biogas. Carbon deposition is observable during operation with methane as evidenced by a weak vibrational band at 1556 cm(-1). This feature is assigned to highly ordered graphite. In situ FTIRES corroborates these results by identifying relative amounts of CO2 and CO produced during electrochemical removal of anodic carbon previously formed from an incident fuel feed. Taken together, these three optical techniques illustrate the promise that complementary, in situ methods have for identifying electrochemical oxidation mechanisms and carbon-forming pathways in high temperature electrochemical devices.