Molten salt reactors (MSRs) have the potential to safely support green energy goals while meeting baseload energy needs with diverse energy portfolios. While reactor designers have made tremendous strides with these systems, licensing and deployment of these reactors will be aided through the development of new technology such as on-line and remote monitoring tools. Of particular interest is quantifying reactor off-gas species, such as iodine, within off-gas streams to support the design and operational control of off-gas treatment systems. Here, the development of advanced Raman spectroscopy systems for the on-line analysis of gas composition is discussed, focusing on the key control species I2(g). Signal response was explored with two Raman instruments, utilizing 532 and 671 nm excitation sources, as a function of I2(g) pressure and temperature. Also explored is the integration of advanced data analysis methods to enable real-time and highly accurate analysis of complex optical data. Specifically, the application of chemometric modeling is discussed. Raman spectroscopy paired with chemometric analysis is demonstrated to provide a powerful route to analyzing I2(g) composition within the gas phase, which lays the foundation for applications within molten salt reactor off-gas analysis and other significant chemical processes producing iodine species.
Rough electrochromic phosphotungstic acid (PWA) films were fabricated by spraying a gel of phosphotungstate anions with a molar ratio of P:W = 1:12 onto glass substrates precoated with transparent and electrically conducting SnO 2 :F at 300 °C. The analysis by X-ray photoelectron spectroscopy (XPS) determined that the P:W molar ratio in the films was approximately 1:14. Infrared spectroscopy (IR) and X-ray diffraction (XRD) showed that the film is a polycrystalline phosphotungstic acid. SEM micrographs showed that the films present a rough morphology based on fiber-shape bridges. Optoelectrochemical measurements demonstrated pronounced electrochromism in the PWA films upon H + intercalation/deintercalation with a high diffuse reflectance (R d) and transmittance (T d). We found for as-deposited films that R d /total reflectance (R t) and T d /total transmittance (T t) at 550 nm was around 0.83 and 0.68, respectively. This ratio decreases at bleached state to 0.74 and 0.41 for R d /R t and T d /T t , respectively.
The goals of this work were 1) to demonstrate lanthanum preconcentration/deposition on electrodes, 2) to elucidate the mechanism of deposition, and 3) to use electrodeposition to detect lanthanum on carbon fiber microelectrodes. Lanthanum was preconcentrated via electroprecipitation on carbon electrodes using unbuffered electrolyte. To measure the amount of La deposited on the surface, we used eQCM to observe the mass change (quantified as frequency change) while La precipitated on the surface of the electrode. The chemical state of the deposited film was determined using X-ray photoelectron spectrometry and Auger electron spectrometry. We used a pH microelectrode with a tip diameter of less than 20 μm near the electrode surface to determine surface pH changes. We found that lanthanum preconcentration on electrodes is a result of pH changes at the electrode surface due to water electrolysis. La(OH) 3 was determined to be the predominant state of the film, with La and O atoms colocalized in the precipitates. Based on this discovery, the current responses to lanthanum electroprecipitation on carbon fiber microelectrodes and a mercury-filmed carbon fiber microelectrode were compared. We found that both microelectrode responses were concentration-dependent.
Lanthanum can be detected using cathodic deposition followed by anodic stripping. The deposition process controls the detection limit. In this work, lanthanum deposition was characterized using an electrochemical quartz crystal microbalance (eQCM), and surface pH near the electrode surface was quantified using microelectrodes. The eQCM was used to correlate the lanthanum mass deposited on the electrode to the applied potential. Two different lanthanum responses were identified based on pH control. In the absence of pH control, the lanthanum film remained on the electrode surface until a large anodic potential was applied (1.8 V Ag/AgCl or greater). In the presence of pH control, the lanthanum film was stripped off immediately after the applied potential was greater than −2.0 V Ag/AgCl . When we measured surface pH near the electrode surface using needle-type microelectrodes, it was found that the pH near the surface increased from 4 to above the detection limit (>10), which indicated that the surface pH was responsible for the two different observed lanthanum responses despite the bulk pH being the same. This is the first study to use eQCM and needle-type microelectrodes to correlate lanthanum deposition with surface pH rather than bulk pH. The concentrations of lanthanum and other lanthanides are typically measured by depositing them as amalgams with mercury 1 or, more recently, mercury films 2 , followed by stripping. As early as 1915 3 , mercury pools were used as cathodes that replaced platinum and copper electrodes for the electrolysis of rare earth elements. The reason for this was the fouling of the cathode with insoluble hydroxides, in which the pH at the cathode surface was thought to play a critical role. Recently, similar concerns were raised for lanthanide deposition on mercury-filmed microelectrodes. 4 The authors claimed that pH was responsible for the stability of La deposition. The effect of pH is a consequence of electrolysis or electrochemistry in aqueous solution. Considering the generation of high currents (mA/cm 2 level) on small electrodes during metal deposition, it is expected that pH changes significantly near the electrode surface. Researchers generally control bulk pH, but the pH on an electrode surface has not previously been quantified because the technology for doing this was not available until the present day. Interest in lanthanides stems primarily from electroanalysis and the need for rapid methods of detection 2 and their chemical similarity to the actinides. 5In addition, the surface pH of deposited La films needs to be characterized in order for us to understand the deposition mechanism. Often, post-treatment analysis via inductively coupled plasma mass spectrometry is used successfully to identify the composition of electrochemically deposited films 6,7 or quantify the amount of material sequestered by the electrochemical method.2 However, transient processes such as the formation of pH gradients near an electrode surface during deposition limit the usefulness of post-treatm...
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