RESUMEN
In the past, neutron imaging has been the little brother of advanced neutron spectroscopy techniques due to its apparent simplicity. However, this simplicity allows the studying of complex chemical and electrochemical processes and related devices even under harsh reaction conditions such as high pressure, high temperature, corrosive and/or air sensitive environments. We review a number of highly relevant case studies as archetypal examples of modern energy technology; that is heat storage, power-to-X, batteries, fuel cells, and catalysis. The promising results trigger the further development of neutron imaging towards a chemical imaging method.
RESUMEN
Efficiency losses due to side reactions are one of the main challenges in battery development. Despite providing valuable insights, the results of standard analysis on the individual components cannot be simply extrapolated to the full operating system. Therefore, non-destructive, and high resolution approaches that allow the investigation of the full system are desired. Herein, we combined neutron radiography and tomography with electrical monitoring of the state of charge of commercial Ni-mischmetal hydride batteries, to track the exchange and transport of hydrogen under operating conditions. This non-destructive approach allowed both the quantification of the hydrogen distribution in the electrodes in 4D, and the distinction between the electrochemically exchanged hydrogen and the hydrogen gas pressure generated by side reactions, as a function of the applied potential and current. One of the most counter-intuitive observation is that the generation of hydrogen gas during discharge depends on the charging state of the battery. The results presented provide critical new insights in the mechanisms governing the electrochemical processes during Nimischmetal hydride battery operation, and also pave the way for the extrapolation of this approach to the investigation of state-of-the-art Li-ions batteries.
RESUMEN
Heterogeneous catalysts are materials with a complex structure at the atomic to mesoscopic scale, which depends on a variety of empirical parameters applied during preparation and processing. Although model systems clarified the general physical and chemical phenomena relevant to catalysis, such as hydrogen spillover, a rational design of heterogeneous catalysts is impeded by the sheer number of parameters. Combinatorial methods and high-throughput techniques have the potential of accelerating the development of optimal catalysts. We describe here a combinatorial approach based on hydrogen adsorption/absorption and hydrogen-deuterium exchange quantified by neutron imaging. The method coined CONI is capable of measuring more than 50 samples simultaneously. As a proof of concept, we study Pt catalyzed WO3 as an archetypal spillover system, and a Ni-catalyst supported on Al2O3 and SiO2. CONI is ideally suited to distinguish between irreversible surface adsorption and reversible bulk absorption, providing quantitative information. Concretely, CONI yields the number of reversibly adsorbed/absorbed hydrogen atoms in and on a great number of various catalysts in a single experiment.
RESUMEN
The kinetics of most of chemical energy storage and conversion processes is rate-limited by the mass transport through matter. There is an uncertainty on the corresponding kinetic models, especially if based solely on kinetic theory. Henceforth analytical strategies coupled to setups, in order to capture data for overcoming this limitation are essential. Operando chemical imaging of the kinetics process supports the identification of rate-limiting barriers and definition of actionable kinetic insights. After an overview of the chemical and physical processes in various energy storage/conversion systems, and examples of chemical imaging applied on them, analytical challenges are discussed with particular focus on novel methods and fundamental limitations. Despite convincing success technologies, various scientific challenges of operando chemical kinetics await solution. Apart from technical improvements of the analysis instrumentation, promising developments are seen in advanced digital science.
RESUMEN
Understanding hydrocarbon generation in the zeolite-catalysed conversions of methanol and methyl chloride requires advanced spectroscopic approaches to distinguish the complex mechanisms governing C-C bond formation, chain growth and the deposition of carbonaceous species. Here operando photoelectron photoion coincidence (PEPICO) spectroscopy enables the isomer-selective identification of pathways to hydrocarbons of up to C14 in size, providing direct experimental evidence of methyl radicals in both reactions and ketene in the methanol-to-hydrocarbons reaction. Both routes converge to C5 molecules that transform into aromatics. Operando PEPICO highlights distinctions in the prevalence of coke precursors, which is supported by electron paramagnetic resonance measurements, providing evidence of differences in the representative molecular structure, density and distribution of accumulated carbonaceous species. Radical-driven pathways in the methyl chloride-to-hydrocarbons reaction(s) accelerate the formation of extended aromatic systems, leading to fast deactivation. By contrast, the generation of alkylated species through oxygenate-driven pathways in the methanol-to-hydrocarbons reaction extends the catalyst lifetime. The findings demonstrate the potential of the presented methods to provide valuable mechanistic insights into complex reaction networks.