110 research outputs found

    The Necessity for Multiscale In Situ Characterization of Tailored Electrocatalyst Nanoparticle Stability †

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    Tailored nanoparticles have opened up several exciting avenues to boost the activity and selectivity of structure-sensitive electrocatalytic reactions, such as the electrochemical carbon dioxide (CO2) reduction (eCO2RR). Colloidal chemistry provides the perfect toolbox to synthesize electrocatalyst nanoparticles on demand with atomic precision, in order to control and steer the electrocatalytic reactions of interest to the desired products. Not only does colloidal chemistry offer a means to prepare nanoparticles with well-defined sizes and shapes, it also allows easy deposition on any desired substrate (e.g., porous substrates) due to the solution processability. But what you see after synthesis with ex situ characterization techniques is not always what you get during the electrocatalytic reaction. Like any other electrocatalyst material, colloidal nanoparticles are prone to restructuring, and hence, the reaction output is altered due to destabilization of the electrocatalyst. This destabilization of the electrocatalyst nanoparticles is currently one of the major bottlenecks for the widespread implementation of electrocatalysts in the chemical industry. This calls for the necessary development and application of in situ characterization techniques to probe the morphology and composition of the tailored electrocatalyst nanoparticles over multiple length scales, in order to rationally design the next generation of stable electrocatalyst nanoparticles. Through detailed spatiotemporal in situ characterization, we can take full advantage of the possibilities that colloidal chemistry offers for electrocatalyst preparation with superior activity, selectivity, and stability. In this perspective, the necessity for in situ characterization of electrocatalyst nanoparticle stability is highlighted. For this purpose, first the progress of colloidal nanoparticles for electrocatalytic conversion reactions is briefly discussed, after which the focus shifts toward in situ characterization of the (in)stability of the tailored nanoparticles during the reaction of interest, ideally under industrially relevant conditions. This perspective shows that in situ characterization of electrocatalyst deactivation requires a multiscale approach, and that without combined in situ characterization we will remain blind to several aspects that are known to influence electrocatalyst performance

    In situ spectroscopy and diffraction to look inside the next generation of gas diffusion and zero-gap electrolyzers

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    Electrolyzers allow for the sustainable conversion of chemical waste (e.g. nitrous oxides, NOx, or carbon dioxide, CO2) into valuable chemicals or building blocks (e.g. ammonia or hydrocarbons). There is a constant search for new and improved materials (electrocatalysts) that can facilitate these complex chemical reactions with optimized activity, selectivity, and stability. In order for electrolyzers to become economically feasible, it is of utmost importance that they perform at high current density >100 mA/cm2 (activity), since this scales with chemical reaction rate. However, if high current density is only achieved for a short period of time (stability), the electrolyzer has to be regenerated, which is a costly endeavor. For this purpose, chemical engineers have focused on gas diffusion electrodes (GDE) or membrane electrode assemblies (MEA) in recent years, but these cell configurations are prone to rapid deactivation and salting. In situ spectroscopy and diffraction techniques can shed light on the parameters that influence catalyst (de)activation, but application of the technique of choice depends heavily on the reaction conditions and hence is not straightforwardly applied to electrolyzers that operate at high current density. This review addresses the recent developments within the community for in situ characterization of GDE and MEA electrolyzers, and opportunities for future studies are highlighted, which are aimed to stimulate discussion and advancement of the field

    Описание и генерация перестановок, содержащих циклы

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    Запропоновано загальний підхід до генерації перестановок, що містять цикли, на основі введених конструктивних засобів опису комбінаторних множин. Формулюються та розв’язуються різні задачі генерації перестановок заданого класу. Для опису перестановок, представлених у вигляді добутку заданої кількості циклів, вводиться комбінаторна множина. Для введеної множини будуються комбінаторний вид та відповідний твірний ряд. Наводяться приклади.The paper proposes a general approach to generating permutations that contain cycles, based on constructive tools introduced to describe combinatorial sets. Different generation problems for permutations of definite class are formulated and solved. A combinatorial set is introduced to define permutations represented as the multiplication of a definite number of cycles. For this set, combinatorial species and associated generating series are constructed. Examples are given

    Low-Variance Surface-Enhanced Raman Spectroscopy Using Confined Gold Nanoparticles over Silicon Nanocones

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    Surface-enhanced Raman spectroscopy (SERS) substrates are of utmost interest in the analyte detection of biological and chemical diagnostics. This is primarily due to the ability of SERS to sensitively measure analytes present in localized hot spots of the SERS nanostructures. In this work, we present the formation of 67 ± 6 nm diameter gold nanoparticles supported by vertically aligned shell-insulated silicon nanocones for ultralow variance SERS. The nanoparticles are obtained through discrete rotation glancing angle deposition of gold in an e-beam evaporating system. The morphology is assessed through focused ion beam tomography, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The optical properties are discussed and evaluated through reflectance measurements and finite-difference time-domain simulations. Lastly, the SERS activity is measured by benzenethiol functionalization and subsequent Raman spectroscopy in the surface scanning mode. We report a homogeneous analytical enhancement factor of 2.2 ± 0.1 × 107 (99% confidence interval for N = 400 grid spots) and made a comparison to other lithographically derived assemblies used in SERS. The strikingly low variance (4%) of our substrates facilitates its use for many potential SERS applications.All authors acknowledge the financial support by the Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), an NWO Gravitation programme. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 801359.Peer reviewe

    Overcoming the Exciton Binding Energy in Two-Dimensional Perovskite Nanoplatelets by Attachment of Conjugated Organic Chromophores

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    In this work we demonstrate a novel approach to achieve efficient charge separation in dimensionally and dielectrically confined two-dimensional perovskite materials. Two-dimensional perovskites generally exhibit large exciton binding energies that limit their application in optoelectronic devices that require charge separation such as solar cells, photo-detectors and in photo-catalysis. Here, we show that by incorporating a strongly electron accepting moiety, perylene diimide organic chromophores, on the surface of the two-dimensional perovskite nanoplatelets it is possible to achieve efficient formation of mobile free charge carriers. These free charge carriers are generated with ten times higher yield and lifetimes of tens of microseconds, which is two orders of magnitude longer than without the peryline diimide acceptor. This opens a novel synergistic approach, where the inorganic perovskite layers are combined with functional organic chromophores in the same material to tune the properties for specific applications. Functionalizing two-dimensional (2D) hybrid perovskites with organic chromophores is a novel approach to tune their optoelectronic properties. Here, the authors report efficient charge separation and conduction in 2D hybrid perovskite nanoplatelets by incorporating an electron acceptor chromophoreThis work has received funding from the European Research Council Horizon 2020 ERC Grant Agreement No. 648433

    Spatiotemporal Mapping of Local Heterogeneities during Electrochemical Carbon Dioxide Reduction

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    The activity and selectivity of a copper electrocatalyst during the electrochemical CO2 reduction reaction (eCO2RR) are largely dominated by the interplay between local reaction environment, the catalyst surface, and the adsorbed intermediates. In situ characterization studies have revealed many aspects of this intimate relationship between surface reactivity and adsorbed species, but these investigations are often limited by the spatial and temporal resolution of the analytical technique of choice. Here, Raman spectroscopy with both space and time resolution was used to reveal the distribution of adsorbed species and potential reaction intermediates on a copper electrode during eCO2RR. Principal component analysis (PCA) of the in situ Raman spectra revealed that a working electrocatalyst exhibits spatial heterogeneities in adsorbed species, and that the electrode surface can be divided into CO-dominant (mainly located at dendrite structures) and C-C dominant regions (mainly located at the roughened electrode surface). Our spectral evaluation further showed that in the CO-dominant regions, linear CO was observed (as characterized by a band at ∼2090 cm-1), accompanied by the more classical Cu-CO bending and stretching vibrations located at ∼280 and ∼360 cm-1, respectively. In contrast, in the C-C directing region, these three Raman bands are suppressed, while at the same time a band at ∼495 cm-1 and a broad Cu-CO band at ∼2050 cm-1 dominate the Raman spectra. Furthermore, PCA revealed that anodization creates more C-C dominant regions, and labeling experiments confirmed that the 495 cm-1 band originates from the presence of a Cu-C intermediate. These results indicate that a copper electrode at work is very dynamic, thereby clearly displaying spatiotemporal heterogeneities, and that in situ micro-spectroscopic techniques are crucial for understanding the eCO2RR mechanism of working electrocatalyst materials

    Alternative nano-lithographic tools for shell-isolated nanoparticle enhanced Raman spectroscopy substrates

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    Chemically synthesized metal nanoparticles (MNPs) have been widely used as surface-enhanced Raman spectroscopy (SERS) substrates for monitoring catalytic reactions. In some applications, however, the SERS MNPs, besides being plasmonically active, can also be catalytically active and result in Raman signals from undesired side products. The MNPs are typically insulated with a thin (∼3 nm), in principle pin-hole-free shell to prevent this. This approach, which is known as shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), offers many advantages, such as better thermal and chemical stability of the plasmonic nanoparticle. However, having both a high enhancement factor and ensuring that the shell is pin-hole-free is challenging because there is a trade-off between the two when considering the shell thickness. So far in the literature, shell insulation has been successfully applied only to chemically synthesized MNPs. In this work, we alternatively study different combinations of chemical synthesis (bottom-up) and lithographic (top-down) routes to obtain shell-isolated plasmonic nanostructures that offer chemical sensing capabilities. The three approaches we study in this work include (1) chemically synthesized MNPs + chemical shell, (2) lithographic substrate + chemical shell, and (3) lithographic substrate + atomic layer deposition (ALD) shell. We find that ALD allows us to fabricate controllable and reproducible pin-hole-free shells. We showcase the ability to fabricate lithographic SHINER substrates which report an enhancement factor of 7.5 × 103 ± 17% for our gold nanodot substrates coated with a 2.8 nm aluminium oxide shell. Lastly, by introducing a gold etchant solution to our fabricated SHINER substrate, we verified that the shells fabricated with ALD are truly pin-hole-free.</p

    How Temperature Affects the Selectivity of the Electrochemical CO2 Reduction on Copper

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    Copper is a unique catalyst for the electrochemical CO2 reduction reaction (CO2RR) as it can produce multi-carbon products, such as ethylene and propanol. As practical electrolyzers will likely operate at elevated temperatures, the effect of reaction temperature on the product distribution and activity of CO2RR on copper is important to elucidate. In this study, we have performed electrolysis experiments at different reaction temperatures and potentials. We show that there are two distinct temperature regimes. From 18 up to ∼48 °C, C2+ products are produced with higher Faradaic efficiency, while methane and formic acid selectivity decreases and hydrogen selectivity stays approximately constant. From 48 to 70 °C, it was found that HER dominates and the activity of CO2RR decreases. Moreover, the CO2RR products produced in this higher temperature range are mainly the C1 products, namely, CO and HCOOH. We argue that CO surface coverage, local pH, and kinetics play an important role in the lower-temperature regime, while the second regime appears most likely to be related to structural changes in the copper surface

    Low-Variance Surface-Enhanced Raman Spectroscopy Using Confined Gold Nanoparticles over Silicon Nanocones

    Get PDF
    Surface-enhanced Raman spectroscopy (SERS) substrates are of utmost interest in the analyte detection of biological and chemical diagnostics. This is primarily due to the ability of SERS to sensitively measure analytes present in localized hot spots of the SERS nanostructures. In this work, we present the formation of 67 ± 6 nm diameter gold nanoparticles supported by vertically aligned shell-insulated silicon nanocones for ultralow variance SERS. The nanoparticles are obtained through discrete rotation glancing angle deposition of gold in an e-beam evaporating system. The morphology is assessed through focused ion beam tomography, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The optical properties are discussed and evaluated through reflectance measurements and finite-difference time-domain simulations. Lastly, the SERS activity is measured by benzenethiol functionalization and subsequent Raman spectroscopy in the surface scanning mode. We report a homogeneous analytical enhancement factor of 2.2 ± 0.1 × 107 (99% confidence interval for N = 400 grid spots) and made a comparison to other lithographically derived assemblies used in SERS. The strikingly low variance (4%) of our substrates facilitates its use for many potential SERS applications
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