Electronic Circuit Simulations as a Tool to Understand Distorted Signals in Single-Entity Electrochemistry

Electrochemical analysis relies on precise measurement of electrical signals, yet the distortions caused by potentiostat circuitry and filtering are rarely addressed. Elucidation of these effects is essential for gaining insights behind sensitive low-current and short-duration electrochemical signals, e.g., in single-entity electrochemistry. We present a simulation approach utilizing the Electrical Simulation Program with Integrated Circuit Emphasis (SPICE), which is extensively used in electronic circuit simulations. As a proof-of-concept, we develop a universal electrical circuit model for single nanoparticle impact experiments, incorporating potentiostat and electronic filter circuitry. Considering these alterations, the experimentally observed transients of silver nanoparticle oxidation were consistently shorter and differently shaped than those predicted by established models. This reveals the existence of additional processes, e.g., migration, partial or asymmetric oxidation. These results highlight the SPICE approach’s ability to provide valuable insights into processes occurring during single-entity electrochemistry, which can be applied to various electrochemical experiments, where signal distortions are inevitable

Piece by Piece-Electrochemical Synthesis of Individual Nanoparticles and their Performance in ORR Electrocatalysis

The impact of individual HAuCl4 nanoreactors is measured electrochemically, which provides operando insights and precise control over the modification of electrodes with functional nanoparticles of well‐defined size. Uniformly sized micelles are loaded with a dissolved metal salt. These solution‐phase precursor entities are then reduced electrochemically—one by one—to form nanoparticles (NPs). The charge transferred during the reduction of each micelle is measured individually and allows operando sizing of each of the formed nanoparticles. Thus, particles of known number and sizes can be deposited homogenously even on nonplanar electrodes. This is demonstrated for the decoration of cylindrical carbon fibre electrodes with 25±7 nm sized Au particles from HAuCl4‐filled micelles. These Au NP‐decorated electrodes show great catalyst performance for ORR (oxygen reduction reaction) already at low catalyst loadings. Hence, collisions of individual precursor‐filled nanocontainers are presented as a new route to nanoparticle‐modified electrodes with high catalyst utilization

Facet-Dependent Intrinsic Activity of Single Co₃O₄ Nanoparticles for Oxygen Evolution Reaction

Deciphering the influence of nanocatalyst morphology on their catalytic activity in the oxygen evolution reaction (OER), the limiting reaction in water splitting process, is essential to develop highly active precious metal-free catalysts, yet poorly understood. The intrinsic OER activity of Co3O4 nanocubes and spheroids is probed at the single particle level to unravel the correlation between exposed facets, (001) vs. (111), and activity. Single cubes with predominant (001) facets show higher activity than multi-faceted spheroids. Density functional theory calculations of different terminations and reaction sites at (001) and (111) surfaces confirm the higher activity of the former, expressed in lower overpotentials. This is rationalized by a change in the active site from octahedral to tetrahedral Co and the potential-determining step from *OH to *O for the cases with lowest overpotentials at the (001) and (111) surfaces, respectively. This approach enables the identification of highly active facets to guide shape-selective syntheses of improved metal oxide nanocatalysts for water oxidation

Multimodal characterization of carbon electrodes\u27 thermal activation for vanadium redox flow batteries

Thermal activation has proven to be a valuable procedure to improve the performance of carbon electrodes in vanadium redox flow batteries (VRFBs). This work investigates how different activation temperatures impact the rayon-based carbon felt\u27s structure, surface composition, wettability, and electrochemical activity. A unique combination of non-standard techniques, including atomic force microscopy (AFM), dynamic vapor sorption (DVS), and electrochemical impedance spectroscopy (EIS) combined with the distribution of relaxation times (DRT) analysis, was used for the first time in the context of VRFB electrodes. The wettability of the carbon felts improved, and the process impedances decreased with higher activation temperatures. However, severe carbon decomposition occurs at high activation temperatures. The optimum electrochemical performance of the carbon felts in the vanadium(IV)/vanadium(V) redox reaction was observed after activation at 400 °C. Thus, we conclude that the optimum activation temperature for this type of carbon felt concerning the investigated properties is around 400 °C. Furthermore, we want to highlight the successful approach of using AFM, DVS, and EIS combined with DRT analysis for an integral investigation of key properties such as structure, wettability, and performance of VRFB electrodes

Electrochemical dealloying as a tool to tune the porosity, composition and catalytic activity of nanomaterials

Electrochemical dealloying as a post-Treatment can greatly improve the catalytic activity of nanoparticles. To date, selecting suitable conditions to reach desired porosity, composition and catalytic activity is based on trial-And-error-Attempts, due to insufficient understanding of the electrochemically induced morphological and compositional changes of the nanoparticles. These changes are elucidated here by combining electrochemistry with identical location electron microscopy analyses and linking them to the electrocatalytic properties of the obtained nanocatalysts. Using AgAu alloy nanoparticles and the hydrogen evolution reaction as a model system, the influence of cyclic voltammetry parameters on the catalytic activity upon electrochemical dealloying is investigated. Increasing the number of cycles initially results in a decreased Ag content and a sharp improvement in activity. Additional dealloying increases the nanoparticle porosity, while marginally altering their composition, due to surface motion of atoms. Since this is accompanied by particle aggregation, a decrease in catalytic activity results upon extensive cycling. This transition between porosity formation and particle aggregation marks the optimum for nanocatalyst post-production. The gained insights may aid speeding up the development of new materials by electrochemical dealloying as an easy-To-control post-processing route to tune the properties of existing nanoparticles, instead of having to alter usually delicate synthesis routes as a whole. © The Royal Society of Chemistry

Partikel für Partikel – elektrochemische Einschlagsexperimente zur Synthese oberflächenimmobilisierter Goldnanopartikel für die Elektrokatalyse

Wir demonstrieren die sukzessive elektrochemische Umsetzung einzelner HAuCl4-gefüllter Nanoreaktoren auf einer Kohlefaserelektrode zur Funktionalisierung mit Nanopartikeln (NP). Dabei können Größe und Anzahl der einzeln abgeschiedenen NP während des Prozesses kontrolliert werden. Zunächst werden Mizellen von enger Größenverteilung mit Metallsalz beladen. Der sporadische Einschlag dieser Mizellen auf einer polarisierten Elektrode führt zur Reduktion der Metallionen und es entsteht ein einzelner NP. Die während eines Einschlags übertragene Ladung wird gemessen und ermöglicht die operando‐Größenbestimmung des gebildeten NP. Wir zeigen dies für die Beladung von zylindrischen Kohlefaserelektroden mit 25±7 nm großen AuNP, die bereits bei niedrigen Katalysatorbeladungen eine hervorragende Leistung für die Sauerstoffreduktion (ORR) zeigen. Diese Form der Nanoeinschlagsmethode wird daher als neuer Weg zu nanopartikelmodifizierten Elektroden mit effektiver Katalys‐atorausnutzung vorgestellt

Исследование оптических свойств реконденсатов CCl4, полученных методом криоматричной изоляции

Объектом исследования являются тетрахлорметаан (четырёххлористый углерод) CCl4, которые были получены методом газофазной конденсации с матричным газом в различных концентрационных соотношениях с азотом и аргоном. Целью работы является изучение процессов формирования и эволюции свойств тонких пленок реконденсатов молекул фреона CCl4, образующихся в результате структурно-фазовых превращений и релаксационных процессов в твердых растворах исследуемых веществ при низких и сверхнизких температурах. Для достижения, были поставлены такие задачи: определить взаимосвязь между условиями криоосаждения и свойствами образующейся криоконденсированной пленки, а также изучить особенности криоконденсации тетрахлорометана и определить температуру стеклования образованных при низких температурах криопленок.The object of the study is carbon tetrachloride, which were obtained by gas-phase condensation with matrix gas in various concentration ratios with nitrogen and argon. The aim of the work is to study the processes of formation and evolution of the properties of thin films of recondensates of CCl4 freon molecules formed as a result of structural-phase transformations and relaxation processes in solid solutions of the studied substances at low and ultra-low temperatures. To achieve this, the following tasks were set: to determine the relationship between the conditions of cryopreservation and the properties of the resulting cryocondensated film, as well as to study the features of cryocondensation of tetrachloromethane and to determine the glass transition temperature of cryofilms formed

Nanoparticle impacts reveal magnetic field induced agglomeration and reduced dissolution rates.

Superparamagnetic nanoparticles (NPs) are used in a variety of magnetic field-assisted chemical and medical applications, yet little of their fate during magnetic field interrogation is known. Here, fundamental and new insights in this are gained by cathodic particle coulometry. This methodology is used to study individual Fe3O4 NPs in the presence and absence of a magnetic field. It is first noticed that no major NP agglomeration occurs in the absence of a magnetic field even in a suspension of high ionic strength. In contrast, a significant magnetic field-induced agglomeration of NPs is observed in a magnetic field. A second new finding is that the dissolution of Fe3O4 NPs is strongly inhibited in a magnetic field. This is explained as a result of the magnetic field gradient force trapping the released Fe(2+) ions near the surface of a magnetized Fe3O4 NP and thus hindering the mass-transport controlled NP dissolution. Consequently, fundamental magnetic field effects are measured and quantified on both the single NP scale and in suspension and two novel effects are discovered