Identifying the intrinsic electrocatalytic activity of nanomaterials is challenging, as their characterization usually requires additives and binders whose contributions are difficult to dissect. Herein, we use nano impact electrochemistry as an additive-free method to overcome this problem. Due to the efficient mass transport at individual catalyst nanoparticles, high current densities can be realized. High-resolution bright-field transmission electron microscopy and selected area diffraction studies of the catalyst particles before and after the experiments provide valuable insights in the transformation of the nanomaterials during harsh oxygen evolution reaction (OER) conditions. We demonstrate this for 4 nm sized CoFe 2 O 4 spinel nanoparticles. It is revealed that these particles retain their size and crystal structure even after OER at current densities as high as several kA•m −2 . The steady-state current scales with the particle size distribution and is limited by the diffusion of produced oxygen away from the particle. This versatilely applicable method provides new insights into intrinsic nanocatalyst activities, which is key to the efficient development of improved and precious metal-free catalysts for renewable energy technologies.

Despite the frequent use of silver nanoparticles in consumer products and medical treatments, their reactivity and degradation in aqueous suspensions are still under debate. Here we elucidate this reactivity by an in situ opto- and spectro-electrochemical approach. Using dark-field microscopy coupled to a spectrophotometer and to an electrochemical cell, redox reactions of individual silver nanoparticles are studied in the presence of chloride. The intensity and spectral position of the plasmon resonance of an individual particle are tracked simultaneously in real time during cyclic voltammetry. They both change almost instantaneously with the detected current in a chemically reversible way. Thus, it is evidenced that the intensity decrease of the optical signal at the silver peak position is caused by the reversible formation of silver chloride and not by dissolution of silver. Moreover, at large positive potentials, further transformation to silver oxide or chlorite is revealed spectroscopically, although the electrochemical current is hidden by water and chloride oxidation. Thus, the combination of electrochemistry with dark-field microscopy and hyperspectral imaging is introduced as a new tool for real-time analysis of (electro-)chemical reactions of nanoparticles on a single-entity level.

Spherical bimetallic AgAu nanoparticles in the molar ratios 30:70, 50:50, and 70:30 with diameters of 30 to 40 nm were analyzed together with pure silver and gold nanoparticles of the same size. Dynamic light scattering (DLS) and differential centrifugal sedimentation (DCS) were used for size determination. Cyclic voltammetry (CV) was used to determine the nanoalloy composition, together with atomic absorption spectroscopy (AAS), energy-dispersive X-ray spectroscopy (EDX) and ultraviolet-visible (UV/Vis) spectroscopy. Underpotential deposition (UPD) of lead (Pb) on the particle surface gave information about its spatial elemental distribution and surface area. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were applied to study the shape and the size of the nanoparticles. X-ray powder diffraction gave the crystallite size and the microstrain. The particles form a solid solution (alloy) with an enrichment of silver on the nanoparticle surface, including some silver-rich patches. UPD indicated that the surface only consists of silver atoms.

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Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

The influence of CH3/CHF2/CF3-exchange on the molecular arrangement in the solid state of the low melting compounds α-toluene 1, (difluoromethyl)­benzene 2, and (trifluoromethyl)­benzene 3 was investigated by crystal structure determinations and theoretical calculations. The compounds were crystallized by in situ crystallization directly on the diffractometer and analyzed by X-ray diffraction. The crystal packing motifs were also analyzed based on ab initio quantum-chemical calculations of the intermolecular interaction energy, using the B97-D3/def2-TZVP method.

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Wird emonstrieren die sukzessive elektrochemische Umsetzung einzelner HAuCl 4 -gefüllter Nanoreaktoren auf einer Kohlefaserelektrode zur Funktionalisierung mit Nanopartikeln (NP). Dabei kçnnen Grçße und Anzahl der einzeln abgeschiedenen NP während des Prozesses kontrolliert werden. Zunächst werden Mizellenv on enger Grçßenverteilung mit Metallsalz beladen. Der sporadischeEinschlag 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 ermçglichtdie operando-Grçßenbestimmung des gebildeten NP. Wirz eigen dies fürd ie Beladung von zylindrischen Kohlefaserelektroden mit 25 AE 7nmg roßen AuNP,d ie bereits bei niedrigen Katalysatorbeladungen eine hervorragende Leistung fürd ie Sauerstoffreduktion (ORR) zeigen. Diese Form der Nanoeinschlagsmethode wird daher als neuer Wegz un anopartikelmodifizierten Elektroden mit effektiver Katalysatorausnutzung vorgestellt.