The activity of heterogeneous catalysts-which are involved in some 80 per cent of processes in the chemical and energy industries-is determined by the electronic structure of specific surface sites ...that offer optimal binding of reaction intermediates. Directly identifying and monitoring these sites during a reaction should therefore provide insight that might aid the targeted development of heterogeneous catalysts and electrocatalysts (those that participate in electrochemical reactions) for practical applications. The invention of the scanning tunnelling microscope (STM) and the electrochemical STM promised to deliver such imaging capabilities, and both have indeed contributed greatly to our atomistic understanding of heterogeneous catalysis. But although the STM has been used to probe and initiate surface reactions, and has even enabled local measurements of reactivity in some systems, it is not generally thought to be suited to the direct identification of catalytically active surface sites under reaction conditions. Here we demonstrate, however, that common STMs can readily map the catalytic activity of surfaces with high spatial resolution: we show that by monitoring relative changes in the tunnelling current noise, active sites can be distinguished in an almost quantitative fashion according to their ability to catalyse the hydrogen-evolution reaction or the oxygen-reduction reaction. These data allow us to evaluate directly the importance and relative contribution to overall catalyst activity of different defects and sites at the boundaries between two materials. With its ability to deliver such information and its ready applicability to different systems, we anticipate that our method will aid the rational design of heterogeneous catalysts.
Heterogeneous electrocatalysis plays a central role in the development of sustainable, carbon-neutral pathways for energy provision and the production of various chemicals. It determines the overall ...efficiency of electrochemical devices that involve catalysis at the electrode/electrolyte interface. In this perspective, we discuss key aspects for the identification of active centers at the surface of electrocatalysts and important factors that influence them. The role of the surface structure, nanoparticle shape/size and the electrolyte composition in the resulting catalytic performance is of particular interest in this work. We highlight challenges that from our point of view need to be tackled, and provide guidelines for the design of "real life" electrocatalysts for renewable energy provision systems as well as for the production of industrially important compounds.
In this perspective, key aspects for the identification, design and optimization of active centers at the surface of electrocatalysts are analyzed.
Mesoporous carbons are highly porous materials, which show large surface area, chemical inertness and electrochemical performances superior to traditional carbon material. In this study, we report ...the preparation of nitrogen-doped and undoped mesoporous carbons by an optimized hard template procedure employing silica as template, sucrose and ammonia as carbon and nitrogen source, respectively. Surface area measurements assert a value of 900 and 600 m2 g–1 for the best doped and undoped samples, respectively. Such supports were then thoroughly characterized by surface science and electron microscopy tools. Afterward, they were decorated with Pt and Pd nanoparticles, and it was found that the presence of nitrogen defects plays a significant role in improving the metal particles dimension and dispersion. In fact, when doped supports are used, the resulting metal nanoparticles are smaller (2–4 nm) and less prone to aggregation. Photoemission measurements give evidence of a binding energy shift, which is consistent with the presence of an electronic interaction between nitrogen atoms and the metal nanoparticles, especially in the case of Pd. The catalytic properties of electrodes decorated with such catalyst/support systems were investigated by linear sweep voltammetry and by rotating disk electrode measurements, revealing excellent stability and good activity toward oxygen reduction reaction (ORR). In particular, although Pd nanoparticles always result in lower activity than Pt ones, both Pt and Pd electrodes based on the N-doped supports show an increased activity toward ORR with respect to the undoped ones. At the same mass loading, the Tafel slope and the stability test of the Pt@N-doped electrocatalysts indicate superior performances to that of a commercial Pt@C catalysts (30 wt % Pt on Vulcan XC-72, Johnson Matthey).
•A practical method to determine mass sensitivity of ring-shaped electrode QCM using electrodeposition.•The QCM resonators with modified electrode structure improved the mass sensitivity.•The ...modified electrode QCM resonators can be effectively used in electrochemical processes.•Effect of electrode thicknesses on the mass sensitivity of ring and disc electrodes.•Mass sensitivity of the ring electrodes is higher than those of the disc electrodes.
A practical method for calculating the mass sensitivity of quartz crystal microbalance (QCM) resonators with ring-shaped Au electrodes on one side based on electrodeposition is presented in this communication. While for standard QCMs, an average mass sensitivity can be calculated despite its approximately Gaussian distribution, the mass sensitivity of QCMs with an asymmetrical electrode structure is difficult to calculate. However, non-standard electrode geometries might be beneficial for sensor applications especially in the area of electrochemistry. By measuring the resonance frequency change of a quartz crystal during deposition and applying Faraday’s law, we determined the mass sensitivity of QCM resonators with a ring electrode. We also studied the influence of the gold electrode thicknesses on the mass sensitivity of the ring-shaped and disc shaped electrodes. The experimental results showed that the mass sensitivity of the ring-shaped electrodes was 5%∼20% higher than those of the disc shaped electrodes. This method is practical and convenient for determining the mass sensitivity of the QCM with ring electrode, and it can be extended to measure QCMs with symmetrical and asymmetrical electrode structures. Such resonators with modified electrode structures may be of interest for studying electrochemical processes where a higher mass sensitivity is desirable.
Na-ion batteries have recently attracted great attention regarding their application in large-scale energy storage systems. Among different types of electrode materials for those classes of ...batteries, so-called Prussian blue analogues (PBAs) are among the very attractive ones due to their comparatively simple and low-cost methods of synthesis coupled with a promising cycle performance. In this study, one of the state-of-the-art PBA battery materials, namely electrodeposited Na2NiFe(CN)6 (NiHCF) thin films, were tested under simulated battery conditions in aqueous and mixed (H2O/organic) electrolytes. Prolonged stability tests in aqueous electrolytes were performed together with in-operando electrochemical AFM monitoring. It is demonstrated that degradation of this material is not associated with noticeable morphological changes (mechanical stress) but is likely caused by changes in the chemical composition of the films. Intercalation and deintercalation reversibility of Na+ and thin film stability in aqueous electrolytes appear to be unaffected negatively by changes in the pH to values below 7. However, the films showed unstable behavior in basic media (pH > 10). The increase of the content of acetonitrile, which was used as an additive to simulate the influence of antifreezes in aqueous electrolytes, appears to primarily affect the deintercalation of Na ions in Na2SO4-based aqueous electrolytes.
Access to haptic technology is on the rise, in smartphones, virtual reality gear, and open-source education kits. However, engineers and interaction designers are often inexperienced in designing ...with haptics, and rarely have tools and guidelines for creating multisensory experiences. To examine the impact of this deficit, we supplied a haptic design kit, custom software, and technical support to nine teams (25 students) for an innovation challenge at a major haptics conference. Teams (predominantly undergraduate engineers with little haptics, interaction design, or education training) designed and built haptic environments to support learning of science topics. Qualitative analysis of surveys, interviews, team blogs, and expert assessments of teams' final demonstrations exposed three themes in these design efforts. 1) Novice teams tended to ignore many of ten design choices that experts navigate, such as explicitly choosing whether haptic and graphic feedback should reinforce versus complement one other. 2) Their design activities differed in timing and inclusion from the ten activities observed in expert process. 3) We identified three success strategies in how teams devised useful and engaging interactions and interpretable multimodal experiences, and communicated about their designs. We compare novice and expert design needs and highlight where future haptic design tools and theory need to support novice practice and training.
•Comparison of absolute mass sensitivity of ring QCM and standard QCM using electrodeposition;•The ring QCM resonators improved the absolute mass sensitivity;•Changing the design of QCM electrode ...structure is an important way to improve absolute mass sensitivity.
In this work, we experimentally measured the absolute mass sensitivity of quartz crystal microbalance (QCM) resonators with one ring electrode on the sensing side and compared it to standard QCM resonators with disc electrodes on both sides using electrodeposition. This method allows to compare the absolute mass sensitivity of a ring electrode QCM and standard QCM resonators. The results showed that the average absolute mass sensitivity of a QCM resonator with a ring electrode on one side and a disc electrode on the other side is larger than the one of standard resonators with disc electrodes on both sides. If the ring electrode is facing the electrolyte, the absolute mass sensitivity is 10.28% higher, and for the disc electrode side it is still 5.33% higher. This shows that the ring electrode geometry improves the absolute mass sensitivity in comparison to a standard electrode structure, and therefore reveals a path to improve QCM detection sensitivity in electrochemical research.
The antimicrobial activity of silver has attracted significant research interest and contributes to an exponentially growing use of this noble metal in commodity products. In this investigation, we ...describe a general approach to increase the antimicrobial activity of a silver‐containing surface by two to three orders of magnitude. The use of 1–2‐nm silver particles decorating the surface of 20–50‐nm carrier particles consisting of a phosphate‐based, biodegradable ceramic allows the triggered release of silver in the presence of a growing microorganism. This effect is based on the organism's requirements for mineral uptake during growth creating a flux of calcium, phosphate, and other ions to the organism. The growing micro‐organism dissolves the carrier containing these nutrients and thereby releases the silver nanoparticles. Further, we demonstrate the rapid self‐sterilization of polymer surfaces containing silver on calcium phosphate nanoparticles using a series of human pathogens. Colony‐forming units (viable bacteria or fungi counts) have been routinely reduced below detection limit and suggest application of these self‐sterilizing surfaces in hospital environments, food and pharmaceutical processing, and personal care.
Self‐sterilizing surfaces. Based on a detailed study of the mechanism of silver release in antimicrobial coatings, the activity of silver is improved by two to three orders of magnitude. Using the metabolism of growing bacteria as a trigger, polymer surfaces are designed that release silver nanoparticles only when required or stimulated by the presence of microorganism (see figure).
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