Interaction of Reactive Gases with Platinum Aerosol Particles at Room Temperature: Effects on Morphology and Surface Properties

Nanoparticles produced in technical aerosol processes exhibit often dendritic structures, composed of primary particles. Surprisingly, a small but consistent discrepancy was observed between the results of common aggregation models and in situ measurements of structural parameters, such as fractal dimension or mass-mobility exponent. A phenomenon which has received little attention so far is the interaction of agglomerates with admixed gases, which might be responsible for this discrepancy. In this work, we present an analytical series, which underlines the agglomerate morphology depending on the reducing or oxidizing nature of a carrier gas for platinum particles. When hydrogen is added to openly structured particles, as investigated by tandem differential mobility analysis (DMA) and transmission electron microscopy (TEM) analysis, Pt particles compact already at room temperature, resulting in an increased fractal dimension. Aerosol Photoemission Spectroscopy (APES) was also able to demonstrate the interaction of a gas with a nanoscaled platinum surface, resulting in a changed sintering behavior for reducing and oxidizing atmospheres in comparison to nitrogen. The main message of this work is about the structural change of particles exposed to a new environment after complete particle formation. We suspect significant implications for the interpretation of agglomerate formation, as many aerosol processes involve reactive gases or slightly contaminated gases in terms of trace amounts of unintended species.

Illustrating catalysis with a handmade molecular model set: catalytic oxidation of carbon monoxide over a platinum surface

Catalytic converters (automotive catalysts) and the chemical reactions they catalyze appear in general and introductory chemistry textbooks. Although the detailed mechanisms of the chemical reactions that occur in catalytic converters have been clearly revealed via recent developments in surface and computational chemistry research, the description and illustration of the catalysis are still ambiguous in textbooks. In this paper, we describe an extracurricular lecture whereby a handmade teaching aid was employed to illustrate the basic principle of the catalytic oxidation of carbon monoxide over platinum surface, which is an essential reaction occurring in catalytic converters. The teaching aid, constructed combining easily available materials, can illustrate the positions and motions of the molecules on the platinum surface during catalytic oxidation. The lecture was favorably received by non-chemistry majors and high school students. Despite the difficulty of the topic, the audience displayed a relatively high level of understanding.

An Atomistic View of Electrodics at the Platinum Surface

<div><div><div><p>Platinum (Pt) is a benchmarked catalyst for several electrochemical processes, however an atomistic insight into its electrodics at the electrode-electrolyte interface is still lacking. In this study, we aim to capture the chemical changes of Pt surfaces brought on by an applied potential in an electrolyte of pH~5, which can address the catalytic efficacy and stability of different crystallographic orientations under varying applied bias. Through a combined experimental and reactive molecular dynamics simulation approach, we uncover the effect of charge build up on the surface of the Pt electrode, which can be directed towards capacitive and faradaic processes. By introducing a simulated applied potential, which is compared to experimental potential by equating charge density ( in the range -0.2 mC/cm2 to 0.2 mC/cm2 ), we unravel the electrochemical processes on Pt (in slightly acidic pH). At reductive potentials of ~0.3-0.0 V vs RHE, we visualize phenomenon such as under potential hydrogen adsorption (HUPD) and hydrogen evolution/oxidation reaction. While oxidative potentials in the range ~1.2-1.6 V vs RHE see platinum oxide (Pt-O) formation, and platinum leaching off the surface. The theoretical potential and plane dependence of these phenomenon (HUPD, Pt-O, etc.) are verified with experiments, and hence it brings a new platform for computationally viable electrode-electrolyte studies.</p></div></div></div>

An Atomistic View of Electrodics at the Platinum Surface

<div><div><div><p>Platinum (Pt) is a benchmarked catalyst for several electrochemical processes, however an atomistic insight into its electrodics at the electrode-electrolyte interface is still lacking. In this study, we aim to capture the chemical changes of Pt surfaces brought on by an applied potential in an electrolyte of pH~5, which can address the catalytic efficacy and stability of different crystallographic orientations under varying applied bias. Through a combined experimental and reactive molecular dynamics simulation approach, we uncover the effect of charge build up on the surface of the Pt electrode, which can be directed towards capacitive and faradaic processes. By introducing a simulated applied potential, which is compared to experimental potential by equating charge density ( in the range -0.2 mC/cm2 to 0.2 mC/cm2 ), we unravel the electrochemical processes on Pt (in slightly acidic pH). At reductive potentials of ~0.3-0.0 V vs RHE, we visualize phenomenon such as under potential hydrogen adsorption (HUPD) and hydrogen evolution/oxidation reaction. While oxidative potentials in the range ~1.2-1.6 V vs RHE see platinum oxide (Pt-O) formation, and platinum leaching off the surface. The theoretical potential and plane dependence of these phenomenon (HUPD, Pt-O, etc.) are verified with experiments, and hence it brings a new platform for computationally viable electrode-electrolyte studies.</p></div></div></div>

Micrometer-sized electrically programmable shape-memory actuators for low-power microrobotics

Shape-memory actuators allow machines ranging from robots to medical implants to hold their form without continuous power, a feature especially advantageous for situations where these devices are untethered and power is limited. Although previous work has demonstrated shape-memory actuators using polymers, alloys, and ceramics, the need for micrometer-scale electro–shape-memory actuators remains largely unmet, especially ones that can be driven by standard electronics (~1 volt). Here, we report on a new class of fast, high-curvature, low-voltage, reconfigurable, micrometer-scale shape-memory actuators. They function by the electrochemical oxidation/reduction of a platinum surface, creating a strain in the oxidized layer that causes bending. They bend to the smallest radius of curvature of any electrically controlled microactuator (~500 nanometers), are fast (<100-millisecond operation), and operate inside the electrochemical window of water, avoiding bubble generation associated with oxygen evolution. We demonstrate that these shape-memory actuators can be used to create basic electrically reconfigurable microscale robot elements including actuating surfaces, origami-based three-dimensional shapes, morphing metamaterials, and mechanical memory elements. Our shape-memory actuators have the potential to enable the realization of adaptive microscale structures, bio-implantable devices, and microscopic robots.