Nanotechnology is expected to open new avenues to fight and prevent disease using atomic scale tailoring of materials. Among the most promising nanomaterials with antibacterial properties are metallic nanoparticles, which exhibit increased chemical activity due to their large surface to volume ratios and crystallographic surface structure. The study of bactericidal nanomaterials is particularly timely considering the recent increase of new resistant strains of bacteria to the most potent antibiotics. This has promoted research in the well known activity of silver ions and silver-based compounds, including silver nanoparticles. The present work studies the effect of silver nanoparticles in the range of 1-100 nm on Gram-negative bacteria using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). Our results indicate that the bactericidal properties of the nanoparticles are size dependent, since the only nanoparticles that present a direct interaction with the bacteria preferentially have a diameter of approximately 1-10 nm.

https://iopscience.iop.org/article/10.1088/0957-4484/16/10/059/pdf

The bactericidal effect of silver nanoparticles

Advanced materials for electrocatalytic and photoelectrochemical water splitting are central to the area of renewable energy. In this work, we developed a selective solvothermal synthesis of MoS2 nanoparticles on reduced graphene oxide (RGO) sheets suspended in solution. The resulting MoS2/RGO hybrid material possessed nanoscopic few-layer MoS2 structures with an abundance of exposed edges stacked onto graphene, in strong contrast to large aggregated MoS2 particles grown freely in solution without GO. The MoS2/RGO hybrid exhibited superior electrocatalytic activity in the hydrogen evolution reaction (HER) relative to other MoS2 catalysts. A Tafel slope of ∼41 mV/decade was measured for MoS2 catalysts in the HER for the first time; this exceeds by far the activity of previous MoS2 catalysts and results from the abundance of catalytic edge sites on the MoS2 nanoparticles and the excellent electrical coupling to the underlying graphene network. The ∼41 mV/decade Tafel slope suggested the Volmer–Heyrovsky mec...

MoS2 Nanoparticles Grown on Graphene: An Advanced Catalyst for the Hydrogen Evolution Reaction

To date, copper is the only heterogeneous catalyst that has shown a propensity to produce valuable hydrocarbons and alcohols, such as ethylene and ethanol, from electrochemical CO2 reduction (CO2R). There are variety of factors that impact CO2R activity and selectivity, including the catalyst surface structure, morphology, composition, the choice of electrolyte ions and pH, and the electrochemical cell design. Many of these factors are often intertwined, which can complicate catalyst discovery and design efforts. Here we take a broad and historical view of these different aspects and their complex interplay in CO2R catalysis on Cu, with the purpose of providing new insights, critical evaluations, and guidance to the field with regard to research directions and best practices. First, we describe the various experimental probes and complementary theoretical methods that have been used to discern the mechanisms by which products are formed, and next we present our current understanding of the complex reaction networks for CO2R on Cu. We then analyze two key methods that have been used in attempts to alter the activity and selectivity of Cu: nanostructuring and the formation of bimetallic electrodes. Finally, we offer some perspectives on the future outlook for electrochemical CO2R.

/pdf/progress-and-perspectives-of-electrochemical-co2-reduction-hut0der0e7.pdf

Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte

The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited

Interfacial processes involving electrocatalytic evolution and oxidation of H2, and the role of chemisorbed H

ac Impedance of Faradaic reactions involving electrosorbed intermediates—I. Kinetic theory

A microfluidic fuel cell architecture incorporating flow-through porous electrodes is demonstrated. The design is based on cross-flow of aqueous vanadium redox species through the electrodes into an orthogonally arranged co-laminar exit channel, where the waste solutions provide ionic charge transfer in a membraneless configuration. This flow-through architecture enables improved utilization of the three-dimensional active area inside the porous electrodes and provides enhanced rates of convective/diffusive transport without increasing the parasitic loss required to drive the flow. Prototype fuel cells are fabricated by rapid prototyping with total material cost estimated at 2 USD/unit. Improved performance as compared to previous microfluidic fuel cells is demonstrated, including power densities at room temperature up to 131 mW cm-2. In addition, high overall energy conversion efficiency is obtained through a combination of relatively high levels of fuel utilization and cell voltage. When operated at 1 microL min-1 flow rate, the fuel cell produced 20 mW cm-2 at 0.8 V combined with an active fuel utilization of 94%. Finally, we demonstrate in situ fuel and oxidant regeneration by running the flow-through architecture fuel cell in reverse.

A microfluidic fuel cell with flow-through porous electrodes.

Membrane drying, fuel cell flooding, and anode catalyst poisoning by carbon monoxide are investigated on Hydrogenics production-type proton exchange membrane fuel cell (PEMFC) stacks similar to the stacks used in Hydrogenics HyPM 10-kW fuel cell power modules. Changes in fuel cell voltage and impedance with time are presented for each type of fault, the fuel cell stacks being controlled in galvanostatic mode. This study shows that these PEMFC stack faults can be differentiated by their impedance responses while fuel cell voltage monitoring alone is insufficient to distinguish between failure types. Membrane drying leads to an increase in the fuel cell impedance magnitude and phase angle at all frequencies studied. Fuel cell flooding leads to an increase in the impedance magnitude at low frequencies (f < 10 Hz) and to a decrease in the impedance phase angle at frequencies less than 100 Hz. Anode catalyst poisoning by CO is characterized by an increase in the fuel cell impedance magnitude at frequencies less than a few hundred Hz. For this fault, the impedance phase angle decreases within a large frequency range and is characterized by a minimum value appearing at 20-25 Hz at moderate current density.

Detection of Membrane Drying, Fuel Cell Flooding, and Anode Catalyst Poisoning on PEMFC Stacks by Electrochemical Impedance Spectroscopy

Behavior of overpotential—deposited species in Faradaic reactions—II. ac Impedance measurements on H2 evolution kinetics at activated and unactivated Pt cathodes

David A. Harrington

Papers

ac Impedance of Faradaic reactions involving electrosorbed intermediates—I. Kinetic theory

A microfluidic fuel cell with flow-through porous electrodes.

Detection of Membrane Drying, Fuel Cell Flooding, and Anode Catalyst Poisoning on PEMFC Stacks by Electrochemical Impedance Spectroscopy

Behavior of overpotential—deposited species in Faradaic reactions—II. ac Impedance measurements on H2 evolution kinetics at activated and unactivated Pt cathodes

Mechanism and equivalent circuits in electrochemical impedance spectroscopy