Hydrogen sensors and hydrogen-activated switches were fabricated from arrays of mesoscopic palladium wires. These palladium "mesowire" arrays were prepared by electrodeposition onto graphite surfaces and were transferred onto a cyanoacrylate film. Exposure to hydrogen gas caused a rapid (less than 75 milliseconds) reversible decrease in the resistance of the array that correlated with the hydrogen concentration over a range from 2 to 10%. The sensor response appears to involve the closing of nanoscopic gaps or "break junctions" in wires caused by the dilation of palladium grains undergoing hydrogen absorption. Wire arrays in which all wires possessed nanoscopic gaps reverted to open circuits in the absence of hydrogen gas.

n electrical energy storage science, "nano" is big and getting bigger. One indicator of this increasing importance is the rapidly growing number of manuscripts received and papers published by ACS Nano in the general area of energy, a category dominated by electrical energy storage. In 2007, ACS Nano's first year, articles involving energy and fuels accounted for just 1.6% of the journal's 64 papers published (we published just one paper!), whereas in 2017, the fraction was over 10% of the 1296 publications (149 papers). Moreover, 6 of the 10 most-cited papers published in ACS Nano between 2013 and 2017 deal with energy-related topics.Among other impacts, "nano" has enabled electrically insulating pseudocapacitive materials, like transition-metal oxides, to be used more efficiently in both batteries and capacitors. 1 There are increasing numbers of new electrode materials (e.g., transition−metal oxides, hydroxides, sulfides, carbides, nitrides, conducting polymers, etc.) that display electrochemical characteristics that are neither purely capacitive nor purely Faradaic. The introduction of these new materials has contributed to blurring of the distinctions between these two fundamentally different energy-storage modalities, leading to confusion for both readers and authors. We are not the only ones grappling with this issue. Recent papers quantitatively discuss the differences between true electrochemical capacitors, pseudocapacitors, and batteries. 2,3 The purpose of this editorial is to sharpen the distinction using a short list of criteria already outlined in these papers, 2,3 so that we are all speaking the same language.

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

Metallic molybdenum (Mo(o)) wires with diameters ranging from 15 nanometers to 1.0 micrometers and lengths of up to 500 micrometers (0.5 millimeters) were prepared in a two-step procedure. Molybdenum oxide wires were electrodeposited selectively at step edges and then reduced in hydrogen gas at 500 degrees C to yield Mo(o). The hemicylindrical wires prepared by this technique were self-uniform, and the wires prepared in a particular electrodeposition (in batches of 10(5) to 10(7)) were narrowly distributed in diameter. Wires were obtained size selectively because the mean wire diameter was directly proportional to the square root of the electrolysis time. The metal nanowires could be embedded in a polystyrene film and lifted off the graphite electrode surface. The conductivity and mechanical resiliency of individual embedded wires were similar to those of bulk molybdenum.

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The electrodeposition of metal onto a low energy electrode surface like graphite or H-terminated silicon produces mesoscopic metal particles that are broadly distributed in diameter. Broad size distributions are observed even in cases where the nucleation of metal is temporally controlled. For this reason, electrodeposition has been infrequently used as a means for obtaining metal nanostuctures. The central problem is the diffusional "cross-talk" that exists between neighboring metal nanostructures on the electrode surface. Evidence for this diffusional interparticle coupling is encoded into particle size and position distributions obtained from experimental data and from Brownian Dynamics computer simulations of nanostructure growth. Diffusional cross-talk between nanostructures can be turned off using either of two growth strategies described in this paper. These methods permit the size-selective electrodeposition of metal nanoparticles and nanowires that are narrowly distributed in diameter.

Although Li-ion batteries have emerged as the battery of choice for electric vehicles and large-scale smart grids, significant research efforts are devoted to identifying materials that offer higher energy density, longer cycle life, lower cost, and/or improved safety compared to those of conventional Li-ion batteries based on intercalation electrodes. By moving beyond intercalation chemistry, gravimetric capacities that are 2–5 times higher than that of conventional intercalation materials (e.g., LiCoO2 and graphite) can be achieved. The transition to higher-capacity electrode materials in commercial applications is complicated by several factors. This Review highlights the developments of electrode materials and characterization tools for rechargeable lithium-ion batteries, with a focus on the structural and electrochemical degradation mechanisms that plague these systems.

Platinum nanocrystals were deposited on basal plane oriented graphite surfaces from dilute (1.0 mM) PtCl 6 2-containing electrolytes using a pulsed potentiostatic method. The deposition of platinum nanocrystals occurred via an instantaneous nucleation and diffusion-limited growth mechanism which resulted in narrow particle size distributions (relative standard deviation <35%) for mean crystallite diameters smaller than 40 Å. The number of particles per unit area on these surfaces was 10 9 -10 10 cm -2 . Noncontact atomic force microscopy images reveal that platinum nanocrystals nucleated both at defect sitesssuch as step edgessand on apparently defect-free regions of the atomically smooth graphite basal plane. Using electron transparent graphite surfaces, selected area electron diffraction analyses revealed that the structure of deposited platinum nanocrystals was fcc with a lattice constant that was indistinguishable from bulk fcc platinum. Platinum nanocrystals were not epitaxially oriented on the graphite basal plane surface.