Metallic zinc (Zn) has been regarded as an ideal anode material for aqueous batteries because of its high theoretical capacity (820 mA h g), low potential (-0.762 V versus the standard hydrogen electrode), high abundance, low toxicity and intrinsic safety. However, aqueous Zn chemistry persistently suffers from irreversibility issues, as exemplified by its low coulombic efficiency (CE) and dendrite growth during plating/ stripping, and sustained water consumption. In this work, we demonstrate that an aqueous electrolyte based on Zn and lithium salts at high concentrations is a very effective way to address these issues. This unique electrolyte not only enables dendrite-free Zn plating/stripping at nearly 100% CE, but also retains water in the open atmosphere, which makes hermetic cell configurations optional. These merits bring unprecedented flexibility and reversibility to Zn batteries using either LiMnO or O cathodes-the former deliver 180 W h kg while retaining 80% capacity for >4,000 cycles, and the latter deliver 300 W h kg (1,000 W h kg based on the cathode) for >200 cycles.

Using molecular dynamics simulations, small-angle neutron scattering, and a variety of spectroscopic techniques, we evaluated the ion solvation and transport behaviors in aqueous electrolytes containing bis(trifluoromethanesulfonyl)imide. We discovered that, at high salt concentrations (from 10 to 21 mol/kg), a disproportion of cation solvation occurs, leading to a liquid structure of heterogeneous domains with a characteristic length scale of 1 to 2 nm. This unusual nano-heterogeneity effectively decouples cations from the Coulombic traps of anions and provides a 3D percolating lithium-water network, via which 40% of the lithium cations are liberated for fast ion transport even in concentration ranges traditionally considered too viscous. Due to such percolation networks, superconcentrated aqueous electrolytes are characterized by a high lithium-transference number (0.73), which is key to supporting an assortment of battery chemistries at high rate. The in-depth understanding of this transport mechanism establishes guiding principles to the tailored design of future superconcentrated electrolyte systems.

Neutron reflectometry measurements show that lamellar structures composed of thin alternating water-rich and Nafion-rich layers exist at the interface between SiO 2 and the hydrated Nafion film. Lamellae thickness and number of layers increase with humidity. Some lamellae remain in the film after dehydration. Multilayer lamellae are not observed for Nafion on Au or Pt surfaces. Instead, a thin partially hydrated single interfacial layer occurs and decreases in thickness to a few angstroms as humidity is reduced to zero. The absorption isotherm of the rest of the Nafion film is similar to that of bulk Nafion for all three surfaces investigated. The observed interfacial structures have implications for the performance, reliability, and improvements of fuel cell proton exchange membranes and membrane electrode assemblies.

Designing materials to function in harsh environments, such as conductive aqueous media, is a problem of broad interest to a range of technologies, including energy, ocean monitoring and biological applications. The main challenge is to retain the stability and morphology of the material as it interacts dynamically with the surrounding environment. Materials that respond to mild stimuli through collective phase transitions and amplify signals could open up new avenues for sensing. Here we present the discovery of an electric-field-driven, water-mediated reversible phase change in a perovskite-structured nickelate, SmNiO. This prototypical strongly correlated quantum material is stable in salt water, does not corrode, and allows exchange of protons with the surrounding water at ambient temperature, with the concurrent modification in electrical resistance and optical properties being capable of multi-modal readout. Besides operating both as thermistors and pH sensors, devices made of this material can detect sub-volt electric potentials in salt water. We postulate that such devices could be used in oceanic environments for monitoring electrical signals from various maritime vessels and sea creatures.

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The total accumulated charge collected from test points b-i can be viewed as Supplemental Figure 1. As such, the charge per unit area in test point b represents only the charge collected at b; each successive test point contains the sum of charge collected at all previous test points in addition to the current test point.Supporting Figure 1: Charge Accumulation as a function of test point. Ex Situ Characterization of the SEI Layer: Sample PreparationUpon completion of in situ testing and associated radiation screening (approximately 60 days after NR experiments), cells were disassembled in a glovebox with atmospheric specifications as stated in the methods section. The working electrodes with SEI were rinsed with diethyl carbonate, DEC, and dried.

Neutron reflectometry analysis methods for under-determined, multi-layered structures are developed and used to determine the composition depth profile in cases where the structure is not known a priori. These methods, including statistical methods, sophisticated fitting routines, and coupling multiple data sets, are applied to hydrated and dehydrated Nafion nano-scaled films with thicknesses comparable to those found coating electrode particles in fuel cell catalyst layers. These results confirm the lamellar structure previously observed on hydrophilic substrates, and demonstrate that for hydrated films they can accurately be described as layers rich in both water and sulfonate groups alternating with water-poor layers containing an excess of fluorocarbon groups. The thickness of these layers increases slightly and the amplitude of the water volume fraction oscillation exponentially decreases away from the hydrophilic interface. For dehydrated films, the composition oscillations die out more rapidly. The Nafion-SiO2 substrate interface contains a partial monolayer of sulfonate groups bonded to the substrate and a large excess of water compared to that expected by the water-to-sulfonate ratio, λ, observed throughout the rest of the film. Films that were made thin enough to truncate this lamellar region showed a depth profile nearly identical to thicker films, indicating that there are no confinement or surface effects altering the structure. Comparing the SLD profile measured for films dried at 60 °C to modeled composition profiles derived by removing water from the hydrated lamellae suggests incomplete re-mixing of the polymer groups upon dehydration, indicated limited polymer mobility in these Nafion thin films.

An elastic neutron scattering instrument, the advanced neutron diffractometer/reflectometer ͑AND/R͒, has recently been commissioned at the National Institute of Standards and Technology Center for Neutron Research. The AND/R is the centerpiece of the Cold Neutrons for Biology and Technology partnership, which is dedicated to the structural characterization of thin films and multilayers of biological interest. The instrument is capable of measuring both specular and nonspecular reflectivity, as well as crystalline or semicrystalline diffraction at wave-vector transfers up to approximately 2.20 Å −1 . A detailed description of this flexible instrument and its performance characteristics in various operating modes are given.