Surfaces and interfaces determine the performance and long-term durability of solid-oxide fuel cells (SOFCs). In most cases, the surface chemical composition of the materials used in these electrochemical energy conversion devices shows significant deviations from the bulk chemistry. This might be as a result of surface cation segregation processes, as well as long-term surface poisoning due to external impurities. Both processes have implications for the electrochemical performance of the devices, leading to the degradation of the cell components. In order to suppress this degradation, an effort to lower the operation temperature to 500–800°C has been made. This article provides an overview of present research progress related to surface segregation and poisoning for low-temperature SOFCs.

Markets for energy storage that go beyond portable electronics have emerged rapidly this decade, including powering electric vehicles and “leveling the grid” fed by renewable sources such as solar energy, which are intermittent in supply. These new demands require a significant step-up in energy density that will probably not be met by Li-ion batteries; estimates suggest they are starting to approach their theoretical limits. But in the world of “beyond Li-ion,” the options are limited. One of the most hopeful is the Li-S battery, for which greater energy storage can potentially be realized through phase-transformation chemistry using elemental sulfur as a positive electrode material, which converts to lithium sulfide. These future generation systems offer up to a five-fold increased specific energy and greatly reduced cost factors, but commercialization has been hindered owing to key challenges. Efforts over the last two years to better manipulate the cell chemistry and overcome these challenges are presented.

The primary objective of this article is twofold: to address the key concept of topology that impacts materials science in a major way and to convey the excitement to the materials community of recent significant advances in our understanding of the important topological notions in a wide class of materials with potential technological applications. A paradigm of topology/geometry → property → functionality is emerging that goes beyond the traditional microscopic structure → property → functionality relationship. The new approach delineates the active roles of topology and geometry in design, fabrication, characterization, and predictive modeling of novel materials properties and multifunctionalities. After introducing the essentials of topology and geometry, we elucidate these concepts through a gamut of nanocarbon allotropes of de novo carbons, hierarchical self-assembled soft- and biomaterials, supramolecular assemblies, and nanoporous materials. Applications of these topological materials range from sensing, energy storage/conversion, and catalysis to nanomedicine.

The study of water’s functional role on hydrophilic surfaces of biological and soft materials benefits from experimental measurements that operate at finer length and time scales than contact-angle-measurement-derived surface wettability. We show that local translational diffusivity permits the empirical determination of local hydrophilicity by means of Overhauser dynamic nuclear polarization (ODNP) amplified 1H NMR relaxometry. Large unilamellar vesicles (LUVs) in dilute bulk water solution serve as good model hydrophilic surfaces, and their surface water diffusion was shown to be partially or entirely decoupled from the bulk water viscosity, with the extent of decoupling dependent on the surface activity of the particular viscogen chosen. The effective hydrophilicity of a hydrated LUV surface in solution was further shown to be tunable by specific ions or osmolytes dissolved in solution, and the chemical makeup of a surface can give rise to a heterogeneous hydration dynamics landscape, as demonstrated on protein surfaces. ODNP-derived surface water diffusivity is suggested to be a unique tool for the site-specific mapping of the interaction landscape of a wide range of functional materials operating in aqueous solution, from wet adhesives to fuel cell membranes.

Diamond films with good electron emission properties show great potential for applications such as electron sources. For single-crystalline diamond, the negative electron affinity at hydrogen-terminated surfaces enables efficient emission of conduction electrons into vacuum. Although electrons are not naturally present in the diamond conduction band, p–n junction diode structures make this possible; electrons are injected from n-type diamond to the conduction band of p-type diamond, giving rise to electron emission with efficiencies exceeding 1%. Alternatively, impacting electron beams can be used to inject “secondary” electrons into the conduction band, resulting in high emission gain. For ultrananocrystalline diamond (UNCD) films with versatile granular structure, enhanced electron field emission (EFE) properties can be achieved by altering the granular structure of the films. Utilization of nanoscale tips as templates for growing UNCD film or direct reactive ion etching of the film further enhances their EFE behavior. On the other hand, the release of electrons through application of thermal energy can be utilized in a thermionic energy converter to directly transform heat into electricity. With the addition of ion current from doped diamond emitters to the thermionic electron current, power output enhancement of the converter can be realized.

Lithium-air batteries have received extraordinary attention recently owing to their theoretical gravimetric energies being considerably higher than those of Li-ion batteries. There are, however, significant challenges to practical implementation, including low energy efficiency, cycle life, and power capability. These are due primarily to the lack of fundamental understanding of oxygen reduction and evolution reaction kinetics and parasitic reactions between oxygen redox intermediate species and nominally inactive battery components such as carbon in the oxygen electrode and electrolytes. In this article, we discuss recent advances in the mechanistic understanding of oxygen redox reactions in nonaqueous electrolytes and the search for electrolytes and electrode materials that are chemically stable in the oxygen electrode. In addition, methods to protect lithium metal against corrosion by water and dendrite formation in aqueous lithium-air batteries are discussed. Further materials innovations lie at the heart of research and development efforts that are needed to enable the development of lithium-oxygen batteries with enhanced round-trip efficiency and cycle life.

This article reviews the potential of graphene and related two-dimensional (2D) materials for applications in micro- and nanoelectronics. In addition to graphene, special emphasis is placed on transition metal dichalcogenides (TMDs). First, we discuss potential solutions for application-scale material growth, in particular chemical vapor deposition. We describe challenges for electrical contacts and dielectric interfaces with 2D materials. The device-related sections in this review first weigh the pros and cons of semi-metal graphene as a field-effect transistor (FET) channel material for logic and radio frequency applications. This is followed by an introduction to alternate graphene switch concepts that utilize the particular properties of the material, namely tunnel FETs, vertical devices, and bilayer pseudospin FETs. The final section is dedicated to semiconducting TMDs and their integration in FETs using the examples of n-type molybdenum disulfide (MoS2) and p-type tungsten diselenide (WSe2).

Magnetic metal-organic complexes and coordination polymer frameworks can exhibit a transition between two different spin states of the integrated transition-metal ion, an attribute known as a spin-crossover (SCO) transition. This is a spectacular phenomenon that provides magnetic bi-stability and reversible spin-switchability to the material. Consequently, the magnetic state of the metal-organic center can be externally steered by temperature, pressure, or light irradiation. SCO molecules therefore are promising materials for various technological applications, such as spintronics devices, photo-switches, color displays, and information storage units. In spite of the importance of SCO materials in spintronics and other applications, the materials-specific understanding of the SCO phenomenon has remained a challenge. Here we survey recent developments in first-principles computational design of SCO metal-organic materials. A major outcome of recent state-of-the-art investigations is that an accurate quantitative description and even computational design of SCO materials can be provided by density functional theory-based electronic structure calculations combined with ab initio molecular dynamics simulations.

Engineered nanomaterials (ENMs) strongly interact with biomolecules and cells due to their similar size scales. Consequently, ENMs are beginning to emerge as new medical diagnostic tools, probes in cell biology, and delivery vehicles, compelling us to understand the interactions at the nano-bio interface. Optical spectroscopic tools are excellent probes to characterize ENMs and investigate their interactions with complex biological systems, including biomolecules, cells, and even whole animals alike. Here, we discuss the role of many optical spectroscopic techniques such as fluorescence, Raman, surface plasmon, and infrared spectroscopy in elucidating nano-bio interactions. While these spectroscopic tools have the ability to provide valuable information on ENM distribution in biosystems, ENM interaction with proteins, and the mechanisms by which ENMs elicit an adverse physiological response, there are many challenges that remain to be addressed to improve their scope, resolution, and throughput.

Particles ranging in size from a few nanometers to tens of micrometers have a strong tendency to adsorb at interfaces between two immiscible fluids (e.g., water and oil or air). The driving force for this strong interfacial attachment is a reduction in interfacial area, and thus, interfacial energy. To design and engineer the structure and properties of materials constructed by such colloidal systems, it is imperative to understand the behavior of particles at fluid interfaces at the single-particle level and to establish the relationship between the microscopic behavior of interfacial particles and the bulk properties of particle-laden interfaces. In this article, we present background information on the behavior of particles at fluid–fluid interfaces and highlight recent advances in understanding the effects of particle shape and surface wettability on the behavior of particles at the interfaces. We also discuss recent advances in using interfacial attachment to direct the assembly of nanomaterials to create hierarchical structures with designed properties.

Phonons—quanta of crystal lattice vibrations—reveal themselves in electrical, thermal, optical, and mechanical phenomena in materials. Phonons carry heat, scatter electrons, and affect light–matter interactions. Nanostructures opened opportunities for tuning the phonon spectrum and related properties of materials for specific applications, thus realizing what was termed phonon engineering. Recent progress in graphene and two-dimensional van der Waals materials has led to a better understanding of phonon physics and created additional opportunities for controlling phonon interactions and phonon transport at room temperature. This article reviews the basics of phonon confinement effects in nanostructures, describes phonon thermal transport in graphene, discusses phonon properties of van der Waals materials, and outlines practical applications of low-dimensional materials that rely on phonon properties.

A number of systems based on synthetic molecules, among them cationic liposomes and poly(ethylene imine)-based polymers, have been proposed as delivery vehicles for nucleic acids. Some of these systems have even reached the market, ensuring efficient and transient transfection levels in a variety of cell types. However, toxicity issues have limited their application in vivo. In this context, chitosan, a biocompatible and biodegradable polysaccharide, has been proposed as a promising alternative for the delivery of nucleic acid-based molecules. Here we present an overview of the state of the art of chitosan-based vectors for nucleic acid delivery and the most recent data on the in vivo testing of the proposed systems. We additionally express our view on the barriers that might be hampering the translation of this knowledge into clinical practice and the challenges that need to be fulfilled for these promising vehicles to reach patients.

The nanogap is possibly the single most important physical entity in surface-enhanced Raman scattering. Nanogaps between noble metal nanostructures deliver extremely high electric field-enhancement, resulting in an extraordinary amplification of both the excitation rate and the emission rate of Raman active molecules situated in the gap. In some cases, the resulting surface-enhancement in the gap can be so high that Raman spectra from single molecules can be measured. Here, we briefly review some important concepts and experimental results on nanoscale gaps for SERS applications.

In this article, we review focused ion beam serial sectioning microscopy paired with analytical techniques, such as electron backscatter diffraction or x-ray energy-dispersive spectrometry, to study materials chemistry and structure in three dimensions. These three-dimensional microanalytical approaches have been greatly extended due to advances in software for both microscope control and data interpretation. Samples imaged with these techniques reveal structural features of materials that can be quantitatively characterized with rich chemical and crystallographic detail. We review these technological advances and the application areas that are benefitting. We also consider the challenges that remain for data collection, data processing, and visualization, which collectively limit the scale of these investigations. Further, we discuss recent innovations in quantitative analyses and numerical modeling that are being applied to microstructures illuminated by these techniques.

A novel multifunctional and biocompatible ultrananocrystalline diamond (UNCD) film technology developed recently represents a new material with a unique combination of functionalities, including biocompatibility, to enable a new generation of implantable medical devices and scaffolds for tissue engineering. Following a description of the synthesis and properties of UNCD films and a comparison with other diamond film technologies, this article focuses on descriptions of key UNCD-based medical devices to treat specific medical conditions requiring effective therapies: (1) A UNCD-coated microchip (artificial retina) implantable inside the eye on the retina to restore partial vision to people blinded by retinitis pigmentosa and macular degeneration produced by genetically induced degeneration of the retina photoreceptors. (2) A UNCD-coated intraocular device for treatment of glaucoma in the eye. (3) UNCD-coated metal dental implants with potential order of magnitude longer life and superior performance than current implants.

Thin-film electrocaloric and pyroelectric sources for electrothermal energy interconversion have recently emerged as viable means for primary and auxiliary solid-state cooling and power generation. Two significant advances have facilitated this development: (1) the formation of high-quality polymeric and ceramic thin films with figures of merit that project system-level performance as a large percentage of Carnot efficiency and (2) the ability of these newer materials to support larger electric fields, thereby permitting operation at higher voltages. This makes the power electronic architectures more favorable for thermal to electric energy interconversion. Current research targets to adequately address commercial device needs including reduction of parasitic losses, increases in mechanical robustness, and the ability to form nearly freestanding elements with thicknesses in the range of 1–10 μm. This article describes the current state-of-the-art materials, thermodynamic cycles, and device losses and points toward potential lines of research that would lead to substantially better figures of merit for electrothermal energy interconversion.