The energy-efficient manipulation of the properties of functional materials is of great interest from both a scientific and an applied perspective. The application of electric fields is one of the most widely used methods to induce significant changes in the properties of materials, such as their structural, transport, magnetic, and optical properties. This article presents an overview of recent research on the manipulation of the electronic and magnetic properties of various material systems via electrolyte-based ionic gating. Oxides, magnetic thin-film heterostructures, and van der Waals 2D layers are discussed as exemplary systems. The detailed mechanisms through which ionic gating can induce significant changes in material properties, including their crystal and electronic structure and their electrical, optical, and magnetic properties, are summarized. Current and potential future functional devices enabled by such ionic control mechanisms are also briefly summarized, especially with respect to the emerging field of neuromorphic computing. Finally, a brief outlook and some key challenges are presented.
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Hydrous transition metal oxides (TMOs) are redox-active materials that confine structural water within their bulk, organized in 1D, 2D, or 3D networks. In an electrochemical cell, hydrous TMOs can interact with electrolyte species not only via their outer surface but also via their hydrous inner surface, which can transport electrolyte species to the interior of the material. Many TMOs operating in an aqueous electrochemical environment transform to hydrous TMOs, which then serve as the electrochemically active phase. This review summarizes the physicochemical properties of hydrous TMOs and recent mechanistic insights into their behavior in electrochemical reactions of interest for energy storage, conversion, and environmental applications. Particular focus is placed on first-principles calculations and operando characterization to obtain an atomistic view of their electrochemical mechanisms. Hydrous TMOs represent an important class of energy and environmental materials in aqueous and nonaqueous environments. Further understanding of their interaction with electrolyte species is likely to yield advancements in electrochemical reactivity and kinetics for energy and environmental applications.
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Piezoelectric materials possess the capability to interchangeably convert electrical energy into a mechanical response. While current piezoelectric materials exhibit strong properties, known limitations have inhibited further development. This review describes the ability to combine different piezoelectric materials into a composite to create well-rounded properties. The different types of connectivity classes are described as well as important design considerations and theoretical models. The contributions from the active and passive phases are outlined, focusing primarily on ferroelectric ceramics and polymer-based composites. The key advantage of piezoelectric composites is their ability to combine the flexibility of polymers with the high electromechanical coupling and piezoelectric coefficients of ferroelectric ceramics or single crystals appropriate for a variety of applications. Composites are prominent in medical ultrasound imaging and therapy, underwater acoustic sensing, industrial structural health monitoring, energy harvesting, and numerous other emerging applications.
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Superconductors offer major advantages for the electric power grid, including high current and power capacity, high efficiency arising from the lossless current flow, and a unique current-limiting functionality arising from a superconductor-to-resistive transition. These advantages can be brought to bear on equipment such as underground power cables, fault current limiters, rotating machinery, transformers, and energy storage. The first round of significant commercial-scale superconductor power-equipment demonstrations, carried out during the past decade, relied on a first-generation high-temperature superconductor (HTS) wire. However, during the past few years, with the recent commercial availability of high-performance second-generation HTS wires, power-equipment demonstrations have increasingly been carried out with these new wires, which bring important advantages. The foundation is being laid for commercial expansion of this important technology into the power grid.
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Natural wood has been used for construction, fuel, and furniture for thousands of years because of its versatility, renewability, and aesthetic appeal. However, new opportunities for wood are arising as researchers have developed ways to tune the material`s optical, thermal, mechanical, and ionic transport properties by chemically and physically modifying wood`s naturally porous structure and chemical composition. Such modifications can be used to produce sustainable, functional materials for various emerging applications such as automobiles, construction, energy storage, and environmental remediation. In this review, we highlight recent advancements in engineered wood for sustainable technologies, including thermal and light management, environmental remediation, nanofluidics, batteries, and structural materials with high strength-to-weight ratios. Additionally, the current challenges, opportunities, and future of wood research are discussed, providing a guideline for the further development of next-generation, sustainable wood-based materials.
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Soft robotics aims to close the performance gap between built and biological machines through materials design. Soft robots are constructed from soft, actuatable materials to be physically intelligent, or to have traits that living organisms possess such as passive adaptability and morphological computation through their compliant, deformable bodies. However, materials selection for physical intelligence often involves low-performance and/or energy-inefficient, stimuli-responsive materials for actuation. Additional challenges in soft robot sensorization and control further limit the practical utility of these machines. Recognizing that electrically controllable materials are crucial for the development of soft machines that are both physically and computationally intelligent, we review progress in the development of electroprogrammable materials for soft robotic actuation. We focus on thermomechanical, electrostatic, and electrochemical actuation strategies that are directly controlled by electric currents and fields. We conclude with an outlook on the design and fabrication of next-generation robotic materials that will facilitate true bioinspired autonomy.
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Natural wood has been used for construction, fuel, and furniture for thousands of years because of its versatility, renewability, and aesthetic appeal. However, new opportunities for wood are arising as researchers have developed ways to tune the material`s optical, thermal, mechanical, and ionic transport properties by chemically and physically modifying wood`s naturally porous structure and chemical composition. Such modifications can be used to produce sustainable, functional materials for various emerging applications such as automobiles, construction, energy storage, and environmental remediation. In this review, we highlight recent advancements in engineered wood for sustainable technologies, including thermal and light management, environmental remediation, nanofluidics, batteries, and structural materials with high strength-to-weight ratios. Additionally, the current challenges, opportunities, and future of wood research are discussed, providing a guideline for the further development of next-generation, sustainable wood-based materials.
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Soft robotics aims to close the performance gap between built and biological machines through materials design. Soft robots are constructed from soft, actuatable materials to be physically intelligent, or to have traits that living organisms possess such as passive adaptability and morphological computation through their compliant, deformable bodies. However, materials selection for physical intelligence often involves low-performance and/or energy-inefficient, stimuli-responsive materials for actuation. Additional challenges in soft robot sensorization and control further limit the practical utility of these machines. Recognizing that electrically controllable materials are crucial for the development of soft machines that are both physically and computationally intelligent, we review progress in the development of electroprogrammable materials for soft robotic actuation. We focus on thermomechanical, electrostatic, and electrochemical actuation strategies that are directly controlled by electric currents and fields. We conclude with an outlook on the design and fabrication of next-generation robotic materials that will facilitate true bioinspired autonomy.
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Noncentrosymmetric (NCS) materials feature an exciting array of functionalities such as nonlinear optical (NLO) responses and topological spin textures (skyrmions). While NLO materials and magnetic skyrmions display two different sets of physical properties, their design strategies are deeply connected in terms of atomic-scale precision, structural customization, and electronic tunability. Despite impressive progress in studying these systems separately, a joint road map for navigating the chemical principles for NCS materials remains elusive. This review unites two subtopics of NCS systems, NLO materials and magnetic skyrmions, offering a multifaceted narrative of how to translate the often-abstract fundamentals to the targeted functionalities while inviting innovative approaches from the community. We outline the design principles central to the desired properties by exemplifying relevant examples in the field. We supplement materials chemistry with pertinent electronic structures to demonstrate the power of the fundamentals to create systems integration relevant to foreseeable societal impacts in frequency-doubling instrumentation and spin-based electronics.
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