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As a result of the depletion of conventional oil reserves and the unprecedented growth in world energy demand, increasing attention has focused on the extraction and utilization of unconventional o...

Through diversity of composition, sequence, and interfacial structure, hybrid materials greatly expand the palette of materials available to access novel functionality. The NSF Division of Materials Research recently supported a workshop (October 17–18, 2019) aiming to (1) identify fundamental questions and potential solutions common to multiple disciplines within the hybrid materials community; (2) initiate interfield collaborations between hybrid materials researchers; and (3) raise awareness in the wider community about experimental toolsets, simulation capabilities, and shared facilities that can accelerate this research. This article reports on the outcomes of the workshop as a basis for cross-community discussion. The interdisciplinary challenges and opportunities are presented, and followed with a discussion of current areas of progress in subdisciplines including hybrid synthesis, functional surfaces, and functional interfaces.

The presence of H2O has been linked to enhancements in the reactivity of cathodes for Mg2+ electrochemistry. If the enhancements were mimicked by nonaqueous solvents, they could enable Mg batteries...

Metal–insulator transition materials such as VO2 have garnered much attention in the field of neuromorphic devices because of their nonlinear behavior and orders of magnitude scale property changes...

As a result of the increasing emphasis on accessing unconventional deposits of heavy oil and bitumen to meet global energy needs, there is an intense focus on addressing the rheological challenges ...

Solar fuel generation mediated by semiconductor heterostructures represents a promising strategy for sustainable energy conversion and storage. The design of semiconductor heterostructures for photocatalytic energy conversion requires the separation of photogenerated charge carriers in real space and their delivery to active catalytic sites at the appropriate overpotentials to initiate redox reactions. Operation of the desired sequence of light harvesting, charge separation, and charge transport events within heterostructures is governed by the thermodynamic energy offsets of the two components and their photoexcited charge-transfer reactivity, which determine the extent to which desirable processes can outcompete unproductive recombination channels. Here, we map energetic offsets and track the dynamics of electron transfer in MoS2/CdS architectures, prepared by interfacing two-dimensional MoS2 nanosheets with CdS quantum dots (QDs), and correlate the observed charge separation to photocatalytic activity in the hydrogen evolution reaction. The energetic offsets between MoS2 and CdS have been determined using hard and soft X-ray photoemission spectroscopy (XPS) in conjunction with density functional theory. A staggered type-II interface is observed, which facilitates electron and hole separation across the interface. Transient absorption spectroscopy measurements demonstrate ultrafast electron injection occurring within sub-5 ps from CdS QDs to MoS2, allowing for creation of a long-lived charge-separated state. The increase of electron concentration in MoS2 is evidenced with the aid of spectroelectrochemical measurements and by identifying the distinctive signatures of electron-phonon scattering in picosecond-resolution transient absorption spectra. Ultrafast charge separation across the type-II interface of MoS2/CdS heterostructures enables a high Faradaic efficiency of ∼99.4 ± 1.2% to be achieved in the hydrogen evolution reaction (HER) and provides a 40-fold increase in the photocatalytic activity of dispersed photocatalysts for H2 generation. The accurate mapping of thermodynamic driving forces and dynamics of charge transfer in these heterostructures suggests a means of engineering ultrafast electron transfer and effective charge separation to design viable photocatalytic architectures.

An energy storage paradigm orthogonal to Li-ion battery chemistries can be conceptualized by employing anions as the primary charge carriers. F-ion conversion chemistries show promise but have limi...

The operation of a Li-ion battery involves a concerted sequence of mass and charge transport processes, which are underpinned by alternating dilation/contraction of the active electrode materials. Several Li-ion battery failure mechanisms can be directly traced to lattice-mismatch strain arising from local compositional heterogeneities. The mechanisms of chemo-mechanical coupling that effect phase separation and the resulting complex evolution of internal stress fields remain inadequately understood. This work employs X-ray microscopy techniques to image the evolution of composition and stress across individual bent V2O5 particles. Experimental findings show that lattice strain imposed by the deformation of an individual cathode particle profoundly modifies phase separation patterns, yielding striated Li-rich domains ensconced within a Li-poor matrix. Particle-level inhomogeneities compound across scales resulting in fracture and capacity fade. Coupled phase field modeling of the evolution of domains reveals that the observed patterns minimize the energetic costs incurred by the geometrically imposed strain gradients during lithiation of the material and illustrate that phase separation motifs depend sensitively on the particle geometry, dimensions, interfacial energetics, and lattice incommensurability. Sharp differences in phase separation patterns are observed between lithiation and delithiation. This work demonstrates the promise of strain-engineering and particle geometry to deterministically control phase separation motifs such as to minimize accumulated stresses and mitigate important degradation mechanisms.

Summary The decarbonization of heavy industry and the emergence of renewable energy technologies are inextricably linked to access to mineral resources. As such, there is an urgent need to develop benchmarked assessments of the role of critical elements in reducing greenhouse gas emissions. Here, we explore the role of vanadium in decarbonizing construction by serving as a microalloying element and enabling the energy transition as the primary component of flow batteries used for grid-level storage. We estimate that vanadium has enabled an avoided environmental burden totaling 185 million metric tons of CO2 on an annual basis. A granular analysis estimates savings for China and the European Union at 1.15% and 0.18% of their respective emissions, respectively. Our results highlight the role of critical metals in developing low-carbon infrastructure while underscoring the need for holistic assessments to inform policy interventions that mitigate supply chain risks., Graphical abstract, Highlights • Enabling the energy transition and deep decarbonization hinges on strategic minerals • The versatility of vanadium chemistries enables technologies that lower CO2 emissions • In structural applications, vanadium enables a greater economy of materials use • Vanadium redox flow batteries balance the intermittency of wind and solar power, Energy resources; Energy sustainability; Materials science; Materials chemistry; Energy materials

Achieving the efficacious and rapid separation of mixed water/oil streams has emerged as a fundamental imperative in order to facilitate extraction of fossil fuels by methods such as cyclic steam s...

The design of a chemical synthesis often relies on a combination of chemical intuition and Edisonian trial-and-error methods. Such methods are not just inefficient but inherently limited in their a...

Ionic compounds wherein lanthanide cations are arrayed alongside anions adopt a wide range of crystal structures as a result of the variation of ionic radii and electronic configurations across the lanthanide series. Owing to the constricted nature of 4f orbitals, local coordination environments and structural preferences in such compounds are primarily dictated by electrostatic interactions and steric considerations with the primary driving force being the minimization of the crystal lattice energy. In this review, we examine a broad class of dianionic rare-earth compounds, lanthanide oxyhalides that present a multidimensional design space for tuning of functional properties by dint of the possibilities for extensive alloying on cationic and anionic sublattices; the considerable span of ionic radii and hardness across the lanthanide series and down the halide group, respectively; a large tolerance window for point defects such as oxide and halide vacancies; as well as multiple accessible polymorphs. In addition to their structural versatility, control over functional properties is accessible based on alteration of microstructure and surface chemistry. Synthetic strategies for accessing atomistic, nanoscale, and mesoscale control are discussed using illustrative examples placing particular emphasis on non-hydrolytic sol—gel processes that provide access to well-defined solid-solution nanocrystals. The reactivity and post-synthetic modification of these compounds is further delineated. Methods for defining color centers within these compounds, cooperativity of the optical response of the color centers with the host lattice (determined by overlap integrals specific to each structure type and the polarization and ligand field effects of different halide ions) and adjacent color centers (reliant on energy transfer schema), and their practical application in phosphors are further detailed. Mechanisms facilitating down- and up-conversion of energy absorbed from incident electromagnetic radiation or high-energy particles are delineated with particular emphasis on X-ray and electron-beam excitation. The accessible energy conversion mechanisms, efficacious radiative recombination channels, and opportunities for systematically tuning color through compositional modulation have led to the emergence of these materials as potential candidates for phosphors. These materials have potential applications in solid-state lighting, radiation detection, and as the active elements of imaging devices. The tolerance towards large concentrations of anion vacancies and the facile diffusivity of anions in these compounds further underpins the function of lanthanide oxyhalides as ion conductors, gas sensors, and heterogeneous catalysts. Increasing interest has focused on utilization of well-defined color centers for quantum information science and multiplexed sensing in biological systems. Such applications require additional control of the positioning of dopant atoms and understanding of their interactions with the host lattice and other dopant atoms.

Metastable materials that represent excursions from thermodynamic minima are characterized by distinctive structural motifs and electronic structure, which frequently underpins new function. The binary oxides of hafnium present a rich diversity of crystal structures and are of considerable technological importance given their high dielectric constants, refractory characteristics, radiation hardness, and anion conductivity; however, high-symmetry tetragonal and cubic polymorphs of HfO2 are accessible only at substantially elevated temperatures (1720 and 2600 °C, respectively). Here, we demonstrate that the core–shell arrangement of VO2 and amorphous HfO2 promotes outwards oxygen diffusion along an electropositivity gradient and yields an epitaxially matched V2O3/HfO2 interface that allows for the unprecedented stabilization of the metastable cubic polymorph of HfO2 under ambient conditions. Free-standing cubic HfO2, otherwise accessible only above 2600 °C, is stabilized by acid etching of the vanadium oxide core. In contrast, interdiffusion under oxidative conditions yields the negative thermal expansion material HfV2O7. Variable temperature powder X-ray diffraction demonstrate that the prepared HfV2O7 exhibits pronounced negative thermal expansion in the temperature range between 150 and 700 °C. The results demonstrate the potential of using epitaxial crystallographic relationships to facilitate preferential nucleation of otherwise inaccessible metastable compounds.

Owing to their enormous capacities, Li-S batteries have emerged as a prime candidate for economic and sustainable energy storage. Still, potential mechanics-based issues exist that must be addressed: lithiation of sulfur produces an enormous volume expansion (~ 80%). In other high capacity electrodes, large expansions generate considerable stresses that can lead to mechanical damage and capacity fading. However, the mechanics of electrochemical cycling of sulfur is fundamentally distinct from other systems due to solid-to-liquid, liquid-to-liquid, and liquid-to-solid phase transformations, and thus remains poorly understood. To this end, we measure the evolution of stresses in composite sulfur cathodes during electrochemical cycling and link these stresses to structural evolution. We observe that nucleation and growth of solid lithium-sulfur phases induces significant stresses, including irreversible stresses from structural rearrangements during the first cycle. However, subsequent cycles show highly reversible elastic mechanics, thereby demonstrating strong potential for extended cycling in practical applications.

Covalently networked polymers offer desirable non-crystallinity and mechanical strength for solid polymer electrolytes (SPEs), but the chemically active cross-links involved in their construction could deteriorate the compatibility with high-energy cathode materials that are electrophilic and/or in the charged state. Herein we reveal a strong dependence of cyclability of such cathodes on the reactivity of covalently networked SPEs and demonstrate a polymer design that renders these SPEs chemically inert. We designed and synthesized two hybrid networks, both with polyethylene oxide as the cation conducting component and polyhedral oligomeric silsesquioxane as the branch point, but respectively use alkylamino and chemically inert triazole groups as cross-links. All-solid-state cells using the alkylamino-containing SPE underwent rapid degradation while cells using triazole SPEs showed stable cycling.

The manuscript presents a detailed analysis of embodied energy and carbon footprint reduction enabled by microalloying of steel, thereby providing a rich global perspective of the (outsized) role of chemical elements added in trace concentrations on the overall footprint of the construction industry. As such, the manuscript addresses an important and timely topic at the intersection of materials criticality, structural performance, life cycle assessment, and policy interventions. The United Nations estimates that the worldwide energy consumption of buildings accounts for 30—40% of global energy production, underlining the importance of the judicious selection of construction materials. Much effort has focused on the use of high-strength low-alloy steels in reinforcement bars whose economy of materials use is predicated upon improved yield strengths in comparison to low-carbon steels. While microalloying is known to allow for reduced steel consumption, a sustainability analysis in terms of embodied energy and CO 2 has not thus far been performed. Here we calculate the impact of supplanting lower grade reinforcement bars with higher strength vanadium microalloyed steels on embodied energy and carbon footprint. We find that the increased strength of vanadium microalloyed steel translates into substantial material savings over mild steel thus reducing the total global fossil carbon footprint by as much as 0.385%. A more granular analysis pegs savings for China and the European Union at 1.01 and 0.19%, respectively, of their respective emissions.

The construction industry is being buffeted by winds of change, balancing the urgent need to remedy deteriorating infrastructure in the developed world and the push to build new infrastructure in emerging economies whilst devising means to better its catastrophic carbon footprint. Much of the deleterious environmental impact of construction results from the utilization of concrete as well as inefficiencies across the construction process that result in considerable waste and energy expenditure. Additive manufacturing methods stand poised to substantially transform the industry by enhancing automation, enabling economy of materials use, and allowing for unprecedented fusion of form and function; however, reliance on concrete as the extrusive material of choice has the potential to greatly compound mounting environmental challenges. In this perspective, we discuss our efforts to develop an altogether new palette of naturally sourced construction materials based on natural soils, which are reconfigured into extrudable formulations compatible with additive manufacturing. We furthermore delineate a roadmap bringing together soil chemistry with composite science, modeling of mesoscale phenomena, rheological studies of extrudable soil “inks”, generative design, post-synthetic modification, and the development of robust structure—function correlations relating atomistic and mesoscale structures as well as geometry of the architectures to load-bearing capabilities and mechanical response. We illustrate this approach using a naturally harvested burlewash clay sample crosslinked through formation of a siloxane framework, which has been 3D printed into a load-bearing structure. The need for an integrated life cycle assessment approach is emphasized to ensure development of a new palette of sustainable construction materials.

The significant heat loss and severe thermal fluctuations inherent in steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) impose considerable constraints on well cementing. In order to obtain better energy efficiency and mechanical robustness, there is considerable interest in the development of low-thermal-conductivity cement that can provide a combination of enhanced thermal insulation and mechanical resilience upon thermal cycling. However, the current palette of thermal cements is exceedingly sparse. In this article, we illustrate a method for decreasing the thermal conductivity of cement by inclusion of hydroxyethylcellulose-functionalized halloysite nanotubes. Halloysite/hydroxyethylcellulose inclusions offer an abundance of disparate interfaces and void space that can effectively scatter phonons, thereby bringing about a pronounced reduction of thermal conductivity. The microstructure of the nanocomposite cementitious matrix is strongly modified even as the compositional profile remains essentially unaltered. Modified cement nanocomposites incorporating halloysite nanotubes along with hydroxyethylcellulose in a 8:1 ratio with an overall loading of 2 wt.% exhibit the lowest measured thermal conductivity of 0.212 ± 0.003 W/m.K, which is substantially reduced from the thermal conductivity of unmodified cement (1.252 W/m.K). The ability to substantially decrease thermal conductivity without deleterious modification of mechanical properties through alteration of microstructure, inclusion of encapsulated void spaces, and introduction of multiple phonon-scattering interfaces suggests an entirely new approach to oilwell cementing based on the design of tailored nanocomposites.

In a recently published paper in Chem, Zhu, Zhang, Yan, and colleagues unlock diffusion pathways for potassium ions within a double-layered V2O5 structure and demonstrate a potassium-ion battery with unprecedented performance characteristics including an average voltage of 3.2 V, an initial capacity of 131 mAh·g−1, and rapid charge/discharge capabilities even at high rates. The study serves as a remarkable illustration of the utility of mining metastable phase space to identify structural motifs that allow for mitigation of the diffusion challenges plaguing larger cations.

Fenestration elements that enable spectrally selective dynamic modulation of the near-infrared region of the electromagnetic spectrum are of great interest as a means of decreasing the energy consumption of buildings by adjusting solar heat gain in response to external temperature. The binary vanadium oxide VO2 exhibits a near-room-temperature insulator–metal electronic transition accompanied by a dramatic modulation of the near-infrared transmittance. The low-temperature insulating phase is infrared transparent but blocks infrared transmission upon metallization. There is considerable interest in harnessing the thermochromic modulation afforded by VO2 in nanocomposite thin films. However, to prepare a viable thermochromic film, the visible-light transmittance must be maintained as high as possible while maximizing thermochromic modulation in the near-infrared region of the electromagnetic spectrum, which necessitates the development of high-crystalline-quality VO2 nanocrystals of the optimal particle siz...

Lead halide perovskites are a versatile class of semiconductors that provide considerable opportunities for tunability of absorption maxima, exciton binding energies, and band gaps as a function of composition and dimensional confinement. Considerable attention has focused on the design and synthesis of related frameworks with reduced structural dimensionality that provide an expanded palette of optical transitions with varying degrees of exciton localization. In this work, we demonstrate the ligand-mediated navigation of the cesium—lead—bromine ternary phase diagram demarcating distinctive regimes wherein 3D CsPbBr3 and 0D Cs4PbBr6 nanocrystals can be stabilized. The denticity, steric bulk, and concentration of aliphatic amine ligands strongly modifies the supersaturation of lead monomers, scaling proportionately to their complexation coefficients and ability to form ordered passivating ligand shells. The added ligands strongly alter the trajectory of nucleation and growth processes, stabilizing either P...

The known crystal structures of solids often correspond to the most thermodynamically stable arrangement of atoms. Yet, oftentimes there exist a richly diverse set of alternative structural arrangements that lie at only slightly higher energies and can be stabilized under specific constraints (temperature, pressure, alloying, point defects). Such metastable phase space holds tremendous opportunities for nonequilibrium structural motifs and distinctive chemical bonding and ultimately for the realization of novel function. In this Feature Article, we explore the challenges with the prediction, stabilization, and utilization of metastable polymorphs. We review synthetic strategies that allow for trapping of such states of matter under ambient temperature and pressure including topochemical modification of more complex crystal structures; dimensional confinement wherein surface energy differentials can alter bulk phase stabilities; templated growth exploiting structural homologies with molecular precursors; i...

The invention of rechargeable batteries has dramatically changed our landscapes and lives, underpinning the explosive worldwide growth of consumer electronics, ushering in an unprecedented era of electric vehicles, and potentially paving the way for a much greener energy future. Unfortunately, current battery technologies suffer from a number of challenges, e.g., capacity loss and failure upon prolonged cycling, limited ion diffusion kinetics, and a rather sparse palette of high-performing electrode materials. Here, we discuss the origins of diffusion limitations in oxide materials using V2O5 as a model system. In particular, we discuss constrictions in ionic conduction pathways, narrow energy dispersion of conduction band states, and the stabilization and self-trapping of polarons as local phenomena that have substantial implications for introducing multiscale compositional and phase heterogeneities. Strategies for mitigating such limitations are discussed such as reducing diffusion path lengths and the ...

The steam-assisted gravity-drainage (SAGD) method has emerged as among the leading methods of enhanced oil recovery and is predicated on the injection of steam within the wellbore followed by extraction of emulsions of viscous oil and water. The emulsions are stabilized by endogenous surfactants, necessitating extensive processing such as addition of chemical de-emulsifiers and slow gravity-based separation methods. Here, we show that a hierarchically textured membrane exhibiting orthogonal wettability, specifically, superoleophilic but superhydrophobic behavior, allows for effective separation of the water and viscous oil fractions of SAGD emulsions. The membrane is constructed by integrating ZnO nanotetrapods onto stainless steel meshes using a conformal amorphous SiO2 layer and is both mechanically resilient and thermally robust. The intrinsic surface energy characteristics of the ZnO tetrapods as well as their three-dimensional texture when arrayed atop the stainless steel mesh substrates contribute t...

Summary The Li-ion paradigm of battery technology is constrained by the monovalency of the Li ion. A straightforward solution is to transition to multivalent-ion chemistries, where Mg 2+ is the most obvious candidate because of its size and mass. The realization of Mg batteries has faced myriad obstacles, including a sparse selection of cathode materials demonstrating the ability to reversibly insert divalent ions. Here, we provide evidence of reversible topochemical and electrochemical insertion of Mg 2+ into a metastable one-dimensional polymorph of V 2 O 5 up to a capacity of 0.33 Mg 2+ per formula unit. An electrochemical capacity of 90 mA hr g −1 was retained after 100 cycles with an average operating potential of 1.65 V versus Mg 2+ /Mg 0 . Not only does ζ-V 2 O 5 represent a rare addition to the pantheon of functional Mg battery cathode materials, but it is also distinctive in exhibiting a combination of high stability, high specific capacity, and moderately high operating voltage.

As the quest toward novel materials proceeds, improved characterization technologies are needed. In particular, the atomic thickness in graphene and other 2D materials renders some conventional technologies obsolete. Characterization technologies at wafer level are needed with enough sensitivity to detect strain in order to inform fabrication. In this work, NEXAFS spectroscopy was combined with simulations to predict lattice parameters of graphene grown on copper and further transferred to a variety of substrates. The strains associated with the predicted lattice parameters are in agreement with experimental findings. The approach presented here holds promise to effectively measure strain in graphene and other 2D systems at wafer levels to inform manufacturing environments.

The insertion of Li-ions within cathode materials during the discharging of a battery oftentimes brings about one or more structural transformations. The spatiodynamic propagation of phase transformations within a matrix of particles is determined by highly localized intercalation phenomena rather than the global voltage profile. Multiscale inhomogeneities resulting from variations in electrode reactions strongly influence the proportion of actively intercalating electrode materials, define local “hot-spots” wherein the current is greatly amplified during charge/discharge processes, and consequently dictate localized energy dissipation profiles. Multiphasic domains further give rise to localized stress gradients that can induce electrode degradation. However, a clear picture of chemical and stress inhomogeneities remains to be developed for most cathode materials. Here we demonstrate compositional striping modulations between Li-rich and Li-poor domains along the edges of individual nanowires of Li-ion-intercalated V2O5 based on analysis of hyperspectral X-ray microscopy data. Analysis of scanning transmission X-ray microscopy data using singular value decomposition and principal component analysis provides a means to map compositional inhomogenieties across individual nanowires and ensembles of nanowires alike. The compositional maps are further transformed to stress and strain maps, which depict the localization of tensile stress and strain within individual nanowires of LixV2O5. The core–shell and compositional striping modulations manifested here and the resulting strain gradients point to the need to design cathode materials and electrode architectures to mitigate such pronounced local inhomoegeneities in Li-ion intercalation and diffusion.

The unique mechanical properties and transport features of grain boundaries (GBs) in polycrystalline materials have been widely investigated. However, studies which focus on the unique chemo-mechanics phenomena resulting from GBs’ are exceedingly sparse. In this work, a thermodynamically consistent framework has been developed to explore the multi-physics coupling between mechanics and species diffusion. Constitutive laws for the bulk and the across-GB interaction laws have been derived for large deformations from the system free energies. A chemo-mechanically coupled cohesive zone model is developed which takes into account mode-dependent fracture properties in the presence of GBs. Polycrystalline LiNi x Mn y Co z O 2 (NMC) particles and Li x V 2 O 5 nanowires haveueen selected to demonstrate the impact of GBs on the modeled and observed chemo-mechanics. The model has been implemented in the open-source finite element (FE) package MOOSE. Simulation results indicate that the chemical process and the mechanical degradation go hand-in–hand, where enhanced intergranular chemical inhomogeneities weaken the mechanical strength of the GBs, while damage to the GBs affects or even block transport across the GB. Furthermore, experimentally observed characteristics of chemo-mechanical degradation, e.g., chemical “hot-spots” and surface layer delamination can be accurately predicted by the model.

A continuous increase in the global demand for liquid fuels has led to increased reliance on unconventional sources of fossil fuels such as bitumen. The extraction, midstream transportation, and ultimate processing of heavy oils presents a distinctive set of challenges. For example, the high viscosity of bitumen poses a challenge to its transportation through conventional transportation systems such as pipelines. Conventional approaches to address the challenging rheological properties of bitumen involve dilution of bitumen with natural gas condensates, addition of surfactants, ultrasonic heating, thermal jacketing of pipelines, and high pump pressures. These solutions require considerable investments in infrastructure, frequent inspection and maintenance, and pose a risk of spillage to vulnerable environments. As such, much interest has focused on the design of solid-state transportation methodologies. In this article, we propose a viable and safe transportation alternative wherein bitumen is reconfigured such that the droplets of lighter fractions of bitumen (saturates, aromatics, resins) are encapsulated within conformal shells of asphaltenes. The tendency of asphaltenes to aggregate has been exploited to obtain cross-linked shells without requiring the use of extraneous chemical additives. Thermally mediated crosslinking of the asphaltenes shells allow the microcapsules to hold their form and result in the emergence of mechanical strength. The stress-withstanding abilities and velocity impact resistance of these microcapsules have been studied to establish their viability for industrial use, and demonstrate that microcapsules with diameters of ca. 1.25 mm can withstand stresses as high as 576 kN/m2. Since the bitumen microcapsules have been formulated by simply reconfiguring the intrinsic components of bitumen, they can be readily fluidized by mechanical means to recover the encapsulated lighter fractions. The solid microcapsules demonstrate the viability of solid-state transportation of bitumen via roadways or marine tankers, thereby mitigating a primary impediment to the utilization of viscous oils.

Materials exhibiting pronounced metal–insulator transitions such as VO2 have acquired great importance as potential computing vectors and electromagnetic cloaking elements given the large accompanying reversible modulation of properties such as electrical conductance and optical transmittance. As a first-order phase transition, considerable phase coexistence and hysteresis is typically observed between the heating insulator → metal and cooling metal → insulator transformations of VO2. Here, we illustrate that substitutional incorporation of tungsten greatly modifies the hysteresis of VO2, both increasing the hysteresis as well as introducing a distinctive kinetic asymmetry wherein the heating symmetry-raising transition is observed to happen much faster as compared to the cooling symmetry-lowering transition, which shows a pronounced rate dependence of the transition temperature. This observed kinetic asymmetry upon tungsten doping is attributed to the introduction of phase boundaries resulting from stabi...

The design of cathodes for intercalation batteries requires consideration of both atomistic and electronic structure to facilitate redox at specific transition metal sites along with the concomitant diffusion of cations and electrons. Cation intercalation often brings about energy dissipative phase transformations that give rise to substantial intercalation gradients as well as multiscale phase and strain inhomogeneities. The layered α-V2O5 phase is considered to be a classical intercalation host but is plagued by sluggish diffusion kinetics and a series of intercalation-induced phase transitions that require considerable lattice distortion. Here, we demonstrate that a 1D tunnel-structured ζ-phase polymorph of V2O5 provides a stark study in contrast and can reversibly accommodate Li-ions without a large distortion of the structural framework and with substantial mitigation of polaronic confinement. Entirely homogeneous lithiation is evidenced across multiple cathode particles (in contrast to α-V2O5 partic...

Buildings consume an inordinate amount of energy, accounting for 30–40% of worldwide energy consumption. A major portion of solar radiation is transmitted directly to building interiors through windows, skylights, and glazed doors where the resulting solar heat gain necessitates increased use of air conditioning. Current technologies aimed at addressing this problem suffer from major drawbacks, including a reduction in the transmission of visible light, thereby resulting in increased use of artificial lighting. Since currently used coatings are temperature-invariant in terms of their solar heat gain modulation, they are unable to offset cold-weather heating costs that would otherwise have resulted from solar heat gain. There is considerable interest in the development of plastic fenestration elements that can dynamically modulate solar heat gain based on the external climate and are retrofittable onto existing structures. The metal–insulator transition of VO2 is accompanied by a pronounced modulation of n...

Unconventional deposits such as extra heavy oil and bitumen represent a steadily increasing proportion of extracted fuels. The rheological properties of viscous crude oil represents a formidable impediment to their extraction, transportation, and processing and have necessitated considerable retooling and changes to process design. In this work, we demonstrate that highly textured inorganic substrates generated by depositing ZnO nanotetrapods onto periodically ordered stainless steel mesh substrates exhibit viscous oil contact angles exceeding 150° as well as enable the facile gliding of viscous oil. Such functionality is derived as a result of multiscale texturation and porosity achieved within these substrates, which are characterized by trapping of plastronic air pockets at the solid/liquid interface. Further reduction of the surface energy has been achieved by constituting a helical highly ordered self-assembled monolayer of a perfluorinated phosphonic acid on the ZnO surfaces. Such structures are str...

The practical realization of energy-efficient computing vectors is imperative to address the break-down in the scaling of power consumption with transistor dimensions, which has led to substantial underutilized chip space. Memristive elements that encode information in multiple internal states and reflect the dynamical evolution of these states are a promising alternative. Herein we report the observation of pinched loop hysteretic type-II memristive behavior in single-crystalline nanowires of a versatile class of layered vanadium oxide bronzes with the composition δ[M(H2O)4]0.25V2O5 (M= Co, Ni, Zn), the origin of which is thought to be the diffusion of protons in the interlayer regions.

The promise from graphene to produce devices with high mobilities and detectors with fast response times is truncated in practice by strain and deformation originating during growth and subsequent processing. This work describes effects from graphene growth, multiple layer transfer, and substrate termination on out of plane deformation, critical to device performance. Synchrotron spectroscopy data was acquired with a state-of-the-art hyperspectral large-area detector to describe growth and processing with molecular sensitivity at wafer length scales. A study of methodologies used in data analysis discouraged dichroic ratio approaches in favor of orbital vector approximations and data mining algorithms. Orbital vector methods provide a physical insight into mobility-detrimental rippling by identifying ripple frequency as main actor, rather than intensity; which was confirmed by data mining algorithms, and in good agreement with electron scattering theories of corrugation in graphene. This work paves the wa...

Multivalent intercalation batteries have the potential to circumvent several fundamental limitations of reigning Li-ion technologies. Such batteries will potentially deliver high volumetric energy densities, be safer to operate, and rely on materials that are much more abundant than Li in the Earth’s crust. The design of intercalation cathodes for such batteries requires consideration of thermodynamic aspects such as structural distortions and energetics as well as kinetic aspects such as barriers to the diffusion of cations. The layered α-V2O5 system is a canonical intercalation host for Li-ions but does not perform nearly as well for multivalent cation insertion. However, the rich V–O phase diagram provides access to numerous metastable polymorphs that hold much greater promise for multivalent cation intercalation. In this article, we explore multivalent cation insertion in three metastable polymorphs, γ′, δ′, and ρ′ phases of V2O5, using density functional theory calculations. The calculations allow fo...

Crystalline vanadium pentoxide (V2O5) has attracted significant interest as a potential cathode material for energy storage applications due to its high theoretical capacity. Unfortunately, the material suffers from low conductivity as well as slow lithium ion diffusion, both of which affect how fast the electrode can be charged/discharged and how many times it can be cycled. Colloidal crystal templating (CCT) provides a simple approach to create well-organized 3-D nanostructures of materials, resulting in a significant increase in surface area that can lead to marked improvements in electrochemical performance. Here, a single layer of open shell V2O5 architectures ca. 1 μm in height with ca. 100 nm wall thickness was fabricated using CCT, and the electrochemical properties of these assemblies were evaluated. A decrease in polarization effects, resulting from the higher surface area mesostructured features, was found to produce significantly enhanced electrochemical performance. The discharge capacity of ...

Intercalation phenomena are at the heart of modern electrochemical energy storage. Nevertheless, as out-of-equilibrium processes involving concomitant mass and charge transport, such phenomena can be difficult to engineer in a predictive manner. The rational design of electrode architectures requires mechanistic understanding of physical phenomena spanning multiple length scales, from atomistic distortions and electron localization at individual transition metal centers to phase inhomogeneities and intercalation gradients in individual particles and concentration variances across ensembles of particles. In this review article, we discuss the importance of the electronic structure in mediating electrochemical storage and mesoscale heterogeneity. In particular, we discuss x-ray spectroscopy and imaging probes of electronic and atomistic structure as well as statistical regression methods that allow for monitoring of the evolution of the electronic structure as a function of intercalation. The layered α-phase of V2O5 is used as a model system to develop fundamental ideas on the origins of mesoscale heterogeneity.

The thermally driven orders-of-magnitude modulation of resistance and optical transmittance observed in VO2 makes it an archetypal first-order phase transition material and underpins functional applications in logic and memory circuitry, electromagnetic cloaking, ballistic modulation, and thermochromic glazing to provide just a few representative examples. VO2 can be reversibly switched from an insulating to a metallic state at an equilibrium transition temperature of 67 °C. Tuning the phase diagram of VO2 to bring the transition temperature closer to room temperature has been a longstanding objective and one that has tremendous practical relevance. Substitutional incorporation of dopants has been the most common strategy for modulating the metal—insulator transition temperature but requires that the dopants be incorporated during synthesis. Here we demonstrate a novel postsynthetic diffusive annealing approach for incorporating interstitial B dopants within VO2. The postsynthetic method allows for the tr...

Solid-state compounds wherein electrons cannot be described as noninteracting particles and instead show strongly correlated behavior are of interest both as systems manifesting novel quantum chemical phenomena as well as for electronic device applications. In the absence of predictive theoretical descriptors, modulation of the properties of these compounds tends to be challenging, and generalizable strategies for modulating closely coupled lattice, orbital, and spin degrees of freedom are exceedingly sparse. Here, it is shown that exfoliation mediated by cation intercalation can serve as a powerful means of modulating the electronic structure of layered correlated materials. Using a strongly correlated and charge-ordered layered compound, δ-Sr0.50V2O5, as a model system, it is shown that the band gap can be drastically altered from ca. 1.07 to 2.32 eV and the electron correlation strength can be greatly modified by intercalation-driven exfoliation to 2D nanosheets upon elimination of structural coherence...

Lithium transport and phase separation in and across interconnected electrode particles are investigated in this paper. This paper signifies the influential role of particle size variation on battery performance with phase-separating electrodes. In this work, a model is developed which accounts for lithium transport in the particles, phase separation, and interface reactions across the particle network. The implementation in 3D is carried out using the B-spline based finite cell method for a straightforward treatment of the Cahn–Hilliard equation and a flexible representation of particle geometry. Representative examples based on scanning transmission X-ray microscopy (STXM) images are simulated to discuss the factors that will influence phase separation during non-equilibrium lithiation and delithiation, as well as relaxation towards equilibrium. The simulations reveal that particles with a slight advance during (de-)lithiation at the beginning will strengthen their advance at the expense of neighboring particles, in a “winner-takes-all” fashion. Moreover, rapid reaction can suppress phase separation, both inside a single particle and across the particle network. Lastly, both particle size and size variation in electrodes composed of phase-separating materials ought to be small to avoid intra- and inter-particle phase separation. This study can serve as a guide for the design of battery electrodes composed of phase-separating materials.

The discovery and deployment of earth-abundant electrocatalysts for hydrogen evolution is central to the use of molecular hydrogen as a viable fuel. The edges of molybdenum sulfide are able to mediate proton adsorption and dihydrogen formation at relatively low overpotentials in acidic media. From a practical perspective, an optimal electrocatalyst must combine electrode level efficiency (reflected by high current densities and low Tafel slopes and overpotentials) with high intrinsic catalytic activity (measured by turnover frequency). Herein, we map both sets of parameters for molybdenum sulfide catalysts as a function of the annealing temperature across their amorphous to crystalline phase transition. Studies of local structure indicate that with increasing annealing temperature, molecular precursors are initially cross-linked to form [Mo3S13]2− clusters characterized by both apical/bridging S22− and unsaturated/terminal S22− moieties, which in turn are consumed to nucleate ultra-thin crystalline MoS2 domains. With increase of the annealing temperature, these nuclei coalesce to form larger nanosheets. Annealing and the resulting amorphous to crystalline transition involves a trade-off between the number of available sites (which is decreased with increasing crystallite size) and the intrinsic activity of the sites (which is improved with increasing crystallinity). Optimal hydrogen evolution reaction (HER) activity is observed for the molybdenum sulfide sample prepared by annealing at 300 °C, which comprises ultra-thin MoS2 nuclei embedded within a matrix of [Mo3S13]2− clusters. This sample is characterized by an overpotential value η10 of 176 mV, a Tafel slope of 49.2 mV dec−1, a turnover frequency of 1.15H2 per s per active site at −0.2 V versus reversible hydrogen electrode (RHE), and furthermore exhibits reasonable stability upon prolonged electrochemical cycling. The amorphous samples are found to be more susceptible to oxidation, which degrades the stability of the catalysts. The mapping of electrode-level parameters and intrinsic activity as a function of crystallite size provides vital design principles for constructing a viable electrocatalyst.

Electrochemical reactions within Li-ion batteries occur far from equilibrium and are accompanied by considerable heterogeneity. Many electrode materials undergo phase transformations upon insertion of cations. The sequence and propagation of these phase transformations determine energy dissipation and the proportion of actively intercalating materials, which play a vital role in influencing characteristics such as cyclability, degradation, and hysteresis. The heterogeneity within electrode materials stems in large measure from local variations of structure, surface states, and position within the electrode; these factors are poorly understood given limited studies of local structure. Here, we show based on scanning transmission X-ray microscopy studies of Li-ion intercalation within interconnected V2O5 particle networks that interconnects between cathode particles strongly influence the transport of Li-ions and the resulting spatial propagation of phase transformations across the network. Considerable phase heterogeneity is observed across interfaces that are rationalized based on phase field models that suggest that the propagation of Li-rich domains occurs preferentially across a single particle instead of concurrent lithiation and nucleation of Li-rich domains across the entire network. Further phase heterogeneity arises from defects and secondary growth of Li-rich phases at nanowire tips. These findings suggest that mesoscale architectures can potentially be designed with appropriately positioned interconnects to maximize the proportion of actively intercalating regions and to ensure equilibration of local current densities.

The perovskite cesium lead bromide (CsPbBr3) has emerged as an attractive thermally and chemically robust alternative to hybrid lead perovskite halides and analogues of this material show excellent tunability of exciton binding energies, high absorption cross-sections, and intense photoluminescence. Dimensional reduction, particularly in proximity of the Bohr exciton radius, allows for substantial tunability of the photophysical properties of this material as a result of quantum confinement. The use of surface passivating ligands, particularly alkylammonium cations, has been developed as a means of inducing directional growth and facilitates dimensional confinement of the obtained perovskite nanocrystals. Here, we demonstrate that the crystalline order of the ligand-shell assembly, as dictated by the length of the alkyl chains, the degree of branching, the reaction temperature, and ligand concentration, strongly influences the extent of dimensional confinement attainable for the perovskite nanoplatelets. The spatial extent of the ligand shell and the degree of ordering of ligand molecules greatly impact the diffusion and addition of monomeric species. The interplay between enthalpic stabilization from crystalline packing and entropic loss from loss of configurational degrees of freedom provides substantial opportunity to tune the parameter space as a function of ligand structure and reaction variables. Mechanistic understanding of thermodynamic and kinetic regimes provides a means to rationally optimize synthetic parameters to obtained desired dimensionality and thus allows for control over nanocrystal thickness in precise increments.

Selective elimination of network connectivity has emerged as an effective means of modifying the electronic structure of materials. Given its unique properties and diversity of polymorphs, V2O5 is an outstanding candidate. Recent studies have highlighted the benefit of utilizing metastable materials as cathode materials for multivalent ion batteries. In particular, novel polymorphs accessible from topochemical modification of ternary vanadium oxide bronzes have been identified as particularly interesting intercalation hosts. This is a study of the electronic structure of one such polymorph, e′-V2O5, using soft X-ray spectroscopy measurements and density functional theory calculations. This new double-layered polymorph of V2O5 has an increased interlayer separation that is found to lead to a dramatic increase in the band gap. Furthermore, the distortions brought on by the exfoliation process lead to a complex RIXS spectrum, showing d–d excitations, as well as low-energy charge transfer excitations. The comparison of the measurements and calculations is used to refine the crystal structure of e′-V2O5, which cannot be directly determined from X-ray diffraction data. In addition, distinct aspects of the electronic structure that make such polymorphs useful for correlated electron devices and electrode materials for intercalation batteries are discussed and linked to the crystal structure.

Semiconductor heterostructures for solar energy conversion interface light-harvesting semiconductor nanoparticles with wide-band-gap semiconductors that serve as charge acceptors. In such heterostructures, the kinetics of charge separation depend on the thermodynamic driving force, which is dictated by energetic offsets across the interface. A recently developed promising platform interfaces semiconductor quantum dots (QDs) with ternary vanadium oxides that have characteristic midgap states situated between the valence and conduction bands. In this work, we have prepared CdS/β-Pb0.33V2O5 heterostructures by both linker-assisted assembly and surface precipitation and contrasted these materials with CdSe/β-Pb0.33V2O5 heterostructures prepared by the same methods. Increased valence-band (VB) edge onsets in X-ray photoelectron spectra for CdS/β-Pb0.33V2O5 heterostructures relative to CdSe/β-Pb0.33V2O5 heterostructures suggest a positive shift in the VB edge potential and, therefore, an increased driving force...

Understanding the diffusion mechanisms of Li ions through host materials and the resulting phase evolution of intercalated phases is of paramount importance for designing electrode materials of rechargeable batteries. The formation of lithiation gradients and discrete domains during intercalation leads to the development of strain within the host material and is responsible for the observed capacities of most cathode materials being well below theoretically predicted values. Such mesoscale heterogeneity has also been implicated in the loss of capacity upon cycling. Due to their inherent complexity, the analysis of such heterogeneity is rather complex and precise understanding of the evolution of metal sites remains underexplored. In this work, we use phase-pure, single-crystalline V2O5 nanowires with dimensions of 183 ± 50 nm and lengths spanning tens of microns as a model cathode material and demonstrate that V K-edge X-ray absorption near-edge structure can be used as an effective probe of the local val...

Organic metal halide perovskites have rapidly emerged as among the leading candidates for the next generation of photovoltaic and light-emitting devices. The band gap, exciton binding energy, and absorption cross-section of these materials are tunable to some extent by compositional variation. Dimensional confinement represents an attractive alternative to compositional variation for tuning these properties via quantum confinement close to the Bohr radius. While the stabilization of few-layered nanoplatelets of methylammonium lead bromide has recently been demonstrated, mechanistic understanding of synthetic parameters resulting in dimensional confinement remains to be developed. Here we show that the layer thickness can be precisely modulated as a function of the chain length and concentration of the added alkylammonium cations. Surface capping ligands bind preferentially to sheets of corner sharing PbBr6 octahedra and thereby buffer the extent of supersaturation of monomeric units enabling precise modul...

Transition metal oxides are usually used as catalysts in the air cathode of lithium-air (Li-air) batteries. This study elucidates the mechanistic origin of the oxygen reduction reaction catalyzed by δ-MnO2 monolayers and maps the conditions for Li2O2 growth using a combination of first-principles calculations and mesoscale modeling. The MnO2 monolayer, in the absence of an applied potential, preferentially reacts with a Li atom instead of an O2 molecule to initiate the formation of LiO2. The oxygen reduction products (LiO2, Li2O2, and Li2O molecules) strongly interact with the MnO2 monolayer via the stabilization of Li-O chemical bonds with lattice oxygen atoms. As compared to the disproportionation reaction, direct lithiation reactions are the primary contributors to the stabilization of Li2O2 on the MnO2 monolayer. The energy profiles of (Li2O2)2 and (Li2O)2 nucleation on δ-MnO2 monolayer during the discharge process demonstrate that Li2O2 is the predominant discharge product and that further reduction to Li2O is inhibited by the high overpotential of 1.21 V. Interface structures have been examined to study the interaction between the Li2O2 and MnO2 layers. This study demonstrates that a Li2O2 film can be homogeneously deposited onto δ-MnO2 and that the Li2O2/MnO2 interface acts as an electrical conductor. A mesoscale model, developed based on findings from the first-principles calculations, further shows that Li2O2 is the primary product of electrochemical reactions when the applied potential is smaller than 2.4 V.