Capacitive deionization (CDI) is a promising desalination technology, which operates at low pressure, low temperature, requires little infrastructure, and has the potential to consume less energy for ...brackish water desalination. However, CDI devices consume significantly more energy than the theoretical thermodynamic minimum, and this is at least partly due to resistive power dissipation. We here report our efforts to characterize electric resistances in a CDI system, with a focus on the resistance associated with the contact between current collectors and porous electrodes. We present an equivalent circuit model to describe resistive components in a CDI cell. We propose measurable figures of merit to characterize cell resistance. We also show that contact pressure between porous electrodes and current collectors can significantly reduce contact resistance. Lastly, we propose and test an alternative electrical contact configuration which uses a pore-filling conductive adhesive (silver epoxy) and achieves significant reductions in contact resistance.
3D‐Printed Transparent Glass Nguyen, Du T.; Meyers, Cameron; Yee, Timothy D. ...
Advanced materials (Weinheim)
29, Issue:
26
Journal Article
Peer reviewed
Open access
Silica inks are developed, which may be 3D printed and thermally processed to produce optically transparent glass structures with sub‐millimeter features in forms ranging from scaffolds to monoliths. ...The inks are composed of silica powder suspended in a liquid and are printed using direct ink writing. The printed structures are then dried and sintered at temperatures well below the silica melting point to form amorphous, solid, transparent glass structures. This technique enables the mold‐free formation of transparent glass structures previously inaccessible using conventional glass fabrication processes.
Transparent glasses are 3D printed using direct ink writing. Colloidal silica is suspended in a liquid, forming a shear‐thinning viscoelastic ink. The ink is printed into the desired shape, dried, and sintered, resulting in a transparent glass. Complex structures including lattices and multicomponent glasses are fabricated using this process.
We describe the synthesis and characterization of monolithic, ultralow density WS2 and MoS2 aerogels, as well as a high surface area MoS2/graphene hybrid aerogel. The monolithic WS2 and MoS2 aerogels ...are prepared via thermal decomposition of freeze-dried ammonium thio-molybdate (ATM) and ammonium thio-tungstate (ATT) solutions, respectively. The densities of the pure dichalcogenide aerogels represent 0.4% and 0.5% of full density MoS2 and WS2, respectively, and can be tailored by simply changing the initial ATM or ATT concentrations. Similar processing in the presence of the graphene aerogel results in a hybrid structure with MoS2 sheets conformally coating the graphene scaffold. This layered motif produces a ∼50 wt % MoS2 aerogel with BET surface area of ∼700 m2/g and an electrical conductivity of 112 S/m. The MoS2/graphene aerogel shows promising results as a hydrogen evolution reaction catalyst with low onset potential (∼100 mV) and high current density (100 mA/cm2 at 260 mV).
Carbon aerogels (CAs) are a unique class of high surface area materials derived by sol–gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility, ...and chemical inertness make them very promising materials for many applications, such as energy storage, catalysis, sorbents, and desalination. Since the first CAs were made via pyrolysis of resorcinol–formaldehyde (RF)-based organic aerogels in the late 1980s, the field has really grown. Recently, in addition to RF-derived amorphous CAs, several other carbon allotropes have been realized in aerogel form: carbon nanotubes (CNTs), graphene, graphite, and diamond. Furthermore, the popularity of graphene aerogels has inspired research into aerogels made of a host of graphene analog materials (e.g., boron nitride, transition metal dichalcogenides, etc.), with potential for an even wider array of applications. Finally, the development of three-dimensional-printed aerogels provides the potential for CAs to have an even broader impact on energy-related technologies. Here, we will present recent work covering the novel synthesis of RF-derived, CNT, graphene, graphite, diamond, and graphene analog aerogels.
We report the synthesis of ultra-low-density three-dimensional macroassemblies of graphene sheets that exhibit high electrical conductivities and large internal surface areas. These materials are ...prepared as monolithic solids from suspensions of single-layer graphene oxide in which organic sol−gel chemistry is used to cross-link the individual sheets. The resulting gels are supercritically dried and then thermally reduced to yield graphene aerogels with densities approaching 10 mg/cm3. In contrast to methods that utilize physical cross-links between GO, this approach provides covalent carbon bonding between the graphene sheets. These graphene aerogels exhibit an improvement in bulk electrical conductivity of more than 2 orders of magnitude (∼1 × 102 S/m) compared to graphene assemblies with physical cross-links alone (∼5 × 10−1 S/m). The graphene aerogels also possess large surface areas (584 m2/g) and pore volumes (2.96 cm3/g), making these materials viable candidates for use in energy storage, catalysis, and sensing applications.
Nanoporous metals have many technologically promising applications, but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate ...that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only 1 nm thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000°C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO2 ALD coatings. Our results open the door to high-temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.
The effects of nanoconfinement on the structural phase transition, H2 release and uptake, and the emission of toxic diborane (B2H6) on desorption of LiBH4 have been comprehensively investigated in ...the presence of various porous hard carbon templates at a variety of pore sizes. Calorimetry signatures of both the structural phase transition and melting of nanoconfined LiBH4 shifted to a lower temperature with respect to the bulk, finally vanishing below a pore size around 4 nm. The desorption of LiBH4 confined in these nanoporous carbons shows a systematic and monotonic decrease in the desorption temperature and concomitantly, mass spectroscopic analysis indicated a gradual reduction of the partial pressure of B2H6 with decreasing pore size, suggesting that formation of stable closoborane salts may be avoided by interrupting the reaction pathway. This represents a major breakthrough in the reversibility of boron-based hydrogen storage systems, where capacity is lost in the formation of stable B−H species on cycling. Different carbon preparation techniques suggest that the confinement size, and not solely surface interactions, may be used to tune the properties of complex hydrides for kinetic and reaction pathway improvements for hydrogen storage applications.
Using atomic layer deposition (ALD), we show that Pt nanoparticles can be deposited on the inner surfaces of carbon aerogels (CA). The resultant Pt-loaded materials exhibit high catalytic activity ...for the oxidation of CO even at loading levels as low as ∼0.05 mg Pt/cm2. We observe a conversion efficiency of nearly 100% in the 150−250 °C temperatures range, and the total conversion rate seems to be limited only by the thermal stability of the CA support in ambient oxygen. The ALD approach described here is universal in nature, and can be applied to the design of new catalytic materials for a variety of applications, including fuel cells, hydrogen storage, pollution control, green chemistry, and liquid fuel production.
Porous electrode capacitors are used extensively in systems which store energy, harvest mixing energy, or desalinate water. These electrodes can possess a hierarchical pore structure with larger ...macroscale pores allowing for facile ion and fluid transport, and smaller, nanometer-scale pores enabling significant ion storage. We here present a combined theoretical (linear circuit model) and experimental (electrochemical impedance spectroscopy) study of porous carbon electrode capacitors which integrate nanoscale pores into a micron-scale porous network. Our experiments are performed on a set of custom-fabricated hierarchical carbon aerogel electrodes with varying pore structure, including electrodes with sub-nanometer (sub-nm) pores. Our combined theory and experimental approach allows us to demonstrate the utility of our model, perform detailed characterizations of our electrodes, study the effects of pore structure variations on impedance, and propose hierarchical electrode design and characterization guidelines. Further, we demonstrate that our approach is promising toward the detailed study of ion storage mechanisms in sub-nm pores.
•Novel framework for characterizing hierarchical and bimodal supercapacitor electrodes.•First detailed characterization of hierarchical carbon aerogel monolith electrode set.•Novel measurements and analysis of an HCAM electrode with sub-nanometer sized pores.
Ultrahigh-Temperature Ceramic Aerogels Cahill, James T; Turner, Sally; Ye, Jianchao ...
Chemistry of materials,
05/2019, Volume:
31, Issue:
10
Journal Article
Peer reviewed
Open access
We demonstrate the synthesis of high-surface-area, low-density refractory aerogels. The monolithic hafnium boride (HfB2) and zirconium boride (ZrB2) aerogels are prepared via borothermal reduction of ...precursor hafnia and zirconia aerogels, respectively, consisting of a fine mixture of boron nanoparticles and the metal oxide. This precursor boron–metal oxide (B–MO2) composite aerogel was synthesized by modifying the pure ethanol solvent typically used in the epoxide-initiated sol–gel synthesis of metal oxide aerogels with an ethanolic boron nanoparticle suspension. After reduction, precursor aerogels are converted to metal boride aerogels containing primary particles in the sub-100 nm regime. The relative densities of the HfB2 and ZrB2 aerogels are 3 and 7%, respectively, and could be tailored by simply changing the density of the precursor aerogels via modifying the reagent concentrations or the drying conditions. Thermal conductivities of the ZrB2 monoliths ranged from 0.18 to 0.33 W/(m K). The surface areas of the HfB2 and ZrB2 aerogels were 10 and 19 m2/g, respectively. Successful reduction of the aerogels to the diboride phase was confirmed by X-ray diffraction.
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