Applications In Energy Devices Research Articles

Intrinsically Electrochromic Deep Eutectic Solvents

AbstractMulti‐colored intrinsically electrochromic based Deep Eutectic Solvents (IEDES) have been firstly developed. IEDES composed by the suitable mixing between viologen salt derivatives as HBA and ethylene glycol (EG), glycerol (Gly) and poly(ethylene glycol) (PEG) as HBD have been prepared and characterized by thermal and electrochemical studies. A detailed electrochemical characterization of the IEDES using cyclic voltammetry studies in 2‐electrodes (ECDs) configuration cells were performed. The most promissory IEDES based on viologen salt derivatives can act simultaneously as electrolyte and electrochromic. Preliminary redox cycling studies showed a reversible and stable ECD composed by [(C5O2)2bpy]I2:EG at least until 1300 minutes. The coloration efficiency and reversibility can be tuned changing only the alcohol counterpart and/or the side chains and anion of the viologen derivatives. These IEDES can be explored as functional and efficient multi‐colored ECDs. Also, these innovative materials can open attractive applications for material science and energy devices.

Atomic-scale symmetry breaking for out-of-plane piezoelectricity in two-dimensional transition metal dichalcogenides

It is known that only in-plane piezoelectricity exists in pristine two dimensional (2D) transition metal dichalcogenides (TMDs). In this study, we demonstrate the creation of strong out-of-plane piezoelectricity in semiconducting 2H-MoTe2 flakes by an artificial atomic-scale symmetry breaking. The atomic-scale symmetry breaking associated with flexoelectricity was realized through Te vacancy formation by a simple thermal annealing of the 2D TMDs. The strong out-of-plane piezoelectricity was experimentally measured and confirmed by theoretical calculations. This strategy of atomic-scale symmetry modulation for out-of-plane piezoelectricity can be easily applied to a broader class of 2D TMD materials that have not been used for applications with out-of-plane piezoelectricity. Accordingly, it can stimulate the expansion of practical energy device applications with 2D TMD materials.

Stretchable/flexible silver nanowire Electrodes for energy device applications.

Research on sustainable and high-efficiency energy devices has recently emerged as an important global issue. These devices are now moving beyond the form of a bulk, rigid platform to a portable, flexible/stretchable format that is easily available in our daily lives. Similar to the development of an active layer for the production of next-generation energy devices, the fabrication of flexible/stretchable electrodes for the easy flow of electrons is also very important. Silver nanowire electrodes have high electronic conductivity even in a flexible/stretchable state due to their high aspect ratio and percolation network structures compared to conventional electrodes. Herein, we summarize the research in the field of flexible/stretchable electronics on energy devices fabricated using silver nanowires as the electrodes. Additionally, for a systematic presentation of the current research trends, this review classifies the surveyed research efforts into the categories of energy production, storage, and consumption.

Mesophase micelle-assisted electrodeposition and magnetisation behavior of meso-porous nickel films for efficient electrochemical energy and magnetic device applications

Mesoporous magnetic materials have found interesting potential applications in electrochemical energy harvesting and energy-efficient magnetic actuation device applications. Here we report on the electrodeposition and magnetic properties of mesoporous nickel films from lyotropic liquid crystal (LLC) templates formed by cetyltrimethylammoniumbromide (CTAB) cationic surfactant. Diffusion-controlled electrodeposition mechanism of nickel is determined. Films are electrodeposited under a constant current ranging from 1 to 7.5 mA cm−2 from an aqueous solution containing 0.1 M nickel sulphate, 0.2 M boric acid solution and CTAB with a concentration ranging from 0 to 50 wt.%. Mesopores develop an arranged hexagonal structure due to the micellar positional and orientational order reaching its highest value at 30 wt.% of CTAB at 2 mA cm−2. This is confirmed by transmission electron microscopy (TEM) and electrocatalytic surface area measurement. Electrodeposition current density and pH modify the mesoporous dimensions and therefore the magnetic properties change, tough hydrogen evolution as a side reaction influences the mesoporous structure. We observe an increased in-plane magnetic coercivity value to a maximum of 214 Oe for the mesoporous nickel film, which correlates with the increased interaction field. The widening of the coercivity distribution in first-order reversal curve (FORC) diagrams indicates that films with higher CTAB content have more inhomogeneous structure, which can lead to complex magnetization reversal mechanisms. The results of this study will help to exploit novel multifunctional magnetic and electrochemical energy materials and devices.

Low-energy hydrothermal fabrication of α-Ni(OH)2 nanosheet arrays as efficient electrodes for sustainable supercapacitors

This paper reports a low-energy pressure-free hydrothermal fabrication of α-Ni(OH)2 nanosheet arrays (NSAs) as effective electrodes for binder-free aqueous supercapacitors. The hydrothermal temperature was critical for the microstructure and electrochemical properties. At the low temperature of 95 °C, a highly interlaced α-Ni(OH)2 NSA was achieved. The successful preparation of uniform α-Ni(OH)2 NSAs was confirmed by several characterization techniques. For electrode applications in sustainable supercapacitors,the present α-Ni(OH)2 NSAs revealed a great capacitance of 1759 F/g, great rate capability of 50% at 20 A/g, and great cycle stability of 90.3% after 5000 cycles. Furthermore, aqueous two-electrode supercapacitors made of Ni(OH)2 NSAs possessed a large energy density of 44.5 Wh/kg at 400 W/kg. Therefore, this reduced energy hydrothermal preparation of α-Ni(OH)2 NSAs has great potential for efficient sustainable energy device applications.

Quantitative evaluation of skin shrinkage associated with non-invasive skin tightening: a simple method for reproducible linear measurement using microtattoos.

Non-invasive skin-tightening devices can induce thermal denaturation and skin shrinkage via externally applied radiofrequency emissions or high-frequency ultrasound. Therefore, the purpose of this study is to develop and test a method for measurement of skin reduction associated with application of such energy devices. Twenty-five healthy participants with mild to moderate skin laxity of the arms were enrolled. Pinpoint microtattoos were placed at each of the treatment sites to delineate two 6 × 12cm rectangles per subject. A non-stretchable filament, tape and marking pen apparatus was used to measure the size of each rectangle before treatment and at follow-up visit by two blinded investigators. After randomization, one side received a single pass with a radiofrequency device (6.78MHz), while the contralateral side received multiple passes. Participants underwent two treatment sessions to each side 2weeks apart, and returned for follow-up 4weeks after the second treatment. Length and area measurement were analyzed to assess precision and accuracy of measurements and to compare efficacy of treatment between pre- and post-treatment. Concordance correlation coefficients (CCC) demonstrated substantial inter-investigator reliability and precision in length measurements (CCC, 0.94 to 0.98 in pre-treatment; 0.95 to 0.98 in post-treatment). Measurements at the 6-week post-treatment follow-up demonstrated a statistically significant skin reduction in all six of the measured parameters. A simple skin measurement method requiring minimal instrumentation can quantitatively evaluate skin shrinkage associated with non-invasive skin-tightening devices.

Metal-organic framework patterns and membranes with heterogeneous pores for flow-assisted switchable separations

Porous metal-organic-frameworks (MOFs) are attractive materials for gas storage, separations, and catalytic reactions. A challenge exists, however, on how to introduce larger pores juxtaposed with the inherent micropores in different forms of MOFs, which would enable new functions and applications. Here we report the formation of heterogeneous pores within MOF particles, patterns, and membranes, using a discriminate etching chemistry, called silver-catalyzed decarboxylation. The heterogeneous pores are formed, even in highly stable MOFs, without altering the original structure. A decarboxylated MOF membrane is shown to have pH-responsive switchable selectivity for the flow-assisted separation of similarly sized proteins. We envision that our method will allow the use of heterogeneous pores for massive transfer and separation of complex and large molecules, and that the capability for patterning and positioning heterogeneous MOF films on diverse substrates bodes well for various energy and electronic device applications.

Polymer-Based Approach in Ceramic Materials Processing for Energy Device Applications

Polymer-Based Approach in Ceramic Materials Processing for Energy Device Applications

Surface Passivated Zinc Oxide (ZnO) Nanorods by Atomic Layer Deposition of Ultrathin ZnO Layers for Energy Device Applications

Chemically stoichiometric and electrically low-resistive high-quality zinc oxide (ZnO) nanostructures have been developed by surface passivation with atomic layer deposited ZnO layers. The impacts of homogeneous ZnO layer growth and its thickness on the physical properties ZnO nanorods were investigated. Vertically aligned ZnO nanorod structures were synthesized by two-step process, and the surface passivation was performed by atomic layer deposition ZnO at low temperatures. Surface passivated ZnO nanorods exhibit excellent improvement in crystallinity, chemical stoichiometry, optical, and electrical properties. Further, the surface passivated structures show significant enhancement in water-oxidation performance (nearly 3 orders of magnitude, i.e., μA → mA) with greatly reduced overpotentials. These investigations emphasize that surface passivation of hydrothermally grown ZnO nanostructures with the homogeneous materials can significantly enhance the structural and optical quality along with their device...

Investigations of half-metallic ferromagnetism and thermoelectric properties of cubic XCrO3 (X = Ca,Sr,Ba) compounds via first-principles approaches

In this paper, the physical aspects of the cubic phase XCrO3 (X=Ca,Sr,Ba) perovskites are studied by employing full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. These compounds have been found stable in ferromagnetic (FM) phase since they possess lower energy in FM phase compared to non-FM phase and their stability is also confirmed by calculating the enthalpy of formation (ΔH). The electronic structures of these compounds are analyzed with Trans and Blaha modified Becke–Johnson potential (TB-mBJ) for both spin up and spin down channels, which indicate their half-metallic characters. Analysis of density of states (DOS) shows major contributions of O-2p states in the valence band and Cr 3d-state in conduction band. A comparative analysis of crystal field effect (ΔEcrystal) and the exchange energies (direct Δx(d) and indirect Δx(pd)) tells about the main part of electronic spin in ferromagnetic character. The calculated magnetic moments make these compounds favorable for spintronic applications. In the end, thermoelectric parameters are computed for 200 K–800 K temperature range to explore potential of these compounds for applications in renewable energy devices.

Robust flexible WS2/PEDOT:PSS film for use in high-performance miniature supercapacitors

Layered WS2 nanosheet has advantages in the application of energy devices because of its distinctive structure and high electrochemical behaviors. The fabrication of high-quality free-standing WS2 film is anticipant and challenging in developing its flexible and miniature device. Here, using a highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as binder, flexible free-standing WS2/PEDOT:PSS film as miniature supercapacitors electrode materials was easily prepared by vacuum filtration method. The WS2/PEDOT:PSS film was characterized by scanning electron microscopy, high resolution transmission electron microscopy, atomic force microscopy, Raman spectrum, X-ray photoelectron spectroscopy and electrochemical technology. The free-standing WS2/PEDOT:PSS film with conductivity of 44 S cm−1 showed a good flexibility, robustly mechanical property and high electrochemical behaviors. The flexible film can bear 300 g weight and be used as a conducting wire in a circuit. The WS2/PEDOT:PSS film with thickness of ~2.1 μm exhibited high areal capacitance of 86 mF cm−2 and volumetric capacitance of 411 F cm−3 at 40 mV s−1 in 1.0 M H2SO4 solution. Besides, the capacitance retention could reach 107% of initial specific capacitance after 5000 charge-discharge cycles. Moreover, the flexible device based on WS2/PEDOT:PSS films could be assembled without any substrates and showed a volumetric capacitance of 87 F cm−3 at 10 mV s−1 and 86% capacitance retention of initial specific capacitance after 5000 cycles. These results implied the flexible free-standing WS2/PEDOT:PSS film has a potential application in flexible and miniature supercapacitors without any other substrates as current collectors.

Room-temperature growth (“farming”) and high-performance supercapacitor applications of highly crystalline CuO nanowires/graphene nanoplatelet nanopowders

We report a first-of-its-kind farming-like growth of nanopowders of CuO nanowires (NWs) via room-temperature thermal oxidation. Compared to conventional thermal annealing methods for producing copper oxide nanostructures, which require elevated temperatures (300–600 °C), the present method yields a large amount of highly crystalline CuO NW nanopowders at a much lower temperature (i.e., room temperature). Two-dimensional carbon nanostructures such as graphene nanoplatelets (GNPs) were used as supports for the growth of the CuO NWs. The GNPs were coated with Cu seed layers by the electroless plating method, which is suitable for mass production. After electroplating of Cu layers, the GNP supports were kept at room temperature and under constant humidity (50 or 60% relative humidity) for over 24 h, resulting in the dense wire-like morphology of copper oxide. Scanning electron microscopy, energy dispersive X-ray diffraction, X-ray diffraction, and Raman spectroscopy measurements revealed that the NWs consisted of highly crystalline monoclinic CuO. Once the NWs were formed, their morphology was stable for up to 168 h at room temperature. The as-prepared CuO nanopowders were tested as electrodes of electrochemical capacitors (or supercapacitors). In a three-electrode configuration, a working electrode made of CuO NWs exhibited an excellent mass-specific capacitance of 145 F g−1 at 5 mV s−1 in a 3 M KOH aqueous electrolyte. The growth of CuO nanopowders on GNPs illustrated in this study demonstrates a novel approach for the room-temperature synthesis of nanopowders, with promising applications in next-generation energy devices.

The pressure-induced indirect to direct bandgap transition and thermoelectric response in SrTiO3: An ab-initio study

In this paper, we investigate the electronic structure, optical and thermoelectric properties of the SrTiO3 (STO) at a variant pressure from 0 to 120 GPa. The thermodynamic and structural stability has been confirmed by the enthalpy of formation and tolerance factor. The implementation of pressure has been found to shift the indirect bandgap to direct bandgap at 107 GPa to tune the optical and thermoelectric properties. The optical behavior of STO has been discussed by the dielectric constant and refraction of light in the visible and ultraviolet region. Furthermore, the thermoelectric behavior has been explored by investigating the electrical conductivity, thermal conductivity, See-beck coefficient and power factor. The thermal efficiency has been elaborated from the figure of merit, which shows the studied materials are highly valuable for energy device applications.

Compensated thermal conductivity of metallically conductive Ta-doped TiO2

Electrical and thermal conductivities of epitaxial, high-quality Ta-doped TiO2 (Ta:TiO2) thin films were experimentally investigated in the temperature range of 35–375 K. Structurally identified as the anatase phase, degenerate Ta doping leads to high electrical conductivity in TiO2, reaching >105 (Ω-m)−1 at 5 at. % of Ta, making it a potential candidate for indium-free transparent conducting oxides. In stark contrast, Ta doping suppresses the thermal conductivity of TiO2 via strong phonon-impurity scattering imposed by the Ta dopant which has a high mass contrast with Ti that it substitutes. For instance, the near-peak value shows a >50% reduction, from 9.0 down to 4.4 W/m-K, at just 2 at. % doping at 100 K. Interestingly, further Ta doping beyond 2 at. % no longer reduces the measured total thermal conductivity, which is attributed to a high electronic contribution to thermal conduction that compensates the alloy-scattering loss, as well as possibly the renormalization of phonon dispersion relation in the heavy doping regime originating from doping-induced lattice stiffening. As a result, at high Ta doping, TiO2 exhibits high electrical conductivity without much degradation of thermal conductivity. For example, near room temperature, 5 at. % Ta doped TiO2 shows over 3 orders of magnitude enhancement in electrical conductivity from undoped TiO2, but with only less than 10% reduction in thermal conductivity. The metallic Ta:TiO2 maintaining reasonable good thermal conductivity might find application in energy devices where good conduction to both charge and heat is needed.

Bio-inspired design of hierarchical FeP nanostructure arrays for the hydrogen evolution reaction

Hierarchical FeP nanoarray films composed of FeP nanopetals were successfully synthesized via a bio-inspired hydrothermal route followed by phosphorization. Glycerol, as a crystal growth modifier, plays a significant role in controlling the morphology and structure of the FeO(OH) precursor during the biomineralization process, while the following transfer and pseudomorphic transformation of the FeO(OH) film successfully give rise to the FeP array film. The as-prepared FeP film electrodes exhibit excellent hydrogen evolution reaction (HER) performance over a wide pH range. Theoretical calculations reveal that the mixed P/Fe termination in the FeP film is responsible for the high catalytic activity of the nanostructured electrodes. This new insight will promote further explorations of efficient metal phosphoride-based catalysts for the HER. More importantly, this study bridges the gap between biological and inorganic self-assembling nanosystems and may open up a new avenue for the preparation of functional nanostructures with application in energy devices.

Large-area, low-cost, ultra-broadband, infrared perfect absorbers by coupled plasmonic-photonic micro-cavities

Perfect absorption of electromagnetic wave is emerging as a promising technology for its potential applications in harvesting solar energy, infrared detection and photovoltaic devices. Recent studies have reported a variety of plasmonic or meta-material structures, which are designed and fabricated to provide broadband absorption by utilizing multiple resonators in a composite unit cell. Coupled plasmonic-photonic micro-cavities, formed by using the colloidal crystal that does not have closed packed structure as the structural template, are surprisingly found to be efficient infrared absorption devices in an ultra-broadband frequency range. Taking the absorptivity above 0.9 into account, the operation bandwidth is up to 2.851 μm in the infrared range. The excellent absorption capability can be attributed to the cooperation effects of the plasmonic resonances by the metal caps and the photonic modes by the colloids. The absorber exhibits polarization-independent and wide-angle behaviors. These findings not only reveal the advantages of colloidal crystals as low-cost materials for ultra-broadband absorbers, but also provide inspiration for future development of high-performance, large-area infrared optoelectronic devices.

Contact Angle Analysis for the Prediction of Defect States of Graphene Grafted with Functional Groups

AbstractMass production of graphene is being actively pursued for applications in electronics and energy devices. However, a rapid and simple method to identify the defect states of graphene (which significantly affects the electronic property), prior to the fabrication of the devices, needs to be developed. The manufacturing process requires an easy assessment tool to identify the characteristics of the defects while avoiding cumbersome measurements. This study demonstrates the contact angle analysis to be a plausible assessment tool with the help of molecular dynamics simulations and experiments. The simulations are performed for water droplets on graphene grafted with the most probable functional groups. The contact angle and the shape of the water droplets are interpreted to estimate the type and density of the defects in graphene. This technique can be used as a screening step to identify defective graphene.

Amorphous MOF Introduced N-Doped Graphene: An Efficient and Versatile Electrocatalyst for Zinc–Air Battery and Water Splitting

Recently, developing metal–organic framework (MOF) derived carbon-based electrocatalysts has become more and more popular for large-scale application of renewable energy devices. However, the rational conversion of MOFs into a versatile platform for high-efficiency catalyst is still very challenging. Moreover, the relationship between the crystallinity of MOF precursor and the catalytic activity of resultant carbon-based catalyst is still not well-understood. In this work, a strategy for the synthesis of sheet-like mesoporous nitrogen-doped graphene (MNG) derived from amorphous MOFs is demonstrated. The amorphous MOF derived MNG showed much higher catalytic activity than that of nitrogen-doped carbon (MNC) derived from highly crystallized MOFs. This rationally designed MNG catalyst served as a multifunctional electrode in a zinc–air battery and a water splitting device, both of which showed electrocatalytic performance superior to those of platinum group metal (PGM) catalysts. The characterization analysi...

Robust Fabrication of Quantum Dots on Few‐Layer MoS2 by Soft Hydrogen Plasma and Post‐Annealing

AbstractApart from unique properties of layered transition‐metal dichalcogenide nanosheets like MoS2, quantum dots (QDs) from these layered materials promise novel science and applications due to their quantum confinement effect. However, the reported fabrication techniques for such QDs all involve the use of liquid organic solvents and the final material extraction from such liquid dispersions. Here a novel and convenient dry method for the synthesis of MoS2 quantum dots interspersed on few‐layer MoS2 using soft hydrogen plasma treatment followed by post‐annealing is demonstrated. The size of MoS2 nanodots can be well controlled by adjusting the working pressure of hydrogen plasma and post‐thermal annealing. This method relies on the cumulative hydrogen ion bombardment effect which can destroy the hexagonal structure of the top MoS2 layer and disintegrate the top layer into MoS2 nanodots and even QDs. Post‐thermal annealing can further reduce the size. Such MoS2 quantum dots interspersed on few‐layer MoS2 exhibit two new photoluminescence peaks at around 575 nm because of the quantum confinement effect. This dry method is versatile, scalable, and compatible with the semiconductor manufacturing processes, and can be extended to other layered materials for applications in hydrogen evolution reaction, catalysis, and energy devices.

Conjugated polymer-mediated synthesis of sulfur- and nitrogen-doped carbon nanotubes as efficient anode materials for sodium ion batteries

Heteroatom-doped carbon nanomaterials have attracted significant attention as anode materials for sodium-ion batteries (SIBs). Herein, we demonstrate a conjugated polymer-mediated synthesis of sulfur and nitrogen co-doped carbon nanotubes (S/N-CT) via the carbonization of sulfur-containing polyaniline (PANI) nanotubes. It is found that the carbonization technique greatly influences the structural features and thus the Na-storage behavior of the S/N-CT materials. The carbon nanotubes developed using a two-step carbonization process (heating at 400 °C and then at 900 °C) exhibit a high specific surface area, enlarged interlayer distance, small charge transfer resistance, enhanced reaction kinetics, as well as a large number of defects and active sites; further, they exhibit a high reversible capacity of 340 mAh·g–1 at 0.1 A·g–1 and a remarkable cycling stability with a capacity of 141 mAh·g–1 at 5 A·g–1 (94% retention after 3,000 cycles). Direct carbonization of conjugated polymers with a specific morphology is an eco-friendly and low-cost technique for the synthesis of dual atom-doped carbon nanomaterials for application in energy devices. However, the carbonization process should be carefully controlled in order to better tune the structure–property relationship.