Agri-waste derived electroactive carbon-iron oxide nanocomposite for oxygen reduction reaction: an experimental and theoretical study.

Herein, we have utilized agri-waste and amalgamating low Fe3+, to develop an economic iron oxide-carbon hybrid-based electrocatalyst for oxygen reduction reaction (ORR) with water as a main product following close to 4e- transfer process. The electrocatalytic activity is justified by electrochemical active surface area, synergetic effect, and density functional theory calculations.

The Origin of Thermal Gradient-Induced Voltage in Polyelectrolytes.

Ionic thermoelectric materials can generate large thermal voltages under temperature gradients while also being low-cost and environmentally friendly. Many electrolytes with large Seebeck coefficients are reported in recent years, however, the mechanism of the thermal voltage is remained elusive. In this work, three types of polyelectrolytes are studied with different cations and identified a significant contribution to their thermal voltage originating from a concentration gradient. This conclusion is based on studies of the loss and gain of water upon temperature changes, variations in conductivity with water content and temperature, and the voltages induced by changes in water content. The results are analyzed by the "hopping mode" dynamics of charge transport in electrolytes. The hydration of different cations influences the water concentration gradient, which affects the barrier height and ion-induced potential in the electrodes. This work shows that the hydro-voltage in ionic thermoelectric devices can be one order of magnitude larger than the contribution from thermodiffusion-induced potentials, and becomes the main contributor to energy harvesting when implemented into ionic thermoelectric supercapacitors. Together with the rationalized theoretical discussion, this work clarifies the mechanism of thermal voltages in electrolytes and provides a new path for the development of ionic thermoelectric materials.

Does Water-in-Salt Electrolyte Subdue Issues of Zn Batteries?

Zn-metal batteries (ZnBs) are safe and sustainable because of their operability in aqueous electrolytes, abundance of Zn, and recyclability. However, the thermodynamic instability of Zn metal in aqueous electrolytes is a major bottleneck for its commercialization. As such, Zn deposition (Zn2+ → Zn(s)) is continuously accompanied by the hydrogen evolution reaction (HER) (2H+ → H2 ) and dendritic growth that further accentuate the HER. Consequently, the local pH around the Zn electrode increases and promotes the formation of inactive and/or poorly conductive Zn passivation species (Zn + 2H2 O → Zn(OH)2 + H2 ) on the Zn. This aggravates the consumption of Zn and electrolyte and degrades the performance of ZnB. To propel HER beyond its thermodynamic potential (0 V vs standard hydrogen electrode (SHE) at pH 0), the concept of water-in-salt-electrolyte (WISE) has been employed in ZnBs. Since the publication of the first article on WISE for ZnB in 2016, this research area has progressed continuously. Here, an overview and discussion on this promising research direction for accelerating the maturity of ZnBs is provided. The review briefly describes the current issues with conventional aqueous electrolyte in ZnBs, including a historic overview and basic understanding of WISE. Furthermore, the application scenarios of WISE in ZnBs are detailed, with the description of various key mechanisms (e.g., side reactions, Zn electrodeposition, anions or cations intercalation in metal oxide or graphite, and ion transport at low temperature).

2D Zinc Oxide - Synthesis, Methodologies, Reaction Mechanism, and Applications.

Zinc oxide (ZnO) is a thermally stable n-type semiconducting material. ZnO 2D nanosheets have mainly gained substantial attention due to their unique properties, such as direct bandgap and strong excitonic binding energy at room temperature. These are widely utilized in piezotronics, energy storage, photodetectors, light-emitting diodes, solar cells, gas sensors, and photocatalysis. Notably, the chemical properties and performances of ZnO nanosheets largely depend on the nano-structuring that can be regulated and controlled through modulating synthetic strategies. Two synthetic approaches, top-down and bottom-up, are mainly employed for preparing ZnO 2D nanomaterials. However, owing to better results in producing defect-free nanostructures, homogenous chemical composition, etc., the bottom-up approach is extensively used compared to the top-down method for preparing ZnO 2D nanosheets. This review presents a comprehensive study on designing and developing 2D ZnO nanomaterials, followed by accenting its potential applications. To begin with, various synthetic strategies and attributes of ZnO 2D nanosheets are discussed, followed by focusing on methodologies and reaction mechanisms. Then, their deliberation toward batteries, supercapacitors, electronics/optoelectronics, photocatalysis, sensing, and piezoelectronic platforms are further discussed. Finally, the challenges and future opportunities are featured based on its current development.

Understanding of the Electrochemical Behavior of Lithium at Bilayer-Patched Epitaxial Graphene/4H-SiC.

Novel two-dimensional materials (2DMs) with balanced electrical conductivity and lithium (Li) storage capacity are desirable for next-generation rechargeable batteries as they may serve as high-performance anodes, improving output battery characteristics. Gaining an advanced understanding of the electrochemical behavior of lithium at the electrode surface and the changes in interior structure of 2DM-based electrodes caused by lithiation is a key component in the long-term process of the implementation of new electrodes into to a realistic device. Here, we showcase the advantages of bilayer-patched epitaxial graphene on 4H-SiC (0001) as a possible anode material in lithium-ion batteries. The presence of bilayer graphene patches is beneficial for the overall lithiation process because it results in enhanced quantum capacitance of the electrode and provides extra intercalation paths. By performing cyclic voltammetry and chronoamperometry measurements, we shed light on the redox behavior of lithium at the bilayer-patched epitaxial graphene electrode and find that the early-stage growth of lithium is governed by the instantaneous nucleation mechanism. The results also demonstrate the fast lithium-ion transport (~4.7-5.6 × 10-7 cm2∙s-1) to the bilayer-patched epitaxial graphene electrode. Raman measurements complemented by in-depth statistical analysis and density functional theory calculations enable us to comprehend the lithiation effect on the properties of bilayer-patched epitaxial graphene and ascribe the lithium intercalation-induced Raman G peak splitting to the disparity between graphene layers. The current results are helpful for further advancement of the design of graphene-based electrodes with targeted performance.

VO2 Nanostructures for Batteries and Supercapacitors: A Review.

Vanadium dioxide (VO2 ) received tremendous interest lately due to its unique structural, electronic, and optoelectronic properties. VO2 has been extensively used in electrochromic displays and memristors and its VO2 (B) polymorph is extensively utilized as electrode material in energy storage applications. More studies are focused on VO2 (B) nanostructures which displayed different energy storage behavior than the bulk VO2 . The present review provides a systematic overview of the progress in VO2 nanostructures syntheses and its application in energy storage devices. Herein, a general introduction, discussion about crystal structure, and syntheses of a variety of nanostructures such as nanowires, nanorods, nanobelts, nanotubes, carambola shaped, etc. are summarized. The energy storage application of VO2 nanostructure and its composites are also described in detail and categorically, e.g. Li-ion battery, Na-ion battery, and supercapacitors. The current status and challenges associated with VO2 nanostructures are reported. Finally, light has been shed for the overall performance improvement of VO2 nanostructure as potential electrode material for future application.

High-Resolution Filtration Patterning of Silver Nanowire Electrodes for Flexible and Transparent Optoelectronic Devices.

Silver nanowire (AgNW) electrodes attract significant attention in flexible and transparent optoelectronic devices; however, high-resolution patterning of AgNW electrodes remains a considerable challenge. In this study, we have introduced a simple technique for high-resolution solution patterning of AgNW networks, based on simple filtration of AgNW solution on a patterned polyimide shadow mask. This solution process allows the smallest pattern size of AgNW electrodes, down to a width of 3.5 µm. In addition, we have demonstrated the potential of these patterned AgNW electrodes for applications in flexible optoelectronic devices, such as photodetectors. Specifically, for flexible and semitransparent UV photodetectors, AgNW electrodes are embedded in sputtered ZnO films to enhance the photocurrent by light scattering and trapping, which resulted in a significantly enhanced photocurrent (up to 800%) compared to devices based on AgNW electrodes mounted on top of ZnO films. In addition, our photodetector could be operated well under extremely bent conditions (bending radius of approximately 770 µm) and provide excellent durability even after 500 bending cycles.

Can Hybrid Na-Air Batteries Outperform Nonaqueous Na-O2 Batteries?

In recent years, there has been an upsurge in the study of novel and alternative energy storage devices beyond lithium-based systems due to the exponential increase in price of lithium. Sodium (Na) metal-based batteries can be a possible alternative to lithium-based batteries due to the similar electrochemical voltage of Na and Li together with the thousand times higher natural abundance of Na compared to Li. Though two different kinds of Na-O2 batteries have been studied specifically based on electrolytes until now, very recently, a hybrid Na-air cell has shown distinctive advantage over nonaqueous cell systems. Hybrid Na-air batteries provide a fundamental advantage due to the formation of highly soluble discharge product (sodium hydroxide) which leads to low overpotentials for charge and discharge processes, high electrical energy efficiency, and good cyclic stability. Herein, the current status and challenges associated with hybrid Na-air batteries are reported. Also, a brief description of nonaqueous Na-O2 batteries and its close competition with hybrid Na-air batteries are provided.

2D MoS2 -Based Nanomaterials for Therapeutic, Bioimaging, and Biosensing Applications.

Molybdenum disulfide (MoS2 ), a typical layered 2D transition metal dichalcogenide, has received colossal interest in the past few years due to its unique structural, physicochemical, optical, and biological properties. While MoS2 is mostly applied in traditional industries such as dry lubricants, intercalation agents, and negative electrode material in lithium-ion batteries, its 2D and 0D forms have led to diverse applications in sensing, catalysis, therapy, and imaging. Herein, a systematic overview of the progress that is made in the field of MoS2 research with an emphasis on its different biomedical applications is presented. This article provides a general discussion on the basic structure and property of MoS2 and gives a detailed description of its different morphologies that are synthesized so far, namely, nanosheets, nanotubes, and quantum dots along with synthesis strategies. The biomedical applications of MoS2 -based nanocomposites are also described in detail and categorically, such as in varied therapeutic and diagnostic modalities like drug delivery, gene delivery, phototherapy, combined therapy, bioimaging, theranostics, and biosensing. Finally, a brief commentary on the current challenges and limitations being faced is provided, along with a discussion of some future perspectives for the overall improvement of MoS2 -based nanocomposites as a potential nanomedicine.

PVA-PDMS-Stearic acid composite nanofibrous mats with improved mechanical behavior for selective filtering applications.

In this work, we report a facile way to fabricate composite nanofibrous mats of polyvinyl alcohol (PVA), polydimethylsiloxane (PDMS), and stearic acid (SA) by employing the electrospinning-technique, with PDMS fraction ranging from 40w% to nearly 80w%. The results show that for a predetermined fraction of PVA and SA, incorporation of an optimal amount of PDMS is necessary for which the mats exhibit the best mechanical behavior. Beyond this optimal PDMS fraction, the mechanical properties of the composite mats deteriorate. This result has been attributed to the ability of the SA molecules to mediate binding between the PVA and PDMS long-chain molecules via van-der-Waals bonding. The morphological, structural, mechanical, and thermal characterizations respectively using SEM, XRD, DMA/tensile test, and DSC lend support to this explanation. By this method, it is possible to control the hydrophilicity/oleophilicity of the mats, and the mats show an excellent selective permeability to oil as compared to water and successfully filter water from a water-in-oil emulsion. Incorporation of SA not only serves to aid in electrospinning of a PDMS-rich nanofibrous mat with good mechanical strength and control over hydrophilicity/oleophilicity, but also has a potential use in fabricating sheets impregnated with phase change materials for thermal energy storage.

Facile Synthesis of SnS2 Nanostructures with Different Morphologies for High-Performance Supercapacitor Applications.

SnS2 is an emerging candidate for an electrode material because of the considerable interlayer spaces in its crystal structures and the large surface area. SnS2 as a photocatalyst and in lithium ion batteries has been reported. On the other hand, there are only a few reports of their supercapacitor applications. In this study, sheetlike SnS2 (SL-SnS2), flowerlike SnS2 (FL-SnS2), and ellipsoid-like SnS2 (EL-SnS2) were fabricated via a facile solvothermal route using different types of solvents. The results suggested that the FL-SnS2 exhibited better capacitive performance than the SL-SnS2 and EL-SnS2, which means that the morphology has a significant effect on the electrochemical reaction. The FL-SnS2 displayed higher supercapacitor performance with a high capacity of approximately ∼431.82 F/g at a current density of 1 A/g. The remarkable electrochemical performance of the FL-SnS2 could be attributed to the large specific surface area and better average pore size. These results suggest that a suitable solvent is appropriate for the large-scale construction of SnS2 with different morphologies and also has huge potential in the practical applications of high-performance supercapacitors.

Large-Area Cross-Aligned Silver Nanowire Electrodes for Flexible, Transparent, and Force-Sensitive Mechanochromic Touch Screens.

Silver nanowire (AgNW) networks are considered to be promising structures for use as flexible transparent electrodes for various optoelectronic devices. One important application of AgNW transparent electrodes is the flexible touch screens. However, the performances of flexible touch screens are still limited by the large surface roughness and low electrical to optical conductivity ratio of random network AgNW electrodes. In addition, although the perception of writing force on the touch screen enables a variety of different functions, the current technology still relies on the complicated capacitive force touch sensors. This paper demonstrates a simple and high-throughput bar-coating assembly technique for the fabrication of large-area (>20 × 20 cm2), highly cross-aligned AgNW networks for transparent electrodes with the sheet resistance of 21.0 Ω sq-1 at 95.0% of optical transmittance, which compares favorably with that of random AgNW networks (sheet resistance of 21.0 Ω sq-1 at 90.4% of optical transmittance). As a proof of concept demonstration, we fabricate flexible, transparent, and force-sensitive touch screens using cross-aligned AgNW electrodes integrated with mechanochromic spiropyran-polydimethylsiloxane composite film. Our force-sensitive touch screens enable the precise monitoring of dynamic writings, tracing and drawing of underneath pictures, and perception of handwriting patterns with locally different writing forces. The suggested technique provides a robust and powerful platform for the controllable assembly of nanowires beyond the scale of conventional fabrication techniques, which can find diverse applications in multifunctional flexible electronic and optoelectronic devices.

Rational design of hyperbranched 3D heteroarrays of SrS/CdS: synthesis, characterization and evaluation of photocatalytic properties for efficient hydrogen generation and organic dye degradation.

Hyperbranched 3D SrS/CdS nanostructures were synthesized using a one pot hydrothermal method. Transmission Electron Microscopy (TEM) and Field Emission-Scanning Electron Microscopy (FE-SEM) analysis showed the formation of flower-like structure and the crystalline phase was confirmed by powder X-ray diffraction. The prepared 3D SrS/CdS exhibited improved photocatalytic activity for water splitting leading to H(2) generation (AQY 10%) and nearly complete degradation of methyl orange (MO) dye. The dye degradation followed first order kinetics and the apparent reaction rate constant (k(app)) was 0.136 min(-1). The present 3D SrS/CdS structure promise to be efficient photocatalysts due to (i) the facile intersystem charge transfer resulting from their band alignment (ii) enhanced specific surface area and (iii) crystallinity.