Potential Gradient-Driven Dual-Functional Electrochromic and Electrochemical Device Based on a Shared Electrode Design.

The integration of electrochromic devices and energy storage systems in wearable electronics is highly desirable yet challenging, because self-powered electrochromic devices often require an open system design for continuous replenishment of the strong oxidants to enable the coloring/bleaching processes. A self-powered electrochromic device has been developed with a close configuration by integrating a Zn/MnO2 ionic battery into the Prussian blue (PB)-based electrochromic system. Zn and MnO2 electrodes, as dual shared electrodes, the former one can reduce the PB electrode to the Prussian white (PW) electrode and serves as the anode in the battery; the latter electrode can oxidize the PW electrode to its initial state and acts as the cathode in the battery. The bleaching/coloring processes are driven by the gradient potential between Zn/PB and PW/MnO2 electrodes. The as-prepared Zn||PB||MnO2 system demonstrates superior electrochromic performance, including excellent optical contrast (80.6%), fast self-bleaching/coloring speed (2.0/3.2 s for bleaching/coloring), and long-term self-powered electrochromic cycles. An air-working Zn||PB||MnO2 device is also developed with a 70.3% optical contrast, fast switching speed (2.2/4.8 s for bleaching/coloring), and over 80 self-bleaching/coloring cycles. Furthermore, the closed nature enables the fabrication of various flexible electrochromic devices, exhibiting great potentials for the next-generation wearable electrochromic devices.

Room temperature sensing of primary alcohols via polyaniline/zirconium disulphide.

Among the primary alcohols, ethanol is referred to as a heavy chemical due to its many applications in a variety of industries. Detection of primary alcohols can be deployed as a non-invasive method in medical diagnosis and safety measures in food processing companies. Zirconium disulphide is a novel 2D layered material with exotic features when in mono or few layers, which include fast electron transport, high carrier mobility and sizeable band gap. ZrS2 and PANI were fabricated using liquid exfoliation and chemical polymerization methods respectively. Functionalization of the conducting polyaniline with ZrS2 was done using facile sonication process. The sensor showed good sensitivities (43%, 58% and 104%) which were estimated from slopes of the linear fitted plots with fast response-recovery times of 8 s and 27 s (111 ppm); 12 s and 130 s (77 ppm); and 58 s and 88 s (58 ppm). Good reproducibility at three repeated measurements (111 ppm, 77 ppm and 58 ppm) was also observed for methanol, ethanol, and isopropanol vapours respectively. Meanwhile, the sensor displayed more linearity and sensitivity towards isopropanol compared to methanol and ethanol. The sensor showed good performance even at RH values close to 100% making it a potential alcohol breath analyser.

Synthesis, Characterization, and Electrochemical Evaluation of Copper Sulfide Nanoparticles and Their Application for Non-Enzymatic Glucose Detection in Blood Samples.

Glutathione-capped copper sulfide (CuxSy) nanoparticles with two different average sizes were successfully achieved by using a simple reduction process that involves only changing the reaction temperature. Temperature-induced changes in the size of CuxSy nanoparticles resulted in particles with different optical, morphological, and electrochemical properties. The dependence of electrochemical sensing properties on the sizes of CuxSy nanoparticles was studied by using voltammetric and amperometric techniques. The spherical CuxSy nanoparticles with the average particle size of 25 ± 0.6 nm were found to be highly conductive as compared to CuxSy nanoparticles with the average particle size of 4.5 ± 0.2 nm. The spherical CuxSy nanoparticles exhibited a low bandgap energy (Eg) of 1.87 eV, resulting in superior electrochemical properties and improved electron transfer during glucose detection. The sensor showed a very good electrocatalytic activity toward glucose molecules in the presence of interference species such as uric acid (UA), ascorbic acid (AA), fructose, sodium chloride, and sucrose. These species are often present in low concentrations in the blood. The sensor demonstrated an excellent dynamic linear range between 0.2 to 16 mM, detection limit of 0.2 mM, and sensitivity of 0.013 mA/mM. The applicability of the developed sensor for real field determination of glucose was demonstrated by use of spiked blood samples, which confirmed that the developed sensor had great potential for real analysis of blood glucose levels.

Novel 2D-AuSe nanostructures as effective platinum replacement counter electrodes in dye-sensitized solar cells.

Studies to improve the efficiency of dye-sensitized solar cells (DSSCs) include, but are not limited to, finding alternatives such as 2D layered materials as replacement counter electrodes (CEs) to the commonly used Pt. Herein, we report for the first time, the use of AuSe as a counter electrode for the reduction of triiodide ions (I3 -) to iodide ions (I-). The colloidal synthesis of gold selenide nanostructures produced α-AuSe and ß-AuSe dominated products as determined by XRD. Electron microscopy showed α-AuSe having belt-like structures while ß-AuSe had a plate-like morphology. EDS mapping confirmed the elemental composition and homogeneity of the AuSe CEs. Cyclic voltammetry curves of the AuSe CEs displayed the double set of reduction-oxidation peaks associated with the reactions in the I3 -/I- electrolyte and therefore were comparable to the Pt CV curve. The α-AuSe CE showed better electrocatalytic activity with a reduction current of 6.1 mA than that of ß-AuSe and Pt CEs, which were 4.2 mA and 4.8 mA, respectively. The peak-to-peak separation (ΔE pp) for the α-AuSe CE was also more favourable with a value of 532 mV over that of the ß-AuSe CE of 739 mV however, both values were larger than that of the Pt CE, which was found to be 468 mV. The EIS and Tafel plot data showed that α-AuSe had the best catalytic activity compared to ß-AuSe and was comparable to Pt. The DSSC using α-AuSe as a CE had the highest PCE (6.94%) as compared to Pt (4.89%) and ß-AuSe (3.47%). The lower efficiency for Pt was attributed to the poorer fill factor. With these novel results, α-AuSe is an excellent candidate to be used as an alternative CE to Pt in DSSCs.

Lignocellulosic Biomass Waste-Derived Cellulose Nanocrystals and Carbon Nanomaterials: A Review.

Rapid population and economic growth, excessive use of fossil fuels, and climate change have contributed to a serious turn towards environmental management and sustainability. The agricultural sector is a big contributor to (lignocellulosic) waste, which accumulates in landfills and ultimately gets burned, polluting the environment. In response to the current climate-change crisis, policymakers and researchers are, respectively, encouraging and seeking ways of creating value-added products from generated waste. Recently, agricultural waste has been regularly appearing in articles communicating the production of a range of carbon and polymeric materials worldwide. The extraction of cellulose nanocrystals (CNCs) and carbon quantum dots (CQDs) from biomass waste partially occupies some of the waste-recycling and management space. Further, the new materials generated from this waste promise to be effective and competitive in emerging markets. This short review summarizes recent work in the area of CNCs and CQDs synthesised from biomass waste. Synthesis methods, properties, and prospective application of these materials are summarized. Current challenges and the benefits of using biomass waste are also discussed.

Laser Assisted Catalytic Growth of Silicon Nanowires Using Gold and Nickel Catalysts.

Laser assisted synthesis of silicon nanowires (SiNWs) was successfully achieved through the use of gold and nickel as catalysts. The diameter of the resulting SiNWs was found to be dependent on that of the catalyst in the case of gold catalyst. The gold catalysed silicon nanowires were unevenly curved and branched owing to the high kinetic energy possessed by gold nanoparticles (AuNPs) at relatively high processing temperature. The use of nickel as catalyst resulted in the formation of several SiNWs on a single nickel catalyst crystallite due to interconnection of the nickel metal crystallites at processing temperature. The morphology of SiNWs catalysed by both nickel and gold was controlled by optimising the laser energy during ablation.

Evaluating the Effect of Varying the Metal Precursor in the Colloidal Synthesis of MoSe2 Nanomaterials and Their Application as Electrodes in the Hydrogen Evolution Reaction.

Herein we report on the use of different metal precursors in the synthesis of MoSe2 nanomaterials in order to control their morphology. The use of Mo(CO)6 as the metal precursor resulted in the formation of wrinkled few-layer nanosheets, while the use of H2MoO4 as the metal precursor resulted in the formation of nanoflowers. To investigate the effect of the morphologies on their performance as catalysts in the hydrogen evolution reaction, electrochemical characterization was done using linear sweep voltammetry (LSV), cyclic voltammetry (CV), and electrical impedance spectroscopy (EIS). The MoSe2 nanoflowers were found to have superior electrochemical performance towards the hydrogen evolution reaction with a lower Tafel slope, on-set potential, and overpotential at 10 mA/cm2 compared to the wrinkled few-layer nanosheets. This was found to be due to the higher effective electrochemical surface area of the nanoflowers compared to the nanosheets which suggests a higher number of exposed edge sites in the nanoflowers.

Probing the stoichiometry dependent catalytic activity of nickel selenide counter electrodes in the redox reaction of iodide/triiodide electrolyte in dye sensitized solar cells.

Nickel selenide (Ni x Se y ) systems have received much attention in recent years as potential low cost counter electrodes (CEs) in dye sensitized solar cells (DSSCs). Their electrocatalytic activities are comparable to that of the conventional platinum CE. Despite their achievements, the effect of stoichiometry on their catalytic performance as CEs in DSSCs still remains unclear, hence the motivation for this work. Different stoichiometries of Ni x Se y were synthesized via a colloidal method in oleylamine or oleylamine/oleic acid mixture at the appropriate synthetic temperature and Ni to Se precursor ratio. X-ray diffraction revealed that different stoichiometries of nickel selenide were formed namely, NiSe2, Ni3Se4, Ni0.85Se, NiSe and Ni3Se2. Scanning electron microscopy showed that all the stoichiometries had predominantly spherical-like morphologies. Cyclic voltammetry, electrochemical impedance spectroscopy analysis and the photovoltaic performances of the DSSCs fabricated using the different Ni x Se y CEs revealed that selenium rich stoichiometries performed better than the nickel rich ones. Consequently, the catalytic activity towards the redox reaction of the triiodide/iodide electrolyte and hence the power conversion efficiency (PCE) followed the order of NiSe2 > Ni3Se4 > Ni0.85Se > NiSe > Ni3Se2 with PCE values of 3.31%, 3.25%, 3.17%, 2.35% and 1.52% respectively under ambient conditions.

Elucidating the effect of precursor decomposition time on the structural and optical properties of copper(i) nitride nanocubes.

To study the effect of time on the colloidal synthesis of Cu3N nanoparticles, copper(ii) nitrate was thermally decomposed at 260 °C for up to 60 min in octadecylamine as a stabilizing ligand. Thermolysis of the nitrate followed four steps which included; nucleation, growth, ripening and decomposition. At 5 min, partially developed nanocubes were found in a dense population of Cu3N nuclei. Well-defined Cu3N nanocubes were obtained at 15 min with no presence of the nuclei. TEM images showed disintegration of the cubes at 20 min and as time progressed, all the Cu3N decomposed to Cu by 60 min. The formation of the Cu3N nanocubes was confirmed by XRD and XPS. FTIR suggested the formation of a nitrile (RCN) as a result of the thermal decomposition in octadecylamine (ODA) and this was confirmed using NMR and hence, a reaction mechanism was then proposed. The optical properties of the as-synthesized Cu3N were studied using UV-vis and photoluminescence spectroscopies. The absorption spectra for particles synthesized from 5 min to 15 min showed a singular exciton peak while from 20 min to 60 min two peaks were observed. The two peaks may both be associated with the two direct transitions observed in Cu3N or the more red-shifted peak could be a result of localized surface plasmon resonance due to the Cu nanoparticles. Nevertheless, similar to other studies, it is clear that the optical properties of Cu3N are complex.

Fabrication of a Schottky Device Using CuSe Nanoparticles: Colloidal versus Microwave Digestive Synthesis.

Herein we report on a nearly ideal Schottky diode device fabricated from Cu(2-x)Se nanoparticles synthesized using the microwave digestive method. The thermionic theory using data extracted from the experimental I-V curve resulted in the ideality factor of 4.35 and the barrier height of 0.895 eV whilst the Cheung's method resulted in the ideality factor, barrier height and series resistance of 1.04, 0.00259 eV and 0.870 Ω respectively. The Cheung's method is thought to be the most accurate as it takes into account the series resistance. The obtained values therefore are indicative of good diode behaviour of the device and this is a highly sought after goal in all electronic materials development.

Efficient luminescent down-shifting detectors based on colloidal quantum dots for dual-band detection applications.

A colloidal quantum dot (QD) luminescent down-shifting (LDS) layer is used to sensitize an InGaAs short wavelength infrared photodetector to the near UV spectral band. An average improvement in the external quantum efficiency (EQE) from 1.8% to 21% across the near UV is realized using an LDS layer consisting of PbS/CdS core/shell QDs embedded in PMMA. A simple model is used to fit the experimental EQE data. A UV sensitive InGaAs imaging array is demonstrated and the effect of the LDS layer on the optical resolution is calculated. The bandwidth of the LDS detector under UV illumination is characterized and shown to be determined by the photoluminescence lifetime of the QDs.

CoS-carbon nanotube heterostructure: one-step synthesis and optical properties.

This article reports on the synthesis, characterization, and optical properties of a cobalt sulphide (CoS) quantum dot (QD)-decorated multi-walled carbon nanotube (MWCNT) heterostructure. A novel one-pot chemical-solution route has been used for the in situ synthesis of a CoS-decorated MWCNT heterostructure without disturbing the inherent structure of the MWCNTs. The synthesized heterostructure has been extensively characterized by scanning electron microscopy, scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier transform infrared spectrometry. The UV-absorption and fluorescence spectral properties of pristine MWCNTs are significantly improved after heterostructure formation with CoS-QDs.

A facile route for the synthesis of poly(N-vinylcarbazole)/manganese sulphide quantum dots nanocomposites with enhanced optical properties.

This communication describes a facile route for the synthesis of manganese sulphide (MnS) quantum dots (QDs) contained in poly(N-vinyl carbazole) (PNVC) nanocomposites. MnS QDs were synthesized using the single-source precursor method by thermolysing tetramethylthiuram disulfide manganese complex in hexadecylamine (HDA). Two different methods were used for the synthesis of MnS QD incorporated PNVC nanocomposites. The first method entailed the stirring of a mixture of MnS QDs and PNVC in chloroform (CHCl3) at room temperature and the second method was the refluxing of MnS QDs and PNVC solution in CHCl3 at an elevated temperature. A field emission electron microscope (FESEM) study revealed that the dispersion of MnS QDs in a PNVC matrix was improved in the case of nanocomposites prepared by the second method. The optical properties of pure PNVC were significantly altered for the case of nanocomposite prepared by the second route.