Inkjet-printed graphene electrodes for dye-sensitized solar cells

We present a stable inkjet printable graphene ink, formulated in isopropyl alcohol via liquid phase exfoliation of chemically pristine graphite with a polymer stabilizer. The rheology and low deposition temperature of the ink allow uniform printing. We use the graphene ink to fabricate counter electrodes (CE) for natural and ruthenium-based dye-sensitized solar cells (DSSCs). The repeatability of the printing process for the CEs is demonstrated through an array of inkjet-printed graphene electrodes, with ∼5% standard deviation in the sheet resistance. As photosensitizers, we investigate natural tropical dye extracts from Pennisetum glaucum, Hibiscus sabdariffa and Caesalpinia pulcherrima. Among the three natural dyes, we find extracts from C. pulcherrima exhibit the best performance, with ∼0.9% conversion efficiency using a printed graphene CE and a comparable ∼1.1% efficiency using a platinum (Pt) CE. When used with N719 dye, the inkjet-printed graphene CE shows a ∼3.0% conversion efficiency, compared to ∼4.4% obtained using Pt CEs. Our results show that inkjet printable graphene inks, without any chemical functionalization, offers a flexible and scalable fabrication route, with a material cost of only ∼2.7% of the equivalent solution processed Pt-based electrodes.Authors acknowledge support from CAPREX, Cambridge Africa Alborada Fund, Carnegie-University of Ghana Next Generation of Africa Academics programme and the Royal Academy of Engineering (RAEng) through a research fellowship (Graphlex)

Nanostructured stannic oxide: Synthesis and characterisation for potential energy storage applications

SnO2 nanoparticles were synthesized using the hydrothermal technique. Well crystalline particles with different morphologies and crystallite size in the range of 2 nm–10 nm were obtained by using Urea and Soduim Borohydride as reducing agents, and deploying Dioctyl Sulfosuccinate Sodium Salt (AOT) and Cetyl Trimethyl ammonium bromide (CTAB) as the surfactants. Samples have been characterised by X-ray diffraction, Scanning Electron microscopy, Energy Dispersive X-ray spectroscopy, specific surface area, porosity, and Fourier Transform Infrared spectroscopy. Preliminary studies on the potential electrochemical properties of the as-produced nanoparticles were investigated using cyclic voltammetry, electrochemical impedance spectroscopy and potentiostatic charge-discharge in aqueous KOH electrolyte. The surfactant and reducing agents used in the synthesis procedure of SnO2 nanoparticles influenced the particle size and the morphology, which in turn influenced the capacitance of the SnO2 nanoparticles. The SnO2 electrode material showed pseudocapacitor properties with a maximum capacitance value of 1.6 Fg−1 at a scan rate of 5 mVs−1, an efficiency of 52% at a current of 1 mA and a maximum capacitance retention of about 40% after 10 cycles at a current of 1 mA. From the Nyquist plot, The ESR for the samples increase accordingly as SCA (31.5 Ω) < SAA (31.85 Ω) < SE (36.3 Ω) < SAT (36.92 Ω) < SCT (40.41 Ω) < SA < SC (53.97 Ω). These values are a confirmation of the low capacitance, efficiencies and capacitance retention recorded. The results obtained demonstrate the potential electrochemical storage applications of SnO2 nanoparticles without the addition of conductive materials. Keywords: SnO2 nanoparticles, Supercapacitor, Hydrothermal technique, Cyclic voltammetr

Extraction of bio-oil during pyrolysis of locally sourced palm kernel shells: Effect of process parameters

The aim of this study was to determine the effect of particle size, pyrolysis temperature and residence time on the pyrolysis of locally sourced palm kernel shells and to characterize the bio-oil products. Pyrolysis experiments were performed at pyrolysis temperatures between 350 °C and 550 °C and particles sizes of 1.18 mm, 2.36 mm and 5 mm for a residence time not greater than 120 min. The maximum bio-oil yield was 38.67 wt% at 450 °C for a feed particle size of 1.18 mm with a residence time of 95 min. It was observed that the percentage of liquid collection was 28% of the total biomass feed for particle size of 1.18 mm. In terms of the effect of temperature, the lowest bio-oil yield was 28% of the total biomass feed at temperature of 550 °C. For the variation in residence time and the associated effects, the maximum liquid product was 38.67 wt% of biomass feed, at a particle size of 1.18 mm for 95 min. As observed, the optimum residence time was 95 min as times either side led to a decrease in the liquid yield. The bio-oil products were analysed by Fourier Transform Infra-Red Spectroscopy (FTIR) and Gas Chromatography-Mass Spectrometry (GC-MS). The FTIR analysis showed that the bio-oil was dominated by phenol and its derivatives. The phenol (38.44%), 2-methoxy-phenol (17.34%) and 2, 6-dimethoxy phenol (8.65%) that were identified by GC-MS analyses are highly suitable for extraction from bio-oil as value-added chemicals. The highly oxygenated oils can therefore be upgraded in order to be used in other applications such as transportation fuels. Keywords: Fixed bed reactor, Pyrolysis, Biomass, Palm kernel shell, Bio-oi

Catalytic abatement of CO species from incomplete combustion of solid fuels used in domestic cooking

This study reveals a first time approach to catalytic based interventions primarily on indoor air pollution emanating from commercial and household solid fuel burning in a region in Nigeria. An intensive survey of the temperatures at different locations in the common stoves used for cooking was conducted so as to ascertain temperatures suitable for catalyst efficiency and stability. Furthermore, cobalt and iron based catalysts were prepared using ultra stable Y type zeolite as supports. The synthesized catalysts were characterized for its physico-chemical properties. The catalytic efficiency of the supported catalysts was tested using simulated exhaust gases in a fix bed reactor. The study further explored real time testing of the catalyzed ceramic monolith using two different wood species. First, the best catalyst in terms of simulated exhaust testing was selected. Consequently, a small layer of zeolite Y was deposited at 3% of the monolith weight to enhance the subsequent adhesion of the best catalyst powder to the structured monolith. Then to catalyze the zeolite Y wash-coated monolith with the cobalt precursor, the dip coating technique was used. From the results, the average values of temperatures observed from the surveyed cook stoves using wood and plant residue as fuel were confirmed to be in the range of 203–425 °C which is considered suitable for catalysts activity. The Co/ZY catalyst showed approximately 100% CO conversion (T100) at 250 °C for initial CO concentration of 1000 ppm, making it the most effective, while T100 was increased to 275 °C and 325 °C for Fe/ZY and Co-Fe/ZY catalyst respectively at an exhaust residence time of 20000 h−1. The catalytic converter in real time testing for CO abatement performed well for both wood species. Only minor differences have been noticed

A comparative study of DFT/LDA with higher levels of theory on π-π interactions: A typical case for the benzene dimer

Abstract The description of the interactions involving species that have π-π configuration presents a real challenge in utilizing theoretical calculations. The problem arises from the kind of theoretical approaches employed to describe the nature of these non-covalent interactions. Various workers have described the interactions purely as Van der Waals, whilst others consider it as a competition between many other Pi-pi interactions; a typical case for the benzene-dimer forces. Present approaches describing these interaction effects are computationally expensive. We report a pseudopotential base density functional theory (DFT) calculations within the local density approximation (LDA) and compared our results with other higher theories describing the π-π stacking interactions. By using benzene dimer as a prototype species, we find that, DFT/LDA compares favourably well with other descriptions as a reliable alternative method

Design of novel hybrid 2D nanomaterials for optical, optoelectronic and micro-electro-mechanical systems applications

Novel hybrid 2D class of ternary nanoheterostructures have been designed by mixing aluminium nitride (AlN), boron nitride (BN) with 2D graphene with the aim of designing innovative 2D nanoheterostructures for applications in electronics and other industries. The structural stability and electronic properties of these nanoheterostructures have been analysed using “first-principles based calculations done in the framework of density functional theory. Different structural patterns have been analysed to identify the most stable nanoheterostructures. It has been found to be more energetically favourable that the aluminium nitride and boron nitride atom chains occupy the positions of the carbon atoms in a clustered pattern in the nanoheterostructures. Carbon atom chains sandwiched between aluminium nitride and boron nitride chains of atoms is a preferred choice over isolated chains of BN, AlN and CC in the nanoheterostructures. The calculated band gaps of the novel nanoheterostructures are found to be 0.87, 0.43 and 0.65 ​eV respectively. These novel hybrid 2D nanoheterostructures are energetically favoured materials with both direct and indirect band gaps. They have potential applications in nanoscale semiconducting and optoelectronic devices, notably optical, optoelectronic and micro-electro-mechanical systems

Dataset on the comparison of synthesized and commercial zeolites for potential solar adsorption refrigerating system

The purpose of this dataset is to provide a comparison between synthesized and commercial 4A and 13X type zeolites. Metakaolin produced from the calcination of beneficiated kaolin at 750 °C for 4 h was dealuminated using sulphuric acid to get the required silica to alumina ratio for the zeolite synthesis. Zeolite 4A and 13X samples were characterized along-side with the commercial variants using X-ray fluorescence (XRF), X-ray diffraction (XRD), Brunauer, Emmett and Teller (BET) and scanning electron microscopy (SEM) techniques. These analyses revealed that, the zeolites synthesized are of comparatively acceptable quality. The pore size of 120.859 nm, pore volume of 0.0065 cm3/g and surface area of 22 m2/g were obtained from BET analyses for zeolite 4A synthesized from kaolin, while the commercial zeolite 4A used as control gave pore size of 58.143 nm, pore volume of 0.2462 cm3/g and surface area of 559.13 m2/g. In the same vein, the pore size of 10.5059 nm, pore volume of 0.135847 cm3/g and surface area of 324.584 m2/g were obtained from BET analyses for zeolite 13X synthesized from kaolin, while the commercial zeolite 13X gave pore size of 7.2752 nm, pore volume of 0.135951 cm3/g and surface area of 310.0906 m2/g

The effect of NaOH catalyst concentration and extraction time on the yield and properties of Citrullus vulgaris seed oil as a potential biodiesel feed stock

In this work, oil was extracted from Citrullus vulgaris (watermelon) seeds for potential feedstock in biodiesel production. The results showed that, the oil content from Citrullus vulgaris seeds oil during extraction reached an average yield of 50%. Biodiesel was produced via transesterification using NaOH as catalyst. The effect of NaOH on the yield of the biodiesel was investigated at three different concentrations; 0.13, 0.15 and 0.18 g and oil to methanol ratio of 5:1 under different reaction times; 90, 120 and 150 min at 60 °C. The yield of biodiesel from NaOH concentration of 0.13 g was found to be 70% as compared to those of concentrations, 0.15 g and 0.18 g which were 53% and 49% respectively.Gas chromatography was used to identify the methyl ester groups present in the biodiesel and the results revealed both concentration and time-dependent increase in oil yield. The physicochemical properties of the watermelon seed oil such as flash point (141.3 ± 0.4–143.4 ± 0.2), density (0.86 ± 0.04–0.91 ± 0.01 g/cm3), kinematic viscosity (30.50 ± 0.1–31.20 ± 0.04 mm2/s) and acid value (mg KOH/g) are similar to conventional vegetable oils. This work therefore, highlights the potential utility of water melon seeds for biodiesel production. Keywords: Citrullus vulgaris, Gas chromatography, Catalys

Inkjet-printed graphene electrodes for dye-sensitized solar cells

We present a stable inkjet printable graphene ink, formulated in isopropyl alcohol via liquid phase exfoliation of chemically pristine graphite with a polymer stabilizer. The rheology and low deposition temperature of the ink allow uniform printing. We use the graphene ink to fabricate counter electrodes (CE) for natural and ruthenium-based dye-sensitized solar cells (DSSCs). The repeatability of the printing process for the CEs is demonstrated through an array of inkjet-printed graphene electrodes, with ∼5% standard deviation in the sheet resistance. As photosensitizers, we investigate natural tropical dye extracts from Pennisetum glaucum, Hibiscus sabdariffa and Caesalpinia pulcherrima. Among the three natural dyes, we find extracts from C. pulcherrima exhibit the best performance, with ∼0.9% conversion efficiency using a printed graphene CE and a comparable ∼1.1% efficiency using a platinum (Pt) CE. When used with N719 dye, the inkjet-printed graphene CE shows a ∼3.0% conversion efficiency, compared to ∼4.4% obtained using Pt CEs. Our results show that inkjet printable graphene inks, without any chemical functionalization, offers a flexible and scalable fabrication route, with a material cost of only ∼2.7% of the equivalent solution processed Pt-based electrodes