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