15 results found
Aitchison CM, Andrei V, Antón-García D, et al., 2019, Synthetic approaches to artificial photosynthesis: general discussion., Faraday Discuss, Vol: 215, Pages: 242-281
Bedoya Lora FE, Hankin A, Kelsall G, 2017, En route to a unified model for photo-electrochemical reactor optimization. I - Photocurrent and H₂ yield predictions, Journal of Materials Chemistry A, Vol: 5, Pages: 22683-22696, ISSN: 2050-7496
A semi-empirical model was developed for prediction of photocurrent densities and implemented to predict the performance of a photo-electrochemical reactor for water splitting in alkaline solutions, using Sn-doped α-Fe₂O₃ photo-anodes produced by spray pyrolysis. Photo-anodes annealed at different temperatures were characterized using photo-electrochemical impedance spectroscopy, cyclic voltammetry in the presence and absence of a hole scavenger and also the open circuit potential under high intensity illumination. Mott-Schottky analysis was used cautiously to estimate charge carrier concentration and the flat band potential. In addition to overpotential/current distribution and ohmic potential losses, the model also accounts for absorbed photon flux, surface and bulk electron-hole recombination rates, gas desorption, bubble formation and (H₂-O₂) cross-over losses. This allows the model to estimate the total yield of hydrogen, charge and gas collection efficiencies. A methodology is presented here in order to evaluate parameters required to assess the performance of a photo-electrochemical reactor in 1D and 2D geometries. The importance of taking into account bubble generation and gas desorption is discussed, together with the difficulties of measuring charge carrier concentration and electron-hole recombination in the bulk of the semiconductor, which are of major importance in the prediction of photocurrent densities.
Bedoya-Lora FE, Hankin A, Holmes-Gentle I, et al., 2017, Effects of low temperature annealing on the photo-electrochemical performance o tin-doped hematite photo-anodes, Electrochimica Acta, Vol: 251, Pages: 1-11, ISSN: 0013-4686
The effects of post-deposition annealing at 400 and 500 °C on the photo-electrochemical performance of SnIV-doped α-Fe2O3 photo-anodes are reported. Samples were fabricated by spray pyrolysis on fluorine-doped tin oxide (FTO) and on titanium substrates. Photo-electrochemical, morphological and optical properties were determined to explain the shift in photocurrent densities to lower electrode potentials and the decrease of maximum photocurrent densities for alkaline water oxidation after annealing. Annealing at 400 and 500 °C in air did not affect significantly the morphology, crystallinity, optical absorption or spatial distributions of oxygen vacancy concentrations. However, XPS data showed a redistribution of SnIV near SnIV-doped α-Fe2O3 | 1 M NaOH interfaces after annealing. Thus, electron-hole recombination rates at photo-anode surfaces decreased after annealing, shifting photocurrents to lower electrode potentials. Conversely, depletion of SnIV in the α-Fe2O3 bulk could increase recombination rates therein and decrease photon absorption near 550 nm, due to an increased dopant concentration in the semiconductor depletion layer. This accounted for the decrease of maximum photocurrents when electron-hole recombination rates were suppressed using HO2− ions as a hole scavenger. The flat band potential of SnIV-doped α-Fe2O3 remained relatively constant at ca. 0.7 V vs. RHE, irrespective of annealing conditions.
Hankin A, Shah N, 2017, Process exploration and assessment for the production of methanol and dimethyl ether from carbon dioxide and water, Sustainable Energy & Fuels, Vol: 1, Pages: 1541-1556, ISSN: 2398-4902
A thermodynamic, model-based, study was carried out to assess the relative performance of methanol and dimethyl ether (DME) synthesis systems using CO- and CO2-based syngas feeds. The upstream production of a range of syngas feed compositions was simulated using CO2 and H2O as the sole chemical building blocks, a requirement motivated by the increasing constraints on permissible CO2 emissions and the successful adaptation by some industrial methanol plants to the direct utilisation of CO2. The objective was to establish whether the energy requirements and CO2 emissions associated with upstream conversion of CO2 to CO were justified by increased productivity in the methanol/DME systems. In the first part of the study, the performance of four systems was evaluated and compared in terms of energy efficiency and CO2 conversion: (1) methanol synthesis system, (2) direct DME synthesis system, (3) two-step DME synthesis system with an interposed syngas separation step between the methanol production reactor and methanol dehydration reactor and (4) two-step DME synthesis system with no separation step between the two reactors. Based on equilibrium yields at 250 °C and 50 bar, the direct DME synthesis system was found to exhibit the highest energy conversion efficiencies with both CO2- and CO-based syngas. Although this system demonstrated the lowest CO2 emissions per methanol equivalent product with a CO-based feed, the benefits were offset by emissions associated with the upstream conversion of H2O and CO2 to H2 and CO, evaluated in the second part of the study. It was determined that CO2 could be utilised directly in the direct DME synthesis route, whereas upstream conversion of CO2 to CO was necessary to achieve effective yields in the methanol/two-step DME systems. CO-based syngas production via high temperature co-electrolysis of H2O and CO2, or alternatively high temperature CO2 electrolysis coupled with the water–gas shift process, was identified as the bes
Hankin A, Bedoya-Lora FE, Ong CK, et al., 2016, From millimetres to metres: the critical role of current density distributions in photo-electrochemical reactor design, Energy & Environmental Science, Vol: 10, Pages: 346-360, ISSN: 1754-5706
0.1×0.1 m2 tin-doped hematite photo-anodes were fabricated on titanium substrates by spray pyrolysis and deployed in a photo-electrochemical reactor for photo-assisted splitting of water into hydrogen and oxygen. Hitherto, photo-electrochemical research focussed largely on the fabrication, properties and behaviour of photo-electrodes, whereas both experimental and modelling results reported here address reactor scale-up issues of minimising inhomogeneities in spatial distributions of potentials, current densities and the resultant hydrogen evolution rates. Such information is essential for optimising the design and photon energy-to-hydrogen conversion efficiencies of photo-electrochemical reactors to progress their industrial deployment. The 2D and 3D reactor models presented here are coupled with a modified micro-kinetic model of oxygen evolution on hematite thin films both in the dark and when illuminated. For the first time, such a model is applied to a scaled-up photo-electrochemical reactor and validated against experimental data.
Kleiminger L, Farandos N, Li T, et al., 2016, Three-dimensional Inkjet Printed Solid Oxide Electrochemical Reactors.I. Yttria-stabilized zirconia Electrolyte, Electrochimica Acta, Vol: 213, Pages: 324-331, ISSN: 0013-4686
Solid oxide fuel cell (SOFC) and electrolyser (SOE) performances can be enhanced significantly by increasing the densities of (electrode | electrolyte | pore) triple phase boundaries and improving geometric reproducibility and control over composite electrode | electrolyte microstructures, thereby also aiding predictive performance modelling. We developed stable aqueous colloidal dispersions of yttria-stabilized zirconia (YSZ), a common SOFC electrolyte material, and used them to fabricate 2D planar and highly-customisable 3D microstructures by inkjet printing. The effects of solids fraction, particle size, and binder concentration on structures were investigated, and crack-free, non-porous electrolyte planes were obtained by tailoring particle size and minimising binder concentration. Micro-pillar arrays and square lattices were printed with the optimised ink composition, and a minimum feature size of 35 μm was achieved in sintered structures, the smallest published to-date. YSZ particles were printed and sintered to a 23 μm thick planar electrolyte in a Ni-YSZ|YSZ|YSZ-LSM|LSM electrolyser for CO2 splitting; a feed of 9:1 CO2:CO mixture at 1.5 V and 809 °C produced a current density of −0.78 A cm−2 even without more complex 3D electrode | electrolyte geometries.
Bedoya-Lora F, Hankin A, Kelsall GH, 2016, Photo-electrochemical Hydrogen Sulfide Splitting using SnIV-doped Hematite Photo-anodes, Electrochemistry Communications, Vol: 68, Pages: 19-22, ISSN: 1388-2481
Spray-pyrolysed SnIV-doped α-Fe2O3 photo-anodes were used for photo-assisted splitting of HS- ions in alkaline aqueous solutions, producing polysulfide (Sn2-) ions together with hydrogen at the cathode. Subsequent aerial oxidation of polysulfide could be used to produce elemental sulfur. At an applied electrode potential of 1.07 V (RHE) and an irradiance of 5.6 kW m-2, stable photocurrents of ca. 11 A m-2 (210-3 A W-1) were recorded over 75 hours, polysulfide concentrations increasing linearly with time. Despite being predicted thermodynamically to form iron sulfide(s) in sulfide solutions, such photo-anodes appeared to be stable. In comparison with conventional water splitting under alkaline conditions, the coupled processes of hydrogen sulfide ion oxidation and water reduction had a lower energy requirement.
Videira JJH, Barnham KWJ, Hankin A, et al., 2015, Introducing novel light management to design a hybrid high concentration photovoltaic/water splitting system, 2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), Publisher: IEEE
We present a novel way to utilize high-concentrationphotovoltaic (HCPV) radiative losses and diffuse light, otherwiseunused in conventional HCPV systems, to power an ImperialCollege designed photoelectrochemical reactor (PECR) producingH2 fuel through water splitting. A high efficiency photovoltaic(HEPV) is embedded inside a Luminescent Solar Concentrator(LSC). Edge emission from the radiative recombination lossmechanism in the HEPV is guided within the LSC to the PECRphotocathode, whilst the LSC emitted light is guided to thephotoanode. The photon streams can be independently optimisedin intensity and wavelength. We demonstrate how photon streamswith balanced intensity can be achieved.
Hankin A, Kelsall GH, Ong CK, et al., 2014, Photo-electrochemical production of H2 using solar energy, Chemical Engineering Transactions, Vol: 41, Pages: 199-204, ISSN: 2283-9216
Ti | SnIV-Fe2O3 photo-anodes are implemented in a photo-electrochemical reactor for photo-assistedsplitting of water into hydrogen and oxygen. Attention is focused on the issues concerning electrode scaleupwith the aim of addressing the present need for the design, optimisation and demonstration of thecommercial feasibility of photo-electrochemical reactors.
Hankin A, Alexander JC, Kelsall GH, 2014, Constraints to the flat band potential of hematite photo-electrodes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 16176-16186, ISSN: 1463-9076
Droushiotis N, Hankin A, Rozain C, et al., 2014, Phase Inversion and Electrophoretic Deposition Processes for Fabrication of Micro-Tubular Hollow Fiber SOFCs, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 161, Pages: F271-F279, ISSN: 0013-4651
Droushiotis N, Hankin A, Kelsall GH, 2013, New fabrication techniques for micro-tubular hollow finer solid oxide fuel cells, ECS Transactions, Vol: 50, ISSN: 1938-6737
A novel combination of phase inversion and electrophoretic deposition was used in the fabrication of anode supported micro tubular (hollow fiber) solid oxide fuel cells (MT-HF-SOFCs). The phase inversion process was used to produce ca. 240 μm thick, highly porous 60 wt. % NiO-40 wt. % yttria-stabilised zirconia (YSZ) hollow fiber anode precursors. The electrophoretic deposition process was then used to apply ca. 40 μm thick, particulate YSZ electrolyte layers onto the unsintered NiO-YSZ HFs from an ethanol suspension at an applied electric field of ca. 0.22 kV cm-1. The YSZ-coated NiO-YSZ HFs were sintered at 1500 oC for twelve hours. Dispersions of YSZ-LSM particles were then painted on top of the electrolyte layer, as ‘graded’ YSZ-LSM porous cathode precursors that were sintered at 1200 oC for three hours. The fabrication process was completed by winding silver wire current collectors spirally round the cathodes and through the lumen of the fibers to enable current collection from the anodes. Single MT-HF-SOFCs delivered peak power densities of 0.20, 0.18 and 0.14 W cm-2 at 800, 750 and 700 oC, respectively, with flow rates of 15 cm3 min-1 H2 (97% H2-3% H2O) and 30 cm3 min-1 of air.
Kelsall GH, 2013, Electrochemical Recovery of Nickel from Nickel Sulfamate Plating Effluents, J.Appl.Electrochem.
Kelsall GH, Hankin A, Electrodeposition of nickel from sulfamate effluents, ECS Transactions, ISSN: 1938-6737
Kelsall GH, Kovaleva A, 2010, Electrodeposition of Nickel from Sulfamate Effluents, 8th International Symposium on Electrochemistry in Mineral and Metal Processing (EMMP) Held During the 217th Meeting of the Electrochemical-Society, Publisher: ELECTROCHEMICAL SOC INC, Pages: 317-327, ISSN: 1938-5862
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