194 results found
Yao JG, Tan S-Y, Metcalfe P, et al., 2021, Demetallization of Sewage Sludge Using Low-Cost Ionic Liquids, ENVIRONMENTAL SCIENCE & TECHNOLOGY, Vol: 55, Pages: 5291-5300, ISSN: 0013-936X
Sadeek S, Kelsall G, Sedransk Campbell K, et al., 2020, Electrochemical Behaviour of Steel in Aqueous Alkanolamines for CO2 capture, ECS Meeting Abstracts, Vol: MA2020-02, Pages: 3876-3876
Abouelela AR, Tan S-Y, Kelsall GH, et al., 2020, Toward a Circular Economy: Decontamination and Valorization of Postconsumer Waste Wood Using the ionoSolv Process, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 8, Pages: 14441-14461, ISSN: 2168-0485
Hankin A, Bedoya-Lora FE, Alexander JC, et al., 2019, Flat band potential determination: avoiding the pitfalls, Journal of Materials Chemistry A, Vol: 7, Pages: 26162-26176, ISSN: 2050-7488
The flat band potential is one of the key characteristics of photoelectrode performance. However, its determination on nanostructured materials is associated with considerable uncertainty. The complexity, applicability and pitfalls associated with the four most common experimental techniques used for evaluating flat band potentials, are illustrated using nanostructured synthetic hematite (α-Fe2O3) in strongly alkaline solutions as a case study. The motivation for this study was the large variance in flat band potential values reported for synthetic hematite electrodes that could not be justified by differences in experimental conditions, or by differences in their charge carrier densities. We demonstrate through theory and experiments that different flat band potential determination methods can yield widely different results, so could mislead the analysis of the photoelectrode performance. We have examined: (a) application of the Mott–Schottky (MS) equation to the interfacial capacitance, determined by electrochemical impedance spectroscopy as a function of electrode potential and potential perturbation frequency; (b) Gärtner–Butler (GB) analysis of the square of the photocurrent as a function of electrode potential; (c) determination of the potential of transition between cathodic and anodic photocurrents during slow potentiodynamic scans under chopped illumination (CI); (d) open circuit electrode potential (OCP) under high irradiance. Methods GB, CI and OCP were explored in absence and presence of H2O2 as hole scavenger. The CI method was found to give reproducible and the most accurate results on hematite but our overall conclusion and recommendation is that multiple methods should be employed for verifying a reported flat band potential.
Bystron T, Horbenko A, Syslova K, et al., 2018, 2-Iodoxybenzoic acid synthesis by oxidation of 2-Iodobenzoic acid at a Boron-doped diamond anode, ChemElectroChem, Vol: 5, Pages: 1002-1005, ISSN: 2196-0216
For the first time, the electrochemical synthesis of 2-iodoxybenzoic acid (IBX), a benign, well-established, popular and highly selective oxidising agent, is described. The objective of the work was to investigate the possibility of generating IBX electrochemically in aqueous solutions by using boron-doped diamond anodes. In 0.2 M H2SO4 aqueous solution, 2-iodobenzoic acid (IBA) was found to be oxidised at potentials >1.6 V vs. SCE, initially to 2-iodosobenzoic acid (IsBA), which was oxidised to IBX at potentials >1.8 V vs. SCE. Reductions of IBX to IsBA and IsBA to IBA occurred at similar potentials of ca. −0.7 V vs. SCE. The voltammetry results were confirmed by performing a series of batch electrolyses at different electrode potentials. Thus, depending on the electrode potential chosen, IBA can be oxidised anodically either to IsBA or IBX with 100 % overall selectivity. The only side-reaction was O2 generation, but charge yields did not decrease below 55 % even at conversions >95 %.
Farandos NM, Li T, Kelsall GH, 2018, 3-D inkjet-printed solid oxide electrochemical reactors. II. LSM - YSZ electrodes, Electrochimica Acta, Vol: 270, Pages: 264-273, ISSN: 0013-4686
Inkjet printing is an economical additive manufacturing technique with minimal material waste, which offers a high degree of control over vertical resolution, so lending itself well to the fabrication of the functional layers of solid oxide electrochemical reactors. We formulated a printable and stable colloidal dispersion of La0.8Sr0.2MnO3 (LSM) -(Y2O3)0.08(ZrO2)0.92 (YSZ) ink to print sequentially onto an inkjet-printed YSZ electrolyte sintered to a Ni-YSZ substrate to form the cell: Ni-YSZ|YSZ|YSZ-LSM|LSM. After sintering, the electrolyte and YSZ-LSM electrode were 9 and 20 μm thick, respectively. The performances of these reactors were determined as fuel cells, operating with dry H2, and as electrolysers, operating with CO/CO2 in the ratio 1/9. At 788 °C, the peak fuel cell power density was 0.69 W cm-2, and at a cell potential difference of 1.5 V, the electrolysis current density was 3.3 A cm-2, indicating that the performance of inkjet-printed YSZ-LSM electrodes can exceed those fabricated by conventional powder mixing processes.
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, Bedoya-Lora FE, Ong CK, et al., 2017, From millimetres to metres: the critical role of current density distributions in photo-electrochemical reactor design, Energy and Environmental Science, Vol: 10, Pages: 346-360, ISSN: 1754-5692
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.
Li T, Rabuni MF, Kleiminger L, et al., 2016, Highly-robust solid oxide fuel cell (SOFC): simultaneous greenhouse gas treatment and clean energy generation, RSC Energy and Environment Series, Vol: 9, Pages: 3682-3686, ISSN: 2044-0774
Herein, results of combined greenhouse gas treatment with clean energy conversion is reported for the first time. Multi-channel tubular SOFCs were operated with N2O instead of air as the oxidant leading to a 50% increase in power density. Techno-economic evaluation suggested the feasibility of the combined approach eliminating the cost penalty for N2O abatement.
Dawson RJ, Kelsall GH, 2016, Recovery of platinum from secondary materials: electrochemical reactor for platinum deposition from aqueous iodide solutions, JOURNAL OF APPLIED ELECTROCHEMISTRY, Vol: 46, Pages: 1221-1236, ISSN: 0021-891X
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.
Hong J, Chen C, Bedoya FE, et al., 2016, Carbon nitride nanosheet/metal–organic framework nanocomposites with synergistic photocatalytic activities, Catalysis Science & Technology, Vol: 6, Pages: 5042-5051, ISSN: 2044-4753
Heterogeneous photocatalysis plays a key role in the implementation of novel sustainable technologies, e.g. CO2 conversion into fuel, H2 production from water or organics degradation. The progress of photocatalysis relies on the development of tuneable photocatalysts and particularly the ability to build nanocomposites exhibiting synergistic properties with reduced electron–hole recombination rates. We report for the first time the in situ synthesis of nanocomposites of carbon nitride nanosheets (CNNSs) and metal–organic frameworks (MOFs) for application as photocatalysts. This approach leads to the ‘nano-scale mixing’ of the components, thereby enabling a greater performance compared to other types of 2D materials/MOF composites typically obtained via physical mixing. The objective is to take advantage of the complementary features of the materials while forming a heterojunction. The structural, chemical, photophysical and electrochemical properties of the nanocomposites are characterized and compared to those of the parent materials and their physical mixture. The nanocomposites retain the high specific surface area and strong visible light absorbance of MIL-100(Fe). The intimate contact between the CNNSs and the MOF particles is found to promote the electron–hole separation significantly due to the formation of a heterojunction. Hence, more efficient photocatalytic dye degradation is achieved over the composites than the physical mixture.
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.
Kleiminger L, 2015, Solid oxide electrochemical reactors and processes for carbon dioxide and water splitting
Kelsall GH, Kleiminger L, Li K, et al., 2015, Syngas (CO-H₂) production using high temperature micro-tubular solid oxide electrolysers, Electrochimica Acta, Vol: 179, Pages: 565-577, ISSN: 1873-3859
CO₂ and/or H₂O were reduced to CO/H₂ in micro-tubular solid oxide electrolysers with yttria-stabilized zirconia (YSZ) electrolyte, Ni-YSZ cermet cathode and strontium(II)-doped lanthanum manganite (LSM) oxygen-evolving anode. At 822 °C, the kinetics of CO₂ reduction were slower (ca. −0.49 A cm−2 at 1.8 V) than H₂O reduction or co-reduction of CO₂ and H₂O, which were comparable (ca. −0.83 to −0.77 A cm−2 at 1.8 V). Performances were improved (−0.85 and −1.1 A cm−2 for CO₂ and H₂O electrolysis, respectively) by substituting the silver current collector with nickel and avoiding blockage of entrances to pores on the inner lumen of micro-tubes induced by silver paste applied previously to decrease contact losses. The change in current collector materials increased ohmic potential losses due to substituting the lower resistance Ag with Ni wire, but decreased electrode polarization losses by 80–93%. For co-electrolysis of CO₂ and H₂O, isotopically-labelled C¹⁸O₂ was used to try to distinguish between direct cathodic reduction of CO₂ and its Ni-catalysed chemical reaction with hydrogen from reduction of steam. Unfortunately, oxygen was exchanged between C¹⁸O₂ and H₂¹⁶O, enriching oxygen-18 in the steam and substituting oxygen-16 in the carbon dioxide, so the anode off-gas isotopic fractions were meaningless. This occurred even in alumina and YSZ tubes without the micro-tubular reactor, i.e. in the absence of Ni catalyst, though not in quartz tubes. Unfortunately, larger differences between the thermal expansion coefficients of quartz and YSZ precluded using a quartz tube to house the micro-tubular reactor. However, the kinetic results, CO/H₂ yields from off-gas analysis, diffusional considerations and model predictions of reactant and product gas adsorption on Ni suggested that syngas should be produced by electrochemical reduction of steam to H₂, followed by its Ni-catalysed chemical reaction with CO₂
Bumroongsakulsawat P, Kelsall GH, 2015, Tinned graphite felt cathodes for scale-up of electrochemical reduction of aqueous CO2, ELECTROCHIMICA ACTA, Vol: 159, Pages: 242-251, ISSN: 0013-4686
Rix K, Kelsall GH, Hellgardt K, et al., 2015, Chemo- And diastereoselectivities in the electrochemical reduction of maleimides, ChemSusChem, Vol: 8, Pages: 665-671, ISSN: 1864-5631
The electrochemical cathodic reduction of cyclic imides (maleimides) to succinimides can be achieved chemoselectively in the presence of alkene, alkyne, and benzyl groups. The efficiency of the system was demonstrated by using a 3D electrode in a continuous flow reactor. The reduction of 3,4-dimethylmaleimides to the corresponding succinimides proceeds with a 3:2 diastereomeric ratio, which is independent of the nitrogen substituent and electrode surface area. The stereoselectivity of the process was rationalized by using DFT calculations, involving an acid-catalyzed tautomerization of a half-enol occurring through a double hydrogen-transfer mechanism.
Kleiminger L, Kelsall GH, Li T, et al., 2015, Effects of current collector materials on performances of micro-tubular solid oxide electrolysers for splitting CO<inf>2</inf>, Pages: 3449-3458, ISSN: 1938-6737
Specific surface areas of micro-tubular solid oxide electrolysers (MT-SOEs) increase with the reciprocal of their lumen diameters. However, this benefit over planar counterparts may be offset by difficulties in fabricating effective current collectors for < 1 mm diameter inner electrodes, causing significant potential losses, decreasing their performance. Hence, the effects were investigated of different current collector materials for the inner cathodes of such SOEs for splitting CO2. Ohmic area-specific resistances were lowest for silver wire-based compared to nickel wire-based current collectors, due to silver's higher electronic conductivity. However, silver's lower mechanical strength required addition of silver paste for effective connections, but the paste interfered with the electrode process, increasing the area-specific electrode polarization at 1.5 V by > 300% at 700 and 800°C. Microstructural analysis suggested the silver paste caused partial blockage of surface pores. MT-SOEs with only nickel wire current collectors achieved 1 A cm-2 at 1.5 V.
Bumroongsakulsawat P, Kelsall GH, 2014, Effect of solution pH on CO: formate formation rates during electrochemical reduction of aqueous CO2 at Sn cathodes, ELECTROCHIMICA ACTA, Vol: 141, Pages: 216-225, ISSN: 0013-4686
Kleiminger L, Li T, Li K, et al., 2014, CO₂ splitting into CO and O₂ in micro-tubular solid oxide electrolysers, RSC Adv., Vol: 4, Pages: 50003-50016
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: 1463-9084
We revisit the fundamental constraints that apply to flat band potential values at semiconductor photo-electrodes. On the physical scale, the Fermi level energy of a non-degenerate semiconductor at the flat band condition, EF(FB), is constrained to a position between the conduction band, EC, and the valence band, EV,: |EC| < |EF(FB)| < |EV| throughout the depth of the semiconductor. The same constraint applies on the electrode potential scale, where the values are referenced against a common reference electrode: UC(FB) < UF(FB) < UV(FB). Some experimentally determined flat band potentials appear to lie outside these fundamental boundaries. In order to assess the validity of any determined flat band potential, the boundaries set by the conduction band and the valence band must be computed on both scales a priori, where possible. This is accomplished with the aid of an analytical reconstruction of the semiconductor|electrolyte interface in question. To illustrate this approach, we provide a case study based on synthetic hematite, α-Fe2O3. The analysis of this particular semiconductor is motivated by the large variance in the flat band potential values reported in the literature.
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.
Ong CK, Dennison S, Fearn S, et al., 2014, Behaviour of Titanium-based Fe2O3 Photo-Anodes in Photo-Electrochemical Reactors for Water Splitting, ELECTROCHIMICA ACTA, Vol: 125, Pages: 266-274, ISSN: 0013-4686
Silverwood IP, Keyworth CW, Brown NJ, et al., 2014, An Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopic Study of Gas Adsorption on Colloidal Stearate-Capped ZnO Catalyst Substrate, APPLIED SPECTROSCOPY, Vol: 68, Pages: 88-94, ISSN: 0003-7028
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
Cheng C-Y, Kelsall GH, Kleiminger L, 2013, Reduction of CO2 to CO at Cu-ceria-gadolinia (CGO) cathode in solid oxide electrolyser, JOURNAL OF APPLIED ELECTROCHEMISTRY, Vol: 43, Pages: 1131-1144, ISSN: 0021-891X
Bebelis S, Bouzek K, Cornell A, et al., 2013, Highlights during the development of electrochemical engineering, CHEMICAL ENGINEERING RESEARCH & DESIGN, Vol: 91, Pages: 1998-2020, ISSN: 0263-8762
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.
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