Imperial College London

Professor Nigel Brandon OBE FREng

Faculty of Engineering

Dean of the Faculty of Engineering
 
 
 
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Contact

 

+44 (0)20 7594 8600n.brandon Website

 
 
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Location

 

2.06Faculty BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

424 results found

Trudgeon DP, Qiu K, Li X, Mallick T, Taiwo OO, Chakrabarti B, Yufit V, Brandon NP, Crevillen-Garcia D, Shah Aet al., 2019, Screening of effective electrolyte additives for zinc-based redox flow battery systems, JOURNAL OF POWER SOURCES, Vol: 412, Pages: 44-54, ISSN: 0378-7753

Journal article

Speirs J, Balcombe P, Blomerus P, Stettler M, Brandon N, Hawkes Aet al., 2019, Can natural gas reduce emissions from transport?: Heavy goods vehicles and shipping

Report

Ouyang M, Bertei A, Cooper SJ, Wu Y, Liu X, Boldrin P, Kishimoto M, Wu B, Brandon NPet al., 2019, Design of fibre Ni/CGO anode and model interpretation, ECS Transactions, Vol: 91, Pages: 1721-1739, ISSN: 1938-6737

© The Electrochemical Society. A new structure of Ni/gadolinium-doped ceria (CGO) is prepared by a highly tuneable and facile combination of electrospinning and tape-casting method. The structure consists of a network made by continuous Ni fibres and filled in with CGO matrices. When used as the anode of solid oxide fuel cell (SOFC), though it has a lower triple phase boundary (TPB) density, it exhibits better performance compared with impregnated and cermet Ni/CGO with higher nickel loading. An algorithm is developed to determine the ceria-pore double phase boundary (DPB) density with different distance from nickel phase. Using the results, the relative electrochemical reaction rate on DPB and TPB of three different electrodes are calculated and proves that fibre-matrices structure has the morphology advantage of efficiently making use of all ceria-pore DPB. The relative contribution of DPB and TPB in anode reaction of SOFC is quantified in the first time and the importance of DPB is further stressed. This work provides new inspirations in material design of SOFC/SOEC and develops a novel strategy to evaluate the performance of electrodes quantitatively.

Journal article

Rubio-Garcia J, Kucernak A, Zhao D, Lei D, Fahy K, Yufit V, Brandon N, Gomez-Gonzalez Met al., 2019, Hydrogen/manganese hybrid redox flow battery, JPhys Energy, Vol: 1, ISSN: 2515-7655

Electrochemical energy storage is a key enabling technology for further integration of renewables sources. Redox flow batteries (RFBs) are promising candidates for such applications as a result of their durability, efficiency and fast response. However, deployment of existing RFBs is hindered by the relatively high cost of the (typically vanadium-based) electrolyte. Manganese is an earth-abundant and inexpensive element that is widely used in disposable alkaline batteries. However it has hitherto been little explored for RFBs due to the instability of Mn(III) leading to precipitation of MnO2 via a disproportionation reaction. Here we show that by combining the facile hydrogen negative electrode reaction with electrolytes that suppress Mn(III) disproportionation, it is possible to construct a hydrogen/manganese hybrid RFB with high round trip energy efficiency (82%), and high power and energy density (1410 mW cm−2, 33 Wh l−1), at an estimated 70% cost reduction compared to vanadium redox flow batteries.

Journal article

Stevenson GR, Boldrin P, Brandon NP, 2019, Liquid-based synthesis of nickel- And lanthanum- co-doped strontium titanates for use as anodes in all-ceramic solid oxide fuel cell anodes, Pages: 1761-1770, ISSN: 1938-6737

© The Electrochemical Society. Nickel- lanthanum- co-doped compositions of strontium titanate have been synthesized and characterized by a scaleable liquid-based synthesis that may offer an alternative to conventional solid-state synthesis. La0.52Sr0.28Ti0.94Ni0.06O3 is synthesized from soluble precursors followed by calcination in air. The materials can be made phase pure at temperatures as low as 1250°C, as highlighted by X-ray diffraction, and nickel exsolves in hydrogen in the same way as solid-state-synthesized materials. The particle size can be varied by calcination temperature and ball milling between 2 µm and 20 µm. The material is then measured electrochemically by electrochemical impedance spectroscopy and 4-point DC conductivity. A reduction in particle size from 20 µm to 9 µm results in a large improvement in impedance response measured.

Conference paper

Budinis S, Krevor S, Mac Dowell N, Brandon N, Hawkes Aet al., 2018, An assessment of CCS costs, barriers and potential, Energy Strategy Reviews, Vol: 22, Pages: 61-81, ISSN: 2211-467X

© 2018 Elsevier Ltd Global decarbonisation scenarios include Carbon Capture and Storage (CCS) as a key technology to reduce carbon dioxide (CO2) emissions from the power and industrial sectors. However, few large scale CCS plants are operating worldwide. This mismatch between expectations and reality is caused by a series of barriers which are preventing this technology from being adopted more widely. The goal of this paper is to identify and review the barriers to CCS development, with a focus on recent cost estimates, and to assess the potential of CCS to enable access to fossil fuels without causing dangerous levels of climate change. The result of the review shows that no CCS barriers are exclusively technical, with CCS cost being the most significant hurdle in the short to medium term. In the long term, CCS is found to be very cost effective when compared with other mitigation options. Cost estimates exhibit a high range, which depends on process type, separation technology, CO2transport technique and storage site. CCS potential has been quantified by comparing the amount of fossil fuels that could be used globally with and without CCS. In modelled energy system transition pathways that limit global warming to less than 2 °C, scenarios without CCS result in 26% of fossil fuel reserves being consumed by 2050, against 37% being consumed when CCS is available. However, by 2100, the scenarios without CCS have only consumed slightly more fossil fuel reserves (33%), whereas scenarios with CCS available end up consuming 65% of reserves. It was also shown that the residual emissions from CCS facilities is the key factor limiting long term uptake, rather than cost. Overall, the results show that worldwide CCS adoption will be critical if fossil fuel reserves are to continue to be substantively accessed whilst still meeting climate targets.

Journal article

Balcombe P, Speirs JF, Brandon NP, Hawkes ADet al., 2018, Methane emissions: choosing the right climate metric and time horizon, Environmental Science: Processes and Impacts, Vol: 20, Pages: 1323-1339, ISSN: 2050-7895

Methane is a more potent greenhouse gas (GHG) than CO2, but it has a shorter atmospheric lifespan, thus its relative climate impact reduces significantly over time. Different GHGs are often conflated into a single metric to compare technologies and supply chains, such as the global warming potential (GWP). However, the use of GWP is criticised, regarding: (1) the need to select a timeframe; (2) its physical basis on radiative forcing; and (3) the fact that it measures the average forcing of a pulse over time rather than a sustained emission at a specific end-point in time. Many alternative metrics have been proposed which tackle different aspects of these limitations and this paper assesses them by their key attributes and limitations, with respect to methane emissions. A case study application of various metrics is produced and recommendations are made for the use of climate metrics for different categories of applications. Across metrics, CO2 equivalences for methane range from 4–199 gCO2eq./gCH4, although most estimates fall between 20 and 80 gCO2eq./gCH4. Therefore the selection of metric and time horizon for technology evaluations is likely to change the rank order of preference, as demonstrated herein with the use of natural gas as a shipping fuel versus alternatives. It is not advisable or conservative to use only a short time horizon, e.g. 20 years, which disregards the long-term impacts of CO2 emissions and is thus detrimental to achieving eventual climate stabilisation. Recommendations are made for the use of metrics in 3 categories of applications. Short-term emissions estimates of facilities or regions should be transparent and use a single metric and include the separated contribution from each GHG. Multi-year technology assessments should use both short and long term static metrics (e.g. GWP) to test robustness of results. Longer term energy assessments or decarbonisation pathways must use both short and long-term metrics and where this has a lar

Journal article

Crow DJG, Anderson K, Hawkes AD, Brandon Net al., 2018, Impact of drilling costs on the US gas industry: prospects for automation, Energies, Vol: 11, ISSN: 1996-1073

Recent low gas prices have greatly increased pressure on drilling companies to reduce costs and increase efficiency. Field trials have shown that implementing automation can dramatically reduce drilling costs by reducing the time required to drill wells. This study uses the DYNamic upstreAm gAs MOdel (DYNAAMO), a new techno-economic, bottom-up model of natural gas supply, to quantitatively assess the economic impact of lower drilling costs on the US upstream gas industry. A sensitivity analysis of three key economic indicators is presented, with results quoted for the most common field types currently producing, including unconventional and offshore gas. While all operating environments show increased profitability from drilling automation, it is found that conventional onshore reserves can benefit to the greatest extent. For large gas fields, a 50% reduction in drilling costs is found to reduce initial project breakevens by up to 17 million USD per billion cubic metres (MUSD/BCM) and mid-plateau breakevens by up to 8 MUSD/BCM. In this same scenario, additional volumes of around 160 BCM of unconventional gas are shown to become commercial due to both the lower costs of additional production wells in mature fields and the viability of developing new resources held in smaller fields. The capital efficiency of onshore projects increases by 50%-100%, with initial project net present value (NPV) gains of up to 32%.

Journal article

Zhang D, Cai Q, Taiwo OO, Yufit V, Brandon NP, Gu Set al., 2018, The effect of wetting area in carbon paper electrode on the performance of vanadium redox flow batteries: A three-dimensional lattice Boltzmann study, Electrochimica Acta, Vol: 283, Pages: 1806-1819, ISSN: 0013-4686

The vanadium redox flow battery (VRFB) has emerged as a promising technology for large-scale storage of intermittent power generated from renewable energy sources due to its advantages such as scalability, high energy efficiency and low cost. In the current study, a three-dimensional(3D) Lattice Boltzmann model is developed to simulate the transport mechanisms of electrolyte flow, species and charge in the vanadium redox flow battery at the micro pore scale. An electrochemical model using the Butler-Volmer equation is used to provide species and charge coupling at the surface of active electrode. The detailed structure of the carbon paper electrode is obtained using X-ray Computed Tomography(CT). The new model developed in the paper is able to predict the local concentration of different species, over-potential and current density profiles under charge/discharge conditions. The simulated capillary pressure as a function of electrolyte volume fraction for electrolyte wetting process in carbon paper electrode is presented. Different wet surface area of carbon paper electrode correspond to different electrolyte volume fraction in pore space of electrode. The model is then used to investigate the effect of wetting area in carbon paper electrode on the performance of vanadium redox flow battery. It is found that the electrochemical performance of positive half cell is reduced with air bubbles trapped inside the electrode.

Journal article

Tariq F, Rubio-Garcia J, Yufit V, Bertei A, Chakrabarti BK, Kucernak A, Brandon Net al., 2018, Uncovering the mechanisms of electrolyte permeation in porous electrodes for redox flow batteries through real time in situ 3D imaging, SUSTAINABLE ENERGY & FUELS, Vol: 2, Pages: 2068-2080, ISSN: 2398-4902

Journal article

Bertei A, Yufit V, Tariq F, Brandon Net al., 2018, A novel approach for the quantification of inhomogeneous 3D current distribution in fuel cell electrodes, Journal of Power Sources, Vol: 369, Pages: 246-256, ISSN: 0378-7753

The electrode microstructural properties significantly influence the efficiency and durability of many electrochemical devices including solid oxide fuel cells. Despite the possibility of simulating the electrochemical phenomena within real three-dimensional microstructures, the potential of such 3D microstructural information has not yet been fully exploited. We introduce here a completely new methodology for the advanced characterization of inhomogeneous current distribution based on a statistical analysis of the current of each particle within the microstructure. We quantify the large variation in local current distributionand link it to the particle size dispersion, indicating how particle coarsening can trigger further degradation. We identify two classes of particles: those transferring more current than average, which show 10-40% more particle-particle contacts, and those producing more current than average, characterized by ~2.5 times larger three-phase boundary length per unit volume. These two classes of particles are mutually exclusive, which implies that up to the 30% of the electrode volume within the functional layer is underutilized. This fundamental insight goes well beyond the predictions of continuum modeling, allowing us to revisit the current standards regarding safe operating conditions and to suggest alternative strategies based on nanoparticle infiltration, template-assisted synthesis and additive manufacturing for designing more durable electrodes.

Journal article

Song B, Ruiz-Trejo E, Brandon N, 2018, Enhanced mechanical stability of Ni-YSZ scaffold demonstrated by nanoindentation and electrochemical impedance spectroscopy, Journal of Power Sources, Vol: 395, Pages: 205-211, ISSN: 0378-7753

The electrochemical performance of Ni-YSZ SOFC anodes can quickly degrade during redox cycling. Mechanical damage at interfaces significantly decreases the number of active triple phase boundaries. This study firstly focuses on the sintering temperature impact on YSZ scaffold mechanical properties. The YSZ scaffold sintered at 1200 °C exhibited 56% porosity, 28.3 GPa elastic modulus and 0.97 GPa hardness and was selected for further redox cycling study. The Ni infiltrated YSZ scaffold operated at 550 °C had an initial stabilized polarisation resistance equal to 0.62 Ω cm2 and only degraded to 2.85 Ω cm2 after 15 redox cycles. The active triple phase boundary density was evaluated by FIB-SEM tomography, and degraded from 28.54 μm−2 to 19.36 μm−2. The YSZ scaffold structure was robust after 15 redox cycles, as there was no observation of the framework fracturing in both SEM and FIB-SEM images, which indicated that the mechanical stability of YSZ scaffold improves the anode stability during redox cycling. Nonetheless, Ni agglomeration could not be prevented within Ni-YSZ scaffolds and this needs further consideration.

Journal article

Balcombe P, Speirs J, Johnson E, Martin J, Brandon N, Hawkes Aet al., 2018, The carbon credentials of hydrogen gas networks and supply chains, Renewable and Sustainable Energy Reviews, Vol: 91, Pages: 1077-1088, ISSN: 1364-0321

Projections of decarbonisation pathways have typically involved reducing dependence on natural gas grids via greater electrification of heat using heat pumps or even electric heaters. However, many technical, economic and consumer barriers to electrification of heat persist. The gas network holds value in relation to flexibility of operation, requiring simpler control and enabling less expensive storage. There may be value in retaining and repurposing gas infrastructure where there are feasible routes to decarbonisation. This study quantifies and analyses the decarbonisation potential associated with the conversion of gas grids to deliver hydrogen, focusing on supply chains. Routes to produce hydrogen for gas grids are categorised as: reforming natural gas with (or without) carbon capture and storage (CCS); gasification of coal with (or without) CCS; gasification of biomass with (or without) CCS; electrolysis using low carbon electricity. The overall range of greenhouse gas emissions across routes is extremely large, from − 371 to 642 gCO 2 eq/kW h H2 . Therefore, when including supply chain emissions, hydrogen can have a range of carbon intensities and cannot be assumed to be low carbon. Emissions estimates for natural gas reforming with CCS lie in the range of 23–150 g/kW h H2 , with CCS typically reducing CO 2 emissions by 75%. Hydrogen from electrolysis ranges from 24 to 178 gCO 2 eq/kW h H2 for renewable electricity sources, where wind electricity results in the lowest CO 2 emissions. Solar PV electricity typically exhibits higher emissions and varies significantly by geographical region. The emissions from upstream supply chains is a major contributor to total emissions and varies considerably across different routes to hydrogen. Biomass gasification is characterised by very large negative emissions in the supply chain and very large positive emissions in the gasification process. Therefore, improvements in total emissions are large if even small i

Journal article

Gadoue S, Chen K-W, Mitcheson P, Yufit V, Brandon Net al., 2018, Electrochemical Impedance Spectroscopy State of Charge Measurement for Batteries using Power Converter Modulation, 9th International Renewable Energy Congress (IREC), Publisher: IEEE, ISSN: 2378-3435

Conference paper

Chen X, Liu X, Childs P, Brandon N, Wu Bet al., 2018, Design and fabrication of a low cost desktop electrochemical 3D printer, Pro-AM Conference in 2014, Pages: 395-400, ISSN: 2424-8967

Copyright © 2018 by Nanyang Technological University. Additive manufacturing (AM) (3D printing) is the process of creating 3D objects from digital models through the layer by layer deposition of materials. Electrochemical additive manufacturing (ECAM) is a relatively new technique which can create metallic components based depositing adherent layers of metal ions onto the surface of conductive substrate. In this paper, the design considerations for a meniscus confined ECAM approach is presented which demonstrates superior print speeds to equivalent works. This is achieved through the increase of the meniscus diameter to 400 \im which was achieved through the integration of a porous sponge into the print head to balance the hydraulic head of the electrolyte. Other piston based methods of controlling the electrolyte meniscus are discussed.

Conference paper

Speirs JF, balcombe P, johnson E, martin J, brandon N, hawkes Aet al., 2018, A Greener Gas Grid: What Are the Options?, Energy Policy, Vol: 118, Pages: 291-297, ISSN: 0301-4215

There is an ongoing debate over future decarbonisation of gas networks using biomethane, and increasingly hydrogen, in gas network infrastructure. Some emerging research presents gas network decarbonisation options as a tractable alternative to ‘all-electric’ scenarios that use electric appliances to deliver the traditional gas services such as heating and cooking. However, there is some uncertainty as to the technical feasibility, cost and carbon emissions of gas network decarbonisation options. In response to this debate the Sustainable Gas Institute at Imperial College London has conducted a rigorous systematic review of the evidence surrounding gas network decarbonisation options. The study focuses on the technologies used to generate biomethane and hydrogen, and examines the technical potentials, economic costs and emissions associated with the full supply chains involved. The following summarises the main findings of this research. The report concludes that there are a number of options that could significantly decarbonise the gas network, and doing so would provide energy system flexibility utilising existing assets. However, these options will be more expensive than the existing gas system, and the GHG intensity of these options may vary significantly. In addition, more research is required, particularly in relation to the capabilities of existing pipework to transport hydrogen safely.

Journal article

Liu X, Naylor Marlow M, Cooper S, Song B, Chen X, Brandon N, Wu Bet al., 2018, Flexible all-fiber electrospun supercapacitor, Journal of Power Sources, Vol: 384, Pages: 264-269, ISSN: 0378-7753

We present an all-fiber flexible supercapacitor with composite nanofiber electrodes made via electrospinning and an electrospun separator. With the addition of manganese acetylacetonate (MnACAC) to polyacrylonitrile (PAN) as a precursor for the electrospinning process and subsequent heat treatment, the performance of pure PAN supercapacitors was improved from 90 F.g-1 to 200 F.g-1 (2.5 mV.s-1) with possible mass loadings of MnACAC demonstrated as high as 40 wt%. X-ray diffraction measurements showed that after thermal treatment, the MnACAC was converted to MnO, meanwile, the thermal decomposition of MnACAC increased the graphitic degree of the carbonised PAN. Scanning electron microscopy and image processing showed that static electrospinning of pure PAN and PAN-Mn resulted in fiber diameters of 460 nm and 480 nm respectively after carbonisation. Further analysis showed that the fiber orientation exhibited a slight bias which was amplified with the addition of MnACAC. Use of focused ion beam scanning electron microscopy tomography also showed that MnO particles were evenly distributed through the fiber at low MnACAC concentrations, while at a 40 wt% loading the MnO particles were also visible on the surface. Comparison of the electrospun separators showed improved performance relative to a commercial Celgard separator (200 F.g-1 vs 141 F.g-1).

Journal article

Mazur CM, Offer G, Contestabile MSM, Brandon Net al., 2018, Comparing the effects of vehicle automation, policy making and changed user preferences on the uptake of electric cars and emissions from transport, Sustainability, Vol: 10, ISSN: 2071-1050

Switching energy demand for transport from liquid fuels to electricity is the most promising way to significantly improve air quality and reduce transport emissions. Previous studies have shown this is possible, that by 2035 the economics of alternative powertrain and energy vectors will have converged. However, they don’t address if the transition is likely or plausible. Using the UK as a case study, we present a systems dynamics model based study informed by transition theory and explore the effects of technology progress, policy making, user preferences and; for the first time, automated vehicles on this transition. We are not trying to predict the future, but to highlight what is necessary in order for different scenarios to become more or less likely. Worryingly we show that current policies with the expected technology progress and expectations of vehicle buyers are insufficient to reach global targets. Faster technology progress, strong financial incentives or a change in vehicle buyer expectations are crucial, but still insufficient. In contrast the biggest switch to alternatively fuelled vehicles could be achieved by the introduction of automated vehicles. The implications will affect policy makers, automotive manufactures, technology developers and broader society.

Journal article

Hack J, Heenan TMM, Iacoviello F, Mansor N, Meyer Q, Shearing P, Brandon N, Brett DJLet al., 2018, A structure and durability comparison of membrane electrode assembly fabrication methods: self-assembled versus hot-pressed, Journal of The Electrochemical Society, Vol: 165, Pages: F3045-F3052, ISSN: 1945-7111

The most common means of fabricating membrane electrode assemblies (MEAs) for polymer electrolyte fuel cells (PEFCs) involves a hot-press step. The conditions used to perform the hot-press impacts the performance and durability of the fuel cell. However, the hot-press process is not essential for achieving operational MEAs and some practitioners dispense with the hot-press stage altogether by using a self-assembled approach. By performing the integration of the components in-situ during fuel cell assembly, there is the potential to lower the cost and time of manufacture. This study investigates the electrochemical performance and mechanical microstructure of MEAs that were either hot-pressed or self-assembled (non-hot-pressed) and compared at beginning-of-test (BOT) and end-of-test (EOT), following accelerated stress testing. Hot-pressed and self-assembled MEAs were found to show negligible difference in their performance and almost identical performance degradation. X-ray computed tomography (X-ray CT) showed distinct differences in the microstructure of the electrodes. In addition to a crack network in the catalyst layer, the self-assembled samples exhibit indentations that were not present in the hot-pressed sample. It was concluded that in-situ assembly of MEAs could be a suitable means of fabricating PEFC MEAs.

Journal article

Wang X, Chen Z, Atkinson A, Brandon Net al., 2018, Numerical study of solid oxide fuel cell contacting mechanics, Fuel Cells, Vol: 18, Pages: 42-50, ISSN: 1615-6846

Assembly of a planar solid oxide fuel cell (SOFC) or solid electrolyzer (SOE) stack involves the lamination of cells and interconnect plates under an applied load. In most designs a pattern of ribs on the interconnector makes contact with a porous ceramic current collector layer on the air side. These localized contacts are regions of increased stress on the cells and can cause damage if the stresses become too large. In this paper the mechanical response of an anode-supported cell to localized loads from interconnector ribs is simulated. The simulations show that the critical stress for initiating and propagating a crack in the electrolyte (∼300MPa for a 10 μm thick electrolyte) is reached when the interconnector displacement reaches 20 μm (after touching the cathode) with reduced support, or 30 μm when in an oxidized state. The difference is due to the lower stiffness of the reduced support. The residual compressive stress in the electrolyte layer has a major protective effect for the electrolyte. It is concluded that fracture is very unlikely for a geometrically perfect contact, but if the contact is non-uniform due to manufacturing variability in the contact plate or cell, local displacements >∼20 μm can be dangerous. The simulations are used in an example of contacting geometry optimization.

Journal article

Few SPM, Schmidt O, Offer GJ, Brandon N, Nelson J, Gambhir Aet al., 2018, Prospective improvements in cost and cycle life of off-grid lithium-ion battery packs: An analysis informed by expert elicitations, Energy Policy, Vol: 114, Pages: 578-590, ISSN: 0301-4215

This paper presents probabilistic estimates of the 2020 and 2030 cost and cycle life of lithium-ion battery (LiB) packs for off-grid stationary electricity storage made by leading battery experts from academia and industry, and insights on the role of public research and development (R&D) funding and other drivers in determining these. By 2020, experts expect developments to arise chiefly through engineering, manufacturing and incremental chemistry changes, and expect additional R&D funding to have little impact on cost. By 2030, experts indicate that more fundamental chemistry changes are possible, particularly under higher R&D funding scenarios, but are not inevitable. Experts suggest that significant improvements in cycle life (eg. doubling or greater) are more achievable than in cost, particularly by 2020, and that R&D could play a greater role in driving these. Experts expressed some concern, but had relatively little knowledge, of the environmental impact of LiBs. Analysis is conducted of the implications of prospective LiB improvements for the competitiveness of solar photovoltaic + LiB systems for off-grid electrification.

Journal article

Bertei A, Ruiz-Trejo E, Clematis D, Carpanese MP, Barbucci A, Nicolella C, Brandon Net al., 2018, A perspective on the role of the three-phase boundary in solid oxide fuel cell electrodes, Bulgarian Chemical Communications, Vol: 50, Pages: 31-38, ISSN: 0861-9808

© 2018 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria. Within composite electrodes for solid oxide fuel cells (SOFCs), electrochemical reactions take place in the proximity of the so-called three-phase boundary (TPB), the contact perimeter where the electron-conducting, the ionconducting and the porous phases meet. Strictly speaking, the TPB is a line and efforts have been made to increase its length per unit of electrode volume in order to reduce the activation losses. In this communication, by integrating physically-based modelling, 3D tomography and electrochemical impedance spectroscopy (EIS), a renovated perspective on electrocatalysis in SOFCs is offered, showing that the electrochemical reactions take place within an extended region around the geometrical TPB line. Such an extended region is in the order of 4 nm in Ni/Sc0.2Zr0.9O 2 .1 (Ni/ScSZ) anodes while approaches hundreds of nanometres in La0.8Sr0.2MnO 3 -x/Y0.16Zr0.92O 2 .08 (LSM/YSZ) cathodes. These findings have significant implications for preventing the degradation of nanostructured anodes, which is due to the coarsening of the fractal roughness of Ni nanoparticles, as well as for the optimisation of composite cathodes, indicating that the adsorption and surface diffusion of oxygen limit the rate of the oxygen reduction reaction (ORR). In both anodes and cathodes, the results point out that the surface properties of the materials are key in determining the performance and lifetime of SOFC electrodes.

Journal article

Munoz CAP, Dewage HH, Yufit V, Brandon NPet al., 2017, A unit cell model of a regenerative hydrogen-vanadium fuel cell, Journal of The Electrochemical Society, Vol: 164, Pages: F1717-F1732, ISSN: 1945-7111

In this study, a time dependent model for a regenerative hydrogen-vanadium fuel cell is introduced. This lumped isothermal model is based on mass conservation and electrochemical kinetics, and it simulates the cell working potential considering the major ohmic resistances, a complete Butler–Volmer kinetics for the cathode overpotential and a Tafel–Volmer kinetics near mass-transport free conditions for the anode overpotential. Comparison of model simulations against experimental data was performed by using a 25 cm2 lab scale prototype operated in galvanostatic mode at different current density values (50−600Am−2). A complete Nernst equation derived from thermodynamic principles was fitted to open circuit potential data, enabling a global activity coefficient to be estimated. The model prediction of the cell potential of one single charge-discharge cycle at a current density of 400Am−2 was used to calibrate the model and a model validation was carried out against six additional data sets, which showed a reasonably good agreement between the model simulation of the cell potential and the experimental data with a Root Mean Square Error (RMSE) in the range of 0.3–6.1% and 1.3–8.8% for charge and discharge, respectively. The results for the evolution of species concentrations in the cathode and anode are presented for one data set. The proposed model permits study of the key factors that limit the performance of the system and is capable of converging to a meaningful solution relatively fast (s–min).

Journal article

Song B, Ruiz Trejo E, Bertei A, Brandon Net al., 2017, Quantification of the degradation of Ni-YSZ anodes upon redoxcycling, Journal of Power Sources, Vol: 374, Pages: 61-68, ISSN: 0378-7753

Ni-YSZ anodes for Solid Oxide Fuel Cells are vulnerable to microstructural damage during redox cycling leading to a decrease in the electrochemical performance. This study quantifies the microstructural changes as a function of redox cycles at 800 °C and associates it to the deterioration of the mechanical properties and polarisation resistance. A physically-based model is used to estimate the triple-phase boundary (TPB) length from impedance spectra, and satisfactorily matches the TPB length quantified by FIB-SEM tomography: within 20 redox cycles, the TPB density decreases from 4.63 μm−2 to 1.06 μm−2. Although the polarisation resistance increases by an order of magnitude after 20 cycles, after each re-reduction the electrode polarisation improves consistently due to the transient generation of Ni nanoparticles around the TPBs. Nonetheless, the long-term degradation overshadows this transient improvement due to the nickel agglomeration. In addition, FIB-SEM tomography reveals fractures along YSZ grain boundaries, Ni-YSZ detachment and increased porosity in the composite that lead to irreversible mechanical damage: the elastic modulus diminishes from 36.4 GPa to 20.2 GPa and the hardness from 0.40 GPa to 0.15 GPa. These results suggest that microstructural, mechanical and electrochemical properties are strongly interdependent in determining the degradation caused by redox cycling.

Journal article

Balcombe P, Brandon NP, Hawkes AD, 2017, Characterising the distribution of methane and carbon dioxide emissions from the natural gas supply chain, Journal of Cleaner Production, Vol: 172, Pages: 2019-2032, ISSN: 0959-6526

Methane and CO2 emissions from the natural gas supply chain have been shown to vary widely butthere is little understanding about the distribution of emissions across supply chain routes,processes, regions and operational practises. This study defines the distribution of total methaneand CO2 emissions from the natural gas supply chain, identifying the contribution from each stageand quantifying the effect of key parameters on emissions. The study uses recent high-resolutionemissions measurements with estimates of parameter distributions to build a probabilistic emissionsmodel for a variety of technological supply chain scenarios. The distribution of emissions resemblesa log-log-logistic distribution for most supply chain scenarios, indicating an extremely heavy tailedskew: median estimates which represent typical facilities are modest at 18 – 24 g CO2 eq./ MJ HHV,but mean estimates which account for the heavy tail are 22 – 107 g CO2 eq./ MJ HHV. To place thesevalues into context, emissions associated with natural gas combustion (e.g. for heat) areapproximately 55 g CO2/ MJ HHV. Thus, some supply chain scenarios are major contributors to totalgreenhouse gas emissions from natural gas. For methane-only emissions, median estimates are 0.8 –2.2% of total methane production, with mean emissions of 1.6 - 5.5%. The heavy tail distribution isthe signature of the disproportionately large emitting equipment known as super-emitters, whichappear at all stages of the supply chain. The study analyses the impact of different technologicaloptions and identifies a set of best technological option (BTO) scenarios. This suggests thatemissions-minimising technology can reduce supply chain emissions significantly, with this studyestimating median emissions of 0.9% of production. However, even with the emissions-minimisingtechnologies, evidence suggests that the influence of the super-emitters remains. Therefore,emissions-minimising technology is only part of the soluti

Journal article

Jing R, Wang M, Wang W, Brandon N, Li N, Chen J, Zhao Yet al., 2017, Economic and environmental multi-optimal design and dispatch of solid oxide fuel cell based CCHP system, Energy Conversion and Management, Vol: 154, Pages: 365-379, ISSN: 0196-8904

Combined cooling, heating and power system (CCHP) is an efficient alternative for building energy supply. Meanwhile, the advantages of high energy efficiency and low emission for solid oxide fuel cells (SOFCs) make the technology a promising prime mover for CCHP systems. In this study, a SOFC based CCHP system design and operation optimization model has been developed using the Mixed Integer Non-linear Programming (MINLP) approach. The model provides two capacity sizing options of the fixed size (user specified), and the optimal sizing. In the fixed size option, four dispatch strategies are considered, namely baseload, day/night, full-load, and electrical load following. In the optimal sizing option, the installed capacity of devices and the dispatch strategy are both optimized. Moreover, multi-objective optimizations are also conducted to optimize two conflicting objectives simultaneously by the Ɛ-constraint method. The optimal results are displayed by Pareto frontiers and the most desired solutions have been identified and verified by two decision-making approaches of LINMAP and TOPSIS. To make the model applicable to real world operation, novel constraints including part-load efficiency, equipment on/off, and numbers of start constraints are applied. Finally, the proposed model is applied to a case study of a hospital in Shanghai, China considering state-of-the-art technical specifications, time-of-use energy pricing, and emission factors. The results indicate environmental advantages of SOFC based CCHP system. Moreover, the levelized cost of energy (LCOE) identified by the proposed optimal design and dispatch model would be 0.17 $/kWh, which is lower than the conventional energy system.

Journal article

Riveros M, Guo M, van dam, Bustos-Turu G, Brandon Net al., 2017, Carbon Arbitrage with Stationary Batteries in the City of London, 27th European Symposium on Computer Aided Process Engineering, Publisher: Elsevier, Pages: 529-534, ISSN: 1570-7946

Stationary batteries could facilitate provision of carbon arbitrage services in cities. Such services offer a smart solution to integrate low-carbon energy technology into grid electricity supply and help tackle climate change. In this paper the environmental implications and overall profitability of this approach are assessed. A modelling framework has been developed to design an energy storage system with optimal capacity to maximise carbon savings. The City of London was used as a case study to demonstrate model applicability and analyse the potential effect of intermittent renewable energy sources in the supply system. The total savings obtained for the carbon arbitrage service were economically valorised using carbon market prices. In addition, a critical profitability thresholds for carbon trading prices are identified. Results show that this approach could bring environmental benefits depending on the carbon intensity of the grid, but that high carbon trading prices are required before it is economically feasible.

Conference paper

Jing R, Wang M, Brandon N, Zhao Yet al., 2017, Multi-criteria evaluation of solid oxide fuel cell based combined cooling heating and power (SOFC-CCHP) applications for public buildings in China, Energy, Vol: 141, Pages: 273-289, ISSN: 0360-5442

This study aims to evaluate the feasibility of solid oxide fuel cell based combined cooling heating and power (SOFC-CCHP) applications in public buildings of China from different perspectives. Operations of the natural gas fueled SOFC-CCHP systems for 20 years’ have been simulated for five categories of public buildings in five locations of China. Parallel simulations of combustion based CCHP systems and conventional system have been conducted for comparison. By single criterion assessment, SOFC-CCHP systems demonstrate outstanding performance on energy efficiency as well as reducing carbon emission, air pollution and human health damage cost. The levelized cost of energy (LCOE) turns out to be competitive with commercial electricity price, but a long payback period (SPP) has also been identified. To further assess the overall performance of SOFC-CCHP systems, a multi-criteria assessment model has been developed by combining the gray relational analysis (GRA) approach and the entropy-weighting method. The result indicates that hospital, hotel, and supermarket achieve more benefits than office and school; warmer regions rank slightly higher than colder regions. In addition, sensitivity analysis has been performed on SPP and LCOE. Overall, this paper provides theoretical guidance and evaluation approach for SOFC-CCHP demonstrations in China.

Journal article

Biton M, Tariq F, Yufit V, Chen Z, Brandon Net al., 2017, Integrating multi-length scale high resolution 3D imaging and modelling in the characterisation and identification of mechanical failure sites in electrochemical dendrites, Acta Materialia, Vol: 141, Pages: 39-46, ISSN: 1359-6454

The Zn-air battery system is attractive because of its potentially high power density, environmental compatibility and low-cost materials [1]. This paper is focused on understanding the degradation of Zn air batteries, in particular the evolution of Zn dendrites, one of the main degradation mechanisms. Complementary tomographic techniques allow the direct 3D imaging and characterisation of complex microstructures, including the observation and quantification of dendrite growth. Here we present results from 3D x-ray and FIB-SEM tomography of Zn dendrite formation in a zinc-air battery, down to resolutions of tens of nanometers, enabling analysis of complex micro-structures. This approach is shown to be effective in understanding how electrochemical dendrites grow, and demonstrates that tomography coupled with modelling can provide new insights into dendrite growth in electrochemical systems.

Journal article

Chen X, Liu X, Childs P, Brandon N, Wu Bet al., 2017, A low cost desktop electrochemical metal 3D printer, Advanced Materials Technologies, Vol: 2, ISSN: 2365-709X

Additive manufacturing (AM), or 3D printing as it is more commonly known, is the process of creating 3D objects from digital models through the sequential deposition of material in layers. Electrochemical 3D printing is a relatively new form of AM that creates metallic structures through electrochemical reduction of metal ions from solutions onto conductive substrates. The advantage of this process is that a wide range of materials and alloys can be deposited under ambient conditions without thermal damage and more importantly at low cost, as this does not require expensive laser optics or inert gas environments. Other advantages include the fact that this process can be both additive and subtractive through reversal of potential allowing for recycling of components through electrochemical dissolution. However, one main limitation of this technology is speed. Here, a novel electrochemical 3D printer design is proposed using a meniscus confinement approach which demonstrates deposition rates three orders of magnitude higher than equivalent systems due to improved mass transport characteristics afforded through a mechanical electrolyte entrainment mechanism. Printed copper structures exhibit a polycrystalline nature, with decreasing the grain size as the potential is increased resulting in a higher Vickers hardness and electronic resistivity.

Journal article

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