Publications

Journal article

Téllez Lozano H, Druce J, Cooper SJ, Kilner JAet al., 2017,

Double perovskite cathodes for proton-conducting ceramic fuel cells: are they triple mixed ionic electronic conductors?

, Science and Technology of Advanced Materials, Vol: 18, Pages: 977-986, ISSN: 1468-6996

Published by National Institute for Materials Science in partnership with Taylor & Francis. 18 O and 2 H diffusion has been investigated at a temperature of 300 °C in the double perovskite material PrBaCo 2 O 5+δ (PBCO) in flowing air containing 200 mbar of 2 H 2 16 O. Secondary ion mass spectrometry (SIMS) depth profiling of exchanged ceramics has shown PBCO still retains significant oxygen diffusivity (~1.3 × 10 −11 cm 2 s −1 ) at this temperature and that the presence of water ( 2 H 2 16 O), gives rise to an enhancement of the surface exchange rate over that in pure oxygen by a factor of ~3. The 2 H distribution, as inferred from the 2 H 2 16 O − SIMS signal, shows an apparent depth profile which could be interpreted as 2 H diffusion. However, examination of the 3-D distribution of the signal shows it to be nonhomogeneous and probably related to the presence of hydrated layers in the interior walls of pores and is not due to proton diffusion. This suggests that PBCO acts mainly as an oxygen ion mixed conductor when used in PCFC devices, although the presence of a small amount of protonic conductivity cannot be discounted in these materials.

Conference paper

Ouyang M, Boldrin P, Brandon NP, 2017,

Methane Pulse Study on Nickel Impregnated Gadolinium Doped Ceria

, 15th International Symposium on Solid Oxide Fuel Cells (SOFC), Publisher: ELECTROCHEMICAL SOC INC, Pages: 1353-1366, ISSN: 1938-5862

Book chapter

Cooper SJ, brandon NP, 2017,

Solid Oxide Fuel Cell Lifetime and Reliability

, Solid Oxide Fuel Cell Lifetime and Reliability Critical Challenges in Fuel Cells, Editors: Ruiz-Trejo, BOLDRIN, Publisher: Academic Press, Pages: 1-15, ISBN: 9780128097243

For its holistic approach, this book can be used both as an introduction to these issues and a reference resource for all involved in research and application of solid oxide fuel cells, especially those developing understanding in ...

Book

Brandon NP, Ruiz-Trejo E, Boldrin P, 2017,

Solid Oxide Fuel Cell Lifetime and Reliability: Critical Challenges in Fuel Cells

Solid Oxide Fuel Cell Lifetime and Reliability: Critical Challenges in Fuel Cells presents in one volume the most recent research that aims at solving key issues for the deployment of SOFC at a commercial scale and for a wider range of applications. To achieve that, authors from different regions and backgrounds address topics such as electrolytes, contaminants, redox cycling, gas-tight seals, and electrode microstructure. Lifetime issues for particular elements of the fuel cells, like cathodes, interconnects, and fuel processors, are covered as well as new materials. They also examine the balance of SOFC plants, correlations between structure and electrochemical performance, methods for analysis of performance and degradation assessment, and computational and statistical approaches to quantify degradation. For its holistic approach, this book can be used both as an introduction to these issues and a reference resource for all involved in research and application of solid oxide fuel cells, especially those developing understanding in industrial applications of the lifetime issues. This includes researchers in academia and industrial R&D, graduate students and professionals in energy engineering, electrochemistry, and materials sciences for energy applications. It might also be of particular interest to analysts who are looking into integrating SOFCs into energy systems. Brings together in a single volume leading research and expert thinking around the broad topic of SOFC lifetime and durability. Explores issues that affect solid oxide fuel cells elements, materials, and systems with a holistic approach. Provides a practical reference for overcoming some of the common failure mechanisms of SOFCs. Features coverage of integrating SOFCs into energy systems.

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Citations: 38

Book chapter

Cassidy M, Neagu D, Savaniu C, Boldrin Pet al., 2017,

New Materials for Improved Durability and Robustness in Solid Oxide Fuel Cell

, SOLID OXIDE FUEL CELL LIFETIME AND RELIABILITY: CRITICAL CHALLENGES IN FUEL CELLS, Editors: Brandon, RuizTrejo, Boldrin, Publisher: ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD, Pages: 193-216, ISBN: 978-0-08-101102-7

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Citations: 1

Conference paper

Millan M, Lorente E, Boldrin P, Brandon Net al., 2016,

Integration of gasification and fuel cells: Interaction between the anode and contaminants in the syngas

Fouling due to carbon deposition on the fuel cell anode reduces the performance of the cell. • The addition of steam above S/C of 1 was found to reduce carbon deposition from tars but not fully suppress coke formation. • A combination of high S/C=ratio and current density may effectively inhibit carbon formation, maintaining cell performance. • Benzene and toluene represent a "worst-case scenario" as tar models and light fractions are more likely to produce carbon deposits.

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Conference paper

Lomberg M, Boldrin P, Tariq F, Offer G, Wu B, Brandon NPet al., 2015,

Additive manufacturing for solid oxide cell electrode fabrication

, ECS Conference on Electrochemical Energy Conversion & Storage with SOFC-XIV, Publisher: Electrochemical Society, Pages: 2119-2127, ISSN: 1938-6737

Additive manufacturing can potentially offer a highly-defined electrode microstructure, as well as fast and reproducible electrode fabrication. Selective laser sintering is an additive manufacturing technique in which three-dimensional structures are created by bonding subsequent layers of powder using a laser. Although selective laser sintering can be applied to a wide range of materials, including metals and ceramics, the scientific and technical aspects of the manufacturing parameters and their impact on microstructural evolution during the process are not well understood. In the present study, a novel approach for electrode fabrication using selective laser sintering was evaluated by conducting a proof of concept study. A Ni-patterned fuel electrode was laser sintered on an yttria-stabilized zirconia substrate. The optimization process of laser parameters (laser sintering rate and laser power) and the electrochemical results of a full cell with a laser sintered electrode are presented. The challenges and prospects of using selective laser sintering for solid oxide cell fabrication are discussed.

Journal article

Mazur C, Contestabile M, Offer GJ, Brandon NPet al., 2015,

Assessing and comparing German and UK transition policies for electric mobility

, ENVIRONMENTAL INNOVATION AND SOCIETAL TRANSITIONS, Vol: 14, Pages: 84-100, ISSN: 2210-4224

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Citations: 46

Journal article

Duboviks V, Maher RC, Kishimoto M, Cohen LF, Brandon NP, Offer GJet al., 2014,

A Raman spectroscopic study of the carbon deposition mechanism on Ni/CGO electrodes during CO/CO2 electrolysis

, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 13063-13068, ISSN: 1463-9076

Journal article

Howey DA, Mitcheson PD, Yufit V, Offer GJ, Brandon NPet al., 2014,

Online measurement of battery impedance using motor controller excitation

, IEEE Transactions on Vehicular Technology, Vol: 63, Pages: 2557-2566, ISSN: 0018-9545

This paper presents a fast cost-effective technique for the measurement of battery impedance online in an application such as an electric or hybrid vehicle. Impedance measurements on lithium-ion batteries between 1 Hz and 2 kHz give information about the electrochemical reactions within a cell, which relates to the state of charge (SOC), internal temperature, and state of health (SOH). We concentrate on the development of a measurement system for impedance that, for the first time, uses an excitation current generated by a motor controller. Using simple electronics to amplify and filter the voltage and current, we demonstrate accurate impedance measurements obtained with both multisine and noise excitation signals, achieving RMS magnitude measurement uncertainties between 1.9% and 5.8%, in comparison to a high-accuracy laboratory impedance analyzer. Achieving this requires calibration of the measurement circuits, including measurement of the inductance of the current sense resistor. A statistical correlation approach is used to extract the impedance information from the measured voltage and current signals in the presence of noise, allowing a wide range of excitation signals to be used. Finally, we also discuss the implementation challenges of an SOC estimation system based on impedance.

Journal article

Tariq F, Yufit V, Eastwood DS, Merla Y, Biton M, Wu B, Chen Z, Freedman K, Offer GJ, Peled E, Lee PD, Golodnitsky D, Brandon NPet al., 2014,

In-Operando X-ray Tomography Study of Lithiation Induced Delamination of Si Based Anodes for Lithium-Ion Batteries

, Electrochemistry Letters, Vol: 3

Silicon-Lithium based rechargeable batteries offer high gravimetric capacity. However cycle life and electrode microstructure failure mechanisms remain poorly understood. Here we present an X-ray tomography method to investigate in-operando lithiation induced stress cracking leading to the delamination of a composite Si based electrode. Simultaneous voltage measurements show increased cell resistance correlating with severe delamination and microstructural changes. 3D analysis revealed 44.1% loss of the initial electrode-current collector area after 1 hour of operation at 2.4 mA/cm2 and a 21.2% increase in new anode surface area. The work represents a new basis for future investigation of Si based anodes.

Journal article

Wu B, Parkes MP, Yufit V, De Benedetti L, Veismann S, Wirsching C, Vesper F, Martinez-Botas RF, Marquis AJ, Offer GJ, Brandon NPet al., 2014,

Design and testing of a 9.5 kWe proton exchange membrane fuel cell-supercapacitor passive hybrid system

, International Journal of Hydrogen Energy, Vol: 39, Pages: 7885-7896, ISSN: 0360-3199

The design and test of a 9.5 kWe proton exchange membrane fuel cell passively coupled with a 33 × 1500 F supercapacitor pack is presented. Experimental results showed that the system reduced dynamic loads on the fuel cell without the need for additional DC/DC converters. Fuel efficiency gains of approximately 5% were achieved by passive hybridisation in addition to addressing two main operational degradation mechanisms: no-load idling and rapid load cycling.Electrochemical Impedance Spectroscopy measurements indicated that the supercapacitor capacitance dropped with decreasing cell voltage and suggested that operation below 1.3 V is not recommended. Knee-frequency measurements suggested little benefit was gained in using passive systems with load cycles that have frequency components above 0.19 Hz. Analysis of system sizing suggested using the minimum number of supercapacitors to match the open circuit voltage of the fuel cell to maximise load buffering.

Journal article

Wu B, Yufit V, Marinescu M, Offer GJ, Martinez-Botas RF, Brandon NPet al., 2013,

Coupled thermal–electrochemical modelling of uneven heat generation in lithium-ion battery packs

, Journal of Power Sources, Vol: 243, Pages: 544-554, ISSN: 0378-7753

Abstract In battery packs with cells in parallel, the inter-cell connection resistances can cause unequal loads due to non-uniform interconnect overpotentials and consequentially lead to non-uniform heating. This article explores how load imbalances are generated in automotive applications, by describing a battery pack with finite interconnect resistances. Each cell inside the pack is represented by a pseudo 2D electrochemical model coupled with a lumped thermal model. Increasing the number of cells in parallel results in a linear increase in load non-uniformity, whilst increasing the ratio of interconnect to battery impedance results in a logarithmic increase in load non-uniformity, with cells closest to the load points experiencing the largest currents. Therefore, interconnect resistances of the order of mΩ can have a significant detrimental impact. Under steady state discharge the cell impedance changes until the loads balance. This process, however, can take hundreds of seconds and therefore may never happen under dynamic load cycles. Cycling within a narrow state-of-charge range and pulse loading are shown to be the most detrimental situations. Upon load removal, re-balancing can occur causing further heating. Simulation of a 12P7S pack under a real world load cycle shows that these effects could cause localised thermal runaway.

Journal article

Maher RC, Duboviks V, Offer GJ, Kishimoto M, Brandon NP, Cohen LFet al., 2013,

Raman Spectroscopy of Solid Oxide Fuel Cells: Technique Overview and Application to Carbon Deposition Analysis

, FUEL CELLS, Vol: 13, Pages: 455-469, ISSN: 1615-6846

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Citations: 41

Conference paper

Ruiz-Trejo E, Boldrin P, Lubin A, Tariq F, Brandon N, Fearn S, Chater R, Atkinson A, Tighe C, Darr Jet al., 2013,

Silver-ceria composites for oxygen separation from air

, 224th Electrochemical society meeting

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Journal article

Marinescu M, Wu B, Von Srbik M, Yufit V, Offer GJet al., 2013,

The effect of thermal gradients on the performance of battery packs in automotive applications

, IET Conference Publications, Vol: 2013

Thermal gradients arising inside a battery pack for automotive applications are calculated for 200 A discharge via a multiparticle thermal-electrochemical coupled high fidelity model for a 12P7S 4.8 Ah cell pack. The effect of such gradients at the cell level are studied in a first approximation under a corresponding discharge at 15 A, by discretising the cell into units at fixed temperatures throughout the discharge. The immediate time evolution of load distribution through the various parts of the cell shows a complex behaviour, dependent on parameters such as temperatures, state of charge and load characteristics.

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Citations: 3

Journal article

Wu B, Yufit V, Campbell J, Offer GJ, Martinez-Botas RF, Brandon NPet al., 2013,

Simulated and experimental validation of a fuel cell-supercapacitor passive hybrid system for electric vehicles

, IET Conference Publications, Vol: 2013

The concept of a fuel cell-supercapacitor hybrid system involves the direct coupling of the two devices to achieve the same benefits of hybridisation but without the need for costly DCDC converters. Using an experimentally validated steady state fuel cell model and a transmission line based supercapacitor model, it has been shown that the passive hybridisation allows for efficiency gains of approximately 16% compared to a pure fuel cell system. Under load, the supercapacitors meets the peak power requirement due to their lower impedance giving the FC time to ramp up. Under no load conditions, the fuel cell gradually charges the supercapacitors back to the steady state thermodynamic equilibrium potential. A fast fourier transform analysis of the respective loads under an automotive drive cycle showed that the supercapacitors act as a low pass filter, reducing the magnitude of load oscillations from the fuel cell. This therefore addresses two of the main modes of fuel cell degradation in automotive applications: rapid power cycling and no load idling.

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Citations: 4

Journal article

Troxler Y, Wu B, Marinescu M, Yufit V, Patel Y, Marquis AJ, Brandon NP, Offer GJet al., 2013,

The effect of thermal gradients on the performance of lithium ion batteries

, Journal of Power Sources, Pages: accepted-accepted, ISSN: 0378-7753

Abstract An experimental apparatus is described, in which Peltier elements are used for thermal control of lithium-ion cells under isothermal and non-isothermal conditions, i.e. to induce and maintain thermal gradients. Lithium-ion battery packs for automotive applications consist of hundreds of cells, and depending on the pack architecture, individual cells may experience non-uniform thermal boundary conditions. This paper presents the first study of the impact of artificially induced thermal gradients on cell performance. The charge transfer resistance of a 4.8 Ah is verified to have a strong temperature dependence following the Arrhenius law. Thermal cycling of the cell, combined with slow rate cyclic voltammetry, allows to rapidly identify phase transitions in electrodes, due to the thermal effect of entropy changes. A cell with a temperature gradient maintained across is found to have a lower impedance than one held at the theoretical average temperature. This feature is attributed to details of the inner structure of the cell, and to the non-linear temperature dependence of the charge transfer resistance.

Conference paper

von Srbik MT, Martinez-Botas R, 2012,

Vehicle Optimisation for Regenerative Brake Energy Maximisation

, IMechE Sustainable Vehicles Technologies Conference

Regenerative braking is an effective method to increase the driving range of Hybrid Electric Vehicles (HEV) and to reduce overall vehicle fuel consumption. This paper presents the potential savings due to regenerative braking and the resulting driving range extension. A Cooperative Regenerative Braking Strategy (CRBS) Matlab/Simulink environment has been developed. The regenerative energy and efficiency are evaluated for given driving cycle time-trace and vehicle component configuration in a flexible simulation platform architecture containing reduced-order component models.The paper focuses on vehicle configuration comparison and quantification including economic considerations. A sensitivity study yielded the isolated dependency of regeneration efficiency performance on several parameters, in decreasing order of impact: electric machine efficiency, drive type, power train configuration, brake torque application, shifting strategy, air resistance and vehicle mass. The resulting significance to improvements of the overall vehicle includes the likelihood of advances in the respective technologies.Optimum configurations for specific vehicle types and driving scenarios have been devised and potential savings due to CRBS implementation quantified; pointing towards the great significance of vehicle configuration optimisation for a particular application rather than the broadest customer base possible.Future projections in terms of Carbon Dioxide emission reduction due to regenerative braking and component optimisation (up to 40%) were made. The likelihood of technology advances and acceleration of innovation market diffusion following consumption trends were taken into account.Barriers to quick market implementation were explored, including initial capital investment, consumer reluctance to change, and marketing difficulties. Future development challenges in the Hybrid vehicle industry are discussed.

Report

Contestabile M, Offer GJ, North R, 2012,

Electric Vehicles: A Synthesis of the Current Literature with a Focus on Economic and Environmental Viability

, Publisher: LCAworks

Journal article

Brightman E, Maher R, Offer GJ, Duboviks V, Heck C, Cohen LF, Brandon NPet al., 2012,

Designing a miniaturised heated stage for <i>in situ</i> optical measurements of solid oxide fuel cell electrode surfaces, and probing the oxidation of solid oxide fuel cell anodes using <i>in situ</i> Raman spectroscopy

, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 83, ISSN: 0034-6748

Journal article

Offer GJ, Yufit V, Howey DA, Wu B, Brandon NPet al., 2012,

Module design and fault diagnosis in electric vehicle batteries

, Journal of Power Sources

Systems integration issues, such as electrical and thermal design and management of full battery packs–often containing hundreds of cells–have been rarely explored in the academic literature. In this paper we discuss the design and construction of a 9 kWh battery pack for a motorsports application. The pack contained 504 lithium cells arranged into 2 sidepods, each containing 3 modules, with each module in a 12P7S configuration. This paper focuses particularly on testing the full battery pack and diagnosing subsequent problems related to cells being connected in parallel. We demonstrate how a full vehicle test can be used to identify malfunctioning strings of cells for further investigation. After individual cell testing it was concluded that a single high inter-cell contact resistance was causing currents to flow unevenly within the pack, leading to cells being unequally worked. This is supported by a Matlab/Simulink model of one battery module, including contact resistances. Over time the unequal current flowing through cells can lead to significant differences in cells’ state of charge and open circuit voltages, large currents flowing between cells even when the load is disconnected, cells discharging and aging more quickly than others, and jeopardise capacity and lifetime of the pack.

Conference paper

Wu B, Offer GJ, Yufit V, Howey DA, Brandon NPet al., 2012,

Fault analysis in battery module design for electric and hybrid vehicles

, Power Electronics, Machines and Drive

Journal article

Wu B, Matian M, Offer GJ, 2012,

Hydrogen PEMFC system for automotive applications

, International Journal of Low Carbon Technologies

A balance of plant (BOP) system for a 9.5-kWe Nedstack P9.5-75 low-temperature proton exchange membrane fuel cell (FC) stack was tested up to a power of 2 kWe. The system has been designed to act as a range extender for a series hybrid electric vehicle driven under urban duty cycles. Vehicle simulations have estimated that an average gross power requirement of 4 kWe is needed from the FC, whilst simulations of the FC stack and BOP components have allowed for characterisation of transient behaviour and performance degradation.