Imperial College London

Dr Ainara Aguadero

Faculty of EngineeringDepartment of Materials

Reader in Energy Materials
 
 
 
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Contact

 

+44 (0)20 7594 5174a.aguadero CV

 
 
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Location

 

1.07Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

75 results found

Brugge RH, Chater RJ, Kilner JA, Aguadero Aet al., 2021, Experimental determination of Li diffusivity in LLZO using isotopic exchange and FIB-SIMS, JOURNAL OF PHYSICS-ENERGY, Vol: 3, ISSN: 2515-7655

Journal article

Celorrio V, Tiwari D, Calvillo L, Leach A, Huang H, Granozzi G, Alonso JA, Aguadero A, Pinacca RM, Russell AE, Fermin DJet al., 2021, Electrocatalytic Site Activity Enhancement via Orbital Overlap in A(2)MnRuO(7) (A = Dy3+, Ho3+, and Er3+) Pyrochlore Nanostructures, ACS APPLIED ENERGY MATERIALS, Vol: 4, Pages: 176-185, ISSN: 2574-0962

Journal article

Skinner S, Aguadero A, Tsai C-Y, 2020, High electrical conductivity and crystal structure of the solid oxide cell electrode Pr4Ni3O10-δ, Journal of Solid State Chemistry, Vol: 289, Pages: 1-9, ISSN: 0022-4596

Pr4Ni3O10-δ is a promising air electrode for solid oxide fuel cells and electrolysers with comparable performance to Pr2NiO4+δ but with improved thermodynamic stability at a cell operating temperature of 600 ​°C–800 ​°C. To fully understand and integrate Pr4Ni3O10-δ into commercial devices there are several aspects that remain to be addressed. This study provides a systematic analysis of the synthesis kinetics, crystal structure, oxygen content and electrical conductivity providing clear paths for the development of Pr4Ni3O10-δ-based low temperature solid oxide electrochemical devices with enhanced performance and stability. We prove that the material can reach a remarkable electrical conductivity of 235 Scm-1 at 700 ​°C in air, much higher than the previously reported values of 86 Scm-1 and 56 Scm-1, rising to 278 Scm-1 at 450 ​°C. High resolution neutron powder and in-situ X-ray diffraction confirmed that Pr4Ni3O10-δ crystallises in the monoclinic P21/a space group, and that no phase transitions were observed on heating to 1000 ​°C in air. An electrical conductivity anomaly was found at ~300 ​°C and is attributed to a subtle change in the local structure of the material, potentially associated with changes in the oxygen content.

Journal article

Celikbilek O, Cavallaro A, Kerherve G, Fearn S, Chaix-Pluchery O, Aguadero A, Kilner JA, Skinner SJet al., 2020, Surface restructuring of thin-film electrodes based on thermal history and its significance for the catalytic activity and stability at the gas/solid and solid/solid interfaces, ACS Applied Materials & Interfaces, Vol: 12, Pages: 34388-34401, ISSN: 1944-8244

Electrodes in solid-state energy devices are subjected to a variety of thermal treatments, from film processing to device operation at high temperatures. All these treatments influence the chemical activity and stability of the films, as the thermally induced chemical restructuring shapes the microstructure and the morphology. Here, we investigate the correlation between the oxygen reduction reaction (ORR) activity and thermal history in complex transition metal oxides, in particular, La0.6Sr0.4CoO3−δ (LSC64) thin films deposited by pulsed laser deposition. To this end, three ∼200 nm thick LSC64 films with different processing and thermal histories were studied. A variety of surface-sensitive elemental characterization techniques (i.e., low-energy ion scattering, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry) were employed to thoroughly investigate the cationic distribution from the outermost surface to the film/substrate interface. Moreover, electrochemical impedance spectroscopy was used to study the activity and the stability of the films. Our investigations revealed that, despite the initial comparable ORR activity at 600 °C, the degradation rates of the films differed by twofold in the long-term stability tests at 500 °C. Here, we emphasize the importance of processing and thermal history in the elemental surface distribution, especially for the stability of LSC64 electrodes and propose that they should be considered as among the main pillars in the design of active surfaces.

Journal article

Brugge RH, Pesci FM, Cavallaro A, Sole C, Isaacs MA, Kerherve G, Weatherup RS, Aguadero Aet al., 2020, The origin of chemical inhomogeneity in garnet electrolytes and its impact on the electrochemical performance, Journal of Materials Chemistry A, Vol: 8, Pages: 14265-14276, ISSN: 2050-7488

The interface between solid electrolytes and lithium metal electrodes determines the performance of an all-solid-state battery in terms of the ability to demand high power densities and prevent the formation of lithium dendrites. This interface depends strongly on the nature of the solid electrolyte surface in contact with the metallic anode. In the garnet electrolyte/Li system, most papers have focused on the role of current inhomogeneities induced by void formation in the Li metal electrode and the presence of insulating reaction layers following air exposure. However, extended defects in the solid electrolyte induced by chemical and/or structural inhomogeneities can also lead to uneven current distribution, impacting the performance of these systems. In this work, we use complementary surface analysis techniques with varying analysis depths to probe chemical distribution within grains and grain boundaries at the surface and in the bulk of garnet-type electrolytes to explain their electrochemical performance. We show that morphology, post-treatments and storage conditions can greatly affect the surface chemical distribution of grains and grain boundaries. These properties are important to understand since they will dictate the ionic and electronic transport near the interfacial zone between metal and electrolyte which is key to determining chemo-mechanical stability.

Journal article

Pesci FM, Bertei A, Brugge RH, Emge SP, Hekselman AKO, Marbella LE, Grey CP, Aguadero Aet al., 2020, Establishing ultra-low activation energies for lithium transport in garnet electrolytes., ACS Applied Materials and Interfaces, Vol: 12, Pages: 32086-32816, ISSN: 1944-8244

Garnet-type structured lithium ion conducting ceramics represent a promising alternative to liquid-based electrolytes for all-solid-state batteries. However, their performance is limited by their polycrystalline nature and the inherent inhomogeneous current distribution due to the different ion dynamics at grains, grain boundaries and interfaces. In this study we use a combination of electrochemical impedance spectroscopy, distribution of relaxation times analysis and solid state nuclear magnetic resonance (NMR), in order to understand the role that bulk, grain boundary and interfacial processes play in the ionic transport and electrochemical performance of garnet based cells. Variable temperature impedance analysis reveals the lowest activation energy (Ea) for Li transport in the bulk of the garnet electrolyte (0.15 eV), consistent with pulsed field gradient NMR spectroscopy measurements (0.14 eV). We also show a decrease in grain boundary activation energy at temperatures below 0 °C, that is followed by the total conductivity, suggesting that the bottleneck to ionic transport resides in the grain boundaries. We reveal that the grain boundary activation energy is heavily affected by its composition that, in turn, is mainly affected by the segregation of dopants and Li. We suggest that by controlling the grain boundary composition, it would be possible to pave the way towards targeted engineering of garnet-type electrolytes and ameliorate their electrochemical performance in order to enable their use in commercial devices.

Journal article

Roman Acevedo W, van den Bosch CAM, Aguirre MH, Acha C, Cavallaro A, Ferreyra C, Sanchez MJ, Patrone L, Aguadero A, Rubi Det al., 2020, Large memcapacitance and memristance at Nb:SrTiO3/La0.5Sr0.5Mn0.5Co0.5O3-delta topotactic redox interface (vol 116, 063502, 2020), APPLIED PHYSICS LETTERS, Vol: 116, ISSN: 0003-6951

Journal article

Roman Acevedo W, van den Bosch CAM, Aguirre MH, Acha C, Cavallaro A, Ferreyra C, Sanchez MJ, Patrone L, Aguadero A, Rubi Det al., 2020, Large memcapacitance and memristance at Nb:SrTiO3/La0.5Sr0.5Mn0.5Co0.5O3-delta topotactic redox interface, APPLIED PHYSICS LETTERS, Vol: 116, ISSN: 0003-6951

Journal article

van den Bosch C, Cavallaro A, Moreno R, Cibin G, Kerherve G, Caciedo J, Lippert T, Doebeli M, Santiso J, Skinner S, Aguadero Aet al., 2020, Revealing strain effects on the chemical compositionof Perovskite oxide thin films surface, bulk, and interfaces, Advanced Materials Interfaces, Vol: 7, ISSN: 2196-7350

Understanding the effects of lattice strain on oxygen surface and diffusion kinetics in oxides is a controversial subject that is critical for developing efficient energy storage and conversion materials. In this work, high-quality epitaxial thin films of the model perovskite La0.5Sr0.5Mn0.5Co0.5O3-δ (LSMC), under compressive or tensile strain, were characterized with a combination of in situ and ex situ bulk and surface-sensitive techniques. The results demonstrate a non-linear correlation of mechanical and chemical properties as a function of the operation conditions. It was observed that the effect of strain on reducibility is dependent on the “effective strain” induced on the chemical bonds. In plain strain, and in particular the relative B-O length bond, are the key factor controlling which of the B-site cation would be reduced preferentially. Furthermore, the need to use a set of complimentary techniques to isolate different chemically-induced strain effects was proven. With this, it was confirmed that tensile strain favors the stabilization of a more reduced lattice, accompanied by greater segregation of strontium secondary phases and a decrease of oxygen exchange kinetics on LSMC thin films.

Journal article

Tsai C-Y, McGilvery CM, Aguadero A, Skinner SJet al., 2019, Phase evolution and reactivity of Pr2NiO4+δ and Ce0.9Gd0.1O2-δ composites under solid oxide cell sintering and operation temperatures, International Journal of Hydrogen Energy, Vol: 44, Pages: 31458-31465, ISSN: 0360-3199

In developing a new compositae air electrode for Solid Oxide Cells (SOCs) it is essential to fully understand the phase chemistry of all components. Ruddlesden-Popper type electrodes such as Pr2NiO4+δ have previously been proposed as attractive alternatives to conventional La0·6Sr0·4Fe0·8Co0·2O3-δ/Ce1-xGdxO2-δ compositae air electrodes for both fuel cell and electrolyser modes of operation. However, Pr2NiO4+δ have been shown to have limited stability, reacting with a Ce1-xGdxO2-δ interlayer to form a Ce1-x-yGdxPryO2-δ (CGPO) phase of unknown stoichiometry. Additionally, Pr2NiO4+δ are known to decompose to Pr4Ni3O10 ± δ under certain conditions.In this work detailed understanding of the chemical reaction between Pr2NiO4+δ and Ce0.9Gd0.1O2-δ (CGO10) under normal solid oxide cell fabrication and operating temperatures was obtained, identifying the composition of the resulting CGPO phase reaction products. It is shown that, in addition to the unreacted CGO10 present after sintering the compositae at 1100 °C for up to 12 h, a series of CGPO chemical compositions were formed with various Ce, Gd and Pr ratios depending on the relative distance of the doped ceria phases from the Pr2NiO4+δ phases. The extent of the chemical reaction was found to depend on the sintering time and the contact area of the two phases. Further thermal treatment of the resulting products under SOC air electrode operating temperature (800 °C) resulted in the initiation of Pr2NiO4+δ decomposition, forming Pr4Ni3O10 ± δ and Pr6O11 with no detectable change in the composition of previously formed Pr-substituted ceria phases. It is apparent that the Pr2NiO4+δ/CGO10 compositae is unsuitable as an air electrode, but there is evidence that the decomposition products, Pr4Ni3O10 ± δ and Ce1-x-yGdxPryO2-δ are stable and suitable candidates for SOC electrodes.

Journal article

Edge J, Cooper SJ, Aguadero A, George C, Titirici M, Goddard Pet al., 2019, UK Research on Materials for Electrochemical Devices, JOHNSON MATTHEY TECHNOLOGY REVIEW, Vol: 63, Pages: 255-260, ISSN: 2056-5135

Journal article

Brugge RH, Kilner JA, Aguadero A, 2019, Germanium as a donor dopant in garnet electrolytes, Solid State Ionics, Vol: 337, Pages: 154-160, ISSN: 0167-2738

Cubic Li 7 La 3 Zr 2 O 12 (LLZO) garnet electrolytes continue to be viewed as an enabler of all-solid-state lithium battery technologies, or as protective membranes for next-generation lithium battery systems. Supervalent dopants at the lithium sublattice are commonly used to stabilise the conductive cubic phase, through the creation of lithium vacancies. The use of germanium (Ge 4+ ) as a higher valent dopant substituting for Li + was studied here and shown to stabilise the cubic LLZO phase through substitution of x = 0.10 mol of Ge (at the tetrahedral 24d Li sites of the space group Ia-3d, based on the neutron powder diffraction result). This substitution preference follows that of Al 3+ (having a similar ionic radius and reported to reside at 24d sites), but with a lower critical concentration for cubic phase stabilisation, in agreement with charge neutrality arguments to obtain the required Li content (ca. 6.4–6.6 per formula unit) for optimum conductivity. The x = 0.10 composition gave the highest bulk Li ion conductivity of 2.8 × 10 −4 S cm −1 at 25 °C, on the order of reported values for Al-doped LLZO. Surface chemical analysis using time of flight secondary ion mass spectrometry showed Ge homogeneously distributed within the grains as well as some Li-, O- and Ge- enrichment along the grain boundaries. Cyclic voltammetry of the cells containing Ge-doped LLZO showed a redox stability up to +5 V.

Journal article

Manalastas W, Rikarte J, Chater RJ, Brugge R, Aguadero A, Buannic L, Llordés A, Aguesse F, Kilner Jet al., 2019, Mechanical failure of garnet electrolytes during Li electrodeposition observed by in-operando microscopy, Journal of Power Sources, Vol: 412, Pages: 287-293, ISSN: 0378-7753

Metallic Li anodes are key to reaching high energy densities in next-generation solid-state batteries, however, major problems are the non-uniform deposition of Li at the interface and the penetrative power of Li metal during operation, which cause failure of the ceramic electrolyte, internal short-circuits and a premature end of battery life. In this work, we explore the anode-electrolyte interface instability of a Li metal-garnet electrolyte system during Li electrodeposition, and its implications for mechanical fracture, Li metal propagation, and electrolyte failure. The degradation mechanism was followed step-by-step during in-operando electrochemical cycling using optical and scanning electron microscopy. High amounts of Li electrodeposition in a localized zone of the interface lead to ceramic fracture followed by an electrode-to-electrode electrical connection via a conductor Li metal filament. This work enables deeper understanding of battery failure modes in all-solid-state batteries containing a ceramic electrolyte membrane.

Journal article

Yatoo M, Aguadero A, Skinner S, 2019, LaPr3Ni3O9.76 as a candidate solid oxide fuel cell cathode: Role of microstructure and interface structure on electrochemical performance, APL Materials, Vol: 7, ISSN: 2166-532X

A new higher-order Ruddlesden-Popper phase composition LaPr3Ni3O9.76 was synthesised by a sol-gel route and studied forpotential intermediate-temperature solid oxide fuel cell cathode properties by electrochemical impedance spectroscopy. The focus of the work was optimisation of the microstructure and interface structure to realise the best performance, and thereforesymmetrical cells after impedance testing were subsequently studied by scanning electron microscopy for post-microstructuralanalysis. It was observed that the cathode ink prepared after ball milling the material and then triple roll milling the prepared inkgave the lowest area specific resistance (ASR) of 0.17Ωcm2 at 700◦C when a La0.8Sr0.2Ga0.8Mn0.2O3-δ (LSGM) electrolyte thathad been previously polished was used. The post-microstructural studies, as expected, showed an improved interface structureand relatively good particle interconnectivity and much less sintering when compared to the symmetrical half-cells constructedusing the ink prepared from the as-synthesised material. The interface structure was further improved significantly by adding a∼10μm thick LSGM ink interlayer, which was reflected in the electrochemical performance, reducing the ASR of the material from 0.17Ωcm2 to 0.08Ωcm2 at 700◦C. This is to date the best performance reported for an n = 3 Ruddlesden-Popper phase material with LSGM as the electrolyte.

Journal article

Pesci FM, Brugge RH, Hekselman AKO, Cavallaro A, Chater RJ, Aguadero Aet al., 2018, Elucidating the role of dopants in the critical current density for dendrite formation in garnet electrolytes, Journal of Materials Chemistry A, Vol: 6, Pages: 19817-19827, ISSN: 2050-7488

Garnet-type solid electrolytes have attracted great interest in solid state battery research thanks to their high ionic conductivity at room temperature (10−3 S cm−1) and their electrochemical stability against lithium metal anodes. However, the formation of lithium dendrites following charge/discharge limits their applicability and commercialisation. Although widely investigated, no clear explanation of dendrite formation has been previously reported. In this work, we employ cubic Al- and Ga-doped Li7La3Zr2O12, which represent two of the solid electrolytes with higher technological importance, to investigate the formation and chemical composition of dendrites. For the first time, this study elucidates the role that the dopants play in determining the critical current density for dendrite formation and highlights the importance of controlling the dopant distribution in the garnet structure. We use a combination of techniques including Secondary Electron Microscopy and Secondary Ion Mass Spectrometry in order to analyse the microstructure and chemical composition of dendrites in Li7La3Zr2O12. We show that, following electrochemical cycling, Li6.55Ga0.15La3Zr2O12 systematically displays a critical current density 60% higher than Li6.55Al0.15La3Zr2O12. Chemical analysis revealed that in Li6.55Al0.15La3Zr2O12 the dendritic features are composed of a mixture of Al and Li species, whereas in Li6.55Ga0.15La3Zr2O12 they are uniquely composed of Li. We also show that only in pristine Li6.55Al0.15La3Zr2O12, the dopant segregates at the grain boundaries suggesting that local chemical inhomogeneity can have a fundamental role in the nucleation and propagation of dendrites.

Journal article

Celorrio V, Calvillo L, van den Bosch CAM, Granozzi G, Aguadero A, Russell AE, Fermin DJet al., 2018, Mean Intrinsic Activity of Single Mn Sites at LaMnO3 Nanoparticles Towards the Oxygen Reduction Reaction, CHEMELECTROCHEM, Vol: 5, Pages: 3044-3051, ISSN: 2196-0216

Journal article

Vardar G, Bowman WJ, Lu Q, Wang J, Chater RJ, Aguadero A, Seibert R, Terry J, Hunt A, Waluyo I, Fong DD, Jarry A, Crumlin EJ, Hellstrom SL, Chiang YM, Yildiz Bet al., 2018, Structure, chemistry, and charge transfer resistance of the interface between Li7La3Zr2O12 electrolyte and LiCoO2 cathode, Chemistry of Materials, Vol: 30, Pages: 6259-6276, ISSN: 0897-4756

All-solid-state batteries promise significant safety and energy density advantages over liquid-electrolyte batteries. The interface between the cathode and the solid electrolyte is an important contributor to charge transfer resistance. Strong bonding of solid oxide electrolytes and cathodes requires sintering at elevated temperatures. Knowledge of the temperature dependence of the composition and charge transfer properties of this interface is important for determining the ideal sintering conditions. To understand the interfacial decomposition processes and their onset temperatures, model systems of LiCoO2 (LCO) thin films deposited on cubic Al-doped Li7La3Zr2O12 (LLZO) pellets were studied as a function of temperature using interface-sensitive techniques. X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and energy-dispersive X-ray spectroscopy (EDS) data indicated significant cation interdiffusion and structural changes starting at temperatures as low as 300°C. La2Zr2O7 and Li2CO3 were identified as decomposition products after annealing at 500°C by synchrotron X-ray diffraction (XRD). X-ray absorption spectroscopy (XAS) results indicate the presence of also LaCoO3, in addition to La2Zr2O7 and Li2CO3. Based on electrochemical impedance spectroscopy, and depth profiling of the Li distribution upon potentiostatic hold experiments on symmetric LCO|LLZO|LCO cells, the interfaces exhibited significantly increased impedance, up to 8 times that of the as-deposited samples after annealing at 500°C. Our results indicate that lower-temperature processing conditions, shorter annealing time scales, and CO2-free environments are desirable for obtaining ceramic cathode-electrolyte interfaces that enable fast Li transfer and high capacity.

Journal article

Yatoo MA, Du Z, Zhao H, Aguadero A, Skinner SJet al., 2018, La2Pr2Ni3O10±δ Ruddlesden-Popper phase as potential intermediate temperature-solid oxide fuel cell cathodes, Solid State Ionics, Vol: 320, Pages: 148-151, ISSN: 0167-2738

Ruddlesden-Popper phases are layered oxides composed of nABO 3 perovskite layers sandwiched between two AO rock-salt layers. Herein a new composition of n = 3 Ruddlesden-Popper phases, La 2 Pr 2 Ni 3 O 10±δ , synthesised by the citrate sol-gel method is reported. A preliminary microstructure investigation combined with studies of the electrochemical performance of this new composition, La 2 Pr 2 Ni 3 O 10±δ as a potential cathode material in both symmetrical and single cell configurations is reported. The area specific resistance of the La 2 Pr 2 Ni 3 O 10±δ cathode was found to be 0.34 Ω cm 2 at 800 °C, which is significantly better than previous reports for the La 4 Ni 3 O 10±δ analogue under similar conditions. A modest peak power density of 0.19 W cm −2 at 800 °C was found, whilst electrode adhesion was identified as contributing to the modest performance.

Journal article

Brugge R, Hekselman A, Cavallaro A, Pesci F, Chater R, Kilner J, Aguadero Aet al., 2018, Garnet electrolytes for solid state batteries: visualization of moisture-induced chemical degradation and revealing its impact on the Li-ion dynamics, Chemistry of Materials, Vol: 30, Pages: 3704-3713, ISSN: 0897-4756

In this work, we reveal the impact of moisture-induced chemical degradation and proton–lithium exchange on the Li-ion dynamics in the bulk and the grain boundaries and at the interface with lithium metal in highly Li-conducting garnet electrolytes. A direct correlation between chemical changes as measured by depth-resolved secondary ion mass spectrometry and the change in transport properties of the electrolyte is provided. In order to probe the intrinsic effect of the exchange on the lithium kinetics within the garnet structure, isolated from secondary corrosion product contributions, controlled-atmosphere processing was first used to produce proton-free Li6.55Ga0.15La3Zr2O12 (Ga0.15-LLZO), followed by degradation steps in a H2O bath at 100 °C, leading to the removal of LiOH secondary phases at the surface. The proton-exchanged region was analyzed by focused ion beam secondary ion mass spectrometry (FIB-SIMS) and found to extend as far as 1.35 μm into the Ga0.15-LLZO garnet pellet after 30 min in H2O. Impedance analysis in symmetrical cells with Li metal electrodes indicated a greater reactivity in grain boundaries than in grains and a significantly detrimental effect on the Li transfer kinetics in the Li metal/garnet interface correlated to a 3-fold decrease in the Li mobility in the protonated garnet. This result indicates that the deterioration of Li charge transfer and diffusion kinetics in proton-containing garnet electrolytes have fundamental implications for the optimization and integration of these systems in commercial battery devices.

Journal article

Riley DJ, Song W, Xie F, Shearing PR, Brett D, Aguadero A, Kangyu Jet al., 2018, Co3O4 hollow nanospheres doped with ZnCo2O4 via thermal vapor mechanism for fast lithium storage., Energy Storage Materials, Vol: 14, Pages: 324-334, ISSN: 2405-8297

Binary metal oxides offer improved anode materials in lithium ion batteries owing to enhanced electrical conductivity but suffer from large volume expansion on lithiation. A novel route to hollow Co3O4 nanospheres doped with ZnCo2O4 is demonstrated that mitigates the expansion issue and shows excellent performance at high current densities. The synthetic route is based on the pyrolysis of binary metal-organic-frameworks (MOFs) with the controlled loss of zinc tuning the micro and nanostructure of the material through a thermal vapor mechanism. The optimal structures, that contain hollow Co3O4 spheres of ca. 50 nm diameter doped with ZnCo2O4, show a specific capacity of 890 mAh g−1 at a current rate of 0.1 A g−1 and show a similar specific capacity at 1 A g−1 after 120 cycles at high current densities. The kinetics of lithiation/delithiation changes from diffusion-controlled to a surface-controlled process by the nanosizing of the particles. The resultant faster ion diffusion and capacitive storage for lithium ions are responsible for the extraordinary high-rate performance of the hollow structures.

Journal article

Shih D, Aguadero A, Skinner SJ, 2018, Improvement of Ionic Conductivity in A-site Lithium Doped Sodium Bismuth Titanate, Solid State Ionics, Vol: 317, Pages: 32-38, ISSN: 0167-2738

Oxide-ion conductors play a significant role in various applications such as solid oxide fuel cells (SOFCs), oxygen separation membranes and sensors. Recently, high ionic conductivity (~ 1 × 10− 4 S cm− 1 at 600 °C) was found in sodium bismuth titanate (NBT), which originates from oxygen vacancies compensating the introduced Bi-deficiency. By providing pathways with low diffusion barriers, the highly polarizable Bi3 + ions with 6s2 lone pair electrons and weak Bisingle bondO bonds are also beneficial for the migration of oxygen ions. Here we report the influence of lithium doping on the electrical properties of NBT. The optimal doping level of 4 at% Li on the Bi-site improves the ionic conductivity by one order of magnitude to ~ 7 × 10− 3 S cm− 1 at 600 °C without changing the conduction mechanism, which could be attributed to an increase in the oxygen vacancy concentration based on an acceptor doping mechanism. A further increase in Li content does not improve the total conductivity. Oxygen diffusion data were acquired by the Isotope Exchange Depth Profile (IEDP) method in combination with Secondary Ion-Mass Spectrometry (SIMS). The oxygen self-diffusion coefficients (e.g. 7.04 × 10− 9 cm2 s− 1 at 600 °C) are in excellent agreement with the values derived from impedance spectroscopy data, suggesting that the oxygen ions are the main charge carriers in the system. Furthermore, a degradation test was performed for 100 h under a variety of atmospheres, showing only a slight decrease in conductivity in both air and oxygen atmospheres attributed to the loss of material from the A-site. Comparison with other oxide-ion conductors indicates that Li-doped NBT materials are promising candidates for intermediate temperature SOFC applications.

Journal article

Song W, Brugge R, Theodorou IG, Lim AL, Yang Y, Zhao T, Burgess CH, Johnson ID, Aguadero A, Shearing PR, Brett DJL, Xie F, Riley DJet al., 2017, Enhancing Distorted Metal Organic Framework Derived ZnO as Anode Material for Lithium Storage by the Addition of Ag2S Quantum Dots., ACS Applied Materials and Interfaces, Vol: 9, Pages: 37823-37831, ISSN: 1944-8244

The lithium storage properties of the distorted metal-organic framework (MOF) derived nanosized ZnO@C are significantly improved by the introduction of Ag2S quantum dots (QDs) during the processing of the material. In the thermal treatment, the Ag2S QDs react to produce Ag nanoparticles and ZnS. The metal nanoparticles act to shorten electron pathways and improve the connectivity of the matrix and the partial sulfidation of the ZnO surface improves the cycling stability of the material. The electrochemical properties of ZnO@C, Ag2S QDs treated ZnO@C and the amorphous carbon in ZnO@C have been compared. The small weight ratio of Ag2S QDs to ZnO@C at 1:180 shows the best performance in lithium storage. The exhibited specific capacities are improved and retained remarkably in the cycling at high current rates. At low current densi-ties (200 mA g-1) treatment of ZnO@C with Ag2S QDs results in a 38% increase in the specific capacity.

Journal article

Bishop SR, Liu X, Aguadero A, 2017, Preface-JES Focus Issue on Oxygen Reduction and Evolution Reactions for High Temperature Energy Conversion and Storage, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 164, Pages: Y11-Y11, ISSN: 0013-4651

Journal article

Cascos V, Aguadero A, Harrington G, Fernandez-Diaz MT, Alonso JAet al., 2017, Design of Sr0.7R0.3CoO3-delta (R = Tb and Er) perovskites performing as cathode materials in solid oxide fuel cells, Journal of The Electrochemical Society, Vol: 164, Pages: F3019-F3027, ISSN: 1945-7111

Sr0.7R0.3CoO3-δ (R = Tb and Er) tetragonal perovskites have been prepared and evaluated as mixed ionic-electronic cathodes for SOFC. Neutron powder diffraction (NPD) measurements evidenced that both compounds are oxygen hypo-stoichiometric with long-range order of oxygen vacancies that leads to a tetragonal perovskite-type superstructure (s.g. I4/mmm) stable within the whole temperature range under study. The oxygen vacancies located mainly in the equatorial oxygen positions exhibit large displacement factors. The high oxygen mobility in Sr0.7Tb0.3CoO3-δ was confirmed by 18O oxygen labeling followed by Secondary Ion Mass Spectrometry (SIMS) with values of oxygen self-diffusion of 1.29 × 10−10 cm2/s at 525°C. Polarization resistances with LSGM as electrolyte gave values as low as 0.011 Ω⋅cm2 and maximum output powers of 570 mW/cm2 at 850°C were obtained in test cells set in electrolyte-supported configuration. Electrical conductivity, thermal and chemical expansion and stability measurements confirm the potential of these materials as cathodes for SOFC.

Journal article

Celorrio V, Calvillo L, Dann E, Granozzi G, Aguadero A, Kramer D, Russell AE, Fermin DJet al., 2016, Oxygen reduction reaction at LaxCa1-xMnO3 nanostructures: interplay between A-site segregation and B-site valency, Catalysis Science and Technology, Vol: 6, Pages: 7231-7238, ISSN: 2044-4753

The mean activity of surface Mn sites at LaxCa1−xMnO3 nanostructures towards the oxygen reduction reaction (ORR) in alkaline solution is assessed as a function of the oxide composition. Highly active oxide nanoparticles were synthesised by an ionic liquid-based route, yielding phase-pure nanoparticles, across the entire range of compositions, with sizes between 20 and 35 nm. The bulk vs. surface composition and structure are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). These techniques allow quantification of not only changes in the mean oxidation state of Mn as a function of x, but also the extent of A-site surface segregation. Both trends manifest themselves in the electrochemical responses associated with surface Mn sites in 0.1 M KOH solution. The characteristic redox signatures of Mn sites are used to estimate their effective surface number density. This parameter allows comparing, for the first time, the mean electrocatalytic activity of surface Mn sites as a function of the LaxCa1−xMnO3 composition. The ensemble of experimental data provides a consistent picture in which increasing electron density at the Mn sites leads to an increase in the ORR activity. We also demonstrate that normalisation of electrochemical activity by mass or specific surface area may result in inaccurate structure–activity correlations.

Journal article

Troncoso L, Alonso JA, Fernandez-Diaz MT, Aguadero Aet al., 2015, Introduction of interstitial oxygen atoms in the layered perovskite LaSrIn1 (-) xBxO4+delta system (B=Zr, Ti), SOLID STATE IONICS, Vol: 282, Pages: 82-87, ISSN: 0167-2738

Journal article

Troncoso L, Alonso JA, Aguadero A, 2015, Low activation energies for interstitial oxygen conduction in the layered perovskites La1+xSr1-xInO4+delta, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 3, Pages: 17797-17803, ISSN: 2050-7488

Journal article

Aguesse F, Lopez del Amo JM, Roddatis V, Aguadero A, Kilner JAet al., 2014, Enhancement of the Grain Boundary Conductivity in Ceramic Li0.34La0.55TiO3 Electrolytes in a Moisture-Free Processing Environment, ADVANCED MATERIALS INTERFACES, Vol: 1, ISSN: 2196-7350

Journal article

Tellez H, Aguadero A, Druce J, Burriel M, Fearn S, Kilner J, McPhail Det al., 2014, New perspectives in the surface analysis of energy materials by combined time-of-flight secondary ion mass spectrometry (ToF-SIMS) and high sensitivity low-energy ion scattering (HS-LEIS), Journal of Analytical Atomic Spectrometry, Vol: 29, Pages: 1361-1370, ISSN: 0267-9477

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and low-energy ion scattering (LEIS) are recently attracting great interest in energy materials research due to their capabilities in terms of surface sensitivity and specificity, spatial resolution and their ability to analyse the isotopic chemical composition. This work shows the synergy provided by this powerful combination to further our understanding of the surface chemistry and structure that ultimately determines the electrochemical performance in advanced electro-ceramic materials for energy storage and energy conversion applications. In particular, this novel approach has been applied to the analysis of (Li3xLa2/3−x□1/3−2x)TiO3 perovskite materials used as the electrolyte in lithium batteries and (La, Sr)2CoO4+δ epitaxial thin films used as oxygen electrodes in solid oxide fuel cells and solid oxide electrolysers. The analysis of these two promising materials requires the development and optimisation of new analytical approaches that take advantage of the recent instrumental developments in order to characterise the outermost and near-surfaces at the atomic scale.

Journal article

Bernuy-Lopez C, Manalastas W, Lopez del Amo JM, Aguadero A, Aguesse F, Kilner JAet al., 2014, Atmosphere controlled processing of ga-substituted garnets for high Li-Ion conductivity ceramics, Chemistry of Materials, Vol: 26, Pages: 3610-3617, ISSN: 0897-4756

Ga-substituted La3Zr2Li7O12 garnet is shown to be a promising Li-ion conducting electrolyte material. The strategy adopted in this study is the substitution of Li by Ga, thereby creating Li vacancies and enhancing the Li conductivity. Solid State Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) measurements have been used to identify the location of the substituted Ga in the structure and its effect on the Li distribution and mobility. In addition MAS NMR was used to follow the effect of protonation due to atmospheric moisture on the sintering behavior of these materials. In particular, it is shown that the Ga atoms are located in tetrahedral positions promoting the random distribution of lithium over the available sites, hence promoting an increase in the conductivity. Control of the sintering conditions by using a dry O2 atmosphere leads to the formation of dense ceramic materials and avoids the degradation process due to the exchange of Li+ by H+ from atmospheric moisture. Electrochemical Impedance Spectroscopy data show total conductivities as high as 1.3 and 2.2 mS cm–1 at 24 and 42 °C, respectively, which are among the highest Li ion conductivities reported for garnet-structured materials to date.

Journal article

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