Reversible, all-perovskite SOFCs based on La, Sr gallates

In this contribution, a reversible Solid Oxide Cell based on perovskites was developed. La0.6Sr0.4Ga0.3Fe0.7O3 (LSGF) was chosen as electrode and deposited onto La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte. The cell was investigated from the morphological (SEM) and compatibility (XRD) point of view. Electrochemical investigation confirmed that the cell can operate in fuel cell and in electrolyser modes. Impregnation with CGO and Pd allowed a 15 times increment of the power density (until limit is the cell architecture). The same cell with an impregnated negative electrode was then tested in steam electrolysis mode in a non-reducing environment. The overall performance is slightly lower than state-of-the-art materials and comparable with similar perovskites, and in general is fair considering the needed cell optimization (i.e an anode supported configuration is necessary). The cell (impregnated and not) activates at 0.7 V. Obtained data suggest thus LSGF/LSGM/LSGF cell, is promising as reversible SOC for intermediate temperature.PostprintPeer reviewe

Aqueous thick-film ceramic processing of planar solid oxide fuel cells using La0.20Sr0.25Ca0.45TiO3 anode supports

HEXIS AG and the EPSRC projects: EP/L017008/1 “Capital for Great Technologies”; EP/ P024807/1 “Hydrogen and Fuel Cells Hub” for funding.Recent research into the upscaling and implementation of Rh/Ce0.80Gd0.20O1.90 co-impregnated La0.20Sr0.25Ca0.45TiO3 (LSCTA-) anodes in electrolyte-supported SOFC at short-stack industrial scales has resulted in extremely robust performance under realistic operation and tolerance to harsh conditions. Furthermore, evaluation of the mechanical strength of LSCTA- and incorporation of this material into anode-supported SOFC also yielded promising performance at the button cell scale (using Ni and CeO2 catalyst impregnates). The knowledge on ceramic processing obtained during these previous research campaigns may be used to develop anode-supported SOFC with LSCTA- 'backbones' that have been optimised for high mechanical strength, high 'effective' electronic conductivity and sufficient porosity. Therefore, this manuscript details the preparation of anode-supported SOFC using the thick-film ceramic processing technique of aqueous tape casting, the optimisation of anode microstructure through addition of aqueous solvent-compatible graphitic and methacrylate polymer pore formers and the co-sintering of a LSCTA- support with a typical SOFC electrolyte material.PostprintPeer reviewe

Protons in lattice confinement: Static pressure on the Y-substituted, hydrated BaZrO3 ceramic proton conductor decreases proton mobility

Yttrium substituted BaZrO3, with nominal composition BaZr0.9Y0.1O3, a ceramic proton conductor, was subject to impedance spectroscopy for temperatures 300 K < T < 715 K at mechanical pressures 1 GPa < p < 2 GPa. The activation energies Ea of bulk and grain boundary conductivity from two perovskites synthesized by solid-state reaction and sol-gel method were determined under high pressures. At high temperature, the bulk activation energy increases with pressure by 5% for sol-gel derived sample and by 40% for solid-state derived sample. For the sample prepared by solid-state reaction, there is a large gap of 0.17 eV between the activation energy at 1.0 GPa and > 1.2 GPa. The grain boundary activation energy is around a factor two times as that of the bulk, and it reaches a maximum at 1.25 - 1.5 GPa, and then decrease as the pressure increases, indicating higher proton mobility in the grain boundaries at higher pressure. Since this effect is not reversible, it is suggested that the grain boundary resistance decreases as a result of pressure induced sintering. The steady increase of the bulk resistivity upon pressurizing suggests that the proton mobility depends on the space available in the lattice. In return, an expanded lattice with a/a0 > 1 should thus have a lower activation energy, suggesting that thin films expansive tensile strain could have a larger proton conductivity with desirable properties for applications

Ce(Mn,Fe)O2 –(La,Sr)(Fe,Mn)O3 composite as an active cathode for electrochemical reduction of CO2 in proton conducting solid oxide cells

We thank EPSRC (EP/I022570/1, EP/K015540/1, EP/I038950/1) and the Royal Society (Wolfson Research Merit award) for support.A solid oxide electrolysis cell concept for reducing CO2 to CO was studied using a proton conducting mixed oxide- BaCe0.7Zr0.1Y0.1Yb0.06Zn0.04O3-δ (BCZYYZ) as an electrolyte. The oxide composite mixture: Ce0.6Mn0.3Fe0.1O2 – La0.6Sr0.4Fe0.9Mn0.1O3 (12.5-87.5 wt%) was examined as enhancing catalyst electrode for CO2 reduction and proton oxidation reaction on the cathode side for avoiding coke formation. Here we demonstrate the successful electrochemical reduction of CO2 in proton conducting SOECs. During electrochemical reduction of CO2 at 700oC, current densities as high as 0.5 A/cm2 and 1 A/cm2 at 1.3 V and 2.2 V respectively, were withdrawn even though the cell employed a 400 μm thick BCZYYZ electrolyte support.Publisher PDFPeer reviewe

The exsolution of Cu particles from doped barium cerate zirconate via barium cuprate intermediate phases

This research was supported by EPSRC research grants EP/R023522/1, EP/T019298/1, EP/R023751/1, EP/L017008/1 the China Scholarship Commission (MW) received financial support from the UK Catalysis Hub funded by EPSRC Grant reference EP/R027129/1.As a low-cost alternative to noble metals, Cu plays an important role in industrial catalysis, such as water-gas shift reaction, methanol or ethanol oxidation, hydrogenation of oils, CO oxidation, among many others. An important step in optimizing Cu catalyst performance is control of nanoparticles size, distribution, and the interface with the support. While proton conducting perovskites can enhance the metal catalytic activity when acting as the support, there has been limited investigation of in situ growth of Cu metal nanoparticles from the proton conductors and its catalytic performance. Here, Cu nanoparticles are tracked exsolved from an A-site-deficient proton-conducting barium cerate-zirconate using scanning electron microscopy, revealing a continuous phase change during exsolution as a function of reduction temperature. Combined with the phase diagram and cell parameter change during reduction, a new exsolution mechanism is proposed for the first time which provides insight into tailoring metal particles interfaces at proton conducting oxide surfaces. Furthermore, the catalytic behavior in the CO oxidation reaction is explored and, it is observed that these new nanostructures can rival state of the art catalysts over long term operation.Publisher PDFPeer reviewe

Novel layered perovskite SmBaMn2O5+δ for SOFCs anode material

The authors Abdalla M. Abdalla and Shahzad Hossain are thankful to the Graduate Research Office of Universiti Brunei Darussalam for Graduate Research Scholarship (GRS) for funding this research work done.SmBaMn2O5+δ (SBMO), a novel layered perovskite compound with samarium based material (Sm+3) as rare earth doped in A-site was synthesized and processed by using dry chemistry method (solid state solution). Structural characterization of SBMO has been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). While, thermal and electrochemical testing were done by using thermogravimetric analysis (TGA) and current voltage measurements. The Rietveld analysis of XRD data shows that SBMO was crystallized in the orthorhombic structure with the Pmmm space group. The surface morphology images showed a porous structure which indicates that this material can be used as a potential electrode in solid oxide fuel cells (SOFCs). TGA result showed the mass loss of 0.022% for SmBaMn2O5+δ which is very small and indicates that the material is very stable. DC conductivity and performance test were done at RT in air atmosphere. The performance tests have done at 800 °C and 750 °C and the maximum power density was found to be 0.4 W/cm2 at 800 °C.PostprintPeer reviewe

Homo simpliciter or imago Dei. From the regional bio-psycho-social concentricity to eccentric-theological integrity of the human being

Polazeći od kršćansko-teološke kategorije slike Božje, koju autor naziva antropološko-ekscentričnom jer se čovjek kao osoba može razumjeti i izvan granica puke pojavnosti svojega »ja«, dakle u Bogu kao »ne-ja«, čineći upravo stabilnim i cjelovitim taj isti ljudski »ja«, želi se i kritički osvrnuti na psihologijske i sociologijske pozitivističko-redukcionističke slike čovjeka koje uporište njegova definiranja utemeljuju na pojedinim strukturno-naravnim stratumima ili društvenim funkcijama čovjeka, nazivajući naprotiv takav parcijalni pristup antropološko koncentričnim. Dok se s konceptom imago Dei želi naglasiti ono cjelovito, bazično i teologalno u čovjeku, s homo simpliciter želi se samo znanstveno-metodski zahvatiti čovjek kao takav u svojoj pukoj pojavnoj bio-psiho-socijalnoj koncentričnosti i segmentiranosti sebe. U prva dva poglavlja u najosnovnijim crtama izlaže se kršćansko-antropološko određenje kategorijâ slike Božje i osobe, a u nastavku članka autor se kritički osvrće na načine kako se »znanstveno kreira« slika o čovjeku u psihologijskom i sociologijskom smislu. U zadnjem poglavlju autor se pita kako se to čovjek može realistično i optimalno personalizirati i socijalizirati na osnovi prethodno konstatiranih »znanstvenih slikâ« o njemu, ako ga se shvaća samo kao homo simpliciter.Starting with the Christian-theological category of the imago Dei, called anthropological-eccentric by the author, because the human being as a person can understand something also outside of boundaries of mere manifestation of his/her »I«, hence in God as »non-I«, which makes the human »I« stabile and integral. The author also wants to critically reflect on psychological and sociological positivistic-reductionist images of the human being, whose basis for defining the human being is found in certain structural-natural stratums or social functions of the human being, while calling such partial approach anthropologically concentric. While the concept of imago Dei emphasises what is integral, fundamental, and theological in the human being, the concept of homo simpliciter understands the human being in a scientific-methodological way in his/her mere manifested, bio-psycho-social concentricity and segmentation of himself/herself. The first two chapters present the Christian-anthropological determination of the categories of the image of God and person in the most basic way, while in the continuation of the article the author reflects critically on ways in which the image of the human being is »scientifically created« in the psychological and sociological sense. In the last chapter the author poses the question of how the human being could be personalised realistically and optimally, and socialised on the basis of aforementioned »scientific images« of him/her, if he/she is understood only as homo simpliciter

High oxide ion and proton conductivity in a disordered hexagonal perovskite

This research was supported by the Leverhulme trust and EPSRC (MISE). We also acknowledge STFC-GB for provision of beamtime at the ILL.Peer reviewedPostprintPostprin

Use of interplay between A-site non-stoichiometry and hydroxide doping to deliver novel proton-conducting perovskite oxides

Funding: UK Engineering and Physical Sciences Research Council (Grant Number(s): EP/R023522, EP/R023751, EP/L017008, EP/P007821, EP/L000202, EP/R029431); Diamond Light Source (Grant Number(s): SP17198-8); Rutherford Appleton Laboratory (Grant Number(s): RB1920629).The magnitude of ionic conductivity is known to depend upon both mobility and number of available carriers. For proton conductors, hydration is a key factor in determining the charge–carrier concentration in ABO3 perovskite oxides. Despite the high reported proton mobility of calcium titanate (CaTiO3), this titanate perovskite has thus far been regarded as a poor proton conductor due to the low hydration capability. Here, the enhanced proton conductivity of the defective calcium titanate Ca0.92TiO2.84(OH)0.16 prepared by replacing lattice oxygens with hydroxyl groups via a solvothermal route is shown. Conductivity measurements in a humidified Ar atmosphere reveal that, remarkably, this material exhibits one order of magnitude higher bulk conductivity (10−4 Scm−1 at 200 °C) than hydrated stoichiometric CaTiO3 prepared by traditional solid-state synthesis due to the higher concentration of protonic defects and variation in the crystal structure. The replacement of Ca2+ by Ni2+ in the Ca1−xTi1O3−2x(OH)2x, which mostly exsolve metallic Ni nanoparticles along orthorhombic (100) planes upon reduction, is also demonstrated. These results suggest a new strategy by tailoring the defect chemistry via hydration or cation doping followed by exsolution for targeted energy applications.Publisher PDFPeer reviewe

Highly dense and novel proton conducting materials for SOFC electrolyte

S. Hossain and A. M. Abdalla are thankful to graduate studies office of Universiti Brunei Darussalam for graduate research scholarship (GRS) for this research work done. Authors are also grateful to Professor John T. S. Irvine for managing a visiting scholarship for SH and AMA to perform the research work at University of St Andrews, Scotland, UK.Highly dense proton conducting materials of BCZYSZn (BaCe0.8-xZrxY0.15Sm0.05O3-δ (x = 0.15, 0.20) with 4 wt.% ZnO as sintering additive), to be used as an intermediate temperature solid oxide fuel cells (IT-SOFCs) electrolyte, have been processed by the conventional solid state reaction method. The crystalline phase, microstructure, electrical properties, cell performance and chemical stability of the materials have been investigated. The ionic conductivity of BCZYSZn 3 (x = 0.20) material has been measured to be ~2.56 × 10-3 S cm−1 and ~8.32 × 10-3 S cm−1 at 600 °C and 850 °C, respectively in wet 5%H2 in Ar atmosphere. Microstructural characterizations of the zinc containing materials (BCZYSZn) show the formation of highly dense morphology with very large grains. The chemical stability test of BCZYSZn in pure CO2 shows that the material is very stable up to 1000 °C. The maximum power density for the BCZYSZn 3 electrolyte cell is found to be 0.42 W/cm2 at 700 °C under the testing atmosphere. The performed characterizations reveal that these are suitable proton-conducting candidate materials for efficient electrochemical devices.PostprintPeer reviewe