Calcium manganite as oxygen electrode materials for reversible solid oxide fuel cell

The authors thank EPSRC for funding under the contract of H2FC hub EPSRC: EP/J016454/1 and Platform EPSRC: EP/K006800/1 and JTSI thanks Wolfson Merit of Royal Society: WRMA 2012/R2For an efficient high-temperature reversible solid oxide fuel cell (RSOFC), the oxygen electrode should be highly active for the conversion between oxygen anions and oxygen gas. CaMnO3-δ(CM) is a perovskite that can be readily reduced with the formation of Mn3+ giving rise to oxygen defective phases. CM is examined here as the oxygen electrode for a RSOFC. CaMn0.9Nb0.1O3-δ (CMN) with Nb doping shows superior electric conductivity (125 S cm-1 at 700 ºC) to CM (1-5 S cm-1 at 700 ºC) in air and is also examined for comparison. X-ray diffraction (XRD) data show that CM and CMN are compatible with the widely used yttria-stabilized zirconia (YSZ) electrolyte up to 950 oC. Both materials show a thermal expansion coefficient (TEC) close to 10.8-10.9 ppm K-1 in the temperature range between 100-750 ºC, compatible with that of YSZ. Polarization curves and electrochemical impedance spectra for both fuel cell and steam electrolysis modes were investigated at 700 ºC, showing that CM presented a polarization resistance of 0.059 Ωcm2 under a cathodic bias of -0.4 V while CMN gave a polarization resistance of 0.081 Ω cm2 under an anodic bias of 0.4 V. The phase stability up to 900 ºC of these materials was investigated with thermogravimetric analysis (TGA) and variable temperature XRD.Publisher PDFPeer reviewe

Gasification of glycerol over Ni/γ-Al2O3 for hydrogen production : tailoring catalytic properties to control deactivation

Authors thank the Petroleum Technology Development Fund (PTDF), Nigeria for funding this research and the University of St Andrews, Scotland UK for the consideration to work with them and to use their facilities.The effects of catalyst loading, calcination and reaction temperatures on the structural properties and catalytic behavior of Ni/γ-Al2O3 catalyst system in relation to steam reforming of glycerol and catalyst deactivation were investigated. The results showed that catalyst loading, reaction and calcination temperatures had a profound influence on the structure and catalytic activity in glycerol conversion. Use of high calcination temperature (900-1000 °C) led to phase transformation of the active Ni/Al2O3 to less active spinel specie NiAl2O4 that resulted in a successive change of texture and color. The particle size growth and phase change at this temperature were responsible for the catalyst deactivation and low performance especially among the catalyst calcined at high temperatures. Conversely, at low reaction temperatures, catalyst surfaces were marred by carbon deposition. Whilethe polymeric carbon deposited at metal-support interface was associated with low reaction temperatures, high reaction temperatures were characterized predominantly by both amorphous carbon deposited on the active metal surface and polymeric or graphitic carbon deposited at metal-support interface respectively. Calcination temperature showed no significant influence on the location and type of coke deposited on the catalyst surface. Hence, catalyst loading, calcination and reaction temperatures could be tailored to enhance structural and catalytic properties and guard against catalyst deactivation.Publisher PDFPeer reviewe

Alkaline modified A-site deficient perovskite catalyst surface with exsolved nanoparticles and functionality in biomass valorisation

The authors would like to thank the Petroleum Technology Development Fund (Nigeria) for funding this research and University of St Andrews (Scotland, UK) for the opportunity to carry out the research.Environmental problems associated with the use of fossil fuels and increase in energy demands due to rise in population and rapid industrialisation, are the driving forces for energy. Catalytic conversion of biomass to renewable energies is among the promising approaches to materialize the above. This requires development of robust catalysts to suppress deactivation due to carbon deposition and agglomeration. In this work, surface properties and chemistry such as exsolution of B-site metal catalyst nanoparticles, particle size and distribution, as well as catalyst-support interactions were tailored through the use of alkaline dopants to enhance catalytic behaviour in valorisation of glycerol. The incorporation of alkaline metals into the lattice of an A-site deficient perovskite modified the surface basic properties and morphology with a consequent robust catalyst-support interaction. This resulted in promising catalytic behaviour of the materials where hydrogen selectivity of over 30% and CO selectivity of over 60% were observed. The catalyst ability to reduce fouling of the catalyst surface as a result of carbon deposition during operation was also profound due to the robust catalyst-support interaction occurring at the exsolved nanoparticles due to their socketing and the synergy between the dopant metals in the alloy in perovskite catalyst systems. In particular, one of the designed systems, La0.4Sr0.2Ca0.3Ni0.1Ti0.9O3±δ, displayed almost 100% resistance to carbon deposition. Therefore, lattice rearrangement using exsolution and choice of suitable dopant could be tailored to improve catalytic performance.Publisher PDFPeer reviewe

Demonstration of high performance in a perovskite oxide supported solid oxide fuel cell based on La and Ca co-doped SrTiO3

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n° 256730 and Energy Technology Partnership (ETP).Perovskite electrodes have been considered as an alternative to Ni-YSZ cermet-based anodes as they afford better tolerance towards coking and impurities and due to redox stability can allow very high levels of fuel utilisation. Unfortunately performance levels have rarely been sufficient, especially for a second generation anode supported concept. A-site deficient lanthanum and calcium co-doped SrTiO3, La0.2Sr0.25Ca0.45TiO3 (LSCTA-) shows promising thermal, mechanical and electrical properties and has been investigated in this study as a potential anode support material for SOFCs. Flat multilayer ceramics cells were fabricated by aqueous tape casting and co-sintering, comprising a 450 μm thick porous LSCTA- scaffold support, a dense YSZ electrolyte and a thin layer of La0.8Sr0.2CoO3-δ (LSC)-La0.8Sr0.2FeO3-δ (LSF)-YSZ cathode. Impregnation of a small content of Ni significantly enhanced fuel cell performance over naked LSCTA-. Use of ceria as a co-catalyst was found to improve the microstructure and stability of impregnated Ni and this in combination with the catalytic enhancement from ceria significantly improved performance over Ni impregnation alone. With addition of CeO2 and Ni to a titanate scaffold anode that had been pre-reduced at 1000 oC, a maximum powder density of 0.96 W cm-2 can be achieved at 800 oC using humidified hydrogen as fuel. The encouraging results show that an oxide anode material, LSCTA- can be used as anode support with YSZ electrolyte heralding a new option for SOFC development.PostprintPeer reviewe

High-performance and durable alcohol-fueled symmetrical solid oxide fuel cell based on ferrite perovskite electrode

This work is supported by the NSFC (grant No. 51702264; 41371275) and National Key Research and Development Program of China (grant No. 2018FYD0200701) and research funding for central universities (XDJK2020B066). C.N. also thanks to the award of Chongqing Bayu Young Scholar from Chongqing Teaching Committee and Funding for Oversea Returnees, while J.N. thanks to the support from Chongqing Yingcai Talent.A solid oxide fuel cell utilizing bio-fuels such as methanol and ethanol could provide a carbon–neutral electricity generation and facilitate its applications in transport or stationary power unit. Herein, Ce4+ doping in SrFe0.95Ni0.05O3 imparts FeNi3 exsolution and CeO2 precipitation in a reducing condition, contributing to the fuel reforming, C-C bond cleavage and coke consumption in the anode chamber. The ferrite perovskites are stable in ethanol/steam at 800 °C, whereas they are unstable in ethanol vapor with the high C fugacity inducing the formation of Fe0 and carbides. However, the Ce0.2Sr0.8Fe0.95Ni0.05O3 anode maintains mostly the perovskite and is free from coke after the 300 h’ operation under C2H5OH fuel at 0.5 V or 0.7 V because of the dynamic balance between the carbon deposition and consumption since an operation for 10 h shows a clear carbon deposition. A maximum power density of 0.58 W cm−2 and a polarization resistance of 0.21 Ω cm2 at 800 °C can be obtained for the symmetrical solid oxide fuel cell with identical Ce0.2Sr0.8Fe0.95Ni0.05O3 cathode and anode under an ethanol fuel. The results demonstrate that the reversible and stable SrFeO3 with Ce/Ni co-doping has a bright prospect for alcohol fuel oxidation.PostprintPostprintPeer reviewe

Evaluating sulfur-tolerance of metal/Ce0.80Gd0.20O1.90 co-impregnated La0.20Sr0.25Ca0.45TiO3 anodes for solid oxide fuel cells

The authors acknowledge funding from the University of St Andrews, HEXIS AG and the EPSRC Grants: EP/M014304/1 “Tailoring of Microstructural Evolution in Impregnated SOFC Electrodes” and EP/L017008/1 “Capital for Great Technologies”.The Ni-based cermet Solid Oxide Fuel Cell (SOFC) anode is prone to poisoning by sulfur-based odourising agents, and naturally occurring sulfur species, present in unprocessed natural gas feeds. Next generation SOFC anodes should be able to withstand exposure to these poisons in the event of a malfunction or breakdown of desulfurisation units. Here, we present results pertaining to the sulfur-tolerance of Ni/Ce0.80Gd0.20O1.90 (CGO), Pt/CGO and Rh/CGO co-impregnated La0.20Sr0.25Ca0.45TiO3 anode ‘backbone’ microstructures and their ability to recover performance after being exposed to H2S. The Ni/CGO co-impregnated system exhibited severe poisoning by H2S, however, the Rh/CGO system displayed good stability in Area Specific Resistance (ASR) upon introduction of 1–2 ppm of H2S and the Pt/CGO system showed minimal increases in ASR with the addition of 1–8 ppm H2S. Recovery measurements performed in non-humidified H2 at 300 mA cm−2, after exposure to 8 ppm H2S, indicated that the Pt/CGO and Rh/CGO systems could recover within 10 min, whilst 60 min were required to achieve almost a full recovery of performance for the Ni/CGO system. Additionally, all three impregnate systems showed good stability in operating voltage, after an initial drop, in a fuel gas containing simulated syngas (2:1 H2:CO) with 8 ppm H2S.PostprintPeer reviewe

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

Investigation of tin liquid anode on hybrid direct carbon fuel cells

A novel carbon fuel cell mode was designed for improving the cell performance on hybrid direct carbon fuel cells (HDCFCs). In this paper, the effects of Sn phase as the liquid anode on HDCFCs' performance was investigated. The comparative results indicated that the cell performance was strongly dependent on the amount of Sn loading. With selectivity of different weight ratios, 20 wt% Sn additive was optimized to be the best behavior, corresponding to considerably decreased ohmic and polarization resistance. However, other compositions showed inferior performance than that of Sn-free anode, probably due to the Li2SnO3 impurity formation impeding catalytic properties of liquid Sn and Li-K salt. Stability testing further implied the cell with 20 wt% Sn addition was the best choice because of maximum fuel efficiency and reasonable durability. Based on these results, the possible completing mechanisms of Sn participating in electrochemical reaction on HDCFCs were proposed.Postprin

Mixing regime simulation and cellulose particle tracing in a stacked frame photocatalytic reactor.

To sustainably meet the global energy demand, unconventional methods to produce renewable energy must emerge. Biofuels from cellulose (via fermentable sugar production) mediated via photocatalysis provides an alternative to conventional fossil fuels. In order to effectively drive photocatalytic processes an effective reactor design is required, the design of which is influenced by a number of key factors such as the catalyst to reactant ratio and residence time, catalyst illumination time, light penetration and distribution for the system, mass transfer limitations (mixing) and product recovery. In this study we use COMSOL Multiphysics® to simulate and assess one of the mentioned parameters – mixing regime of cellulose particles in a Stacked Frame Photocatalysis Reactor (SFPR). In the reactor design, we compare two mixers: a ‘plus’ shaped magnetic stirrer bar and an 8 blade Rushton impeller. The simulations reveal that the Rushton impeller offers a radial mixing pattern with a higher fluid velocity of 1.2m/s when compared to the stirrer bar that offers a fluid velocity of 0.9m/s. Cellulose particle tracing simulations confirm that the particle dispersion is superior in the case of the Rushton impeller as the vorticity generated during the mixing push the particles to the reactor's walls. Since the particles are forced towards the walls, there is a probability of more particles being illuminated than in the case of no or improper mixing

Synthesis and electrochemical characterization of La0.75Sr0.25Mn0.5Cr0.5‐xAlxO3, for IT- and HT- SOFCs

The authors, A M Abdalla and S Hossain, are grateful to Suez Canal University and Universiti Brunei Darussalam and their collaborative for supporting this research work.The main emphasis of this work is to create a new perovskite material with three different compositions (La0.75Sr0.25Mn0.5Cr0.5‐xAlxO3, x = 0.1, 0.2, 0.3) applied in both Intermediate and high Temperature ‐ Solid Oxide Fuel Cells (IT & HT‐SOFCs). Perovskite‐type polycrystalline La0.75Sr0.25Mn0.5Cr0.5‐xAlxO3‐δ (x = 0.1, 0.2, 0.3) powders were synthesized and formed in a single phase structure by a dry chemistry route (standard solid‐state reaction method). The effect of Al‐doping on physicochemical and surface properties has been discovered. The compounds were crystallized in single phase rhombohedral symmetry (R‐3C Space. Group). Total conductivity of Al‐doping in wet 5% H2 was higher than both dry 5% H2 and air. The obtained results enhance the electro‐catalytic performance and the material conductivity as well, which will be good for anode materials in IT‐ HT‐SOFCs and the optimum doping is 10%.PostprintPeer reviewe