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In energy systems, multi-generation including co-generation and tri-generation has gained tremendous interest in the recent years as an effective way of waste heat recovery. Solid oxide fuel cells are efficient power plants that not only generate electricity with high energy efficiency but also produce high quality waste heat that can be further used for hot and chilled water production. In this work, we present a concept of combined cooling, heating and power (CCHP) energy system which uses solar power as a primary energy source and utilizes a reversible solid oxide fuel cell (R-SOFC) for producing hydrogen and generating electricity in the electrolyser (SOEC) and fuel cell (SOFC) modes, respectively. The system uses “high temperature” metal hydride (MH) for storage of both hydrogen and heat, as well as “low temperature” MH's for the additional heat management, including hot water supply, residential heating during winter time, or cooling/air conditioning during summer time. The work presents evaluation of energy balances of the system components, as well as heat-and-mass transfer modelling of MH beds in metal hydride hydrogen and heat storage system (MHHS; MgH2), MH hydrogen compressor (MHHC; AB5; A = La + Mm, B Ni + Co + Al + Mn) and MH heat pump (MHHP; AB2; A = Ti + Zr, B Mn + Cr + Ni + Fe). A case study of a 3 kWe R-SOFC is analysed and discussed. The results showed that the energy efficiencies are 69.4 and 72.4% in electrolyser and fuel cell modes, respectively. The round-trip COP's of metal hydride heat management system (MHHC + MHHP) are close to 40% for both heating and cooling outputs. Moreover, the tri-generation leads to an improvement of 36% in round-trip energy efficiency as compared to that of a stand-alone R-SOFC.

A method, based on tape-casting, is developed for the manufacture of ceramic interconnects for SOFCs. The development of an optimized process is shown with a discussion of the effects on the precursor-slurry quality and viscosity of, among other things, the concentrations of ammonia, binder and solid particles. Furthermore the effects of some processing modifications, such as the drying rate in the tape casting machine, the speed of the transport band and the doctor blade height on the quality (density and homogeneity) of the green tapes and the finished product are discussed. Improving the degree of dispersion of the primary particles in the slurry was found to make possible improved densification and quality of the thick plates produced as did reducing the drying rate of the wet tapes during the casting process.

Temperature distribution over a Solid oxide fuel cell (SOFC) surface is a crucial parameter for design of a SOFC stack. The selection of both materials and the operating point of a stack is heavily affected by temperature gradient. Temperature distribution can also be used for control and monitoring purposes. An experimental set-up consisting of a cross flow type stack of six cells was built to measure the temperature distribution in different current densities and in two oven temperatures. Five thermocouples were inserted inside the middle cell to measure temperatures in four corners and in the middle of the cell. Voltage was also measured for different cells using platinum wires. Low fuel utilization (meaning low current density) and high excess air caused maximum temperature at the fuel inlet-air outlet corner. Higher oven temperature caused more uniform temperature distribution, while increasing the current density resulted in higher temperature gradient over the cell surface. This paper provides measurement data and analysis of the results from the test runs.

Electrolyte supports for SOFC applications were obtained by water-based tape-casting. Slurries of commercial 3YSZ and 8YSZ and mixtures with a mass ratio of 25/75 and 75/25, respectively, were prepared. A commercial acrylic polymer binder with dispersive properties was used. The drying conditions for obtaining crack-free green tapes were studied. Crack formation during drying was greatly affected by the carrier speed at a fixed temperature. Thermal analysis was performed on the green tapes to study the binder burn out properties. Weight loss of the green tapes occurred until 400 °C and a pre-heating step was therefore included in the sintering program. The microstructure of the green and sintered tapes were investigated by SEM. Fully densified tapes were obtained after sintering at 1450 °C. The ionic conductivity of pressed pellets were characterized by impedance spectroscopy in the temperature range of 200–1000 °C. Phase and crystal structure of pressed pellets were analyzed by XRD. The crystallinity varied from a majority of monoclinic structure (pure 3YSZ) to a majority of tetragonal structure with increasing the 8YSZ content. A cubic single phase structure was obtained by further increasing the 8YSZ content. It was shown that the ionic conductivity of the composite samples were modified with respect to the pure materials. At high temperatures the pure cubic structure gave rise to high conductivity. At low temperatures the conductivity was affected by the grain boundary resistance which was the lowest for the pure 3YSZ, the highest for the pure 8YSZ and decreased as a function of increasing 8YSZ content.

A dip-coating method was used to obtain 8YSZ thin films formed from nanoparticles on anode support for SOFC applications. 8YSZ nanopowder was obtained via a modified sol–gel method using sucrose and pectin as organic precursors. The nanoparticles were suspended in ethanol using phosphate ester (PE) and polyvinyl butyral (PVB) as dispersant and binder, respectively. The microstructure of the sintered films were analyzed with SEM. The suspension preparation conditions were tuned in order to achieve high initial green density of the 8YSZ films subsequently determining the final sintered microstructure. In addition, the effect of the linear shrinkage of the anode substrate on the 8YSZ film microstructure was studied.

Preparation conditions for obtaining dense 8YSZ electrolyte films by dip-coating on NiO–YSZ anode electrode substrates for SOFC application were investigated with focus on the co-sintering process. The NiO–YSZ substrates were prepared from nanoparticles which were obtained by a single modified sol–gel process using sucrose and pectin as organic precursors. The microstructure and the morphology of the product powders were analyzed by X-ray diffraction and TEM. A thin film of 8YSZ was obtained by a single-step dip-coating process using phosphate ester (PE) as dispersant and polyvinyl butyral (PVB) as binder. The microstructure of the sintered films was analyzed with SEM. The effect of the sinterability of the anode substrate on the 8YSZ film quality was studied. Fully dense electrolyte films were obtained on anode substrates which held a linear shrinkage of ∼23%. The use of substrates with a linear shrinkage below 23%, resulted in a poorly densified 8YSZ microstructure.

In this work 4YSZ nanoparticles were produced with a variant of the sol–gel method, the particles were sintered using two different heating schemes, and the properties of the resulting pellets investigated. XRD spectra show the crystal structure of the particles to be mainly cubic, and TEM pictures reveal their size to be around 20 nm. The relative densities of the sintered pellets are found with the Archimedes method to lie between 87 and 97% of the theoretical material density, and the grain size, using thermal etching and SEM imaging, found to lie between 0.2 and 5 μ m, depending on the sintering temperature and the presence of impurities. The pellets were subjected to electrical impedance spectroscopy making it possible to distinguish the internal crystal and grain boundary impedances due to their different time-constants. With the “brick layer model” the approximate grain boundary thickness was found to lie between 4 and 8 nm, depending on the sintering conditions and on the presence of impurities. The specific resistances of the grain interiors and the grain boundaries, and the activation energies for ion diffusion in both, are presented. The ionic conductivities of the pellets are compared with literature values, and are found to compare favorably with these, at some temperatures even with data for 8YSZ, which is the standard material used for electrolytes due to its higher ionic conductivity, but which is also mechanically weaker than 4YSZ.

Cation tracer diffusion coefficients in La 1− x Sr x FeO 3− δ , ( x = 0 and 0.1) at temperatures ranging from 1173 to 1373 K have been investigated by secondary ion mass spectrometry (SIMS) for both A-site and B-site diffusion applying Y 3+ and Cr 3+ as tracer ions. B-site impurity (represented by Cr) diffusion was found to be faster than A-site impurity (represented by Y) diffusion for LaFeO 3 in the whole temperature interval investigated and for La 0.9 Sr 0.1 FeO 3 at temperatures less than 1273 K. The obtained activation energies for bulk diffusion in La 0.9 Sr 0.1 FeO 3− δ were 168 ± 24 kJ/mol for the Y tracer and 150 ± 30 kJ/mol for the Cr tracer, which are significantly lower than activation energies reported from diffusion couple experiments. The large variation in reported activation energies can be explained in terms of the difference in cation vacancy populations between the two experimental techniques. The diffusion coefficients were also clearly affected by a first order phase transition at approx. 1263 K in pure LaFeO 3. The obtained grain boundary diffusion coefficients were about five order of magnitude higher than the bulk diffusion coefficients, with an activation energy of 128 ± 28 kJ/mol.

The electrical conductivity of polycrystalline LaFeO 3 is reported as a function of temperature. The conductivity of LaFeO 3 was shown to be affected by annealing for extended periods (about one week) at temperatures above 1000 °C prior to the conductivity measurements. Higher annealing temperatures resulted in higher conductivity. This effect was explained by the formation of Schottky cation defects, which act as electron acceptors, leading to an increasing conductivity with increasing annealing temperature. Below 1000 °C, the conductivity was unaffected by the annealing temperature, probably due to the low mobility of cation vacancies. A model for the defect chemistry and conductivity of LaFeO 3 , including the formation of Schottky defects is proposed. The model reproduces quantitatively the dependence of the conductivity with respect to the partial pressure of oxygen at 1000 °C. The electronic mobilities of the charge carriers in the material were determined by the conductivity of La 0.99 Sr 0.01 FeO 3 , where the charge carrier concentration is given by the dopant level. The model also predicts that the concentration of p -type charge carriers in air is increasing with temperature due to the formation of Schottky defects, for a limited temperature interval above 1000 °C.

Heteroepitaxial LaFeO 3 (1 1 0) thin films with a thickness of 150 nm were grown on LaAlO 3 (0 0 1) by reactive sputtering in an inverted cylindrical magnetron geometry. Equilibrium conductivity was measured as a function of partial pressure of oxygen at T =1000 °C, and log σ plotted vs. log P (O 2 ) showed a minimum in conductivity for P (O 2 )=10 −11 atm and a linear response between 10 −10 and 1 atm. This linear response makes thin films of LaFeO 3 a promising material for oxygen sensor applications. We have also measured the time response of the film conductivity upon an abrupt change in the partial pressure of ambient oxygen from 10 −2 to 10 −3 atm, which was determined at 60 s for T =700 °C and T =1000 °C.

Tracer diffusion coefficients in La 1− x Sr x FeO 3 , x =0 and 0.1 from 900 to 1100 °C for both A- and B-site diffusions were examined with secondary ion mass spectrometry (SIMS) applying Y 3+ and Cr 3+ as tracers. In both compositions, the B-site diffusion, represented by Cr, was found to be faster than the A-site diffusion, represented by Y. The obtained activation energies for bulk diffusion in La 0.9 Sr 0.1 FeO 3 were 168±24 kJ/mol for the Y tracer and 150±30 kJ/mol for the Cr tracer. The 18 O-tracer diffusion coefficients were found to be significantly higher in La 0.9 Sr 0.1 FeO 3 compared with LaFeO 3 .