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Our SOFC stack development technology is based on the unique SOFConnexTM concept, using flexible gas distribution layers between metal sheet interconnect and thin ASE cells. Flexibility is given both in material and design. This ensures proper electrical contact over the whole cell (50 cm2 active), without necessitating restrictive cell fabrication tolerances, and allows easy adaptation and evolution of the flowfields. With the presently used configuration, several multiple cell stacks were assembled and tested. Reproducible stack power density (H2 fuel, λ = 1.5-2, 800°C maximum local temperature) is 0.5 W/cm2 at 0.7 V average cell voltage (1.5 kWe/L), for 67% fuel utilisation (35% LHV electrical efficiency). Performance with simulated POX-syngas (H2/CO/N2) was close to that with H2. Degradation is the focus of attention now that adequate power density and efficiency using the SOFConnex™ approach have been established and reproduced.

The Laboratory for Applied Mechanical Design (LAMD) designed, manufactured, and experimentally tested a novel steam-driven anode off-gas recirculation (AOR) fan for 10 kWel solid oxide fuel cell (SOFC) systems. Due to the dynamic steam-lubricated bearings, the AOR unit is expected to have a high lifetime, even at elevated rotational speeds and temperatures. Additional, the unit is oil-free, explosion-proof, very compact, and cheap to manufacture. The AOR fan diameter is at 19.2 mm and the nominal rotational speed is 175 krpm. The unit was coupled to a 6 kWel SOFC system, reaching electrical gross DC efficiencies, based on the fuel LHV, of 66 % in part load (4.5 kWel gross DC) and 61 % in full load (6.3 kWel) for a global fuel utilization of 85 %. To the best of the authors' knowledge, this was the first time that a steam-driven AOR fan was demonstrated in-situ with an SOFC system.

Internal steam reforming (IR) of methane was investigated on Ni-YSZ anode supported cells, looking in particular at the effect of the steam to carbon (S/C) ratio on the degradation rate. The cells were fed with different H2O/CH4 mixtures during 100 hours sequences, alternating with sequences of dry H2 feeding. V-I characterization was performed before and after each sequence, and EIS measurements were performed regularly. A marked degradation was observed during the IR sequences while it was negligible under dry H2 feed. The observed degradation, attributed to carbon deposition on the anode active sites, was partially reversible for S/C >1.5, whereas it became irreversible at lower S/C.

Our planar SOFC stacking technology uses unprofiled metallic interconnects (MIC) and thin cells of tape cast anode supported YSZ. The key element is the gas diffusion layer (GDL) between cell and MIC, which consists of so-called SOFConnex™. Using square cells with internal manifolds, 0.5 W/cm2 stack power density (800°C) can be obtained on short stacks. However, this open design configuration limits the assembly of large stacks and the durability of operation, owing to postcombustion and redox cycling occurring at unprotected cell edges. A new design, inspired from modeling work and the adaptability of the SOFConnex™ GDL, led to oblong-shaped cells, assembled in a closed stack casing with external air manifolding and fuel recovery manifolding, avoiding postcombustion. While stack power density in both designs remains similar, the operation at increased fuel utilization has become more stable in the 2nd design. Furthermore, a correlation of performance homogeneity during stack testing was drawn to assembly quality control. A 36-cell stack in dilute H2 at 800°C achieved 625 Wel (28% LHV efficiency, 0.35 W/cm2) under continuous polarisation, with all 6 clusters of 6 cells showing coincident i-V-output.

Electrochemical Impedance Spectroscopy (EIS) is extensively used to characterize Solid Oxide Cells (SOCs) to extract information on the elementary loss mechanisms. However, these individual mechanisms usually overlap in the frequency domain, requiring dedicated data processing for unambiguous identification. A powerful method for discriminating process contributions is the analysis by the Distribution of Relaxation Times (DRT). The de-convoluted spectrum of SOC generally presents, six peaks from mHz to hundreds of kHz. DRT peak-to-process attribution is often obtained by experimental sensitivity analysis. In the study, six parameters have been systematically varied: temperature, current density, partial pressure of O2 at the oxygen electrode, partial pressure of steam at the fuel electrode, total flow rates and fuel composition. The effect of wires inductance and different cell geometries has also been analyzed. The study provides detailed information about the contribution of the elementary processes to the total losses over a wide range of operation regimes. It further refines peak-to-process attributions by using a dynamic numerical model that includes gas and solid phase transport coupled with charge transfer and chemical reactions. Moreover, the non-univocal literature attribution of processes in the middle frequency range is clarified: strongly overlapping peaks cannot be separated even by DRT.