Laboratoire d'Évaluation des Matériels Implantables

Long term durability was demonstrated on high-performance direct ethanol solid oxide fuel cell operating in gradual internal reforming. Anode supported single cells, fabricated at Forschungszentrum Jülich, composed of (La,Sr)MnO3 cathode, 8 mol% yttria-stabilized zirconia (YSZ) electrolyte, and YSZ-Ni anode were used for long term testing on anhydrous (direct) ethanol. Gadolinia-doped ceria (CGO), with 0.1 wt.% of Ir, catalyst was produced by the impregnation of Ir salt in commercial CGO (Praxair) and mixed with organic additives. The CGO-Ir suspension was deposited onto the surface of the YSZ-Ni anode support with an air brush. Such a catalytic layer acts both as a physical barrier to avoid direct contact of the fuel with Ni-based anode and to promote the gradual internal reforming of ethanol. The CGO-Ir catalyst was designed for the reforming of the main compounds resulting from the thermal decomposition of ethanol at high temperature and to inhibit the formation of ethylene, which is a known source of carbon deposits. After deposition the sample was heated at 850ºC in inert atmosphere to ensure good adhesion between the catalytic layer and the anode. Gold grid and paint were used as current collectors in both cathode and anode sides. The single fuel cells were mounted in the test apparatus, sealed with gold rings and alumina cement and heated to the measuring temperature (850°C) under inert atmosphere. After gas tightness was checked by flowing air on the cathode side and argon on the anode side, the anode was reduced under hydrogen. The fuel cell was kept at 0.6 V while monitoring the current drained from the cell at 850 °C. Samples were initially operated in hydrogen for a few hours and fuel was switched to dry ethanol, carried by nitrogen. It is important to mention that no oxidizing agent was added to the fuel and that water produced by the electrochemical reaction of hydrogen at the anode promoted the reforming of the ethanol in the CGO-based layer, in the so-called gradual internal reforming. In such conditions the current output was recorded and observed to not be significantly different form that under hydrogen. Moreover, the direct ethanol fuel cell was continuously operated for 650 hours without major losses due to carbon formation. The experimental results demonstrate that the water released by the electrochemical oxidation of reformate hydrogen at the electrolyte/anode active interfaces is sufficient for the reforming of the primary fuel in the catalytic layer, provided that a minimum fuel utilization is respected. After the durability tests, energy dispersive X-ray spectroscopy and scanning electron microscopy analyses of the samples revealed no carbon deposit formation in the anode. The experimental results provided compelling evidence for the viability of gradual internal reforming of ethanol in high performance solid oxide fuel cells.

Among energy conversion systems, high temperature Fuel Cells are considered of great interest for delocalized, renewable and clean electricity and heat power production. The high operating temperature (500°C - 800°C) is likely to allow the use of various types of hydrocarbons instead of hydrogen as the fuel with high efficiency and flexibility. Theoretically, the fuel can be catalytically converted into hydrogen directly at the anodic side. Practically, the most important drawback is the formation of carbon deposits on the anode, poisoning the electrocatalytic activity of the electrode. Hence, one of the main current challenges remains the increase of the life-time of these systems (especially avoiding carbon deposition and anode pollution), and long term reliable operation with fuel flexibility. Such performances have not been achieved yet. We recently demonstrated the fundamental importance of the fuel utilization on the carbon deposition limits. The quantity of steam released by the anode is directly proportional to the current density, and then to the fuel utilization UF. Below a given value of UF, the system does not produce enough steam to ensure the internal catalytic conversion of the hydrocarbon flux, resulting in irreversible degradation of the cell by carbon methane cracking. This observation and the deep understanding of the anode operation in methane allowed us to achieve long term operation with pure hydrocarbons without carbon deposition at the surface of conventional Ni-YSZ anodes. The thermodynamical limits of carbon deposition as a function of fuel utilization were also investigated. Current developments and technological simplifications based on new principles of operation and original architectures designed in this finality will be presented. In particular the presentation will emphasize on the Gradual Internal Reforming and Electro-catalytic separation principles applied to the design of original anodic systems, and on the demonstration of the reliability of the systems in different pure hydrocarbons or carbon-based fuels (no H2O, CO2, O2 or carrier gas addition) [1-4]. The effect of the fuel utilization on the limits of carbon deposition will be discussed and the long term durability in pure dry methane will be demonstrated. The perspectives of direct operation of SOFC on waste fuels in order to decrease the amount of CO2 rejects in delocalized energy production systems will be discussed. 1. J-M. Klein et al., Journal of Power Sources 193, (2009) 331 2. S. D. Nobrega et al., Journal of Power Sources (2012) 156-159 4. S. Georges et al., ECS Transactions 57(1) (2013) 3023-3030 4. S.D. Nobrega et al., Journal of the Electrochemical Society, 161(3) (2014) F354-F359 5. J. Puig et al., Fuel Cells 14 (6) (2014) 1014-1021 6. K. Girona et al., Canadian Journal of Chemical Engineering 93 (2) (2015) 285-296

An anode-supported solid oxide fuel cell (SOFC) was continuously operated with direct (anhydrous) ethanol for ~600 hours, with a high current density. The operation of the SOFC under ethanol was made possible with the deposition of a ceria-based catalytic layer onto the cermet anode support, which efficiently converts the primary fuel in hydrogen. The catalytic layer associated with the gradual internal reforming (GIR) process avoids carbon deposition on the Ni surface. The results provide a significant advance towards the development of direct ethanol solid oxide fuel cells.

The evaluation of a potential biomaterial is based on two approaches: firstly, the study of the local and systemic effects of the biomaterial implanted in the host; and secondly the study of the behaviour of the biomaterial itself with increasing time. The progress achieved in human cell culturing allows in vitro evaluation of a new biomaterial using the human cell(s) system(s) characteristic of the tissue which it will be exposed to in vivo. This kind of approach permits the assessment of the biodegradation of a biomaterial whatever it is: metal; alloy; ceramic; glass; polymer; with or without specialized coating.... The experimental approach is as follows: discs representative of the biomaterial (surface state, cleaning, sterilization process) are manufactured in order to cover the bottom of the culture wells. Thereafter, they are either brought in the presence of complete culture medium alone, or in the presence of a subconfluent cell layer. A kinetic analysis is performed using various incubation periods at 37 degrees C. Released biodegradation products are identified and quantified, in both the medium and cell compartment, and on the other hand cytotoxicity is assessed. A Co-Cr alloy was studied over a 9-day period according to the experimental schedule, and showed a higher corrosion rate in the presence of osteoblasts in the range of 25-30%. Moreover, an intracellular uptake of both Cr and Co was detected, which will have physiological importance.