This work investigates the catalytic properties of Ir/Ce0.9Gd0.1O2–x (Ir/CGO) catalyst and CGO support in steam reforming of methane in the absence or presence of H2S (50 ppm) for further application in a solid oxide fuel cell (SOFC) working under methane at intermediate temperatures and integrating a gradual internal reforming concept. The catalytic activity was measured at 750 °C by using a 50 mol.% CH4/5 mol.% H2O/45 mol.% N2 mixture and a 10 mol.% CH4/90 mol.% N2 mixture. The addition of Ir to CGO improves the catalytic activity in hydrogen production by two orders of magnitude with respect to that of CGO alone. Temperature programmed oxidation experiments were performed after reaction in both types of mixtures to study the eventual formation of carbon deposits. Over Ir/CGO, carbon formed in little amounts (even in the absence of H2O in the feed), being highly reactive toward O2. Upon H2S addition, the CGO support exhibited surprisingly an improved catalytic activity on the contrary to Ir/CGO which partly deactivated. Upon suppression of H2S in the feed the initial catalytic activity was fully restored for both catalysts. The catalytic behavior of CGO in the presence of H2S was discussed, based upon temperature programmed reaction of CH4.
Methane appears to be a fuel of great interest for solid oxide fuel cell (SOFC) systems because it can be directly converted into hydrogen by Internal Reforming within the SOFC anode. To cope with carbon formation, a new SOFC cell configuration combining a catalyst layer with a classical anode was developed. The rate of the CH 4 consumption in the catalyst layer (Ir-CGO) was determined experimentally for small values of steam to carbon ratios. This paper proposes a modelling and a simulation, using the CFD-Ace software package, of the behaviour of a SOFC operated in Gradual Internal Reforming (GIR) conditions. This model of SOFC takes into account the kinetics of the steam reforming reaction in the catalyst layer in order to assess the influence of the steam to carbon ratio and the cell polarization. Because the risk of carbon formation is greater under GIR operation, a detailed thermodynamic analysis was carried out. Thermodynamic equilibrium calculations allowed us to predict the conditions of carbon formation occurrence.
This work concerns the feasibility of SOFC operation directly on biogas and more specifically, the optimization of biogas internal dry reforming conditions. A special attention is paid to the carbon deposition risk. For such a purpose simulation tools have been developed, based on thermodynamic and electrochemical modelling, in order to determine the risk of carbon formation within the anode during operation. Safe operation conditions in terms of temperature, fuel composition and cell polarization have been established and validated experimentally. In conditions where carbon deposition is expected, performance degradation upon operation has been followed over more than hundred hours on complete cells (Cermet Ni-8YSZ//8YSZ//LSM) by electrochemical impedance spectroscopy. The carbon deposited has been characterized by scanning electron microscopy with particular attention given to its morphology and distribution.
Methane appears to be a fuel of great interest for SOFC systems because it can be directly converted into hydrogen by Gradual Internal Reforming (GIR) within the SOFC anode with a new cell configuration. This study proposes a model of SOFC which takes into account the kinetics of the reforming reaction on the catalyst in order to assess the limitations under current of this new configuration of the SOFC cell. The aim of this work is to investigate the influence of the catalytic properties of methane steam reforming reaction on the SOFC cell electrochemical behavior in GIR operation.
A methodology has been proposed to analyze the electrochemical degradation of the ASC configuration. This methodology, based on the measurement of the cell response by impedance spectroscopy, has been applied to study the cell performances degradation, (i) when the anode is re-oxidized under an ionic current, and (ii) upon direct methane reforming. In the first case, a thin cermet layer growing from the anode/electrolyte interface has been oxidized and then reduced. This 'redox' cycle has been repeated until the complete degradation of the cell. It has been found that the impedance diagram's evolution is consistent with a delamination between the ACC/AFL interface. In the second case, the cell has been operated under methane conditions known to favour the coking. The analysis of the impedance diagrams has shown a degradation of the current collection. This result has been found to be consistent with the location of carbon deposit inside the cell.
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