Detailed Multi-dimensional Modeling of Direct Internal Reforming Solid Oxide Fuel Cells

Fuel flexibility is a significant advantage of solid oxide fuel cells (SOFCs) and can be attributed to their high operating temperature. Here we consider a direct internal reforming solid oxide fuel cell setup in which a separate fuel reformer is not required. We construct a multidimensional, detailed model of a planar solid oxide fuel cell, where mass transport in the fuel channel is modeled using the Stefan-Maxwell model, whereas the mass transport within the porous electrodes is simulated using the Dusty-Gas model. The resulting highly nonlinear model is built into COMSOL Multiphysics, a commercial computational fluid dynamics software, and is validated against experimental data from the literature. A number of parametric studies is performed to obtain insights on the direct internal reforming solid oxide fuel cell system behavior and efficiency, to aid the design procedure. It is shown that internal reforming results in temperature drop close to the inlet and that the direct internal reforming solid oxide fuel cell performance can be enhanced by increasing the operating temperature. It is also observed that decreases in the inlet temperature result in smoother temperature profiles and in the formation of reduced thermal gradients. Furthermore, the direct internal reforming solid oxide fuel cell performance was found to be affected by the thickness of the electrochemically-active anode catalyst layer, although not always substantially, due to the counter-balancing behavior of the activation and ohmic overpotentials

In-situ Raman spectroscopy study of Ru/TiO2 catalyst in the selective methanation of CO

Raman spectroscopic technique has been used to characterize a Ru/TiO2 catalyst and to follow in situ their structural changes during the CO selective methanation reaction (S-MET). For a better comprehension of the catalytic mechanism, the in-situ Raman study of the catalysts activation (reduction) process, the isolated CO and CO2 methanation reactions and the effect of the composition of the reactive stream (H2O and CO2 presence) have been carried out. Raman spectroscopy evidences that the catalyst is composed by islands of TiO2¿RuO2 solid solutions, constituting Ru¿TiO2 interphases in the form of RuxTi1 xO2 rutile type solid solutions. The activation procedure with H2 at 300 °C promotes the reduction of the RuO2¿TiO2 islands generating Ruo ¿Ti3+ centers. The spectroscopic changes are in agreement with the strong increase in chemical reactivity as increasing the carbonaceous intermediates observed. The selective methanation of CO proceeds after their adsorption on these Ruo ¿Ti3+ active centers and subsequent C-O dissociation throughout the formation of CHx/CnHx/CnHxO/CHx-CO species. These intermediates are transformed into CH4 by a combination of hydrogenation reactions. The formation of carbonaceous species during the methanation of CO and CO2 suggests that the CO presence is required to promote the CO2 methanation. Similar carbonaceous species are detected when the selective CO methanation is carried out with water in the stream. However, the activation of the catalysts occurs at much lower temperatures, and the carbon oxidation is favored by the oxidative effect of water.España Mineco ENE2012- 37431-C03-03Unión Europea Junta de Andalucia FEDER TEP-819

Advances in reforming and partial oxidation of hydrocarbons for hydrogen production and fuel cell applications

One of the most attractive routes for the production of hydrogen or syngas for use in fuel cell applications is the reforming and partial oxidation of hydrocarbons. The use of hydrocarbons in high temperature fuel cells is achieved through either external or internal reforming. Reforming and partial oxidation catalysis to convert hydrocarbons to hydrogen rich syngas plays an important role in fuel processing technology. The current research in the area of reforming and partial oxidation of methane, methanol and ethanol includes catalysts for reforming and oxidation, methods of catalyst synthesis, and the effective utilization of fuel for both external and internal reforming processes. In this paper the recent progress in these areas of research is reviewed along with the reforming of liquid hydrocarbons, from this an overview of the current best performing catalysts for the reforming and partial oxidizing of hydrocarbons for hydrogen production is summarized

Thermodynamic and economic analysis of a steam reformer-solid oxide fuel cell system fed by natural gas and ethanol

In the present work, ethanol and methane are compared as candidate fuels for solid oxide fuel cells (SOFCs). The thermodynamic analysis of both alternatives was undertaken considering that a SOFC stack operates by being fed by the equilibrium products of the steam reforming of each raw fuel. The comparison was made at atmospheric total pressure assuming low reforming factors (steam/fuel feed ratios) and SOFC operation in the temperature range of 800 to 1200 K. All operation conditions have been selected so that carbon deposition in the SOFC anode is thermodynamically impossible. Results were obtained in terms of the maximum theoretical electromotive force and the thermodynamic efficiency of total energy conversion. It was found that both fuels exhibit similar thermodynamic behavior when fed in a SOFC stack, and some qualitative advantages with respect to ethanol are discussed