Modeling of CH4-assisted SOEC for H2O/CO2 co-electrolysis

This research was supported by a grant of SFC/RGC Joint Research Scheme (X-PolyU/501/14) from Research Grant Council, University Grants Committee, Hong Kong SAR.Co-electrolysis of H2O and CO2 in a solid oxide electrolysis cell (SOEC) is promising for simultaneous energy storage and CO2 utilization. Fuel-assisted H2O electrolysis by SOEC (SOFEC) has been demonstrated to be effective in reducing power consumption. In this paper, the effects of fuel (i.e. CH4) assisting on CO2/H2O co-electrolysis are numerically studied using a 2D model. The model is validated with the experimental data for CO2/H2O co-electrolysis. One important finding is that the CH4 assisting is effective in lowering the equilibrium potential of SOEC thus greatly reduces the electrical power consumption for H2O/CO2 co-electrolysis. The performance of CH4-assisted SOFEC increases substantially with increasing temperature, due to increased reaction kinetics of electrochemical reactions and CH4 reforming reaction. The CH4-assisted SOFEC can generate electrical power and syngas simultaneously at a low current density of less than 600 Am−2 and at 1123 K. In addition, different from conventional SOEC whose performance weakly depends on the anode gas flow rate, the CH4-assisted SOFEC performance is sensitive to the anode gas flow rate (i.g. peak current density is achieved at an anode flow rate of 70 SCCM at 1073 K). The model can be used for subsequent design optimization of SOFEC to achieve high performance energy storage.PostprintPeer reviewe

Solid Oxide Fuel Cells: Numerical and Experimental Approaches

Solid oxide fuel cell (SOFC) is a promising electrochemical technology that can produce electrical and thermal power with outstanding efficiencies. A systematic synergetic approach between experimental measurements and modelling theory has proved to be instrumental to evaluate performance and correct behaviour of a chemical process, like the ones occurring in SOFC. For this purpose, starting from SIMFC (SIMulation of Fuel Cells) code set-up by PERT-UNIGE (Process Engineering Research Group) for Molten Carbonate Fuel Cells [1], a new code has been set-up for SOFCs based on local mass, energy, charge and momentum balances. This code takes into account the proper reactions occurring in the SOFC as well as new geometries and kinetics thanks to experiments carried out on single cells and stack in ENEA laboratories of C.R. Casaccia and VTT Fuel Cell Lab in Finland. In particular using an innovative experimental setup it has been possible to study experimentally the influence of a multicomponent mixtures on the performance of SOFC and also validate locally a 2-D model developed starting from SIMFC code. The results obtained are good, showing a good agreement between experimental and numerical results. The obtained results are encouraging further studies which allow the model validation on a greater quantity of data and under a wider range of operating conditions

Reviews on Solid Oxide Fuel Cell Technology

oai:www.engj.org:article/25Solid Oxide Fuel Cell (SOFC) is one type of high temperature fuel cell that appears to be one of the most promising technology to provide the efficient and clean energy production for wide range of applications (from small units to large scale power plants). This paper reviews the current status and related researches on SOFC technologies. In details, the research trend for the development of SOFC components(i.e. anode, electrolyte, cathode, and interconnect) are presented. Later, the current important designs of SOFC (i.e. Seal-less Tubular Design, Segmented Cell in Series Design, Monolithic Design and Flat Plate Design) are exampled. In addition, the possible operations of SOFC (i.e. external reforming, indirect internal reforming, and direct internal reforming) are discussed. Lastly, the research studies on applications of SOFCs with co-generation (i.e. SOFC with Combined Heat and Power (SOFC-CHP), SOFC with Gas Turbine (SOFC-GT)) and SOFC with chemical production) are given

Co – extruded triple layer hollow fiber solid oxide fuel cell using methane

Solid oxide fuel cell (SOFC) is one of the most promising fuel cells and it has been developed extensively in recent years. However, carbon deposition on the anode site is the main issue of this system when methane is used as the fuel. Therefore, the objective of the research is to develop a methane-fueled micro tubular solid oxide fuel cell (MT-SOFC) with excellent carbon resistant property. In the first phase of this work, triple layer hollow fiber, which consisted of anode which used nickel oxide (NiO) and yttria stabilized zirconia (YSZ), anode functional layer (AFL) also made of NiO and YSZ, and electrolyte from YSZ, was fabricated via phase inversion-based coextrusion/ co-sintering technique with varied fabrication parameters (i.e. ratio NiO/YSZ in the AFL and sintering temperature) and such triple layer design that has been previously reported is able to possess several advantages such as high power output and high thermal expansion coefficient. Further, the cell was tested using methane gas as fuel. The hollow fiber with the ratio of 2:8 of NiO to YSZ of AFL suspension shows crack-free properties. After sintering between 1400 oC and 1500 °C, the hollow fiber recorded an increase from 110.1 to 130 MPa on three-point bending tests and 1.26×10-5 to 4.6×10-6 mol m-2 s-2 Pa-1 for gas tightness tests. The maximum power densities obtained at 800 °C were 0.8 W/cm2. In the second stage of the study, the prolonged operation of the SOFC was done using methane fuel to observe the carbon deposition phenomenon. The fuel cell showed significant reduction of power density from 0.8 W/cm2 at 800 °C to 0.2 W/cm2 after 90 min. In the third stage of the work, ceria gadolinium oxide (CGO) was incorporated in the anode suspension to increase the resistance towards carbon poisoning. With the addition of 3wt.% of CGO at the anode layer, the performance degradation was reduced to only 50% from the initial power density after 90 min, in comparison to the cell without CGO (the reduction of 75% after 90 min), although the initial power density of the modified one was slight lower (0.4 W/cm2) than the unmodified cell (0.8 W/cm2). It was shown that the CGO able to reduce the degradation of the cell under methane as fuel

Configuration Development of Autothermal Solid Oxide Fuel Cell: A Review

Solid Oxide Fuel Cell (SOFC) is typically operated at high temperature. Both electricity and heat are generated during operation. Therefore, SOFC can be efficiently designed to integrate the endothermic reformer with the cell for optimizing heated utilization, as called autothermal operation. However, the mismatch between rate of exothermic electrochemical reaction and endothermic reforming reaction is easily resulted in material cracking of those integrated structure. In order to overcome the thermal mismatch limitation, various approaches for autothermal SOFC configurations have been widely developed; these configurations can be classified into 2 main groups including direct internal reforming (as called DIR-SOFC) and indirect internal reforming (as called IIR-SOFC) operations. This review focuses on the technological progress of these various configurations. In detail, computer simulation technique has been applied to study the thermal behavior inside the autothermal SOFC configurations using various primary hydrocarbon fuels. In addition, the advantage and disadvantage on thermal stress reduction of each configuration are also discussed

Durability Model of SOFC Anode Structure under Thermo-Mechanical and Fuel Gas Contaminants Effects

Solid Oxide Fuel Cells (SOFCs) operate under harsh environments, which cause the deterioration of anode material properties and reduce their service life. In addition to electrochemical performance, structural integrity of the SOFC anode is essential for successful long-term operation. Anode-supported SOFCs rely on the anode to provide mechanical strength to the positive-electrolyte-negative (PEN) structure. The stress field in the anode may arise from a variety of phenomena including thermal expansion mismatch between layers in the PEN structure, thermal/redox cycles and external mechanical loads. Moreover, some fuel contaminants such as phosphine (PH3) interact with the anode materials which lead to the formation of secondary phases and grain growth. These mechanisms result in the formation of microcracks, and degrade anode structural and electrochemical properties. Assessments of the evolution of anode mechanical properties during long-term operation are therefore essential to predict SOFC working life.;The principal objective of this research is to develop a structural durability model for the SOFC anode that takes into account thermo-mechanical and fuel contaminants effects on the anode material properties. The model is implemented in finite element analysis through a user defined subroutine to predict anode long-term structural integrity. The model is exploited to predict the stress-strain relations of Ni-YSZ at temperatures and porosities which are difficult to generate experimentally. Accelerated exposure tests under high contaminant concentrations dictate that the electrochemical degradation is the principal mode of cell failure while the cell structure is still intact. However, the model predicts that under lower contaminant concentrations, the anode structural degradation may be significant as compared to the electrochemical degradation in long-term operation.;The proposed model is enhanced for the planar-SOFC configurations exposed to PH3. The model predicts that under pure thermo-mechanical effect, the critical location for structure failure is near the corner of highest thermal gradient. However when fuel contaminant structural effect is superimposed on the thermo-mechanical effect, the critical location may shift depending on the flow configuration. Under similar operating conditions, i.e. same current density, co-flow configuration yields a higher anode structural life than counter-flow or cross-flow configurations. The knowledge obtained from this research will be useful to establish control parameters to achieve desired service life of the SOFC stack under various operating conditions

Modelling of a Solid Oxide Fuel Cell for Integrated Coal Gasification Hybrid Power Plant Simulation

Now and in the mid-term future, coal remains an important energy source for electricity generation for reasons of energy supply security and economics. The expectation for low CO2-emissions and high plant efficiencies make solid oxide fuel cells an essential part of numerous innovative power plant concepts. For that reason, simplified and flexible models for solid oxide fuel cells are needed, which can be implemented easily in complex power plant system simulations. A model for a tubular solid oxide fuel cell based on a semi-empirical approach has been developed. The created model is successfully validated with operating data of demonstration plants published in literature. For the target application in a hybrid power plant with high temperature fuel cells, a parametric study of fuel gas composition, operating pressure and temperature, fuel utilization and electrical power density is presented. By means of these, the model of the fuel cell is qualified for implementation in hybrid power plants system models. Additionally, characteristic diagrams obtained by variation of the operating pressure and the fuel utilization are discussed. With the help of the diagrams, the electric and energetic performance of the SOFC over a wide range of these parameters is described by isolines for discrete values of the electrical efficiency and voltage of the fuel cell