Multiscale model for solid oxide fuel cell with electrode containing mixed conducting material

Abstract

Solid oxide fuel cells (SOFCs) with electrodes that contain mixed conducting materials usually show very different relationships among microstructure parameters, effective electrode characteristics, and detailed working processes from conventional ones. A new multiscale model for SOFCs using mixed conducting materials, such as LSCF or BSCF, was developed. It consisted of a generalized percolation micromodel to obtain the electrode properties from microstructure parameters and a multiphysics single cell model to relate these properties to performance details. Various constraint relationships between the activation overpotential expressions and electric boundaries for SOFC models were collected by analyzing the local electrochemical equilibrium. Finally, taking a typical LSCF‐SDC/SDC/Ni‐SDC intermediate temperature SOFC as an example, the application of the multiscale model was illustrated. The accuracy of the models was verified by fitting 25 experimental I‐V curves reported in literature with a few adjustable parameters; additionally, and several conclusions were drawn from the analysis of simulation results. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3786–3803, 2015

The Geometry Effect of Cathode/Anode Areas Ratio on Electrochemical Performance of Button Fuel Cell Using Mixed Conducting Materials

“…'=' in Equation (4b) represents the energy equilibrium state at local place. In this case, the local electromotive force based on local working condition instead of the open circuit condition can be got as [18] E…”

“…Combing with the above e − -O 2− charge transfer rates within the composite electrodes and electrode/dense electrolyte interfaces, multi-physics model can be completed by further coupling momentum, mass, electronic and ionic electric current conservation equations. The relationship among electric current densities, electric potentials and e − -O 2 charge transfer rates can be solved by [18]…”

“…Furthermore, proton conducting oxides [14], such as BaZr 0.7 Pr 0.1 Y 0.2 O 3_d [15] and BaZr 0.1 Ce 0.7 Y 0.2 O 3_d [16] were also greatly invented to be used in IT-SOFCs because of their low activation energy and high ionic conductivity around IT-range.Generally, the electrochemical reaction processed within an IT-SOFC using mixed conducting materials or proton conducting oxides are very different from those using conventional composite electrodes [17]. Taking the cathode of LSCF-SDC/SDC/NI-SDC IT-SOFC using mixed conducting materials as an example [13], the electrochemically active sites not only can be taken placed around the percolated three phase boundary sites (i.e., LSCF-SDC-pores and LSCF-dense electrolyte interfaces), but also can happen around the percolated double phase boundary sites (e.g., LSCF-pore) [18]. Up to now, many IT-SOFC button cells using the mixed conducting materials have been reported by many researchers by adopting different compositions (or materials), volume fractions, microstructure parameters, manufacture processes, operating conditions and different cell geometry sizes.…”

“…Thus, the volumetric current sources for the transfer of e − -O 2− electric charges around the TPBs are i V e−O 2− ,TPB = j TPB λ V TPB.per in A m −3 . The area metric current sources over electrode/electrolyte interfaces are i S e−O 2− ,TPB = j TPB λ S TPB.per in A m −2 .Similarly, the e --O 2charge transfer rate over per LSCF-pore DPB area can be evaluated as[18]…”

A Simple Expression for the Tortuosity of Gas Transport Paths in Solid Oxide Fuel Cells’ Porous Electrodes

“…However, it is a challenging task to simulate the gas transport in electrodes accurately because the presence of the solid phase causes the transport paths of gas to deviate from straight lines. In order to take the effect of tortuous gas transport paths into account, the effective gas diffusion coefficient D eff is usually corrected by introducing the tortuosity, which is commonly expressed as [5][6][7][8][9]:…”