Effect of characteristic lengths of electron, ion, and gas diffusion on electrode performance and electrochemical reaction area in a solid oxide fuel cell

Abstract

A precise evaluation of the active reaction zone in the electrodes is important to design an effective solid oxide fuel cell (SOFC). A scale analysis and one‐dimensional numerical simulations are conducted to obtain a better understanding of the electrochemical reaction zone in a SOFC anode. In the scale analysis, the characteristic lengths of the electron, oxide ion, and gas transports are evaluated from their conservation equations. Relative comparisons of the characteristic lengths show that the transport phenomena in the SOFC anode are primarily governed by the oxide‐ion conduction under standard operating conditions. The gas diffusion may affect the extent and the location of the active reaction zone at high temperature and/or low reaction gas concentration conditions. The one‐dimensional numerical simulations for an anode provided detailed information such as the electric potential of electron‐ and ion‐conducting phases, the gas concentration, and local charge‐transfer current distributions. It is found that the electrochemical reaction actively occurs in the vicinity of the anode–electrolyte interface. The effective thickness increases as the characteristic length of the ion conduction is increased resulting in better power generation performance. The effective thickness is also increased when the gas‐diffusion length is short. The cell performance is, however, lowered in this case because the low gas diffusivity yields the increase of the ohmic loss of ion conduction as well as the concentration overpotential. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20373

Effect of Composition Ratio of Ni‐YSZ Anode on Distribution of Effective Three‐Phase Boundary and Power Generation Performance

“…Although the active reaction region also changes with other factors such as oxideion conductivity and the TPB density [13,14], the effect of Ni percolation is more drastic as discussed above; poor Ni percolation shifts the active region far away from the electrolyte. Although the active reaction region also changes with other factors such as oxideion conductivity and the TPB density [13,14], the effect of Ni percolation is more drastic as discussed above; poor Ni percolation shifts the active region far away from the electrolyte.…”

“…For the optimization of the anode microstructure, our primary concern should be the Ni percolation from the anode surface to the anode-electrolyte interface because it largely determines the active reaction region. Although the active reaction region also changes with other factors such as oxideion conductivity and the TPB density [13,14], the effect of Ni percolation is more drastic as discussed above; poor Ni percolation shifts the active region far away from the electrolyte. Under the well-connected Ni phase, we can then proceed to the optimization of other microscopic feature of the anodes.…”

“…Reaction region is also a major subject of interest in optimizing the electrode microstructure [11][12][13][14]. In the case of anode supported SOFC cells, the anodes often consist of two layers with different microstructure: function layer and support layer.…”

Improvement in the Electrochemical Performance of Anode‐supported Solid Oxide Fuel Cells by Meso‐ and Nanoscale Structural Modifications

“…For a desirable cell performance even at low operating temperatures, it is necessary to increase the volumetric density of reaction sites, which mainly contribute to the electrochemical reaction. From the viewpoint that the reaction sites are distributed in a very thin region near the electrode-electrolyte interface [1][2][3][4][5][6][7][8], which is called an electrochemical reaction region, various approaches to increasing the density of reaction sites have been reported in a wide range of length scales. For instance, attaching a functional layer between an electrode and an electrolyte is a common approach to improving cell performance [3,[9][10][11][12].…”

Wavy Micro Channels in Micropatterned Ceramic Sheet Formed by Combined Process of Laser Beam Machining and Imprinting

“…The micro powder imprinting method has been proposed to enable micro patterning on the surface of ceramic sheets. Micro patterned ceramic sheets can effectively improve the performance of solid oxide fuel cells [14][15][16][17] . This method combines powder metallurgy (P/M) process and nanoimprinting lithography [18][19][20][21][22] , which is an approach to transfer fine patterns to plastic polymer materials by using patterned moulds.…”