This paper investigates the effect of cell design on solid oxide fuel cells (SOFC) stack performance。 Based on 3-dimensional numerical simulations, it is found that the performance of stack is strongly dependent on cell design。 The average current density of the anode-supported SOFC (ASC) stack is only 5580 A m-2, a reduction of 20。7% from the cathode-supported SOFC (CSC) stack of 7033 A m−2。 This can be explained that compared with CSC stack, thin cathode in ASC stack leads to the smaller

effective reaction zone and the larger cathode ohmic losses。 The discrepancy between the ASC stack and the CSC stack are examined by varying rib width, contact resistance and pitch width。 The results show conclusively that with the optimal rib width, the performance of the CSC stack is much superior to that of the ASC stack for any practical contact resistance and pitch width。 The analyses provided in this paper assist in understanding the effect of cell design on cell performance in the stack level and playing the full potential of the stack by optimizing the cell design。86037

Keywords: Solid oxide fuel cell; Anode-supported cell; cathode-supported cell; stack model; charge or gas transport

1。INTRODUCTION

As one of the common SOFC configurations, planar-type has attracted much more attention due to shorter current paths and higher power density over tubular-type design [1]。 To date, two main types planar SOFC have been studied。 They are electrolyte- and electrode-supported designs。 For electrolyte-supported SOFC, high working temperature is required in order to reduce the electrolyte ohmic loss [2]。 However, high working temperature is also a rigorous limit for materials of SOFC and decreases fuel cell lifetime and increases fabrication cost [1, 3-5]。 For electrode-supported SOFC,

electrolyte is very thin (for example, about 10 m ), which drastically reduces the electrolyte ohmic

Int。 J。 Electrochem。 Sci。, Vol。 10, 2015

loss。  Thus  electrode-supported  SOFC  can  be  operated  at  intermediate  or  low  temperature  and is

 preferred over electrolyte-supported design [6]。

Much recent effort for the electrode-supported SOFC is mainly based on the anode-supported SOFC (ASC) [7-11]。 Noh et al。 showed that the cell performance was improved by a factor of 1。6 by the optimization of the current collection configuration of ASC [12]。 Author's previous study systematically examined the influence of the rib width on the stack-cell performance and revealed that the optimal rib width of anode is quite different from that of cathode for ASC[13]。 Park et al investigated the effect of the anode functional layer thickness on the performance of ASC[14]。 Lim et al。 studied the degradation mechanism of ASC。 The results indicated that the increase of the ohmic resistance is the main cause leading to the cell degradation [15]。

Comparatively, there has been little attention paid to the cathode-supported SOFC (CSC), though CSC shows various advantages over ASC such as using the low-cost cathode supporting material strontium-doped lanthanum manganese, relatively thin anode preventing the  depositing carbon when operating on hydrocarbon fuels and also providing benefits in terms of tolerance to volume contraction/expansion resulting from the accidental anode redox cycles [6, 16-19]。 This can be highly attributed to the fabrication difficulty of the CSC。 For example, a relatively high sintering temperature may lead to the chemical reactions between cathode and electrolyte。 However, the electrolyte will not be dense if sintered at a low temperature[18]。

Figure 1。 Schematic representation of charge and gases transport processes in the button cell。

For the button cell, silver paste is often used as current collector [20, 21]。 Therefore, the charge or gases transport processes in the parallel electrode surface direction can be neglected, as shown in Fig。1。 The ohmic and concentration losses of electrodes are mainly due to the transport processes in the vertical electrode surface direction。 As we all know, anode conductivity is about 6 times higher than the cathode conductivity。 Hydrogen diffusion coefficient is also larger than oxygen diffusion coefficient。 Thus the performance of the ASC is superior to that of the CSC for the button cell [1, 22, 23]。