Modelling of finger-like channelled anode support for SOFCs application

Abstract

This paper established a numerical model for a solid oxide fuel cell (SOFC) button cell, focusing on the effects of finger-like channels on the gas transport process in the anode support. The current densities of channelled button cell and un-channelled button cell are compared at different operating temperature and voltage with H₂ as the fuel. The H₂ transport is discussed in detail, such as the mole fraction distribution of H₂ in the porous layer, the diffusion flux and convective flux of H₂. It is found that the performance of SOFC can be improved by 2.60 % at 800 °C, 0.5 V, compared with un-channelled SOFC due to the improved gas transport by the finger-like channels. Then, the model is further extended to study 2D-planar SOFC fuelled with syngas. The mole fraction gradients of H₂, CO, CH₄ and CO are all substantially reduced by the finger-like channels compared to un-channelled planar cell. It is found that the SOFC performance is improved by 5.93 % at 800 °C, 0.5 V, when syngas fuel is used. The present study clearly demonstrated that the use of finger-like channels in the anode support is effective in improving the gas transport and the SOFC performance. The present model can be employed for subsequent optimization of the channel configuration for further performance improvement.

摘要

本文建立了固体氧化物纽扣燃料电池的数学模型,研究了阳极支撑中指孔状通道对气体传输过程的影响。比较了当氢气作为燃料,加通道和未加通道的纽扣燃料电池在不同温度和工作电压下的电流密度。讨论了电池多孔阳极内的氢气的摩尔分数分布、扩散通量以及对流通量分布。发现在800 ^oC, 0.5 V 下, 加通道的纽扣电池由于气体传输的优化,性能比未加通道提高了2.60 %。模型被用于模拟合成气作为燃料的平板固体氧化物燃料电池。在有指孔状通道的情况下,H₂,CO,CH₄ 和CO的摩尔分数梯度被有效降低,800 ^oC,0.5 V时,电池性能提高了5.93 %。本文论证了指孔状结构应用于阳极支撑层时,对气体传输优化和电池性能提升的有效性。模型可被用于进一步的通道结构设计和优化。

Appendix: List of symbols

$AV$ :

Specific surface area ratio, 2.381 × 10⁵ m⁻¹

D _y :

Distance from the anode-electrolyte interface (AEI), in y direction (μm)

D _x :

Distance from the middle cut line of the button cell, in x direction (μm)

D _{x, p} :

Distance from the inlet of the planar cell, in x direction (μm)

$F$ :

Faraday constant, 96,485 C/mol

$i_{\text{c}}$ :

Local current source for cathode (A/m³)

$i_{{{\text{a}},{\text{H}}_{2} }}$ :

Local current source by H₂ (A/m³)

$i_{{{\text{a}},{\text{CO}}}}$ :

Local current source by CO (A/m³)

$i_{{{\text{o}},{\text{c}}}}$ :

Exchange current density for cathode reaction (A/m²)

$i_{{{\text{o}},{\text{H}}_{2} }}$ :

Exchange current density for oxidation of H₂ (A/m²)

$i_{{{\text{o}},{\text{CO}}}}$ :

Exchange current density for oxidation of CO (A/m²)

$N_{{{\text{conv}}.{\text{H}}_{2} }}$ :

Convective flux of H₂ in y direction (kg/(m² s))

$N_{{{\text{diff}}.{\text{H}}_{2} }}$ :

Diffusive flux of H₂ in y direction (kg/(m² s))

$P_{\text{ch}}$ :

Average power density of channelled cell (W/m²)

$P_{{{\text{un}} - {\text{ch}}}}$ :

Average power density of un-channelled cell (W/m²)

$p_{{{\text{H}}_{2} }}$ :

Species partial pressure, atm, subscript “.ref” meaning the reference value

$R$ :

Gas constant, 8.314 J/(mol K)

T :

Operating temperature (K)

$\sigma$ :

Conductivity of material as subscripted (S/m)

$\eta_{{{\text{act}}.{\text{a}}/{\text{c}}}}$ :

Activation overpotential (V)

η :

Percentage of power density enhancement (%)

η _{conc, u} :

Concentration overpotential of the un-channelled button cell

η _{conc, c} :

Concentration overpotential of the channelled button cell

$\varepsilon$ :

Porosity

$\xi$ :

Tortuosity