各向异性膨胀石墨双极板对燃料电池性能的影响

doi:10.3969/j.issn.1674-8484.2024.04.009

摘要/Abstract

摘要：

该文分析了膨胀石墨双极板（EGBPs）各向异性结构对燃料电池水热管理与输出性能的影响。建立了三维两相非等温数值模型，对比了4种典型复合材料结构下温度、电流密度、水含量等参数的分布特征，揭示了双极板传热特性与输出性能的耦合效应。结果表明：沿质子传递方向热导率（k_z）对燃料电池性能具有显著影响，在2.2 A cm^-2电流密度下，将k_z从常规结构的5 W·m^-1·K^-1提升至280 W·m^-1·K^-1，可以使输出性能提高22 mV；沿流道气体流动方向的热导率（k_y）是影响散热能力的关键因素，将k_y与k_z提高至280 W·m^-1·K^-1，或者实现各向同性结构（k_x = k_y = k_z = 20 W·m^-1·K^-1），均能够使膜电极组件（MEA）核心区域的温度降低2 ℃左右。因此，提高k_y与k_z并实现各向同性结构是膨胀石墨双极板技术的未来发展目标之一。

关键词: 质子交换膜燃料电池（PEMFC）, 膨胀石墨双极板（EGBPs）, 各向异性导热, 水热管理, 散热能力

Abstract:

Established a three-dimensional, two-phase, non-isothermal fuel cell single channel model to investigate the influence of anisotropic structure of Expanded Graphite Bipolar Plates (EGBPs) on thermal management and the performances of proton exchange membrane fuel cell (PEMFC). The distribution of temperature, the current density and the membrane water content under four main material orientations were compared. The coupling effect between EGBPs heat transfer characteristics and the outperformance were revealed. The results show that increasing the conductivity along proton-transport direction k_z from the 5 W·m^-1·K^-1 for a traditional structure to the 280 W·m^-1·K^-1, enhances the voltage by 22 mV under 2.2 A cm^-2. The conductivity along gas-flow direction k_y plays an important role in heat dissipation. Increasing k_y and k_z to 280 W·m^-1·K^-1, or accomplishing isotropic conductivity (k_x = k_y = k_z = 20 W·m^-1·K^-1), reduces the Membrane-Electrode-Assembly (MEA) core-area peak-temperature by 2 ℃. Therefore, enhancing the gas-flow and proton-transport direction conductivities and accomplishing isotropic structure are one of the future main development goal of expanded graphite bipolar plates.

Key words: proton exchange membrane fuel cell (PEMFC), expanded graphite bipolar plates (EGBPs), anisotropic conductivity, thermal and water management, heat dissipation

中图分类号:

TM911.4

丁玉杰, 甘全全, 邵扬斌, 徐梁飞, 李建秋, 欧阳明高. 各向异性膨胀石墨双极板对燃料电池性能的影响[J]. 汽车安全与节能学报, 2024, 15(4): 526-535.

DING Yujie, GAN Quanquan, SHAO Yangbin, XU Liangfei, LI Jianqiu, OUYANG Minggao. Influence of anisotropic conductive expanded graphite bipolar plates on performance of proton exchange membrane fuel cell[J]. Journal of Automotive Safety and Energy, 2024, 15(4): 526-535.

图/表 16

图1 膨胀石墨双极板截面示意图

图2 膨胀石墨双极板材料结构示意图

结构编号	石墨片层取向	热导率，k / (W·m^-1·K^-1)			电导率，σ / (S·cm^-1)
结构编号	石墨片层取向	x方向	y方向	z方向	x方向	y方向	z方向
Ⅰ	x - y	280	280	5	1 100	1 100	20
Ⅱ	y - z	5	280	280	20	1 100	1 100
Ⅲ	x - z	280	5	280	1 100	20	1 100
Ⅳ	各向同性	20	20	20	100	100	100

表1 不同膨胀石墨双极板分布结构的性能参数

图3 膨胀石墨三维单流道模型示意图

厚度 (j = GDL, MPL, CL, PEM)	δ_j = 151, 10, 15, 18 μm
孔隙率(j = GDL, MPL, CL)	ε_j = 0.77, 0.6, 0.5
绝对渗透率(j = GDL, MPL, CL, PEM)	K_j = 23, 0.25, 0.1, 1.0×10^-6 μm²
CL曲折度	τ_d = 1.5
扩散系数^[28] (i = O₂, H₂)	D_0,_i = 2.652×10^-5, 1.055×10^-4 m² s^-1
活性比表面积	a₀ = 5.0×10⁷ m² m^-3
阳极/阴极参考交换电流密度	j_a,ref = 500 A m^-2, j_c,ref = 10 μm^-2
参考H₂/O₂浓度	C_H₂,ref = 56.4 mol m^-3, C_O2,ref = 3.39 mol m^-3
阳极/阴极传递系数	α_a,a = 0.5, α_a,c = 1.5, α_c,a = 3, α_c,c = 1
阳极/阴极反应级数	γ_H₂ = 0.5, γ_O2 = 1
活化能	ΔG = 8.314 kJ mol^-1
焓差	ΔS = -163.3 J (mol K)^-1
参考温度	T_ref = 343 K
电导率^[29](j = GDL, MPL, CL, PEM)	σ_s,_j = 5.0 kS m^-1
膜干态密度	ρ_m = 1.98 t m^-3
膜离子交换当量	EW = 1.1 kg mol^-1
阳极/阴极CL中离聚物体积分数	l_m,a = 0.6, l_m,c = 0.6

表2 模型参数

边界	类型	取值
阳极(a)、阴极(b)气体流道入口	质量入口	$m a = ρ a ξ a I a a 2F C H 2$ , $m c = ρ c ξ c I a c 4F C O 2$
阳极(a)、阴极(b)气体流道出口	压力出口	p_b,a, p_b,c
阳极(a)、阴极(b)双极板端面	壁面	$\varphi_{\mathrm{e}}=0 ; \frac{\partial \varphi_{\mathrm{m}}}{\partial y}=0 ; q_{\mathrm{h}, \text { cool }, \mathrm{a}}=\frac{q_{\mathrm{h}, \text { cool }}}{2} \quad \varphi_{\mathrm{e}}=U ; \frac{\partial \varphi_{\mathrm{m}}}{\partial y}=0 ; q_{\mathrm{h}, \text { cool, } \mathrm{a}}=\frac{q_{\mathrm{h}, \mathrm{cool}}}{2}$
侧面边界	对称边界	$\frac{\partial \varphi_{\mathrm{m}}}{\partial x}=0 ; \frac{\partial \varphi_{\mathrm{m}}}{\partial z}=0 ; \frac{\partial \varphi_{\mathrm{e}}}{\partial x}=0 ; \frac{\partial \varphi_{\mathrm{e}}}{\partial z}=0$

边界	类型	取值
阳极(a)、阴极(b)气体流道入口	质量入口	$m a = ρ a ξ a I a a 2F C H 2$ , $m c = ρ c ξ c I a c 4F C O 2$
阳极(a)、阴极(b)气体流道出口	压力出口	p_b,a, p_b,c
阳极(a)、阴极(b)双极板端面	壁面	$\varphi_{\mathrm{e}}=0 ; \frac{\partial \varphi_{\mathrm{m}}}{\partial y}=0 ; q_{\mathrm{h}, \text { cool }, \mathrm{a}}=\frac{q_{\mathrm{h}, \text { cool }}}{2} \quad \varphi_{\mathrm{e}}=U ; \frac{\partial \varphi_{\mathrm{m}}}{\partial y}=0 ; q_{\mathrm{h}, \text { cool, } \mathrm{a}}=\frac{q_{\mathrm{h}, \mathrm{cool}}}{2}$
侧面边界	对称边界	$\frac{\partial \varphi_{\mathrm{m}}}{\partial x}=0 ; \frac{\partial \varphi_{\mathrm{m}}}{\partial z}=0 ; \frac{\partial \varphi_{\mathrm{e}}}{\partial x}=0 ; \frac{\partial \varphi_{\mathrm{e}}}{\partial z}=0$

表3 边界条件

图4 实验测试中冷却液入口温度与单流道质量流量

图5 膨胀石墨三维单流道模型极化曲线与功率密度

图6 膨胀石墨三维单流道模型阴极冷却流道出口温度

图7 EGBP结构对极化曲线的影响

图8 EGBP结构对功率密度的影响

图9 不同EGBP结构(Ⅰ-Ⅳ)在输出电压0.675 V下CCL-CMPL界面处电流密度分布

图10 不同EGBP结构(Ⅰ-Ⅳ)下阴极冷却液出口温度

图11 不同EGBP结构(Ⅰ-Ⅳ)在2.1 A·cm-2下温度分布

图12 不同EGBP结构(Ⅰ-Ⅳ)在2.1 A·cm-2下阴极冷却液流动方向(直线3)温度分布

图13 不同EGBP结构(Ⅰ-Ⅳ)在2.1 A·cm-2下CCL-PEM界面处分布云图对比

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