基于DRT和ADIS的SOFC/SOEC电堆电化学阻抗谱研究

doi:10.15541/jim20150652

摘要/Abstract

摘要：

固体氧化物燃料电池(SOFC)和固体氧化物电解池(SOEC)电堆的电化学分析和诊断是国际上的研究难点。明确多片电堆的本征电化学反应机理和性能规律, 是SOFC/SOEC技术实用化的关键。本研究采用弛豫时间分布法(DRT)耦合阻抗谱差异分析法(ADIS)对电堆在燃料电池模式和电解池模式下的复杂电化学行为进行了研究, 通过弛豫时间解析出各个过程对应的特征峰, 区分出不同的物理化学过程。研究表明, 电堆在SOFC模式运行时, 其氢电极含水量应大于20%, 而SOEC模式运行时, 含水量应小于80%, 以最小化电池的气体扩散阻抗。本方法可应用于SOFC/SOEC电堆的分析诊断, 简化电堆测量分析的复杂性, 有助于电堆衰减机理和原因的实时诊断, 并对电堆性能提高给出理论依据和指导建议。

关键词: 电化学阻抗谱, 弛豫时间分布法, 固体氧化物电解池, 阻抗谱差异分析法, 衰减机理

Abstract:

Electrochemical analysis and diagnosis of the SOC stacks, including Solid Oxide Fuel Cells (SOFC) and Solid Oxide Electrolysis Cells (SOEC), are one of the research challenges in world. In order to optimize performance and realize practical SOC application, it is crucial to investigate kinetic mechanisms and reaction principle of the multiple-cells stack. In this paper, the relaxation time distribution method (DRT) combined with the analysis of difference in impedance spectra method (ADIS) were employed to research the complex electrochemical behavior of SOC stacks under different operation modes. The DRT characteristic peaks were identified through the analysis and as-segment of the relaxation time. The changes in the DRT peaks were correlated with the different electrochemical process. The research achievements indicate that the water content should be more than 20% when operated at SOFC mode, while less than 80% when operated at SOEC mode to minimize the gas diffusion resistance. The research achievements can provide theoretical data and establish technical foundation for the further study and application of this novel method, which can reduce the SOC complexity of EIS analysis, apply for the degradation identification and online diagnosis of stacks, and help to improve the SOC performance.

Key words: electrochemical impedance spectroscopy, distribution of relaxation times, solid oxide electrolysis cell, analysis of the difference in impedance spectra, degradation mechanisms

中图分类号:

TQ174

王雪, 张文强, 于波, 陈靖. 基于DRT和ADIS的SOFC/SOEC电堆电化学阻抗谱研究[J]. 无机材料学报, 2016, 31(12): 1279-1288.

WANG Xue, ZHANG Wen-Qiang, YU Bo, CHEN Jing. SOC Stack Impedance Characterization and Identification Based on DRT and ADIS Methods[J]. Journal of Inorganic Materials, 2016, 31(12): 1279-1288.

图/表 21

图1 EIS分析流程图

Fig. 1 Main analysis process of EIS

图2 电池片与电堆结构示意图

Fig. 2 Sketch of solid oxide cell and stack

表1 阻抗测试参数

Table 1 EIS test parameters

Item	Parameter
DC current/A	5
AC current/A	2
Frequency range /kHz	10
Number of test points	10

图3 典型的K-K关系图

Fig. 3 Kramers-Kronig test residuals of a typical impedance spectrum

图4 SOFC和SOEC模式下Cell-1和Cell-2的阻抗谱(a)以及I-V曲线(b)

Fig. 4 Impedance spectra (a) and I-V curves (b) of Cell-1 and Cell-2 in SOEC&SOFC mode

表2 阻抗谱和I-V曲线所得面电阻比较表

Table 2 Comparison of ASR tested from I-V curves & impedance spectra

Measurement	Cell-1		Cell-2
Measurement	SOFC	SOEC	SOFC	SOEC
EIS/ (Ω·cm^-2)	0.20	0.20	0.18	0.18
IV/ (Ω·cm^-2)	0.22	0.21	0.20	0.19

图5 SOFC模式下四片电堆的初始I-V曲线

Fig. 5 Initial I-V curves of a 4-cell stack in SOFC mode

图6 阻抗与氧分压的(a) Nyquist曲线和(b) Bode曲线

Fig. 6 Dependence of (a) Nyquist plot and (b) Bode plot on oxygen partial pressures

图7 阻抗与氧分压的ADIS法解谱和ADIS修正过的DRT方法解谱

Fig. 7 Dependence of ADIS plot and (b) DRT plot modified by ADIS on oxygen partial pressures

图8 阻抗与氧电极侧氧分压的关系DRT图

Fig. 8 Dependence of DRT plot on oxygen partial pressure of oxygen electrode^ (T = 700℃, SOFC mode, 80%H2 and 20% H2O in the hydrogen electrode)

图9 阻抗与氢电极侧水含量的(a) ADIS图和(b) DRT图

Fig. 9 Dependence of (a) ADIS plot and (b) DRT plot on steam content of the hydrogen electrode^(T = 700℃, SOFC mode, 0~30% H2O in the hydrogen electrode)

图10 阻抗与氢电极侧氢气流量(a)和与氢电极侧惰性载气流量(b)的DRT图

Fig. 10 Dependence of DRT plot on hydrogen flow rate of the hydrogen electrode (a), and on nitrogen flow rate of the hydrogen electrode (b)^(T = 700℃, SOFC mode, 100%H2 or 100%N2 in the hydrogen electrode)

图11 (a)氢电极侧水含量和(b)氢电极侧惰性载气含量对阻抗的影响

Fig. 11 Dependence of DRT plot on steam content of the hydrogen electrode (a) and on nitrogen flow rate of the hydrogen electrode (b)

图12 阻抗与温度关系的DRT图

Fig. 12 Dependence of DRT plot on operating temperature^(a) SOFC mode, 20%H2O in the hydrogen electrode, air in the oxygen electrode; (b) SOEC mode, 80%H2O in the hydrogen electrode, air in the oxygen electrode

图13 可逆电池的Arrhenius曲线

Fig. 13 Arrhenius plots of the reversible SOC^(a) SOFC mode; (b) SOEC mode (50%H2+50%H2O in the hydrogen electrode, air in the oxygen electrode, Temperature range: 700℃~750℃)

表3 DRT特征峰对照表

Table 3 Processes identified by DRT analysis

Process	Equivalent circuit	Frequency range /Hz	Dependencies	Physical process
P1	RQ	0.01-1		Gas diffusion in oxygen electrode
P2	RQ	1-10	, p_Ar,	Gas diffusion in substrate (fuel electrode) overlapped with gas conversion impedance
P3	Gerischer	10-100		Chemical surface exchange of O₂ and O^2- bulk diffusion in air electrode
P4	RQ	100-10000		Charge transfer reactions and ionic transport in YSZ and TPB

图14 SOFC模式下Cell-2和Cell-3在不同条件下的DRT曲线

Fig. 14 DRT plots of the Cell-2 and Cell-3 under different conditions in SOFC mode Change of gas composition of hydrogen electrode (a), gas composition of oxygen electrode (b) and operating temperature (c)

图15 Cell-2和Cell-3的欧姆阻抗和极化阻抗对比

Fig. 15 Comparison of the ohm impedance and polarization impedance for Cell-2 and Cell-3

图16 SOFC模式下Cell-2和Cell-3的Arrhenius曲线

Fig. 16 Arrhenius plots of the Cell-2 and Cell-3 in SOFC mode

表4 Cell-2和Cell-3衰减前后阻抗对比

Table 4 Comparison of the resistances of cell-2 and cell-3 before and after degradation

	Before degradation		After degradation		Impedance growth rate
	Cell-2	Cell-3	Cell-2	Cell-3	Cell-2	Cell-3
Ohmic resistance/ (Ω·cm^-2)	0.612	0.471	1.010	0.485	65%	3%
Polarization impedance /(Ω·cm^-2)	1.029	1.066	2.521	1.511	145%	42%

图17 衰减前后DRT图

Fig. 17 DRT plots of the cell-2 and cell-3 before and after degradation^(T=700℃, SOECmode, 100%H2 in the hydrogen electrode, air in the oxygen electrode)

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