SOC Stack Impedance Characterization and Identification Based on DRT and ADIS Methods

doi:10.15541/jim20150652

Abstract

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

CLC Number:

TQ174

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.

Figures/Tables 21

Fig. 1 Main analysis process of EIS

Fig. 2 Sketch of solid oxide cell and stack

Table 1 EIS test parameters

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

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

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

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

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

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

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

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)

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)

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)

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

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

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℃)

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

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)

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

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

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%

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)

References 19

[1]	WACHSMAN E D, LEE K T.Lowering the temperature of solid oxide fuel cells.Science, 2011, 334(6058): 935-939.
[2]	EBBESEN S D, JENSEN S H, HAUCH A,et al. High temperature electrolysis in alkaline cells, solid proton conducting cells, and solid oxide cells. Chemical Reviews, 2014, 114: 10697-10734.
[3]	YU B, ZHANG W Q, XU J M,et al. Status and research of highly efficient hydrogen production through high temperature steam electrolysis at INET. International Journal of Hydrogen Energy, 2009, 35(7): 2829-2835.
[4]	MAWDSLEY J R, CARTER J D, KROPF A J,et al.Post-test evaluation of oxygen electrodes from solid oxide electrolysis stacks. International Journal of Hydrogen Energy, 2009, 34(9): 4198-4207.
[5]	MENZLER N H, BATFALSKY P, GROß S,et al. Post-Test characterization of an SOFC short-stack after 17, 000 hours of steady operation. ECS Transactions, 2011, 35(1): 195-206.
[6]	NECHACHE A, CASSIR M, RINGUEDÉ A.Solid oxide electrolysis cell analysis by means of electrochemical impedance spectroscopy: review. Journal of Power Sources, 2014, 258(15): 164-181.
[7]	ORAZEM M E, TRIBOLLET B. Electrochemical Impedance Spectroscopy. J. Wiley & Sons, Hobo-ken,New Jersey, 2008, 153-162.
[8]	VIRKAR A V.Transport through mixed proton, oxygen ion and electron (hole) conductors: Goldman-Hodgkin-Katz type equation.Journal of Power Sources , 2009, 194(2): 753-762.
[9]	YU B, LIU M Y, ZHANG W Q,et al. Polarization loss of single solid oxide electrolysis cells and microstructural optimization of the cathode. Acta Physico-Chimica Sinica, 2011, 27(2): 395-402.
[10]	SCHICHLEIN H,MÜLLER A C, VOIGTS M,et al. Deconvolution of electrochemical impedance spectra for the identification of electrode reaction mechanisms in solid oxide fuel cells. Journal of Applied Electrochemistry, 2002, 32: 875-882.
[11]	LEONIDE A, SONN V, WEBER A,et al. Evaluation and modeling of the cell resistance in anode-supported solid oxide fuel cells. Journal of The Electrochemical Society, 2008, 155(1): B36-B41.
[12]	SCHONLEBER M, IVERS-TIFFEE E.Approximability of impedance spectra by RC elements and implications for impedance analysis.Electrochemistry Communications, 2015, 58(9): 15-19.
[13]	JENSEN S H, HAUCH A, HENDRIKSEN P V,et al. A method to separate process contributions in impedance spectra by variation of test conditions. Journal of The Electrochemical Society, 2007, 154(12): B1325-B1330.
[14]	EBBESEN S D, GRAVES C, HAUCH A,et al. Poisoning of solid oxide electrolysis cells by impurities. Journal of the Electrochemical Society, 2010, 157(10): B1419-B1429.
[15]	KUZNECOV M, OTSCHIK P, OBENAUS P,et al. Diffusion controlled oxygen transport and stability at the perovskite/ electrolyte interface. Solid State Ionics, 2003, 157(1-4): 371-378.
[16]	WEESE J.A reliable and fast method for the solution of Fredhol integral equations of the first kind based on Tikhonov regularization.Computer Physics Communications, 1992, 69(1): 99-111.
[17]	BARFOD R, HAGEN A, RAMOUSSE S,et al. Break down of losses in thin electrolyte SOFCs. Fuel Cells, 2006, 6(2): 141-145.
[18]	JORGENSEN M J, MOGENSEN M.Impedance of solid oxide fuel cell LSM/YSZ composite cathodes.Journal of The Electrochemical Society, 2001, 148(5): A433-A442.
[19]	FU Y.Theoretical and Experimental Study of Solid Oxide Fuel Cell (SOFC) Using Impedance Spectra. Massachusetts Institute of Technology, 2014.