US 12,424,642 B1 · Prediction method of electrochemical and mechanical performances in SOFC cold and hot cycle

Abstract

The present disclosure provides a prediction method of electrochemical and mechanical performances of a Solid Oxide Fuel Cell (SOFC) in a cold-hot cycle, and belongs to the technical field of SOFCs. In the present disclosure, a cold-hot cycle test is performed on SOFC pile, a polarization curve and an electrochemical impedance spectroscopy are measured by an electrochemical workstation, and contributions of different electrode reaction processes to voltage attenuation are analyzed quantitatively; the mechanical performance (bending strength, elastic modulus and hardness) after different numbers of cold-hot cycle services is tested, and based on change of Ni particles, the electrochemical performance and the mechanical performance of the SOFC pile are quantitatively associated; an attenuation coupling relationship of the electrochemical performance and the mechanical performance of the SOFC pile is disclosed and an attenuation theory model of the electrochemical performance and the mechanical performance of the SOFC pile is built. In this way, a change law of the electrochemical performance and the mechanical performance of the SOFC pile after different numbers of cold-hot cycles and a cold-hot cycle service life of the SOFC pile can be accurately predicted, which is of great significance to improve the thermal shock resistance of the cold-hot cycles of the SOFC pile, so as to promote SOFC commercialization applications.

A prediction method of electrochemical performance and mechanical performance of a Solid Oxide Fuel Cell (SOFC) in a cold-hot cycle, comprising the following steps:

at step S1, preparing composition materials of an SOFC pile, completing assembling and test preparation work of an SOFC pile power generation and test system, and determining operation parameters of a cold-hot cycle test of the SOFC pile based on actual service working condition;
at step S2, by using the SOFC pile power generation and test system, carrying out the cold-hot cycle test of the SOFC, and by using an electronic load controller and an electrochemical workstation, collecting a polarization curve and an electrochemical impedance spectroscopy of the SOFC pile during each cold-hot cycle test;
at step S3, by using a distribution of relaxation time method and an equivalent circuit model, performing analysis and fitting processing on electrochemical impedance spectroscopy data of the SOFC pile and calculating voltage losses resulting from each of electrochemical reaction processes of the SOFC and contribution values to voltage attenuations in the cold-hot cycles;
at step S4, testing a mechanical performance of cells in the SOFC pile after different numbers of cold-hot cycle services;
at step S5, by using scanning electron microscope and X-ray energy dispersive spectrometer, analyzing a micro-structural change law of each composition part of the SOFC pile after and before the cold-hot cycle test of the SOFC, and calculating a content and an average particle diameter of each element in the SOFC pile;
at step S6, disclosing an attenuation coupling relationship of the electrochemical performance and the mechanical performance of the SOFC pile and building an attenuation theory model of the electrochemical performance and the mechanical performance of the SOFC pile;
based on a change law of a SOFC output voltage, a bending strength of the cells in the SOFC pile, an average equivalent circular diameter φECD of Ni element particles, an elastic modulus and a hardness along with a number of cold-hot cycles, a theory model showing the attenuation coupling relationship of the electrochemical performance and the mechanical performance of the SOFC pile is built:
y
=
-
C
n
·
ln
⁡
(
x
)
+
C
;
(
5
)
wherein y is a parameter value of any performance of the SOFC output voltage, the bending strength of the cells in the SOFC pile, the average equivalent circular diameter φECD of the Ni element particles, the elastic modulus and the hardness;
x is a number of cold-hot cycles, wherein x≥1 and is a positive integer;
C is an initial value of any performance of the SOFC output voltage, the bending strength of the cells in the SOFC pile, the average equivalent circular diameter φECD of the Ni element particles, the elastic modulus and the hardness;
the specific value of Cis obtained by test in the first cold-hot cycle;
n is an attenuation coefficient;
and
at step S7, predicting the electrochemical performance and the mechanical performance of the SOFC pile after different numbers of cold-hot cycles and a cold-hot cycle service life of the SOFC pile;
wherein in the step S3, by using the distribution of relaxation time method, the electrochemical impedance spectroscopy data in the cold-hot cycle process is processed, and based on characteristics of different electrochemical reaction processes in the SOFC pile, peaks on a distribution of relaxation time diagram are distinguished to qualitatively distinguish a change law of different electrochemical reaction processes;
based on a relaxation time distribution law obtained by the distribution of relaxation time method, the electrochemical reaction processes are determined and a reasonable initial value is provided for an element of the equivalent circuit model;
the equivalent circuit model formed by ohmic impedance Rohm, inductance L and RQ unit is used to fit the electrochemical impedance spectroscopy data, quantitatively determine contributions of different electrochemical reaction processes to a voltage attenuation in the cold-hot cycle and determine a contribution value of each electrochemical reaction process to the voltage attenuation as well as ranking;
in the distribution of relaxation time method, a total impedance Z(ω) of the SOFC pile represents a sum of the ohmic impedance Rohm and a polarization impedance Rpol;
the relaxation time τ refers to a time required for the electrochemical reaction process to achieve an equilibrium state;
wherein the polarization impedance represents an integral of the relaxation time τ from 0 to ∞ seconds;
the expression of the total impedance Z(ω) is shown below:
Z
⁡
(
ω
)
=
R
o
⁢
h
⁢
m
+
R
p
⁢
o
⁢
l
=
R
o
⁢
h
⁢
m
+
∫
0
∞
γ
⁡
(
ln
⁢
τ
)
1
+
j
⁢
ω
⁢
τ
⁢
d
⁢
ln
⁢
τ
;
(
1
)
wherein j and ω are an imaginary unit and an angular frequency;
by solving γ(τ) corresponding to different relaxation times τ, the distribution of relaxation time diagram corresponding to the electrochemical impedance spectroscopy data is obtained, with the expression of the γ(τ) shown below:
γ
⁡
(
τ
)
=
R
2
⁢
π
·
sin
[
(
1
-
n
)
⁢
π
]
cos
⁢
h
[
n
⁢
ln
⁡
(
τ
/
τ
0
)
]
-
cos
[
(
1
-
n
)
⁢
π
]
;
(
2
)
wherein R is resistance, cosh is hyperbolic cosine function, n is an electron transfer number, τ0 is a relaxation time at an initial moment;
a characteristic frequency f is expressed below:
f
=
1
2
⁢
π
⁢
τ
;
(
3
)
in the equivalent circuit model, the equivalent circuit model is formed by series-connected ohmic impedance Rohm, inductance L and RQ unit, wherein the RQ unit is formed by parallel-connecting the resistance R and a constant phase element (CPE), and each RQ unit represents an electrode process on a specific time scale;
the total impedance of the equivalent circuit model is calculated in the following formula:
Z
⁡
(
ω
)
=
R
o
⁢
h
⁢
m
+
2
⁢
j
⁢
π
⁢
fL
self
+
2
⁢
π
⁢
fL
wire
+
∑
R
1
+
(
j
⁢
ωτ
)
α
+
∑
R
1
+
j
⁢
ω
⁢
τ
;
(
4
)
wherein Lself is a self-inductance of the equivalent circuit, Lwire is a mathematical compensation term for a mutual inductance, and Lwire is used to eliminate a disturbance between the self-inductance and the mutual inductance in a calculation result of the equivalent circuit model.

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Prediction method of electrochemical and mechanical performances in SOFC cold and hot cycle

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Prediction method of electrochemical and mechanical performances in SOFC cold and hot cycle

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Abstract

Claims6