全钒液流电池用磺化聚醚醚酮/锂皂石质子膜的结构及性能

doi:10.7503/cjcu20190190

摘要/Abstract

摘要：

通过溶液流延法制备了磺化聚醚醚酮/锂皂石(SPEEK/Lap)复合膜, 对其物理化学性质、机械性能、化学稳定性及单电池性能进行了测试. 在SPEEK基质中引入的Lap有效改善了复合膜的质子传导率、溶胀率和机械性能. 当Lap添加量(质量分数)从0.2%增到1.5%时, 复合膜的质子传导率随之增加(19.9~23.6 mS/cm). SPEEK/Lap-0.2复合膜的自放电时间为57.2 h, 是Nafion 117膜的2.4倍和纯SPEEK膜的1.5倍. 在80 mA/cm ²电流密度下, SPEEK/Lap-0.2复合膜的电压效率(VE, 86.5%)和能量效率(EE, 84.0%)明显高于Nafion 117膜(VE: 83.8%, EE: 80.7%)和纯SPEEK膜(VE: 81.4%, EE: 78.9%). 同时, SPEEK/Lap-0.2复合膜经100次充放电循环测试后具有良好的循环稳定性和结构稳定性.

关键词: 质子交换膜, 磺化聚醚醚酮, 锂皂石, 全钒液流电池

Abstract:

A series of sulfonated poly(ether ether ketone)/laponite(SPEEK/Lap) composite membranes was prepared by solution-casting method using SPEEK with a sulfonation degree of 58% as membrane matrix. The membrane properties such as water uptake(WU), swelling ratio(SR), proton conductivity(σ), vanadium ion permeability and ion selectivity were detailly characterized and discussed. The results show that the introduced Lap nanofillers effectively improve σ, SR and mechanical properties of SPEEK composite membranes. The tensile strength of the SPEEK/Lap-0.2 composite membrane is 1.64 times that of pure SPEEK membrane. When the mass fraction of Lap increases from 0.2% to 1.5%, σ(19.9—23.6 mS/cm) increases accordingly. The ion selectivity of SPEEK/Lap-0.2 composite membrane is the best(5.55×10 ³ S·min·cm ^-3), which is about 1.39 times that of Nafion 117 membrane(3.99 S·min·cm ^-3). In the single cell test, the self-discharge time of SPEEK/Lap-0.2 composite membrane is 57.2 h, which is 2.4 times that of Nafion 117 and 1.5 times that of pure SPEEK membrane. At a current density of 80 mA/cm ², the voltage efficiency(VE, 86.5%) and energy efficiency(EE, 84.0%) of SPEEK/Lap-0.2 composite membrane are much higher than those of Nafion 117(VE: 83.8%, EE: 80.7%) and SPEEK membrane(VE: 81.4%, EE: 78.9%). During the 100 times charge-discharge test, SPEEK/Lap-0.2 composite membrane exhibits a stable energy efficiency, proving its good structure stability. In addition, SPEEK/Lap composite membranes exhibit a higher chemical stability in harsh oxidizing environment as compared with SPEEK membrane. Laponite nanofillers demonstrate a promising application as the low-cost high proton conductor, which can be used to prepare the proton exchange membrane(PEM) with high ion selectivity and low vanadium ion permeability for vanadium redox flow battery(VRFB) application.

Key words: Proton exchange membrane, Sulfonated poly(ether ether ketone), Laponite, Vanadium redox flow battery

中图分类号:

O646
O631

TrendMD:

刘博,邹楠,张雨霞,石海峰. 全钒液流电池用磺化聚醚醚酮/锂皂石质子膜的结构及性能. 高等学校化学学报, 2019, 40(10): 2186.

LIU Bo,ZOU Nan,ZHANG Yuxia,SHI Haifeng. Structure and Properties of Sulfonated Poly(ether ether ketone)/Laponite Proton Exchange Membrane for All Vanadium Redox Flow Battery ^†. Chem. J. Chinese Universities, 2019, 40(10): 2186.

图/表 10

Fig.1 FTIR spectra of SPEEK(a), SPEEK/Lap-0.2(b), SPEEK/Lap-0.5(c), SPEEK/Lap-1(d), SPEEK/Lap-1.5(e) membranes

Fig.2 Cross-section SEM images(A1—D1) and the relevant EDX element mapping of Mg(A2—D2) and Si(A3—D3) of composite membrans SPEEK/Lap-0.2(A1—A3), SPEEK/Lap-0.5(B1—B3), SPEEK/Lap-1(C1—C3) and SPEEK/Lap-1.5(D1—D3)

Table 1 Physicochemical properties of Nafion 117, SPEEK and SPEEK/Lap-x membranes

Sample	Thickness/ μm	IEC/ (mmol·g^-1)	WU(%)	SR_in-plane(%)	SR_{through-plane}(%)	σ/ (mS·cm^-1)	Tensile strength/ MPa	Tensile modulus/ GPa
Nafion 117	186±1	0.88±0.01	21.1±0.3	28.9±0.4	23.5±0.2	26.8±0.3	19.4±0.3	0.11±0.03
SPEEK	81±1	1.74±0.01	39.9±0.4	15.6±0.2	14.7±0.1	18.6±0.3	37.4±0.3	0.90±0.05
SPEEK/Lap-0.2	80±1	1.74±0.01	39.6±0.3	11.1±0.1	8.6±0.1	19.9±0.2	61.4±0.3	1.26±0.07
SPEEK/Lap-0.5	81±1	1.75±0.01	39.7±0.2	12.0±0.1	9.8±0.1	20.6±0.3	62.0±0.4	1.25±0.07
SPEEK/Lap-1.0	82±1	1.81±0.01	41.3±0.3	12.2±0.1	10.9±0.1	22.8±0.4	66.3±0.4	1.62±0.05
SPEEK/Lap-1.5	81±1	1.87±0.01	43.8±0.4	13.4±0.2	12.6±0.1	23.6±0.4	68.5±0.4	1.75±0.07

Fig.3 Vanadium ion permeability(A) and ion selectivity(B) of SPEEK/Lap-x and Nafion 117 membranes a. Nafion117; b. SPEEK; c. SPEEK/Lap-0.2; d. SPEEK/Lap-0.5; e. SPEEK/Lap-1.0; f. SPEEK/Lap-1.5.

Fig.4 VRFB efficiency of Nafion 117(a), SPEEK(b) and SPEEK/Lap-0.2(c) at current density of 80 mA/cm2

Fig.5 Self-discharge curves of Nafion 117(a), SPEEK(b) and SPEEK/Lap-0.2(c) membranes

Table 2 VRFB performance with different composite membranes

Membrane	Current density/(mA·cm^-2)	VE(%)	EE(%)	Ref.
SPEEK/Lap-0.2	80	86.5	84	This work
SPEEK/g-C₃N₄-1.5	30	85.7	83.6	[16]
SPEEK/SGO-3	30	84.8	81.1	[19]
SPEEK/PPD-GO-1	30	85.4	82.5	[24]
SPEEK/PAN-20	80	86.8	83.5	[30]

Fig.6 Cycling efficiencies of Nafion 117 and SPEEK/Lap-0.2 membranes at 50 mA/cm2 during 100 charge-discharge cycles

Fig.7 Charge capacity retention of Nafion 117(a) and SPEEK/Lap-0.2(b) membrane at 50 mA/cm2 during 100 charge-discharge cycles

Table 3 Chemical stability of Nafion 117, SPEEK, SPEEK/Lap-0.2 and SPEEK/Lap-1.5 after soaked by 1.5 mol/L VO2+ solution for 20 d

Membrane	Mass loss(%)	Reductionrate rate of V $O 2 +$ to VO²⁺(%)	Decreased tensile strength(%)
Nafion 117	1.1	1.6	12.1
SPEEK	3.5	4.3	22.4
SPEEK/Lap-0.2	1.7	3.3	15.3
SPEEK/Lap-1.5	1.3	3.0	13.5

Table 3 Chemical stability of Nafion 117, SPEEK, SPEEK/Lap-0.2 and SPEEK/Lap-1.5 after soaked by 1.5 mol/L VO2+ solution for 20 d

Membrane	Mass loss(%)	Reductionrate rate of V $O 2 +$ to VO²⁺(%)	Decreased tensile strength(%)
Nafion 117	1.1	1.6	12.1
SPEEK	3.5	4.3	22.4
SPEEK/Lap-0.2	1.7	3.3	15.3
SPEEK/Lap-1.5	1.3	3.0	13.5

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