湖南大学学报投稿最后

溶剂对导电聚吡咯防腐蚀性能的影响

李国希, 高桂红, 汤小辉, 孙涛, 谢香伦, 曾静 (湖南大学化学化工学院, 湖南长沙 410082)

摘要：采用循环伏安法在吡咯和NaClO4的乙腈溶液中或水溶液中在不锈钢表面制备了聚吡咯(PPy)膜. 用扫描电子显微镜观察PPy膜的表面形貌, 用1 mol/L H2SO4溶液中的动电位极化曲线和电化学阻抗谱研究PPy膜对不锈钢的防腐蚀性能. 结果表明, 两种PPy膜都是由球状粒子组成, 但在水溶液中制备的PPy膜结节较多. 有PPy膜保护的不锈钢的自腐蚀电位比不锈钢的显著正移, 自腐蚀电流密度从不锈钢的3580 μA/cm2下降到40 μA/cm2(水溶液)和9 μA/cm2(乙腈溶液). 乙腈中制备的PPy的界面电荷转移电阻总大于水中制备的PPy的界面电荷转移电阻. 在乙腈中制备的PPy膜对不锈钢有较好的抗腐蚀性能. 这是由于溶剂乙腈的亲核性较水小, 与中间聚合体的作用小, 终止链反应较难, 使得PPy聚合链共轭度长、结构缺陷少.

关键词：聚吡咯；不锈钢；防腐蚀；导电高分子中图分类号：O646 文献标识码：A

Effect of Solvents On Anticorrosion of Conducting

Polypyrrole

LI Guo Xi*, GAO Gui Hong, TANG Xiao Hui, SUN Tao, XIE Xiang Lun, ZENG Jing (College of Chemistry and Chemical Engineering, Hunan Univ, Changsha 410082) Abstract: The Polypyrrole(PPy) film was synthesized in pyrrole and NaClO4 aqueous solutions or acetonitrile solutions on stainless steel by cyclic voltammetry. The surface morphology of PPy was observed by SEM, and its anticorrosion property was investigated by potentiodynamic polarization curves in 1 mol/L H2SO4. As it turned out, it has more Spherical Particles' irregular stacking formed lump of breast gland that preparated in aqueous electrolyte. The PPy film shift the corrosion potential



作者简介: 李国希(1956-), 湖南娄底人, 湖南大学博士生导师

通讯联系人: 李国希. Tel：(0)[1**********], E-mail: [email protected]

of stainless steel visible to positive direction, and decrease the corrosion current density from 3580 μA/cm2 to 40 μA/cm2 and 9 μA/cm2. The impedance of interfacial charge transfer of PPy made in acetonitrile solutions is always greater than the other. The good corrosion resistance of PPy film polymerizated in acetonitrile solutions may be due to the effect of solvents on polymerization process. The Nucleophilicity of acetonitrile is smaller than water that effect little on middle polymer and difficult to end the chain reactions. It is made the conjugacy-lengths and have little structure defect.

Keywords: Polypyrrole; stainless steel; anticorrosion;conducting polymers

在电化学制备聚吡咯(PPy)时, 吡咯先氧化成阳离子自由基, 再由阳离子自由基发生偶合, 形成PPy[1, 2]. 溶剂的亲核性质对吡咯聚合有很大影响. 溶剂的亲核性越大, 溶剂分子与聚合过程中产生的带正电荷的中间产物的作用越强烈, 导致PPy膜的导电性和力学强度越低[3], 吡咯的聚合电位约为0.7 V(vs.SCE), 有机溶剂和水都可以用于吡咯电化学聚合. 有机溶剂具有本身不参加反应、吡咯的溶解度高、对基体金属的腐蚀性小和电化学窗口宽等优点. 常用的有机溶剂有乙腈和1,2-丙二醇碳酸酯, 支持电解质可采用NaClO4、NaBF4和R4NClO4. 关于在水溶液中制备PPy及其对金属防腐蚀性的研究比较多,在有机溶液中制备PPy的研究比较少.

本文采用循环伏安法在NaClO4的乙腈溶液中和水溶液中制备PPy膜, 研究溶剂性质对PPy防止不锈钢腐蚀性能的影响.

1 实验

采用循环伏安法在304不锈钢(SS,1 cm2)表面制备PPy膜, 辅助电极为大面积铂片, 参比电极为饱和甘汞电极(SCE). 水溶液中循环伏安电位扫描范围为0~0.8 V, 电位扫描速度为0.05 V/s, 聚合电量为0.8 C. 由于吡咯在乙腈溶液中在这个电位范围的聚合速度比较小,电位扫描范围改为0~0.9 V. 在0.1 mol/L吡咯+0.2 mol/L NaClO4的水溶液中制备的PPy标记为PPy(H2O), 在0.1 mol/L吡咯+0.2 mol/L NaClO4的乙腈溶液中制备的PPy标记为PPy(ACN). 不锈钢表面用1~5号金

相砂纸逐级打磨至镜面光亮后, 依次用酒精和二次蒸馏水清洗. 吡咯经蒸馏提纯后使用.

采用JSM-6700F扫描电子显微镜(SEM)观察PPy膜的形貌, 用动电位极化曲线和电化学阻抗谱(EIS)测量PPy膜对不锈钢在1 mol/L H2SO4溶液中的防腐蚀性能. 动电位扫描速度为0.002 V/s. 阻抗测试的频率范围为0.01~100 kHz, 正弦波信号幅值为8 mV. 电化学实验都采用CHI660b电化学工作站进行.

2 结果与讨论 2. 1 循环伏安曲线

i(mA/cm)

15th

10th 5th

1st

2nd

i(mA/cm)

-2

213th

10-1

0.0

0.2

0.4E/V

0.40.60.8

E /V

0.00.20.60.81.0

图1 在0.1 mol/L吡咯+0.2 mol/L NaClO4的水溶液(a)和在0.1 mol/L吡咯+0.2 mol/L

NaClO4的乙腈溶液(b)中的循环伏安曲线 Fig. 1 Cyclic voltammetry curve of stainless steel electrode in 0.1 mol/L pyrrole+0.2 mol/L NaClO4 aqueous solutions(a)and 0.1 mol/L pyrrole+0.2 mol/L NaClO4 acetonitrile solutions(b)

图1是不锈钢在0.1 mol/L吡咯+0.2 mol/L NaClO4的水溶液中和在0.1 mol/L吡咯+0.2 mol/L NaClO4的乙腈溶液中的循环伏安曲线. 在水溶液中, 第一圈循环伏安扫描时的吡咯聚合电位较高, 约为0.75 V(vs SCE), 聚合电流也较小；随扫描圈数的增加, 聚合电位负移至0.6 V, 聚合电流也增大. 在乙腈溶液中, 吡咯的聚合电位约为0.7 V, 也随扫描圈数增加而降低, 但降低幅度较小. 当扫描圈数较大时, 两种溶液在低电位时的氧化还原电流都随扫描圈数增加而增大, 但高电位时的氧化电流基本不变. 经过两圈扫描后不锈钢表面均有黑色的聚吡咯薄膜生成. 2. 2 聚吡咯膜的形貌

图2 PPy膜的扫描电子显微照片. a：PPy(H2O), b：PPy(ACN)

Fig. 2 SEM of Polypyrrole film. a：PPy(H2O), b：PPy(ACN)

图2是PPy膜的扫描电子显微照片. 在水和乙腈溶液中制备的PPy膜的表面形貌相似, 都是由球状粒子堆积组成. 但由于在水溶液中吡咯聚合电流密度大, 使PPy颗粒堆积比较快, 造成PPy膜的结节较多. 2. 3 极化曲线

logi/A cm

-2-3

-2

-4-5-6-7

-0.4

SS/PPy(ACN)SS/PPy(HO)

0.0

E/V

0.40.8

图3 SS和SS/PPy在1 mol/L H2SO4中的动电位极化曲线.点线为实验数据，实线为拟合数据

Fig. 3 Potentiodynamic polarization curves of SS and SS/PPy in 1 mol/L H2SO4 solution.

Point-line is experiment curves and solid line is the curve fitting

图3为不锈钢和PPy膜保护的不锈钢在1 mol/L H2SO4溶液中的动电位极化曲线. 没有PPy膜的不锈钢呈现典型的阳极钝化行为. 电极过程为电化学控制的阳极极化曲线符合iA=icorr[exp(a/a)-exp(-a/c)], 对极化曲线进行非线性拟合[4, 5], 结果如表1, PPy膜对不锈钢有很好的保护作用. 用PPy保护的不锈钢的自腐蚀电位比裸不锈钢正移0. 8 V以上, 自腐蚀电流密度从裸不锈钢的3580 μA/cm2分别下

降到40 μA/cm2(水溶液)和9 μA/cm2(乙腈溶液). 因为PPy膜具有氧化还原性[6, 7] 加速不锈钢表面钝化层的形成及其修复, 维持钝化金属基体表面较高的自腐蚀电位和较小的自腐蚀电流, 减缓金属的腐蚀[8, 9]. PPy膜还能机械阻隔腐蚀性溶液

[8, 10]

. PPy(ACN)的保护作用最好.

表1 SS和SS/PPy在1 mol/L H2SO4中的拟合电化学参数

Table 1 The electrochemical parameters of SS and SS/PPy in 1mol/L H2SO4

SS SS/PPy(H2O) SS/PPy(ACN)

Ecorr (V) -0.423 0.385 0.458

icorr (μA/cm2) 3580 40 9

a (V) 0.065 0.124 0.084

a (V)

0.560 0.032 0.077

2. 4电化学阻抗谱及等效电路

400

-Z

300

3002001000

100

cm -Z

200

100

200Z' /  cm

300

400

03060Z' /  cm

90120

图4 SS/PPy在1 mol/L H2SO4中的电化学阻抗谱. a: SS/PPy (ACN), b: SS/PPy (H2O)

Fig. 4 EIS for SS/PPy in 1 mol/L H2SO4 solution. a: SS/PPy (ACN), b: SS/PPy (H2O)

图4为SS/PPy浸在1 mol/L H2SO4溶液中的电化学阻抗谱. 在高频端的半圆与实轴的交点代表溶液的欧姆电阻(Rs), 阻抗谱的高频区为溶液/PPy膜界面的电荷转移电阻(Rct)和双电层电容(Cd1), 中低频区为Warburg阻抗(W)、PPy膜电阻(Rf1)以及膜电容(Cf); 低频区为不锈钢钝化膜[11]/溶液的界面双电层电容(Cd2)和钝化膜电阻(Rf2). 图5为SS/PPy电化学等效电路,等效电路的的非线性拟合曲线见图4.

图5 不锈钢/PPy膜在1 mol/LH2SO4溶液中浸泡测得的阻抗图等效电路 Fig. 5 Equivalent circuit of PPy-coated stainless steel in 1 mol/LH2SO4 solution

溶液电阻Rs的值很小(一般为1.5 Ω). 阻抗谱在高频区半圆的直径越大, 溶液/PPy膜的界面电荷转移电阻Rct越大[12]. 根据等效电路图5拟合得到SS/PPy(ACN)在浸泡5, 10和15天时的Rct分别为161, 208和274 Ω; SS/PPy(H2O)的Rct分别为13.5, 31和42 Ω. Rct与浸泡时间都呈线性关系, 随浸泡时间增加而增大. 这是因为硫酸破坏了PPy的结构, 导致PPy的电子的离域性减弱, PPy提供的电子较少, 电荷传递变困难. 不锈钢和PPy膜发生电化学反应, 在不锈钢表面生成保护层, 也使电荷转移电阻变大. 这都导致不锈钢的腐蚀速度降低.

在浸泡过程中, 在乙腈中制备的PPy的界面电荷转移电阻Rct总大于水中制备的PPy的Rct, 说明在乙腈中制备的PPy膜对不锈钢保护效果最好. 当PPy聚合时, 吡咯在电极表面氧化为阳离子自由基, 两个阳离子自由基发生偶合形成二聚体. 二聚体被氧化成自由基, 再形成四聚体. 经过一连串的氧化-偶合, 聚合度增大. 由于电负性较强的N原子上存在孤对电子, 因而部分吡咯单体与质子结合,为了维持电中性, 阴离子也掺杂到PPy链中. 溶剂分子进攻PPy链末端的自由基,形成C=O和C=CHC≡N键, 使链反应终止[13, 14]. 乙腈的亲核性比水小, 与中间聚合体的作用小, 终止链反应较难, 使得聚合链较长. 因此, 在乙腈中制备的PPy的共轭度长、结构缺陷少, 使SS/PPy(ACN)的防腐蚀性能较好.

3结论

PPy膜显著降低了不锈钢在1 mol/LH2SO4溶液中的腐蚀速度. PPy膜使不锈钢的自腐蚀电位正移0.8 V以上, 自腐蚀电流密度从裸不锈钢的3580 μA/cm2

下降

到40 μA/cm2(水溶液)和9 μA/cm2(乙腈溶液). 以乙腈为溶剂制备的PPy膜对不锈钢的防腐蚀性能较好. 参考文献

[1] GENIES E M, BIDAN G, DIAZ A F. Spectroelectrochemical study of Polypyrrole film [J].

Electroanalytical. Chemistry. 1983, 149(1-2):101-113.

[2] 李永舫. 导电聚合物的电化学制备和电化学性质研究[J]. 电化学. 2004, 10(4):369-378.

LI Yong-fang. Studies on the Electrochemical Preparation and Electrochemical Properties of Conducting Polymers. Electrochemistry, 2004, 10(4):369-378.

[3] OUYANG J Y, LI Y F. Effect of electrolyte solvent on the conductivity and structure of

as-prepared polypyrrole films[J]. Polymer, 1997, 38:1971-1976.

[4] HOSSEINI M G, SABOURIB M, SHAHRABI T. Corrosion protection of mild steel by

polypyrrole phosphate composite coating[J]. Progress in Organic Coating, 2007, 60(3):178-185.

[5] 蒋金武, 李国希, 高桂红等. 掺杂态和本征态聚苯胺对不锈钢的保护作用[J], 腐蚀与防

护. 2010, 31:936-938.

JIANG Jin-wu, LI Guo-xi, GAo Gui-hong, et al. Protection Performance of Doped and Eigenstate Polyaniline on Staninless Steel[J]. Corrossion Protection, 2010, 31:936-938. [6] REDONDO M I, BRESLIN C B. Polypyrrole electrodeposited on copper from an aqueous

phosphate solution:Corrosion protection properties[J]. Corrosion Science, 2007, 49:1765-1776.

[7] BAZZAOUI M, MARTINS J I, COSTA S C, et al. Sweet aqueous solution for

electrochemical synthesis of polypyrrole: Part 2. On ferrous metals[J], Electrochimica Acta, 2006, 51:4516-4527.

[8] TÜKEN T, YAZICI B, ERBIL M. The electrochemical synthesis and corrosion performance

of polyprrole on brass and copper[J]. Progress Organic Coating, 2004, 51(2):152-160. [9] GRGUR B N, KRSTAJIĆ N V, VOJNOVIĆ M V, et al. The influence of polypyrrole films on

the corrosion behavior of iron in sulfate acid solutions[J], Progress Organic Coating, 1998,

3(1):l-6.

[10] DINISE M, LENZ M D, FERREIRA A J, et al. Application of polypyrrole/TiO2 composite

films as corrosion protection of mild steel[J]. Electroanalytical Chemistry, 2003, 540:35-44. [11] 朱日龙, 李国希, 刘晓阳. 聚吡咯的电化学合成及其对不锈钢的保护作用, 中国腐蚀与

防护学报, 2008, 2:7-10.

ZHU Ri-Long, LI Guo-xi, LIU Xiao-yang. Electrosynthesis of Polypyrrole and Corrosion Protection for Stainless Steel [J]. Journal of Chinese Socience Corrosion Protection, 2008, 2:7-10.

[12] EHRENBECK C, JÜTTNER K, LUDWIG S, et al. The electrochemical impedance of a

free-standing polypyrrole membrane[J]. Electrochimica Acta, 1998, 43(19-20):2781-2789. [13] GABRIELLI C, HAAS O, TAKENOUTI H. Impedance analysis of electrodes modified with

a reversible redox polymer film[J]. Apply Electrochemistry, 1987, 17(1):82-90.

[14] SAIDMAN S B, BESSONE J B. Electrochemical preparation and characterization of

polypyrrole on aluminium in aqueoussolution[J]. Electroanalytical Chemistry, 2002, 521:87-91.

溶剂对导电聚吡咯防腐蚀性能的影响

李国希, 高桂红, 汤小辉, 孙涛, 谢香伦, 曾静 (湖南大学化学化工学院, 湖南长沙 410082)

关键词：聚吡咯；不锈钢；防腐蚀；导电高分子中图分类号：O646 文献标识码：A

Effect of Solvents On Anticorrosion of Conducting

Polypyrrole



作者简介: 李国希(1956-), 湖南娄底人, 湖南大学博士生导师

通讯联系人: 李国希. Tel：(0)[1**********], E-mail: [email protected]

Keywords: Polypyrrole; stainless steel; anticorrosion;conducting polymers

本文采用循环伏安法在NaClO4的乙腈溶液中和水溶液中制备PPy膜, 研究溶剂性质对PPy防止不锈钢腐蚀性能的影响.

1 实验

相砂纸逐级打磨至镜面光亮后, 依次用酒精和二次蒸馏水清洗. 吡咯经蒸馏提纯后使用.

2 结果与讨论 2. 1 循环伏安曲线

i(mA/cm)

15th

10th 5th

1st

2nd

i(mA/cm)

-2

213th

10-1

0.0

0.2

0.4E/V

0.40.60.8

E /V

0.00.20.60.81.0

图1 在0.1 mol/L吡咯+0.2 mol/L NaClO4的水溶液(a)和在0.1 mol/L吡咯+0.2 mol/L

图2 PPy膜的扫描电子显微照片. a：PPy(H2O), b：PPy(ACN)

Fig. 2 SEM of Polypyrrole film. a：PPy(H2O), b：PPy(ACN)

logi/A cm

-2-3

-2

-4-5-6-7

-0.4

SS/PPy(ACN)SS/PPy(HO)

0.0

E/V

0.40.8

图3 SS和SS/PPy在1 mol/L H2SO4中的动电位极化曲线.点线为实验数据，实线为拟合数据

Fig. 3 Potentiodynamic polarization curves of SS and SS/PPy in 1 mol/L H2SO4 solution.

Point-line is experiment curves and solid line is the curve fitting

[8, 10]

. PPy(ACN)的保护作用最好.

表1 SS和SS/PPy在1 mol/L H2SO4中的拟合电化学参数

Table 1 The electrochemical parameters of SS and SS/PPy in 1mol/L H2SO4

SS SS/PPy(H2O) SS/PPy(ACN)

Ecorr (V) -0.423 0.385 0.458

icorr (μA/cm2) 3580 40 9

a (V) 0.065 0.124 0.084

a (V)

0.560 0.032 0.077

2. 4电化学阻抗谱及等效电路

400

-Z

300

3002001000

100

cm -Z

200

100

200Z' /  cm

300

400

03060Z' /  cm

90120

图4 SS/PPy在1 mol/L H2SO4中的电化学阻抗谱. a: SS/PPy (ACN), b: SS/PPy (H2O)

Fig. 4 EIS for SS/PPy in 1 mol/L H2SO4 solution. a: SS/PPy (ACN), b: SS/PPy (H2O)

图5 不锈钢/PPy膜在1 mol/LH2SO4溶液中浸泡测得的阻抗图等效电路 Fig. 5 Equivalent circuit of PPy-coated stainless steel in 1 mol/LH2SO4 solution

3结论

PPy膜显著降低了不锈钢在1 mol/LH2SO4溶液中的腐蚀速度. PPy膜使不锈钢的自腐蚀电位正移0.8 V以上, 自腐蚀电流密度从裸不锈钢的3580 μA/cm2

下降

到40 μA/cm2(水溶液)和9 μA/cm2(乙腈溶液). 以乙腈为溶剂制备的PPy膜对不锈钢的防腐蚀性能较好. 参考文献

[1] GENIES E M, BIDAN G, DIAZ A F. Spectroelectrochemical study of Polypyrrole film [J].

Electroanalytical. Chemistry. 1983, 149(1-2):101-113.

[2] 李永舫. 导电聚合物的电化学制备和电化学性质研究[J]. 电化学. 2004, 10(4):369-378.

LI Yong-fang. Studies on the Electrochemical Preparation and Electrochemical Properties of Conducting Polymers. Electrochemistry, 2004, 10(4):369-378.

[3] OUYANG J Y, LI Y F. Effect of electrolyte solvent on the conductivity and structure of

as-prepared polypyrrole films[J]. Polymer, 1997, 38:1971-1976.

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