Electrical and electrochemical properties of some cobalt phthalocyanine based electrocatalysts

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ELECTRICAL AND ELECTROCHEMICAL PROPERTIES OF SOME COBALT

PHTHALOCYANINE BASED ELECTROCATALYSTS

by

NEELAM PHOUGAT

NE - r

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t7 ft/'()

CENTRE FOR RURAL DEVELOPMENT Et APPROPRIATE TECHNOLOGY

Submitted

in fulfilment of the requirements of the degree of

DOCTOR OF PHILOSOPHY

Aivm-tit /( 9 ²

to the

INDIAN INSTITUTE OF TECHNOLOGY, DELHI INDIA

December 1991

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CERTIFICATE

This is to certify that the thesis entitled ELECTRICAL AND ELECTROCHEMICAL PROPERTIES OF SOME COBALT PHTHALOCYANINE BASED ELECTROCATALYST submitted by Mrs. NEELAM PHOUGAT ( NEE - MANN ) to the Indian Institute of Technology, Delhi for the Award of Degree of DOCTOR OF PHILOSOPHY in Rural Development and Appropriate Technology is a record of bonafide research work carried out by her . Mrs. NEELAM PHOUGAT has worked under our supervision and guidance and has fulfilled the requirement for submission of this thesis . In our opinion , the thesis is worthy of consideration for the award of degree of DOCTOR OF PHILOSOPHY in accordance with regulations of the Institute .

The research work embodied in this thesis have not been submitted , in part , or in full , to any other University or Institute for the Award of any other Degree or Diploma.

TAL

"1,1 •.

( SANTOSH ).

Senior Scientific Officer Centre for Rural Development and Appropriate Technology, Indian Institute of

Technology, Delhi Date :

Place :Delhi

0

(P. VASUDEVAN ) Professor and Head

Centre for Rural Development and Appropriate Technology,

Indian Institute of Technology, Delhi

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ACKNOWLEDGEMENT

I.have great pleasure in expressing deep sense of gratitude to my research supervisors professor (Mrs.) P. Vasudevan and Dr.

(Mrs.) Santosh for their valuable guidance constant encouragement , fruitful discussions and kind help at every stage of this work.

I am extremely grateful to Dr. A. K. Shukla, Prof. R. R. Gaur, Prof. P. L. Thar and Prof, S. C. Mathur for their support, encouragement and help.

I am. thankful to Sh. Sube Singh Mann, Sh. S. S. Sharma, Dr. A.

K. Tripathi, Dr. Anita Tripathi, Sh. R. C. Sharma, Sh. Jaiprakash, Sh. Jagat Singh, Sh. M. S. Bedi, Sh. Ramashankar, Miss Sarita Laxmi, Sh. S. Murli, Dr. J. K. Srivastava and Dr. R. Sekar for their kind help, co - operation and encouragement during the course of this work.

I wish to express my thanks to all the faculty members , staff members and students of the Centre for Rural Development and.

Appropriate Technology for their kind help and co - operation.

(NEELAM PHOUGAT)

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ABSTRACT

Phthalocyanines ( both monomers and polymers ) have a highly conjugated structure and exhibit good stability to heat, light, moisture and air,making them useful under different environmental conditions. Commercial application of these compounds as pigment is well known and other .uses as catalyst, electrocatalysts, gas detectors etc. are also reported. Phthalocyanines are also found to exhibit good semiconductor properties. The versatility of the system lies in the possibility of substituting metal ion centrally for hydrogen ion in the macrocycle ligand combined with the possibility of peripheral substitution and as well as oligomerization and polymerization. Thus, this system presents exciting prospects for developing the desired kind of properties for any given application through structural modifications. It is undoubtly possible to prepare semiconducting materials from phthalocyanines, but owing to considerable variations in the reported values, an indepth study is required. Without a full scale understanding of the effect of structural modifications on the electrical and electrochemical behaviour, reliable applications in the industry would not be possible.

In view of this, it was proposed to synthesize and study the electrical and electrochemical properties of following phthalocyanines for establishing structure property correlations and evaluate them for applications in electronic and electrocatalytic systems :

1. Cobalt phthalocyanine polymer with imido end groups (A)

2. Cobalt phthalocyanine polymer with carboxylic end groups (B) 3. Cobalt [bis(3,4-phthalimidocarbonyl)]phthalocyanine (C)

4. Cobalt [bis(3,4-dicarboxybenzoy1)]phthalocyanine (D)

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5. Cobalt[bis(3,4-dicarboxybenzoyl)]phthalocyanine dianhydride (E) 6. N,N'-diphcnyl-cobalt[bis(3,4-dicarboxybenzoyl).] phthalocyanine

diimide (F)

CuPc polymer and commercially available CoPc and FePc are also studied for electrocatalytic activity determination.

These compounds were characterized by elemental analysis, IR and UV - visible spectroscopy and it was found that structure of synthesized compounds was matching well with reported structure.

These compounds were found to be thermally stable with exothermic decomposition peak in DTA curves occuring beyond 5000C.

Marked effect of end groups/substituent was observed on dielectric properties of these compounds.Compounds with imido end groups/substituents (A, C and. F) exhibit low dielectric constant of the order of tens while compounds with carboxylic end groups/substituents (B, D and E) have dielectric constant in the range of 103-104

. Dielectric constant increases with increasing temperature and decreasing frequency. The compounds show loss tangent in the region 0.1 to 20. Further, compound B, D and E have relatively low loss tangent although the dielectric constant is very high.

All the compounds are semiconductors having conductivity value as high as 10'4 -

11. cm . All the compounds show pyroelectric current even without polarization.

In most of the electrolytes, the electrocatalytic activity of the substituted compounds was higher than that of unsubstituted' CoPc monomer. Further, in Naf.ionR bound electrodes the electrocatalytic activity of the compounds was found to be higher than that on ordinary electrodes.

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CONTENTS

Page No.

CHAPTER 1 INTRODUCTION 1

1.1. BACKGROUND 1

1.2. ELECTRICAL CONDUCTANCE 3

1.2.1. Monomeric Phthalocyanine 3.

1.2.2. Effect of Substitution in the Macrocycle 6 1.2.3. Polymeric Phthalocyanine 8 1.2.4. Bridged Phthalocyanine Complexes 9

1.2.5. Effect of Doping 11

1.2.5.1. Effect of Doping Condition 16 1.2.6. Origin of n - type and p - type Conductance 17

1,2.7. Effect of Humidity 18

1,2.8. Effect of Gases and Application as Gas Detectors 18

1.2.9. Effect of Impurity 19

1.3, DIELECTRIC BEHAVIOUR 20

1.3.1. Monomeric Phthalocyanine 21

1.3.2. Effect of Doping 22

1.3.3. Polymeric Phthalocyanine 23

1.4. PYROELECTRIC CURRENT 26

1.5. ELECTROCHEMICAL BEHAVIOUR in DIOXYGEN REDUCTION 27 1.5;1, Monomeric Phthalocyanine 30 1.5.2. Substituted Phthalocyanine 31 1.5.3. Polymeric Phthalocyanine 33 1.5.4. Bridged Phthalocyanine 34 1,5.5. Effect of Electrode Preparation on Electrocatalysis 35

1.5.6. Stability 36

1.5.7. Effect of Heat. Treatment 37 1,5.8. Photoelectrochemical Reduction of Oxygen 38

1.6,, SCOPE OF THE WORK 38

CHAPTER 2 SYNTHESIS AND CHARACTERIZATION 40 2.1. SYNTHESIS of METAL PHTHALOCYANINES 40

2.1.1. Background

2.1.2. Synthesis of Cobalt Phthalocyanine Polymer with Imido End Groups (A)

2.1,3, Synthesis of Cobalt Phthalocyanine Polymer with Carboxylic End Groups ( B )

2.1.4. Synthesis of Cobalt ( bis ( 3,4-phthalimidocar- bony1)] phthalocyanine ( C )

2.1.5, Synthesis of Cobalt [ bis( 3,4-dicarboxybenzoyl)]

phthalocyanine (D)

40 42 43 43 44

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2.1.6. Synthesis of Cobalt [bis ( 3,4-dicarboxybenzoy1)]

phthalocyanine Dianhydride (E) 45 2.1.7, Synthesis of N,111 - diphenyl - cobalt - Ibis (3,4-

dicarboxybenzoy1)] phthalocyanine diimide (F) 46

2.2.CHARACTERIZATION 46

2.2.1. Elemental Analysis 46

2.2.2. UV - Visible Spectroscopy ⁴⁷

2.2.3. I.R. Spectroscopy ⁴⁹

2.2.4. Thermal Properties ⁵³

2.2.5. X - ray Diffraction 56

CHAPTER 3 DIELECTRIC PROPERTIES 57

3.1. BACKGROUND 57

3.2. EXPERIMENTAL 61

3.2.1. Measurement Cell 61

3.2.2. HP LF Impedance Analyzer 62 3.2.3. Measurement of Dielectric Parameters 63

3.3. RESULTS AND DISCUSSION 63

CHAPTER 4 ELECTRICAL PROPERTIES 69 SECTION A : V - I CHARACTERISTICS 69

4.1. BACKGROUND 69

4.2. Measurement Technique 74

SECTION B PYROELECTRIC PROPERTIES 78

4.4. BACKGROUND 78

4.5. MEASUREMENT OF PYROELECTRIC CURRENT 81

CHAPTER 5 ELECTROCATALYTIC ACTIVITY FOR OXYGEN REDUCTION 88

5.1. BACKGROUND 88

5.2. TYPE OF FUEL CELLS 90

5.2.1. Acid Fuel Cell 91

5.2.2. Alkaline Fuel Cell 91

5.2.3. Molten Carbonate Fuel Cell 91 5.2.4. Solid - Oxide fuel cell 92 5.2.5. Solid Polymer Electrolyte Fuel Cell 93

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5.3. ELECTRODE KINETICS 96

5.4, SUBSTRATE FOR ELECTRODE 99

5.5. EXPERIMENTAL ¹⁰¹

5.5.1. Preparation of Active Carbon 102 5.5.2. Fabrication of Electrode 103

5.5.3. Cell Design 106

5.6.1. Polarization Curves 107

5,6,1.1. Effect of Method of Preparation of Compounds 109 5.6.1.2. Effect of Heat Treatment 109

5.6.2. Kinetic Parameters 112

5.7. Conclusions 117

CHAPTER 6 SUMMARY AND CONCLUSIONS 118

6.1. SUMMARY 118

6.2. CONCLUSIONS 119

6.3. SCOPE OF THE FUTURE WORK 122

REFERENCES 123

Electrical and electrochemical properties of some cobalt phthalocyanine based electrocatalysts