High performance catalytic materials for heterogeneous oxidative organic functional group transformations

Development of heterogeneous metal oxide catalytic system with selective redox transition and highly recyclic feature is of challenging research in synthetic organic chemistry. In consideration with stability and reusability, very limited attention has been given so for. Nafion® is a rigid perfluropolymer backbone containing polymer bearing ion-exchangeable sulfonic acid terminal group (-SO3-.H+), extensively used as a solid-state protonic conductor in fuel cell applications and seldom used for chemical modification and in synthetic organic chemistry. In this thesis, we are presenting nano ruthenium oxide pyrochlore (Ru2Pb2O7, Pyc) modified Nafion® membrane (designated as |NPyc|) catalyst for selective organic functional group transformations including oxidation of alcohols to aldehyde and ketone, amine to nitriles under ambient conditions. We are covering preparation, characterization by XRD, SEM, SECM, AFM, TGA, XAS and catalytic organic synthesis in triphasic medium with cooxidants such as H2O2, NaOCl and O2. Under optimal working condition, the membrane catalyst showed very good selectivity and good turnover for wide range of organic compounds. The |NPyc| catalyst can be recycled over >100 times without any catalytic degradation. As to the mechanism, a high valent-oxo ruthenium redox species, perruthenate/ruthenate redox couple (Pyc-RuO4-/Pyc-RuO42-) exists in the |NPyc| believed to participate in the oxidation reaction with the co-oxidants. In continuation to the above studies, a novel ruthenium functionalized nickel hydroxide (designated as Ru/Ni(OH)2) catalyst containing specific Ru-Ru and Ru-OHhydroxo bondings was prepared by simple solution phase procedures and characterized by XRD, IR, TGA, SEM, XPS and XAS (EXAFS and XANES). By using this as a new catalyst, series of alcohols were cleanly oxidized to corresponding aldehydes and ketones with higher turnover factors (~132 h-1) than that of the literature reports, which were based on the monomeric Ru and Ru-Ru bonded catalysts. The Ru/Ni(OH)2 can be recycled and reused without any leaching of metals. As to the mechanism, a low valent-hydroxo ruthenium species (Ru-OH) exists on the surface of the Ru/Ni(OH)2 believed to participate in the aerobic alcohol oxidation reaction via a hydridometal pathway.Chapter1:GeneralIntroduction………………………………… 1 1.1. Abstract…………………………………………………… 1 1.2. Introduction……………………………………………… 2 1.3. Traditional methods……………………………………… 2 1.4. Homogeneous catalysis…………………………………… 13 1.4.1. Copper complexes……………………………………… 14 1.4.2. Cobalt complexes………………………………………. 18 1.4.3. Vanadium complexes…………………………………… 21 1.4.4. Iron……………………………………………………… 24 1.4.5. Ruthenium complexes…………………………………… 25 1.4.6. Palladium complexes…………………………………… 29 1.4.7. Gold complexes………………………………………… 34 1.4.8. Bimetallic systems………………………………………36 1.5. Heterogeneous catalysis………………………… 37 1.5.1. Pt and Pd Supported catalysts…………………… 37 1.5.2. Gold (Au) Supported catalysts……………………… 43 1.5.3. Ruthenium (Ru) Supported catalysts……………… 47 1.5.4. Other metal supported catalysts…………………… 55 1.5.5. Polyoxometalate catalysts………………… 55 1.5.6. Silica and polymer supported TEMPO……………… 57 1.5.7. Oxidation of alcohols with hydrogen peroxide… 59 1.5.8. Oxidation of alcohols with sodium hypo chlorite (NaOCl…………………………………………………… 66 1.5.9. Oxidation of alcohols under anaerobic conditions68 1.6. Aim and Scope of the present work………………… 70 1.7. References………………………………………………… 71 Chapter 2: Synthesis, characterization and catalysis of nano crystalline Ruthenium oxide pyrochlore in an ionic clusters of nafion polymer……………………………………86 2.1. Abstract…………………………………………………. 86 2.2. Introduction…………………………………………….. 87 2.3. Experimental……………………………………………… 88 2.3.1. Materials and reagents……………………………… 88 2.3.2. Apparatus and measurementsc……………… 89 2.3.3. In situ precipitation of Pyc into Nafion® 417 membrane ……………………………………………………………90 2.3.4. General procedure for selective benzyl alcohol oxidation reaction……………………………………………… 90 2.4. Results and discussion…………………………………. 92 2.4.1. Physico-chemical characteristics of the |NPyc| catalyst………………………………………………………… 92 2.4.1.1. X-ray diffraction measurements………………… 92 2.4.1.2. Scaning electron microscopy (SEM) …………… 94 2.4.1.3. Atomic force microscopic analysis (AFM) …… 95 2.4.1.4. Scaning electrochemical microscopy (SECM) … 96 2.4.1.5 Thermo gravimetric analysis (TGA) ……………… 97 2.4.1.6 Cation exchange property (CEP) ……………………99 2.4.1.7. X-ray absorption spectroscopy analysis (XAS) 100 2.4.1.7.1. Extended X-ray absorption near edge structure (XANES)………………………………………………………………100 2.4.1.7.2. Extended X-ray absorption spectroscopy (EXAFS)100 2.4.1.8. Selective benzyl alcohol oxidation reaction… 103 2.5. Conclusions………………………………………………… 107 2.6. References…………………………………………………. 107 Chapter 3: A nano crystalline ruthenium oxide pyrochlore - nafion polymer composite for highly selective oxidation of alcohols………………………………………………………………111 3.1. Abstract ………………………………………………………111 3.2. Introduction…………………………………………………112 3.3. Experimental……………………………………………… 113 3.3.1. Chemicals………………………………………………… 113 3.3.2. Apparatus and measurements……………… 114 3.3.3. Catalyst preparation and oxidation procedure 115 3.3.4. Preparation of the NPycCME……………………… 115 3.4. Results and discussion………………………………… 116 3.4.1. Catalytic performance………………………………… 116 3.4.2. |NPyc|-catalyzed alcohol oxidation reactions… 119 3.4.3. Catalytic mechanism …………………………………. 121 3.4.4. Kinetics of 2-pyridine methanol oxidation reactions.... 123 3.4.4.1. Effect of stirring speed……………………………125 3.4.4.2. Effect of catalyst amount……………………... 126 3.4.4.3. Effect of [substrate] …………………………… 127 3.4.4.4. Effect of amount of NaOCl……………………… 128 3.4.4.5. Effect of the amount of solvent (CH2Cl2) … 129 3.4.4.6. Effect of temperature………………………….. 129 3.4.4.7. Mechanism……………………………………………. 131 3.4.5. |NPyc| stability ……………………………………….132 3.5. Conclusions……………………………………………... 133 3.6. References…………………………………………………. 134 Chapter 4 : Oxidation of alcohols with molecular oxygen promoted by nano ruthenium oxide pyrochlore composite at room temperature……………………………………………………136 4.1. Abstract…………………………………………………. 136 4.2. Introduction………………………………….......... 137 4.3. Experimental Section…………………………………... 138 4.3.1. Chemicals and Reagents…………………………... 138 4.3.2. Apparatus and Measurements……………………….. 138 4.3.3. Catalyst Preparation…………………………...... 138 4.3.4. Adsorbed Alcohol Oxidation Reaction……………. 139 4.3.5. Typical alcohol oxidation reactions…………….. 139 4.3.6. Membrane Catalyst Regeneration……………………. 139 4.4. Results and Discussion………………………………. 140 4.5. Conclusion…………………………………………………. 147 4.6. References………………………………………………. 147 Chapter 5: Nano ruthenium oxide pyrochlore-nafion composite assisted aerobic oxidation of amine at room temperature…………………………………………………………149 5.1. Abstract……………………………………………………. 149 5.2. Introduction…………………………………………….. 150 5.3. Experimental Section…………………………………………………... 151 5.3.1. Chemicals and Reagents……………………………………………... 151 5.3.2. Apparatus and Measurements………………………………………... 152 5.3.3. Catalyst Preparation…………………............. 152 5.3.4. Adsorbed Amine Oxidation ………………………….. 152 5.3.5. Typical amine oxidation reactions……………… 153 5.3.6. Membrane Catalyst Regeneration…………………… 153 5.4. Results and discussion…………………………………. 153 5.5. Conclusion ………………………………………………… 159 5.6. References…………………………………………………. 160 Chapter 6: Ruthenium Functionalized Nickel Hydroxide Catalyst Containing Ru-Ru and Ru-Ohydroxo Bondings for Highly Efficient Alcohol Oxidations ………………………163 6.1. Abstract …………………………………………………… 163 6.2. Introduction ……………………………………………. 164 6.3. Experimental …………………………………………... 165 6.3.1. Chemicals ………………………………………………. 165 6.3.2. X-ray absorption spectroscopic analysis (XAS) …………………………………………………………… 165 6.3.3. Apparatus and measurements………………………… 166 6.3.4. Product analysis……………………………………………………… 166 6.3.5. Preparation of βbc-Ni(OH)2 powder…………….. 166 6.3.6. Preparation of Ru/Ni(OH)2 powder………………… 168 6.3.7. Typical procedures for the aerobic oxidation of alcohols…………………………………………………… 168 6.4. Result and discussion ……………………………….. 168 6.4.1. X -ray diffraction (XRD) ………………………. 168 6.4.2. IR spectroscopy………………………………………. 169 6.4.3. TGA analysis……………………………………………. 170 6.4.4. SEM and SEM-EDAX analysis…………………………… 171 6.4.5. XPS analysis……………………………………..... 173 6.4.6. X-ray absorption spectroscopy analysis (EXAFS & XANES) ………………………………………………………… 174 6.5. Conclusions………………………………………………. 184 6.6. References…………………………………………………. 18

High performance catalytic materials for heterogeneous oxidative organic functional group transformations

Development of heterogeneous metal oxide catalytic system with selective redox transition and highly recyclic feature is of challenging research in synthetic organic chemistry. In consideration with stability and reusability, very limited attention has been given so for. Nafion® is a rigid perfluropolymer backbone containing polymer bearing ion-exchangeable sulfonic acid terminal group (-SO3-.H+), extensively used as a solid-state protonic conductor in fuel cell applications and seldom used for chemical modification and in synthetic organic chemistry. In this thesis, we are presenting nano ruthenium oxide pyrochlore (Ru2Pb2O7, Pyc) modified Nafion® membrane (designated as |NPyc|) catalyst for selective organic functional group transformations including oxidation of alcohols to aldehyde and ketone, amine to nitriles under ambient conditions. We are covering preparation, characterization by XRD, SEM, SECM, AFM, TGA, XAS and catalytic organic synthesis in triphasic medium with cooxidants such as H2O2, NaOCl and O2. Under optimal working condition, the membrane catalyst showed very good selectivity and good turnover for wide range of organic compounds. The |NPyc| catalyst can be recycled over >100 times without any catalytic degradation. As to the mechanism, a high valent-oxo ruthenium redox species, perruthenate/ruthenate redox couple (Pyc-RuO4-/Pyc-RuO42-) exists in the |NPyc| believed to participate in the oxidation reaction with the co-oxidants. In continuation to the above studies, a novel ruthenium functionalized nickel hydroxide (designated as Ru/Ni(OH)2) catalyst containing specific Ru-Ru and Ru-OHhydroxo bondings was prepared by simple solution phase procedures and characterized by XRD, IR, TGA, SEM, XPS and XAS (EXAFS and XANES). By using this as a new catalyst, series of alcohols were cleanly oxidized to corresponding aldehydes and ketones with higher turnover factors (~132 h-1) than that of the literature reports, which were based on the monomeric Ru and Ru-Ru bonded catalysts. The Ru/Ni(OH)2 can be recycled and reused without any leaching of metals. As to the mechanism, a low valent-hydroxo ruthenium species (Ru-OH) exists on the surface of the Ru/Ni(OH)2 believed to participate in the aerobic alcohol oxidation reaction via a hydridometal pathway.Chapter1:GeneralIntroduction………………………………… 1 1.1. Abstract…………………………………………………… 1 1.2. Introduction……………………………………………… 2 1.3. Traditional methods……………………………………… 2 1.4. Homogeneous catalysis…………………………………… 13 1.4.1. Copper complexes……………………………………… 14 1.4.2. Cobalt complexes………………………………………. 18 1.4.3. Vanadium complexes…………………………………… 21 1.4.4. Iron……………………………………………………… 24 1.4.5. Ruthenium complexes…………………………………… 25 1.4.6. Palladium complexes…………………………………… 29 1.4.7. Gold complexes………………………………………… 34 1.4.8. Bimetallic systems………………………………………36 1.5. Heterogeneous catalysis………………………… 37 1.5.1. Pt and Pd Supported catalysts…………………… 37 1.5.2. Gold (Au) Supported catalysts……………………… 43 1.5.3. Ruthenium (Ru) Supported catalysts……………… 47 1.5.4. Other metal supported catalysts…………………… 55 1.5.5. Polyoxometalate catalysts………………… 55 1.5.6. Silica and polymer supported TEMPO……………… 57 1.5.7. Oxidation of alcohols with hydrogen peroxide… 59 1.5.8. Oxidation of alcohols with sodium hypo chlorite (NaOCl…………………………………………………… 66 1.5.9. Oxidation of alcohols under anaerobic conditions68 1.6. Aim and Scope of the present work………………… 70 1.7. References………………………………………………… 71 Chapter 2: Synthesis, characterization and catalysis of nano crystalline Ruthenium oxide pyrochlore in an ionic clusters of nafion polymer……………………………………86 2.1. Abstract…………………………………………………. 86 2.2. Introduction…………………………………………….. 87 2.3. Experimental……………………………………………… 88 2.3.1. Materials and reagents……………………………… 88 2.3.2. Apparatus and measurementsc……………… 89 2.3.3. In situ precipitation of Pyc into Nafion® 417 membrane ……………………………………………………………90 2.3.4. General procedure for selective benzyl alcohol oxidation reaction……………………………………………… 90 2.4. Results and discussion…………………………………. 92 2.4.1. Physico-chemical characteristics of the |NPyc| catalyst………………………………………………………… 92 2.4.1.1. X-ray diffraction measurements………………… 92 2.4.1.2. Scaning electron microscopy (SEM) …………… 94 2.4.1.3. Atomic force microscopic analysis (AFM) …… 95 2.4.1.4. Scaning electrochemical microscopy (SECM) … 96 2.4.1.5 Thermo gravimetric analysis (TGA) ……………… 97 2.4.1.6 Cation exchange property (CEP) ……………………99 2.4.1.7. X-ray absorption spectroscopy analysis (XAS) 100 2.4.1.7.1. Extended X-ray absorption near edge structure (XANES)………………………………………………………………100 2.4.1.7.2. Extended X-ray absorption spectroscopy (EXAFS)100 2.4.1.8. Selective benzyl alcohol oxidation reaction… 103 2.5. Conclusions………………………………………………… 107 2.6. References…………………………………………………. 107 Chapter 3: A nano crystalline ruthenium oxide pyrochlore - nafion polymer composite for highly selective oxidation of alcohols………………………………………………………………111 3.1. Abstract ………………………………………………………111 3.2. Introduction…………………………………………………112 3.3. Experimental……………………………………………… 113 3.3.1. Chemicals………………………………………………… 113 3.3.2. Apparatus and measurements……………… 114 3.3.3. Catalyst preparation and oxidation procedure 115 3.3.4. Preparation of the NPycCME……………………… 115 3.4. Results and discussion………………………………… 116 3.4.1. Catalytic performance………………………………… 116 3.4.2. |NPyc|-catalyzed alcohol oxidation reactions… 119 3.4.3. Catalytic mechanism …………………………………. 121 3.4.4. Kinetics of 2-pyridine methanol oxidation reactions.... 123 3.4.4.1. Effect of stirring speed……………………………125 3.4.4.2. Effect of catalyst amount……………………... 126 3.4.4.3. Effect of [substrate] …………………………… 127 3.4.4.4. Effect of amount of NaOCl……………………… 128 3.4.4.5. Effect of the amount of solvent (CH2Cl2) … 129 3.4.4.6. Effect of temperature………………………….. 129 3.4.4.7. Mechanism……………………………………………. 131 3.4.5. |NPyc| stability ……………………………………….132 3.5. Conclusions……………………………………………... 133 3.6. References…………………………………………………. 134 Chapter 4 : Oxidation of alcohols with molecular oxygen promoted by nano ruthenium oxide pyrochlore composite at room temperature……………………………………………………136 4.1. Abstract…………………………………………………. 136 4.2. Introduction………………………………….......... 137 4.3. Experimental Section…………………………………... 138 4.3.1. Chemicals and Reagents…………………………... 138 4.3.2. Apparatus and Measurements……………………….. 138 4.3.3. Catalyst Preparation…………………………...... 138 4.3.4. Adsorbed Alcohol Oxidation Reaction……………. 139 4.3.5. Typical alcohol oxidation reactions…………….. 139 4.3.6. Membrane Catalyst Regeneration……………………. 139 4.4. Results and Discussion………………………………. 140 4.5. Conclusion…………………………………………………. 147 4.6. References………………………………………………. 147 Chapter 5: Nano ruthenium oxide pyrochlore-nafion composite assisted aerobic oxidation of amine at room temperature…………………………………………………………149 5.1. Abstract……………………………………………………. 149 5.2. Introduction…………………………………………….. 150 5.3. Experimental Section…………………………………………………... 151 5.3.1. Chemicals and Reagents……………………………………………... 151 5.3.2. Apparatus and Measurements………………………………………... 152 5.3.3. Catalyst Preparation…………………............. 152 5.3.4. Adsorbed Amine Oxidation ………………………….. 152 5.3.5. Typical amine oxidation reactions……………… 153 5.3.6. Membrane Catalyst Regeneration…………………… 153 5.4. Results and discussion…………………………………. 153 5.5. Conclusion ………………………………………………… 159 5.6. References…………………………………………………. 160 Chapter 6: Ruthenium Functionalized Nickel Hydroxide Catalyst Containing Ru-Ru and Ru-Ohydroxo Bondings for Highly Efficient Alcohol Oxidations ………………………163 6.1. Abstract …………………………………………………… 163 6.2. Introduction ……………………………………………. 164 6.3. Experimental …………………………………………... 165 6.3.1. Chemicals ………………………………………………. 165 6.3.2. X-ray absorption spectroscopic analysis (XAS) …………………………………………………………… 165 6.3.3. Apparatus and measurements………………………… 166 6.3.4. Product analysis……………………………………………………… 166 6.3.5. Preparation of βbc-Ni(OH)2 powder…………….. 166 6.3.6. Preparation of Ru/Ni(OH)2 powder………………… 168 6.3.7. Typical procedures for the aerobic oxidation of alcohols…………………………………………………… 168 6.4. Result and discussion ……………………………….. 168 6.4.1. X -ray diffraction (XRD) ………………………. 168 6.4.2. IR spectroscopy………………………………………. 169 6.4.3. TGA analysis……………………………………………. 170 6.4.4. SEM and SEM-EDAX analysis…………………………… 171 6.4.5. XPS analysis……………………………………..... 173 6.4.6. X-ray absorption spectroscopy analysis (EXAFS & XANES) ………………………………………………………… 174 6.5. Conclusions………………………………………………. 184 6.6. References…………………………………………………. 18

Tetracycline Immobilization as Hydroquinone Derivative at Dissolved Oxygen Reduction Potential on Multiwalled Carbon Nanotube

Upon continuous potential cycling of multiwalled carbon nanotube modified electrode (GCE/MWCNT) with Tetracycline antibiotic (Tet) at −0.5 to 0.4 V vs Ag/AgCl in pH 7 phosphate buffer solution, the Tet drug gets selectively immobilized as Tet-hydroquinone derivative (Tet-HQ) on the GCE/MWCNT (GCE/Tet-HQ@MWCNT) and showed a specific surface confined redox peak at E1/2 =−0.24 ± 0.02 V vs Ag/AgCl. Control potential cycling experiment with o-cresol resulted to similar electrochemical characteristic too. But with p-cresol, no such surface confined redox peak was noticed. Dissolved oxygen reduction to hydrogen peroxide (as an intermediate species) at −0.45 V vs Ag/AgCl and its chemical oxidation of the surface bound Tet@MWCNT to Tet-HQ@MWCNT is proposed as a plausible mechanism. Separate ring-disk screen-printed carbon electrode assembly, where MWCNT and a H2O2 detection catalyst (nano-MnO2) modified on the ring and disk respectively, coupled with flow injection analysis showed specific current signals for oxygen reduction reaction at −0.45 V vs Ag/AgCl on the disk and subsequent H2O2 oxidation on ring at 0.8 V vs Ag/AgCl. The surface confined redox system showed highly selective electrocatalytic reduction signal to hydrogen peroxide at ∼0.22 V vs Ag/AgCl without any interference from the ascorbic acid, uric acid, cysteine and nitrite

Nafion/lead oxide-manganese oxide combined catalyst for use as a highly efficient alkaline air electrode in zinc-air battery

In this study, we report the application of an inexpensive and easily prepared lead oxide-manganese oxide catalyst combined with Nation (designated as Nf/PbMnO(x)) as a highly efficient air-cathode for a zinc-air battery. We verify the mechanistic study of the reduction of O(2) for Nf/PbMnO(x) in alkaline aqueous solution using rotating ring/disk electrode voltammetry, and also an electrochemical approach using a wall-jet screen-printed ring disk electrode. The presence of Nf/PbMnO(x) shows great catalytic activity for the disproportionation reaction of HO(2)(-) to O(2) and OH(-) with an overall 4e(-) reduction of O(2) in the first reduction reaction. The 4e(-) reduction O(2) was eventually achieved at the Nf/PbMnO(x) through evidence from the slope of Koutecky-Levich plots. With these inherent features, we then fabricated the zinc-air battery with the Nf/PbMnO(x) catalyst and examine the performance for a practical application with air cathodes. (C) 2011 Elsevier Ltd. All rights reserved

Monolithic Quasi-Solid-State Dye Sensitized Solar Cells Prepared Entirely by Printing Processes

A complete printing process was developed to fabricate the quasi-solid-state dye-sensitized solar cells with monolithic structures (m-QS-DSSCs). First, a structure of m-DSSCs was constructed by sequentially printing TiO2 layers (main and scattering), a ZrO2 insulating layer, and a carbon counter electrode (CE) onto an FTO substrate (FTO/TiO2/ZrO2/carbon CE). Then, a quasi-solid-state printable electrolyte (QS-PE), prepared using polyethylene oxide/polymethyl methacrylate, was printed directly on top of the porous carbon counter electrode (CE), enabling the m-QS-DSSCs to be prepared entirely by printing processes. In this study, the porous structures and characteristics of the ZrO2 and carbon layers were optimized by controlling the film thicknesses and heat treatment conditions; furthermore, the Pt layer was coated to improve the catalytic activity of carbon CEs. The results revealed that an appropriate porous structure of carbon and ZrO2 films could be obtained by heating the films from 200 to 500 °C. Through these porous layers, the QS-PE can penetrate well into the photoelectrodes, increasing the charge transport in the cells and at the electrode/electrolyte interfaces; therefore, the m-QS-DSSCs can achieve an efficiency of 6.79% under 1 sun illumination. Furthermore, the structures can also be utilized to fabricate liquid cells for application in a dim light environment. The m-QS-DSSCs remained stable during a long-term stability test at room temperature

Graphene Oxide Sponge as Nanofillers in Printable Electrolytes in High-Performance Quasi-Solid-State Dye-Sensitized Solar Cells

A graphene oxide sponge (GOS) is utilized for the first time as a nanofiller (NF) in printable electrolytes (PEs) based on poly­(ethylene oxide) and poly­(vinylidene fluoride) for quasi-solid-state dye-sensitized solar cells (QS-DSSCs). The effects of the various concentrations of GOS NFs on the ion diffusivity and conductivity of electrolytes and the performance of the QS-DSSCs are studied. The results show that the presence of GOS NFs significantly increases the diffusivity and conductivity of the PEs. The introduction of 1.5 wt % of GOS NFs decreases the charge-transfer resistance at the Pt-counter electrode/electrolyte interface (<i>R</i>_pt) and increases the recombination resistance at the photoelectrode/electrolyte interface (<i>R</i>_ct). QS-DSSC utilizing 1.5 wt % GOS NFs can achieve an energy conversion efficiency (8.78%) higher than that found for their liquid counterpart and other reported polymer gel electrolytes/GO NFs based DSSCs. The high energy conversion efficiency is a consequence of the increase in both the open-circuit potential (<i>V</i>_oc) and fill factor with a slight decrease in current density (<i>J</i>_sc). The cell efficiency can retain 86% of its initial value after a 500 h stability test at 60 °C under dark conditions. The long-term stability of the QS-DSSC with GOS NFs is higher than that without NFs. This result indicates that the GOS NFs do not cause dye-desorption from the photoanode in a long-term stability test, which infers a superior performance of GOS NFs as compared to TiO₂ NFs in terms of increasing the efficiency and long-term stability of QS-DSSCs

Effects of TiO₂ and TiC Nanofillers on the Performance of Dye Sensitized Solar Cells Based on the Polymer Gel Electrolyte of a Cobalt Redox System

Polymer gel electrolytes (PGEs) of cobalt redox system are prepared for dye sensitized solar cell (DSSC) applications. Poly­(vinylidene fluoride-<i>co</i>-hexafluoropropylene) (PVDF-HFP) is used as a gelator of an acetonitrile (ACN) liquid electrolyte containing tris­(2,2′-bipyridine)­cobalt­(II/III) redox couple. Titanium dioxide (TiO₂) and titanium carbide (TiC) nanoparticles are utilized as nanofillers (NFs) of this PGE, and the effects of the two NFs on the conductivity of the PGEs, charge-transfer resistances at the electrode/PGE interface, and the performance of the gel-state DSSCs are studied and compared. The results show that the presence of TiC NFs significantly increases the conductivity of the PGE and decreases the charge-transfer resistance at the Pt counter-electrode (CE)/PGE interface. Therefore, the gel-state DSSC utilizing TiC NFs can achieve a conversion efficiency (6.29%) comparable to its liquid counterpart (6.30%), and, furthermore, the cell efficiency can retain 94% of its initial value after a 1000 h stability test at 50 °C. On the contrary, introduction of TiO₂ NFs in the PGE causes a decrease of cell performances. It shows that the presence of TiO₂ NFs increases the charge-transfer resistance at the Pt CE/PGE interface, induces the charge recombination at the photoanode/PGE interface, and, furthermore, causes a dye desorption in a long-term-stability test. These results are different from those reported for the iodide redox system and are ascribed to a specific attractive interaction between TiO₂ and cobalt redox ions