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Fuel cells are attractive power sources for both stationary and electric vehicle applications as power generators due to their high conversion efficiencies and low pollution. Among the various types of fuel cells, the proton exchange membrane fuel cells (PEMFC) are the most suitable candidates for electric vehicles as they can be operated at a low temperature of <100 ◦C. Platinum supported on Carbon Black is widely used as the electrocatalyst in PEMFC. However, platinum is expensive and the world’s supply of Pt is limited. Therefore, improving the electrocatalytic activity of Platinum with minimum loading level is important. The search for hydrogen oxidation reaction (HOR) catalysts that are more active, less expensive and with greater stability than Pt has resulted in the development of Pt alloys and nano composites. From both the scientific and the technological point of view, binary or ternary nanoparticles composed of two or three different metal elements are of greater interest and importance than monometallic nanoparticles. Scientists have especially focused on binary or ternary nanoparticles as catalysts in view of their novel catalytic behaviors and the synergy exhibited by the addition of the second or third metal element. This effect of the second or third metal element can often be explained in terms of an ensemble and a ligand effect in catalysis. In a typical Fuel Cell, gaseous fuels are fed continuously to the anode (negative electrode) compartment and an oxidant (i.e., oxygen from air) is fed continuously to the cathode (positive electrode) compartment. The Electrochemical reactions take place at the electrodes to produce an electric current. A fuel cell, although having components and characteristics similar to that of a typical battery, differs in several aspects. The battery is an energy storage device. The maximum energy available or deliverable is determined by the amount of chemical reactants stored within the battery itself. The battery will cease to produce electrical energy when the chemical reactants are consumed (i.e., discharged). In a secondary battery, the reactants are regenerated by recharging, which involves putting energy into the battery from an external source. The fuel cell, on the other hand, is an energy conversion device that theoretically has the capability of producing electrical energy for as long as the fuel and oxidant are supplied to the electrodes. In reality, degradation, primarily corrosion, or malfunction of components limits the practical operating life of fuel cells. Chapter I Introduction, Describes the chronological development of Fuel cells, Themodynamic principle of fuel cell operation, types of fuel cell and its importance. Brief introduction of Polymer Electrolyte Membrane Fuel Cell (PEMFC) components and its working principle are discussed. In the same chapter, the existing problems in PEMFC are also discussed. Further the importance of improvement in new catalyst material development and important requirements of catalysts are highlighted. Various preparation methods of catalysts are given in this chapter. Finally, Characterization techniques of electrocatalyst and the Fuel Cell applications are discussed. Chapter II deals with the detailed Literature survey of fuel cell development work, Catalyst support material, Hydrogen Oxidation Reaction (HOR) at the anode, Oxygen reduction reaction (ORR) at the cathode and various methods of preparation of the electrocatalysts attempted by different researchers. At the end of the chapter, the scope and objective of the present investigation is discussed. Chapter III describes the preparation method of different catalysts and Experimental techniques followed during the course of the investigation. Materials and chemicals used for the preparation of catalysts are listed. In this chapter brief details about the construction of the Polymer Electrolyte Membrane Fuel Cell set up and testing arrangements are given. The electrochemical techniques like single cell evaluation for optimizing catalysts, long-term stability test of the optimized catalysts, cyclic voltammetry studies were also engaged. The physico-chemical methods like X-ray diffraction, Scanning Electron microscopic (SEM) with Energy Dispersive X-ray Spectroscopy and Transmission Electron microscopy were employed to study the crystallography, surface area of the active sites, composition of elements, particle size respectively. Chapter IV presents the Results and Discussion on the nano-structured Carbon supported binary catalysts Pt-WO3/C, Pt-TiO2/C and ternary Pt-WO3-TiO2/C prepared by Precipitation method (Chemical reduction of metal salts) using Chloroplatinic acid (H2PtCl6). Sodium tungstate, Titanium III sulphate were used as Precursors. These salts were precipitated by the addition of Sodium hydroxide and further the reduction process was carried out by adding Sodium boro hydride solution. Incorporation of various compositions of WO3 and TiO2 molecules into the Platinum particles has been effectively done. Three different methods were adopted for preparing WO3 and TiO2 binary and ternary nano-composite electrocatalysts. Results and discussion of the preparation and characterization studies are summarized and presented in three parts, Part I deals with the Pt-WO3/C nano-composite catalyst, Part II deals with Pt-TiO2/C nano-composite catalyst, Part III deals with Pt-WO3-TiO2/C nano-composite catalyst. Finally Part IV describes the comparison of the optimized catalyst from each part (Part I to Part III) with 10% Pt/C and 10% Pt/C (commercial) catalysts. Part I Synthesized 5 different compositions of Carbon (Vulcan XC-72R) supported Pt-WO3/C (Pt-W 0:10, 2:8, 4:6, 6:4, 8:2) anode material by precipitation method using sodium boro hydride as reducing agent.. Sodium tungstate was used as precursor for the inclusion of WO3 by addition hydrochloric acid followed by heat treatment. The Carbon supported (Vulcan XC-72R) 10% Pt/C was also prepared as control sample. The six types of prepared catalysts and one commercial 10% Pt/C (reference sample) catalyst were used for single cell evaluation. The maximum power density at maximum Current of 221mWmg-1 was obtained in Pt-WO3/C (Pt-W 6:4). The Optimized catalysts were further characterized by Cyclic Volammetry, XRD, Long-Term stability, SEM with EDX and TEM analysis. The Optimized Pt-WO3/C (Pt-W 6:4) having the average particle size of platinum was 2 nm to 3 nm (confirmed by TEM analysis and XRD analysis). The size of Pt particles deposited on carbon particle was 30 nm (confirmed by SEM). The Optimized nano-composite catalyst Pt-WO3/C (Pt-W 6:4) of particle size 2.37 nm (XRD) and surface area (roughness factor) 121 (m2 g-1) calculated using the Debye-Scherrer formula Particle size d = kλ / (β½ x cosθmax) ----- 1 Roughness factor (surface area) S = 6000 / ρd (m2 g-1) ----- 2 Part II Synthesized 5 different compositions of Carbon (Vulcan XC-72R) supported Pt-TiO2/C (Pt-Ti 0:10, 2:8, 4:6, 6:4, 8:2) anode material by precipitation method using sodium boro hydride as reducing agent and Titanium III sulphate as precursor for inclusion of TiO2. The five types of Pt-TiO2/C prepared catalyst, 10% Pt/C and one commercial 10% Pt/C (reference sample) catalyst were used for single cell evaluation. The maximum power density at maximum Current of 149 mWmg-1 was obtained in Pt-TiO2/C (Pt-Ti 8:2). The Optimized catalysts were further characterized by Cyclic Volammetry, XRD, Long-Term stability, SEM with EDX and TEM analysis. The Optimized Pt-TiO2/C (Pt-Ti 8:2) having the average particle size of platinum was 2 nm to 3 nm (confirmed by TEM analysis and XRD analysis). The size of Pt particles deposited on carbon particle was 30 nm (confirmed by SEM). The Optimized Pt-TiO2/C (Pt-Ti 8:2) was of particle size 2.37 nm (XRD) and surface area (roughness factor) 121 (m2 g-1). Part III Synthesized 5 different compositions of Carbon (Vulcan XC-72R) supported Pt-WO3-TiO2/C (Pt-W-Ti 0:5:5, 2:4:4, 4:3:3, 6:2:2, 8:1:1) anode electrocatalysts by precipitation method using sodium borohydride as reducing agent . Sodium tungstate and Titanium III sulphate were used as precursor for inclusion of WO3 and TiO2. The Carbon supported (Vulcan XC-72R) 10% Pt/C was prepared as control sample. The five types of Pt-WO3-TiO2/C prepared catalyst, 10% Pt/C and one commercial 10% Pt/C (reference sample) catalyst were used for single cell evaluation. The maximum power density at maximum Current of 214 mWmg-1 was obtained in Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3). The Optimized catalysts were further characterized by Cyclic Voltammetry, XRD, Long-Term stability, and TEM analysis. The Optimized Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3) having the average particle size of platinum was 2 nm to 3 nm (confirmed by TEM analysis and XRD analysis). The size of Pt particle deposited on carbon particle was 30 nm (confirmed by SEM). The Optimized Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3) was of particle size 2.4 nm (XRD) and surface area (roughness factor) 113.9 (m2 g-1). . Part IV Finally the Optimized catalysts Pt-WO3/C (Pt-W 6:4), Pt-TiO2/C (Pt-Ti 8:2), Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3), prepared catalysts 10% Pt/C and commercial 10% Pt/C were evaluated using electrochemical performance, structural morphology, long-term stability test and chemical composition (by EDX spectroscopic technique). The results of the three types of optimized catalysts are discussed to choose the best catalyst among them. Chapter V Presents the Conclusions of this study. This study has successfully developed a novel method for the preparation of three types of carbon supported Pt-WO3, Pt-TiO2, and Pt-WO3-TiO2 electrocatalysts with various compositions at different weight percentages, Pt-W 0:10, 2:8, 4:6, 6:4, 8:2 of Pt-WO3/C, Pt-Ti 0:10, 2:8, 4:6, 6:4, 8:2 of Pt-TiO2/C of binary nano-composite electocatalysts, Pt-W-Ti 0:5:5, 2:4:4, 4:3:3, 6:2:2, 8:1:1 for Pt-WO3-TiO2/C of ternary nano-composites and 10 % Pt/C. These anode electrocatalysts were prepared by precipitation method (Salt reduction process). The performance of prepared catalysts and that using commercial catalyst were optimized through single cell evaluation and characterization methods. The optimized catalysts Pt-WO3/C (Pt-W 6:4) Pt-TiO2/C (Pt-Ti 8:2) and Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3), 10% Pt/C and 10% Pt/C (commercial) were further characterized using XRD, SEM, EDX, TEM techniques and Long term electrochemical stability tests. The electrocatalytic activities of optimized Pt-WO3/C (Pt-W 6:4), Pt-TiO2/C (Pt-Ti 8:2) and Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3) nanocomposites have shown better performances than 10% Pt/C and commercial 10% Pt/C in PEMFC. Through experimental results it was established that, even lower amounts of platinum catalyst enhances the power density of electrodes. Through this work, it is further established that, the presence of WO3 molecule enhances the proton transport within the platinum surface through the inclusion of WO3 into the Platinum particles. The novel approach followed for doping WO3 and TiO2 into the Pt particles has been fully established in the present work and this method has not been reported so far. The technique followed in this work for the inclusion of second and third elements into Platinum prevents the agglomeration of platinum particles. Another novel approach established through the present work was based on Nafion emulsion for the incorporation of TiO2 and WO3 particles into the ionomer. The metal oxide provides an internal humidification to retain water within the ionomer, enhances the proton conductivity at the anode side and ensures long-term stability of the catalyst. The quantity of Platinum content was reduced from 1.76 to 1.056 mgcm-2 for Pt-WO3/C, 1.408 mgcm-2 for Pt-TiO2/C and 0.706 mgcm-2 for Pt-WO3-TiO2/C compositions. The optimized Pt-WO3/C (Pt-W, 6:4), Pt-TiO2/C (Pt-Ti, 8:2) and Pt-WO3-TiO2/C (Pt-W-Ti, 4:3:3) catalysts have shown better catalytic activity for anodic oxidation (HOR) due to the non-aggregated dispersion of Pt particles and the presence of metal oxide prevents agglomeration of Platinum particles. The experimental results establish that even lower amount of platinum catalyst enhances the power density of electrodes. The effective utilization of platinum is much higher than 10% Pt/C, when WO3 or TiO2 as binary molecules and WO3-TiO2 as ternary molecules were introduced within the Pt nano particles which is the main scope of this work. To conclude that, the Pt-WO3/C (Pt-W 6:4), Pt-TiO2/C (Pt-Ti, 8:2) and Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3) are used as highly promising, cost effective, very stable and enhanced performance anode electrocatalysts for Polymer Electrolyte Membrane Fuel Cell in the order of Pt-WO3/C (Pt-W, 6:4) > Pt-WO3 TiO2/C (Pt-W-Ti, 4:3:3) > Pt-TiO2/C (Pt-Ti 8:2) and enhances the scope for future work in many directions.

Научная область

Химические науки
– Неорганическая химия

P SYNTHESIS AND CHARACTERIZATIONS OF CARBON SUPPORTED NANO-COMPOSITE ELECTROCATALYSTS FOR POLYMER ELECTROLYTE MEMBRANE FUEL CELL APPLICATIONS

From both the scientific and the technological point of view, binary or ternary nanoparticles composed of two or three different metal elements are of greater interest and importance than monometallic nanoparticles. Scientists have especially focused on binary or ternary nanoparticles as catalysts in view of their novel catalytic behaviors and the synergy exhibited by the addition of the second or third metal element.  This effect of the second or third metal element can often be explained in terms of an ensemble and a ligand effect in catalysis.

In a typical Fuel Cell, gaseous fuels are fed continuously to the anode (negative electrode) compartment and an oxidant (i.e., oxygen from air) is fed continuously to the cathode (positive electrode) compartment. The Electrochemical reactions take place at the electrodes to produce an electric current. A fuel cell, although having components and characteristics similar to that of a typical battery, differs in several aspects. The battery is an energy storage device. The maximum energy available or deliverable is determined by the amount of chemical reactants stored within the battery itself. The battery will cease to produce electrical energy when the chemical reactants are consumed (i.e., discharged). In a secondary battery, the reactants are regenerated by recharging, which involves putting energy into the battery from an external source. The fuel cell, on the other hand, is an energy conversion device that theoretically has the capability of producing electrical energy for as long as the fuel and oxidant are supplied to the electrodes. In reality, degradation, primarily corrosion, or malfunction of components limits the practical operating life of fuel cells.
 
Chapter I Introduction, Describes the chronological development of Fuel cells, Themodynamic principle of fuel cell operation, types of fuel cell and its importance.  Brief introduction of Polymer Electrolyte Membrane Fuel Cell (PEMFC) components and its working principle are discussed.  In the same chapter, the existing problems in PEMFC are also discussed.  Further the importance of improvement in new catalyst material development and  
important requirements of catalysts are highlighted.  Various preparation methods of catalysts are given in this chapter.  Finally, Characterization techniques of electrocatalyst and the Fuel Cell applications are discussed.

Chapter II deals with the detailed Literature survey of fuel cell development work, Catalyst support material, Hydrogen Oxidation Reaction (HOR) at the anode, Oxygen reduction reaction (ORR) at the cathode and various methods of preparation of the electrocatalysts attempted by different researchers.  At the end of the chapter, the scope and objective of the present investigation is discussed.

Chapter III describes the preparation method of different catalysts and Experimental techniques followed during the course of the investigation. Materials and chemicals used for the preparation of catalysts are listed. In this chapter brief details about the construction of the Polymer Electrolyte Membrane Fuel Cell set up and testing arrangements are given.  The electrochemical techniques like single cell evaluation for optimizing catalysts, long-term stability test of the optimized catalysts, cyclic voltammetry studies were also engaged. The physico-chemical methods like X-ray diffraction, Scanning Electron microscopic (SEM) with Energy Dispersive X-ray Spectroscopy and Transmission Electron microscopy were employed to study the crystallography, surface area of the active sites, composition of elements, particle size respectively. 
Chapter IV presents the Results and Discussion on the nano-structured Carbon supported binary catalysts Pt-WO3/C, Pt-TiO2/C and ternary Pt-WO3-TiO2/C prepared by Precipitation method (Chemical reduction of metal salts) using Chloroplatinic acid (H2PtCl6).  Sodium tungstate, Titanium III sulphate were used as Precursors.  These salts were precipitated by the addition of Sodium hydroxide and further the reduction process was carried out by adding Sodium boro hydride solution.  Incorporation of various compositions of WO3 and TiO2 molecules into the Platinum particles has been effectively done. Three different methods were adopted for preparing WO3 and TiO2 binary and ternary nano-composite electrocatalysts.

Results and discussion of the preparation and characterization studies are summarized and presented in three parts, Part I deals with the Pt-WO3/C nano-composite catalyst, Part II deals with Pt-TiO2/C nano-composite catalyst, Part III deals with Pt-WO3-TiO2/C nano-composite catalyst.  Finally Part IV describes the comparison of the optimized catalyst from each part (Part I to Part III) with      10% Pt/C and 10% Pt/C (commercial) catalysts.

Part I  
Synthesized 5 different compositions of Carbon (Vulcan XC-72R) supported Pt-WO3/C (Pt-W 0:10, 2:8, 4:6, 6:4, 8:2) anode material by precipitation method using sodium boro hydride as reducing agent..  Sodium tungstate was used as precursor for the inclusion of WO3 by addition hydrochloric acid followed by heat treatment. The Carbon supported (Vulcan XC-72R) 10% Pt/C was also prepared as control sample.   The six types of prepared catalysts and one commercial 10% Pt/C (reference sample) catalyst were used for single cell evaluation. The maximum power density at maximum Current of 221mWmg-1 was obtained in Pt-WO3/C (Pt-W 6:4). The Optimized catalysts were further characterized by Cyclic Volammetry, XRD, Long-Term stability, SEM with EDX and TEM analysis.  The Optimized Pt-WO3/C (Pt-W 6:4) having the average particle size of platinum was 2 nm to 3 nm (confirmed by TEM analysis and XRD analysis).  The size of Pt particles deposited on carbon particle was 30 nm (confirmed by SEM). The Optimized nano-composite catalyst Pt-WO3/C (Pt-W 6:4) of particle size 2.37 nm (XRD) and surface area (roughness factor) 121      (m2 g-1) calculated using the Debye-Scherrer formula
                        Particle size            d   =     kλ / (β½ x cosθmax)   	 -----	1	
 Roughness factor (surface area)	 S   =     6000 / ρd (m2 g-1)	 	-----	2

Part II
	Synthesized 5 different  compositions of Carbon (Vulcan XC-72R) supported Pt-TiO2/C (Pt-Ti 0:10, 2:8, 4:6, 6:4, 8:2)  anode material by precipitation method using sodium boro hydride as reducing agent and Titanium III sulphate as precursor for inclusion of TiO2.  The five types of Pt-TiO2/C prepared catalyst, 10% Pt/C and one commercial 10% Pt/C (reference sample) catalyst were used for single cell evaluation. The maximum power density at maximum Current of 149 mWmg-1 was obtained in Pt-TiO2/C (Pt-Ti 8:2). The Optimized catalysts were further characterized by Cyclic Volammetry, XRD, Long-Term stability, SEM with EDX and TEM analysis.   The Optimized Pt-TiO2/C (Pt-Ti 8:2) having the average particle size of platinum was 2 nm to 3 nm (confirmed by TEM analysis and XRD analysis).  The size of Pt particles deposited on carbon particle was 30 nm (confirmed by SEM). The Optimized Pt-TiO2/C (Pt-Ti 8:2) was of particle size 2.37 nm (XRD) and surface area (roughness factor) 121 (m2 g-1).

Part III 
Synthesized 5 different compositions of Carbon (Vulcan XC-72R) supported Pt-WO3-TiO2/C (Pt-W-Ti 0:5:5, 2:4:4, 4:3:3, 6:2:2, 8:1:1) anode electrocatalysts by precipitation method using sodium borohydride as reducing agent .  Sodium tungstate and Titanium III sulphate were used as precursor for inclusion of WO3 and TiO2. The Carbon supported (Vulcan XC-72R) 10% Pt/C was prepared as control sample.  The five types of Pt-WO3-TiO2/C prepared catalyst, 10% Pt/C and one commercial 10% Pt/C (reference sample) catalyst were used for single cell evaluation. The maximum power density at maximum Current of 214 mWmg-1 was obtained in Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3). The Optimized catalysts were further characterized by Cyclic Voltammetry, XRD, Long-Term stability, and TEM analysis.  The Optimized Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3) having the average particle size of platinum was 2 nm to 3 nm (confirmed by TEM analysis and XRD analysis).  The size of  Pt particle deposited on carbon particle was 30 nm (confirmed by SEM). The Optimized Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3) was of particle size 2.4 nm (XRD) and surface area (roughness factor) 113.9 (m2 g-1).                                    . 
Part IV
Finally the Optimized catalysts Pt-WO3/C (Pt-W 6:4), Pt-TiO2/C (Pt-Ti 8:2), Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3), prepared catalysts 10% Pt/C and commercial 10% Pt/C were evaluated using electrochemical performance, structural morphology, long-term stability test and chemical composition (by EDX spectroscopic technique).  The results of the three types of optimized catalysts are discussed to choose the best catalyst among them.  
Chapter V Presents the Conclusions of this study. This study has successfully developed a novel method for the preparation of three types of carbon supported Pt-WO3, Pt-TiO2, and Pt-WO3-TiO2 electrocatalysts with various compositions at different weight percentages, Pt-W 0:10, 2:8, 4:6, 6:4, 8:2 of Pt-WO3/C, Pt-Ti 0:10, 2:8, 4:6, 6:4, 8:2 of Pt-TiO2/C of binary nano-composite electocatalysts, Pt-W-Ti 0:5:5, 2:4:4, 4:3:3, 6:2:2, 8:1:1 for Pt-WO3-TiO2/C of ternary nano-composites and 10 % Pt/C.  These anode electrocatalysts were prepared by precipitation method (Salt reduction process). The performance of prepared catalysts and that using commercial catalyst were optimized through single cell evaluation and characterization methods. The optimized catalysts Pt-WO3/C (Pt-W 6:4) Pt-TiO2/C (Pt-Ti 8:2) and Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3), 10% Pt/C and 10% Pt/C (commercial) were further characterized using XRD, SEM, EDX, TEM techniques and Long term electrochemical stability tests.  
The electrocatalytic activities of optimized Pt-WO3/C (Pt-W 6:4),         Pt-TiO2/C (Pt-Ti 8:2) and Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3) nanocomposites have shown better performances than 10% Pt/C and commercial 10% Pt/C in PEMFC. Through experimental results it was established that, even lower amounts of platinum catalyst enhances the power density of electrodes. Through this work, it is further established that, the presence of WO3 molecule enhances the proton transport within the platinum surface through the inclusion of WO3 into the Platinum particles.  The novel approach followed for doping WO3 and TiO2 into the Pt particles has been fully established in the present work and this method has not been reported so far.  The technique followed in this work for the inclusion of second and third elements into Platinum prevents the agglomeration of platinum particles.
 Another novel approach established through the present work was based on Nafion emulsion for the incorporation of TiO2 and WO3 particles into the ionomer.  The metal oxide provides an internal humidification to retain water within the ionomer, enhances the proton conductivity at the anode side and ensures long-term stability    of the catalyst.
The quantity of Platinum content was reduced from 1.76 to 1.056 mgcm-2 for Pt-WO3/C, 1.408 mgcm-2 for Pt-TiO2/C and 0.706 mgcm-2 for       Pt-WO3-TiO2/C compositions. The optimized Pt-WO3/C (Pt-W, 6:4), Pt-TiO2/C (Pt-Ti, 8:2) and Pt-WO3-TiO2/C (Pt-W-Ti, 4:3:3) catalysts have shown better catalytic activity for anodic oxidation (HOR) due to the non-aggregated dispersion of Pt particles and the  presence of metal oxide prevents  agglomeration of Platinum particles.  
The experimental results establish that even lower amount of platinum catalyst enhances the power density of electrodes. The effective utilization of platinum is much higher than 10% Pt/C, when WO3 or TiO2 as binary molecules and WO3-TiO2 as ternary molecules were introduced within the Pt nano particles which is the main scope of this work.
To conclude that, the Pt-WO3/C (Pt-W 6:4), Pt-TiO2/C (Pt-Ti, 8:2) and Pt-WO3-TiO2/C (Pt-W-Ti 4:3:3) are used as highly promising, cost effective, very stable and enhanced performance anode electrocatalysts for Polymer Electrolyte Membrane Fuel Cell in the order of Pt-WO3/C (Pt-W, 6:4) > Pt-WO3 TiO2/C (Pt-W-Ti, 4:3:3) > Pt-TiO2/C (Pt-Ti 8:2) and enhances the scope for future work in many directions.

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