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The high-performance sodium metal chloride battery has garnered significant interest in the past decade due to its multiple advantages such as high energy density, deep discharge cycling ability, high safety level, 100% coulombic efficiency, and a broad ambient-temperature operating range. Current development of the sodium-metal chloride batteries is focused on improving its performance and cycling life. This work investigates micro-scale mass transfer and kinetic parameters, which is related to cell performance, for building a complete model. In a typical commercial sodium metal chloride cell, there is mass transfer and conduction throughout the thick positive electrode. The electrode materials participate in redox reactions neither homogeneously nor simultaneously. Therefore, a much thinner positive electrode is introduced in this work in order to remove added macro-scale effects in the electrode from the measurement. Therefore, the number of parameters needed to describe the data was reduced because the experimental design minimizes spatial variations within the cell. Chapter 2 discusses the impact of iron addition to a sodium nickel-chloride cell by investigating ionic transport within the metal chloride phase. The electrochemical performance of a sodium mixed-metal (Ni, Fe) halide cell is characterized for different cathode compositions and at different rates. Charge/discharge data are characterized by a smaller nickel-voltage plateau during discharge than during charge, indicating that some of the NiCl₂ reduces at cell potentials nominally associated with the iron plateau. One means of describing the difference between charge and discharge is to consider transport processes within the mixed NiCl₂/FeCl₂ solid phase. A one-dimensional model has been used to simulate the ionic transport within the (Ni,Fe)Cl₂ phase; the transport model predicts the ratio of discharge to charge iron plateaus reasonably well for most rates and compositions. In order to further investigate complex dynamic behavior of the open-circuit potential (OCP) and galvanic interactions in an iron-doped sodium nickel-chloride cell, a GITT (Galvanostatic Intermittent Titration Technique) method is used in Chapter 3. The response to open-circuit interrupts of porous mixed iron-nickel cathodes has been characterized as a function of state of charge (SOC) for different iron loadings and different charge and discharge rates. After discharge, OCP can evolve in time from the iron plateau to the nickel plateau, and this behavior can be explained by galvanic interactions between iron metal and Ni²⁺. Characteristic times of the OCP transients depend on SOC and can be large. When the OCP has converged on a steady state during discharge, its value may provide an estimate of the mole fraction of NiCl₂ at the interface of the triclinic (Ni,Fe)Cl₂ film that resulted from metal oxidation. Sulfur-containing additives were shown to have dramatic impact on cell resistance and performance. In Chapter 4, the electrochemistry of iron sulfide in nickel/iron porous electrodes in molten sodium tetrachloroaluminate electrolyte was investigated. With the addition of FeS to the electrolyte, results indicate the formation of nickel sulfide species on the metal electrode and an increasing discharge capacity with increasing amount of iron sulfide. The cathode with highest sulfide content appears to be highly resistive. Galvanostatic interrupt experiments shows complex dynamic behavior of sulfide-iron-NiCl₂ galvanic interactions. With a goal of extending knowledge of kinetic and mass transfer parameters for understanding mass transfer, Chapter 5 discusses the performance of nickel/iron cells for a broader range of temperature, composition and current. The experiments were tested at different temperatures. Also, three granule compositions with different iron levels are tested at four different current rates. The data from this study can be for use in a complete model of the sodium-nickel/iron chloride cell and in the optimization of the electrode. In the previous chapters, a thinner positive electrode is used in order to remove the effects of macro-scale mass transfer. Chapter 6 discusses the impact of thickness of the cathode on the mass macro-scale transfer and conduction within the metal chloride and metal phase. The goal is to improve modeling of tortuosity as a function of state of charge because transport is important in real systems, and modeling ohmic resistance, for example, can be challenging.

Electrical double-layer formed at the electrode/electrolyte interface in combination with electron-transfer reaction can lead to many important applications of electrochemistry, including energy storage devices, namely, batteries, fuel cells and electrochemical supercapacitors. Electrochemical supercapacitors are characterized by their higher power density as compared to batteries and higher energy density than the conventional electrostatic and electrolytic capacitors. Thus, supercapacitors are useful as auxiliary energy storage devices along with primary sources such as batteries or fuel cells for the purpose of power enhancement in short pulse applications. These are expected to be useful in hybrid devices together with batteries or fuel cells, in electric vehicle propulsion systems. Among the various materials studied for electrochemical supercapacitors, carbonaceous materials, transition metal oxides and conducting polymers are important. Carbon in various forms is used as a double-layer capacitor material, which stores charge by electrostatic charge separation at the electrode/electrolyte interface. The specific capacitance (SC) of high surface area activated carbon is about 100 F g-1 in aqueous electrolytes. Transition metal oxides have attracted considerable attention as electrode materials for supercapacitors because of the following merits: variable oxidation state, good chemical and electrochemical stability, ease of preparation and convenience in handling. Hydrated RuO2 prepared by sol-gel process exhibited a SC as high as 720 F g-1. However, high cost, low porosity and toxic nature of RuO2 limit its commercialization in supercapacitors. On the otherhand, MnO2 is an attractive electrode material as it is electrochemically active, cheap, environmentally benign, and its resources are abundant in nature. In an early report on the capacitance properties of MnO2 by Lee and Goodenough [J. Solid State Chem. 144 (1999) 220], amorphous hydrous MnO2 synthesized by co-precipitation method exhibited a SC of 203 F g-1 in 2 M KCl electrolyte. According to the charge-storage mechanism of MnO2 involving MnO2 + M+ + e- ↔ (MnOO)-M+ (where M+ = Li+, Na+, K+ etc.), a SC of 1110 F g-1 is expected over a potential window of 1.0 V. However, SC values in the range of 100-200 F g-1 are reported in the literature. The low values of SC are because of the charge-storage is confined to surface region of MnO2 particles or films. It is desirable to enhance the SC of MnO2 to a value close to the theoretical value. In view of this, attempts are made to enhance the SC of MnO2 by adopting different synthetic procedures such as electrochemical method for depositing MnO2 and also nanostructured mesoporous MnO2 by polyol route, hydrothermal route and sonochemical method in the present studies. As the charge-storage mechanism of MnO2 involves the surface insertion/deinsertion of cations from the electrolyte during discharge/charge processes, respectively, the capacitance properties of MnO2 are studied in various aqueous electrolytes containing monovalent (Na+), bivalent (Mg2+, Ca2+, Sr2+ and Ba2+) and trivalent (La3+) cations. The mass variation occurring at the electrode during the charge/discharge of MnO2 is examined by electrochemical quartz crystal microbalance (EQCM) study. In addition to this, the kinetics of electrodeposition and capacitance properties of Mn(OH)2 are studied by employing EQCM. Also, properties of asymmetric capacitors assembled with Mn(OH)2 as the positive electrode and carbon as the negative electrode are studied and compared with symmetric Mn(OH)2 capacitors. Furthermore, attempts are made to increase the potential window of Co(OH)2 in alkaline and neutral electrolytes. The contents of the thesis by Chapter-wise are given below. Chapter 1 introduces the importance of electrochemistry in energy storage and conversion, basics of electrochemical power sources, importance of some electroactive materials in electrochemical energy storage, different synthetic procedures for MnO2 and its application in electrochemical supercapacitors. Transition metal oxides are widely studied because of their variable oxidation states, high electrochemical activity, abundance in nature and environmental compatibility. Various reports appeared in the form of open publications on supercapacitor studies of transition metal oxides such as RuO2, MnO2, Fe3O4, Co(OH)2, Ni(OH)2, NiO, etc., are briefly reviewed. The chapter ends with statements on objectives of the studies carried out and reported in the thesis. Chapter 2 provides experimental procedures and methodologies used for the studies reported in the thesis. Different experimental routes adopted for synthesis of MnO2, Mn(OH)2 and Co(OH)2 used for the studies are described. Also included are brief descriptions of various physicochemical and electrochemical techniques employed for the investigations. In Chapter 3, MnO2 samples synthesized by various routes such as electrochemical method, polyol route, hydrothermal route and sonochemical method are studied. MnO2 and Mn(OH)2 are simultaneously electrodeposited on the anode and the cathode, respectively, in a galvanostatic electrolysis cell consisting of aqueous Mn(NO3)2 electrolyte. MnO2/SS and Mn(OH)2/SS electrodes are used as the negative and the positive electrodes, respectively, in an asymmetric Mn(OH)2//MnO2 supercapacitor. MnO2 samples are prepared at room temperature and in hydrothermal method at a temperature of 140 ◦C by reduction of KMnO4 with poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) or P123 as a reductant. Also, MnO2 is prepared from KMnO4 by hydrothermal method without using any reducing agent. This procedure requires a temperature of 180 ◦C and 24 h duration. MnO2 is also synthesized with an ultrasonic aided procedure. The electrochemical capacitance properties of MnO2 samples synthesized by various routes are investigated. A maximum SC of 264 F g-1 is obtained at a current density of 0.5 mA cm-2 (1.0 A g-1) for MnO2 prepared by sonochemical method. The capacitance properties of MnO2 are generally studied in neutral aqueous Na2SO4 electrolytes. In Chapter 4, electrolytes of NaNO3, Mg(NO3)2, Ca(NO3)2, Sr(NO3)2, Ba(NO3)2 and also La(NO3)3 are studied and the results are compared with Na2SO4 electrolyte. Among the alkaline earth salt solutions, higher SC values are obtained in Mg(NO3)2 and Ca(NO3)2 electrolytes than in the rest of the electrolytes. Furthermore, MnO2 exhibits capacitance behaviour in La(NO3)3 solution with enhanced SC in comparison with NaNO3 and Mg(NO3)2 solutions. The SC increases with an increase in charge on the cation (Na+, Mg2+ and La3+). The values of SC measured in Na+, Mg2+ and La3+ electrolytes are 190, 220 and 257 F g-1, respectively at a c.d. of 0.5 mA cm-2 (1.0 A g-1). Rate capabilities are also found to be different in different electrolytes. Specific energy and specific power are calculated and presented as Ragone plots. The presence of divalent and trivalent cations inserted onto MnO2 is identified by X-ray photoelectron spectroscopy. EQCM is employed to monitor the increased mass variations that accompany reversible adsorption/desorption of Na+, Mg2+ and La3+ ions onto MnO2. In Chapter 5, EQCM has been used to study the kinetics of electrochemical precipitation of Mn(OH)2 on Au-crystal and its capacitance properties. From the EQCM data, it is inferred that NO3- ions get adsorbed on Au-crystal, and then undergo reduction resulting an increase in pH near the electrode surface. Precipitation of Mn2+ occurs as Mn(OH)2, resulting an increase in mass of the Au-crystal. On charging, Mn(OH)2 undergoes oxidation to MnO2, which exhibits electrochemical supercapacitor behaviour on subjecting to cycling in aqueous Na2SO4 electrolyte. EQCM data indicates the mass variations corresponding to surface insertion/extraction of Na+ ions during discharge/charge cycling of Mn(OH)2 in aqueous Na2SO4 electrolyte. In Chapter 6, Mn(OH)2 synthesized by precipitation of MnSO4 with NH4OH solution is studied for capacitance properties. A SC of 141 F g-1 is obtained for the Mn(OH)2 at a c.d. of 0.66 A g-1 in 1.0 M Na2SO4 electrolyte in the potential range of 0-1.0 V vs. standard calomel electrode (SCE). Also, carbon electrode made from high surface area carbon exhibits a SC of 158 F g-1 at a c.d. of 0.81 A g-1 in the potential range of 0 to -1.0 V vs. SCE. Asymmetric capacitors are assembled by combining Mn(OH)2 as the positive and carbon as the negative electrodes. The asymmetric capacitor has a SC of 39 F g-1 at a c.d. of 0.42 A g-1 in the operating voltage of 1.8 V. However, a symmetric capacitor consisting of two Mn(OH)2 electrodes provides a SC of 11 F g-1 only at a c.d. of 0.24 A g-1 in an operating voltage of 1.2 V. In Chapter 7, MnO2 synthesized by reduction of KMnO4 using ethylene glycol is used for fabrication of large area electrodes. Stainless steel (SS) mesh of 3 cm x 3 cm with geometrical area of 18 cm2 is used as current collector. Three symmetrical electrochemical supercapacitors (capacitance of about 100 F per each at a current of 0.2 A) are assembled, each with 11 electrodes positioned in parallel. Six alternate electrodes are stacked as the negative terminal and the other five as the positive terminal. The electrochemical properties of MnO2 supercapacitors are studied by galvanostatic charge-discharge cycling and ac impedance in 1.0 M Na2SO4 electrolyte. Also, the capacitors are combined in parallel as well as in series and the capacitance is evaluated. The practical application of the electrochemical supercapacitors is shown by demonstrating the running of a toy fan connected to the charged capacitor as well as the glowing of LED cell connected to charged supercapacitors connected in series. A parallel combination of batteries and capacitors is also demonstrated. Capacitor studies of Co(OH)2 over a limited potential window in alkaline electrolytes are reported in the literature. A high potential window of a capacitor material is desirable for using in a device. In Chapter 8, experiments are conducted to understand the reason for a low potential window for Co(OH)2 as a capacitor material and also to increase its potential window. Experiments are conducted in aqueous NaOH and Na2SO4 electrolytes of various concentrations using electrochemically precipitated Co(OH)2 on stainless steel current collectors in an aqueous Co(NO3)2 electrolyte. Based on the potential window, specific capacitance and specific energy, it is found that 0.05 M NaOH electrolyte is more appropriate for capacitor properties of Co(OH)2 than the rest of the electrolytes studied. Using a Co(OH)2 electrode with a specific mass of 1.0 mg cm-2 in 0.05 M NaOH, a SC of about 380 F g-1 is obtained with a potential window of 0.85 V at a charge-discharge c.d. of 10 A g-1 (10 mA cm-2). The work presented in this thesis is carried out by the candidate as a part of Ph. D. training program and most of the results have been published in the literature. A list of publications of the candidate is enclosed below. It is hoped that the studies reported here will constitute a worthwhile contribution.

Doctor of Philosophy / Department of Chemistry / Takashi Ito / This research was focused on understanding how external stimuli affect the permeability of the chemically modified electrodes, and how the materials used in modifying the working electrodes respond to the changes in the surface charge. We adopted a voltammetric type electrochemical sensor to investigate the permeability effects induced by pH and organic solvents. The working electrodes used in this research were chemically modified with thioctic acid self assembled monolayer (TA SAM), track etched polycarbonate membranes (TEPCM) and PS-b-PMMA nanoporous films (polystyrene-block-polymethylmethacrylate). We studied the permeability behavior of each of the material upon application of external stimuli. In chapter 3, the permeability changes induced by change in surface charge of thioctic acid SAM was investigated. The surface charge of the monolayer was tuned by changing pH of the medium, which resulted in decrease of redox current of a negatively charged marker due to deprotonation of the surface –COOH groups of TA SAM. Decrease in redox current reflected a decrease in the reaction rate, and by using closed form equations the effective rate constants at several pKa values were extracted. In chapter 4, permeability changes induced by pH in TEPCM were investigated. We assessed the surface charge of these membranes via cyclic voltammetry generated for neutral and charged redox molecules. Limiting current of charged markers were affected by the surface charge induced by pH, where as the redox current for the neutral marker was not affected. Experimental redox currents were larger than the theoretical current, indicating that redox molecules preferentially distributed in a surface layer on the nanopore. Organic solvent induced permeability changes of PS-b-PMMA nanoporous films were investigated via electrochemical impedance spectroscopy and AFM. Higher response of pore resistance in the presence of organic solvents indicated either swelling of the nanoporous film or partitioning of organic solvents in the pores. However AFM data revealed that the permeability changes are due to partitioning of the solvents rather than swelling of the porous film, since there was no appreciable change if the pore diameter in the presence of solvents.

The method of the deposition of films of small molecules for use in electronic applications is just as important as the molecule design itself as the film’s morphology and continuity influence the performance of the devices that they are incorporated in. The purpose of the work in this thesis was to develop a method of electrochemically depositing films of small molecules for potential use in electronic applications. A method of electrochemically depositing films of chemically reduced low solubility dye molecules was successfully pioneered. The process was developed using N,N dibutyl-3,4,9,10-perylene-bis(dicarboxime), a simplified version of 3,4,9,10-perylene-tetracarboxylic bisbenzimidalzole. Both of these dyes have been used in electronic applications, but low solubility makes them difficult to deposit by traditional solution techniques. A series of films was electrochemically deposited onto FTO coated glass and field effect transistors using coulometry. These films were characterised by absorption spectroscopy, photoluminescence, scanning electron microscopy, X-ray diffraction and photo-electrochemistry. The same deposition method was applied to copper phthalocyanine. These films were characterised by absorption spectroscopy, photoluminescence, scanning electron microscopy and X-ray diffraction. The developed method was used to deposit films of bilayers of dyes and to investigate the dye penetration during the deposition of copper phthalocyanine onto porous titanium dioxide. Films of neutral copper and nickel dithiolenes were electrodeposited from air-stable TMA salts to investigate the absorbance of the near infrared species formed, as well as to investigate the conductivity of both complexes and the magnetoresponse of the neutral copper dithiolene which is air unstable when formed chemically.