An electrochemical double-layer capacitor (EDLC) is a potential buffer for current power and energy supply. In this work, activated carbon derived from fluid coke as a brand new electrode material was studied due to its high specific surface area (SSA) and large portion of mesopores. A suitable electrode material formula, current collector, and cell configuration were investigated to fabricate a testable system and ensure the reproducibility of measurements. Cyclic voltammetry (CV) and constant current charge/discharge (CD) techniques were used to characterize the performance of the electrode material, as well as to study its fundamental behaviour. A new procedure was established for quantifying the capacitance (Cc) of EDLC from CV which isolates the effect of internal resistance on the measured capacitance (CM). The specific capacitance of single electrode made of activated carbon (~1900 m2/g) with approximately 80% mesopores and macropores was able to reach 180 F/g at scan rate of 0.5mV/s.

This thesis presents thermodynamic studies performed by electrochemical methods (cyclic voltammetry, electrochemical impedance and chronopotenciometry) in three of the most important electrochromic materials: a-WO3, conducting polymers and viologens. Electrochromic materials are very promising as a low-consuming technology. By incorporating these materials in windows of buildings or vehicles, approximately a 30% of the consumed energy in these systems can be saved.Regarding the a-WO3, apart from other contributions, a new model based on lattice distortions, able to explain the intercalation thermodynamic in this material, is proposed. In the conducting polymers field, a Gaussian energy distribution is proved to account for the initial part of the so broad oxidation peaks observed in cyclic voltammetry. Finally, the coloration kinetics of the viologen modified n-TiO2 electrode is explained.

Electrochemical detection of metals can be done at polycrystalline gold ultramicroelectrodes using repetitive cyclic voltammetry (RCV), a detection method sharing some similarities with anodic stripping voltammetry (ASV). Each cycle of the potential waveform for RCV involves application of a negative preconcentration potential (for 50 to 300 ms) followed by a cyclic voltammetry (CV) scan at 20 to 1000 V/s. The response due to the metals is evident at potentials negative of the region for oxide formation in the resulting CVs. Metals are deposited at the Au surface by underpotential deposition (UPD) processes. Any metal that can be analyzed by RCV could potentially be quantified using UPD-ASV at Au (rather than by ASV at Hg). The UPD kinetics of Pb and Cu at polycrystalline Au were examined by setting kinetic parameters (rate constant, symmetry factor, and electrosorption valency) within a simulation program used to generate simulated CVs. Reasonably good agreement between experimental and simulated CVs was possible using the simulation, with the same kinetic parameters used to generate simulated CVs to match experimental CVs over a range of sweep rates for each system. Using this method, the following rate constants (k) were estimated: for UPD of Cu in H2SO4 and HClO4, ks ~ 36000 s−1 and 11000 s−1, respectively, and for UPD of Pb in H2SO4, ks ~ 400000 s−1. <p> Repetitive cyclic voltammetry was applied to the detection of metals separated by capillary electrophoresis. Separation of Tl+, Cd2+, Cu2+, Pb2+, Zn2+, Ni2+, Co2+ and Mn2+ was demonstrated in 0.01 mol/L acetic acid and 0.01 mol/L ammonium acetate(pH ~ 4.6) using RCV. While stacking is commonly exploited for sensitivity enhancement during injection, it was shown that detection-end stacking is also useful. A novel technique named electrophoretic extraction (EE) was developed for analysis of particle-containing solutions (e.g. soil extracts or other colloidal suspensions). EE involves application of backpressure during CE to prevent particles from entering the separation capillary: the applied pressure is regulated so analyte ions enter the capillary and migrate to the detector, whereas other particles are prevented from entering the capillary. The feasibility of this approach was demonstrated.

Trace metals (e.g. Fe, Mn, Zn, Cu, Cd, Ni) are important micronutrients that have historically been regarded as toxic pollutants rather than essential components of riverine and estuarine environments. The toxicity and behavior of trace metals, in response to physical and biogeochemical processes, are determined by their individual physico-chemical properties. In this dissertation, the vertical transformation of trace metals across oxic-anoxic interfaces was investigated at two sites, a Fe-rich freshwater river with minimal sulfide and an estuary with elevated Mn and H2S concentrations. Sediment profiles obtained from the Chattahoochee River showed that dissolved arsenic, present as As(V) only, is scavenged by Fe-oxides and accumulates directly below the sediment-water interface. Depth profiles also indicate that As(V) fluxes into the overlying water during baseflow conditions as well as after storm events. The significant correlation between Fe(II) and As(V) suggest that As(V) is released from Fe-oxides during their microbial reduction. By implementing a series of sediment incubations under increasing As(V) loads, it was determined that adsorption onto Fe-oxides and microbially mediated reductive dissolution of these mineral phases drive arsenic cycling in this sediment. These incubations also reveal for the first time that arsenic, even in low concentrations, n turn, arsenic loading impacts iron cycling by stimulating anaerobic respiration of Fe-oxides and promoting recrystallization of authigenic Fe-oxides, up to a toxicity threshold up to a few micromolar in concentrations. A combination of in situ measurements with discrete water sampling was utilized to determine the effects of tidal cycling on the distribution of trace metals under changing redox conditions during two consecutive tidal cycles at Station 858 in the Chesapeake Bay. Estuarine circulation patterns driven by tidal oscillations, a defined pycnocline, and the shallow sill (~20 m) of the Chesapeake Bay promoted bottom water anoxia during the summer months that allowed dissolved sulfide and reduced manganese to accumulate below the oxycline. The distribution of barium (conservative freshwater tracer) and uranium (conservative seawater tracer) across the pycnocline over the two tidal cycles indicated that the source of dissolved species was surficial sediments. During ebb and flood tides, the shear stress from the bottom waters flowing over the sediment seems to episodically promote the advection of porewaters enriched in dissolved sulfide, manganese, uranium, barium, lead, chromium, and copper. The selective enrichment of these trace metals appears to be controlled by their reactivity with sulfide. In contrast, cobalt and nickel are retained in sediments by adsorbed or incorporated in FeS and FeS2, while arsenic co-precipitates with sulfide or iron sulfide minerals. Overall, this study demonstrates that natural aquatic systems are complex environments where the interplay between biological, chemical, and physical processes affects the distribution of trace metals over short time scales. While a great wealth of knowledge can be obtained by laboratory experiments with synthetic solutions or pure cultures of organisms, a combination of in situ measurements and incubations with real samples in necessary to characterize the processes regulating the cycling of trace metals in aquatic systems.

This research is to synthesize PANI (polyaniline) thin film for polymer organic solar cells as a hole transport layer on the top of ITO substrate by using electrochemical (cyclic voltammetry) method. The device structure is ITO (150 nm) / PANI (50 nm) / P3HT: PCBM (100 nm) / Al (200 nm). We investigated surface morphology, conductivity, and light transmission of the PANI thin film from different aniline monomer concentration and studied the factors on device efficiency, also compared with the device structured with hole transport layer PEDOT:PSS. In this study, we found PANI thin films synthesized with different aniline monomer concentration, their light transmission over 80% at the range of 450 nm ~ 650nm wavelength and the conductivity up to 0.6 S/cm. It shows that PANI thin film suitably act as hole transport layer. In addition, we found morphology of PANI thin film that varied with different aniline monomer concentration. The power conversion efficiency of the device mainly affected by morphology with different aniline monomer concentration. Comparing to other parameters of concentration, the 0.3M aniline monomer concentration polymerized PANI thin film owned the most appropriate surface morphology, and the power conversion efficiency up to 1.76%.

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Verapamil is a commonly used medicine for the treatment of supraventricular arrhythmias, angina and hypertension. Recently, some newly developed applications of Verapamil, such as treating hypomania and chemotherapy for cancers, have been reported. Thus, monitoring the concentration of Verapamil accurately is very important. The major clinical analytical methods of Verapamil concentration determination are high performance liquid chromatography (HPLC) with UV or with fluorescence detector. However, these analytical methods have some disadvantages, like expensive instruments, complex operation, and time-consuming etc. The chemical structure and properties of Verapamil are very stable. The preliminary result of electrochemical analysis doesn¡¦t show any electrochemical activity. In this study, we developed an innovative ozone pre-treatment method to oxidize Verapamil to the smaller molecules and change its structure. Verapamil have excellent electrochemical activity after ozone pre-treatment. The spectroscopy and mass spectrometry show the changes of Verapamil structure. The products of Verapamil treated with ozone are also predicted by mass spectrometry. The gold nanoelectrode ensemble electrodes (GNEE) are used as working electrode for its good catalytic activity of electrochemical reaction, high sensitivity and high selectivity. The overall experimental framework of this study is microchip with GNEE working electrode accompanied by cyclic voltammetry, an electrochemical analytical instrument. Compared with traditional analytical methods, the system has some advantages such as small size, micro sample volume, easy operation, rapid detection and low cost. The limit concentration of Verapamil solution for stable detection in the system is 10 ng/mL. A linear dynamic range with a high correlation factor from 10 ng/mL to 100 £gg/mL was obtained. For the analysis of serum sample, Verapamil present excellent electrochemical activity at 1 ng/mL. A linear dynamic range with a high correlation factor from 1 ng/mL to 100 £gg/mLwas obtained. According to the results, our system for clinical Verapmil concentration analysis has the feasibility of the practical application.

Fuel cells are the tools which convert chemical energy into electricity directly by the effective utilization of hydrogen and oxygen (or air). One of the most important barriers for the fuel cell commercialization is the durability of the fuel cell components in the long term operations. In this study, the durability of the PEM fuel cell electrocatalysts were investigated via cyclic voltammetry (CV) and rotating disk electrode (RDE) experiments in order to determine the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) which corresponds to the half cell reactions in the fuel cell. PEM fuel cell electrodes mainly composed of carbon supported Pt catalysts. In long term operations due to Pt dissolution and carbon corrosion some properties of the electrocatalysts can be changed. Performance losses in catalysts mainly depend on / i) decrease in the total metal surface area (SA) and the electrochemically active surface area (ESA) due to the increase in the particle size ii) decrease in the tafel slope potential in ORR and iii) increase in carbon corrosion. In this study, these properties were examined via accelerated degradation tests performed in CV and RDE. The catalysts having different Pt loadings, synthesized with different ink compositions, pH values and microwave durations were investigated. The commercial catalysts having Pt loadings of 20, 50 and 70 (wt %) were tried and best results were obtained for Pt/V (50 wt %) catalyst. Different carbon to Nafion&reg / ratios of 4, 8, 12 in the ink composition were tried. C/N ratio of 8 gave the best result in Pt dissolution and carbon corrosion degradation tests. The catalysts prepared at different pH values of 1.4, 6.25 and 10 were tried and the catalyst prepared at pH of 10 was less degraded in Pt dissolution test and the catalyst prepared at pH of 6.25 showed better resistance to carbon corrosion. Catalysts prepared under different microwave durations of 50, 60 and 120 s were tried and the catalyst prepared at 60 s gave the best performances.

Three illustrative cases involving the electrodeposition of ultrathin metal films of varying reactivities onto noble-metal substrates were investigated: (i) Pd on Pt(111), a noble admetal on a noble-metal surface; (ii) Bi on Pd(111), a less noble admetal on a noble-metal surface; and (iii) Co on polycrystalline Pd and Pd(111), a reactive metal on a noble-metal surface. The interfacial electrochemistry of these prototypical systems was characterized using a combination of electrochemical methods (voltammetry and coulometry) and ultrahigh vacuum electron spectroscopies (Auger electron spectroscopy, AES; low energy electron diffraction, LEED; and X-ray photoelectron spectroscopy, XPS). Potential-controlled adsorption-desorption cycles of aqueous bromide exerted surface smoothening effects on ultrathin Pd films with defect sites (steps). This procedure, dubbed as electrochemical (EC) annealing, constituted a nonthermal analogue to conventional annealing. EC-annealed ultrathin Pd films exhibited long-range surface order and remained free of oxygen adspecies. Pdadatoms occupying step-sites were selectively dissolved and/or rearranged to assume equilibrium positions in a well-ordered (1x1) film. Electrodeposition of Co was found to be highly surface-structuresensitive. While virtually no Co electrodeposition transpired on a clean Pd(111) surface, Co was voltammetrically deposited on (i) a Pd(111) electrode roughened by oxidation-reduction cycles; and (ii) thermally annealed polycrystalline Pd, which is a composite of the (111) and (100) facets. Electrodeposition of Co was also observed to be kinetically hindered and slow potential scan rates (0.1 mV/s) were required. Well-defined ultrathin Bi films were potentiostatically electrodeposited onto Pd(111); a Stranski-Krastanov growth mode was indicated. The electrochemical reactivity of ultrathin Bi films was characterized using two surface probes: aqueous iodide and D-glucose. (i) Exposure of the prepared Bi adlayers (ΘBi 0.33) to aqueous iodide gave rise to (√3x√7) I-on-Bi superlattice. The same superlattice was obtained if Bi was electrodeposited onto Pd(111)(√3x√3)R30o-I. (ii) With respect to electrooxidation of D-glucose on Pd(111), the presence of Bi adlayers inhibited the by-product-induced "surface poisoning" of Pd(111) but reduced its electrocatalytic efficiency.

Characterized by high levels of terrestrial organic carbon inputs, estuaries and coastal marshes are among the most productive ecosystems on earth and significantly impact the global carbon cycle. Unfortunately, rates of natural organic matter (NOM) degradation in these environments are difficult to quantify directly due to the complex interaction between microbial respiration processes and abiotic reactions in these sediments, yet estuaries and marshes are considered both net sources and sinks of carbon. Typically carbon remineralization rates are determined by measuring total (TOU) and diffusive (DOU) oxygen uptake fluxes assuming oxygen is the ultimate oxidant. This assumption, however, requires any reduced metabolites produced during microbial respiration to be reoxidized by oxygen. In this study, voltammetric sensors were used to measure terminal electron acceptors or their reduced by-products. By simultaneously considering oxygen as well as anaerobic respiration accepting processes, this study demonstrates that oxygen does not function as the ultimate oxidant in coastal marine sediments due to precipitation and burial of reduced species. Furthermore, the biogeochemistry of coastal sediments is typically investigated ex situ after collection of sediment cores. However, coastal sediments are subject to complex subsurface hydrological forcing that cannot be accounted for with ex situ measurements. Consequently, in situ approaches are required to better understand the impact of physical processes on sediment biogeochemistry, and two novel in situ voltammetric systems were developed as part of this research. First, a new autonomous benthic lander equipped with a benthic chamber to measure TOU fluxes with a high temporal resolution and a potentiostat and micromanipulator to simultaneously acquire voltammetric depth profiles of the main redox species in pore waters was deployed in a pristine river-fed estuary to characterize the seasonal variability of coastal sediment biogeochemistry and examine the impact of riverine discharge on carbon remineralization processes. Simultaneously, a new electrochemical analyzer equipped with a solar and wind power charging system to ensure continuous monitoring capability and a VHF radio to transmit data was operated remotely via the internet from the Georgia Tech campus to investigate the dynamic coupling between hydrological, chemical, and biological processes in intertidal marsh sediments. Finally, new microelectrodes were deployed in microbial mats to examine the chemical and biological oxidation of sulfide with submillimeter resolution. Typically, only biological processes are considered to oxidize sulfide in these environments. Depth profiles during diel studies were able to demonstrate the formation of thiosulfate as an intermediate oxidation product of sulfide oxidation, suggesting that the chemical oxidation of sulfide is much more prevalent than previously recognized when compared to biological oxidation. Overall, using a novel in situ sampling technique with high temporal resolution, these studies confirm that biogeochemical processes in coastal sediments vary seasonally. More importantly, these studies also reveal that estuarine sediments are significantly influenced by riverine discharge, demonstrate that the biogeochemical response of these sediments to natural perturbations is rapid, and indicate that respiration processes in continental shelf sediments are controlled by a combination of temperature, supply of inorganic and organic substrates, and hydrological processes, which has important implications regarding the effect of climate change on the biogeochemical cycling of carbon in these environments.