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This dissertation presents the synthesis and characterization of new types of nanostructured materials for use in high-performance aqueous rechargeable batteries and supercapacitors. In the first chapter, nanostructured nickel cobalt sulfide (Ni4.5Co4.5S8) was prepared through pulse-electrodeposition method. In addition, iron oxide nanosheets were prepared from graphite-coated iron carbide/α-Fe in a two-step annealing/electrochemical cycling process. A full-cell battery with supercapacitor-like power behavior was assembled with Ni4.5Co4.5S8 and iron oxide nanosheets as the positive and negative electrodes, respectively. The full-cell device delivers a specific energy of 89 Wh kg−1 at 1.1 kW kg−1 with a rate performance of 61 Wh kg−1 at a very high specific power of 38.5 kW kg−1. In the second chapter, we propose a route towards developing asymmetric supercapacitor devices having high volumetric energy densities though the modification of commercially available current collectors (CCs): nickel foam (NF) and carbon fiber cloth (CFC). A soft templating/solvothermal treatment route was employed to generate NiO/NiOOH nanosheets on NF current collectors (as positive electrode). CFCs were also modified via an electrochemical oxidation/reduction route to generate an exfoliated core-shell structure followed by electropolymerization of pyrrole into the shell structure (as negative electrode). Combining the individual materials resulted in a full-device asymmetric supercapacitor that delivers volumetric energy densities in the range of 1.67-2.65 mWh cm−3 with corresponding power densities in the range of 5.9-273.6 mW cm−3. Such performance is comparable to lithium thin film (0.3-10 mWh cm−3) and better than some commercial supercapacitors (< 1 mWh cm−3). In the third chapter, we established a simple, precise, and reproducible method to construct carbon fiber ultramicroelectrodes (CF-UMEs) with tip radius r < 1 μm. CF-UMEs were successfully used as SECM-tips to examine the “crystal structure orientation-OER electrocatalytic activity” relationship of iridium/iridium oxide catalysts. In addition, CF-UMEs were used as a substrate electrode for the electrodeposition of pH-sensitive iridium oxide. The pH response of these micrometer-sized pH electrodes has a rapid response (< 5 s) over the pH range of 2-12 with a super-Nernstian slope of 65.3 mV/pH. The prepared pH-UMEs were successfully employed as a potentiometric SECM-tip to image the pH changes at different substrates.

The electrochemical properties of graphene were investigated using a novel and clean method to fabricate device structures with mechanically exfoliated graphene samples. Graphene is known as being particularly sensitive to both contaminating fabrication methods and the substrate it is placed on, with these effects being detrimental to accurate research into the fundamental properties and sensing applications of graphene. This thesis presents micron scale graphene electrodes that have not been subject to polymer contamination or micro-lithography methods. The effect of utilising atomically flat hexagonal boron nitride as a substrate material was investigated, believed to be the first example of this for graphene electrochemical measurements. Cyclic voltammetry demonstrated the expected steady-state behaviour for microelectrodes in the hemispherical diffusion regime. The reduction of IrCl62- in weak KCl electrolytes was studied to investigate the electron transfer characteristics of the graphene devices and the reproducibility of the measurements. Average values of the standard rate constant, k0 and the transfer coefficient, alpha were found to be 3.04 ± 0.78 ×10-3 cms-1 and 0.272 ± 0.024 respectively. These values differ significantly from previous similar studies, with the effect of reduced charge doping from the substrate and the potential dependence of the density of electronic states thought to account for the differences. Despite the clean fabrication methods, a relatively large variation between separate devices was found, highlighting an inherent variation in the properties of graphene samples.

Este trabalho descreve o desenvolvimento de um método eletroanalítico para determinação sequencial de nitrito (NO2-) e nitrato (NO3-), utilizando como técnica, a voltametria de pulso diferencial. O método se baseia na redução eletroquímica dos íons nitrato sobre um ultramicroeletrodo de ouro modificado in situ com cádmio depositado em regime de subtensão, e na seqüência, a remoção da monocamada de cádmio e a oxidação eletroquímica dos íons nitritos sobre o ultramicroeletrodo não modificado. Os ensaios voltamétricos para determinação quantitativa de nitrato e nitrito foram realizados em solução de NaClO4 0,1 molL-1 + HClO4 1,0x 10-3 molL-1 (pH = 3,3) preparada com água ultrapura. Utilizando as condições experimentais e os parâmetros voltamétricos otimizados, foram construídas curvas analíticas para determinação de nitrito e nitrato separadamente e também para determinação sequencial dos dois analitos. Para a determinação do NO2-, foi observado uma relação linear entre a corrente de pico e a concentração desse íon dentro do intervalo de concentração de 1,0 x 10-5 molL-1 a 1,1 x 10-4 molL-1, com um limite de detecção igual a 1,151 &plusmn; 0,091 &micro;molL-1 e limite de quantificação igual a 3,838 &plusmn; 0,091 &micro;molL-1. Para a determinação do NO3-, também foi observado uma relação linear entre corrente de pico e concentração desse analito dentro do intervalo estudado, que foi de 2,00 x 10-5 molL-1 a 2,50 x 10-4 molL-1. O limite de detecção encontrado foi 4,839 &plusmn; 0,275 &micro;molL-1 e o limite de quantificação 16,131 &plusmn; 0,275 &micro;molL-1. A determinação sequencial de nitrito e nitrato foi avaliada dentro do intervalo de concentração de 5,00 x 10-5 molL-1 a 2,50 x 10-4 molL-1 para NO3- e 1,00 x 10-5 molL-1 a 4,50 x 10-5 para NO2-. Para ambos os casos, a relação entre corrente de pico versus concentração do analito foi linear. Para a determinação sequencial os limites de detecção são 16,177 &plusmn; 0,794 &micro;molL-1 para NO3- e 2,243 &plusmn; 0,179 &micro;molL-1 para NO2- e os limites de quantificação são 53,922 &plusmn; 0,794 &micro;molL-1 para o NO3- e 7,476 &plusmn; 0,179 &micro;molL-1 para o NO2-. Os limites de detecção, os limites de quantificação e demais parâmetros estatísticos apresentados nesse trabalho, foram obtidos a partir de cálculos baseados em procedimentos descritos em Miller e Miller68 e Silva69. / This work describes the development of an electroanalytical method for sequential determination of nitrite (NO2-) and nitrate (NO3-), using as a technique, differential pulse voltammetry. The method is based on the electrochemical reduction of nitrate ions on a gold ultramicroelectrode modified in situ by underpotential deposition of cadmium, and subsequently, the removal of cadmium monolayer and the electrochemical oxidation of nitrite on ultramicroelectrode unmodified. The voltammetric analysis for quantitative determination of nitrate and nitrite were carried out in NaClO4 0.1 molL-1 + HClO4 1.0 x 10-3 molL-1 (pH = 3.3) prepared with ultrapure water. Using the optimized experimental conditions and voltammetric parameters, analytical curves were constructed for determination of nitrite and nitrate separately and for sequential determination of the two analytes. The relationship between peak current and concentration of NO2- were found to be linear in the concentration range between 1.0 x 10-5 molL-1 and 1.1 x 10-4 molL-1, with a detection limit of 1.151 &plusmn; 0.091 &micro;molL-1 and quantification limit of 3.838 &plusmn; 0.091 &micro;molL-1. For determination of NO3- was also observed a linear relationship between peak current and concentration of analyte within the concentration range studied, which was from 2.00 x 10-5 molL-1 to 2.50 x 10-4 molL-1. The detection limit was 4.839 &plusmn; 0.275 &micro;molL-1 and the quantification limit was 16.131 &plusmn; 0.275 &micro;molL-1. The sequential determination of nitrite and nitrate was assessed within concentration range from 5.00 x 10-5 molL-1 to 2.50 x 10-4 molL-1 for NO3- and from 1.00 x 10-5 molL-1 to 4.50 x 10-5 for NO2-. In both cases, the relationship between peak current versus analyte concentration were found to be linear. The detection limits for sequential determination are 16.177 &plusmn; 0.794 &micro;molL-1 for NO3- and 2.243 &plusmn; 0.179 &micro;molL-1 for NO2- and the quantification limits are 53.922 &plusmn; 0.794 &micro;molL-1 for NO3- and 7.476 &plusmn; 0.179 &micro;molL-1 for NO2-. The detection and quantification limits and other statistical parameters presented in this work were obtained from calculations based on procedures described in Miller and Miller68 and Silva69.

Este trabalho descreve o desenvolvimento de um método eletroanalítico para determinação sequencial de nitrito (NO2-) e nitrato (NO3-), utilizando como técnica, a voltametria de pulso diferencial. O método se baseia na redução eletroquímica dos íons nitrato sobre um ultramicroeletrodo de ouro modificado in situ com cádmio depositado em regime de subtensão, e na seqüência, a remoção da monocamada de cádmio e a oxidação eletroquímica dos íons nitritos sobre o ultramicroeletrodo não modificado. Os ensaios voltamétricos para determinação quantitativa de nitrato e nitrito foram realizados em solução de NaClO4 0,1 molL-1 + HClO4 1,0x 10-3 molL-1 (pH = 3,3) preparada com água ultrapura. Utilizando as condições experimentais e os parâmetros voltamétricos otimizados, foram construídas curvas analíticas para determinação de nitrito e nitrato separadamente e também para determinação sequencial dos dois analitos. Para a determinação do NO2-, foi observado uma relação linear entre a corrente de pico e a concentração desse íon dentro do intervalo de concentração de 1,0 x 10-5 molL-1 a 1,1 x 10-4 molL-1, com um limite de detecção igual a 1,151 &plusmn; 0,091 &micro;molL-1 e limite de quantificação igual a 3,838 &plusmn; 0,091 &micro;molL-1. Para a determinação do NO3-, também foi observado uma relação linear entre corrente de pico e concentração desse analito dentro do intervalo estudado, que foi de 2,00 x 10-5 molL-1 a 2,50 x 10-4 molL-1. O limite de detecção encontrado foi 4,839 &plusmn; 0,275 &micro;molL-1 e o limite de quantificação 16,131 &plusmn; 0,275 &micro;molL-1. A determinação sequencial de nitrito e nitrato foi avaliada dentro do intervalo de concentração de 5,00 x 10-5 molL-1 a 2,50 x 10-4 molL-1 para NO3- e 1,00 x 10-5 molL-1 a 4,50 x 10-5 para NO2-. Para ambos os casos, a relação entre corrente de pico versus concentração do analito foi linear. Para a determinação sequencial os limites de detecção são 16,177 &plusmn; 0,794 &micro;molL-1 para NO3- e 2,243 &plusmn; 0,179 &micro;molL-1 para NO2- e os limites de quantificação são 53,922 &plusmn; 0,794 &micro;molL-1 para o NO3- e 7,476 &plusmn; 0,179 &micro;molL-1 para o NO2-. Os limites de detecção, os limites de quantificação e demais parâmetros estatísticos apresentados nesse trabalho, foram obtidos a partir de cálculos baseados em procedimentos descritos em Miller e Miller68 e Silva69. / This work describes the development of an electroanalytical method for sequential determination of nitrite (NO2-) and nitrate (NO3-), using as a technique, differential pulse voltammetry. The method is based on the electrochemical reduction of nitrate ions on a gold ultramicroelectrode modified in situ by underpotential deposition of cadmium, and subsequently, the removal of cadmium monolayer and the electrochemical oxidation of nitrite on ultramicroelectrode unmodified. The voltammetric analysis for quantitative determination of nitrate and nitrite were carried out in NaClO4 0.1 molL-1 + HClO4 1.0 x 10-3 molL-1 (pH = 3.3) prepared with ultrapure water. Using the optimized experimental conditions and voltammetric parameters, analytical curves were constructed for determination of nitrite and nitrate separately and for sequential determination of the two analytes. The relationship between peak current and concentration of NO2- were found to be linear in the concentration range between 1.0 x 10-5 molL-1 and 1.1 x 10-4 molL-1, with a detection limit of 1.151 &plusmn; 0.091 &micro;molL-1 and quantification limit of 3.838 &plusmn; 0.091 &micro;molL-1. For determination of NO3- was also observed a linear relationship between peak current and concentration of analyte within the concentration range studied, which was from 2.00 x 10-5 molL-1 to 2.50 x 10-4 molL-1. The detection limit was 4.839 &plusmn; 0.275 &micro;molL-1 and the quantification limit was 16.131 &plusmn; 0.275 &micro;molL-1. The sequential determination of nitrite and nitrate was assessed within concentration range from 5.00 x 10-5 molL-1 to 2.50 x 10-4 molL-1 for NO3- and from 1.00 x 10-5 molL-1 to 4.50 x 10-5 for NO2-. In both cases, the relationship between peak current versus analyte concentration were found to be linear. The detection limits for sequential determination are 16.177 &plusmn; 0.794 &micro;molL-1 for NO3- and 2.243 &plusmn; 0.179 &micro;molL-1 for NO2- and the quantification limits are 53.922 &plusmn; 0.794 &micro;molL-1 for NO3- and 7.476 &plusmn; 0.179 &micro;molL-1 for NO2-. The detection and quantification limits and other statistical parameters presented in this work were obtained from calculations based on procedures described in Miller and Miller68 and Silva69.

Carbon fiber ultramicroelectrodes (CF-UMEs) are commonly used as electrochemical probes and sensors due to their small size, fast response, and high signal-to-noise ratio. Surface modification strategies are often employed on CF-UMEs to improve their selectivity and sensitivity for desired applications. However, many modification methods are cumbersome and require expensive equipment. In this study, a simple approach known as soft nitriding is used to prepare nitrogen-doped CF-UMEs (N-CF-UMEs). Nitrogen groups introduced via soft nitriding act as electrocatalytic sites for the breakage of O-O bonds during the reduction of peroxides like H2O2, a common target of biosensing strategies. Voltammetric studies confirm that, compared to CF-UMEs, N-CF-UMEs possess enhanced electrocatalytic activity towards H2O2 reduction as evidenced by an increase in current and positive shift in onset potential for the reaction. N-CF-UMEs also proved capable for amperometric detection of H2O2, exhibiting good linear response from 0.1 to 5.6 mM at -0.4 V vs. Ag/AgCl.

Nanoparticles are used as electrocatalysts due to their large surface area-to-volume ratios. Most studies of nanoparticle electrocatalysis are performed on collections of particles on a support, which represent ensemble average behavior influenced by spatial distribution of the nanoparticles. Therefore, recent emphasis has been placed on analyzing electrocatalytic behavior of single particles. The focus here is to develop carbon ultramicro- and nanoelectrode platforms for studying the electrocatalytic properties of single metal nanoparticles. Ultramicroelectrodes were prepared using chemical vapor deposition of carbon in pulled quartz capillaries. Electrode diameters were determined by cyclic voltammetry. Electrodes were modified using a soft nitriding technique to enable immobilization of platinum nanoparticles through reduction of H2PtCl6 using NaBH4. Cyclic voltammetry was used to determine the presence of platinum particles through characteristic peaks associated with Pt oxide formation and reduction. Ultimately, these electrodes could be used to analyze single uncapped nanoparticles to understand the electrochemical properties of single nanoparticles.

Ultramicroelectrodes (UMEs) are useful as probes for evaluating electroactive species in confined spaces (e.g., inside living cells) and for measuring fast electrochemical reactions. However, UME applications often require modification of the electrode surface to improve selectivity and sensitivity towards target analytes. Previous research in our group demonstrated that a simple soft nitriding method introduces surface nitrogen (N)-containing groups on carbon fiber (CF), leading to improved electroreduction of hydrogen peroxide (H2O2) on CF-UMEs. However, sensitivity for H2O2 detection using N-CF-UMEs was low compared to that for other modified UMEs. As an alternative to N-CF-UMEs, a simple strategy for preparing phosphorus (P)-doped CF-UMEs was first investigated. Since P-CF-UMEs performed similarly to N-CF-UMEs, an alternative epoxy sealing strategy for preparing CF-UMEs and doped-CF-UMEs was also developed. Compared to P-CF-UMEs and N-CF-UMEs prepared by traditional laser-assisted pipette pulling, the epoxy-sealed electrodes exhibited 20-50 times higher sensitivities and 2-3 times lower detection limits for H2O2.

Studies of single, isolated nanoparticles provide better understanding of the structure-function relationship of nanoparticles since they avoid complications like interparticle distance and nanoparticle loading that are typically associated with collections of nanoparticles distributed on electrode supports. However, interpretation of results obtained from single nanoparticle immobilization studies can be difficult to interpret since the underlying nanoelectrode platform can contribute to the measured current, or the immobilization technique can adversely affect electron transfer. Here, we immobilized ligand-free gold nanoparticles on relatively electrocatalytically inert nitrogen-doped carbon ultramicroelectrodes that were prepared via a soft nitriding method. Sizes of the particles were estimated by a recently reported electrochemical method and were found to vary linearly with deposition time. The particles also exhibited electrocatalytic activity toward methanol oxidation. This immobilization strategy shows promise and may be translated to smaller nanoelectrodes in order to study electrocatalytic properties of single nanoparticles.

Le monoxyde d'azote (NO*) et l'anion peroxynitrite (ONOO−) sont deux molécules jouant un rôle clé dans de nombreuses pathologies dont certains cancers, les maladies de Parkinson et Alzheimer, ainsi que les traumatismes crâniens. Ce travail décrit le développement de capteurs électrochimiques permettant la détection simultanée de ces deux analytes d'intérêt biologique. Pour atteindre cet objectif, des dispositifs intégrant plusieurs réseaux d'ultramicroélectrodes (UMEs) d'or ont été fabriqués, à l'aide de techniques photolithographiques. La caractérisation électrochimique de ces réseaux montre qu'ils permettent d'améliorer la sensibilité des mesures, en comparaison avec des UMEs individuelles. Afin de rendre la mesure de NO* sélective vis-à-vis des interférents biologiques, nous avons d'abord étudié l'influence de plusieurs types de membranes électropolymérisées à la surface des électrodes. Ceci nous a permis d'identifier une combinaison de membranes de polyeugénol et polyphénol conférant une bonne sélectivité au capteur. Par la suite, nous nous sommes intéressés à la mise au point d'une méthode de détection électrochimique de ONOO−, basée sur la réduction de son acide conjugué à une électrode d'or non modifiée. À la suite de ces études, la détection électrochimique simultanée de NO* et ONOO− a été réalisée dans des solutions synthétiques. Enfin, nous décrivons la détection de NO* produit par des cellules vivantes, les macrophages RAW 264.7.