Carbon is a unique element. Its uniqueness stems from its ability to bond with itself and form stable allotropes with incredibly diverse physical, chemical, electrical, and electrochemical properties. These allotropes include single- and poly-crystalline diamond (sp3), diamond-like carbon (hybrid sp2/sp3) and graphitic carbon (sp2). Of these, the diamond and diamond-like carbon electrodes are the least studied. Owing to their commercial availability, low cost, wide potential window, low background current, and chemical stability, these allotropes are used as electrode materials in electroanalysis, energy storage technologies, and electrochemical separations. For their optimal use, it is critical to understand and control the parameters that affect their electrochemical behavior. Over the last three decades, structure-property-function relationships for carbon electrodes have been established in traditional aqueous electrolytes. However, this knowledge is missing in the novel electrolytes called room temperature ionic liquids (RTILs).RTILs are liquid salts solely made of charged cations and anions. They contain no solvent. They are finding ever-increasing use as electrolytes due to their excellent properties like wide thermal and electrochemical potential window, negligible vapor pressure, and good ionic conductivity. Since RTILs are highly charged media without any solvent, their organization at electrified interfaces (i.e., charged electrodes) is different from the organization of aqueous and organic electrolyte solutions.The research described in this dissertation focused on understanding the voltammetric properties and capacitance of nanostructured diamond and tetrahedral amorphous carbon thin film electrodes in RTILs. Specific issues investigated included how the RTIL organization change with the applied potential, RTIL type, the carbon electrode type, and the electrode surface chemistry. The physical, chemical, and electronic properties of boron-doped diamond (BDD) and nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) thin-film electrodes are discussed, as are the properties of glassy carbon that was used for comparison studies.Firstly, the effect of RTIL cation size and viscosity on the voltammetric behavior and capacitance of BDD was investigated. Next, the BDD surface was chemically modified to vary the type and coverage of surface groups (H- vs. O-termination). The surface wettability, as well as the voltammetric behavior and capacitance, were studied in two different RTILs and compared with the electrode behavior in an aqueous electrolyte solution. Finally, ta-C:N electrodes of varying nitrogen content were characterized to define their microstructure (sp2/sp3 content), and the voltammetric behavior and capacitance in the two RTILs were studied.
Read
