Mechanistic Electrochemistry: Investigations of Electrocatalytic Mechanisms for H2S Detection Applications
This thesis describes the development of electrochemical analytical approaches for the investigation of sulphide detection in stagnant and fluidic environments. The project reports the use of Fourier transform large amplitude alternating current voltammetry (FTACV) as a novel analytical technique for the investigation of sulphide sensing. Novel reactor technology and FTACV measurements carried out using macro and microelectrodes in stagnant and fluidic conditions are reported for the first time. The novel strategy adopts the use of an electrocatalytic (EC') mechanism by using a redox mediator to facilitate the reaction with sulphide in aqueous solutions. In order to support the analysis of FTACV, other electrochemical analytical techniques, cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were also employed to support the observations from FTACV. Chapter 3 reports the application of the CV and FTACV for the detection of sulphide in stagnant conditions at a macroscale electrode. A split wave phenomenon, which is related to the reaction with sulphide, was observed both in the CV and FTACV. By measuring the current behaviour of the split wave, sulphide content in aqueous solution can be determined. Importantly, the split wave phenomenon of the FTACV is the first documented observation using macroscale electrodes. These observations highlight the potential of FTACV to support the detection of sulphide detection. Numerical models of the system are also presented from the calculation to support the experimental interpretation of the voltammetric responses of the CV and FTACV. In Chapter 4 measurements were focused on the voltammetric response of sulphide containing aqueous solutions using microelectrodes. In conventional CV measurements, the split wave behaviour observed at macroelectode disappears from the DC signal; however, for the FTACV measurements, the split wave can still be observed in the higher harmonics providing a clear and simple strategy for detecting sulphide. The results achieved in the FTACV are the first documented observation under the steady state at microelectrodes. Again numerical simulations are reported for this case to support the experimental results. Chapter 5 extends the FTACV measurements for sulphide detection to hydrodynamic environments. The design, development and application of a microfluidic electrochemical system are reported. Split wave characteristics were for the first time detected in both dc and FTACV measurements. The results support the possibility of using dc and ac voltammetry to detect sulphide, while also being used as a guide to assess the split-wave behaviour of the EC' mechanism under fluidic conditions. Numerical models were used to support the analysis of the experimental measurements.