Experiments (PROVISIONAL)
Hands on practicals with a choice of FIVE out of 10 experiments using state-of-the-art instruments from leading manufacturers:
1. Cyclic Voltammetry (I) - Surface Reactions: Cyclic voltammetry will be used to examine surface changes at electrodes. Adsorption and oxide formation on gold and platinum, as well as the redox cycling of polyaniline, will be considered.
2. Cyclic Voltammetry (II) - Solution Reactions: Cyclic voltammetric measurements provide a simple diagnostic method for the preliminary study of homogeneous reactions coupled to redox processes. In this experiment, the electrochemistry of ferrocene monocarboxylic acid is first investigated, followed by a study of its use as a homogeneous mediation for the oxidation of glucose oxidase and enzyme used in blood glucose measurement.
3. Numerical simulations of electrochemical processes: This experiment uses a commercial simulation package (e.g. DigiSim or DigiElch) to simulate both simple electron transfer reactions and complex mechanisms with coupled homogeneous chemical reaction. The aim is to investigate how the rates of electron transfer and chemical kinetics alter the voltammetric behaviour at macro and microelectrodes. In the final part of the experiment, the simulation package is used to determine the mechanism for a reaction based on the analysis of experimental data provided. The experiment illustrates the underlying principles of voltammetry and the relationship between the concentration profiles and the measured currents.
4. Pulsed Voltammetric Techniques: The combination of potential sweeps and steps has led to a range of voltammetric techniques, e.g. normal pulse voltammetry, differential pulse voltammetry, staircase voltammetry, square wave voltammetry, etc… This experiment will explore the principle of some of the major techniques and compare their advantages and limitations.
5. Rotating Disc Electrode: The rotating disc electrode allows control of the mass transport to the electrode. The rotation dependence of the reduction of Cu2+ to Cu+ and Cu(0) will be investigated.
6. Electrochemical characterization of materials for energy applications: Current-control vs. potential-control approaches for the characterization of materials for energy applications will be compared, and the results will be analyzed taking into account ohmic drop contributions, measurement time scale, diffusion limitations, etc.
7. A.C. Impedance Spectroscopy: The impedance of a simple redox system (ferro / ferricyanide) will be investigated to illustrate the technique and the interpretation of the results. The effect of reducing the supporting electrolyte concentration will be explored.
8. A.C. Impedance of Electrochemical Materials: Electronic conductivity, ionic conductivity, diffusion coefficient and pseudo-capacitance are important parameters for the evaluation of electrochemical materials for many applications. This experiment will investigate the determination of these values by impedance and time domain techniques.
9. Factors Determining Experimental Response: Electrochemistry relies, in most cases, on the measurement of either the current or the potential recorded at an electrode as a function of other physical parameters of the system. These measurements are subject to practical considerations, some of which will be highlighted in this experiment. Factors such as equipment response, uncompensated resistance, cell design and experiment design are demonstrated and simple counteractive measures suggested.
10. Cyclic voltammetry and potential steps interrogated by UV-Vis Spectroelectrochemistry: In this experiment, we employ a UV-Vis spectrometer, a fibre optic reflectance probe, a potentiostat and XYZ positioning system (interfaced to a PC) to monitor spectrophotometric changes of electroactive species with electrode potential. Initially a redox system is investigated using spectroelectrochemistry to follow the changes in local concentration as a function of potential in conventional cyclic voltammetry and potential step experiments. The spectroelectrochemical results are compared to the conventional electrochemistry to highlight the advantages and limitations of the technique. In addition, the effects of local pH are probed with a pH indicator on a platinum electrode and the colour changes of a modified electrode are monitored to elucidate the local pH swings and changes in redox states occurring at the electrode surfaces respectively.