Pt and Au as electrocatalysts for various electrochemical reactions

MSc (Chemistry), North-West University, Potchefstroom Campus, 2015

In this study the focus was on the electrochemical techniques and aspects behind the establishment of the better catalyst (platinum or gold) for the sulphur dioxide oxidation reaction (SDOR). One of the primary issues regarding the SDOR is the catalyst material, thus the comparative investigation of the performance of platinum and gold in the SDOR, as found in this study. Ultimately, the SDOR could lead to an effective way of producing hydrogen gas, which is an excellent energy carrier. The electrochemical application of the oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR) is an integral part of the catalytic process of water electrolysis, and by using fuel cell technology, it becomes even more relevant to this study and can therefore be used as a control, guide and introduction to the techniques required for electrochemical investigation of catalyst effectiveness. Subsequently, the EOR as well as the ORR was used as introduction into the different electrochemical quantification and qualification techniques used in the electrochemical analyses of the SDOR. Considering the ORR, gold showed no viable activity in acidic medium, contrarily in alkaline medium, it showed good competition to platinum. Gold also lacked activity towards the EOR in acidic medium compared to platinum, with platinum the best catalyst in both acidic and alkaline media. Ultimately, platinum was established to be the material with better activity for the ORR with gold a good competitor in alkaline medium, and platinum the better catalyst for the EOR in both acidic and alkaline media. With the main focus of this study being the SDOR, gold proved to be the best catalyst in salt and gaseous forms of SO2 administration compared to platinum when the onset potential, maximum current density, Tafel slope and number of electrons transferred are taken into consideration. The onset potential was determined as 0.52 V vs. NHE for both platinum and gold using SO2 gas and 0.54 V and 0.5 V for gold and platinum respectively, using Na2SO3 salt. The maximum current density using gaseous SO2 for platinum at 0 RPM was 400 mA/cm2 with a Tafel slope of 891 mV/decade whereas gold had a maximum current density of 300 mA/cm2 and a Tafel slope of 378 mV/decade. Using Na2SO3 salt, the maximum current density of gold was 25 mA/cm2 with a Tafel slope of 59 mV/decade whereas platinum only achieved 18 mA/cm2 with a Tafel slope of 172 mV/decade. Concerning the number of electrons transferred, gold achieves a transfer of 2 while platinum only 1 for both SO2 gas and Na2SO3 salt. Taking all these summarised determinations into account, gold was established to be a very competitive catalyst material for the SDOR, compared to platinum.

Masters