This thesis aims to understand of the role of the secondary metal for improvement of alkaline methanol and ethanol oxidation reaction electrocatalysis using different morphologies of Au-Pd and Ag-Pd bimetallic nanocatalysts.
The Direct Methanol Fuel Cell (DMFC) is a fuel cell technology capable of generating energy through the electrochemical oxidation of methanol. The methanol oxidation reaction (MOR), the reaction that occurs at the anode, is of research interest to produce renewable energy. This process relies on precious metal catalysts to efficiently produce energy, namely nanoscale Pt-Ru. Current fuel cell technology is therefore expensive and unsuitable for large-scale implementation. Palladium can act as an electrocatalyst for the process in the same way as platinum, but in its monometallic form suffers from high overpotentials and significant poisoning by carbon monoxide (CO) generated in situ. Previous research has shown improved activity of palladium in alkaline electrolytes which, while unsuitable for platinum, are known to improve alcohol oxidation reaction kinetics through preferred oxidation of methanol to formate. The addition of a secondary metal assists in both modulation of palladium-reactant binding strengths and co-catalysed oxidation of CO when exposed at the surface.
Chapter one reviews the literature on the DMFC and anode electrocatalysts. The current platinum catalysts and foundation knowledge of the mechanism on platinum are compared to current palladium catalysts. The requirements for new nanoscale palladium catalysts and background on their synthesis are outlined. Chapter two details the methods used for characterisation of nanocrystals produced in this thesis. Chapter three validates a modified synthetic method for Au-Pd core shell and develops new syntheses for Ag-Pd core-shell and Au-Pd alloy nanocrystals. Chapter four assesses the activity of Au-Pd core-shell and alloy nanocrystals for MOR electrocatalysis and finds that gold, both at the surface and inside the core, enhances activity and stability. Chapter five correlates increasing electrocatalytic properties with decreasing shell thickness, originating from electron-withdrawing effects of gold on palladium. Chapter six adapts the ideas from MOR and analyses the catalytic activity of Au-Pd bimetallic nanocrystals for the Ethanol Oxidation Reaction (EOR). Chapter seven draws overall conclusions from the thesi