Direct Alcohol Fuel Cells: Nanostructured Materials for the Electrooxidation of Alcohols in Alkaline Media

Abstract

The exploitation of biomass derived alcohols in direct fuel cells is an attractive and simple way to transform their chemical energy into electrical power. Renewable alcohols such as ethanol, ethylene glycol and glycerol could replace methanol in traditional direct methanol fuel cells (DMFCs) due to their high energy densities, low vapor pressure, low toxicity and well established distribution infrastructure. For these devices to be practical alternatives, fast anode electrode kinetics of alcohol electrooxidation are required together with complete oxidation to CO2. To date the most successful exploitation of such alcohols in direct fuel cells have been under alkaline conditions. This is because alcohol electrooxidation kinetics under acidic conditions such as those of DMFCs are very sluggish. This combined with the highly corrosive conditions of the acidic electrolyte limits the choice of electrocatalyst materials to high concentrations of platinum alloys. In alkaline media, platinum can be replaced by more abundant transition metal based materials, either nanoparticles or molecular complexes, that show significantly higher activity and selectivity. This chapter provides an overview of recent developments in the preparation of electrocatalytic materials for alcohol electrooxidation in alkaline media. In addition to maximizing electrical power output these materials can be tuned to optimize the selectivity of oxidation thus leading to the co-production of partially oxidized industrially relevant intermediates. A discussion of recent work on exploiting SMSIs (Strong Metal Support Interactions) to improve activity, fuel efficiency and stability of electrocatalyst materials is also included.