Shelley D. Minteer

Department of Chemistry, Saint Louis University, Missouri

CONTENTS

Introduction………………………………………………………………………………………………….. 191

Direct Ethanol Fuel Cells……………………………………………………………………………….. 192

Ethanol Electrocatalysts……………………………………………………………………………….. 193

PtRu Catalysts………………………………………………………………………………….. 193

PtSn Catalysts………………………………………………………………………………….. 194

Conclusions…………………………………………………………………………………………………… 201

References…………………………………………………………………………………………………….. 201

Abstract This chapter details the background and performance of direct ethanol fuel cells (DEFCs). This chapter compares direct ethanol fuel cells to direct methanol fuel cells and other alcohol-based fuel cells. It discusses recent devel­opments in bimetallic electrocatalysts, membrane electrode assembly (MEA) fabrication techniques, temperature effects, and the effects of fuel concentration on the performance of the direct ethanol fuel cell.

INTRODUCTION

Portable power requires simplistic systems that operate at or near room temper­ature. Most research in fuel cells for use as portable power have employed polymer electrolyte membrane fuel cells. Polymer electrolyte membrane (PEM) fuel cells can be characterized into two categories: reformed and direct systems. Reformed systems require the use of an external reformer to reform a fuel (methane, methanol, ethanol, gasoline, etc.) into hydrogen for use in the fuel cell. In direct systems the fuel is oxidized at the surface of the electrode without treatment. Over the last 40 years, there has been extensive research on direct methanol fuel cells (DMFC) for portable power applications at low to moderate temperatures [1-4]. However, there are a number of problems associated with the use of methanol as a fuel for portable power supplies. Methanol is highly
toxic and could lead to long-term environmental problems because methanol is so miscible in water [5]. These limitations have led researchers to investigate other fuels. Ethanol is an attractive alternative to methanol as a fuel for a fuel cell. Ethanol is a renewable fuel and can be produced from farm products and biomass. Ethanol and its intermediate oxidation products have been shown to be less toxic than other alcohols [6]. The problem with ethanol as a fuel (in com­parison to methanol) is that complete oxidation of ethanol requires the breaking of a C-C bond, which is difficult at traditional Pt-based catalysts. This typically leads to incomplete oxidation of ethanol, which decreases the efficiency of the fuel cells and could provide toxic by-products or electrode passivation. This chapter focuses on the basics of direct ethanol fuel cells and the effects of catalyst, temperature, and fuel concentration on fuel cell performance.