Alcohol fuel cell

Introduction

A fuel cell is an electrochemical device which converts the chemical energy of compounds into electrical energy via electrochemical reactions. Unlike a conventional battery, a fuel cell is not an energy-storing apparatus but reactants are continuously replenished into the cell separately during the operation. A Hydrogen rich compound or pure hydrogen is used as a fuel, while oxygen from the air or pure oxygen commonly serves as oxidant. The benefits obtained using a fuel cell for energy production are high efficiency and low emissions of harmfull effluents.

Alcohol fuel cell

In an alcohol fuel cell, as the name indicates alcohol is used as a fuel to produce electricity.  The cell in which Methanol is directly used as fuel is named as Direct Methanol Fuel cell. The technology behind Direct Methanol Fuel Cells (DMFC), a particular example for alcohol fuel cell.  It is still in the early stages of development, but it has been successfully demonstrated powering mobile phones and laptop computers—potential target end uses in future years.

In the early 1990s, DMFCs were not appreciated because of their low efficiency and power density, as well as other problems. Improvements in catalysts and other recent developments have increased power density to 20-fold and it is expected that the efficiency may eventually reach 40%.

DMFC is very similar to the PEMFC in that the electrolyte is a polymer and the charge carrier is the hydrogen ion (proton). However, in a DMFC, the liquid methanol (CH₃OH) is oxidized in the presence of water at the anode generating CO₂, hydrogen ions and the electrons that travel through the external circuit as the electric output of the fuel cell. The hydrogen ions travel through the electrolyte and react with oxygen from the air or pure oxygen, used as oxidant and the electrons from the external circuit to form water at the anode completing the circuit.

Cell reactions

Reaction at the Anode:      CH₃OH + H₂O => CO₂ + 6H+ + 6e^-
Reaction at the Cathode:   3/2 O₂ + 6 H⁺ + 6e^- => 3 H₂O
Overall Cell Reaction:       CH₃OH + 3/2 O₂ => CO₂ + 2 H₂O

These cells have been tested to work in a temperature range from about 50ºC-120ºC. This low operating temperature and advantage of no requirement for a fuel reformer make the DMFC an excellent candidate for very small to mid-sized applications, such as cellular phones and other consumer products, up to automobile power plants.

One of the drawbacks of this alcohol fuel cell is that the low-temperature oxidation of methanol to hydrogen ions and carbon dioxide requires a more active catalyst, which typically means a larger quantity of expensive platinum catalyst is required than in conventional PEMFCs.

One other demerit of driving the development of alcohol fuel cells is the fact that methanol is toxic. Therefore, some companies have been developing the advantageous Direct Ethanol Fuel Cell (DEFC). The performance of the DEFC is currently only about half that of the DMFC, but this gap is expected to narrow within very short time.