Hydrogen Fuel Cell and PEMFC Technology

Fuel Cells Portal

Fuel Cells are energy conversion devices set to replace combustion engines and compliment batteries in a number of applications. They convert the chemical energy contained in fuels, into electrical energy (electricity), with heat and water generated as by-products. Fuel cells continue to generate electricity for as long as a fuel is supplied, similar to traditional engines. However unlike engines, where fuels are burnt to convert chemical energy into kinetic energy, fuel cells convert fuels directly into electricity via an electrochemical process that does not require combustion. This process enables fuel cells to be more efficient at creating electricity than engines which have to go through an additional step to convert the kinetic energy into electrical energy.

These technologies offer a combination of benefits that can:

• Lower your carbon footprint
• Reduce noise and air pollution
• Reduce fuel bills – through the use of more efficient technology
• Utlise renewable fuels produced onsite.
• Generate heat and power onsite
• Improve environmental credentials and corporate social responsibility
• Potential long-term money savings
• Earn ROQ’s

All fuel cells contain either solid or liquid Electrolytes sandwiched between two electrodes. There are a number of different Types of Fuel Cells, and these are characterised by their particular electrolyte. Different types of fuel cells operate at different temperatures and on a variety of fuels, including both gaseous fuels such as hydrogen, natural gas, propane and biogases, to liquid fuels such as methanol and ethanol. Low temperature fuel cells require pure hydrogen, whereas higher temperature fuel cells can operate directly on hydrocarbon fuels such as natural gas. There are several main types of fuel cells, each more suitable for particular applications.

PEM - Proton Exchange Membrane Fuel Cells Portal

Proton exchange Membrane (PEM) fuel cells, also known as Polymer exchange membrane fuel cells typically operate on pure (99.999%) hydrogen fuel. The PEM fuel cell combines the hydrogen fuel with the oxygen from the atmosphere to produce Water, heat (up to 90°C) and electricity.

How it Works

PEM Fuel cells typically utilise platinum based catalysts on the Anode to split the Hydrogen into positive ions (protons) and negative electrons. The ions pass through the membrane to the cathode to combine with oxygen to produce water. The electrons must pass round an external circuit creating a current to rejoin the H2 ion on the cathode. Chemical Equation:

Anode: 2H₂ »» 4H⁺ + 4e^-
Cathode: O₂ + 4H⁺ + 4e^- »» 2H₂O

Each cell produces approximately 1.1 volts, so to reach the required voltage the cells are combined to produce stacks. Each cell is divided with bipolar plates which while separating them provide a hydrogen fuel distribution channel, as well as a method of extracting the current.

PEM fuel cells are considered to have the highest energy density of all the fuel cells, and due to the nature of the reaction have the quickest start up time (less than 1 sec) so they have been favoured for applications such as vehicles, portable power and backup power applications.

The intolerance of the catalysts to impurities such as carbon monoxide has led to developments of high temperature membranes which operate at 150°C +. This enables the catalysts to tolerate greater impurities in the hydrogen supply.

Image source - http://www.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html