Fuelling the 21st century

Key text

The function of this device – small enough to fit on your desktop – is power generation. Known as a fuel cell, it efficiently produces enough electricity to run all the equipment on the spacecraft, including the crucial life support systems.

What is a fuel cell?

Fuel cells, like batteries, transform chemical energy into electricity. However, unlike batteries, fuels cells don't store electrical energy. Instead, they convert energy from chemical reactions directly into electrical energy (Box 1: How fuel cells work).

William Grove produced the first fuel cell over 150 years ago. He based his experiment on the fact that sending an electric current through water splits the water into its component parts of hydrogen and oxygen. So, Grove tried reversing the reaction – combining hydrogen and oxygen to produce electricity and water. This is the basis of a simple fuel cell.

Generating electricity from coal

In Australia, most of our electricity comes from burning coal. Transforming coal into electricity requires a number of steps. At each step, energy is lost from the system. Additional energy is lost during transmission along power lines. By the time electricity reaches your power point, less than 30 per cent of the energy originally stored in the coal is available to you.

Burning coal to generate electricity is not only inefficient, it is also polluting. It releases oxides of sulfur and nitrogen, contributing to smog and acid rain. (These emissions are more of a problem overseas than in Australia where the coal is relatively clean.) Burning coal also produces large amounts of carbon dioxide, a greenhouse gas.

Fuel cells offer a far more efficient and less polluting way of generating power than fossil fuel power stations or combustion engines. Fuel cells have another advantage - there are no moving parts.

Moving to a new energy source

Today, fuel cells are finding more and more applications as people realise what an effective source of energy they are. They are versatile, produce little pollution and wring almost every last drop of electricity from the fuels. Fuel cells hold so much promise that billions of dollars will be spent on research and development worldwide.

Several companies, such as ONSI Corporation and Fuji Electric, produce fuel cells commercially. Most fuel cells generate from 40 to 200 kilowatts of power – enough to supply office blocks, hospitals, supermarkets, mines and military bases.

Advocates of fuel cell technology say that this form of energy production is ideal for on-site generation of heat and electricity for a wide range of applications, including shopping complexes, educational institutions, and mining and drilling rigs. They can also supply energy for ships and submarines.

The Australian Technology Park in Sydney has a 200-kilowatt fuel cell that uses natural gas as a fuel. It supplies power to the Park's medical centres, laboratories and computer systems. This is the first Australian commercial application of such a cell. Commercial use of fuel cells will grow as better designs and new materials become available, reducing production costs.

Fuel cells for motor vehicles

Because of the need to reduce emissions of air pollutants, automotive manufacturers are exploring the feasibility of replacing the internal combustion engine with fuel cell technology. Electric vehicles are far less polluting than those using petrol or diesel fuel. However, electric vehicles that run on rechargeable batteries are very heavy because of the weight of the batteries and are only able to travel short distances before the batteries have to be recharged.

Related site: Fuel cell vehicles Lists fuel cell vehicles from car manufacturers and their specifications. (Fuel Cells 2000, USA)

Ballard Power Systems, a Canadian company, is a world leader in this technology and has delivered a number of prototype fuel cell buses to city authorities in the USA and Europe, to be used in demonstrations and trials. The city of Perth is taking part in a trial of buses powered by hydrogen fuel cells.

Daimler-Chrysler has been producing a range of fuel cell cars called the NECAR since 1994. Recognising that change is easier in small steps, most major car manufacturers are developing fuel cell vehicles, that run on hydrogen, methanol or petrol. So, motorists will still be able to drive down to the nearest service station to fill their cars.

Outwardly, the fuel-cell powered cars will look similar to current cars. But they are likely to attract curious glances as they glide away from the petrol pump in near silence. Exhaust gases will be little other than nitrogen, carbon dioxide and water vapour. In future as other fuels become avaliable, a mechanic will tune the vehicle's fuell cell to run on them. The Australian Antarctic Division has two hybrid cars – with a combined petrol/electric motor – in its fleet of vehicles in Tasmania.

Power for the 21st century

Industrialised countries like Australia depend on the availability of vast amounts of cheap, convenient energy. Throughout the 20th century, we have relied on fossil fuels to supply this energy. While we will continue to burn fossil fuels in power stations and engines, fuel cells present a clean, efficient alternative for some of our energy needs. As we move into a new century, the devices that power exploration of space will offer us effective new ways of obtaining the energy we need on our own planet.

Box

1. How fuel cells work

Related Nova topic

Which way ahead for hydrogen cars?

Box 1. How fuel cells work

Unlike a battery, a fuel cell does not store chemicals to produce energy. A fuel cell will produce electricity as long as fuel and oxygen are supplied.

The circuit in a simple fuel cell

A simple fuel cell consists of two conductors (an anode and a cathode) separated by an ionic conductor – an electrolyte – (eg, a salt solution). Hydrogen is pumped to the anode, and oxygen to the cathode. Hydrogen reacts with charged particles (ions) in the electrolyte, producing water and electrons. The electrons leave the fuel cell along wires; this is the electric current generated by the cell. The electrons return to the fuel cell cathode where they combine with oxygen and water to form ions which replace those consumed at the anode. And so the cycle continues, with hydrogen and oxygen being turned into water while generating electricity.

Simple fuel cells in space

Each simple fuel cell generates up to 1.23 volts. Individual cells can be wired together to produce greater voltages or higher current. The space shuttle, for example, has 96 individual cells arranged in three stacks. When hydrogen and oxygen are pumped into the shuttle's fuel cells, they generate 28 volts of direct current as well as heat and water. The heat is put to good use, vaporising the liquid fuels before they reach the fuel cells. Water flows into storage containers for drinking and other uses.

Some different types of fuel cells

Fuel cells are based on a simple principle. However, the chemical reactions involved do not occur readily. Unless special materials are used to construct the cells, very little electric current is produced. Much of the research with commercial fuel cells has focused on the development of suitable electrolytes.

Phosphoric acid fuel cells, using acid as the electrolyte and fuelled by hydrogen gas, are the most commercially developed type of fuel cell. They are being used overseas in hospitals, nursing homes, hotels, offices and schools.

Molten carbonate fuel cells promise high efficiency and can be powered by coal-based fuels such as carbon monoxide instead of hydrogen gas. These cells must be run at high temperatures (around 650°C) because they have a carbonate electrolyte that must be kept in a liquid form.

An Australian company, Ceramic Fuel Cells Ltd, is commercially developing highly efficient solid-oxide fuel cells (also known as ceramic fuel cells). These cells, unlike their predecessors, have a solid electrolyte separating the two electrodes. The cells can be fuelled by a variety of gases, including hydrogen, natural gas or coal gas.

They promise to be very efficient. They operate at 800°C and the hot exhaust gases can be fed to a turbine, extracting even more electricity.

The solid electrolyte consists of an exceptionally tough ceramic membrane of zirconia. Zirconia, or zirconium oxide, is a compound of the metal zirconium. (Conveniently, 70 per cent of the world's supply of this metal comes from Australia.) Heat the zirconia and you have a solid-state electrolyte able to rapidly transmit oxide ions from cathode to anode.

The trick in getting the oxide ions to migrate across the solid electrolyte is to add tiny amounts of the element yttrium, a silvery-grey metal, to the zirconia during manufacture. The crystalline array of zirconium oxide (ZrO₂) has two oxide ions to every zirconium ion. But in yttrium oxide there are only 1.5 oxide ions to every yttrium ion. The result: gaps in the crystal structure where oxide ions are missing. So, oxide ions from the cathode leap from hole to hole until they reach the anode.

Once at the anode, the oxide ions readily react with whatever gaseous fuel they encounter – carbon monoxide, hydrogen or methane – liberating electricity.

Proton exchange membrane (PEM) fuel cells, also known as polymer electrolyte fuel cells, are the most promising technology for transport applications. Built from components of carbon and polymer and operating at 60-90°C, proton exchange membrane fuel cells are lightweight and allow fast start-up and shut-down. They are also very compact.

Commercially competitive

Australia is competing with multi-national companies for a slice of the commercial fuel cell market, a market said to be worth billions of dollars worldwide. Ceramic Fuel Cells Ltd has developed a solid-oxide fuel cell the size of a 2-litre milk carton that produces 1.5 kilowatts, enough power to meet the needs of a typical household.

The company has also demonstrated a larger, 5-kilowatt unit, operating it continuously for 200 hours. These solid oxide fuel cells promise to achieve a very efficient conversion of fossil fuels to electricity, while producing only very low levels of pollutants.

Related sites

• Fuel cells – green power (Los Alamos National Laboratory, USA)

• Fuel cell descriptions (Department of Defense, USA)

• Ceramic fuel cells limited: Solid oxide fuel cells (Australian Technology Showcase)

Activities

• California Energy Commission
  • Science projects: Lemon power

• Newton's Apple (USA)
  • Electricity

• Fun Science Gallery, USA
  • Experiments in electrochemistry
    Topics include conductors, batteries, potentials of reduction and galvanic deposition.

• Fuel Cell Institute of Australia
  • Moonshot 2010
    Describes the Australian Hydrogen and Fuel Cell Science and Technology Education Program and how to participate in it.

Activity 1. Making a simple electrochemical cell

Materials (for each small group)

• piece of zinc (about 8 cm x 1 cm)
• piece of copper (about 8 cm x 1 cm)
• emery paper
• distilled water (about 40 mL, for rinsing)
• 25 mL of 0.1 M zinc (II) nitrate in a 50 mL beaker
• 25 mL of 0.1 M copper (II) nitrate in a 50 mL beaker
• ammeter (centre-zero, 0-1 milliamps with 2 leads each with an alligator clip at the free end)
• filter paper strip (about 8 cm x 1 cm)
• saturated solution of sodium nitrate (to make salt bridges)

Procedure

Safety notes:

• Do not allow any solution to come into contact with your mouth or eyes.

• Notify your teacher immediately if a spill occurs.

Set up the equipment as follows:

1. Rub the surfaces of the piece of zinc and the piece of copper with emery paper then rinse with distilled water.

2. Place the piece of zinc into the zinc (II) nitrate solution.

3. Place the piece of copper into the 25 mL of copper (II) nitrate solution.

4. Place the beakers side by side making sure the zinc and copper are NOT touching.

5. Connect the alligator clip of one lead to the zinc; connect the alligator clip of the other lead to the copper.

6. Observe the ammeter needle.

7. Carefully immerse the filter paper strip in the saturated solution of sodium nitrate.

8. Suspend the wet filter paper so that one end is immersed in the zinc (II) nitrate solution and the other is immersed in the copper (II) nitrate solution. This will form a salt bridge. (Make sure that both ends of the strip are immersed.)

9. Observe the needle on the ammeter.

• Was there a difference in the ammeter reading before and after you added the salt bridge? Explain your answer.

Teachers notes

Safety notes

Make sure students read the safety notes outlined at the beginning of the activity. Ideally, students should wear safety glasses to protect against splashing of chemicals.

Preparation

To prepare 1 litre of 0.1 M zinc nitrate: weigh 24.3 grams of Zn(NO₃)₂-3H₂0 and add distilled water to make 1 litre. (For Zn(NO₃)₂-6H₂O, weigh 29.7 grams and add distilled water to make 1 litre.)

To prepare 1 litre of 0.1 M copper nitrate: weigh 24.2 grams of Cu(NO₃)₂-3H₂O and add distilled water to make 1 litre.

To prepare a saturated solution of sodium nitrate: dissolve approximately 900 grams of NaNO₃ in 1 litre of distilled water.

Background information

Before the salt bridge is in place, there should be no ammeter deflection – no current flow. After the salt bridge is added there should be current flow.

Electron flow is from zinc to copper. (Electrons are taken from the more reactive metal, zinc.)

The potential difference between the electrodes of an electrochemical cell when no current is drawn from the cell is called the electromotive force (emf). You can measure the force of the electrochemical cell by replacing the ammeter in this activity with a voltmeter. Connect one terminal of the voltmeter to the zinc, and the other terminal to the copper. If the voltmeter is deflected in the negative direction, reconnect the leads so that a positive scale reading is obtained. The emf of the cell should be about 1.1 volts.

Further reading

Useful sites

This is a good introduction to fuel cells. Includes a simple diagram of a fuel cell.
http://www.fuelcells.org/

How Stuff Works (USA)

• How fuel cells work
  Takes a look at each of the existing or emerging fuel cell technologies, details how one of the most promising technologies works, and discusses a few potential applications of fuel cells.
  http://www.howstuffworks.com/fuel-cell.htm

• How the hydrogen economy works
  Explains the environmental advantages of using hydrogen instead of fossil fuels.
  http://www.howstuffworks.com/hydrogen-economy.htm

• How electric cars work
  Explains how an electric car works by comparing it to a petrol powered car.
  http://auto.howstuffworks.com/electric-car.htm/printable

Fuel cells (Energy Efficiency and Renewable Energy Network, US Department of Energy)

• Basics
  Describes how a fuel cell works.
  http://www.eere.energy.gov/hydrogenandfuelcells/fuelcells/basics.html

• Types of fuel cells
  Classifies fuel cells on the basis of the chemical reactions, the kind of catalysts required and their applications.
  http://www.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html

• Parts of a fuel cell
  Describes the components of the polymer electrolyte membrane fuel cell.
  http://www.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_parts.html

• Fuel cell animation
  Provides an animation to show how a fuel cell uses hydrogen to produce electricity.
  http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcell_animation.html

Electro-Chem-Technic (UK)

This manufacturer presents the basic principles of fuel cell science as well as considerable detail about the different types of fuel cells.
http://www.ectechnic.co.uk/

Beyond batteries

Scientific American describes a simple fuel cell and discusses commercial applications of various types of fuel cells that are being developed.
http://www.sciam.com/article.cfm?articleID=000103AE-74A1-1C76-9B81809EC588EF21

Hydrogen energy and fuel cells: A vision of the future (European Commission)

Summarises the changes required to move to a hydrogen economy.
http://europa.eu.int/comm/research/energy/pdf/hydrogen-report_en.pdf

Australian Broadcasting Corporation

• The hydrogen economy (Earthbeat, 31 May 2003)
  Describes a trial of hydrogen-powered buses in Europe and possible ways to introduce the hydrogen economy in Australia.
  http://www.abc.net.au/rn/science/earth/stories/s868395.htm

• Fuel cells (The Science Show, 30 June 2001)
  Discusses ceramic fuel cells and why they are an efficient and environmentally friendly energy source.
  http://www.abc.net.au/rn/science/ss/stories/s319789.htm

Glossary

battery. A source of electric current. Batteries consist of two electrodes immersed in an electrolyte. The electrolyte reacts chemically with the electrodes generating an electric current. More information about batteries can be found at How batteries work (How Stuff Works, USA)

cathode. The positive electrode in an electrochemical cell. Electrons flow back into a fuel cell through the cathode.

electrode. An electrical conductor. Electrochemical reactions occur on the surface of an electrode.

An electrode can be used to deliver electricity to the body or to receive electricity from it. Delivering electricity to the body is used to stimulate; receiving electricity from the body can be used to detect and record signals. In either case the term refers to the contact formed by the stimulating or recording device within the body.

electrolyte. A substance that produces ions (particles with an electric charge) when dissolved in water. The resulting solution (which can also be referred to as an electrolyte) conducts electricity.

electron. A negatively charged particle that is a constituent of an atom. Electrons can move from atom to atom. When they do, they produce an electric current.

greenhouse gas. A gas that is transparent to incoming solar radiation and absorbs some of the longer wavelength infrared radiation (heat) that the Earth radiates back. The result is that some of the heat given off by the planet accumulates, making the surface and the lower atmosphere warmer. For more information see The greenhouse effect (CSIRO Atmospheric Research, Australia).

turbine. A device in which a stream of water or gas turns a bladed wheel, converting the kinetic energy of the fluid flow into mechanical energy available from the turbine shaft. The earliest turbines were water wheels. Now, steam turbines are driven by jets of high-temperature steam; gas turbines are driven by burning fuel vapour; and wind turbines use the power of moving air.