The fuel cell has recently been termed the “microchip of the energy industry.” . . . The fuel cell may well go down in history as one of the most important technological developments of the coming century, just as the airplane, automobile and computer were for the last one.
—Glenn D. Rambach, Director of Engineering and Applied Science, QuantumSphere, Inc.
Fuel cells are receiving considerable press these days, being heralded as a major part of the solution to global warming and fossil fuel depletion. A fuel cell is an electrochemical device that is two to three times more efficient than an internal combustion engine at converting fuel into power. Fuel cells produce electricity, water, and heat by combining hydrogen with oxygen from the air. A fuel cell only produces electricity while fuel is supplied to it. The reaction occurs at relatively low temperatures, and no combustion takes place in the fuel cell.Even though the first fuel cell was demonstrated by British amateur physicist William Grove in 1839, it took the space program to focus attention and development money on the creation of efficient fuel cells to provide safe, clean electrical power for moon shots. After the patents ran out, General Electric (the developer of the space program fuel cells) mostly lost interest in fuel cell technology. Geoffrey Ballard, an idealistic former geologist, persisted through years of financial hardship to spearhead research into economically feasible fuel cells that could power cars, homes, and industry. Starting in a makeshift lab in Arizona, Ballard Power Systems has brought fuel cell technology to the point where fuel cell–driven vehicles and fuel cell–powered skyscrapers are now a reality. For a fascinating look at the technical and human story behind the Ballard fuel cell, see Powering the Future by Tom Koppel. How Fuel Cells Work Like a battery, fuel cells convert chemical energy into electricity. In the case of a battery, when the battery has discharged its available power and the electrochemical reaction is all used up, the battery is thrown away if it is not reusable. If it is reusable, it is “recharged,” which reverses the electrochemical reaction to separate the chemicals back into a state where they are ready to create more electricity. Unlike batteries, fuel cells use external fuel to convert chemical energy into electricity, so they don’t need recharging, but they do need a steady supply of fuel. Fuel cells generally work by separating an oxygen source from a hydrogen source using a nonconducting permeable barrier, called an “electrolyte.” Oxygen or hydrogen ions flow through the electrolyte to the other side of this barrier, where they are encouraged by a catalyst to combine chemically to form water. To restore electrical balance, the resulting excess electrons left on one side (electrons can’t pass through the nonconducting electrolyte) are transported around the electrolyte through wires and a load, such as an electric motor.
Click for a larger image. There are five primary types of fuel cells, each distinguished by the type of electrolyte used to carry charge between the fuel and the oxygen. Sharon Thomas and Marcia Zalbowitz of the Los Alamos National Laboratory have written Fuel Cells: Green Power, an excellent comprehensive introduction to fuel cells. Fuel Cells covers fuel cell history, basics, chemistry, applications, and the potential impact on global warming and pollution. You can download it for free from http://www.lanl.gov/orgs/mpa/mpa11/Green%20Power.pdf. Efficiency and Environmental Considerations
Today, only about one-third of the energy consumed reaches the actual user because of the low energy conversion efficiencies of power plants. In fact, fossil and nuclear plants in the U.S. vent 21 quads of heat into the atmosphere—more heat than all the homes and commercial buildings in the country use in one year! Using fuel cells for utility applications can improve energy efficiency by as much as 60 percent while reducing environmental emissions.
—Sharon Thomas and Marcia Zalbowitz, Fuel Cells: Green Power
Fuel cells are considerably more efficient than internal combustion engines. Gasoline engines in automobiles are approximately 13 to 25 percent efficient. That means that 75 to 87 percent of the gasoline you put in your tank is wasted as unburned fuel or excess heat. Fuel cells convert fuel directly into electricity through a chemical reaction and already have efficiencies of 45 to 58 percent. Fuel cells attached to an electric motor can have system efficiencies of more than 40 percent, including motor losses (DRI 2000, 1). If the excess heat generated by the fuel cells is captured and used for hot water or space heating, overall system efficiency can rise to over 80 percent (Plug Power 2000).Fuel cell–powered vehicles are no longer just a dream of the future. Most major automobile manufacturers have active fuel cell–powered vehicle programs. Today, you can take a ride in fuel cell–powered taxis in London or ride fuel cell–powered city buses in Vancouver or Chicago. Because a fuel cell produces electricity directly from hydrogen fuel, its application can be for anything that requires power in the form of electricity, rotary power, or heat. Currently, worldwide over 200 midscale 200-kW fuel cell power plants are supplying quiet, clean, efficient electrical power to office buildings and industrial plants. Fuel cells require hydrogen for fuel. At the present time, most fuel cell–driven automobiles have some kind of system to break down liquid hydrocarbon fuels into hydrogen-rich fuels to drive the fuel cell. A fuel cell that operates on pure hydrogen and air has absolutely no harmful emissions (the byproduct is simply water vapor), but a fuel cell system that uses hydrocarbon fuels (gasoline, methanol, natural gas, etc.) does have some emissions, although they are significantly less than emissions from internal combustion engines. For example, General Motor’s Opel Zafira, an experimental fuel cell car that runs on methanol, has nearly zero sulfur dioxide and nitrogen oxide emissions and only about 50 percent of the carbon dioxide (a greenhouse gas) emissions of a comparable internal combustion engine. Currently, hydrogen to power fuel cells is most economically created by breaking down hydrocarbon-based fuels, such as natural gas or methanol. In the future, if renewable energy sources are sufficiently developed to generate most of the world’s electricity, it may become economical to use electricity to crack water molecules into hydrogen and oxygen, producing hydrogen gas to power zero-emission fuel cell cars. Currently, due to electrical generation inefficiencies in fossil fuel power plants, using grid-generated electricity to produce hydrogen for fuel cell cars causes more harmful emissions and greenhouse gases than simply burning gasoline in an internal combustion engine. Fuel Cells in the Home Fuel cells produce quiet, clean electricity on demand at about twice the efficiency of burning fossil fuels and give off clean, usable, low-grade heat as a byproduct. They are a natural match for home cogeneration systems that provide both electricity and heat. Currently, several companies are working on residential fuel cell–powered cogeneration systems. Demonstration units have been built, but commercially available residential systems appear to have run into significant snags, so I do not know whether or not these types of systems will become commercially viable in the near future. Home systems rely on a fuel processor to transform hydrocarbon fuels (typically natural gas or propane) into hydrogen for the fuel cells. Although the main emphasis of government-financed research has been on automotive applications, the technical problems for producing fuel processors for stationary systems are actually much simpler. Click for a larger image.