February 2, 2007
The future of energy is a topic of great debate. Currently the US produces most of its energy from non-renewable fossil fuels, which emit the greenhouse gas carbon dioxide as a byproduct. Alternative sources of energy that do not produce carbon dioxide as a byproduct are clearly more desirable. An alternative future economy could use electrochemical energy storage devices to store electrical energy produced using a sustainable, non-carbon-dioxide-producing, primary source of energy such as solar or wind. In this future economy the internal combustion engine would be replaced by an electric motor that receives electrical energy from a rechargeable battery, or a refillable fuel cell. It is expected that the future economy will depend on a combination of electrical and hydrogen distribution systems. Hydrogen produced from electrolysis of water would be stored on vehicles, or piped into houses and converted back into electrical energy using hydrogen fuel cells with only heat and water as byproducts. Today I will talk about one such fuel cell device, the low temperature Polymer Electrolyte Membrane (PEM) fuel cell. These devices are currently favored as a future replacement for the internal combustion engine in automotive transportation. For this to happen, there are still some important scientific and engineering hurdles to overcome. PEM Fuel Cells electrochemically combine hydrogen and oxygen, producing electricity with non-polluting byproducts of heat and water. In recent years, neutron imaging has been providing fuel cell researchers with a powerful tool to visualize and quantify the formation and flow of water in a PEM fuel cell. During operation, humidified gases (both hydrogen and air) are fed to the fuel cell that operates at temperatures at or less than 80 ºC. In addition to the water produced during the chemical reaction of hydrogen with oxygen, water can also come from condensation from the input humidified gases. It is critical to understand in detail the flow of water in a fuel cell in order to fully develop this device as an affordable and efficient consumer product. Too little water will dry up the proton conducting membranes at the heart of the fuel cell. An overabundance of water will plug up the fuel cell preventing the flow of air that provides oxygen to sustain the fuel cell reaction. In this talk I will discuss the use of neutron imaging as a tool to help in the understanding of how these devices work.
David Jacobson is a physicist at the National Institute of Standards and Technology (NIST) who leads a team responsible for running the NIST Neutron Imaging Facility ( www.physics.nist.gov/fuelcell ). He received his doctorate in physics from the University of Missouri-Columbia in 1996. Shortly after graduating he joined the Physics Laboratory at the NIST working first on a National Research Council fellowship and later as a permanent staff member. He came to NIST to work on basic neutron physics at the NIST Neutron Interferometer and Optics Facility. Later he helped to pioneer the first dedicated neutron imaging facility at the NIST Center for Neutron Research ( www.ncnr.nist.gov ). This facility was built as a joint venture between the NIST and the Department of Energy with the primary interest to study hydrogen fuel cells. The part of his research that is related to fuel cells has focused on the application of neutron imaging to non-destructively analyze liquid water in operating fuel cells.