Traveling the Road Not Taken in Fuel Cell Research
Scientific advancements often arise from patiently building upon previous efforts, clarifying the path to a desired outcome, and following that path to a successful conclusion. Then again, there are times when it's prudent to draw on the past, but cut a new path altogether; heading for the same destination along a different route.
When it comes to Lawrence Berkeley National Laboratory's (Berkeley Lab's) fuel cell work, John Kerr takes the second approach. His group's work complements that of Berkeley Lab researcher Adam Weber's group, which examines fuel cell issues through mathematical modeling and diagnostics. Read a story about Adam Weber's research here.) Both groups collaborate with private industry, universities, and other national laboratories to overcome operational and economic barriers to fuel cell use, but Kerr's group employs a different strategy.
"We're more far out there," he laughs. "As an engineer, Adam is focused on understanding what we have already and how to make it work better. I'm a chemist. I don't need to make it work. My job is to find out why it doesn't work and figure out how it might. There is a strong emphasis on the chemistry."
Kerr's group examines the fundamental mechanisms of fuel cells from a molecular level on up, looking at entirely different materials and processes than those used currently.
"Some fuel cells out there are working better than others, but no one—including the people who developed them—are absolutely certain why they are working better. We look at the why, so that we can find untapped materials and processes to improve overall fuel cell efficiency and reduce costs."
Overcoming Traditional Barriers
Despite their increasing use in both stationary and transportation applications, fuel cells continue to suffer from some persistent weaknesses. In particular, they are only 50% (or less) efficient in converting the hydrogen (H) fuel to electricity. The rest of the energy from the reaction is converted to heat, which, for most applications, must be dissipated. The chemical reaction also produces water. Therefore, there must be efficient mechanisms to manage the heat and the water.
When fuel cells are being used in a vehicle, the equipment needed to store the energy (the hydrogen tank) and get rid of the heat (the radiator) and the water can take up a lot of space. As Kerr says, "There's no room for left for the golf clubs, the groceries—or even the kids." Those kinds of limitations prevent fuel cells from taking what could be a solid game-changing role in marketable vehicles.
For example, the automakers developing fuel cell cars right now have only a brief track record of how well the technology is going to work and hold up in the field. They need a better understanding of the underlying processes to be able to improve the technology, to help bolster confidence in it and improve marketability.
At a technical level, fuel cells only produce about half of their theoretical energy potential, primarily for three reasons:
- Too much resistance to the protons conducted through the membrane
- The inability of oxygen (O2) and H to move efficiently through the cell
- Sluggish rates of the electrochemical processes with the catalysts currently being used
To help fuel cells overcome these barriers and reach their true technical and economic potential, three major issues need to be resolved: (1) catalysts need to use less expensive and more efficient materials, (2) membranes need to conduct the protons that produce electricity without much water and at high temperatures, and (3) the fuel needs to be low volume, liquid, and pumpable, so the existing infrastructure can be used. Increased fuel cell efficiency will mitigate the thermal and water issues, and less infrastructure will be necessary to deal with them.
Kerr is reasonably confident that the issues can be resolved. "The challenges that we're looking at are significant, but tractable," he says. "We do have a handle on the processes underlying fuel cell operation—we're not invoking magic."
Fuel Cell Work of the Kerr Group
At present, Kerr's group is working with General Electric, Yale University, and Stanford University to develop a new high-intensity energy storage system that combines the advantages of a fuel cell and a flow battery. The work, led by GE, is sponsored through the U.S. Department of Energy's Energy Frontier Research Centers (EFRC). Kerr's group is focusing on three areas: replacing platinum catalysts with a cheaper metal, replacing hydrogen with a pumpable liquid fuel, and developing membranes with appropriate selectivity for liquid fuel use.
"None of this work is redundant with other fuel cell work," he says.
The Search for Non-Platinum Catalysts
Platinum group metals (PGM) are the best materials currently known for fuel cell catalysts, and they been used in fuel cells for 150 years. However, they are expensive and the supply chain is unstable. Moreover, platinum is also in demand for other industries, which further affects its price and supply. For example, in 2002, when Intel began mass-producing its dual-core chip, it needed platinum for a switch, which tripled the cost of the already expensive metal. Replacing the metals with less-expensive options such as copper, iron, or cobalt will help ensure that fuel cells can be produced reliably and at a reasonable, consistent cost.
"Some of the replacement metal alternatives that we have evaluated have turned out to be too expensive as well," says Kerr. "However, we've established a clear path for improving performance, and after two years of development work on the catalysts, we are really doing something that is very significant at this point."
Rechargeable Fuel Systems
Devising a rechargeable fuel system could alleviate some of the other challenges that fuel cells continue to face: storing the fuel onboard and generating and distributing the hydrogen. Currently, on-board storage can provide enough energy to carry fuel cell vehicles about 120 miles, limiting their market and requiring the development of an extensive refueling infrastructure. The hydrogen is currently made from natural gas, which is not very efficient and does little to reduce carbon emissions. Using solar energy to split the hydrogen from water continues to be inefficient and cost-prohibitive. And distributing hydrogen in existing pipelines makes them brittle; replacing them with more compatible pipelines would be time-consuming and expensive.
So how are these issues resolved? One approach is to create a liquid fuel system—an idea first posed by Guido Pez at Air Products. In the system being developed for this project, an organic liquid carries the hydrogen. This liquid is charged with hydrogen ("hydrogenated," as is done with trans fats, a very common process) and the hydrogenated liquid fuels the cell by an electrochemical reaction that removes protons and electrons from the fuel. The depleted liquid flows back to a tank. At this point, two options exist for recharging the liquid: (1) the vehicle could be plugged in, and the liquid fuel could be recharged as a hybrid fuel cell/electric vehicle, or (2) when the vehicle is refueled at a fueling station, the depleted fuel would be dropped off and tankers could transport it to a refinery for recharging.
A back-of-the-envelope calculation estimates that a fuel cell vehicle using this method could achieve a range of 300 miles on a 20-gallon tank with a 50 kilowatt fuel cell—all while maintaining the fueling and refinery jobs that currently exist. The system is the answer to all the shortcomings of batteries (no range anxiety, since you can always fill up) and of fuel cells (hydrogen storage and distribution, and better efficiency).
To make this a reality, the project team is conducting research to:
- select the optimal carrier liquids;
- identify the best non-PGM electrocatalysts to facilitate the hydrogenation and dehydrogenation reactions, and the oxygen reduction and evolution;
- develop a membrane and membrane electron assembly (MEA) that will support high proton transport without transporting the fuel across the membrane; and
- ensure component durability.
All of the group's projects involve collaboration among project partners. For the catalyst work, Los Alamos National Laboratory and the University of California, Berkeley, are modeling the actual catalysts to determine how to get the correct reactivity, while 3M is contributing membrane materials for use in the fuel cells. There is considerable overlap among the group's projects.
"We're working with GE and Stanford, and expect to build a complete system for the EFRC program. That will be about a year from now—the operating device is within reach. And we expect to build a non-platinum stack in a couple years. If we're successful, that will be quite significant for fuel cell development."
The collaborations even extend to those who may be developing fuel cell systems in the future. "This summer we plan to engage the summer undergraduate programs like the Science Undergraduate Laboratory Internships, to have students build and run real systems that will give us some hard experience," says Kerr. "It should be fun!"
Leveraging Non-Energy Applications
Kerr is pleased that the membrane and catalyst work is applicable to activities outside of the energy sector, since it offers an opportunity to get technologies into marketable products sooner. For example, the group's catalyst work is similar to the technology used in glucose blood sensors.
"It's difficult to make money right away with the energy applications because energy is so cheap," says Kerr. "Energy is cheaper than bottled water, so it's hard to get a marketplace foothold without government support. By applying the technology to areas that are easier to introduce and getting products out, it's easier to develop the technology and make money to support the energy applications."
Often these technologies can support biotechnology applications, where they can be ramped up to a higher volume scale. In an era of ever-deepening budget cuts, Kerr plans to use this strategy whenever possible to support all of his projects.
From Molecules to Market
"Our work runs the gamut from computation of molecules to MEA design," says Kerr, "all of it based on readily available materials. Some of these projects are based on work that I've done for 30 years, but it's the first time I've had a chance to test it out. We're getting to a point now for much of this where the engineers are getting involved. It's very interesting."
For more information, contact:
- John Kerr
- (510) 486-6279