Robot Tests Resiliency of Hydrogen Refueling
A bright yellow robot the size of a power forward bends and twists a hydrogen fueling hose hundreds of times a day, testing the durability of the hoses that someday soon will refuel America's hydrogen vehicles.
The robot is the colorful keystone of the hose reliability project at the Energy Systems Integration Facility (ESIF), the newest building at the Energy Department's National Renewable Energy Laboratory (NREL).
With a long arm where its nose should be, the robot simulates the bending and twisting that humans do when they refill their gasoline engines today, and what they'll do in slightly different fashion in 2015 and beyond as car manufacturers bring vehicles powered by hydrogen fuel cells to market.
The robot has a twisty wrist that can turn the hose assembly deftly onto a pin to mate with the vehicle's exterior where the refueling will happen. The repetitive motion puts stress on the hose, so researchers can identify opportunities to increase the lifespan and reduce the cost of the hose assembly. The test also includes low-temperature and pressurized hydrogen gas conditions that will be part of the real-world refueling process.
NREL Senior Engineer Kevin Harrison notes that today's gas stations use the same hoses for thousands of fill-ups before they need to be replaced, and hydrogen fuel cell stations will need to reach that same level of reliability with their hose assembly. "This is a matter of adding value and working with industry to reduce the cost of the hose and the hydrogen infrastructure in general," Harrison said. "This facility [ESIF] allows industry to perform testing they can't do anywhere else in the world."
Fuel cells produce electricity directly and can lead to much higher efficiencies than are possible with combustion engines.
Internal combustion engines powered by gasoline burn the carbon-based fuel in the presence of oxygen, producing carbon dioxide and other pollutants such as nitrogen oxides (NOx) as byproducts. In fuel-cell vehicles, the only thing coming out of the tailpipe is water. In fact, they are so clean and efficient that they have provided both the electricity and water used by astronauts in space.
A typical FCEV uses polymer electrolyte membrane (PEM) fuel cells, which combine hundreds of single cells to make a fuel cell stack. The single cells consist of polymer membranes that are coated with catalysts, typically platinum supported on carbon. The high-pressure hydrogen gas cylinders on board release just enough hydrogen through the stack to produce the electricity needed to power the car. The vehicles use compressed hydrogen gas cylinders now, but could someday store the fuel in powder form.
"At NREL, we do a lot of work that is focused on enabling the materials science for the next generation of technologies for fuel cells," Pivovar said. The 2015 FCEVs will entice current and future customers, but the fuel cells will be using more platinum than will ultimately be cost competitive.
NREL scientists also have demonstrated activity and durability improvements for platinum if the surface is extended. "We're trying to make ultra-thin platinum films limited to a few atomic layers, while still making sure it covers the surface," Pivovar said. If platinum levels can be further dropped by two-thirds, hydrogen fuel cells could reach precious metal loadings on parity with catalytic converters in today's internal-combustion engines. The catalytic converters mandated for pollution concerns in conventional vehicles are not needed for the ultra-clean exhaust of fuel cell vehicles.
"We're getting very close to parity with the precious metals on the catalytic converter," he said. "Most of our projects focus on decreasing the platinum loading and making the performance of the cell higher and more durable, while lowering the cost. The key is addressing cost, performance, and durability at the same time."
NREL Analyzing Contaminants, Components
NREL is working with GM on improving the understanding of how contaminants affect fuel cells. Eventually, fuel cell systems will use inexpensive plastic, similar to the kind that is used to make containers, but without some of the added chemicals. NREL is examining which chemicals can be taken out of the plastic — and which need to stay in — in order to ensure reliable performance at a low price.
NREL is analyzing the components that will be needed to power hydrogen fuel cells. One approach is to put promising component materials in water, leach out potential contaminants, and carefully test for possible negative impact. "We perform analytical characterization of what's coming out in what I refer to as our CSI lab," Pivovar said, alluding to the popular Crime Scene Investigation TV series. Test results lead to recommendations for different materials or tweaks to current materials.
NREL's instruments can test efficiency while conditions change on catalyst-coated membranes, or while different contaminants are introduced. NREL also tests the electrochemical performance of the catalysts, a way to discover just how much platinum can be removed from the cell before it hampers efficiency. Considerations are also given for how materials can be recovered and recycled, particularly platinum. For fuel cell component manufacturing, NREL's unique web-line and quality-control diagnostic techniques are being employed to help manufacturers address costs and scale up issues associated with increased production volumes. Specifically, NREL is developing diagnostic techniques and applying them to roll-to-roll goods to ensure product quality requirements can be met at high production volumes.
Industry Demonstrates Commitment to Hydrogen
In the past 18 months, several auto manufacturers have formed partnerships to build platforms for fuel cell vehicles. So, when BMW comes out with its first hydrogen fuel cell vehicle, it will use the same platform as Toyota. Likewise, Nissan, Ford, and Daimler have formed a partnership for a fuel cell and drivetrain platform. Honda and GM also are working together. "They realize that if fuel cells are going to succeed, they can't succeed just for one manufacturer, but for all of them," Pivovar said. "Working together lowers research costs and risks. And having just a few platforms, rather than several, will help them get their volumes up much quicker. It shows a commitment that they are really going to do this."
NREL's data show that fuel cells made striking improvements between 2005 and 2013. An important benchmark will be when fuel cell vehicles cost about the same as other vehicles amortized over a lifetime.
"We look to perform an enabling role," Pivovar says of NREL's hydrogen R&D program, which has a budget of about $13 million a year. "Today's materials still need advances for large-scale deployment. Our role is to help enable the advances to allow them to become cheap enough and durable enough to get to manufacturing."