Hoping to spur progress, Tennessee Tech University researchers, working individually and collaboratively, are helping solve pieces of the fuel cell puzzle. Fuel cells offer zero emissions and could eliminate dependence on fossil fuels because they transform hydrogen and oxygen into electrical energy with only one byproduct, water. But that’s where the simplicity ends and issues about costs and efficiency arise.
“Our goal is to create an industrial base in Tennessee for fuel cells and a hydrogen economy,” said Ken Currie, director of TTU’s Center for Manufacturing Research. “We’re promoting synergy among ourselves, private companies, and research centers such as Oak Ridge National Lab. We’re working toward a goal we think can be reached.”
Currie pointed to the state of California, which recently mandated hydrogen stations along primary interstates in order to promote use of alternative fuels, as an example of a type of program he and colleagues would like to see in Tennessee. However, TTU researchers are still searching for solutions to critical problems that keep fuel cell costs high and inhibit efficiency for commercial use.
At the forefront is John Zhu, a mechanical engineering professor who works on finding materials that will lower fuel cell costs. Backed by a National Science Foundation award, Zhu focuses on solid oxide fuel cells, which operate at high temperatures (around 600-800 degrees C) and are best suited for utility company use.
The structure of a fuel cell depends on a sandwich of plates that allows high conductivity. Ceramic plates work very well at high temperatures, but they are expensive, hard to fabricate and very brittle. Zhu experiments with metal plates, which are cheaper and more reliable. However, they must be coated to reach the same conductivity as ceramic. He leads efforts to find a practical and cost effective coating material.
Mechanical engineering professor Glenn Cunningham specializes in collaborating with industry and higher education institutions to pool talent and compete for federal funding for projects such as Zhu’s. He was the lead on a proposal that brought together Tennessee Tech, Dana-Plumly Corp. of Paris, Tenn., ORNL and another university to work on improving coatings on the all-important plates.
“More common materials, such as iron or nickel chromium, are less expensive, but are also susceptible to corrosion. They’ll be eaten up during the chemical reaction unless properly coated,” explained Cunningham. “We are experimenting with a nitride coating that will not only protect the plates, but actually enhance plate conductivity.”
Some developers see solid oxide fuel cells being used in motor vehicles, but Currie points to one obvious issue with that application— the extreme temperatures are too hot to operate within a vehicle.
On the other end of the spectrum, Chunsheng Wang, a CMR faculty member and assistant professor in chemical engineering, has worked on a different type of fuel cell that operates at about 80 degrees C, a little less than the temperature of boiling water and low enough to be practical for autos, laptops and other portable devices. Labeled a PEM, or proton exchange membrane fuel cell, it still depends on the simple chemical reaction between hydrogen and oxygen. The current version works well in hybrid autos, but users are for the most part limited to using pure hydrogen. Wang is looking for novel materials that will allow varying fuels to be used that are cleaner and more cost effective.
Wang also is tackling an inherent problem of any fuel cell — peak power demand for those times when the user needs a quick burst of power. For that burst, energy has to be stored either in a separate battery or super capacitor (which is costly and inefficient). Wang however, has developed an intrinsic super capacitor that can actually store energy within the fuel cell without requiring additional cost or complexity.
Chemistry assistant professor Titus Albu focuses on the molecular level investigation of another significant obstacle preventing fuel cells from being used in everyday applications — the slow process of the transformation of oxygen to water. Supported by an Oak Ridge Associated Universities award, he is using computer programs to study the reactions of hydrogen and oxygen, seeking a balance that will produce the greatest efficiency. Much like a battery, fuel cells involve positive and negative charges, but oxygen does not accept electrons as easily as hydrogen donates them, making the overall process unbalanced and less efficient.
“If the voltage is too low, there’s not enough electrical power drawn from the chemical reaction ,” said Albu. “New materials, such as different alloys of certain metals, may be the key to finding the balance. Platinum produces the most efficient reaction, but it is expensive and breaks down too quickly.”
Currently, there are no existing computer models for fuel cells that can predict the behavior of the power sources with reasonable accuracy in real time. TTU chemical engineering professor Venkat Subramanian and his research team are addressing the need for an accurate dynamic model.
“Using experimental techniques alone to obtain fuel cell characteristics under a wide range of operating conditions is a time-consuming and formidable task,” said Subramanian. “Modeling and simulation, combined with a limited number of experiments, is the only solution. We focus on simplifying these models without sacrificing accuracy, and we combine models for bettering understanding.
“In current hybrid vehicles, electrical circuits used don’t predict behavior and eventually fail,” explained Subramanian. “Complicated models provide high performance, but require putting a costly computer on board that raises the price of the vehicle. We are working on a simplified model using a microprocessor that will increase performance and reduce costs.”
All TTU researchers working with fuel cells expect that small steps toward improving efficiency and reducing costs will one day add up to seeing fuel cells in common use in vehicles and other commercial uses in this country.
“Twenty years ago, fuel cells still seemed like science fiction,” said Albu. “But with rising gas prices and a strong interest in improving current technology, using fuel cells looks more feasible than ever before.”