Materials and Systems for Hydrogen Production

Levi Thompson and Chang Hwan Kim examine a newly configured system to convert gasoline and diesel into hydrogen. (Photo by David Tuman)

For years vehicle manufacturers have faced the challenges of lowering the levels of emissions, yet delivering better fuel economy and performance. One appealing response to enhance energy efficiency and demonstrate environmental responsibility is the fuel cell. However, the obstacles that stand in the way of commercializing fuel cells are monumental. One of the key obstacles is the availability of hydrogen to power the fuel cells.

In 2001 a team led by Levi Thompson, the Richard E. Balzhiser Professor of Chemical Engineering, set out to develop materials and fuel processor systems to efficiently convert gasoline and other hydrocarbon fuels like ethanol and biodiesel into hydrogen. Since then, the team has had great success and the products and results could help accelerate the commercialization of fuel cells.

The fuel processor accomplishes two principal tasks. The first is to reform – that is, to change – a carbonaceous fuel such as gasoline or diesel into a hydrogen-rich gas sometimes called syngas. This gas typically contains significant amounts of carbon monoxide (CO) in addition to the hydrogen (H2). The second task of the fuel processor is to remove the carbon monoxide, which is a poison for the fuel cell.

Although industry has a lot of experience in large-scale reforming, the small-scale process has remained a huge challenge. “The demonstration of on-board fuel processors that meet industry’s size and cost targets would significantly advance the commercialization of fuel cells and other technologies including reformate-assisted NOx reduction,” Thompson said.  Reformate-assisted NOx reduction is one of the strategies being developed by automobile manufacturers to reduce the levels of nitrogen oxides (NOx) in diesel emissions.

The development of small, inexpensive fuel processors will require better performing catalysts, new reactor designs and better strategies to integrate the various fuel processor components.

According to Erdogan Gulari, the Donald L. Katz Professor of Chemical Engineering, “the development of more active and durable catalysts was among the toughest challenges we faced.” One reason is that fuels such as gasoline and diesel contain sulfur and, during the fuel processing reactions, the sulfur contaminates the catalysts and renders them ineffective.

For example, the water gas shift reactor, which currently takes up about a third of the mass, volume and cost of a fuel processor, typically employs catalysts that are very sensitive to sulfur. This reaction produces carbon dioxide (CO2) and hydrogen from water and carbon monoxide. Catalysts developed at the University of Michigan are not only more active but possess better tolerance to sulfur than other types of catalysts. “In addition to better performing materials, we have demonstrated novel reactor architectures that could reduce the size and cost of the fuel processor” says Jun Ni, Shien-Ming (Sam) Wu Professor of Mechanical Engineering. 

The team’s strategy to improve the overall efficiency of the process involved integrating the various components and catalysts into compact, low-cost fuel processors that were fabricated using micromilling and microdrilling techniques.  These techniques allow the precise production of very fine features and structures with high surface area-to-volume ratios. Several breadboard prototype systems have been fabricated and tested. The most recent tests demonstrated that the devices not only efficiently convert model compounds but also, according to Dr. Chang Kim, a post-doctoral scholar on the project, the microchannel fuel processors “were able to convert gasoline from a local station into reformate with less than 50 parts per million of CO.” Carbon monoxide levels higher than 100 ppm are not suitable for most fuel cells.

“We continue to develop the technology as a thrust in our recently established Hydrogen Energy Technology Laboratory,” Thompson said. “The fuel processing technology -- as well as results from our work on microfabricated fuel cells and devices to convert solar energy and water into hydrogen -- could some day change the way we power everything from our homes, laptops and cell phones to our automobiles. Not only are these technologies energy efficient, they are environmentally-friendly.”