Carbon monoxide, or CO, has long been a major technical barrier to the efficient operation of fuel cells. But now, chemical and biological engineers at UW-Madison have not only cleared that barrier - they also have discovered a method to capture carbon monoxide's energy. To be useful in a power-generating fuel cell, hydrocarbons such as gasoline, natural gas or ethanol must be reformed into a hydrogen-rich gas. A large, costly and critical step to this process requires generating steam and reacting it with carbon monoxide (CO). This process, called water-gas shift, produces hydrogen and carbon dioxide (CO2). Additional steps then are taken to reduce the CO levels further before the hydrogen enters a fuel cell.