- Hydrous Ethanol Reformers
- High Temperature PEM Fuel Cells
- CO Tolerent Anode Design
- Nanostructured Design and Modeling of PEM Fuel Cells
- Direct Methanol Fuel Cells (DMFCs)
Our objective is to develop integrated catalytic reformer-fuel cell systems for the propulsion of future automobiles. Fuel cells emit virtually no emissions, apart from those produced by the reformer, and can provide twice the energy efficiency of conventional IC engines. Fuel cells operating on H2 are the only ones practical ones at the current time. Since H2 storage on vehicles is impractical, however, liquid fuel must be reformed catalytically on-board into H2. Such reformers/fuel cell systems have been adopted in concept by most auto makers. A new Fuel Cell Center has been established at WPI as an university-industry colloboration, where we are involved in the following projects.
Fuel reformers are being developed by a number of companies. However, most of these are planned to be fueled by gasoline, due to its ready availability, or methanol, due to its ease of reforming. We are focusing, at the moment, on hydrous ethanol reforming, since this fuel possesses a number of additional advantages such as renewability, little impact on greenhouse emissions, absence of catalyst poisons such as sulfur, and use of hydrous ethanol (~ 40 vol.%, or 80 proof), which is quite economical. The reformer consists of a catalytic ethanol steam reforming step followed by a water-gas shift (WGS) step to further convert the remaining CO into CO2 and more H2. The ratio of air/fuel-water mixture is adjustable. It is high initially to confer exothermicity and self-starting ability and is reduced subsequently for efficiency. A number of commercial catalysts have been investigated, and a study of the reaction thermodynamics  and micro-kinetics is now in progress. The proton-exchange membrane (PEM) fuel cells slated for use in automobiles cannot tolerate CO levels in excess of around 10 ppm, while the gas from the WGS stage has about 1% CO. Thus, reformer developers plan on removing the last traces of CO through preferential catalytic oxidation in the presence of a large excess of H2. Our approach is to reduce the CO susceptibility of PEM fuel cells as described below.
A reason for the extreme susceptibility of PEM fuel cells to CO poisoning is that the proton-exchange membranes such as Nafion® are limited to a temperature of around 80 ºC due to the requirement of liquid water in their pores for proton transport. At this temperature, the CO binds strongly with the anode catalyst, thus displacing H2 from the surface and poisoning the anode reaction.. If the temperature of the fuel cell could be increased to over 120 °C, the exothermic CO adsorption becomes weaker. However, Nafion ® does not work at this temperature due to its low glass transition temperature and requirement of 100% RH, which means a pressurized system. We are developing organic-inorganic composite membranes  that work effectively at higher temperatures and lower relative humidity. The long-term goal is to develop completely inorganic PEMs that would allow direct methanol and ethanol fed fuel cells.
There has been substantial activity in designing CO tolerant anodes by alloying Pt with other transition metals to reduce CO affinity. The state-of-the-art catalysts thus designed are Pt-Ru and Pt-MO which provide substantial improvements over traditional Pt anodes. We are, instead, doing microkinetic resisted bifunctional anode catalyst design that promotes water-gas shift activity of the anode catalyst so that any CO present is further converted into CO2 without the need for injecting air as proposed by others.
The membrane-electrode-assembly (MFA) of a state-of-the-art PEM fuel cell is a likely standard composite that facilitates the presence of several continuous phases, namely liquid water, gaseous reactants, solid electron collector, proton-conductor, and supported catalyst. Lack of continuity of any of these phases severly jeopardized performance. We are studying in detail the nanostructured reaction modeling viewing the PEM fuel cell as a membrane reactor.
Our development of higher-temperature PEM’s and co-tolerant anodes allows development of DMFCs, which is being pursued based on microkinetic analysis of mechanism and a barrier for methanol transport through the PEM.
Last modified: October 24, 2007 09:58:34