Efforts towards micro fuel cells

Fuel cells have been raising substantial interests these days. In this thesis work, we have explored different aspects concerning fuel cell chemistry and materials.; In the first part, a mechanistic investigation has been carried out to explore the origin of the CO tolerance on a Pt/Ru anode. Ruthenium is known to improve the CO tolerance of platinum based fuel cell catalysts, but the mechanism is unclear. In this study, we have used mainly Temperature Programmed Desorption (TPD) to measure the magnitude of the effects of Ru on Pt in terms of CO tolerance. We find the surface Pt(110)/Ru(0.25 ML) only adsorbs about half as much CO, H₂ and H₂O compared to clean Pt(110). The binding energy of CO experiences a decrease of 2 kcal/mol. The exchange of 180 into H₂16O is substantially enhanced showing that the activation barrier for OH recombination is reduced by 3–5 kcal/mol. Quantification of the data shows that two major effects are responsible for the CO tolerance. Ruthenium slightly weakens the CO binding, which creates a 40 meV decrease in the CO removal potential. OH activation by Ru plays a more important role, which is responsible for 120∼200 meV decrease.; In the second part of this work, we developed a new class of proton conductors based on nanoporous silicon. Proton conducting electrolytes are crucial components in fuel cells. However, the implementation of prevalent polymer electrolyte membranes leads to difficulties in manufacturing the fuel cell structure at the micron scale. Here we show that nanoporous silicon membranes with a thickness around 30∼50 microns exhibit comparable proton conductivities as polymer electrolyte membranes. A non-optimized prototype micro fuel cell made of a nanoporous silicon membrane (37 microns thick) shows very promising performance. While running on formic acid and oxygen, the highest open circuit voltage is 0.79 V and the current density is 13.3 mA/cm2. These initial results show that nanoporous silicon membranes are very promising materials for electrolyte applications especially in silicon-based micro fuel cells. The technique can also be useful for other applications involving proton conduction.