Performance of a Small PEMFC Stack Operated with CO/H2 Mixtures

Abstract

Hydrogen produced by reforming processes may include sulfur (S),carbon monoxide (CO) and other impurities.. Presence of ppm level impurities in hydrogen may adsorp onto Pt catalyst and lower performance and lifetime. There are efforts to overcome cost and performance issues by reducing Pt amount and utilizing new catalyst and support materials, more tolerant to CO. Ru catalyst are often added to oxidize CO before poisoning Pt. Ti0.7Mo0.3O2 was investigated as an alternative support material for anode catalyst. It has been shown that the stoichiometric ratio between Ti and Mo have significant impact on the CO tolerance. Ti0.8Mo0.2O2 was synthesized and used as anode electrode in PEM fuel cell testing. In this paper, titanium/molybdenum alloy on carbon (Ti0.8Mo0.2O2-C) is evaluated as catalyst support to prevent performance decay by CO poisoning. 3-cell stack was developed and tested for performance and degradation issues. Cell hardware with 15 cm2 active area was used for fuel cell measurements. Cathode was loaded with 0.6 mgPt/cm2 (20 wt.% Pt/C) and anode with 0.5 mgPt/cm2 (40 wt.% Pt/Ti0.8Mo0.2O2-C) onto Sigracet 29BC GDL by painting. Bipolar plates for single cell and stack were designed using Solid Works. End plates, anode bipolar plate and cathode bipolar plate with cooling channels on the other surfaces were designed and produced from graphite composite in-house. Seals from silicon was also designed and produced in-house. MEA had active area of 15 cm2. Figure 1 shows stack formation with all components put together in order. Stack was conditioned under 100% humidified hydrogen. There was no effect of stack orientation on performance. Performance for 2-cell stack was better going from atmospheric pressure to 2 bar. When polarization was 0.6V, pressurized operation provided improvement in current density going from 1300 mA/cm2 (no pressure) to 2000 mA/cm2 (15 psig). When this 2-cell stack was subjected to different concentrations of CO, polarization values of Figure 2 was obtained. Increasing concentration of CO caused decrease in current densities. Utilizing a DC/DC converter, stack has provided power to charge a cell phone. More details will be shared for 2, 3 cell stack operation under CO conditions. Figure 1