(538e) Development of Cathode Air Filters for PEM Fuel Cell Using Microfibrous Entrapped Sorbents

The performance of Proton Exchange Membrane Fuel Cell (PEMFC) is degraded significantly as a result of poisoning of cathode catalyst by airborne contaminants, in particular SO₂ and NO_x in trace levels. The inclusion of an adsorptive filtration with a cathode air filter is the most promising approach for addressing fuel cell contamination. This work thus aims at the development of adsorptive cathode air filters, mainly to remove SO₂ because of its irreversible effects on PEMFC. Two types of sorbents were prepared; an alumina support impregnated with different transition metal (Mn, Fe, Ni, Cu and Zn) oxides and inorganic chemicals (KOH and KMnO₄). The adsorption capacity of these sorbents was investigated in a tubular packed column with inlet SO₂ concentration of 70 ppm in air under different relative humidity conditions at room temperature. At 50%RH, both 10% MnO_x/Al₂O₃ and 10% KOH/Al₂O₃ showed higher breakthrough capacities for SO₂ adsorption compared to other sorbents. Based on adsorption performance under wide range of relative humidity, KOH/Al₂O₃ is selected as final sorbent for SO₂ removal from cathode air stream.

SO₂ adsorption performance in packed bed consisting of large size particles (0.85-1.4mm) is compared with that of composite bed. The composite bed consists of packed bed followed by polishing layer of microfibrous media which is bi-component polymer fibers (13 µm diameter) -entrapped KOH/Al₂O₃ sorbent with smaller particle size of 150-180 µm. The composite bed design results in increase in the breakthrough capacity and % adsorbent utilization almost by 2.5 times compared to the packed bed. This improvement is attributed to the high contacting efficiency of small particulates and reduced bed channeling in case of microfibrous media. Thus,the composite bed design successfully combines the high capacity of packed beds and the high contacting efficiency of microfibrous beds with low pressure drop.