(430c) Development of Cathode Air Filters for PEM Fuel Cells 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. Removal of air contaminants by adsorptive filtration is economical and easier way to mitigate cathode air contamination .This work thus aims at designing of adsorptive air filters having high adsorption capacity and high contacting efficiency for removal of SO₂ and NO₂ along with lower pressure drop across a filter. MnO_x/Al₂O₃ prepared by deposition precipitation route with MnSO₄ as a precursor showed the highest saturation (124.1 mg of/cc) and breakthrough capacity (33.7 mg/cc) for SO₂, when challenge gas was 70 ppm of SO_{2 ­}in air with 50% RH. Particularly, it showed 60% higher saturation capacity than commercial KMnO₄/Al₂O₃ sorbent. Granular PICA activated carbon was found to have the highest breakthrough capacity of 62.3 mg/cc and saturation capacity of 139.5 mg/cc for NO₂, when challenge gas was 20 ppm of NO₂ in air with 50%RH. Thus, two layers of filter media are required to efficiently remove both SO₂ and NOx.

For packed beds, use of smaller size particles give high single pass removal efficiency but generally at the expense of higher pressure drop (8.7” of H₂O/cm of bed for ε=0.4, face velocity =50cm/s and dp=200µm),which increases parasitic power loss. Microfibrous media (MFM) prepared by entrapping micron size particles in sinter-locked network of bicomponent polymer fibers have been shown to give higher contacting efficiency with the lower pressure drop. Different filter configurations such as composite bed, pleated filters can be prepared with the use of MFM and their comparison with the conventional packed bed will be discussed in detail in order to find the optimal design of a filter. In one such study, the composite bed consisting of packed bed of MnO_x/Al₂O₃ (1.6cm thick) followed by thin polisher layer of microfibrous media (4mm) yielded ~200% higher breakthrough capacity for SO₂ than that for the packed bed of same sorbent.