Performance of carbon dioxide vent for direct methanol fuel cells

Direct methanol fuel cells have potentially high energy density if the balance of plant and fuel losses can be kept to a minimum. CO₂ accumulation in the fuel tank can lower the efficiency and performance of closed-tank methanol fuel cells. This report discusses the implementation of a passive CO₂ vent fabricated with poly(1-trimethyl silyl propyne) and 1,6-divinylperfluorohexane. The performance of the membrane as a selective vent for carbon dioxide in the presence of methanol has been studied at various operating conditions. First, the selectivity of the vent membrane improved with temperature. Second, the activation energy for permeation through the polymer membrane corresponded to diffusion controlled transport of CO₂ and sorption controlled transport for methanol vapor. The activation energy for CO₂ transport through the poly(1-trimethyl silyl propyne) and 1,6-divinylperfluorohexane membrane was less than that for a pure poly(1-trimethyl silyl propyne) membrane. Finally, the polymer had a high selectivity for carbon dioxide compared to both liquid and vapor phase methanol.