Showing papers by "Niels J. Bjerrum published in 2002"

A Quasi-Direct Methanol Fuel Cell System Based on Blend Polymer Membrane Electrolytes

Abstract: On the basis of blend polymer electrolytes of polybenzimidazole and sulfonated polysulfone, a polymer electrolyte membrane fuel cell was developed with an operational temperature up to 200°C. Due to the high operational temperature, the fuel cell can tolerate 1.0-3.0 vol % CO in the fuel, compared to less than 100 ppm CO for the Nafion-based technology at 80°C. The high CO tolerance makes it possible to use the reformed hydrogen directly from a simple methanol reformer without further CO removal. That both the fuel cell and the methanol reformer operate at temperatures around 200°C opens the possibility for an integrated system. The resulting system is expected to exhibit high power density and simple construction as well as efficient capital and operational cost.

Electrochemical Promotion of Oxidative Coupling of Methane on Platinum/Polybenzimidazole Catalyst

Abstract: The electrochemical promotion of catalytic methane oxidation was studied using a (CH 4 ,O 2 ,Ar),Pt|polybenzimidazole (PBI)-H 3 PO 4 |Pt,(H 2 ,Ar) fuel cell at 135°C. It has been found that C 2 H 2 , CO 2 , and water are the main oxidation products. Without polarization the yield of C 2 H 2 was 0.9%, and the yield of CO 2 was 7.3%. This means that C 2 open-circuit selectivity was approximately 11%. Open-circuit voltage was around 0.6 V. It has been shown that the CH 4 → C 2 H 2 catalytic reaction can be electrochemically promoted at negative polarization and exhibits a clear volcano-type promotion behavior, meaning that there was a maximum promotion effect at a polarization of -0.15 V, or 0.45 V catalyst potential vs. a hydrogen electrode (3.8% C 2 H 2 yield). The catalytic rate enhancement ratio, r(C 2 )/r 0 (C 2 ), at this maximum was 4.2. There was no C 2 H 2 production at polarization ≥ 0.1 and ≤ -0.3 V. The yield of C 2 H 2 decreased with decreasing temperature. Dependence of CO 2 yield on polarization also showed a volcano-type behavior with maximum yield of 8.3% at -0.15 V polarization. The catalytic rate enhancement ratio for CO 2 production, r(CO 2 )/r 0 (CO 2 ), at this maximum was 1.1, which means that this catalytic reaction is only slightly affected by the electrochemical polarization. This indicates that polarization especially affects the C 2 selectivity of the catalyst. The obtained data was explained by the electrochemical production of Pt-H active centers at the electrolyte-catalyst-gaseous reactant interface (λ » 1).