Evaluation of the experimental model for methanol crossover in DMFCs

• Published in: Journal of the Electrochemical Society 2004, Vol.151 (3), p.A413-A417
• Main Authors: DRAKE, Javit A, WILSON, William, KILLEEN, Kevin
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.1646150

Independent transport measurements of carbon dioxide permeation were undertaken to evaluate a standard assumption of attributing cathodic CO2 flux in direct methanol fuel cells (DMFCs) entirely to methanol crossover. With a humid air cathode at ambient conditions, a DMFC cathode emanated 3.5 to 4 x 10-8 mol/(cm2 s) of CO2 (20 to 25 mA/cm2 'leak current density'). From a methanol-free anode feed of either carbonated liquid water or humid CO2 /H2 gas (90%: 10%), carbon dioxide permeated to the cathode at 0.7 x 10-8 mol/(cm2 s) or 20% of the total DMFC flux. Under current (enabled with the presence of H2 in CO2), the permeation rate rose to 1 x 10-8 mol/(cm2 s). The rise with cell current density increase from 24 to 80 mA/cm2 was quantitatively consistent with convection of CO2 with electro-osmosis of water. The indication that anodic CO2 contributes to the total cathodic flux has a positive implication for fuel efficiency in DMFCs.