REAL-TIME MASS-SPECTROMETRIC INVESTIGATION OF THE METHANOL OXIDATION IN A DIRECT METHANOL FUEL-CELL

A mass spectrometric setup was designed which allows an on-line, and t hus real-time, analysis of the products of methanol oxidation in a pro totype direct methanol fuel cell (DMFC) operating at 150 to 190 degree s C. Platinum-black and platinum-ruthenium were used as anode catalyst s. The methanol/water mole ratio in the anode feed and the fuel cell o perating temperature were varied, and the relative product distributio n was determined as a function of these parameters. For pure methanol feed, methanaldimethylacetal was found to be the main product, while a n excess of water in the anode feed led to CO2 as the main product ind icating almost complete oxidation of methanol. Methylformate was also detected under all conditions studied. Increase in the fuel-cell opera ting temperature led to an increase of the relative product distributi on of CO2. Platinum black was found to be more selective toward methyl formate and methanaldimethylacetal formation than platinum-ruthenium. Cycling the fuel cell anode at 1 mV/s, platinum-ruthenium showed lower onset potentials for both CO2 (similar to 0.2 vs. similar to 0.35 V v s. RHE) and methanaldimethylacetal (similar to 0.15 vs. similar to 0.3 V vs. RHE) formation than platinum.