Fuel Cells Using Inorganic Liquids as Fuels

At a temperature of 70°C, a power density of about 50 mW/cm was attained in 12 M HCOOH at a working voltage of 0.4 V. By comparison, the power density in a typical methanol fuel cell under the same conditions is about 30 mW/cm.  

With the experience gathered in the development of DMFCs, Pt-Ru catalysts were used for the anodic process in the early studies on DFAFCs. Ha et al. (2006) showed that much better electrical characteristics can be obtained with palladium black as the catalyst. Importantly, with this catalyst one can work at much lower temperatures. In particular, at a temperature of 30°C, power densities of 300 mW/cm were obtained with a voltage of 0.46 V, and about 120 mW/cm with a voltage of 0.7 V. The differences between the two catalysts probably are due to the fact that with Pt-Ru, formic acid oxidation follows the second of the mechanisms mentioned (chemisorption with dehydration), while palladium black is a highly effective catalyst for the dehydrogenation of formic acid, the first mechanism being followed on it. It must be pointed out that this effect is highly specific in methanol oxidation, the catalytic activity of palladium is lower than that of Pt-Ru. 

Considering all these special features, it will be very convenient to use formic acid as a reactant in fuel cells of small size for a power supply in portable equipment ordinarily operated at ambient temperature. Such fuel cells are described in 

In a review by Yu and Pickup (2008), recent advances in DFAFCs are presented, focusing mainly on anodic catalysts for the electrooxidation of formic acid. The problem of formic acid crossover through Nation membranes is also discussed. 

12 FUEL CELLS USING INORGANIC LIQUIDS AS FUELS 4.12.1 Direct Borohydride Fuel Cells 

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