Hydrocarbons have 50-100 times higher energy per unit weight compared to commercially available batteries, thus harvesting only 10% of the energy from hydrocarbons could provide a far lighter energy source for portable electronic devices. With this motivation, the feasibility of using Polymer Electrolyte Membrane (PEM) fuel cells with propane fuel, operating at low temperatures (&lt; 100C), was explored. Nafion® membranes were used as electrolytes and platinum black was used as catalyst. At a catalyst loading of 15 mg/cm2 at anode and 8 mg/cm2 at cathode, a maximum steady-state power density of 7.5 mW/cm2 was observed. However, with hydrazine treatment of platinum black catalyst nearly doubled the power density of propane fuel and increased power by about 50% with hydrogen fuel. It was interesting to note that there was a significant influence of the current history on the fuel cell performance. In particular, at higher current densities (&gt; 24 mA/cm2) the power output gradually decreases then rapidly “extinguishes” (i.e., produces no power). However, by employing an unconventional operating mode (“load-interrupt”) where the current is shut off for a short period of time and then reapplied, the maximum average power density increased to 11.6 mW/cm2. For dimethyl ether (DME) and hydrogen, no significant effect of current history was observed. It is proposed that the fuel cell “extinction” is associated with the formation of inactive intermediate species on the anode, blocking active sites. A simple model was developed in an effort to interpret “extinction” behavior. This model assumes all sites are in either an “active” or “inactive” state with heuristic kinetic relations to describe the rates of conversion of active to inactive sites and vice versa. This model was found to be in good qualitative agreement with the experiments when the rate of formation of inactive sites was proportional not only to the number of active sites but also the number of already-inactive sites, i.e. in a self-accelerating manner. Possible physical mechanisms for this heuristic model are discussed.

Dynamics of direct hydrocarbon PEM fuel cells

255th National Meeting (2018)

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