Direct Liquid Fuel Cells – The Influence of Temperature and Dynamic Instabilities

The interconversion between chemical and electrical energies plays a pivotal role in the challenge for a sustainable future. Proton exchange membrane (PEMFC) based on the electro-oxidation of hydrogen and reduction of oxygen comprise a relatively mature technology of indisputable relevance. Alternatively, some open questions concerning the use of Direct Liquid Fuel Cells (DLFC) call for further experimental investigations on these systems. In this paper we evaluate the temperature effect on DLFCs under conventional and oscillatory conditions. We studied four molecules: methanol, formic acid, ethanol, and dimethyl ether. The use of identical experimental conditions allowed at studying the role of the fuel on the DLFC performance, providing thus reference values for future investigations. Under regular, non-oscillatory regime, we observed for all cases that the overpotential decreases as the temperature increases mainly because water activation on the catalyst surface is facilitated at high temperatures. By mapping the conditions where oscillatory kinetics manifest itself under galvanostatic mode, only the electro-oxidation of dimethyl ether did not exhibit potential oscillations. The relationship between oscillatory frequency and temperature during the methanol and formic acid electro-oxidation followed a conventional Arrhenius dependence, whereas with ethanol there was no straightforward trend, and temperature compensation prevails. The atypical behavior found for ethanol was addressed in terms of its main electrocatalytic poisons: adsorbed CO and acetate. The absence of oscillations during dimethyl ether electro-oxidation was attributed to its weak interaction with the catalyst surface.