Stationary and Damped Oscillations in a Direct Formic Acid Fuel Cell (DFAFC) using Pt/C

Herein, we report damped and stationary oscillations during Formic Acid oxidation (FAO) under galvanostatic control in a Direct Formic Acid fuel cell (DFAFC). Using Pt/C catalyst in a practical DFAFC, the anodic electrode are allowed to rise its potential up to 600 mV, at the most, which, in turn leads to solely presence of damped oscillations during FAO. When employing dynamic hydrogen electrode (DHE) for measuring anodic voltage values, in a half-DFAFC, larger potential accessed with anodic gas diffusion electrode (GDE) undergoing FAO. With it, stationary oscillatory patterns are observed with an average potential equal to 1 V and with maximum potential equal to 1.25 V. Such high maximum-potential oscillations are reproduced in experiments with rotating disc electrode (RDE), indicating, thus, that such behaviour derives from chemical mechanism rather than possible spatial coupling in a DFAFC. And, to explained it, we suggest to add to current oscillatory mechanism for FAO the steps originally proposed by Tian and Conway (2005) that involves direct chemical reaction of surface oxide with the bulk formic acid (or formate). Finally, we found that maximum potential of stationary oscillations is controlled by bulk formic acid diffusion, thus, a DFAFC with improving FA diffusion on the GDE would allow the presence of stationary oscillation in practical conditions, which is wanted given the improved efficiency as elucidated with the help of overvoltage analysis.

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