Fluorination of polyethylene (PE) films with fluorine gas was studied by using the quartz crystal microbalance technique from the interest for the preparation of wet-proofed carbon black with fluorinated polyethylene (FPE) film for application to gas-diffusion electrodes in fuel cells. The fluorination reaction proceeds clearly in three separated steps, i.e., the first transient step, the 2nd step controlled by the chemical reaction between F2 and PE molecules, and the 3rd step controlled by the diffusion rate of dissolved F2 in FPE. The complete fluorination of PE films of ca. 2—10 μm in thickness can be achieved after sufficient reaction time. It was found that the fluorination at the 2nd step obeys the first order kinetics regarding F2 concentration with the activation energy of only 34.3 kJ mol−1. The fluorination at the 3rd step proceeded linearly with the square-root of the reaction time. Diffusion parameters and apparent activation energies for the fluorination at the 3rd step were determined by solving Fick’s diffusion equation based on those experimental data. Both of them were very large in comparison with that for un-reacting gases, which were ascribed to the fluorination step proceeded by the reactive diffusion process.

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In-plane induction currents in electrodes and bipolar plates by reactant fed into a PEFC were evaluated using a 20-segmented cell. When hydrogen was fed into an anode in the condition of anode (negative electrode) and cathode (positive electrode) exposed air, in-plane currents were detected in both electrodes in spite of the open-circuit condition. In-plane currents of anode and cathode in each segment had opposite directions from each other and nearly equal quantity. Simultaneously, carbon dioxide and oxygen were also detected in the cathode exhaust.

To well understand the mechanism of acid stratification in vented lead-acid batteries, the distributions of sulfuric acid in the vertical direction were measured by a refractive index meter. Also, the measurement of the electrochemical potential distributions in the vertical direction was tried using four dynamic hydrogen electrodes (DHEs). The acid stratification and its relaxation were confirmed by the measurement of sulfuric acid distributions during the charge/discharge and the rest state. There was a difference of four times in the time constant of the acid stratification relaxation between the upper part (top) and the lower part (bottom). This suggests that the acid diffusion is not a dominant reaction of the acid stratification relaxation. The local charge and discharge simultaneously must be occurred on the positive and negative electrode individually due to the electrochemical potential difference. In other words, the electrochemical potential difference probably is the dominant driving force of the acid stratification relaxation. The electrochemical potential distributions in the vertical direction were actually measured using the four DHEs.

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