CHARGE TRANSFER IN HYDROGEN FUEL CELL ELECTRODE CONTAINING CARBON NANOFIBERS

Using the methods of current-voltage characteristics and spectroscopy of electrochemical impedance, the paper studies the features of proton and electron transfer in high-porous electrodes of the hydrogen fuel cell containing Nafion mainly in insular form in a wide range of concentrations.

Electrode structures were manufactured in two steps: 1. Mechanical mixing of platinized carbon black of the E-TEK type, carbon nanofibers of the Taunit MD type (manufactured in Tambov) and the water -i-propanol dispersion of Nafion; 2. Ultrasonic homogenization to obtain a homogeneous dispersion of electrode material. The resulting dispersion was applied directly to a proton-conductive membrane of the Nafion-212 type. The quantities of the initial components were measured gravimetrically, the component composition of the electrode material was monitored by thermogravimetric analysis. The structure of the obtained materials was studied by the methods of scanning and transmission electron microscopy.

The given electrodes in the membrane-electrode assembly were activated by repeatedly cycling the potential difference from the potential of the open circuit to ~ 0 until the voltage-current characteristics stabilized. The ion resistance determined by the resistance to proton transfer was measured by the method of electrochemical impedance in the region of high frequencies of the hodograph and by the method of current-voltage characteristics in a wet (activated) electrode in the membrane-electrode assembly. The electronic resistance was measured in an air-dry electrode in which the ionic resistance of a dry Nafion was several orders of magnitude larger than the electron resistance and practically did not contribute to the value of the measured resistance.

The dependence of the ion resistance on the Nafion content is shown to have a minimum at 40% mass. The electronic resistance increases linearly with the increase in the Nafion content. The extreme nature of the dependence of the ion resistance on the Nafion content is explained by the decrease in the concentration of the water generation centers (platinum nanoparticles) with the increase in the Nafion content to some practical value at which the water produced is not sufficient to completely moisten Nafion.

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