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The ionic resistance of membrane–electrode assemblies of oxygen–hydrogen fuel cell electrodes containing platinum nanoparticles on carbon black, carbon nanofibers, and proton-conducting Nafion polymer in a wide range of compositions (10–80 wt %) are studied in situ by the methods of current–voltage characteristics, electrochemical impedance spectroscopy, and simulation of the impedance hodograph. Conditions that make it possible to correctly determine the ionic resistance of the electrode on the basis of an analysis of the linear approximation of the high-frequency region of the impedance hodograph are found. It is shown that the occurrence of inhomogeneities and an anomalous increase in the ionic resistance with an increase in the content of Nafion in the electrode are associated with a decrease in the volume fraction of water-generation centers (particles of electrochemically active platinum), which leads to incomplete wetting of Nafion.

The ionic resistance of the membrane electrode assembly (MEA) of O_2/H_2 fuel cells is studied in situ in a broad range of MEA compositions by using electrochemical impedance spectroscopy and polarization measurements. The MEAs are composed of platinum on carbon, carbon nanotubes, and Nafion, a proton- conducting polymer. We investigate atypical growth of the MEA resistance with the increasing Nafion content and spatial nonuniformity in the MEA ionic resistivity. A mechanism underlying this phenomenon is proposed.

The article discusses platinum-carbon electrodes with mixed conductivity as part of membrane-electrode assemblies of fuel cells containing structural-modifying additives with structural elements of various types: carbon nanotubes with elongated structural elements and graphene-like materials with almost two-dimensional planes. Based on the data on the limiting current density obtained in potentiodynamic and potentiostatic modes, the mass transport losses of molecular oxygen transfer in these electrodes are investigated. Using different measurement conditions, the baric dependences of the current density were constructed, the limiting factors and mechanisms of oxygen transfer in the studied structures and the role of the introduced modifiers were clarified.

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