In the present contribution, the gas-phase electrolysis of hydrogen chloride in a polymer electrolyte membrane electrolyzer was investigated in detail. Different graphite-based bipolar plate materials were tested for this purpose with the graphite-polymer compound BMA5 being the most suitable among the tested materials regarding porosity as well as corrosion stability and electrical conductivity. Investigation of the membrane pretreatment process revealed that the best results are obtained with sulfuric acid as proton donor. Furthermore, an optimized electrocatalyst distribution with asymmetrical loadings on anode and cathode was found to result in reduced cell voltage at considerably decreased overall noble metal content. Finally, the influence of the cathode gas humidification on the overall cell voltage as well as on the individual anode and cathode potentials, measured with reference electrodes, was determined. It could be shown that a relative humidity ranging from 60 to 80 % is optimal for operation of the gas-phase hydrogen chloride electrolyzer.
Hydrogen chloride (HCl) oxidation was investigated on technical membrane electrode assemblies in a cyclone flow cell. The influences of Nafion loading, temperature and hydrogen chloride mole fraction in the gas phase were studied. The apparent kinetic parameters, such as reaction order with respect to HCl, Tafel slope and activation energy, were determined from the polarization data. The apparent kinetic parameters suggest that the recombination of adsorbed Cl intermediate is the rate-determining step.
Polymer electrolyte membranes have found broad application in a number of processes, being fuel cells, due to energy concerns, the main focus of the scientific community worldwide. Relatively little attention has been paid to the use of these materials in electrochemical production and separation processes. In this review, we put emphasis upon the application of Nafion membranes in electrochemical membrane reactors for chlorine recycling. The performance of such electrochemical reactors can be influenced by a number of factors including the properties of the membrane, which play an important role in reactor optimization. This review discusses the role of Nafion as a membrane, as well as its importance in the catalyst layer for the formation of the so-called three-phase boundary. The influence of an equilibrated medium on the Nafion proton conductivity and Cl− crossover, as well as the influence of the catalyst ink dispersion medium on the Nafion/catalyst self-assembly and its importance for the formation of an ionic conducting network in the catalyst layer are summarized.
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