Material development and process optimization for gas-phase hydrogen chloride electrolysis with oxygen depolarized cathode

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. Graphical Abstract