Hydrobromic Acid Electrolysis Using a Solid Polymer Electrolyte Electrolyzer -Studies on Electrolytic Decompositioonf Aqueous Hydrogen Bromide. III.-

Abstract

Electrolysis of aqueous HBr was investigated by use of an electrolytic cell equipped with a membrane-electrocatalyst composite (Ir-Pt/Nafion 117/Pt-Ir) of 50 cm². The cell voltages increased almost linearly with an increase in current density in the range from 10 to 100A/dm² and were strongly affected by the difference of the theoretical decomposition voltage (Fig.2, Table 1). The IR losses were mainly due to the membrane resistance and decreased with the rise of temperature and with decreasing HBr concentration (Fig.3). The sums of the overvoltages for hydrogen and bromine evolution reactions at 100A/dm² were 0.21 and O.18 V at 25 and 50°C, respectively, and were independent of HBr and Br₂ concentrations (Fig.4). The current efficiencies higher than 97% at 25°C and than 96% at 50°C were obtained above 40 A/dm² (Fig.5). In addition, the electrolytic performances were also examined under such conditions as HBr concentration in the catholyte was different from that in the anolyte (Tables 2 and 3, Fig.6), as external supply -of the catholyte to the cathode was omitted (Fig.7), and as the composite with nonplated anode electrocatalysts was used (Fig.8).