Search

The electrolysis of HCl to form Cl2 is an integral part of the production of polycarbonates and polyurethanes. In recent years, the direct gas-phase electrolysis was shown to be significantly more efficient than the current state-of-the-art process based on the oxidation of hydrochloric acid. Still, three phenomena significantly limit the performance and industrial applicability of this process and have so far only been investigated theoretically. Firstly, a limiting behavior in the HCl oxidation reaction was observed, which seems to be of purely kinetic origin. Secondly, also in the full-cell employing an oxygen depolarized cathode, a limiting behavior was detected, which however appears to have a different origin. Lastly, the performance of the oxygen reduction is significantly reduced in comparison to classical H2 PEM fuel cells. The present work utilizes a combined experimental and theoretical approach to confirm that the HCl oxidation is purely reaction limited while the limiting behavior in the full-cell system employing an oxygen depolarized cathode is caused by flooding at low reactor temperatures and, lastly, that the reduced performance of the oxygen reduction reaction is a consequence of significant HCl crossover that can be mitigated by means of increased cathode humidification. These insights are furthermore used to operate the HCl gas phase electrolyzer employing an oxygen depolarized cathode at current densities of more than 5000 A/m2 for the first time, while also substituting the previously employed platinum based cathode catalyst with RhxSy, decreasing the impact of HCl crossover and allowing for the lowest so far measured cell potentials over a wide interval of current densities.

The use of gas diffusion electrodes (GDEs) in microbial fuel cells (MFCs) can improve their cell performance, but tends to cause fouling. In order to allow long-term stable operation, the search for antifouling methods is necessary. Therefore, an antibacterial coating with ammonium compounds is investigated. Within the first 30 days of operation, the maximum measured power density of a GDE with antibacterial ionomer was 606 mW m−2. The GDE without an antifouling treatment could only reach a maximum of 284 mW m−2. Furthermore, there was an optimum in the loading amount with ionomer below 2.6 mg cm−2. Further investigations showed that additional aeration of the GDEs by a fan had a negative effect on their performance. Despite the higher performance, the antibacterial coating could not prevent biofilm growth at the surface of the GDE. The thickness of the biofilm was only reduced by 14–16%. However, the weight of the biofilm on the treated GDEs was 62–80% less than on a GDE without an antifouling treatment. Consequently, the coating cannot completely prevent fouling, but possibly leads to a lower density of the biofilm or prevents clogging of the pores inside the electrodes and improves their long-term stability. [ABSTRACT FROM AUTHOR]

Hydrogen chloride (HCl) oxidation has been investigated on technical membrane electrode assemblies in a cyclone flow cell. Influence of Nafion loading, temperature and hydrogen chloride mole fraction in the gas phase has been studied. The apparent kinetic parameters like reaction order with respect to HCl, Tafel slope and activation energy have been determined from polarization data. The apparent kinetic parameters suggest that the recombination of adsorbed Cl intermediate is the rate determining step.