Abstract

The application of PFSA ‐based proton exchange membranes was investigated for the production of hydrogen and sulfuric acid using a SO ₂‐depolarized electrolyzer system. Parameters investigated included hot pressing pressure for the membrane electrode assembly ( MEA ) manufacturing, cell temperature, membrane thickness, catalyst loading, membrane type, and SO ₂ anode feed concentration. The effect of cell temperature, membrane thickness, and acid concentrations was also investigated when using a second method, where clean sulfuric acid as cathode and SO ₂ saturated sulfuric acid as anode were used. Electrochemical impedance spectroscopy showed that the pressure exerted in the MEA manufacturing step had a significant influence with 125 kg cm⁻² yielding the highest current density. High temperatures (>80°C) and thin membranes (≈120 μ m) showed the best performance while thicker membranes produced higher acid concentration when using the first system. The SO ₂ concentration in the anode had a significant influence with the over potential increasing with decreasing SO ₂ concentration. When using the second method, it was found that the SO ₂ solubility in sulfuric acid is important as the mass transport of the SO ₂ limits the overall reaction rate. From the two systems tested, the first method, that is, dry SO ₂ anode and liquid water cathode showed the best operational effectiveness reaching a maximum of 0.32 A cm⁻² at 80°C using N115 coated with 1 mgPt cm⁻² while the second system under the same conditions achieved a current density of 0.18 A cm⁻² when using N117.

Electrochemical impedance spectroscopy analysis on the effect of hot pressing pressure used in the membrane electrode assembly manufacturing step indicated that a pressure of 125 kg cm⁻² must be used. An electrical circuit model was used to separate the membrane resistance, charge resistance, and mass transport limitations. It was shown that the charge resistance and mass transport limitations were influenced significantly.