Various operating methods and parameters for SO 2 electrolysis

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.