Sulfur Dioxide Crossover during the Production of Hydrogen and Sulfuric Acid in a PEM Electrolyzer

A proton exchange membrane PEM electrolyzer has been investigated as a viable system for the electrolysis step in the thermochemical conversion of sulfur dioxide to sulfuric acid for the large-scale production of hydrogen. Unfortunately, during operation, sulfur dioxide can diffuse from the anode to the cathode. This has several negative effects, including reduction to sulfur that could potentially damage the electrode, consumption of current that would otherwise be used for the production of hydrogen, introduction of oxygen and SO2 to the hydrogen stream, and loss of sulfur to the cycle. However, proper water management can reduce or eliminate the transport of SO2 to the cathode. Here we present model simulations and experimental data for the flux of SO2 to the cathode as a function of current density and pressure differential across the membrane and show how water transport influences SO2 crossover. Understanding SO2 crossover is important in evaluating both the lifetime of the electrolyzer and membranes developed to limit SO2 crossover. © 2009 The Electrochemical Society. DOI: 10.1149/1.3129444 All rights reserved.