The chemical stability, sulfur dioxide transport, ionic conductivity, and electrolyzer performance have been measured for several commercially available and experimental proton exchange membranes(PEMs) for use in a sulfur dioxide depolarized electrolyzer (SDE). The SDEs function is to produce hydrogen by using the Hybrid Sulfur (HyS) Process, a sulfur-based electrochemical/thermochemical hybrid cycle. Membrane stability was evaluated using a screening process where each candidate PEM was heated at 80 degrees C in 60 wt% H2SO4 for 24 h. Following acid exposure, chemical stability for each membrane was evaluated by FTIR using the ATR sampling technique. Membrane SO2 transport was evaluated using a two-chamber permeation cell. SO2 was introduced into one chamber whereupon SO2 transported across the membrane into the other chamber and oxidized to H2SO4 at an anode positioned immediately adjacent to the membrane. The resulting current was used to determine the SO2 flux and SO2 transport. Additionally, membrane electrode assemblies (MEAs) were prepared from candidate membranes to evaluate ionic conductivity and selectivity (ionic conductivity vs. SO2 transport) which can serve as a tool for selecting membranes. MEAs were also performance tested in a HyS electrolyzer measuring current density vs. a constant cell voltage (1 V. 80 degrees C in SO2 saturated 30 wt% H2SO4). Finally, candidate membranes were evaluated considering all measured parameters including SO2 flux, SO2 transport, ionic conductivity, HyS electrolyzer performance, and membrane stability. Candidate membranes included both PFSA and non-PFSA polymers and polymer blends of which the non-PFSA polymers, BPVE-6F and PBI, showed the best selectivity. (C) 2009 David T. Hobbs. Published by Elsevier B.V. All rights reserved.