Evaluation of proton-conducting membranes for use in a sulfur dioxide depolarized electrolyzer

Abstract

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 SDE's 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 °C in 60 wt. % H 2 SO 4 for 24 hours. Following acid exposure, chemical stability for each membrane was evaluated by FTIR using the ATR sampling technique. Membrane SO 2 transport was evaluated using a two-chamber permeation cell. SO 2 was introduced into one chamber whereupon SO 2 transported across the membrane into the other chamber and oxidized to H 2 SO 4 at an anode positioned immediately adjacent to the membrane. The resulting current was used to determine the SO 2 flux and SO 2 transport.Additionally, membrane electrode assemblies (MEAs) were prepared from candidate membranes to evaluate ionic conductivity and selectivity (ionic conductivity vs. SO 2 transport) which can serve as a tool for selecting membranes. MEAs were also performance tested in a HyS electrolyzer measuring current density versus a constant cell voltage (1V, 80 °C in SO 2 saturated 30 wt% H 2 SO 4 ). Finally, candidate membranes were evaluated considering all measured parameters including SO 2 flux, SO 2 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.

Evaluation of covalently and ionically cross-linked PBI-excess blends for application in SO2 electrolysis

“…This range (640e1270 cm -1 ) is indicative of the presence of H 2 SO 4 within the membrane [13] which could be still present from the acid treatment implying that it had not been washed out completely. The FTIR data for MJK1898 (not shown) showed a clear increase in the lower range (700e1300 cm -1 ) which could be either H 2 SO 4 (still present from the acid treatment) or H 2 SO 3 -salts indicating a degree of sulfonation and further supports the weight and swelling data presented in Fig.…”

Novel cross-linked partially fluorinated and non-fluorinated polyaromatic PBI-containing blend membranes for SO2 electrolysis

“…The small holes forming after electrolysis can possibly be ascribed to the dissolution of membrane fragments during operation within the SO 2 electrolyser [4,36]. However, the stability observed for 01-CEM and Nafion ® 115 during and after voltage stepping (Section Electrolysis) suggests that the measure of structural degradation observed in TEM and SEM images (Figs.…”

“…Of the hydrogen production technologies investigated so far, the thermo-chemical processes prove promising [3], of which the Hybrid Sulphur (HyS) thermo-chemical cycle, using a proton exchange membrane (PEM) based electrolyser, has received increased attention over the last years due to energy efficiency [2,4].…”

Membrane electrolysis—History, current status and perspective

“…In this approach the electrolysis step can also be accomplished utilizing a PEM electrolyzer similar to that used for water electrolysis [118,119] have proven to be stable in this system, but other polymeric membranes have also been studied [120]. However, the PBI membrane has been identified as the best option from the point of view of a combination of performance and minimized SO2 cross-over, with a 27% increase in current density.…”

“…Moreover, significant durability issues have recently been identified for this type of membrane in the water electrolysis process [96]. Besides for water electrolysis, the PBI membrane was found to be promising in thermochemical cycles for SO2 electrolysis at 80°C [120]. In this case the PBI membrane is doped with sulfuric acid.…”