FISCAL YEAR 2006 REPORT ON ELECTROLYZER COMPONENT DEVELOPMENT FOR THE HYBRID SULFUR PROJECT
Thermochemical processes are being developed to provide global-scale quantities of hydrogen. A variant on sulfur-based thermochemical cycles is the Hybrid Sulfur (HyS) Process which uses a sulfur dioxide depolarized electrolyzer (SDE) to produce the hydrogen. In FY05, testing at the Savannah River National Laboratory (SRNL) explored a low temperature fuel cell design concept for the SDE. The advantages of this design concept include high electrochemical efficiency and small volumetric footprint that is crucial for successful implementation on a commercial scale. A key component of the SDE is the ion conductive membrane through which protons produced at anode migrate to the cathode and react to produce hydrogen. An ideal membrane for the SDE should have both low ionic resistivity and low sulfur dioxide transport. These features allow the electrolyzer to perform at high currents with low potentials, along with preventing contamination of both the hydrogen output and poisoning of the catalysts involved. Another key component is the electrocatalyst material used for the anode and cathode. Good electrocatalysts should be chemically stable and low overpotential for the desired electrochemical reactions. This report summarizes results from activities to evaluate different membrane and electrocatalyst materials for the SDE. Several different types of commercially-available membranes were analyzed for ionic resistance and sulfur dioxide transport including perfluorinated sulfonic acid, sulfonated poly-etherketone-ketone, and poly-benzimidazole membranes. Of these membrane types, the poly-benzimidazole (PBI) membrane, Celtec-L, exhibited the best combination of characteristics for use in an SDE. Testing examined the activity and stability of platinum and palladium as electrocatalyst for the SDE in sulfuric acid solutions. Cyclic and linear sweep voltammetry revealed that platinum provided better catalytic activity with much lower potentials and higher currents than palladium. Testing also showed that the catalyst activity is strongly influenced by concentration of the sulfuric acid. Various cell configurations were examined with respect to the deposition of electrocatalyst and use of conductive carbon materials such as carbon cloth and carbon paper. Findings from these evaluations and the results of the membrane and electrocatalyst testing, we prepared three different membrane electrode assemblies (MEA) for electrolyzer testing. The first MEA consisted of a Nafion{reg_sign} membrane with platinum electrocatalyst deposited on carbon cloths, which were heat pressed onto the membrane, an assembly identical to those used in proton exchange membrane fuel cells. The second MEA also used a Nafion membrane with the electrocatalysts deposited directly onto the membrane. The third MEA proved similar to the second but utilized a PBI membrane in place of the Nafion{reg_sign} membrane. Tailor of the membrane and catalysts properties for the SDE system was concluded as a required step for the technology to move forward. It was also recommended the evaluation of the tested and new developed materials at conditions closer to the SDE operating conditions and for longer period of time.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-96SR18500
- OSTI ID:
- 891670
- Report Number(s):
- WSRC-STI-2006-00064; TRN: US200622%%299
- Country of Publication:
- United States
- Language:
- English
Similar Records
HYBRID SULFUR ELECTROLYZER DEVELOPMENT, NHI WORK PACKAGE N-SR07TC0301, FY07 FIRST QUARTER REPORT
FY08 MEMBRANE CHARACTERIZATION REPORT FOR HYBRID SULFUR ELECTROLYZER