HYBRID SULFUR ELECROLYZER DEVELOPMENT, NHI WORK PACKAGE N-SR07TC0301, FY08 FIRST QUARTER REPORT

Abstract

Hydrogen has been identified as a leading candidate to replace petroleum as part of the transition to a sustainable energy system, and major efforts are being conducted worldwide to develop the technologies and supporting activities required for this transition. In the United States, the federal research efforts are led by the U.S. Department of Energy (DOE). The U.S. DOE Hydrogen Program is an integrated inter-office program being conducted by the Office of Energy Efficiency and Renewable Energy, Office of Nuclear Energy (DOE-NE), Office of Fossil Energy and Office of Science. The primary objective of the DOE-NE Nuclear Hydrogen Initiative (NHI) is to develop the nuclear hydrogen production technologies necessary to produce hydrogen at a cost competitive with other alternative transportation fuels. The focus of the NHI is on thermochemical cycles and high temperature electrolysis. The Savannah River National Laboratory (SRNL) has been tasked with the primary responsibility to perform research and development in order to characterize, evaluate and develop the Hybrid Sulfur (HyS) thermochemical process. The HyS Process uses a sulfur dioxide depolarized electrolyzer (SDE) to split water and produce hydrogen. During FY05 and FY06, SRNL designed and conducted proof-of-concept testing for a SDE using a low temperature, PEM fuel cell-type design concept. The advantages of this design concept include high electrochemical efficiency and small footprint, characteristics that are crucial for successful implementation on a commercial scale. During FY07, SRNL extended the range of testing of the SDE to higher temperature and pressure, conducted a 100-hour longevity test, and designed and built a larger, multi-cell stack electrolyzer. The proof of concept of SO2 electrolysis for the HyS Process is a priority research target for the FY 2008 NHI Program. Technical options must be better defined and the challenges better understood. The current status of electrolyzer performance must be established by operation at elevated temperature (>90C) and pressure (>10 atmospheres) and during a long duration run (>100 hours). SRNL is pursuing the liquid-phase sulfur dioxide decoupled electrolyzer (SDE) option, which is the main focus of the NHI work. The rate of development of HyS will depend on the identification of a promising membrane or an alternative means for controlling sulfur formation at the cathode of the cell. SRNL will work with Sandia National Laboratory (SNL), universities, and industry to address this issue. Electrolyzers of larger size will be required as the process development proceeds, and SRNL will test a multi-cell stack that was built in FY 2007. Work will be initiated for a Hybrid Sulfur Integrated Laboratory-Scale (ILS) Experiment that will combine a SRNL electrolyzer with the sulfuric acid decomposer developed by SNL for the S-I ILS. A review will be held at mid-year, and if progress warrants, work will progress to the ILS level including ILS system design, electrolyzer fabrication and infrastructure development. Benchmarks to be considered include electrochemical efficiency, membrane durability, and minimization of SO2 crossover.