Overview of High-Temperature Electrolysis for Hydrogen Production (2007)

Over the last five years there has been a growing interest in the use of hydrogen as an energy carrier, particularly to augment transportation fuels and thus reduce our dependence on imported petroleum. Hydrogen is now produced primarily via steam reforming of methane. However, in the long term, methane reforming is not a viable process for the large-scale hydrogen production since such fossil fuel conversion processes consume non-renewable resources and emit greenhouse gases. Nuclear energy can be used to produce hydrogen without consuming fossil fuels and without emitting greenhouse gases through the splitting of water into hydrogen and oxygen. The Nuclear Hydrogen Initiative of the DOE Office of Nuclear Energy is developing three general categories of high temperature processes for hydrogen production: thermochemical, electrolytic and hybrid thermo-electrolytic. This paper introduces the work being done in the development of high temperature electrolysis of steam. High Temperature Electrolysis (HTE) is built on the technology of solid oxide fuel cells (SOFCs), which were invented over a century ago, but which have been most vigorously developed during the last twenty years. SOFCs consume hydrogen and oxygen and produce steam and electricity. Solid Oxide Electrolytic Cells (SOECs) consume electricity and steam and produce hydrogen and oxygen. The purpose of the HTE research is to solve those problems unique to the electrolytic mode of operation, while building further on continuing fuel cell development. ORGANIZATION Experiments have been conducted for the last three years at the Idaho National Laboratory and at Ceramatec, Inc. on the operation of button cells and of progressively larger stacks of planar cells. In addition, the INL has been performing analyses of the cell-scale fluid dynamics and plant-scale flowsheets in order to determine optimum operating conditions and plant configurations. Argonne National Laboratory has been performing experiments for the development of new electrode materials, as well as modeling of the fluid dynamics and flowsheets for comparison with the work being done at the INL. ANL has also been performing diagnostic measures on components form long-duration tests at the INL and Ceramatec to determine the causes for the slow degradation in cell performance. Oak Ridge National Laboratory has been developing high temperature porous membranes for the separation of hydrogen from the residual steam, thus avoiding the need to condense and reheat the steam. The University of Nevada at Las Vegas has been collaborating with ANL on the development of electrode and electrolyte materials and will soon begin to investigate the causes of cell degradation. HTE research also includes NERI projects at the Virginia Polytechnic Institute on the development of toughened SOEC composite seals and at the Georgia Institute of Technology on the microstructural design of SOEC materials. EXPERIMENTAL RESULTS The most recent large-scale test of HTE was performed from June 28 through Sept 22, 2006 at the Ceramatec plant in Salt Lake City. The test apparatus consists of two stacks of 60 cells each in a configuration that will be used in the Integrated Laboratory Scale (ILS) experiment during FY-07. The ILS will contain three modules of four stacks each. The “Half-Module” initially produced 1.2 normal m3of H2/hour and 0.65 Nm3/hr at the end of the 2040-hour continuous test.