(348b) Materials Development for Improved Efficiency of Hydrogen Production by Steam Electrolysis and Thermochemical-Electrochemical Processes

We are investigating two processes as potential sources of hydrogen for the ?hydrogen economy?. One of these hydrogen production processes is water electrolysis at high temperatures using heat from a nuclear reactor, known as high temperature steam electrolysis (HTSE). The advantage of electrolyzing water at high-temperatures is that the electrical energy needed decreases with increasing temperature whereas the total energy needed changes very little resulting in a replacement of electrical energy with thermal energy. The feasibility of this process is currently being demonstrated at Idaho National Laboratory using solid oxide fuel cell designs and materials. The major source of efficiency loss in both SOFCs and solid oxide electrolysis cells is poor electrode performance and durability resulting in large systems and high materials costs. We will discuss Argonne National Laboratory's work to develop oxygen and hydrogen electrode materials for improved hydrogen production efficiency by HTSE.

The other process that is under investigation is a thermochemical hybrid hydrogen production cycle that produces hydrogen from water, also using heat from a nuclear reactor. The proposed cycle is based on the sulfuric acid (H2SO4) synthesis and decomposition processes developed earlier (the ?Westinghouse? process). The standard Westinghouse process requires temperatures over 800°C for one step in the cycle, the SO3 decomposition reaction. The other reactions in the cycle can be performed below 500°C. In collaboration with the Japan Nuclear Cycle Institute (JNC), we are investigating means for lowering the temperature of the SO3 decomposition to approximately 500°C to allow the use of a lower temperature heat source and to mitigate problems associated with corrosion at the higher temperatures. The focus of the proposed project is the use of an oxide ion-conducting electrolysis cell to decompose SO3 to SO2. JNC has demonstrated the feasibility of this approach using an electrolysis cell comprised of the traditional high-temperature (~1000°C) solid oxide fuel cell electrolyte, yttria-stabilized zirconia (YSZ), and platinum electrodes. The electrolysis rates, and thus efficiencies, of the cells explored by JNC in these feasibility experiments were limited by the low flux of oxide ions through the cell's thick electrolyte layer. We will discuss Argonne National Laboratory's development of improved materials and cell designs for SO3 electrolysis to maximize the efficiency of this step in the hydrogen production cycle for operation at ~500°C.

This work is supported by the U.S. Department of Energy, Office of Nuclear Energy, Science, and Technology, Nuclear Hydrogen Initiative. The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory (?Argonne?) under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.