Development of Durable Materials for Cost Effective Water Splitting

Abstract

Saint-Gobain, a global leader in ceramic and polymer based materials and components has been developing solutions for fuel and electrolysis cells for over 20 years. These solutions include; electrode and electrolyte materials, innovative cell and stack designs, ceramic interconnects, seals (both glass-ceramic and polymer based) and hot box designs. Although high temperature electrolysis promises to be an efficient solution to the production of hydrogen, durability and performance improvements are still required to produce devices that are economically feasible. A promising material family for the air electrode are rare-earth nickelate oxides with the Ruddlesden-Popper structure. These oxides are known to have a point defect structure in which oxygen interstitials play a key role in the oxygen surface exchange and transport through the lattice. Although the performance of the rare-earth nickelates can be high, they unfortunately react and decompose when in contact with rare-earth doped ceria. Ceria is typically added as a second phase from the standpoint of buffering the coefficient of thermal expansion, providing additional oxygen ionic conducting paths, and for forming the buffer layer preventing adverse reactions between the oxygen electrode and the electrolyte which are typically yttrium or scandium doped zirconia.This work focuses on stabilizing the rare-earth nickelate electrodes through compositional modifications while developing cell-design agnostic material solutions using these materials. The driving force for nickelate decomposition was determined to be the high limits for cation solubility within typical ceria-based barrier layers. A solution to this problem is presented. In addition, towards improving the performance of cells the oxygen diffusion mechanism was modeled allowing the calculation of ionic conductivity for a variety of cation substitutions within the nickelate structure. Fundamental material properties such as exchange coefficient, oxygen incorporation into the lattice as a function of partial pressure, and electrode resistance over time were measured. Finally, an innovative processing technique for the simultaneous multilayer coating of highly loaded slurries was developed. This process provides a reduction in the number of processing steps required to produce cells while also allowing for good layer adhesion as well as thickness control at the 2.5 micron range.