Praseodymium Manganate-Based Perovskites as Anode Materials for Fuel-Assisted Solid Oxide Electrolysis Cells

Abstract

Long-term degradation remains the main issue for the viability of solid oxide electrolysis cell (SOEC) technology as a practical hydrogen production system. The major specific degradation mechanism in SOECs relates to delamination phenomena at or near electrolyte/anode interface. The principle of so-called fuel-assisted electrolysis is to supply the carbon-containing species which can react with oxygen at the anode side thus bringing down the oxygen chemical potential at the electrolyte/anode interface and improving its stability. The present work is aimed at the characterization of PrMnO3-based perovskites for potential application as anodes in solid oxide fuel-assisted electrolysis cells.Pr0.6-x A0.4MnO3 ±δ (A = Sr, Ca; x = 0 and 0.05) were synthesized by glycine-nitrate combustion technique. The characterization included XRD, SEM/EDS, XPS, dilatometry and thermogravimetry, measurements of electrical properties and oxygen nonstoichiometry. XRD analysis confirmed the formation of solid solutions with orthorhombic perovskite structure. The oxides exhibit negligible variations of oxygen content under oxidizing conditions, while reducing p(O2) below 10-4 atm results in oxygen losses from the lattice and reduction of Mn cations. The low-p(O2) stability boundary of the perovskite phase at 800°C corresponds to ~10-17-10-16 atm; the stability domain is wider for Ca-substituted compositions and narrows with introduction of A-site vacancies. Dilatometric studies confirmed a good thermomechanical compatibility with common solid electrolytes. The electrical conductivity of Pr0.6-x A0.4MnO3 ±δ ceramics is p-type electronic and decreases with reducing p(O2), but still exceeds 40-50 S/cm under anticipated oxygen electrode operation conditions. The electrochemical performance of Pr0.6-x A0.4MnO3 ±δ electrodes was evaluated in contact with yttria-stabilized zirconia solid electrolyte as function of relevant parameters (fabrication conditions, with and without buffer layers, with praseodymia or ceria-based additives).