Step-change in high temperature steam electrolysis performance of perovskite oxide cathodes with exsolution of B-site dopants

摘要

B-site doped, A-site deficient perovskite oxide titanates with formula La_(0.4)Sr_(0.4)M_x~(n+)Ti_(1-x)O_(3-γ-δ) (M = Fe~(3+) or Ni~(2+); x = 0.06; γ = (4 - n)×12) were employed as solid oxide electrolysis cell (SOEC) cathodes for hydrogen production via high temperature steam electrolysis at 900 ℃ A-site deficiency provided additional driving force for the exsolution of a proportion of B-site dopants at the surface in the form of metallic nanoparticles under reducing SOEC cathode operating conditions. In the case of La_(0.4)Sr_(0.4)Fe_(0.06)Ti_(0.94)O_(2.97), this represents the first time that Fe° has been exsolved from a perovskite in such a way. Exsolution was due in part to the inability of the host lattice to accommodate vacancies (introduced (δ) oxygen vacancies (V_o~¨) and fixed A-site (V_(Sr_~") and inherent (γ) oxygen vacancies) beyond a certain limit. The presence of electrocatalytically active Fe° or Ni° nanoparticles and higher V_o~¨ concentrations dramatically lowered the activation barrier to steam electrolysis compared to the parent material (x = 0). The use of defect chemistry to drive the exsolution of less reducible dopant cations could conceivably be extended to produce new catalytically active perovskites with unique properties.