High Redox Capacity of Al-Doped La Sr MnO Perovskites for Splitting CO and H O at Mn-Enriched Surfaces.

Perovskites are attractive candidates for the solar-driven thermochemical redox splitting of CO and H O into CO and H (syngas) and O . This work investigates the surface activity of La Sr Mn Al O (0≤x≤1, 0≤y≤1) and La Ca Mn Al O . At 1623 K and 15 mbar O , the oxygen non-stoichiometry of La Sr Mn Al O increases with the strontium content and reaches a maximum of δ=0.351. X-ray photoelectron spectroscopy analysis indicates that manganese is the only redox-active metal at the surface. All La Sr Mn Al O compositions exhibit surfaces enriched in manganese and depleted in strontium. We discuss how these compositional differences of the surface from the bulk lead to the beneficially higher reduction extents and lower strontium carbonate concentrations at the aluminum-doped surfaces. Using first principles calculations, we validate the experimental reduction trends and elucidate the mechanism of the partial electronic charge redistribution upon perovskite reduction.