Mayenite-based electride C12A7e−: an innovative synthetic method via plasma arc melting

Abstract

Mayenite-based electrides have been reported as promising support materials for applications in heterogeneous catalysis. However, the current synthetic access to mayenite materials is limited by a method portfolio of complex procedures far from industrial applicability and thus hinders research and application in a broader context. We report the first plasma-based synthesis of the mayenite-based electride [Ca₂₄Al₂₈O₆₄]⁴⁺:(4e⁻) obtained by plasma treatment of oxygen-mayenite solid-reductant precursor mixtures. Aluminum and graphite can be successfully used as solid reductant: while aluminum leads to enhanced secondary phase formation of krotite during the treatment, the use of graphite as solid reductant, leads to phase-pure samples. We further critically discuss challenges and limitations in applying literature reported methods to quantitatively determine the electron concentration of the electrides. For this purpose, EPR-, DRUV/vis-spectroscopy, Rietveld refinement of PXRD and DSC-TG analysis under oxidizing atmosphere were applied and critically revised. We show the possibilities using the facile plasma-based synthesis as a scalable method to obtain semiconducting and close to metallic conducting electrides.