Vacancy-Induced Anionic Electrons in Single-Metal Oxides and Their Possible Applications in Ammonia Synthesis

Abstract

Realizating of a low work function (WF) and room-temperature stability in electrides is highly desired for various applications, such as electron emitters, catalysts, and ion batteries. Herein, a criterion based on the electron localization function (ELF) and projected density of states (PDOS) in the vacancy of the oxide electride [Ca 24 Al 28 O 64 ] 4+ (4e − ) (C12A7) was adopted to screen out 13 electrides in single-metal oxides. By creating oxygen vacancies in nonelectride oxides, we find out 9 of them showed vacancy-induced anionic electrons. Considering the thermodynamic stability, two electrides with ordered vacancies, Nb 3 O 3 and Ce 4 O 3 , stand out and show vacancy-induced zerodimensional anionic electrons. Both exhibit low WFs, namely 3.1 and 2.3 eV for Nb 3 O 3 and Ce 4 O 3 , respectively. In the case of Nb 3 O 3 , the ELF at oxygen vacancies decreases first and then increases during the decrease in the total number of electrons in self-consistent calculations due to Nb's multivalent state. Meanwhile, Ce 4 O 3 displays promise for ammonia synthesis due to its low hydrogen diffusion barrier and low activation energy. Further calculations revealed that CeO with disordered vacancies at low concentrations also exhibits electride-like properties, suggesting its potential as a substitute for Ce 4 O 3 .