Heavy doping of H ion in 12CaO·7Al2O3

12CaO·7Al₂O₃ (C12A7, mayenite), which has a nanoscale porous structure that can accommodate extraframework species such as hydride (H⁻), oxide (O²⁻), hydroxide (OH⁻) ions, and electrons, has been doped with H⁻ ions to investigate its effects as dominant extraframework species. Chemical doping with CaH₂ enables the concentration of H⁻ ions to reach almost the theoretical maximum. The concentration of H⁻ ions is characterized by optical absorption intensity ascribed to photoionization of H⁻ ions, and ¹H magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. Persistent electron generation, which is accompanied by the formation of an F⁺ absorption band and electrical conductivity, by irradiation with ultraviolet light at room temperature increases as the H⁻ ion doping increases until it reaches half the theoretical maximum and then decreases as the H⁻ ion concentration increases further. This dependence indicates that both H⁻ and O²⁻ ions are necessary for the generation of persistent electrons.