First-principles study on OH-functionalized 2D electrides: Ca2NOH and Y2C(OH)2, promising two-dimensional monolayers for metal-ion batteries

Abstract We designed two stable monolayers of Ca 2 NOH and Y 2 C(OH) 2 through replacing the anionic electrons with negatively charged hydroxide ions. Calculation results indicate that these two monolayers are dynamic and thermodynamic stable. Ca 2 NOH is determined as an indirect semiconductor with band gap of 1.51 eV based on hybrid functional calculations, while Y 2 C(OH) 2 possesses a direct band gap of 0.72 eV. Moreover, to investigate the potential applications of Ca 2 NOH and Y 2 C(OH) 2 monolayers, we studied the adsorption and diffusion performance of Li, Na and Mg atoms on their surfaces. The calculated adsorption energies, differential charge density and Bader charge analysis reveal that Li, Na and Mg atoms could anchor on Ca 2 NOH and Y 2 C(OH) 2 surfaces. Nudged Elastic band calculation results suggest that the barriers for Li, Na, and Mg diffusion on Ca 2 NOH surface are 0.79 eV, 0.42 eV and 0.42 eV. While Y 2 C(OH) 2 monolayer exhibits relative low diffusion barriers of 0.60 eV, 0.26 eV and 0.10 eV for Li, Na and Mg, respectively and their corresponding diffusion coefficients are as large as 1.52 × 10 −18 , 1.52 × 10 −12 and 1.52 × 10 −8  m 2 /s. The diffusion barriers and diffusion coefficients. The appropriate adsorption energies, low diffusion barriers and relative large diffusion coefficients of Na/Mg atoms imply that Ca 2 NOH and Y 2 C(OH) 2 monolayers are promising electrode materials for the corresponding metal-ion batteries. All the results serves to modify, stabilize and understand two dimensional electrides and put their properties into practical use.