First‐principles’ study of surface adsorption behaviors of oxygen on Nb₂C MXenes and their modification by PANI

Abstract

Large‐scale application of MXene are mainly limited by their easy oxidation behavior, which destroys their structure stabilities and thereby deteriorates their electrochemical properties as well. In order to understand the mechanism of chemical stability of Nb₂C–X₂ (X = O or OH) against oxygen attack and the modification effects of three types of polyaniline (PANI) [pernigraniline polyaniline (oxid‐PANI), leucoemeraldine polyaniline (red‐PANI), emeraldine polyaniline (rmid‐PANI)], the oxygen adsorption behaviors on surface slabs of Nb₂C–X₂, PANI and PANI‐modified Nb₂C–X₂ are systematically investigated and compared by applying density functional theory (DFT) calculations in this work. Among the 42 adsorption systems studied, the nanocomposite of oxid‐PANI/Nb₂CO₂ stands out due to the oxidation resistance and the structure stability owing to the effects of PANI modification. This is demonstrated by the decreased adsorption activity on the end of Nb₂CO₂ compared with the original Nb₂CO₂. Furthermore, the Bader charge analysis and the electron density difference maps illustrate that around 0.11 e transfers from the PANI‐end to the MXene‐end, which explains the physics behind the improvement of oxidation resistance in the MXene matrix. Therefore, our studies here indicate that the improvement of the oxidation resistance and the structure stability of Nb₂C‐type MXenes can be effectively qualified by the PANI‐modification, which gives theoretical guidelines for the preparation and the applications of MXene materials.