Exploring Hydrogen Adsorption and Release in 2D M2C-MXenes: Structural and Functional Insights.

Abstract

Two-dimensional M2C-MXenes, characterized by their lightweight nature, tunable surface structures, and strong affinity for hydrogen, hold significant promise for addressing various challenges in hydrogen energy utilization. This study focuses on investigating the hydrogen adsorption and desorption properties, as well as the stability of hydrogenated compounds in 19 pure M2C-MXenes nanosheets. The results indicate that hydrogen adsorption on M2C primarily occurs through weak physisorption, with Mn2C and Fe2C from the fourth period, and Ag2C and Cd2C from the fifth period exhibiting the lowest adsorption energies. In contrast, hydrogen atoms are adsorbed on M2C primarily through chemisorption, leading to the potential dissociation of H2 molecules into two hydrogen atoms. Among the M2C-MXenes, Ti2C, and Zr2C in the d4 and d5, respectively, demonstrate the most stable hydrogen atom binding. Hydrogen evolution is most facile on Cu2C and Ag2C surfaces. Two types of stacking configurations, face-centered cubic (fcc) and hexagonal close-packed (hcp), are observed for hydrogenated M2C surfaces (e.g., Co2C and Zr2C), showing excellent thermodynamic stability. This work elucidates the hydrogen utilization performance of pure M2C-MXenes nanosheets and guides future research aimed at achieving high hydrogen storage capacities through the functional tuning of MXenes.