Searching for reversible hydrogen storage materials operated under ambient conditions is a big challenge for material scientists and chemists. In this work, using density functional calculations, we systematically investigated the hydrogen storage properties of the two-dimensional (2D) Ti2C phase, which is a representative of the recently synthesized MXene materials ( ACS Nano 2012 , 6 , 1322 ). As a constituent element of 2D Ti2C phase, the Ti atoms are fastened tightly by the strong Ti-C covalent bonds, and thus the long-standing clustering problem of transition metal does not exist. Combining with the calculated binding energy of 0.272 eV, ab initio molecular dynamic simulations confirmed the hydrogen molecules (3.4 wt % hydrogen storage capacity) bound by Kubas-type interaction can be adsorbed and released reversibly under ambient conditions. Meanwhile, the hydrogen storage properties of the other two MXene phases (Sc2C and V2C) were also evaluated, and the results were similar to those of Ti2C. Therefore, the MXene family including more than 20 members was expected to be a good candidate for reversible hydrogen storage materials under ambient conditions.

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Two-dimensional carbide MXenes (Ti 3 C 2 T x and V 2 CT x ) were prepared by exfoliating MAX phases (Ti 3 AlC 2 and V 2 AlC) powders in the solution of sodium fluoride (NaF) and hydrochloric acid (HCl). The specific surface area (SSA) of as-prepared Ti 3 C 2 T x was 21 m 2 /g, and that of V 2 CT x was 9 m 2 /g. After intercalation with dimethylsulfoxide, the SSA of Ti 3 C 2 T x was increased to 66 m 2 /g; that of V 2 CT x was increased to 19 m 2 /g. Their adsorption properties on carbon dioxide (CO 2 ) were investigated under 0-4 MPa at room temperature (298 K). Intercalated Ti 3 C 2 T x had the adsorption capacity of 5.79 mmol/g, which is close to the capacity of many common sorbents. The theoretical capacity of Ti 3 C 2 T x with the SSA of 496 m 2 /g was up to 44.2 mmol/g. Additionally, due to high pack density, MXenes had very high volume-uptake capacity. The capacity of intercalated Ti 3 C 2 T x measured in this paper was 502 V·v -1 . This value is already higher than volume capacity of most known sorbents. These results suggest that MXenes have some advantage features to be researched as novel CO 2 capture materials. suitable material to adsorb and capture CO 2 .In general, pressure and/or temperature swing approaches are used to capture CO 2 in porous materials. The porous materials, as CO 2 sorbents, should have superior properties in terms of capacity, stability, kinetics, selectivity, and regeneration [1]. Up to now, a wide range of sorbents for CO 2 capture, have been used and studied, including metal organic frameworks (MOFs) [2], functionalized porous silica [3], activated carbon [4], zeolites [5], metal oxides, and microporous polymers [6]. Among these sorbents, MOFs exhibit very high CO 2 uptake up to 54.4 mmol/g under high pressures (5 MPa) at 298 K [2]. Despite the excellent adsorption capacities, MOFs are much more expensive 238