Combinations of V₂C and Ti₃C₂ MXenes for Boosting the Hydrogen Storage Performances of MgH₂

Abstract

Two-dimensional vanadium carbide (V 2 C) and titanium carbide (Ti 3 C 2 ) MXenes were first synthesized by exfoliating V 2 AlC or Ti 3 AlC 2 and then introduced jointly into magnesium hydride (MgH 2 ) to tailor the hydrogen desorption/absorption performances of MgH 2 . The as-prepared MgH 2 −V 2 C−Ti 3 C 2 composites show much better hydrogen storage performances than pure MgH 2 . MgH 2 with addition of 10 wt % of 2V 2 C/Ti 3 C 2 initiates hydrogen desorption at around 180 °C; 5.1 wt % of hydrogen was desorbed within 60 min at 225 °C, while 5.8 wt % was desorbed within 2 min at 300 °C. Under 6 MPa H 2 , the dehydrided MgH 2 −2V 2 C/Ti 3 C 2 can start to recover hydrogen at room temperature, and 5.1 wt % of H 2 is obtained within 20 s at a constant temperature of 40 °C. The reversible capacity (6.3 wt %) does not decline for up to 10 cycles, which shows excellent cycling stability. The addition of 2V 2 C/Ti 3 C 2 can remarkably lower the activation energy for the hydrogen desorption reaction of MgH 2 by 37% and slightly reduce the hydrogen desorption reaction enthalpy by 2 kJ mol −1 H 2 . It was demonstrated that the combination of V 2 C and Ti 3 C 2 promotes the hydrogen-releasing process of MgH 2 compared with addition of only V 2 C or Ti 3 C 2 , while Ti 3 C 2 impacts MgH 2 more significantly than V 2 C in the hydrogen absorption process of MgH 2 at ambient temperatures. A possible mechanism in the hydrogen release and uptake of the MgH 2 −V 2 C−Ti 3 C 2 system was proposed as follows: hydrogen atoms or molecules may preferentially transfer through the MgH 2 /V 2 C/Ti 3 C 2 triple-grain boundaries during the desorption process and through the Mg/ Ti 3 C 2 interfaces during the absorption process. Microstructure studies indicated that V 2 C and Ti 3 C 2 mainly act as efficient catalysts for MgH 2 . This work provides an insight into the hydrogen storage behaviors and mechanisms of MgH 2 boosted by a combination of two MXenes.

The Improvement in Hydrogen Storage Performance of MgH2 Enabled by Multilayer Ti3C2

“…After rehydrogenation, the particles expand and come into close contact. This close particle contact is not conducive to the hydrogen absorption kinetics of pure MgH 2 [45]. However, with the addition of ML-Ti 3 C 2 , hydrogen can easily be spatially transferred through the interface between MgH 2 and ML-Ti 3 C 2 .…”

“…The MgH 2 +5 wt.% of Ti 3 C 2 /TiO 2 can release 5.0 wt.% of hydrogen at a constant temperature of 250 • C, and can absorb 4.0 wt.% of hydrogen at a constant temperature of 125 • C. The layered structures and the Ti-containing compounds with multiple valences were considered to be responsible for the improvement of MgH 2 by Ti 3 C 2 /TiO 2 . Liu et al [45] synthesized V 2 C and Ti 3 C 2 MXenes by exfoliating V 2 AlC and Ti 3 AlC 2 . MgH 2 +10 wt.% of 2V 2 C/Ti 3 C 2 initiated hydrogen desorption at around 180 • C, and 5.1 wt.% of hydrogen was desorbed within 60 min at 225 • C. Hydrogen atoms or molecules may preferentially transfer through the MgH 2 /V 2 C/Ti 3 C 2 triple-grain boundaries during the desorption process, and through the Mg/Ti 3 C 2 interfaces during the absorption process.…”

The Catalytic Role of D-block Elements and Their Compounds for Improving Sorption Kinetics of Hydride Materials: A Review

“…The enhanced hydrogen sorption kinetics is basically attributed to the hybrid design and coupling of many metals together. Furthermore, two kinds of Mxenes were mixed: 2D vanadium carbide (V 2 C) and titanium carbide (Ti 3 C 2 ), in order to check the synergistic effects on decomposition of MgH 2 (see Figure 23) [168]. According to this report, hydrogen atoms or molecules during the desorption process may pass through the MgH 2 /V 2 C/Ti 3 C 2 triple-grain boundaries and through the Mg/Ti 3 C 2 interfaces during the absorption process.…”

“…According to this report, hydrogen atoms or molecules during the desorption process may pass through the MgH 2 /V 2 C/Ti 3 C 2 triple-grain boundaries and through the Mg/Ti 3 C 2 interfaces during the absorption process. [168]. (Reprinted with permission from the American Chemical Society.…”

Enhanced Hydrogen Storage Performance of MgH2 by the Catalysis of a Novel Intersected Y2O3/NiO Hybrid

“…MgH 2 prepared from waste Mg-alloys also show favorable possibility for hydrogen storage [5,6], offering more opportunities to lower the cost. However, the high thermal stability of MgH 2 (∆H = 75 kJ•mol −1 H 2 ) and the reaction barrier (∆E = 161 kJ•mol −1 ) [7] lead to high dehydrogenation temperature, where the peak dehydrogenation temperature is commonly over 360 • C [8], which limit its practical application for hydrogen storage.…”