Combinations of V 2 C and Ti 3 C 2 MXenes for Boosting the Hydrogen Storage Performances of MgH 2

• Published in: ACS applied materials & interfaces Vol. 13; no. 11; pp. 13235 - 13247
• Main Authors: Liu, Haizhen, Lu, Chenglin, Wang, Xinchun, Xu, Li, Huang, Xiantun, Wang, Xinhua, Ning, Hua, Lan, Zhiqiang, Guo, Jin
• Format: Journal Article
• Language: English
• Published: United States 24.03.2021
• Subjects: magnesium hydride; titanium carbide; catalyst; vanadium carbide; hydrogen storage
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.0c23150

Two-dimensional vanadium carbide (V C) and titanium carbide (Ti C ) MXenes were first synthesized by exfoliating V AlC or Ti AlC and then introduced jointly into magnesium hydride (MgH ) to tailor the hydrogen desorption/absorption performances of MgH . The as-prepared MgH -V C-Ti C composites show much better hydrogen storage performances than pure MgH . MgH with addition of 10 wt % of 2V C/Ti C 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 , the dehydrided MgH -2V C/Ti C can start to recover hydrogen at room temperature, and 5.1 wt % of H 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 C/Ti C can remarkably lower the activation energy for the hydrogen desorption reaction of MgH by 37% and slightly reduce the hydrogen desorption reaction enthalpy by 2 kJ mol H . It was demonstrated that the combination of V C and Ti C promotes the hydrogen-releasing process of MgH compared with addition of only V C or Ti C , while Ti C impacts MgH more significantly than V C in the hydrogen absorption process of MgH at ambient temperatures. A possible mechanism in the hydrogen release and uptake of the MgH -V C-Ti C system was proposed as follows: hydrogen atoms or molecules may preferentially transfer through the MgH /V C/Ti C triple-grain boundaries during the desorption process and through the Mg/Ti C interfaces during the absorption process. Microstructure studies indicated that V C and Ti C mainly act as efficient catalysts for MgH . This work provides an insight into the hydrogen storage behaviors and mechanisms of MgH boosted by a combination of two MXenes.