Liu Haizhen, Lu Chenglin, Wang Xinchun, Xu Li, Huang Xiantun, Wang Xinhua, Ning Hua, Lan Zhiqiang, Guo Jin
Guangxi Novel Battery Materials Research Center of Engineering Technology, Guangxi Key Laboratory of Processing for Non-ferrous Metallic and Featured Materials, Guangxi Colleges and Universities Key Laboratory of Novel Energy Materials and Related Technology, School of Physical Science and Technology, Guangxi University, Nanning 530004, China.
State Key Laboratory of Advanced Power Transmission Technology, Global Energy Interconnection Research Institute Co., Ltd., Beijing 102209, China.
ACS Appl Mater Interfaces. 2021 Mar 24;13(11):13235-13247. doi: 10.1021/acsami.0c23150. Epub 2021 Mar 15.
Two-dimensional vanadium carbide (VC) and titanium carbide (TiC) MXenes were first synthesized by exfoliating VAlC or TiAlC and then introduced jointly into magnesium hydride (MgH) to tailor the hydrogen desorption/absorption performances of MgH. The as-prepared MgH-VC-TiC composites show much better hydrogen storage performances than pure MgH. MgH with addition of 10 wt % of 2VC/TiC 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-2VC/TiC 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 2VC/TiC 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 VC and TiC promotes the hydrogen-releasing process of MgH compared with addition of only VC or TiC, while TiC impacts MgH more significantly than VC in the hydrogen absorption process of MgH at ambient temperatures. A possible mechanism in the hydrogen release and uptake of the MgH-VC-TiC system was proposed as follows: hydrogen atoms or molecules may preferentially transfer through the MgH/VC/TiC triple-grain boundaries during the desorption process and through the Mg/TiC interfaces during the absorption process. Microstructure studies indicated that VC and TiC 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.
通过剥离VAlC或TiAlC首次合成了二维碳化钒（VC）和碳化钛（TiC）MXenes，然后将它们共同引入氢化镁（MgH）中，以调节MgH的氢解吸/吸收性能。所制备的MgH-VC-TiC复合材料表现出比纯MgH更好的储氢性能。添加10 wt%的2VC/TiC的MgH在约180°C开始氢解吸；在225°C下60分钟内解吸出5.1 wt%的氢，而在300°C下2分钟内解吸出5.8 wt%的氢。在6 MPa H2下，脱氢后的MgH-2VC/TiC在室温下可以开始吸氢，在40°C恒温下20 s内获得5.1 wt%的H2。可逆容量（6.3 wt%）在多达10个循环中没有下降，显示出优异的循环稳定性。添加2VC/TiC可以显著降低MgH氢解吸反应的活化能37%，并使氢解吸反应焓略微降低2 kJ mol-1 H2。结果表明，与仅添加VC或TiC相比，VC和TiC的组合促进了MgH的氢释放过程，而在室温下MgH的氢吸收过程中，TiC对MgH的影响比VC更显著。提出了MgH-VC-TiC体系氢释放和吸收的一种可能机制如下：在解吸过程中，氢原子或分子可能优先通过MgH/VC/TiC三相晶界转移，而在吸收过程中通过Mg/TiC界面转移。微观结构研究表明，VC和TiC主要作为MgH的有效催化剂。这项工作深入了解了由两种MXenes组合促进的MgH的储氢行为和机制。
