Title : Computational designing of energy storage materials
Abstract:
The pressing global demand for sustainable and clean energy driven by population growth, rising living standards, and the limitations of fossil fuel reserves has brought hydrogen to the forefront as a promising energy carrier. In this talk, I will present insights from first-principles calculations on hydrogen interactions with pristine and metal-functionalized graphene1,2. Pristine carbon nanomaterials bind hydrogen molecules through weak van der Waals interactions, which results in their desorption before ambient temperature. Firstly, I will discuss different strategies such as the application of external strain on the system, or the functionalization of pristine nanostructures with different alkali, alkali-earth, or transition metal (TM) atoms. Transition-metal (TM) atom-functionalized nanomaterials are promising candidates for hydrogen storage due to their ability to adsorb multiple hydrogen molecules through Kubas interactions. However, TM atoms have a strong tendency of clustering which can reduced the hydrogen storage performance of the material. Also, achieving efficient hydrogen desorption at ambient conditions in TM-functionalized carbon nanostructures remain a critical challenge for practical use. I will present a novel approach to modulate the desorption temperature of hydrogen in TM-intercalated bilayer graphene (BLG) using external mechanical forces3. By employing first-principles density functional theory and thermodynamic occupancy probability calculations, we demonstrate that adjusting the interlayer distance allows for precise control over the interaction energy of H2, thereby facilitating its desorption at ambient conditions.
Complete hydrogen desorption occurs when the interlayer distance is reduced below 4.7, 5.3, and 5.1 Å for Sc-, Ti-, and V-intercalated BLG, respectively. Our findings suggest that external mechanical forces can effectively bring hydrogen occupancy to zero by minimizing charge transfer from the TM ????-orbitals to H2 antibonding orbitals. Notably, while the total charge transferred from the TM atoms remains nearly constant at varying interlayer distances, its redistribution between the graphene layers and H2 fine-tunes the interaction strength. This approach can be extended to large interlayer distances, as supported by recent experiments on graphene oxide membranes [ACS Nano 12, 9309 (2018)]. Furthermore, recent experimental advances in noble gas and alkali-metal intercalation in BLG highlight the potential of this approach to overcome the long-standing challenge of high desorption temperatures in TM-functionalized layered nanomaterials. If time permits, I will also discuss other possible strategies such as heterometal atoms doping to minimize the metal clustering in metal functionalized nanomaterials.
