Experimental and theoretical assessment of the enhanced hydrogen adsorption on polycyclic aromatic hydrocarbons upon decoration with alkali metals

• Published in: International journal of hydrogen energy 2024-03, Vol.58, p.525-535
• Main Authors: Reider, Anna Maria, Kollotzek, Siegfried, Scheier, Paul, Calvo, Florent, Yurtsever, Ersin, Pirani, Fernando, Bartolomei, Massimiliano, Hernández, Marta I., González-Lezana, Tomás, Campos-Martínez, José
• Format: Article
• Language: English
• Subjects: Alkali decoration; Enhanced hydrogen storage; Helium nanodroplet experiments; Polycyclic aromatic hydrocarbons
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2024.01.244

Hydrogen storage by physisorption on carbon-based materials is limited by comparatively low adsorption energies. However, decoration of the carbon substrate with alkali, alkaline earth, or other metal atoms has been proposed as a means to enhance adsorption energies. The decoration affects also the stability of these materials since it makes them more stable and resilient in the repeated cycles of charge and discharge that would be required for a good material devoted to storage. We investigate hydrogen storage capacities of small polycyclic aromatic hydrocarbons (PAHs) cations grown in ultracold helium nanodroplets by analyzing the ion abundances and stabilities. The observations are assessed with quantum chemical calculations and atomistic simulations. It is experimentally shown that the addition of an alkali ion significantly enhances the hydrogen adsorption of the studied PAHs, up to 25% over the bare PAH in the experimental conditions studied here, and the simulations confirm this general trend except for some minor residual discrepancies in the special stabilities (magic numbers). Several approaches to study larger and different PAH compounds are also proposed, and for all cases it is found that alkali decoration increases energy stability by more than 100%. [Display omitted] •Experimental evidence for enhanced hydrogen adsorption upon alkali decoration.•Extra stability theoretically confirmed.•Good agreement between theory and experiment.•Simplified model proposed to treat larger substrates.