RESUMEN
Using first-principles calculations based on density functional theory (DFT), we study the aluminum fluoride (AlF3) intercalation in graphite as a new possibility to use this molecule in rechargeable batteries, and understand its role when used as a component of the solvent. We discuss the most stable configuration of the AlF3 molecule in graphite for stage-2 and stage-1 and the diffusion study of the molecule, the migration pathways and the energy barriers. Our results show an average voltage of 3.18 V for stage-2 and 3.44 V for stage-1, which is excellent for anion intercalated batteries. Furthermore, low diffusion energy barriers of the AlF3 intercalant molecules were found (the lowest diffusion energy barrier was 0.17 eV with a diffusion constant in the order of 10-5 cm2 s-1), which could lead to fast (dis)charging of a battery based on AlF3. The present study provides important information to understand the intercalation mechanism of AlF3 graphite layer electrodes, thus encouraging more experimental studies of this system.
RESUMEN
The effect of the Au crystalline plane on the adsorption of different thiols and selenols is studied via reductive desorption (RD) and X-ray photoelectron spectroscopy (XPS) measurements. Self-assembled monolayers (SAMs) using aliphatic (ATs) and aromatic thiols (ArTs) on both Au(111) and Au(100) were prepared. The electrochemical stability of these SAMs on both surfaces is evaluated by comparing the position of the RD peaks. The longer the AT chain the more stable the SAM on Au(100) when compared to Au(111). By means of XPS measurements, we determine that the binding energy (BE) of the S 2p signal corresponding to the S atoms at the thiol/Au interface, commonly assigned at 162.0 eV, shifts 0.2 eV from Au(111) to Au(100) for SAMs prepared using thiols with the C* (C atom bonded to S) in sp3 hybridization, such as ATs. However, when the thiol presents the C* with an sp2 hybridization, such as in the case of ArTs, the BE remains at 162.0 eV regardless of the surface plane. Selenol-based SAMs were characterized comparatively on both Au(100) and Au(111). Our results show that selenol SAMs become even more electrochemically stable on Au(100) with respect to Au(111) than the analogue sulfur-based SAM. According to our results, we suggest that the electronic distribution around the Au-S/Se bond could be responsible for the different structural arrangements reported in the literature (gold adatoms, etc.), which should be dependent on the crystalline face (Au(hkl)-S) and the chemical nature of the environment of the adsorbates (sp3-C* vs sp2-C* and Au-SR vs Au-SeR).
