A theoretical study on the intercalation and diffusion of AlF3 in graphite: its application in rechargeable batteries.

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.

Electronic transport in a graphene single layer: application in amino acid sensing.

We modeled a type of field-effect transistor device based on graphene for the recognition of amino acids with a potential application in the building of a protein sequencer. The theoretical model used was a combination of density functional theory (DFT) with the non-equilibrium Green's function (NEGF) in order to describe the coherent transport in molecular devices. First, we studied the physisorption of each amino acid on a graphene sheet and we reported the adsorption energy, the adsorption distances, the equilibrium configuration and the charge transfer of ten amino acids that can be considered as representative of all of the amino acids: histidine (His), alanine (Ala), aspartic acid (Asp), tyrosine (Tyr), arginine (Arg), glutamic acid (Glu), glycine (Gly), phenylalanine (Phe), proline (Pro) and lysine (Lys). As a result, significant differences were found in the density of states (DOS) after adsorption and there was a change in the semi-metallic character of the graphene due to the lysine and arginine interactions. Furthermore, we noticed changes in the electrical characteristics of the devices, as the amino acids adsorbed onto the surface of the graphene. The curves of current vs. bias voltage (I-Vb) display a distinct response for each amino acid, i.e. the I-Vb curves produce a characteristic footprint for each amino acid. We identified a possible rectification mechanism related to the voltage profile asymmetry, where the amino acids can control the transport characteristics in the device, i.e. Lys and Phe amino acids physisorbed on graphene act as a molecular diode, where electrons can easily flow in one direction and decrease in the other. This may be promising for the prospect of biosensors: graphene could be used as an amino acid detector.