Density functional theory calculations on the effect of adding messo- and beta- halogens (F, Cl, and Br) on iron porphyrin group: An application to hydrogen based fuel cell

• Main Author: Rabe, Rabin R.
• Format: text
• Language: English
• Published: Animo Repository 2006
• Subjects: Density functionals; Halogens; Porphyrins; Oxidation-reduction reaction; Physics
• Online Access: https://animorepository.dlsu.edu.ph/etd_doctoral/165; https://animorepository.dlsu.edu.ph/context/etd_doctoral/article/1164/viewcontent/CDTG004282_P.pdf
• Institution: De La Salle University

One promising energy source is hydrogen based fuel cell specifically Polymer Electrolyte Fuel Cell (PEFC) whose by-product is a non-toxic solvent water. The researchers considered the possibility of using oxygenase-based nanomaterials (Iron (II) porphyrin) in the cathode electrodes of PEFCs, where oxidation reduction reaction takes place (ORR). Specifically, we want to see the effects of halogens (F, Cl, and Br) placed on messo-, and beta- positions of iron porphyrins, on the geometry, electron and spin density, total energy and binding energies of the said molecule by means of Density Functional Theory (DFT) for the proposed catalyst of the PEFC electrodes. The researchers found that adding halogens (Fluorine, Chlorine, and Bromine) to the subsequent positions (messo- and beta-) of iron porphyrin can lower the total energy thus making the molecule more stable. The results also show that increasing number of electronegative atoms lead to greater electron withdrawal from the non-halogen atoms in the FeP resulting to lower total energy. Fluorine being the most electronegative gives the lowest total energy followed by chlorine and bromine. Moreover, halogenations at messo- sites can cause bending of the iron porphyrin while halogenations on beta- sites protect structural deformation on the iron porphyrin upon oxygen adsorption. The position of the halogens, whether opposite or adjacent sides on both messo- and beta- positions, do not account for significant changes in total energy. We also found out that triplet state of halogenated derivatives that have small relative energy gap will correspond to lower binding energies and for singlet state, molecules with small relative energy gap will have higher relative binding energy. The energy gap and binding energies of halogenated iron porphyrin depends greatly on the electron density distribution of the molecule. These can be seen through HOMO/LUMO plot of the molecule being studied.