Theoretical study of the catalytic effect of TM-C4H4 and TM-C5H5 (TM = Cr, Ti, V, Sc) on the activation of O2 at the cathode and CH3OH at the anode in CH3OH-O2 fuel cell via DFT computational method

The study of the interaction of oxygen molecule with organometallic compounds containing transition metals has always been an interesting subject for research, as the O-2 activation by them is a measure of the efficiency of organometallic catalysts. This study examined the catalytic effect of some organometallic compounds containing transition metals with the general formula of TM-CmHm on increasing the reaction rate of methanol-oxygen fuel cell using the method of density functional theory (DFT) and PW91 method as well as the basis set of 6-31G(d) (TM represents each of Sc, Ti, V and Cr and m is equal to 4 or 5). The structures of the mentioned compounds were optimized by the natural bonding orbital calculations (NBO). Then, the diagrams of the density state (DOS) were plotted for them and afterward, gap energy (E-g), chemical hardness (eta), chemical potential (mu) and electrophilicity (omega) were calculated in each case. The Eg and eta of ScC5H5 were smaller than that of the others, indicating greater reactivity. Theoretical calculations showed that each of the TMs in TM-CmHm had a partial negative electric charge, which was higher in ScC5H5 than in others causing higher chemical activity. The adsorption energies of O-2 and CH3OH were calculated and reported on each of the TM-CmHm. The adsorption energy of O-2 and CH3OH on ScC5H5 was more negative than that of the other TM-CmHm used. This confirms that the compound had a greater efficiency and ability to play a catalytic role in the oxygen - methanol fuel cell. The results showed that the bond length of O=O increased by about 24% on average due to its adsorption on ScC5H5. The O-H bond length was significantly increased in response to the methanol adsorption process on ScC5H5. Increasing the bond length caused instability of the bond and raising its chemical activity and reactivity. The adsorption kinetics of each of O-2 and CH3OH on ScC5H5 were also studied by the above-computational method. The potential energy variation of the adsorbate/adsorbent system in terms of reaction coordinate (bond length of O=O or O-H) in each case was evaluated with a one transition state observed in each case. (C) 2021 The Authors. Published by Elsevier B.V. on behalf of King Saud University.

Automated summary

The study investigated the catalytic effect of organometallic compounds with transition metals on the methanol-oxygen fuel cell reaction rate using theoretical calculations. Results showed that ScC5H5 exhibited higher reactivity and stronger adsorption of O-2 and CH3OH, indicating greater efficiency in catalyzing the fuel cell.