Pyrrolic, pyridinic, and graphitic sumanene as metal‐free catalyst for oxygen reduction reaction – A density functional theory study
Thangaraj Thiruppathiraja, Agnes Lincy Arokiyanathan, Senthilkumar Lakshmipathi
Abstract
Abstract This study investigates the nitrogen (N)‐doped sumanene (SUMA) molecule's catalytic behavior for the four‐electron oxygen reduction reaction (ORR) process. Accordingly, the N atom is doped at three different positions on the SUMA molecule to obtain the pyrrolic, pyridinic, and graphitic SUMA. The free energy value for the individual reaction processes in the four‐electron reduction reaction shows high exothermicity and feasibility for the N‐doped SUMA molecules. Moreover, the free energy for the entire four‐electron reduction reaction lies well below the value of O 2 reduction into two water (H 2 O) molecules –474.71 kJ/mol. The N‐doped SUMA molecules exhibit stronger adsorption energy despite being metal‐free. The physisorption of the final product (H 2 O molecule) over the SUMA molecules suggests the possibility of regeneration of the catalyst, thereby controlling catalytic poisoning. Specifically, the graphitic SUMA shows a prominent catalytic behavior due to a lower highest occupied molecular orbital‐lowest unoccupied molecular orbital energy gap, which arises due to the increased charge density of the carbon atoms present near the graphitic N site. Besides, doping carbon‐based materials with N at the central benzene ring significantly enhances their catalytic efficiency due to localized π‐orbitals. Overall, the results reveal that N‐doped SUMA molecules are a promising metal‐free catalyst for ORR activity.