Theoretical Insights of Curvature Effects of FeN4-Doped Carbon Nanotubes on ORR Activity

The advancement of metal-air batteries is critically contingent on the progression of efficient catalysts for the oxygen reduction reaction (ORR). The potential applications of a series of FeN₄-doped carbon nanotubes (Fe-N₄CNTs) of varying diameters as ORR catalysts were examined using density functional theory. We explored the stability and electronic properties of Fe-N₄CNTs by analyzing the energy and examining the density of states. A marked dependence of the catalytic performance on the nanotube diameter was observed: as the transition from (5, 5) to (10, 10) Fe-N₄CNTs occurred, the catalytic activity on the outer surface of the carbon tubes enhanced progressively, with the overpotential reducing from 0.94 to 0.86 V. Conversely, the catalytic activity on the inner surface of the carbon tubes decreased progressively with the overpotential also increasing from 0.62 to 1.04 V. In addition, we found that curvature significantly affected the electronic structure and charge transfer at the FeN₄ site, regulating the adsorption and desorption of reactants, intermediates, and products during electrocatalysis and thus influencing the catalytic activity of the Fe-N₄CNTs. This investigation offers valuable guidance for the design of Fe-based single-atom catalysts and the practical application of Fe-N-C materials.