Revealing the Mechanism and Activity of O2 Reduction Reaction of Co Nanocluster Encapsulated by Carbon Nanotube

Exploration of inexpensive electrocatalysts with excellent catalytic activity and chemical stability for the O₂ reduction reaction (ORR) is crucial for the widespread adoption of sustainable and renewable energy conversion technologies in practical applications. This study explored the potential of Co nanoparticle-encapsulated single-wall carbon nanotube (Co@SWCNT) as efficient electrocatalyst for ORR. We employed a quantum mechanical (QM) periodic hybrid B3LYP density functional theory (DFT) method with the dispersion corrections (-D3) (developed by Grimme and co-workers) to investigate the ORR mechanism. We examined the impact of Co nanoparticles on the electronic properties of the SWCNT and observed that Co@SWCNT has metallic characteristics in nature. The study focused on determining the adsorption energy (ΔE) of ORR species on the Co@SWCNT surface to comprehend its electrocatalytic efficiency and performance toward ORR. Furthermore, we proposed two potential ORR mechanisms: a direct 4e^– transfer reaction pathway and a series of 2e^– transfer reaction pathways. The value of ΔE of the 2O* ORR intermediate has been determined to be −0.35 eV, and for the OOH* ORR intermediate, the value of ΔE is about −3.59 eV. This suggests that the 4e^– dissociative pathway could be the thermodynamically favorable path for the O₂ reduction reaction compared to the 4e^– associative and 2e^– pathways of ORR. This research not only paves the way for the development of cost-effective and highly durable nonmetal catalytic materials but also holds great promise for advancing future renewable energy and fuel cell applications.