Modulating the Cavity Size of Carbon Nanobelts for Enhanced Oxygen Reduction Reaction

The preactivation of reactants within the cavities of carbon nanotubular materials has remained largely unexplored due to the scarcity of materials with well-defined sizes and precisely engineered doping sites. Herein, we demonstrate that the catalytic activity toward the oxygen reduction reaction (ORR) is primarily governed by the cavity sizes of well-defined nanobelt materials with precisely doped <i>sp</i>²-nitrogen atoms. Our results show that the confinement effect induced by cavity size and the electron-rich chemical environment within the cavity are crucial for O₂ adsorption and preactivation, leading to enhanced catalytic activity. <b>Belt2</b>, with its medium-sized cavity (6.3 Å), exhibits superior ORR catalytic performance compared to <b>Belt1</b> with its narrower cavity and <b>Belt3</b>/<b>Belt4</b> with its larger cavities. Notably, <b>Belt2</b> achieves high half-wave and onset potentials of 0.84 and 0.97 V, respectively, along with an open-circuit voltage of 1.32 V and a peak power density of 181 mW cm^-2 in a zinc-air battery. This work not only provides a deeper understanding of the geometric factors influencing the ORR electrocatalysis of nanocarbon materials but also offers insights into the future design of nanocarbon electrocatalysts for enhancing catalytic efficiency. These findings may also be beneficial for other energy conversion and catalytic materials.