Unlocking efficiency in oxygen reduction reaction: Synergistic edge dopants of nitrogen and boron in carbon nano onions

Abstract

Oxygen reduction reaction (ORR) is a crucial process for energy conversion and storage devices. Despite platinum (Pt) being the state-of-the-art material for ORR, the limited performance of Pt-based catalyst, Pt scarcity, and vulnerability of global supply chains for critical minerals, have made it imperative to develop alternative electrocatalysts that either contain no precious metals at all or require only a very low loading of these valuable resources. In this study, we demonstrate that the incorporation of co-dopants, nitrogen (N) and boron (B), with a dissimilar electronegativity is a promising approach to develop metal-free electrocatalysts for ORR. We discovered that the interaction between N and B plays a vital role in both (i) incorporating the dopants in high-curvature carbon nano-onions (CNOs) and (ii) promoting ORR performance. Tuning the annealing temperature was crucial to achieve a desirable N-B chemical configuration and synergistic effects of N and B on ORR catalysis. Our investigation revealed that N,B-doped CNOs prepared at 700 °C exhibit the best ORR performance in 0.1 M KOH with a dominant 4-electron pathway and excellent durability. Based on X-ray photoelectron spectroscopy (XPS), Raman analysis, and high-resolution scanning transmission electron microscopy (HR-STEM), we conclude that abundant N and B sites, especially N-C-B (isolated) sites, at the edges in conjunction with high surface activity of CNOs are responsible for such outstanding performances. This study provide insights into the design of metal-free catalysts for efficient ORR catalysis, and the importance of alternative electrocatalysts in the current global supply chain disrutipn scenario.