Hierarchical Nitrogen-Doped Carbon: A Bifunctional Catalyst for Oxygen Reduction and Evolution Reactions

This study presents the synthesis and characterization of hierarchical nitrogen-doped carbon (HCN-900), demonstrating remarkable electrocatalytic performance for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), outperforming traditional catalysts like RuO₂ and Pt/C. HCN-900 exhibits an onset potential of 0.98 V and a half-wave potential of 0.85 V for ORR, closely matching Pt/C performance while achieving an electron transfer number of 4.0, indicative of a four-electron pathway. For OER, HCN-900 achieves a current density of 10 mA cm⁻ 2 at an overpotential of 223 mV, significantly lower than RuO₂ (288 mV) and Pt/C (363 mV). The material also shows a Tafel slope of 87 mV dec⁻¹, indicating rapid kinetics and efficient electron transfer. This impressive performance is attributed to the optimized structural and electronic properties of HCN-900, including its high surface area, hierarchical porosity, and nitrogen doping, which enhance active site density and promote electron transport. Furthermore, HCN-900 retains approximately 96.72% of its initial performance after 10 h of continuous operation, demonstrating excellent long-term stability. The comprehensive analysis highlights HCN-900 as a promising bifunctional catalyst for advanced energy applications, providing a cost-effective and sustainable alternative to conventional catalysts. Its superior electrocatalytic properties make HCN-900 an excellent candidate for integration into next-generation energy conversion and storage systems.