Small-scale and decentralized production of H₂O₂ via electrochemical reduction of oxygen is of great benefit, especially for sanitization, air and water purification, as well as for a variety of chemical processes. The development of low-cost and high-performance catalysts for this reaction remains a key challenge. Carbon-based materials have drawn substantial research efforts in recent years due to their advantageous properties, such as high chemical stability and high tunability in active sites and morphology. Deeper understanding of structure–activity relationships can guide the design of improved catalysts. We hypothesize that mass transport to active sites is of great importance, and herein we use carbon materials with unique flower-like superstructures to achieve high activity and selectivity for O₂ reduction to H₂O₂. The abundance of nitrogen active sites controlled by pyrolysis temperature resulted in high catalytic activity and selectivity for oxygen reduction reaction (ORR). The flower superstructure showed higher performance than the spherical nanoparticles due to greater accessibility to the active sites. Chemical activation improves the catalysts’ performances further, driving the production of H₂O₂ to a record-setting rate of 816 mmol·g_cat⁻¹·h⁻¹ using a bulk electrolysis setup. This work demonstrates the development of a highly active catalyst for the sustainable production of H₂O₂ through rational design and synthetic control. The understanding from this work provides further insight into the design of future carbon-based electrocatalysts.

The development of high-performance and low-cost oxygen reduction and evolution catalysts that can be easily integrated into existing devices is crucial for the wide deployment of energy storage systems that utilize O₂-H₂O chemistries, such as regenerative fuel cells and metal-air batteries. Herein, we report an NH₃-activated N-doped hierarchical carbon (NHC) catalyst synthesized via a scalable route, and demonstrate its device integration. The NHC catalyst exhibited good performance for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), as demonstrated by means of electrochemical studies and evaluation when integrated into the oxygen electrode of a regenerative fuel cell. The activities observed for both the ORR and the OER were comparable to those achieved by state-of-the-art Pt and Ir catalysts in alkaline environments. We have further identified the critical role of carbon defects as active sites for electrochemical activity through density functional theory calculations and high-resolution TEM visualization. This work highlights the potential of NHC to replace commercial precious metals in regenerative fuel cells and possibly metal-air batteries for cost-effective storage of intermittent renewable energy.