Key Takeaways & Executive Findings
- •• • The Co1-NNH3-C catalyst achieves 99% H2O2 selectivity at −3.5 mA cm−2 in 0.1 M H2SO4, outperforming most acidic 2e− ORR catalysts and enabling efficient on-site H2O2 generation under corrosive conditions. • • Pyridinic N, not Co single atoms, is identified as the direct active site via site-selective poisoning (SCN−/EDTA) and acetyl-group functionalization, which induced a 60% selectivity loss, confirming the metal's indirect role. • • DFT calculations show pyridinic N sites exhibit a near-optimal ΔG*OOH of 4.0 eV and an overpotential of only 0.20 V, providing a rational descriptor for designing high-performance carbon-based catalysts. • • The catalyst delivers a production rate of 907.5 mmol gcat−1 h−1 (or 2500 mg L−1 cm−2 in H-cell) with FE > 90%, demonstrating practical scalability for decentralized H2O2 electrosynthesis.
Abstract
Decoding the nature of catalytically active sites is an essential prerequisite for the rational design of catalysts for electrochemical H2O2 synthesis, but faces significant challenges, particularly for controversial cobalt single-atom catalysts (Co SACs). Herein, we report trace Co single-atom sites embedded within pyridinic N-rich carbon nanospheres (Co1-NNH3-C), synthesized via a self-assembly coupled surface-coating strategy. The Co1-NNH3-C catalyst demonstrates remarkable H2O2 selectivity (99%) and activity at current density of −3.5 mA cm−2 in 0.1 M H2SO4. Through a combined approach of molecular probe experiments, surface modification, and density functional theory (DFT) calculations, we disclose that pyridinic N, rather than Co single atoms, serves as the direct active site for 2e− oxygen reduction reaction (ORR). The trace Co (0.05 wt%) indirectly facilitated pyridinic N formation during pyrolysis but exhibits negligible direct catalytic involvement. DFT reveals pyridinic N sites optimize OOH intermediate adsorption (ΔG*OOH = 4.0 eV) and minimize reaction overpotential of 0.20 V, enabling scalable H2O2 production (907.5 mmol gcat−1 h−1). This work redefines the role of trace metal in SACs, providing a paradigm for designing metal-induced carbon catalysts for sustainable electrosynthesis for H2O2.
1. Introduction
Industrial H2O2 production relies on the energy-intensive anthraquinone process, which requires centralized facilities and poses safety risks during storage and transport. Electrochemical synthesis via the two-electron oxygen reduction reaction (2e− ORR) offers a decentralized, environmentally benign alternative, particularly in acidic media where H2O2 stability is enhanced and compatibility with proton exchange membrane (PEM) electrolyzers is achieved. However, the lack of efficient, selective, and cost-effective catalysts for acidic 2e− ORR has hindered commercial adoption. Noble metal-based catalysts (Pt, Pd) show high activity but suffer from prohibitive costs and scarcity, while non-noble metal single-atom catalysts (SACs) present controversial active site assignments, especially for cobalt-based systems.
This work addresses the bottleneck by synthesizing trace Co single-atom sites embedded in pyridinic N-rich carbon nanospheres (Co1-NNH3-C) via a self-assembly and surface-coating strategy. Through rigorous experimental and computational analyses, the study decodes the true active site, revealing that pyridinic N—not Co—directly governs 2e− ORR activity and selectivity. The trace Co (0.05 wt%) acts as a structural promoter, facilitating pyridinic N formation during pyrolysis. This metal-induced carbon catalysis paradigm provides a clear design principle for sustainable H2O2 electrosynthesis, overcoming the ambiguity that has plagued SAC research.
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Huijuan Yang, Yifan Li, Xiaoyu Yi, Lina Chen, Kang Qi, Guiqiang Cao, Wei Xiao, Chong Xie, Xifei Li (2026). Decoding the true active site in cobalt single-atom catalysts: pyridinic nitrogen-dominated electrosynthesis of hydrogen peroxide in acidic media. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3897-6
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Frequently Asked Questions
What is the evidence that pyridinic N, not Co, is the active site?
Site-selective poisoning experiments with SCN−/EDTA showed no loss in H2O2 selectivity, indicating Co is not directly involved. Acetyl-group functionalization, which selectively blocks pyridinic N, caused a 60% selectivity loss, directly implicating pyridinic N as the active center. DFT calculations further confirmed that pyridinic N sites have near-optimal ΔG*OOH (4.0 eV) and low overpotential (0.20 V).
How does the catalyst perform under industrially relevant conditions?
In 0.1 M H2SO4, the catalyst achieves 99% H2O2 selectivity at −3.5 mA cm−2, with a production rate of 907.5 mmol gcat−1 h−1 (or 2500 mg L−1 cm−2 in H-cell) and Faradaic efficiency >90%, surpassing many state-of-the-art acidic H2O2 electrocatalysts.
What is the role of trace Co (0.05 wt%) in the catalyst?
Trace Co does not participate directly in catalysis. Instead, it facilitates the formation of pyridinic N during pyrolysis, acting as a structural promoter. This is supported by the strong positive linear correlation between pyridinic N content and H2O2 selectivity, and the negligible catalytic contribution of Co confirmed by poisoning experiments.
What are the scalability bottlenecks for this catalyst?
The synthesis involves a self-assembly coupled surface-coating strategy, which may require precise control for scale-up. However, the use of trace Co (0.05 wt%) reduces cost, and the catalyst's high selectivity and activity in acidic media make it compatible with PEM electrolyzers, facilitating integration into existing electrochemical infrastructure.
How does the catalyst compare to noble metal-based catalysts in terms of cost and performance?
The catalyst uses trace Co (0.05 wt%) and carbon nanospheres, significantly reducing material costs compared to Pt or Pd. Performance-wise, it achieves 99% selectivity and a production rate of 907.5 mmol gcat−1 h−1, which is competitive with noble metal systems, while offering better sustainability and lower toxicity.
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