Key Takeaways & Executive Findings
- •• • Achieved a photocatalytic H2O2 production rate of 2.399 mmol g−1 h−1 under visible-light irradiation, a 12-fold enhancement over pristine g-C3N4, demonstrating the potential for scalable solar-driven H2O2 synthesis. • • H2O2 selectivity reached 87.4%, indicating that the Zn/VN-CN catalyst effectively suppresses the competing 4-electron ORR pathway, which is critical for industrial adoption where product purity is paramount. • • Nitrogen vacancy engineering downshifts the d-band center of Zn sites, moderating O2 adsorption strength and lowering the activation energy barrier for *H2O2 formation, as confirmed by combined experimental and theoretical studies. • • The Zn-N3 sites serve as highly active reaction centers, with nitrogen vacancies increasing charge density, thereby enhancing charge separation and photocatalytic efficiency, a key factor for practical solar-to-chemical conversion.
Abstract
Photocatalytic oxygen reduction reaction (ORR) for hydrogen peroxide (H2O2) production via the two-electron pathway offers an environmentally friendly oxidant and a clean fuel. However, challenges exist in optimal oxygen (O2) adsorption capacities and maintaining O–O bond during O2 activation. Herein, we present a zinc single-atom catalyst (Zn/VN-CN) incorporating nitrogen vacancies (VN), designed to modulate the electronic structure of the photocatalyst, leading to optimized O2 adsorption energy and a remarkable enhancement in H2O2 yield. Benefiting from the synergistic effect between nitrogen vacancies and Zn single atoms, the optimized Zn/VN-CN catalyst exhibits a photocatalytic H2O2 production rate of 2.399 mmol g−1 h−1 under visible-light irradiation, representing a 12-fold enhancement compared to pristine g-C3N4 (CN), along with a high H2O2 selectivity of 87.4%. Combined experimental and theoretical studies indicate that the Zn-N3 sites act as highly active reaction centers, while nitrogen vacancies increase the charge density and downshift the d-band center of the Zn sites, thereby moderating O2 adsorption strength, lowering the activation energy barrier for the formation of *H2O2, and further converting it to H2O2. This work proposes an effective strategy for tuning O2 adsorption behavior to achieve highly selective and active photocatalytic H2O2 production.
1. Introduction
Hydrogen peroxide (H2O2) is a versatile green oxidant with applications in chemical synthesis, environmental remediation, and medical disinfection, and it serves as a sustainable energy carrier. However, the dominant anthraquinone oxidation process is energy-intensive and generates organic byproducts, raising environmental concerns. Photocatalytic two-electron oxygen reduction (2e− ORR) using solar energy offers a sustainable, cost-effective alternative. Graphitic carbon nitride (g-C3N4) is a promising photocatalyst due to its favorable band structure and stability, yet it suffers from rapid charge recombination and poor selectivity under visible light, limiting its efficiency.
To overcome these bottlenecks, strategic modification of g-C3N4 is essential to introduce highly active and selective sites for the 2e− ORR pathway. This work presents a zinc single-atom catalyst with nitrogen vacancies (Zn/VN-CN) that modulates the electronic structure to optimize O2 adsorption and enhance H2O2 production. The synergistic effect between nitrogen vacancies and Zn single atoms results in a 12-fold increase in H2O2 yield and high selectivity, addressing the critical challenges of adsorption strength and O–O bond preservation during O2 activation.
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Xiaoyan Zhong, Donghai Wu, Tianwen Liu, Shiyu Li, Yiwen Chen, Ruiyu Liu, Meihuan Liu, Shixun Lian, Hui Su (2026). N-vacancy engineering Zn single-atom site boosts efficient photosynthesis of hydrogen peroxide. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3950-x
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Frequently Asked Questions
What is the long-term stability of the Zn/VN-CN catalyst under continuous visible-light irradiation?
The paper does not provide explicit long-term stability data, but the catalyst demonstrates a high H2O2 production rate of 2.399 mmol g−1 h−1 and 87.4% selectivity. For industrial application, stability over hundreds of hours is required; further cycling tests are necessary to assess deactivation due to potential Zn leaching or structural degradation.
How does the performance of Zn/VN-CN compare to other state-of-the-art photocatalysts for H2O2 production in terms of quantum efficiency?
The paper reports a production rate of 2.399 mmol g−1 h−1 under visible light, which is a 12-fold improvement over pristine g-C3N4. However, apparent quantum efficiency (AQE) is not provided. For benchmarking, AQE at specific wavelengths is essential; future studies should report AQE to enable direct comparison with other catalysts.
What is the scalability potential of the synthesis method for Zn/VN-CN?
The synthesis involves nitrogen vacancy engineering and Zn single-atom incorporation, which typically require precise control and may be challenging to scale. The paper does not discuss scale-up, but the use of earth-abundant Zn and g-C3N4 suggests potential for cost-effective production if the synthesis can be adapted to large-scale methods.
What are the main deactivation mechanisms for Zn/VN-CN under operational conditions?
Potential deactivation mechanisms include photodegradation of the carbon nitride structure, poisoning of active sites by intermediates, and Zn agglomeration. The paper does not provide post-reaction characterization, so further studies are needed to identify and mitigate these issues.
How does the catalyst perform in real water matrices or with impurities that might affect O2 reduction?
The experiments were likely conducted in pure water with dissolved O2. Real water contains organic matter and ions that could compete for active sites or scavenge reactive species. Testing in simulated environmental conditions is necessary to evaluate practical applicability.
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