Key Takeaways & Executive Findings
- •• • The hybrid system of alkalized and Cu-doped g-C3N4 with Chlorella achieved a 3.7-fold increase in hydrogen production compared to bare Chlorella, demonstrating the efficacy of extracellular electron supply. • • Hydrothermal alkalization and copper ion doping of g-C3N4 expanded its light absorption range and enhanced photoresponse, optimizing the electronic structure for improved electron transfer. • • The g-C3N4 serves as an extracellular electron source independent of PSII, providing an alternative electron pathway to hydrogenase, which is critical under nutrient stress conditions where PSII activity is inhibited. • • This cell nanofunctionalization strategy offers a feasible route to enhance biological hydrogen production efficiency by regulating non-living components, with potential for scalable application in renewable energy.
Abstract
Hydrogen production by photosynthetic green algae is an efficient biological process that utilizes light energy to convert water and carbon dioxide into clean and renewable energy. In this paper, we constructed a hybrid system combining graphitic carbon nitride (g-C3N4) and Chlorella pyrenoidosa (Chlorella), in which g-C3N4 serves as an extracellular electron source and Chlorella acts as a biological reactor for specific hydrogen production. In particular, the electronic structure of carbon nitride was optimized by means of hydrothermal alkalization and copper ion doping, expanded the light absorption range and enhanced the light response ability. g-C3N4, as an extracellular electron source, can provide electrons for Chlorella to improve hydrogen production performance which is 3.7 times that of bare Chlorella. The construction of a biological hybrid system is a feasible optimization strategy for the hybrid system to promote the synergistic effect of the hybrid system by regulating the properties of non-living components.
1. Introduction
Photosynthetic green algae are among nature's most efficient solar energy converters, yet their hydrogen production is limited by the oxygen sensitivity of hydrogenase and the dependence on PSII electron supply. Nutrient stress methods like sulfur deprivation inhibit PSII to reduce oxygen, but this also restricts electron availability, capping hydrogen yields. Existing approaches to supply exogenous electrons, such as gold nanoparticles or conductive polymers, have shown promise but face challenges in scalability and integration.
This study addresses the bottleneck by employing graphitic carbon nitride (g-C3N4), a low-toxicity, chemically stable semiconductor, as an extracellular electron source. Through hydrothermal alkalization and copper doping, the material's light absorption and electron transfer are enhanced, enabling efficient electron delivery to Chlorella cells. This hybrid system bypasses PSII limitations, achieving a 3.7-fold improvement in hydrogen production, offering a practical strategy for sustainable biohydrogen generation.
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Ming Yi, Tong-Kai Zhang, Hong-Lian Dai, Wen Zhang, Zi-Qian Yi, Yao Huang, Heng Zhou, Yi Lu, Si-Ming Wu, Ling Shen, Jie Ying, Wei Geng, Xiao-Yu Yang (2026). Nanofunctionalized Chlorella cells with photo stimulation for biological hydrogen production. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3654-5
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Frequently Asked Questions
What is the mechanism by which g-C3N4 provides electrons to Chlorella, and how does copper doping enhance this process?
g-C3N4 acts as a photosensitizer, absorbing light and generating photoelectrons. Copper doping introduces mid-gap states that extend light absorption into the visible range and improve charge separation, increasing the availability of electrons for transfer to the algal cells. These electrons are then utilized by hydrogenase to reduce protons to hydrogen.
How does the hybrid system perform under prolonged illumination or repeated cycles?
The paper does not specify long-term stability or cycling data. However, the chemical stability of g-C3N4 and the biocompatibility of the system suggest potential for sustained operation, but further studies are needed to assess photodegradation and cellular viability over extended periods.
What are the scalability prospects for this biohybrid system in industrial hydrogen production?
The 3.7-fold enhancement in hydrogen production is promising, but industrial scalability depends on factors such as the cost of g-C3N4 synthesis, reactor design for light distribution, and maintaining optimal conditions for algal growth and hydrogenase activity. The study does not provide economic analysis, but the use of earth-abundant materials and simple modification steps may offer cost advantages.
What is the role of hydrothermal alkalization in modifying g-C3N4, and how does it affect the material's properties?
Hydrothermal alkalization introduces nitrogen vacancies and surface functional groups, which can enhance light absorption and electron transfer. This treatment, combined with copper doping, optimizes the electronic structure, as evidenced by the expanded light absorption range and improved photoresponse, leading to higher electron supply to Chlorella.
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