(Nanowerk Spotlight) A transparent leaf bends toward sunlight, its surface gleaming as it splits water into hydrogen and oxygen fuel. This isn’t a natural plant—it’s an artificial photosynthesis device that moves and adapts like living foliage, marking a shift in how we might harness solar energy for fuel production.
The challenge of capturing sunlight efficiently has persisted since the earliest experiments with artificial photosynthesis in 1912, when Italian chemist Giacomo Ciamician first proposed using solar energy to drive chemical reactions (Science, “The Photochemistry of the Future”).
While significant advances emerged, notably Fujishima and Honda’s 1972 demonstration of semiconductor-based water splitting (Nature, “Electrochemical Photolysis of Water at a Semiconductor Electrode”) and Nocera’s 2012 development of the first silicon-based artificial leaf (Accounts of Chemical Research, “The Artificial Leaf”), these systems remained static, their effectiveness diminishing whenever sunlight struck them at an angle. Traditional solar tracking systems attempt to solve this through motors and computers, but these add complexity, cost, and their own energy demands.
Meanwhile, aquatic plants mastered the art of solar tracking through elegant biological mechanisms. Species like Micranthemum glomeratum sense light direction and adjust their leaves accordingly, maintaining optimal energy capture as the sun moves. Their cells protect delicate photosynthetic machinery while allowing efficient gas and water exchange, all coordinated through flexible supporting structures that enable precise movement.
Now, researchers from multiple Chinese universities have created an artificial leaf that mimics these natural adaptations. Their device combines flexible solar-powered electrodes with a protective gel coating and a novel supporting structure made from carbon nanotubes embedded in a temperature-sensitive polymer. When sunlight hits the support, the nanotubes heat up locally, causing the polymer to contract on the illuminated side while remaining expanded on the shaded side. This creates a bending motion that automatically aligns the artificial leaf toward light sources.
Schematic illustration of the designed phototropic artificial aquatic plant for complete water splitting. a) Structure of the natural and biomimetic system. In natural plants, the cytoplasm within plant cells protects the chloroplasts, while the petiole provides structural support to the leaves and facilitates their bending. In the biomimetic design, a hydrogel protection layer mimics the cytoplasm, safeguarding the photoelectrode. The photoanode and photocathode enable artificial photosynthesis. Additionally, a light-responsive hydrogel petiole is engineered to mimic phototropism, providing directional bending and support to the artificial leaves. b) Phototropic behavior of the natural and biomimetic system. c) Bias-free artificial photosynthesis for complete water splitting. This diagram illustrates the roles of the photoanode and photocathode in facilitating water splitting under light irradiation. (Image: reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
The results, reported in Advanced Functional Materials (“Nature Inspired Phototropic Artificial Photosynthesis”), show dramatic improvements over conventional rigid systems. At a 45-degree light angle, the adaptive device maintains 47% higher water-splitting efficiency than fixed alternatives. When light strikes from extreme 90-degree angles—conditions that typically cripple solar devices—the tracking system produces 866% more hydrogen and oxygen fuel.
To achieve this, the researchers developed new fabrication techniques for depositing photoactive materials on lightweight plastic instead of glass. They engineered a transparent hydrogel coating that protects the sensitive components, mimicking the role of cytoplasm in plant cells, while allowing efficient water access and gas release. The photoanode – which splits water into oxygen, protons, and electrons – retains 73% of its activity after 65 hours of continuous operation when protected by this coating, while the photocathode retains 32% of its initial activity over the same period.
The device’s self-powered tracking ability eliminates the need for external motors or controls. Its lightweight construction and water compatibility suit it for aqueous environments where traditional solar panels or artificial leaves would fail. The researchers demonstrated stable hydrogen and oxygen production through complete water splitting, with the products evolving separately at the device’s two electrodes.
Several challenges remain before practical implementation. The responsive support structure shows some performance decline over multiple tracking cycles, with an increasing response time. The team notes that real-world conditions involving wind and water currents could affect the device’s movement and efficiency. However, the core innovation – creating a flexible artificial photosynthesis system that autonomously tracks light sources – demonstrates how mimicking nature’s solutions can overcome persistent technical barriers.
The work advances the field of artificial photosynthesis by addressing the fundamental problem of angular dependence in solar energy capture. By incorporating movement and adaptiveness into the basic design rather than adding external tracking systems, it points toward simpler, more efficient approaches to solar fuel production.
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