Triphase Photocatalytic Water Splitting Revolutionises Hydrogen Production

In recent years, photocatalytic water splitting has emerged as a promising approach for converting solar energy into storable hydrogen fuel, demonstrating significant potential for applications in environmental remediation and energy conversion. However, current research in photocatalytic technology predominantly focuses on material design, overlooking the optimisation of photocatalytic reaction systems.

In response to this, researchers have developed a novel immobilised photothermal-photocatalytic integrated system.

“Specifically, conventional photocatalytic water splitting typically involves uniformly dispersing photocatalysts in the liquid phase, forming a solid-liquid-gas triphase reaction system,” explained Professor Maochang Liu, who led the research.

“This triphase system inherently suffers from low solar energy utilisation efficiency and slow mass transfer processes.”

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What Is Photocatalytic Water Splitting And How Does It Work?

Photocatalytic water splitting is a process that utilises light energy to split water (H₂O) into hydrogen (H₂) and oxygen (O₂), providing a clean method for producing hydrogen.

This reaction relies on a photocatalyst, typically a semiconductor material such as titanium dioxide (TiO₂), which absorbs light – usually sunlight – and generates excited electrons and holes.

When the photocatalyst absorbs photons with energy equal to or greater than its band gap, electrons are promoted from the valence band to the conduction band, leaving behind positive holes. These charge carriers then drive redox reactions: the excited electrons reduce protons (H⁺) to form hydrogen gas, while the holes oxidise water molecules to release oxygen.

Efficient water splitting requires careful design of the photocatalyst to ensure good light absorption, charge separation, and surface reaction activity.

Although promising, challenges such as low efficiency, catalyst stability, and limited light absorption still need to be addressed for large-scale applications.

Enhancing Photocatalytic Efficiency With Full-Spectrum Responsiveness

Typically, conventional photocatalytic reactions primarily rely on ultraviolet and visible light spectra, failing to effectively use near-infrared light, which constitutes over 50% of the solar spectrum.

“The development of novel reaction systems with full-spectrum responsiveness has emerged as a critical breakthrough for enhancing photocatalytic efficiency,” said Liu.

Now, the researchers have successfully developed an immobilised photothermal-photocatalytic water splitting system.

This innovative system combines a photothermal substrate with high-performance photocatalysts, enabling a synergistic process of liquid water evaporation and steam-phase water splitting for hydrogen production under light illumination without requiring additional energy input.

Demonstrating Remarkable Hydrogen Production Rates

A CdS/CoFe₂O₄ (CCF) p-n heterojunction photocatalyst is fabricated by the calcination method, which facilitates consistent spatial transmission and efficient separation of photogenerated carriers.

The construction of the system involved utilising annealed melamine sponge (AMS) as a photothermal substrate, transforming the solid-liquid-gas tri-phase system into a more efficient gas-solid bi-phase configuration.

The optimised CCF/AMS photocatalytic water splitting system demonstrates a remarkable hydrogen evolution rate of 254.1 µmol h–1, representing a significant leap forward compared to the traditional triphase system.

Practical Uses For The Water Splitting System

The system, through innovative material design and reaction system construction, provides crucial insights and practical guidance for enhancing the efficiency of photocatalytic water splitting.

Liu concluded: “This gas-solid biphase system can enhance solar energy utilisation efficiency, elevate the overall reaction temperature, and reduce gas transport resistance at the catalytic interface, thereby significantly improving the efficiency of photocatalytic water splitting.”

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