The Center for Nanoparticle Research at the Institute for Basic Science (IBS) has developed a cutting-edge photocatalyst platform capable of producing hydrogen with world-class efficiency. This platform can efficiently produce hydrogen from various sources, including seawater, lakes, rivers, and even solutions derived from liquefied plastic bottle waste. To understand this research, it's important to first understand some key concepts.

Conventional Hydrogen Production

The world's interest in hydrogen energy is growing rapidly, with some experts predicting that hydrogen will become a crucial energy source in the future. To make hydrogen energy practical, we need processes and facilities that can produce hydrogen efficiently and in an environmentally friendly manner. However, the conventional method of hydrogen production, such as natural gas steam reforming, has significant drawbacks. It consumes a lot of energy and emits a substantial amount of the greenhouse gas carbon dioxide (CO2).

What is Green Hydrogen?

Hydrogen can be classified as brown, gray, blue, or green, depending on how it's produced. Green hydrogen is produced using renewable energy sources and is known for its eco-friendly characteristics because it generates minimal greenhouse gas emissions during its production process. Achieving the widespread use of green hydrogen is crucial for realizing a hydrogen-based society.

Photocatalyst-Based Green Hydrogen Production

Photocatalysts are materials that can initiate chemical reactions using light energy. Using photocatalysts for hydrogen production is an attractive option because it allows us to harness solar energy directly without greenhouse gas emissions. A photocatalyst absorbs solar energy and uses it to generate hydrogen (H2) from water (H2O). Despite many efforts to enhance photocatalysts' performance, they have not been widely adopted yet because of some practical challenges. To be effective, photocatalyst powder needs to be manufactured into panel form, and separate devices are usually required to transport hydrogen from the water, all of which reduce the efficiency and economics of hydrogen production.

[Figure 1] Cu/TiO2 catalyst and its nanostructure.

[Figure 2] Production process of Pt/TiO2 catalyst.

Floating Photocatalyst Platform

In response to these challenges, we have designed a new photocatalyst platform that floats on the surface of water. This platform features a two-layer structure: the upper layer contains the photocatalyst which is exposed to air, and the lower layer serves as a support structure that absorbs and delivers water efficiently. This eliminates the need for separate equipment to collect the hydrogen from the water. The photocatalyst layer is exposed to air above the water, it can receive maximum amount of light for capture.

[Figure 3] Porous rubber-hydrogel composite was used to achieve high surface tension, which allows the structure to float on water. The catalyst is stably fixed within the composite. Thanks to the properties of the hydrogel, water can be continuously delivered to the photocatalyst.

Instead of using panel-shaped photocatalysts, this system employs a gas-filled solid (aerogel nano-composite) form of photocatalyst, which reduces the density of the catalyst. This allows for easy integration of various photocatalysts, including high-performance platinum (Pt) catalysts and cost-effective copper (Cu)- based catalysts. Furthermore, a highly porous structure made of rubber-hydrogel composite was used to ensure the platform remains afloat while also providing excellent water absorption and efficient delivery of water to the photocatalyst.

This platform operates on the water's surface, minimizing the reverse reaction that converts hydrogen back into water. Since the catalyst is not underwater, It maximizes the use of solar energy without loss of light due to absorption or refraction. There need for energy-intensive mechanical mixing (stirring) and it's easy to manufacture, making it an efficient and economical solution for hydrogen production.

Large-Scale Testing for Practical Use

The researchers tested the performance of this platform for solar hydrogen production. It was found that a 1 m2 area panel could produce about 4 liters of hydrogen per hour (conversion rate), which is considered among the highest in the world. Moreover, during long-term operation of over two weeks in natural seawater conditions with a mixture of various microorganisms and suspended particles, the platform was able to maintain high production efficiency with minimal performance degradation.

[Figure 4] Large area hydrogen production experiment and the results.

This groundbreaking research significantly improves the efficiency and economy of hydrogen production, addressing one of the major hurdles to the practical use of photocatalyst technology. It opens up the possibility of hydrogen production from various water sources, including seawater, lakes, rivers, and even solutions of liquefied recycled plastic bottles. The researchers’ efforts culminated in a novel floating photocatalyst platform with world-class hydrogen production capabilities.

(This research was published online in "Nature Nanotechnology" on April 28th at 0:00 Korean time.)