Highly efficient hydrogen gas production using sunlight, water and hematite

Highly efficient hydrogen gas production using sunlight, water and hematite

Researchers from Kobe University’s Molecular Photoscience Research Center in Japan have succeeded in developing a strategy that greatly increases the amount of hydrogen produced from sunlight and water using hematite photocatalysts.

Hydrogen has received attention as a possible next generation energy solution, and it can be produced from sunlight and water using photocatalysts.

In order to make this practicable, it is necessary to develop foundation technologies to optimise the potential of the photocatalysts, in addition to finding new materials for catalysts.

This time, the research group led by Associate Professor Tachikawa Takashi successfully produced a photoanode with an extremely high conductivity.

This was achieved solely by annealing hematite mesocrystals, superstructures consisting of tiny nanoparticles of approx. 5nm, to a transparent electrode substrate.

Hematite can absorb a wide range of visible light and is safe, stable, and inexpensive. With this photoanode, the electrons and holes produced by the light source separated quickly and, at the same time, a large number of holes densely accumulated on the surface of the particles.

The accumulation of holes improved the efficiency of the water oxidation reaction; the slow oxidation of the water has previously been a bottleneck in water-splitting.

In addition to boosting the high efficiency of what is thought to be the world’s highest performing photoanode, this strategy will also be applied to artificial photosynthesis and solar water-splitting technologies via collaborations between the university and industries.

Main points

  • Numerous oxygen vacancies were formed inside the hematite mesocrystals by accumulating and sintering tiny highly-orientated nanoparticles of less than 10 nanometers.
  • The presence of oxygen vacancies improved the conductivity of the photocatalyst electrode, at the same time giving it a significant surface potential gradient, thereby promoting the separation of electrons and holes.
  • At the same time a large amount of holes moved to the surface of the particles, allowing a high rate of oxygen evolution from water. This enabled the researchers to achieve the world’s highest solar water-splitting performance for hematite anodes.
  • This strategy can be applied to a wide range of photocatalysts, beginning with solar water-splitting.

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