According to the company, the results of this development could be used to increase energy-storage capacity through artificial photosynthesis. This development could also hold the promise of becoming a fundamental technology relating to energy and the environment, thus contributing to a more sustainable future with solutions to the problems of global warming and natural resource depletion.
To artificially produce storable energy in the form of hydrogen and organic compounds, reaction electrons need to be extracted from a photocatalyst material using the energy in sunlight, and at the electrode, efficiently reacting with water or CO2. In the past, semiconductor materials and relatively coarse-grained photocatalyst materials have been used in low-density rigid structures for the photoreactive electrodes where sunlight and water react. However, as the usable wavelengths of light in sunlight (visible light) fall in a narrow range, it has been difficult to achieve a sufficient current flow from the chemical reaction.
Fujitsu Laboratories has improved on methods for forming thin films of electroceramics on flexible mounting sheets to create capacitors and other passive elements. It has also developed a process technology for layering thin films on a substrate using a nozzle to spray the raw-material photocatalyst-material particle that fragments the particle on a thin plate. Analyses of the internal structure of the material were performed jointly with the Crystal Interface Laboratory at the University of Tokyo.
Key features of the technology are as follows. After creating a film of the raw-material photocatalyst-material particle, it is formed into a crystalline structure having deviation at the molecular level. This broadens the spectrum of sunlight that can be absorbed from a maximum wavelength of 490 nm using existing technology to 630 nm with this technology, more than doubling the usable sunlight that is captured.
The film has a good crystalline structure lacking in macro- or micro-level flaws, and a precisely formed structure with excellent electrical conductivity between the particles in the material. This enables electrons that are electrically excited by photons in sunlight to be efficiently transmitted to the electrodes.
The film's surface structure increases the surface area that can react with water, and is formed into a systematically structured crystalline surface that boosts electron density throughout the material's crystal structure. This effectively promotes much greater interaction between water and sunlight.
Compared to using photocatalyst material as-is, this technology more than doubles the usable amount of light that can be gathered from sunlight, and increases by more than a factor of 50 the surface area of the material that can react with water. Taken together, these advances have been confirmed to increase efficiency in producing electricity and oxygen by more than a factor of 100.
Fujitsu Laboratories is continuing to work on further advances in photocatalyst materials and process technology to improve the characteristics of photoreactive electrodes. It is also working on developing technologies for the dark-reaction part (CO2-reducing reactions) and the overall system, with the goal of implementing artificial photosynthesis.