Artificial photosynthesis gets closer to viability

Article By : Vivek Nanda

A thin-film process can increase artificial photosynthesis efficiency in producing electricity and oxygen by over a factor of 100.

To artificially produce storable energy in the form of hydrogen and organic compounds requires extracting reaction electrons from a photocatalyst material using the energy in sunlight and, at the electrode, efficiently reacting with water or CO₂. 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 usable wavelengths of visible light (sunlight) fall in a narrow range, it has been difficult to achieve a sufficient current flow from the chemical reaction.

A technology development by Fujitsu Laboratories is set to change that. The company has improved methods for forming thin films (nanoparticle deposition) of electroceramics on flexible mounting sheets to create capacitors and other passive elements. It has developed a thin-film layering process that uses a nozzle to spray the photocatalyst-material particle that fragments particles on a thin plate.

What's so special about that?

Here's what research by Fujitsu Labs together with the Crystal Interface Laboratory at the University of Tokyo has found with their process development:

1. It expands the usable wavelengths of sunlight
   After creating a film of the photocatalyst-material particle, it is formed into a crystalline structure having deviation at the molecular level. That broadens the spectrum of sunlight that can be absorbed from the limit of 490nm to 630nm; a 2x increase in captured sunlight.

 

Figure 1: The thin film absorbs up to 630nm, double the sunlight that is captured.
 
 

2. It offers high electrical conductivity
   The film's crystalline structure lacks macro- and micro-level flaws and is precisely formed, resulting in high electrical conductivity between the particles in the material. This enables electrons electrically excited by photons in sunlight to be efficiently transmitted to the electrodes.

 

Figure 2: The film's crystalline structure allows electrically excited photons to be transmitted to the electrodes.
 
 

3. It offers a large surface area to react with water
   The film's structure increases its surface area and is formed into a systematically structured crystalline surface that boosts electron density throughout the material's crystal structure. This promotes greater interaction between water and sunlight.

 

Figure 3: The film's surface structure allows greater interaction between water and sunlight.
 

Together, these features have been confirmed to increase the efficiency in producing electricity and oxygen by over a factor of 100.