Semiconductor nanocrystals help produce hydrogen fuel

Photosynthesis is the process of converting solar radiation into green energy to produce sugar, which cellular respiration converts into ATP by the plants, bacteria and some protistans green using green chlorophyll pigment using water and releasing oxygen.
Artificial photosynthesis
Artificial photosynthesis systems exploiting light-absorbing molecules or chromophores, typically made of organic dyes, to photo chemically split water into hydrogen and oxygen by half-reactions with reduction and oxidation process. But the light-absorbing dyes are damaged due to Sun's rays and the process is inefficient and unstable.
Researchers at the University of Rochester, USA have generated hydrogen using nanocrystals, sunlight and a cheap nickel catalyst which can continuously produce fuel without slowing down.
Nanocrystals have fewer defects due to their limited size . nanocrystals have very little interior volume and are virtually all surface and the inner impurities can easily migrate the short distance to the surface and be ejected by doping. Doping is the addition of impurities containing electrons to enable electric conductance in a controlled way. The physical properties of these crystals are determined by the interface between the core and the shell.
On the nanoscale doping could lead to an assortment of technologies, including solar cells, light-emitting diodes, lasers or displays, electroluminescent devices and electronic devices.
The system
Artificial photochemical hydrogen-generating system contains cadmium selenide quantum dots, nickel salt catalysts and ascorbic acid. The system when working with water has a quantum efficiency of 36% for every 100 photons absorbed and produces 36 hydrogen molecules. For a solution of a mix of water and ethanol the efficiency increases to 66%. The ascorbic acid acts as an electron donor, gets used up and regularly needs to be replenished during each hydrogen production cycle.
The researchers explain that CdSe quantum dots absorb two photons of light and transfer two electrons to the Ni-catalyst allowing it to take up two protons to produce hydrogen by forming the necessary catalyst locally from the quantum dot ligands. The catalyst-nanocrystal pairs are better than other artificial photosynthesis nanoparticle systems because they are more stable to sunlight.
The finding could be very important for green-energy applications and also for certain industrial processes like those for producing ammonia in the Haber process.


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