Microscopic vibrations and various sounds that are everywhere around us, plus water, can serve as a source of hydrogen – an excellent fuel. Huifang Xu and his colleagues from the University of Wisconsin such an unusual device and incidentally discovered a new effect at the same time.
The basis of Xu’s converter is a mass of elongated zinc oxide and barium titanate (BaTiO3) nanocrystals. When they are acted on by high-frequency vibration, even a weak one, the rods start to oscillate and at the same time charge separation is generated on their bending surfaces.
This piezoelectric effect has been known for a century; however, as the discoverers themselves explain, hardly anyone has made a detailed study of how it works when the crystals are immersed in solutions. Meanwhile, the interaction of the nanocrystals and water gives rise to a piezoelectrochemical (PZEC) effect.
The electrons and holes created by the rods convert the nanocrystals into a catalysts for water decomposition. The vibrating rods turn out to be an intermediary that is not consumed itself (measurements have confirmed this). The experimenters discovered that decreasing the crystal dimensions substantially increases the efficiency factor of the process (it has reached18%). This is not only because of the enormous surface area, but also because thinner rods bend more easily and create more separated charges.
Reaction scheme on the surface of the rods (illustration ACS, Hong et al.)
Xu and his colleagues believe that a large number of such wafers placed on transport means, plant facilities or clothing could produce a small amount of free hydrogen for filling fuel cells in small devices (palm-sized units) or for other equipment.
