Previously, producing hydrogen on a large scale was costly due to the
temperatures exceeding 2,500 degrees C in order to separate water
molecules. But releasing hydrogen by extracting oxygen from water can also
be accomplished using pure zinc, which calls for lower temperatures of 350
degrees C, thereby lowering costs. But heat and electricity, which are
required to extract zinc, considered both an abundant and a natural choice
for producing hydrogen, from zinc oxide, have traditionally been powered
by fossil fuels.
The solar solution to achieve the high temperatures (around 1750 degrees
C) required for the production of zinc from zinc oxide came in 2004, when
the European Union and the Swiss Federal Office of Science and Education
funded research to explore using a 45 kW solar furnace in Villigen,
Switzerland, a 75kW solar simulator in Zurich and a vary large solar
research facility with 1 MW output at the Weitzman Institute in Israel.
A mixture of zinc oxide and small amounts of coal is placed inside the
solar furnace atop the solar tower. Solar light is reflected by a large
array of heliostats (computer guided highly reflective mirrors) to a
hyperbolic mirror located inside the tower, producing highly concentrated
heat inside the solar furnace. At more than 1200 degrees C the zinc oxide
breaks down into zinc and oxygen, which in turn recombines with the carbon
to create CO as a minor byproduct. The zinc is then cooled down to create
a fine powder that can be safely handled and transported.
It is a simpler process to produce hydrogen from the zinc powder: the zinc
is mixed with water at 350 degrees C. The oxygen inside the water
recombines with the zinc to produce zinc oxide once again and the
byproduct is pure hydrogen.
The Weitzman team found that by adding small amounts of carbon in the form
of coal it further reduced the zinc production to a more manageable
temperature. In the future, the team sees the possibility of replacing the
coal completely with biomass.
This entire process is said to have advantages over existing ways of
producing hydrogen, not the least of which is that it is clean and, when
biomass replaces coal as an additive to the zinc oxide mix, the entire
process is potentially nonpolluting. It is also thought that this new
method based on the production of zinc may open the door for a
hydrogen-based economy. Could the future call for filling up our
hydrogen-running cars with zinc powder?
