Environmental Engineering Reference
In-Depth Information
(+ terminal) and oxygen at the anode (- terminal). Steam electrolysis adds
heat to the process and this heat provides some of the energy needed to
split water and makes the process more energy efficient. When hydrogen
is generated from renewable sources, its production and use becomes part
of a clean, natural cycle.
Thermochemical water splitting uses chemicals and heat in sev-
eral steps to split water into hydrogen and oxygen. Photolysis is a pho-
toelectrochemical process that uses sunlight and catalysts to split water.
Biological and photobiological water splitting use sunlight and biological
organisms. Thermal water splitting uses a high temperature of 1000°C.
Biomass gasification uses microbes to break down different biomass feed-
stocks into hydrogen.
Some of the first life forms on Earth were photosynthetic algae that
existed about 4 billion years ago. Hydrogenase is an enzyme that can be
used in extracting hydrogen from carbon. Chlorophyll uses sunlight to ex-
tract hydrogen from water. In the future, developments in Microbiology,
Molecular Biology and Nanotechnology are expected to allow biological
hydrogen production systems to be fully realized.
Cost is one hurdle that is keeping hydrogen from being more widely
as a fuel. Many changes in the energy infrastructure are needed to use hy-
Electricity is required for many hydrogen production methods and
the cost of this electricity tends to make hydrogen more expensive than
the fuels it would replace.
Another matter is hydrogen's flammability since it can ignite in low
concentrations and can leak through seals. Leaks in transport and stor-
age equipment could present public safety hazards. Gasoline transport
and storage presents similar public safety hazards. Older gasoline stor-
age tanks at filling stations have leaked and contaminated groundwa-
ter at many locations. A leaking pipeline contaminated the soil under a
California coastal town and required demolition and rebuilding of the
town in order to replace the soil.
Hydrogen can be stored and transported as a compressed gas, a
cryogenic liquid or in solids. Liquid hydrogen is closer to gasoline in the
areas of volume and vehicular weight. In commercial aircraft, the takeoff
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