Post on 20-Jan-2017
An experimental approach to splitting water might lead to a relatively cheap and clean method for largescale hydrogen production that doesn’t require fossil fuels. The process splits water into hydrogen and oxygen using heat and catalysts made from inexpensive materials. Heatdriven water splitting is an alternative to electrolysis, which is expensive and requires large amounts of electricity. The new approach, developed by Caltech chemicalengineering professor Mark Davis, avoids the key problems with previous heatdriven methods of water splitting. It works at relatively low temperatures and doesn’t produce any toxic or corrosive intermediate products. Almost all the hydrogen used now in industrial processes, such as making gasoline, comes from reforming natural gas. If automakers start selling large numbers of hydrogenfuelcell vehicles, as they’ve said they plan to do eventually, the hydrogen for those is also likely to come from natural gas unless processes like the one at Caltech are commercialized. The basic approach in hightemperature water splitting is to heat up an oxidized metal to drive off oxygen, then add water. In Davis’s case, the starting material is manganese oxide, and the reactions are facilitated by shuttling sodium ions in and out of it. “Without the sodium, the temperatures would go up well over 1,000 °C,” Davis says. With it, the reactions work at temperatures of 850 °C or lower. The technology is probably far from being commercialized. It still requires pretty high temperatures—a couple of hundred degrees higher, for example, than those used to drive steam turbines at coal and nuclear power plants. Producing those temperatures without fossil fuels would probably involve one of two technologies, neither of which is being used commercially right now: hightemperature nuclear reactors or highconcentration solar thermal facilities that use rings of mirrors to concentrate sunlight more intensely than occurs today in solar thermal power plants. The Caltech approach would also need to be tested to make sure the watersplitting cycle can run repeatedly. So far, the researchers have shown that the same materials can be reused five times, but “if you were going to have one of these things work for real, you’d need to run it for thousands of cycles,” Davis says. He says such testing is beyond the scope of his lab. “We feel good about the potential for many cycles on this one, but until you do it, you don’t know,” he says. “All we did here is prove the chemistry could work.” The rate of hydrogen production would also need to be increased—for example, by switching to materials with a higher surface area. And Davis hopes to lower the temperatures needed still further. The goal is to use this process or a similar one to make use of waste heat at steel mills and power plants. “This is a good start, but the lower we go, the better,” he says. Hydrogen Energy
NASA uses hydrogen fuel to launch the space shuttles. Credit: NASA
Hydrogen is the simplest element. An atom of hydrogen consists of only one proton
and one electron. It's also the most plentiful element in the universe. Despite its
simplicity and abundance, hydrogen doesn't occur naturally as a gas on the Earth
it's always combined with other elements. Water, for example, is a combination of
hydrogen and oxygen (H2O).
Hydrogen is also found in many organic compounds, notably the hydrocarbons that
make up many of our fuels, such as gasoline, natural gas, methanol, and propane.
Hydrogen can be separated from hydrocarbons through the application of heat a
process known as reforming. Currently, most hydrogen is made this way from natural
gas. An electrical current can also be used to separate water into its components of
oxygen and hydrogen. This process is known as electrolysis. Some algae and
bacteria, using sunlight as their energy source, even give off hydrogen under certain
conditions.
Hydrogen is high in energy, yet an engine that burns pure hydrogen produces almost
no pollution. NASA has used liquid hydrogen since the 1970s to propel the space
shuttle and other rockets into orbit. Hydrogen fuel cells power the shuttle's electrical
systems, producing a clean byproduct pure water, which the crew drinks.
A fuel cell combines hydrogen and oxygen to produce electricity, heat, and water.
Fuel cells are often compared to batteries. Both convert the energy produced by a
chemical reaction into usable electric power. However, the fuel cell will produce
electricity as long as fuel (hydrogen) is supplied, never losing its charge.
Fuel cells are a promising technology for use as a source of heat and electricity for
buildings, and as an electrical power source for electric motors propelling vehicles.
Fuel cells operate best on pure hydrogen. But fuels like natural gas, methanol, or
even gasoline can be reformed to produce the hydrogen required for fuel cells. Some
fuel cells even can be fueled directly with methanol, without using a reformer.
In the future, hydrogen could also join electricity as an important energy carrier. An
energy carrier moves and delivers energy in a usable form to consumers.
Renewable energy sources, like the sun and wind, can't produce energy all the time.
But they could, for example, produce electric energy and hydrogen, which can be
stored until it's needed. Hydrogen can also be transported (like electricity) to
locations where it is needed.
http://www.nrel.gov/hydrogen/proj_production_delivery.html By , Sanjay kumar patnaik . Vujjasetu