Sunlight and Catalyst Generate Cheap Hydrogen

Nanoptek of Maynard, Massachusetts, has developed a new way to make hydrogen from water using solar energy, reports Technology Review 2008. The company says that its process is inexpensive enough to compete with the cheapest approaches used currently, which strip hydrogen from natural gas, and it has the advantage of releasing no carbon dioxide. Its technology can be located closer to customers than large-scale natural-gas processes, which could significantly reduce transportation costs.

Developing the technology with grants from NASA and the Department of Energy, Nanoptek raised venture-capital of $4.7 million to install its pilot plant. The technology uses titania, an inexpensive and abundant material, to capture energy from sunlight. The absorbed energy releases electrons, which split water to make hydrogen.

The company's approach uses insights from the semiconductor industry to make titania absorb more sunlight. John Guerra, the company's founder and CEO, says that chip makers have long known that straining a material so that its atoms are slightly pressed together or pulled apart alters the material's electronic properties. He found that depositing a coating of titania on dome-like nanostructures caused the atoms to be pulled apart. "When you pull the atoms apart, less energy is required to knock the electrons out of orbit," he says. "That means you can use light with lower energy -- which means visible light rather than just ultraviolet light."

The strain on the atoms also affects the way that electrons move through the material. Too much strain, and the electrons tend to be reabsorbed by the material before they split water. Guerra says that the company has had to find a balance between absorbing more sunlight and allowing the electrons to move freely out of the material.

Nanoptek has also developed cheaper ways to manufacture the nanostructured materials. Initially, the company used DVD manufacturing processes, but has moved to a less expensive proprietary process.

'One-pot' Process Makes More Efficient Materials

Cornell researchers have developed a "one-pot" process to create porous films of crystalline metal oxides that could lead to more efficient fuel cells.

In the CASH (combined assembly by soft and hard chemistries) process, a polymer forms itself into ordered rows of cylinders surrounded by a metal oxide. Heating in the absence of oxygen turns the polymer into a hard carbon framework that holds its shape while the metal oxide is heated to a higher temperature to make it form uniform crystals. Finally, heating in air burns off the carbon to leave a porous material.

In a fuel cell, a material with nanoscale pores offers more surface area over which a fuel can interact with a catalyst. Previously such porous materials have been made on hard templates of carbon or silica, or by using soft polymers that self-assemble into a foamy structure. Making a hard porous template and getting the metal oxides to distribute evenly through it is tedious. The polymer approach is easier and makes a good structure, but the metal oxides must be heated to high temperatures to fully crystallize, causing the polymer pores to collapse.

The Cornell researchers have combined what Ulrich Wiesner, Cornell professor of materials science and engineering, calls "the best of the two approaches," using a soft block copolymer called poly(isoprene-block- ethylene oxide) or PI-b-PEO that carbonizes when heated to high temperatures in an inert gas, providing a hard framework around which the metal oxide crystallizes. Subsequent heating in air burns away the carbon.

The researchers created porous films of titanium oxide, used in solar cells, and niobium oxide, a potential fuel-cell catalyst support. Chemicals that will react to form the metal oxides and a solution of PI-b-PEO are combined. As the reaction proceeds, the PI portion of the copolymer forms cylinders 20 nanometers across surrounded by metal oxides, and subsequent heat treatments leave uniform, highly crystalline metal oxide with cylindrical pores. The pores are neatly ordered in hexagonal patterns, creating a larger surface area than if the pores were randomly distributed. "When the pores are ordered, you can get more of them into the same space," Wiesner explains.

The resulting materials were examined by electron microscopy, X-ray diffraction and a variety of other techniques, all of which confirmed a highly crystalline structure and a uniform porosity, the researchers reported. The next step, Wiesner says, is to apply the CASH process to the creation of porous metals.

Lightweight Solid Storage of Hydrogen

A lightweight method of storing hydrogen in solid form for use in fuel-cell propulsion systems has been developed at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France.

ESRF says 1kg (2.2lb) of lithium borohydride (LiBH4) will contain about 185g of hydrogen and the compound has a density of 678kg/m' (42lb/ft'), which is lighter than water, kerosene and diesel at 998, 810 and 800kg/m', respectively.

Only half as much hydrogen is needed to deliver the same power output as hydrocarbon fuel, but in its normal gaseous state it requires double the volume of kerosene. About 3.23m' of LiBH4 would deliver the same amount of energy as 1m' of kerosene.

"Among the many materials competing for hydrogen this is probably the lightest. Lithium, boron and hydrogen -- these are the lightest elements you can find," says ESRF director of beamline research Vladimir Dmitriev.

With LiBH4 the hydrogen is released when the compound is heated to around 300ºC. But the researchers have created new forms of the compound that could release hydrogen at a lower temperature. This required pressures of up to 200,000bar, but they expect to be able to produce this more unstable version at the atmospheric pressures used to mass-produce chemical pellets.

Fuel Cell Technology Without Platinum Developed

Japan's Daihatsu Motor Co. has developed technology for a new type of basic fuel cell jointly with the National Institute of Advanced Industrial Science and Technology. The new cell does not use platinum and emits no CO2. It uses a safer and more stable fuel of hydrazine hydrate.

The new technology uses an alkaline electrolyte membrane, which allows the use of cobalt and nickel series metals, which are less expensive than platinum, as electrocatalysts. It also employs cheaper materials for such components as separators.

By using highly reactive hydrazine hydrate as fuel and a newly-developed electrolyte, the cells achieved a power output of 0.5W/cm2, equivalent to the output of fuel cells that use platinum. As hydrazine hydrate can take the form of a liquid, it is easy to handle when recharging.

Daihatsu Motor has developed a process in which hydrazine hydrate is solidified by binding with a polymer in the fuel tank to minimize the impacts on human health and the environment from the possibility of fuel spilling from a tank damaged in a crash or other accident. The solid is turned into the right amount of liquid at the right time while the fuel cell is generating power. The company is planning further development to improve the performance of the polymer, increase the capacity and durability of the fuel cell, and build relevant infrastructure.