TAIPEI (Taiwan News) — A Taiwan-based team is accelerating its pace in the race to maximize the potential of hydrogen fuel, one of the amplest and cleanest energy sources.
Despite the high technological barrier, a world powered by hydrogen remains appealing to scientists. Hydrogen is the most abundant element in the universe and can be produced from water through electrolysis and photoelectrochemical splitting. Other methods include natural gas reforming and gasification of coals and biomass.
Although hydrogen can generate approximately 120 megajoules per kilogram of energy, three times more than gasoline, without carbon emissions as a byproduct, the storage of hydrogen poses a tremendous hindrance to its wider application. This is the lightest element on Earth and highly flammable.
How to safely store hydrogen gas for transportation and usage is the major challenge to overcome. Among the available methods of physical storage, compressed gas tanks and liquid hydrogen cylinders are the most common.
However, this method results in significant energy loss during the storage process. About 20 percent of hydrogen energy is lost during the gas compression; the loss amounts to 40 percent for liquefied hydrogen at the required -253 degrees Celsius.
NASA's enormous tank fuels liquid hydrogen to space shuttles (NASA photo)
The potential of hydrogen fuel is predicated on the success of minimizing energy loss while ensuring safety; this is where metal hydrides come into play. Metal hydrides are storage materials made of chemically-bounded hydrogen and alloys that require a series of physical and chemical processes to complete.
To begin with, hydrogen attaches to the surface of metal alloys, such as LaNi5 and TiFe, either as hydrogen molecules (H2) or hydrogen atoms (H) through Van der Waals forces. Then, as the pressure rises, the element penetrates the surface and diffuses into the solid lattice framework of the alloys to form metal hydrides at various temperature requirements.
When the pressure drops, the whole absorption process is reversed and causes the hydrogen to release again.
Process of metal alloy's hydrogenation
The truth is, establishing such a reversible system is not a walk in the park. Scientists must painstakingly modify the molecular structure and test different alloys and catalysts to discover high-capacity hydrides.
"Our lab is focused on improving the weight, volume, and cost of current hydrogen storage systems," said Veeramanikandan Rajagopal (Veera), a Ph.D. student at National Taiwan University of Science and Technology's Department of Mechanical Engineering. He was born in Tamil Nadu, India, and began his graduate study of metal hydrides in Taiwan four years ago.
He and his team are exploring suitable metal alloys and an optimized preparation process that allows fast storage and release of hydrogen within easily reachable temperatures.
"Our metal hydride system reaches the maximum hydrogen storage capacity of 7.0 weight percent (92.1%) and can release the entire hydrogen in less than 5 minutes," he explained.
The possibility of hydrogen fuel to relieve the incessant hunger for fossil fuels is an obvious selling point. Hydrogen fuel-cell vehicles have been one of the earliest adopted, and the opening of the first carbon-free hydrogen-powered steel plant in Sweden also proves a greener twist does exist for carbon-heavy industries.
1. Hydrogen stored in metal hydrides in powder form (Taiwan News photo)
2. Hyundai ix35 FCEV, hydrogen fuel-cell model (Flickr, TIMRAAB227 photo)
According to Veera, material-based hydrogen storage still has several obstacles to overcome, such as the high cost to build the storage system and its inadequate durability. Also, the time for the hydrogen to be refilled has not yet met the requirements for commercialization.
As countries around the world strive to fulfill their promises made in the Paris Agreement, whether scientists can fully leverage the energy stored in these minuscule materials will determine the likelihood of a carbon-neutral future.
Prof. Song-Jeng Huang and his team at NTUST focus on the development of hydrogen storage techniques.