A new cleaning method of hydrogen

Researchers from the USA have developed a new family of porous materials, structured like a honeycomb, which are highly effective in separating hydrogen from complex gas mixtures

US President Barack Obama's ambition for independence in the field of energy spurs the acceleration of research and development of alternative energy sources such as: solar energy, wind and geothermal energy, bio-fuels, hydrogen and biomass.

In the field of the hydrogen economy, one of the barriers to success is the hydrogen itself. The hydrogen must be purified before it is used as fuel for fuel cells, but current methods are not clean and efficient enough.

Two Northwestern University chemists, Mercouri G. Kanatzidis and Gerasimos S. Armatas, have developed a new family of porous, honeycomb-like materials that are highly effective at separating hydrogen from complex gas mixtures. The materials display the highest selectivity, to the best of the researchers' knowledge, in separating hydrogen from its interference with carbon dioxide and methane.

The findings, which present a completely new way of separating gases, were published in February in the scientific journal Nature Materials. The materials constitute a new family of germanium-rich chalcogenides (chalcogenides, elements of group 16 in the periodic table, or the oxygen group: oxygen, sulfur, selenium, tellurium, polonium and the artificial element ununhexium).

"A more selective process means fewer cycles to create pure hydrogen, while increasing efficiency," the researchers note. Our materials can be used as highly effective filters (membranes, membranes) for gas separation. We were able to demonstrate their improved performance."

In common methods for creating hydrogen in the first stage a mixture of hydrogen and carbon dioxide is obtained or such a mixture with the addition of methane gas. The technology used for the next step in the process - removing the hydrogen from these mixtures - separates the gas fractions according to their size, a step that is relatively difficult and complex.

The researchers offer a better solution. Their new materials do not base their separation on the size of the particles, but on their polarization - the interaction of the gas particles with the walls of the material during their passage through the membrane. This is the basis of this new separation method.

Examination of one material from this new family – a form composed of the heavy elements germanium, lead and tellurium – showed that the material is four times more selective in separating hydrogen from carbon dioxide than existing methods, which use lighter elements such as nitrogen, oxygen and carbon.

"We take advantage of what we call "soft" atoms that make up the membrane walls," explains the researcher. "These soft-walled atoms prefer to react with other "soft" particles that pass through them, while slowing down their movement during the passage through the membrane. Hydrogen, the smallest element that exists, is a "hard" particle. It simply moves quickly while softer particles, such as carbon dioxide -Oxygens and methane, linger on their way longer."

The researchers tested their membrane on a complex mixture of four different gases. Hydrogen passed first, followed by carbon monoxide, followed by methane and carbon dioxide. This is due to the fact that the smallest and hardest element, hydrogen, reacts the weakest rate with the membrane, while carbon dioxide, which is the softest element of the four gases, reacts the strongest. Another advantage of this process lies in the fact that the temperature range is extremely comfortable - between zero degrees Celsius and room temperature.

The pulsation of small particles through porous materials is a nanoscopic phenomenon - the researchers explain. All the holes in the honeycomb's hexagonal structure are regular and parallel, with each hole having a diameter of two or three nanometers. All gas particles are at least half a nanometer in size.

The original news from the university