Hydrogen Molecule

Hydrogen is the simplest element known to us, with it’s atom containing just one proton and one electron. It is lighter than air but doesn’t exist alone – it is always found in combination with other elements. Many see hydrogen as the ultimate alternative fuel particularly in fuel cells, but it does have drawbacks, the main one being it’s purification. The current methods of purification are not very efficient or effective.

However, a Northwestern University chemist Mercouri G. Kanatzidis, together with postdoctoral research associate Gerasimos S. Armatas, have come up with a solution. They have developed new porous materials shaped like honeycomb which is very effective at separating the hydrogen from gas mixtures. Carbon dioxide and methane carry hydrogen gas in substantial amounts and this honeycombed shaped porous structure shows great selectivity in separating hydrogen from these two gases. The materials used in constructing the hydrogen purification structure are a new family of germanium-rich chalcogenides. “We are taking advantage of what we call ‘soft’ atoms, which form the membrane’s walls,” said Kanatzidis. “These soft-wall atoms like to interact with other soft molecules passing by, slowing them down as they pass through the membrane. Hydrogen, the smallest element, is a ‘hard’ molecule. It zips right through while softer molecules, like carbon dioxide and methane take more time.”

Why is this separation method better than current methods? Up till now scientists have been depending on the size of the gas molecules when separating hydrogen from carbon dioxide or methane. Firstly, they get hydrogen in combination with carbon dioxide and methane which involves more steps and is difficult to execute. Kanatzidis and Armatas method doesn’t depend on the size of the gas molecules for hydrogen separation. They use the process of polarization, making the interaction of gas molecules with the surface of the honeycombed like structure crucial. Kanatzidis and Armatas tested their membrane on a complex mixture of four gases, hydrogen, carbon monoxide, methane and carbon dioxide. As the smallest and hardest molecule, hydrogen showed the least affinity with the membrane, and carbon dioxide, as the softest molecule of the four, interacted the most.

Kanatzidis, Charles E. and Emma H. Morrison, Professor of Chemistry in the Weinberg College of Arts and Sciences, and the paper’s senior author, speaks out, “A more selective process means fewer cycles to produce pure hydrogen, increasing efficiency.” He further adds, “Our materials could be used very effectively as membranes for gas separation. We have demonstrated their superior performance.” Heavy elements such as germanium, lead and tellurium make the selection of hydrogen separation from carbon dioxide four times more effective.

According to Kanatzidis, another advantage of the process is “convenient temperature range.” which varies from zero degrees Celsius to room temperature!
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