Alternative Energy

This feeling is making inroads into many hearts and minds that we need clean and green fuel. Hydrogen is the simplest element known to us. Its atom contains just one proton. It is also lighter than air and doesn’t exist alone on this planet. It is always found in combination with other elements. People see hydrogen as an alternative fuel but it has its own drawbacks. One of the biggest hurdles in hydrogen fuel is its purification. It can act as fuel for fuel cells but present methods of purification are not so efficient and effective.

But a Northwestern University chemist Mercouri G. Kanatzidis, together with postdoctoral research associate Gerasimos S. Armatas, has come with a solution. They have developed new porous materials shaped like honeycomb. And we think only poets have imagination! This porous honeycombed like structure is very effective at separating hydrogen from gas mixtures. Carbon dioxide and methane carry hydrogen gas in substantial amount. And this honeycombed shaped porous structure shows best selectivity in separating hydrogen from these two gases. The materials used in constructing 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 this separation method can be better than current methods? Till now scientists are depending on the size of the gas molecules while separating hydrogen from carbon dioxide or methane. First they get hydrogen in combination with carbon dioxide and methane. This method involves more steps and is difficult to execute. Kanatzidis and Armatas have a better idea. They don’t depend on the size of the gas molecules for hydrogen separation. They take help of polarization. Here interaction of gas molecules with the surface of the honeycombed like structure is crucial. Kanatzidis and Armatas tested their membrane on a complex mixture of four gases. They had chosen four gases for their experiment. They were hydrogen, carbon monoxide, methane and carbon dioxide. As the smallest and hardest molecule, hydrogen showed 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!