Energy of the future, green hydrogen is produced from renewable energies. But its use for fuel cells requires a very high level of purity. Several research institutes have developed revolutionary new membranes.
Membrane separation makes it possible to achieve a degree of purity greater than 99.9%, essential for operating fuel cells. Simple in theory, this solution offers the advantage of being energy efficient. But this process faces two significant problems: low permeability to hydrogen, swelling due to water.
The membrane, made of polymer, ceramic, metal or liquid, serves as a separator. The hydrogen diffuses there. Japanese researchers at the Nagoya Institute of Technology have developed an organic and inorganic membrane formed from polycarbosilane polymer (PCS) deposited on a layer of permeable aluminum oxide.
Professor Yuji Iwamoto said: “Using a high molecular mass PCS with a melting point above 200 oC, we showed that a superhydrophobic PCS membrane can be deposited on a multilayer, mesoporous y-Al2O3 modified tubular support. /macroporous a‑AI2O3. With this technological development, we expect great progress in sustainable, environmentally friendly hydrogen production. »
This membrane system was tested by photoelectrochemical separation (PEC) and obtained good results, especially for the superhydrophobic PCS membrane.
The conclusions of the tests carried out with this new membrane were published in the journal Separation and Purification Technology.
A new generation separation and purification membrane
In December 2021, Singaporean start-up DiviGas announced a fundraising of $3.6 million for the construction of the first plant to manufacture polymer separation membranes to recover and purify hydrogen.
DiviGas has indicated that each year, $110 billion of hydrogen gas is produced in refineries, chemical and fertilizer plants. However, 15% ($16 billion) of this production is lost due to the flaring technique. DiviGas has therefore developed a membrane to recycle gaseous hydrogen. For a refinery, this means three to six million dollars in profits per year and a return on investment of two to three million dollars.
Divi‑H is, in the words of André Lorenceau, CEO of DiviGas, a revolutionary membrane. A filter to recycle unrecoverable hydrogen burned in factory flares has been installed. Furthermore, the membrane is very resistant to high temperatures and acids, up to 150oC. The membrane is made of new generation polymer fibers. Each tube includes 300 kilometers of polymeric hollow fibers. The gas is thus pushed into these fibers and the pressure produces the molecular separation of the hydrogen. Pure hydrogen comes out at a pressure lower than the starting pressure, which separates it from other gases.
But DiviGas is working on another product: a membrane to purify CO2. The aim is to capture emissions from coal and gas power plants, cement plants and steel mills. This membrane will be used to capture CO2 and storing it, two very expensive sectors in terms of financial and energy costs.
The “ultimate” purification membrane?
Innovation in the hydrogen sector is actually all-round. A research team led by Chris Arges of Pennsylvania State University reported last March that they had found a new way to purify hydrogen using new membranes.
This system converts carbon monoxide into carbon dioxide which itself undergoes an absorption process to isolate the hydrogen. The purified hydrogen is then pressurized using a compressor, either for immediate use or for storage.
According to Chris Arges, the key is to use very high temperatures, but also a polymer electrolyte membrane (MEP), therefore a proton exchanger, capable of separating hydrogen from carbon dioxide and carbon monoxide very quickly and without additional cost. The MEP-equipped electrochemical pump is much more efficient than conventional methods, as it simultaneously separates and compresses hydrogen from the gas mixture. This pump can operate at very high temperatures, around 200 to 250oC, which is 20 to 70°C hotter than other MEP pumps. This improves the separation of hydrogen from other gases.
Chris Arges, says: “This is an effective and potentially inexpensive way to purify hydrogen, especially when there are large quantities of carbon monoxide. No one has achieved this level of purity, especially with a gas supply that contains more than 3% carbon monoxide and using an electrochemical hydrogen pump. »
In the pump, the positively charged electrode breaks the hydrogen into two protons and two electrons. The protons pass through the membrane while the electrons navigate through the pump connected to a wire connected to the positively charged electrode. After crossing the membrane towards the negatively charged electrode, the protons recombine with the electrons to reform hydrogen. The MEP allows the passage of protons, but prevents molecules of carbon monoxide, carbon dioxide, methane and nitrogen from passing through it.
Chris Arges’ team is also working on a fuel cell equipped with a high-temperature polymer electrolyte membrane for heavy vehicles such as cruise ships, trucks and airplanes. “It is difficult to electrify this type of vehicle with conventional batteries, because they are too heavy and the recharge time is too long. However, hydrogen vehicles equipped with fuel cells generate no emissions and do not need to be recharged,” underlined Chris Arges.
