Thin membrane plugs big hole in the hydrogen economy
Some see hydrogen as the energy medium of the future, but getting it from the producer to the consumer is one of the biggest problems in creating a hydrogen economy. To help bridge this gap, Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) is developing a metallic membrane that helps convert ammonia into high-purity hydrogen for fuel-cell powered vehicles.
Hydrogen has many positives as an energy medium. It's the most abundant element in the universe, it burns clean, it's non-toxic, and it's excellent for use in fuel cells. However, it does have a number of very large disadvantages. One of the biggest is that hydrogen molecules are so small and light that the gas is very difficult to transport and store.
Among other things, a hydrogen economy would require a whole new pipeline infrastructure because hydrogen embrittles the steel used in natural gas pipelines and requires high pressure. In addition, hydrogen is a low energy density medium, so to be economical, it requires very special storage systems. This usually means storing the gas under high pressures of 350 to 700 bar (5,000 to 10,000 psi), as a cryogenic liquid cooled to −252.8° C (−423° F), absorbed into solids like metal hydrides, or a combination of these.
Another alternative is to store the hydrogen chemically. By combining hydrogen with nitrogen to produce ammonia (NH3), many of the problems are solved. Ammonia can be stored at room temperature, it's already widely transported, which is useful for countries like Australia with ambitions to become hydrogen exporters, and it can be easily converted back into hydrogen by passing it over a catalyst to release hydrogen and nitrogen gas.
The tricky bit is to recover enough of the hydrogen in a pure form to be economical. CSIRO's approach is to use a membrane reactor technology incorporated into a modular unit that can be installed at the point of delivery, including a fuel-cell car refueling station.
The membrane is designed to allow the smaller hydrogen molecules through while blocking the larger nitrogen molecules. This way, by passing a pressurized stream of a hydrogen/ammonia mix past the membrane, the output is purified hydrogen.
The CSIRO is confident that this technology has the potential to create an Australian hydrogen export industry that could rival liquid natural gas.