(618c) Delivering Clean Hydrogen Fuel from Ammonia Using Metal Membranes

The use of ammonia (NH₃) as a hydrogen vector can potentially enable renewable energy export from Australia to markets in Asia and Europe. With a higher hydrogen density than liquid H₂, plus existing production and transport infrastructure, and well-developed safety practices and standards, the financial and regulatory barriers to this industry are lower than for liquid H₂ transport. The only significant technical barrier which remains, however, is the efficient utilisation of ammonia fuel at or near the point of use, either directly or through the production of H₂.

For H₂ production from NH₃, the purity of the product H₂ is a prime consideration. As NH₃ can degrade the acidic polymer electrolyte in PEM fuel cells, the relevant purity standard for mobile PEM fuel cell applications (ISO14687-2) sets a maximum NH₃ concentration of just 0.1 ppmv. Furthermore, while the standard for stationary PEM fuel cells (14687-3) allows for up to 50% N₂, the mobile PEMFC standard allows for just 100 ppmv N₂, due to the significant energy penalty that N₂ introduces during compression. NH₃ cracking reactors must therefore couple catalytic ammonia decomposition with separation and purification of the H₂product.

Of currently available H₂ separation technologies, metal membranes show particular promise as they combine infinite H₂ selectivity (i.e., a 100% pure H₂ product, assuming a defect-free membrane), high temperature operation (comparable to that required for NH₃ decomposition) and tolerance to NH₃-containing feeds. CSIRO has recently commenced a project to demonstrate a pilot-scale ammonia cracking reactor which will integrate vanadium-based membranes with a cracking catalyst to produce high-purity H₂ directly from NH₃, at a rate of at least 5 kg H₂ per day. Partnerships with industrial gas producers and FCV developers will see this H₂product compressed, distributed and dispensed into FCVs to illustrate the product’s fitness for purpose.

Identification and validation of catalyst and membrane materials, manufacturing scale-up, system design and progress towards the goal of 5 kg H₂ per day will be discussed.