Wax and microwaves could unlock storage roadblock to hydrogen economy

Riversimple's Rasa hydrogen fuel cell car
Riversimple’s Rasa car incorporates a hydrogen fuel cell

The biggest obstacle to developing hydrogen powered vehicles – whether the hydrogen is burned as a conventional fuel or used in a fuel cell to generate electricity – is the lack of a method for storing hydrogen.

The hazardous nature of the gas, with its light weight, tendency to escape, and flammability means that pressurised containers are impractical, and despite much research lightweight and safe materials that can absorb hydrogen in the quantities necessary to power a vehicle have not yet been found.

Now, however, a team from Oxford University believes that it may have found just such a material. Working with researchers in Cambridge and Cardiff in the UK, and with colleagues at the King Abdulaziz City for Science and Technology (KACST) in Saudi Arabia, the team has discovered that hydrocarbon wax rapidly releases large amounts of hydrogen when activated with metal catalysts and microwaves.

Hydrocarbon waxes are derived from crude oil, or can be made in high purity as the end result of a gas-to-liquids process.

The Oxford team theorised that it should be possible to convert up to 14 per cent of the weight of a heavy hydrocarbon wax into hydrogen. The challenge, it explains in a paper in the Nature journal Scientific Reports, was to find a way to dehydrogenate a wax effectively and rapidly, reducing unwanted byproducts.

The team settled on a method using the transition metal ruthenium as a catalyst, with the metal in a nanoparticle form on a carbon support, mixed with paraffin wax. When this substance was placed in a microwave cavity and irradiated, the wax released about seven per cent of its weight as hydrogen.

“Our discovery – that hydrogen can be easily and instantly extracted from wax, a benign material that can be manufactured from sustainable processes – is a major step forward,” said one of the paper’s co-authors, Dr Tiancun Xiao, a senior research fellow at Oxford University. “Wax will not catch fire or contaminate the environment. It is also safe for drivers and passengers.”

“This discovery of a safe, efficient hydrogen storage and production material can open the door to the large-scale application of fuel cells in vehicles,” added fellow co-author Prof Peter Edwards, who leads the KACST-Oxford Petrochemical Research Centre (KOPRC), a KACST Centre of Excellence in Petrochemicals at Oxford University. “Instead of burning fossil fuels, leading to CO2, we use them to generate hydrogen, which with fuel cells produces electric power and pure water. This is the future – transportation without CO2 and hot air.”