Professor Richard Haverkamp and Dr Aaron Marshall are chemical engineers at Massey University, Palmerston North. They have created nanoparticles and catalysts that will help fuel the future. To understand their work, you’ll need to know a little about hydrogen fuel cells and catalysts.
Hydrogen fuel cells
Hydrogen could replace the burning of carbon-based fuels such as gas and oil, which create pollutants that include carbon dioxide.
Hydrogen fuel cells combine the gases hydrogen and oxygen to create electricity. Oxygen is got from air, but the hydrogen needs to be more pure. At the moment, the main sources of hydrogen are oil or natural gas, which are non-renewable resources. There is another source of hydrogen that is much more environmentally friendly – water.
When an electric current is passed through water, the hydrogen and oxygen from which it is made are split apart and can be collected. This process is called electrolysis.
So, you use electricity to get hydrogen from water, then combine hydrogen and oxygen to make electricity and water. That sounds like a waste of energy, so why bother?
The electricity used to get hydrogen from water can be from renewable sources, such as solar or wind power. The hydrogen becomes a mobile source of energy. This makes it suitable for fuel cells, which can be used to power portable equipment when electricity is hard to get, such as in remote places. For example, fuel cells powered the electrical systems of NASA’s space shuttle. Water is produced as a waste product of fuel cells, and this is easily recycled – in the case of the space shuttle, the crew used the waste water from fuel cells for drinking.
Speeding up the reaction – electrocatalysts
Electrocatalysts make the electrolysis of water much more efficient, so more energy ends up as hydrogen. One of the problems with the electrolysis of water is that, without chemical help, a lot of energy is wasted. This is where electrocatalysts come in. An electrocatalyst is a substance that speeds up a chemical reaction that uses or makes electricity.
Aaron Marshall and Richard Haverkamp have been very successful in developing electrocatalysts that greatly reduce the power needed to release hydrogen from water. They have engineered nanoparticles with a shape and composition that makes them very efficient electrocatalysts. In fact, with an efficiency of 76%, their electrocatalysts are world leaders.
The best catalysts are chemically active, last a long time and have a structure with a large surface area that allows lots of atoms to take part in the reaction. Making or improving a catalyst is a chemical balancing act of these aspects.
Nature of science
Many of the scientists working in nanotechnology today had never heard of the subject when they were at school – it is too new – so most scientists have come to nanotechnology from other topics, such as chemistry, physics, engineering, biology, medicine and mathematics. Things have changed, and now you can study nanotechnology at University.
For example, nanoparticles of the metal ruthenium make a very active catalyst, but they are not very stable and do not have a large surface area. Aaron has been adding other metals to ruthenium, in the search to find an electrocatalyst that is active, has a stable structure and a high surface area. Aaron has achieved his best results using a mixture of iridium, ruthenium and tantalum, which are all transition metals on the periodic table.
A new approach to nanoparticle structure
When a number of atoms group together to form a ball-shaped nanoparticle, only the atoms on the outside are available to take part as catalysts in chemical reactions. Atoms on the inside of the particle are in effect wasted, and with material such as ruthenium and iridium, this can be a very expensive waste.
Aaron and Richard are experimenting with structures called core-shell particles. These have a core of cheap, non-reactive material (such as tin oxide), surrounded by a thin shell of very reactive electrocatalyst. Most of the catalyst atoms are available for reaction, making these nanoparticles very efficient. And efficiency is everything!
Useful link
An article about hydrogen and fuel cells.
