Tiny 3D materials may make fuel cells more efficient

Researchers have developed a technique for creating nanoscale materials with unique chemical and physical properties that they say could eventually make hydrogen fuel cells cheaper and more sustainable.

Scientists from UNSW Sydney have demonstrated the technique for creating the tiny 3D materials, the study published in Science Advances.

Researchers from the School of Chemistry at UNSW Science show it’s possible to sequentially ‘grow’ interconnected hierarchical structures in 3D at the nanoscale which have chemical and physical properties to support energy conversion reactions.

There needs to be 10 millimetres of the 3D materials in once centimetre. If you were to count one million tiny segments in just one of those millimetres, each of those would be one nanometre or nm.

“To date, scientists have been able to assemble hierarchical-type structures on the micrometre or molecular scale,” says study senior author and UNSW Electron Microscope Unit director professor Richard Tilley.

“But to get the level of precision needed to assemble on the nanoscale, we needed to develop an entirely new bottom-up methodology.”

The researchers used chemical synthesis which constructs complex chemical compounds from simpler ones. They were able to carefully grow hexagonal crystal–structured nickel branches on cubic crystal–structured cores to create 3D hierarchical structures with dimensions of around 10-20 nanometres.

The resulting interconnected 3D nanostructure has a high surface area, high conductivity due to the direct connection of a metallic core and branches, and has surfaces that can be chemically modified. These properties make it an ideal electrocatalyst support – a substance that helps speed up the rate of reactions – in the oxygen evolution reaction, a crucial process in energy conversion.

The nanostructure’s properties were examined using electrochemical analysis from electron microscopes provided by the Electron Microscope Unit.

“Growing the material step-by-step is a contrast to what we do assembling structures at the micrometre level, which is starting with bulk material and etching it down,” says study lead author Dr Lucy Gloag, a postdoctoral fellow at the UNSW Science School of Chemistry.

“This new method allows us to have excellent control over the conditions, which lets us keep all of the components ultra-small – on the nanoscale – where the unique catalytic properties exist.”

In conventional catalysts, which are often spherical, most atoms are stuck in the middle of the sphere with very few atoms on the surface, meaning most of the material is wasted as it can’t take part in the reaction environment.

These new 3D nanostructures are engineered to expose more atoms to the reaction environment, which can facilitate more efficient and effective catalysis for energy conversion, Tilley explains.

“If this is used in a fuel cell or battery, having a higher surface area for the catalyst means the reaction will be more efficient when converting hydrogen into electricity.”

As less of the material needs to be used for the reaction, costs are expected to drop, making energy production more sustainable.

In the next research stage, the scientists aim to modify the surface of the material with platinum, which is a superior catalytic metal though more expensive. About a sixth of the cost of a hydrogen-powered EV is the platinum powering the fuel cell.