Blowing bubbles with plasma creates better material for hydrogen production
A new production technique for nanostructured electrodes offers the possibility of large scale energy storage without using rare materials.
A metal with a foam-like, fuzzy surface on the nanoscale can produce hydrogen from water, using the energy of sunlight. This way, sustainable energy is stored in the form of solar fuel. One bottleneck in this scheme was proper control over the properties of the nanofuzz. In the journal Applied Materials & Interfaces, Dutch researchers describe how they can precisely control the growth of a fuzzy nanostructure by using a plasma (hot, charged gas) to blow bubbles on a metal surface.
Solar fuels: storing and transporting sustainable energy
To deliver sustainable energy when and where it's needed, scientists propose to store the energy from for instance the sun in so-called solar fuels. One of the techniques in this new research field is producing hydrogen from water. Here, researchers are looking for earth-abundant and chemically stable materials to replace conventional solar cell materials (which are unstable in water), and the rare electrode material platinum that still sets the reference for electrolysis of water.
Porous nanostructures of metal oxides are a promising route. A metal oxide with a surface covered in nanoscale fuzz can capture sunlight and convert it into electrical charge, which then splits water into hydrogen and oxygen via electrolysis.
Blowing bubbles in metal
The research team lead by Greg De Temmerman (FOM institute DIFFER) and Roel van de Krol (TU Delft and Helmholtz-Zentrum Berlin) includes researchers from their institutes and from the University of California in San Diego. In their publication they describe how they can grow the desired fuzzy metal nanostructure by exposing the metal to plasma. Controlled oxidation of the metal nanofuzz then produces the desired metal oxide.
The team used the plasma experiments at DIFFER in their research. These were designed to investigate how wall materials of future fusion reactors will perform, but their uniquely high plasma density and temperature also makes them suitable to structure material surfaces on the nanoscale.
"Our plasma technique grows the nanostructure by creating bubbles in the bulk metal and we can precisely tailor the structure size via the temperature of the material and the processing time - two simple control knobs. What's new here is that we've realised far better control over how we create such a structure", explains De Temmerman.
The performance of the nanofuzz is measured in the form of the photocurrent, the current generated when the material is exposed to light. De Temmerman: "With only modest optimization, we're already producing a photocurrent half as big as the best technology available today".
Eye on large scale applications
The nanofuzz research is currently working with pieces of tungsten as large as a Euro coin, but the physicists are already thinking ahead to large scale applications of their technique. To store and transport sustainable energy in the form of fuel on a global scale, the production technique needs to ultimately avoid rare metals such as tungsten. The challenge is to achieve the same level of control as realised in tungsten and grow a nanostructure that optimally uses incoming sunlight to produce fuels.
"We're currently doing follow-up research with iron", says De Temmerman. The challenge is to control the nanostructure in iron in such a way that it efficiently captures the incoming sunlight, transforms that energy into electrical charges, and transports those to the reaction sites where water is split to produce hydrogen."
Reference
Efficient Plasma-Route to Nanostructure Materials: Case Study on m-WO3 for Solar Water Splitting
DOI: 10.1021/am401936q
Contact information
Dr. Greg De Temmerman, +31 (0)30 609 69 44
Prof.dr.ir. Richard van de Sanden, +31 (0)30 609 69 14