Australasian Science: Australia's authority on science since 1938

Vanadium Research Recharged

By Stephen Luntz

US President Barack Obama has described Maria Skyllas-Kazacos’ research as “one of the coolest things I’ve ever said out loud”.

Vanadium redox batteries could be electricity’s ultimate storage mechanism. With the cost of electricity production from renewable energy falling rapidly, the obstacle to a fossil fuel-free future is the lack of appropriate storage solutions. Vanadium may be the answer.

If so, Em/Prof Maria Skyllas-Kazacos will be no overnight success. After undergraduate and postgraduate degrees at the University of NSW she did a postdoc at Bell Labs in the United States before returning to UNSW to work with solar energy pioneer Prof Martin Green.

In 1984 Green was interested in NASA’s work on redox flow batteries, where discharged electrolytes can be replaced with fully charged substitutes. However, NASA’s iron chromium electrolytes quickly became mixed, requiring reprocessing. Skyllas-Kazacos agreed that the solution would be to use an electrolyte with four oxidation states.

“A colleague was working on extraction of vanadium and pointed out it has lots of oxidation states,” recalls Skyllas-Kazacos. She wasn’t the first to consider vanadium for this role, but others had concluded that the reactions involved were not reversible, and the concentrations too dilute for practical application.

“I spent a year finding ways to make the reactions reversible,” Skyllas-Kazacos says. “Then I found a way to increase the concentration, proving the technology was viable.”

Her battery turns V5+ to V4+ on one side while V2+ ions turn to V3+ on the other. The transfer of electrons across a membrane during the process produces an electric current. The reactions are reversible with the application of external charge.

Nevertheless, the concentrations Skyllas-Kazacos had achieved were still far from ideal, the operating temperature range was narrow, and in those days the membranes available were poor.

The problems were such that Skyllas-Kazacos considered other metals with four oxidation states but found them difficult to keep in solution, particularly at the concentrations required, although she says molybdenum proved “almost viable”.

Having spent the 1980s working on the chemistry, Skyllas-Kazacos spent the 1990s focusing on membranes, finding impregnating resins that could prevent ions from entering the pores. “I stopped because others were bringing new membranes out, but the work I did has now been taken up in China,” she says. Much time also went into battery control.

By this point vanadium batteries were potentially viable for the storage of wind and solar energy. However, renewable energy companies were arguing that storage was unnecessary when their systems were grid-connected, so her work was neglected.

Vanadium batteries also hold potential for electric cars, but size and weight reductions are required. Skyllas-Kazacos kept working on this because vanadium-powered cars could be swiftly recharged by replacing used electrolyte with a fully charged substitute, as well as more slowly electrically.

Skyllas-Kazacos has produced lighter electrodes and is working on battery/fuel cell hybrids, but vanadium battery cars remain some way off.

Obama’s quote came when he was announcing funding for a program to provide storage for a small coal-fired power station in Ohio so it could produce a constant output rather than inefficiently raising and lowering production to match demand. While this shift will save hundreds of thousands of tonnes of carbon dioxide, vanadium’s future lies with renewables.

As solar and wind penetration into grids around the world has increased, governments have started to insist that renewable energy producers include storage in their system. Suddenly vanadium is in vogue.

Recently US researchers announced that mixing hydrochloric acid into the electrolyte can increase vanadium batteries’ storage capacity by 70% while greatly expanding the operating temperature range. Skyllas-Kazacos remains cautious, but points out that large-scale battery production has started both in China and Europe without this development. She is hopeful prices will fall as current labour-intensive production methods give way to automated construction.

Although her battery work continues, Skyllas-Kazacos’ major research today is in finding less carbon-intense ways to smelt aluminium, including finding inert anodes capable of surviving the enormous temperatures, high voltages and aggressive electrolytes used in one of the world’s largest sources of carbon emissions. She says she is “making some really good progress in this area” while also seeking low temperature molten aluminium salts and advanced methods of fault detection.

Considering this, the world is rather lucky that Skyllas-Kazacos chose science, since at school she had no particular interest in the field. “I loved maths, but I loved drama and English and French, and I wanted to do something creative,” she says. “My father said, ‘There are a lot of poor artists,’ so I thought I would have art as a hobby. However, I have discovered that science is also very creative.