Nanotechnology to soup up fuel cells

SCIENTISTS have developed nanofibre electrodes which can boost the power efficiency in automotive hydrogen fuel cells by 30%.

The team led by chemical engineers at Vanderbilt University, and researchers from Nissan North America and Georgia Institute of Technology has received US$2.5m from the Department of Energy (DoE) to apply the new technology to the next generation of automotive fuel cells. The team says the technology can boost the power output of fuel cells while being cheaper and more durable than conventional catalyst layers in electrodes.

In conventional hydrogen/air fuel cells, hydrogen flows into one side of the device and air is pumped into the other. At the anode, the hydrogen is oxidised into protons. The protons flow to the cathode where the air is channelled, reducing the oxygen to form water. Catalysts that use thin sheets of particles – typically made from platinum on carbon powder – mixed with a polymer binder for the electrodes allow these reactions to occur spontaneously, producing electricity in the process. They typically convert fuel to electricity with efficiencies ranging from 40–60%.

The Vanderbilt team’s approach replaces the solid catalyst sheets with mats made from a tangle of polymer fibres that are each a fraction of the thickness of a human hair, made by a process called electrospinning. Particles of catalyst are bonded to the fibres. The small diameter of the fibres means that there is a larger surface area of catalyst available for hydrogen and oxygen gas reactions during fuel cell operation. The pores between fibres in the mat electrode also facilitate the removal of the waste water. The structure results in higher fuel cell power, using 4–5 times less platinum.

Meanwhile the team at Georgia Tech has developed a method for carefully controlling the shape of the nanoparticle catalyst for fuel cells, particularly producing platinum-nickel nanoparticles with a regular octagonal shape. The team say in theory, these particles should be more effective than commercial platinum black powder currently used as the oxygen reduction catalyst in hydrogen/air fuel cells.

In the new DoE project, the Vanderbilt team will make nanofibre mat electrodes containing Georgia Tech’s nanoparticle catalysts. The electrodes will then be sent to Nissan Technical Center North America where another team of researchers will evaluate their performance under automotive operating conditions.

Peter Pintauro, professor of chemical engineering at Vanderbilt University, said: “The combination of the Georgia Tech catalyst with Vanderbilt's nanofibre electrode technology could be a game-changer for the development and commercialisation of automotive fuel cells.”

The teams will also be collaborating with researchers at the DoE’s national laboratories including Oak Ridge and Lawrence Berkeley to understand why fuel cells work better with nanofibre mat electrodes.

Pintauro explained that the current experiments are mainly trial and error at this stage.

“We don't know what will happen when we change the composition or structure of the electrodes in hydrogen/air fuel cells. With a better understanding of the interdependence of composition and nanostructure for fibre electrodes, we could accelerate the pace of our research, which would help us to achieve the cost and performance targets needed for automotive fuel cell commercialisation,” he said.

The project is part of a US$13m DoE programme announced last month to advance fuel cell performance and durability and hydrogen storage technologies.