Scientists have developed a quicker method to make multilayered electrodes for fuel cells.

Led by Marc Michel, a team based at Darmstadt University, Germany, used a sprayed layer-by-layer method to assemble the electrodes for proton exchange membrane (PEM) fuel cells.

PEM fuel cells split hydrogen into protons and electrons at the anode using a platinum catalyst. The protons travel through a polyelectrolyte membrane to the cathode, where they react with oxygen to form water. For high performance, the polyelectrolyte must be permeable to protons but not electrons and the catalyst's structure must allow the hydrogen and protons to diffuse easily through it.

Scientists achieve this by building up the components of the cells in layers. Conventionally, they alternately dip Nafion, the most commonly used polyelectrolyte membrane, into two solutions of oppositely charged polyelectrolytes. Instead, Michel sequentially sprayed the solutions on to Nafion, which he claims can boost performance.

Michel used a mixture of platinum catalyst and polyaniline, a highly conductive polymer, as the positive solution and Nafion as the negative one. He found that polyaniline's high conductivity and fibrous structure improved charge and ion transport through the fuel cell.

Michel says the spraying technique is much faster and doesn't affect the quality of the films produced. '20 layers can be obtained in less than five minutes compared to about two and a half hours for the conventional layer-by-layer dipping method,' he says. Moreover, the amount of platinum used in this method is almost half of that used for conventional carbon-supported platinum catalysts used in fuel cells, making the cells cheaper and less toxic.

Michel says he hopes that the reduced cost and preparation time will make the spraying technique attractive to industries, but first more work has to be done. 'We have to do long term stability investigations to check whether polyaniline is a good candidate for fuel cells,' he says.

Ian Gray