Looking for ways to avoid using costly and scarce platinum in fuel cells, Chinese researchers have reported details of a fuel cell that uses cheap nickel as a catalyst.
In traditional fuel cells, hydrogen is broken down by a platinum catalyst to form protons and electrons. The electrons provide electricity, while the protons pass through an acidic membrane or electrolyte to a second electrode where they combine with oxygen to form water.
But researchers at Wuhan University, led by Lin Zhuang, turned to alkaline fuel cells (those with an alkaline electrolyte), which are much less corrosive than their acidic counterparts. In such a cell, it is hydroxyl ions, not protons, which selectively travel through the membrane separating cathode and anode.
The researchers used a new and particularly stable quaternary ammonia polysulfone film as the alkaline polymer membrane. The less corrosive alkaline environment allowed them to use nickel nanoparticles as a catalyst at the anode, rather than platinum.
However, nickel nanoparticles easily oxidise when exposed to air. The
researchers decorated their sensitive electrode with a protective layer of chromium oxide.
Operating a prototype alkaline fuel cell that feeds on hydrogen and oxygen using a nickel anode and a silver cathode, the team obtained a power output of 50 mW/cm2. This is still a far cry from that required to power a car - typically more than 1W/cm2 - now reached with platinum-based fuel cells.
'I believe the power output will reach [platinum's] level in a couple of years,' says Zhuang. In the meantime his cheaper fuel cells could find low-power applications, such as in computers.
Bjorn Winther-Jensen of Monash University in Australia, who is also researching ways to circumvent platinum in fuel cells, agrees that the low power output is a problem: 'That is the problem for all of us.' And it is still a difficult field: 'I don't think that anybody will come up with 'the' solution, and more contributions on alkaline fuel cells are welcome,' he adds.