Fuel cells are promising energy devices that are currently under much development. Direct methanol fuel cells are an example of promising technology in this field.
Instead of using hydrogen, direct methanol fuel cells use methanol as fuel. They therefore offer a potential technology for portable consumer electronics applications. Mass commercialisation of the fuel cells has not been realised due to technological limitations of the technology. The challenges with direct methanol fuel cells include methanol crossover that limits the efficiency of the fuel cell and the use of expensive platinum catalysts on the electrodes. Reducing or eliminating the use of platinum has therefore been a major research theme.
One of the research groups working on this challenge is the Massachusetts Institute of Technology (MIT). The MIT researchers, working together with researchers from the Brookhaven National Laboratory and the Japan Institute of Science and Technology, found a way to lower the usage of platinum in direct methanol fuel cells by significantly increasing the efficiency of the fuel cell electrodes. Other previous developments to reduce platinum usage include replacing the fixed platinum catalysts on the cathode with a liquid regenerating catalyst system called catholyte solution.
In the MIT research, platinum nanoparticles were deposited on the surface of multiwall carbon nanotubes. The researchers discovered that the key for the efficiency increase is in the surface texture of the electrode material and not the size of the particle as previously thought. Multiple tiny step-like shapes are crated on the surface instead of leaving the surface smooth and in doing so, double the amount of electricity. The researchers found that the surface steps on the platinum nanoparticles correlate with the electrochemical activity and stability, which can be over hundreds of cycles. The activity of carbon monoxide and methanol electro-oxidation were enhanced with the step surface. The researchers reported that increasing surface steps on the platinum nanoparticles of around 2 nm leads to enhanced activity of up to about 200% for electro-oxidation of methanol.
The researchers believe that further development of the surface structure will produce greater electric current. With a given amount of platinum, much greater electric current can be produced. Understanding the mechanism of how this works can lead to the development of fuel cells that have lower amount of platinum in the fuel cells. The researchers are working on creating more surface steps to further increase the activity of the electrode. The team also hopes to understand whether the steps can enhance the oxygen reduction part of the process that takes place in the other side of a fuel cell.
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)18 464 2402, patrick.cairns@frost.com, www.frost.com
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