New catalyst could replace platinum in cheaper fuel cells

This chemical drawing of a nano-island of graphene into which iron-nitrogen complexes have been embedded shows the chemical makeup of this nano-sized material(Credit: HZB and TU Darmstadt)

A more cost-effective fuel cell catalyst material consisting of iron-nitrogen complexes embedded in tiny islands of graphene could be used in place of costly platinum. Research by teams at Helmholtz Zentrum Berlin and TU Darmstadt have produced the catalyst material and found that its efficiency approaches that of platinum.

To synthesize the mix, the researchers had to devise a way of reducing metal contaminants in the catalyst material to near-zero. Inorganics, usually metals, interfere with a catalyst's efficiency by reducing the oxygen reactions that are at the heart of a fuel cell's catalytic function.

The answer was an iron-nitrogen complex "doped" in graphene islands of just a few nanometers in diameter. This Fe-N-C catalyst is being tested and has been found to be capable of achieving levels of activity comparable to common – and expensive – Pt/C (platinum) catalyst materials.

This new process builds on a previous process developed by HZB, which held a world record for its efficiency. The new build aims for higher purification of the catalyst materials, using a combination of thermal treatment and etching, to reduce the amount of foreign material in the catalytic compound.

Junior professor Ulrike Kramm of TU Darmstadt used the process to create a low-cost catalyst that had graphene layers made up exclusively of FeN4 complexes, eliminating the need for iron nanoparticles, as was previously the case, while improving the reactivity of the catalyst greatly. This allows the catalyst's designers to add promoters to improve catalytic production to meet the needs of the intended fuel cell's purpose.

This new catalyst could be used in fuel cells of several types and for many purposes. Fuel cells in the automotive industry, which can include hydrogen, natural gas, and other fuels, would become far less expensive. Fuel cells for scientific and military use would also be improved at reduced cost, while consumer fuel cells for electronics and other devices would likewise see benefit from this new catalytic design.

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