Researchers working on the next generation of fuel cells have been facing a platinum conundrum – and it’s one they’re fighting hard to solve.

Platinum, one of the most costly precious metals, works exceptionally well as the catalyst inside of a fuel cell. At the anode, platinum helps to strip the electron from hydrogen to form single protons, while at the cathode, platinum combines the proton and the electron with oxygen to create water. The electrons flow through the external circuit connected with the fuel cell, generating clean, green electricity.

This second reaction at the cathode is also known as the oxygen reduction reaction. It is the more sluggish one of the two, and therefore it needs more platinum catalyst to function. Scientists have been searching for low-cost catalysts to replace platinum in attempts to make fuel cells more affordable to the public.

In a new study led by Argonne National Laboratory chemist Di-Jia Liu, researchers have identified a new way to synthesize inexpensive, transition metal-based catalysts as an alternative to platinum. These new catalysts offer the promise of substantially reducing the fuel cell cost.  

The new approach developed by Liu and his team uses materials known as metal-organic frameworks (MOFs) as the precursor to prepare the platinum-free catalyst. It overcomes the limitation of the traditional method by eliminating the use of inert carbon material as the catalyst support. The MOF- based method produces the catalyst with a high density of active sites that are uniformly distributed throughout the material.

“Our method transforms the catalyst preparation from conventional, two-dimensional methods to a new three-dimensional approach,” Liu said.

The new study, featured in the February 19 issue of Advanced Materials, applies what Liu called a ​“one-pot,” solid state synthesis approach. ​“We not only substantially reduced the number of steps required and therefore the cost of making such catalysts, but we also significantly expanded the search for a wide range of compositions to improve the catalytic activity,” Liu said.

Liu and his team further tested these new catalysts in fuel cells. ​“We were pleased to note that the catalytic activities are among the highest in the reported literature,” he said.

The research was funded by the U.S. Department of Energy’s Office of Science and Office of Energy Efficiency and Renewable Energy.