Improving the efficiency of fuel cell catalysts Monday, 23 November 2015

The use of scanning transmission electron microscopy is helping researchers at the US Department of Energy’s Oak Ridge National Laboratory (ORNL) optimise the composition of catalysts for fuel cells.

The catalysts are made of platinum and therefore very expensive. Making platinum-cobalt alloys reduces this cost but it hasn’t been easy to predict the performance of these catalysts.

The ORNL team tracked atomic reconfigurations in individual platinum-cobalt nanoparticle catalysts as the particles were heated inside the electron microscope.

Materials scientist and engineer Miaofang Chi said very small changes in the positions of platinum and cobalt atoms affect the catalyst’s overall activity and selectivity, so annealing -- a gradual heating, holding, and cooling process -- is often used to modify the alloy’s surface structure.

“You can anneal something from room temperature to 800 degrees Celsius, but you don’t know at which point you should stop the process to ensure the best catalytic performance,” she said. “Because you don’t know how the particle evolves, you might be missing the optimum surface configuration.”

The atomic-level detail in the ORNL study will guide researchers and manufacturers who want to fine-tune their catalysts’ atomic structure to meet the demands of a specific application.

“This work paves the way towards designing catalysts through post-synthesis annealing for optimized performance,” Chi said.

The measurements, acquired in real time in the vacuum of the microscope column, allowed the researchers to collect atomic level data that could not be obtained with conventional microscopy techniques.

Co-author Karren More this was the first time individual nanoparticles have been tracked this way - to image the structural and compositional changes at the atomic level from the start of an annealing process to the finish.

The team published their results in Nature Communications.


Models of platinum-cobalt nanoparticle catalysts illustrating how specific atomic configurations originate and evolve as the particles are heated. Illustration by Andy Sproles, ORNL.