Researchers at Wayne State University’s Nikolla Research Group uncovered a way to make better-performing electrode surfaces (electrocatalysts). The power density curves in the image above show that the newly designed catalyst (red curve) outperforms a similar catalyst that is not optimized. (image courtesy of American Chemical Society, copyright 2018 (see “Publications”).
Devising efficient metal-air fuel cells, batteries, and other energy conversion and storage depends, in part, on how quickly oxygen molecules gain and lose electrons. To make these systems commercially viable, they need catalysts that are active, and inexpensive, as well as selective, and stable.
However, the reactions are discouragingly slow, and accelerating the reactions demands heat and platinum, which are costly.
Now, researchers have revealed crucial design principles to engineer catalysts that use more readily available metals and require less heat. The catalysts they developed performed well in tests and demonstrated stability over the long term.
For some time, engineers have been looking for better catalysts for electrodes in batteries and fuel cells. These catalysts induce reactions that move electrons to and from oxygen (known as oxygen electrocatalysis). However, creating such catalysts has been difficult. Researchers thus far have mostly used trial-and-error approaches. They needed the underlying design principles to better avoid dead-ends and work on the options with the most encouraging results.
The researchers have been studying promising catalysts made from various ratios of less expensive metals. Specifically, the researchers looked at catalysts that are layered, and mixed ionic-electronic conducting oxides.
They determined that a calculated descriptor, how tightly oxygen binds to a spot where an oxygen atom is missing on the catalyst’s surface, can identify the most promising structures. The team synthesized, characterized, and tested catalysts with different descriptor values to determine how well the descriptor predicted catalytic performance.
They discovered that nano-sized rods composed of cobalt-doped lanthanum nickelate oxide worked well in solid oxide fuel cells at around 1000 degrees Fahrenheit and these rods proved to be stable over the long term.
Mixed-metal oxides present a promising group of electrocatalysts for these processes due to the versatility of their surface compositions and fast oxygen conducting capability.
The researchers demonstrated the use of a combination of theoretical and experimental studies to develop design principles for engineering oxygen electrocatalysis activity of layered, mixed ionic-electronic conducting oxides.
First, they showed that a descriptor derived from density function theory (DFT), and O2 binding energy on a surface oxygen vacancy, can be effective in identifying efficient oxide structures for oxygen reduction reaction (ORR).
They employed a method of controlled synthesis to obtain well-defined nanostructures of the oxides, which along with thermochemical and electrochemical activity studies were used to validate the design principles.
This method led them to identify a highly active oxygen reduction reaction electrocatalyst, nanostructured Co-doped lanthanum nickelate oxide, which when incorporated in solid oxide fuel cell cathodes significantly improves the performance at intermediate temperatures ( of about 550 °C), while maintaining long-term stability.
The findings demonstrated the effectiveness of the developed design principles to create mixed ionic-electronic conducting oxides for efficient oxygen electrocatalysis, and they also demonstrated the promise of using nanostructured Co-doped lanthanum nickelate oxides as catalysts for oxygen electrocatalysis.
The team’s results revealed the effectiveness of the design principles. Further, the work emphasizes the potential of the new catalyst and should serve design efforts for fuel cells and batteries.
Gu, X., S. A. J. S. A. Carneiro, S. Samira, et al. Efficient Oxygen Electrocatalysis by Nanostructured Mixed-Metal Oxides.
J. Am. Chem. Soc., 2018, 140 (26), pp 8128-8137. DOI: 10.1021/jacs.7b11138