November 4, 2016
A University of Illinois research team has invented a highly-efficient method for producing precision catalysts that can be used for cathode reaction in hydrogen fuel cells for automobiles. The technique promises to increase the efficiency of producing shape-controlled catalysts that could have benefits beyond the automotive industry.
Countless chemical and petrochemical processes involve the use of a catalyst. One of the current challenges in developing hydrogen fuel cells is to produce the high-performance, low-cost catalyst at scale.
“The geometric shape of the catalyst is crucial to the highest possible conversion rate of fuel molecules in a hydrogen fuel cell,” said Hong Yang, Richard C. Alkire Professor in Chemical Engineering. “The atomic arrangement determines how close the molecules can get together to react. The challenge is finding the right distribution of surface atoms so that they have the molecule at the right strength. If it is too strong, the molecule won’t leave the surface. If it’s too weak, it won’t adsorb.”
In 2007, researchers proved that platinum combined with another metal (in this case nickel) could enhance the electrocatalyst performance about tenfold simply by improving the geometry.
Typically, researchers produce the catalyst by converting molecule precursors in liquid into nanoparticle catalysts. A shape of a solid-state catalyst is more predictable and consistent if they are produced in well-controlled liquid media. That “batch system” can be quite precise to create those geometric shapes that result in high performance. The Yang group previously used this method and worked with the automobile industry, namely General Motors, to improve the efficiency of catalysts for hydrogen fuel cells, which converts chemical energy stored in hydrogen fuel into electricity and pure water.
The batch system, however, is inefficient in production, as it takes more time and multiple processing steps to produce. A current problem has been producing such precise catalysts at scale.
The technique the group has developed involves a novel conveyor belt system, which produces solid-state platinum (Pt) nanocubes and its nickel alloy (Pt3Ni) nanooctahedra by using an aerosol-assisted airbrush to disperse precursors together with carbon particles as the catalyst support on a substrate and finely controlling the reaction conditions while the substance is transported through a tube with carbon monoxide as a reactive carrier gas. The powders are heated and passed through the tubular reactor, producing the solid-state catalysts. The method thus allows for a continuous production, which is scalable for large-scale production purpose.
“Carbon monoxide can interact predictably with a range of platinum group metals,” Yang said. “Those metals are very active, both in fuel cells and in other chemical industry processes. The conveyor belt transport technique mimics the existing technology for handling the fluid phase. For example, when pumping gasoline, the raw material (crude oil) is pumped continuously at the one end, producing gasoline on the other. We want to translate that principle by using a conveyor belt or solid supported catalyst synthesis in one step. The difference in our method is, in principle, we can continuously make a uniform catalyst on solid support through the conveyor belt system.”
Through transmission electron microscopy (TEM), the team demonstrated that the metal cube catalysts were produced uniformly in both size and shape on the support.
Yang reiterates that although the nanomaterial has a nice property, in order to have the kind of impact on the chemical industry, it must be able to be produced at scale. The ultimate goal for his group is to create a viable commercial product that can do just that.
“We are moving in that direction,” Yang said. “One can start to generate a uniform catalyst using our system. We have been using batch synthesis to make catalysts for fuel cells, but now we want to apply this technology to a high-production run to move to the next phase.”
Although Yang has proven the effectiveness of the technique, he and his group are increasing the efficiency by testing different geometric forms of the resulting catalysts.
“If we can demonstrate applications that show high production rates of the catalyst we generated with dramatic enhancement of performance in comparison with the others, that could be the turning point for this technology,” Yang said. “In the example of the fuel cell catalyst, the challenge is to reduce the cost of the catalyst. You can imagine if one can improve the performance (generating the same amount of power by using less catalyst), the fuel cell itself will be more efficient.”
While the technique is targeted for the hydrogen fuel cell application in the automobile industry, Yang hopes to apply that same technique to produce high-precision catalysts for other chemical conversion processes, such as creation of epoxy from hydrocarbon or conversion of carbon dioxide into commodity chemicals.
“In principle, all these solid catalysts follow the same working principle,” Yang said. “You need to have the right structure and atoms on the surface that can allow molecules quickly react and leave the surface. It has to allow the chemicals to have the right distance for the most efficient adsorption rate.”
Kai-Chieh Tsao (left) and Professor Hong Yang have published their results in Small.
By Mike Koon, Marketing and Communications Coordinator, College of Engineering.
For more information about the technology, contact Professor hy66illinois [dot] edu (Hong Yang).