Solid oxide fuel cells are an excellent alternative to traditional power plants, using an electrochemical method that generates electricity more efficiently than existing combustion-based generators. However, the degradation rate of fuel cells is often too fast, and the increase in cost is directly proportional to the improvement in efficiency. Recently, engineers at the University of Wisconsin-Madison have made a new breakthrough in the chemical reaction of fuel cells. "Fuel cells are a potentially disruptive technology," said Dane Morgan, professor of materials science and engineering at the University of Wisconsin-Madison and leader of the study. "Degradation issues have been a barrier to their entry into the consumer market. A major obstacle." He and his collaborators recently published their findings in the journal Nature Communications. "High temperature" is a cause of fuel cell degradation because these devices must operate at extremely high temperatures—the chemical reactions that produce electricity require temperatures greater than 1,500 degrees Fahrenheit to occur. Fuel cells combine oxygen with an external fuel source, similar to the conversion of heat and light that occurs in fires. However, fuel cells complete these chemical reactions without combustion. This is why fuel cells can produce energy more efficiently than combustion. However, fuel cells work somewhat like batteries, consisting of two electrodes separated by an electrolyte material that transports ions. One of the electrodes breaks down oxygen in the air into individual atoms, which are then combined with fuel for transport. Importantly, the breakdown of oxygen releases electrons that can be passed as electrical current through circuits to power homes or devices. This oxygen decomposition reaction occurs in a component called the positive electrode. But oxygen is chemically stable and does not break down easily, so the challenge of efficiently driving chemical reactions with compatible materials at low temperatures has always been challenging, in part because researchers don't really understand what's happening at the cathode. details of chemical reactions at the atomic scale. In order for oxygen to enter the cathode, the gas molecule must split into two atoms. Each atom must then meet a structure called a vacancy, a small molecular gap on the surface of the material that allows oxygen to enter. Understanding this process is difficult because it occurs in the top atomic layer of the cathode, whose chemistry can be quite different from the bulk of the material. "Measuring the chemical composition and vacancies of these two layers is very challenging," says Morgan, which is why he and his colleagues turned to computer simulations. As leading experts in molecular modeling, they combined density functional theory and kinetic models to gain atomic-level insights into the reactions taking place in the top two layers of the cathode. The team concluded that splitting was not the speed-limiting step in the materials studied. They realized that the process by which oxygen atoms find and move into vacancies on the surface is key to limiting fuel cell efficiency. Therefore, materials with more vacancies could potentially make fuel cells much more efficient. The researchers focused on one particular material, a model compound used in many common fuel cell cathodes, called lanthanum strontium cobaltate. They plan to expand the analysis to other materials soon. The findings could have implications beyond fuel cells. Materials that exchange oxygen with the environment include many applications, such as water splitting, carbon dioxide reduction, gas separation, and electronic components called memristors.

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