Thus far, not much rivals the energy density of the carbon bonds found within petrochemicals; pound-for-pound, they are still the most efficient way to pack potential energy in the least amount of space. That quality means gasoline and its ilk are still the fuel of choice for mobile applications, from portable generators to vehicles.
Transitioning to a post-fossil-fuel future also requires a focused effort on developing green and sustainable fuels. Given its ubiquity, hydrogen would be an ideal choice, so researchers are continuously improving production and utilization methods to ensure this promising energy carrier is both environmentally and economically viable.
Chuancheng Duan, a newly appointed associate professor in the Department of Chemical Engineering, is taking this challenge head-on. Duan’s research portfolio includes a range of devices that increase efficiency or create new high-value chemicals as part of emissions-reduction techniques. Prior to joining the U, Duan received multiple Department of Energy grants to help reduce methane emissions.
He’s now taking his expertise in the interconnection between chemical and electrical energy to smaller scales, extending these principles to portable and mobile applications.
At the core of this work are fuel cells and electrolysis cells. These devices use different sets of chemical reactions to convert chemical energy stored in fuel into electricity, or use electricity to spur the generation of useful chemicals. Combination devices can even function as both a fuel cell and an electrolyzer depending on the operational mode.
Unlike batteries, which only store electricity, fuel cells can continuously generate electricity as long as both fuel and air are supplied, while electrolysis cells can continuously produce chemicals as long as they are provided with electricity and feedstock. The goal, then, is finding the right combination of fuel and electrolysis cell materials, catalysts, and chemical reactions that can rival the energy efficiency, reduce the emissions, and improve the sustainability compared to their gas-burning counterparts.
Duan’s expertise is in fuel cells and electrolysis cells with both oxygen-ion conductor and proton-conductors electrolytes, the layer that separates the cell’s anode and cathode, allowing charged particles — and electricity — to flow. The high operating temperatures, typically above 500 ℃, of solid oxide fuel cells (SOFCs) bring significant benefits, including high energy efficiency and fuel flexibility. SOFCs can operate on various fuels, including hydrogen, hydrocarbons, biogas, and liquid fuels. The high operating temperature enables internal reforming of hydrocarbon fuels, reducing the need for external fuel processing equipment.
“While these fuel cells still rely on hydrocarbons as fuels, they emit significantly lower levels of pollutants and greenhouse gases compared to traditional gas generators as fuel cells can double the energy conversion efficiency,” says Duan. “However, it is equally important to pursue more sustainable fuel alternatives, such as green hydrogen, which emphasizes the need for green and cost-effective hydrogen production. The ultimate goal is to develop systems that not only operate efficiently on renewable fuels like hydrogen, enabling sustainable and clean energy production, but also have the capability to produce sustainable chemicals.”
The high temperatures that SOFCs operate make them unlikely to be used to power consumer cars, but their other qualities make them ideal for portable power generators. With that application in mind, Duan recently received an U.S. Army Early Career Program (ECP) award to further this research.
He’s also collaborating with Feng Zhao, CEO/CTO of Storagenergy, the Salt Lake City startup that manufactures cutting-edge battery and fuel cell components, on a new project to further boost their efficiency. Zhao and Duan recently received a Phase II Small Business Technology Transfer grant to continue their work.
Additionally, Duan is currently leading or collaborating on five other projects funded by the Department of Energy. These projects focus on advancing fuel cell and electrolysis cell technologies to produce low-cost hydrogen, mitigate methane emissions, and convert carbon dioxide into valuable and sustainable chemicals. These efforts align with the goals to decarbonize energy systems, reduce greenhouse gas emissions, and promote carbon-zero economies.
Given the cutting-edge nature of these devices, much fundamental research is still required before they can be meaningfully improved.
“The efficiency, durability, and power density of direct-hydrocarbon SOFCs depends on the surface properties of the anode, but we don’t actually know very much about how the hydrocarbons in the fuel are being converted there,” says Duan. “There are a number of different theories about which properties are the most important, so we’re building the tools needed to probe and understand those theories.”
One theory for improving the longevity of these fuel cells, for example, is preventing “sulfur poisoning.” Impurities in the hydrocarbon fuel are thought to interfere with the anode, slowing down the internal reforming reactions, but the mechanisms and approaches to mitigate sulfur poisoning have not been fully understood. “Coking,” a process where solid carbon if formed, is also thought to be culprit in anode inefficiency.
Duan’s high-temperature spectroscopy platform will be used to analyze the hydrocarbon reaction as it is happening, observing the intermediate molecules and species on the anode. A better understanding of that process would enable engineers to design more active and durable anodes, increasing the overall efficiency and lifetime of the fuel cell.