Fuel cells are electrochemical devices that directly convert chemical energy from a fuel into electrical energy. Unlike batteries, which only store electricity, fuel cells can continuously generate electricity as long as both fuel and air are supplied.
A variety of fuels are being considered for such fuel cells, but the exact chemistries of their electricity-releasing reactions are complicated and not entirely understood. Gaps in this knowledge are some of the most critical barriers to deploying fuel-flexible clean energy technologies. For example, fuel cells that use solid oxides are susceptible to "sulfur poisoning," where trace impurities of that element quickly degrade the system's performance.
Now in a new study, University of Utah researchers have uncovered a previously unknown steam-enabled self-cleaning mechanism that dramatically improves sulfur tolerance in solid oxide fuel cell (SOFC) anodes.
"This work establishes a new design strategy for sulfur-tolerant electrochemical materials," said senior author Chuancheng Duan , an associate professor of chemical engineering. "We show that catalysts can be engineered not just to tolerate sulfur, but to actively clean themselves during operation."
Yue Bao, a graduate student in Duan's Materials Research Laboratory for Sustainable Energy in the John and Marcia Price College of Engineering, is the lead author the study published in the Journal of the American Chemical Society .
The findings demonstrate that the addition of the element rhodium (Rh) to nickel-based SOFC anodes leads to the formation of bimetallic nanoparticles that actively resist sulfur poisoning and autonomously regenerate under steam exposure. This discovery provides the first direct evidence explaining why Rh-modified SOFC anodes maintain performance under sulfur-contaminated fuels. A better understanding of this mechanism will help make these fuel cells viable for real-world applications.
Sulfur impurities such as hydrogen sulfide (H2S), even at trace levels, rapidly deactivate conventional nickel-based SOFC anodes by forming stable nickel-sulfur (Ni-S) species that physically block the anode's surface. Using a powerful combination of in-situ high-temperature infrared spectroscopy, thermochemical analysis, and electrochemical diagnostics, the researchers show that rhodium fundamentally alters the surface chemistry of the anode. The addition of rhodium weakens Ni-S bonding while simultaneously activating water molecules to generate reactive hydroxyl species that oxidize adsorbed sulfur into volatile sulfur dioxide, which then naturally escapes from the surface.
As a result, SOFCs incorporating these Ni-Rh catalyst nanoparticles maintained more than three times higher power output and significantly lower polarization resistance when using fuel with under 100 parts per million H2S contamination, as compared to conventional nickel-based anodes. Remarkably, the catalyst demonstrated self-regeneration under realistic operating conditions, eliminating the need for external sulfur removal or complex regeneration protocols.
"Beyond SOFCs," Bao said, "the findings offer broadly transferable insights for high-temperature catalysis, electrochemical energy systems, and fuel-flexible power technologies, particularly in applications involving natural gas, biogas, syngas or other sulfur-containing fuels.
