Rhodium Nanoparticles Give Fuel Cells a Steam-Powered Self-Cleaning Mechanism

Solid oxide fuel cells have a sulfur problem. Even a few parts per million of hydrogen sulfide in a fuel stream - common in natural gas, biogas, and syngas - can rapidly degrade a nickel-based anode, forming sulfur-nickel compounds that clog the surface and strangle the cell performance. Engineers have known about this vulnerability for years. What nobody had pinned down was a way to make the anode fight back on its own.

A Catalyst That Cleans Itself

A team at the University of Utah has now described exactly how one such mechanism works. Adding rhodium (Rh) to a nickel-based solid oxide fuel cell anode produces bimetallic nanoparticles that do not simply tolerate sulfur - they actively expel it, using the water vapor already present in fuel cell operating conditions.

The findings, published February 19 in the Journal of the American Chemical Society, show that rhodium fundamentally changes the surface chemistry of the anode. On a conventional nickel anode, sulfur forms stable nickel-sulfur bonds that physically block active sites. Rhodium weakens those bonds while simultaneously activating water molecules to generate reactive hydroxyl species. Those hydroxyls oxidize the adsorbed sulfur into sulfur dioxide gas, which then escapes from the surface naturally.

"This work establishes a new design strategy for sulfur-tolerant electrochemical materials," said senior author Chuancheng Duan, associate professor of chemical engineering. "We show that catalysts can be engineered not just to tolerate sulfur, but to actively clean themselves during operation."

Three Times the Power Output Under Contaminated Fuel

The performance numbers are striking. Solid oxide fuel cells incorporating Ni-Rh catalyst nanoparticles maintained more than three times higher power output than conventional nickel-based anodes when running on fuel containing under 100 parts per million of hydrogen sulfide contamination. Polarization resistance - a measure of how much the anode impedes the electrochemical reaction - was also significantly lower in the rhodium-modified cells.

Crucially, the cells demonstrated self-regeneration under realistic operating conditions, without any external sulfur removal system or complex regeneration protocols. That autonomous recovery is what makes this more than a laboratory curiosity. Real-world fuel cells encounter variable fuel compositions, and a system that requires external intervention every time sulfur spikes would not be practical to deploy.

How the Team Figured It Out

The mechanistic picture came from a combination of techniques. Lead author Yue Bao, a graduate student in Duan Materials Research Laboratory for Sustainable Energy at the John and Marcia Price College of Engineering, used in-situ high-temperature infrared spectroscopy, thermochemical analysis, and electrochemical diagnostics together. That combination let the team watch the surface chemistry unfold in real time under operating conditions - rather than inferring it from post-mortem analysis of spent anodes.

The study is titled "Unraveling Sulfur Tolerance Mechanisms in Samarium-Doped Ceria-NiRh Catalysts for Solid Oxide Fuel Cells." It was supported by the U.S. Army Research Office under the Energy Sciences Competency program.

Beyond Fuel Cells

The mechanism is not specific to solid oxide fuel cells. "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," Bao said.

Solid oxide fuel cells are attractive for distributed power generation because they can run on a range of fuels, not just hydrogen. Sulfur poisoning has been one of the major practical barriers to deploying them widely. A self-regenerating anode that works under real operating conditions is a meaningful step toward making that vision practical - though scaling the rhodium-based approach to commercial production will require further engineering work.