Researchers have developed a low-cost catalyst for the production of green hydrogen that operates within 50 millivolts of a ruthenium-based benchmark during oxygen evolution, providing a potential alternative to catalysts made from rare and expensive precious metals.
The team developed catalysts using nickel and iron oxides anchored to carbon nanofibers grown on a conductive two-dimensional material called MXene. The study suggests the approach could help reduce the cost of water electrolysis, a process that produces hydrogen without carbon emissions.
Carbon nanofiber catalysts for green hydrogen
Green hydrogen is produced by splitting water into hydrogen and oxygen using electricity. Unlike traditional hydrogen production, which relies largely on fossil fuels, the process does not release carbon dioxide when powered by renewable energy. However, efficient water splitting requires electrocatalysts, which are typically made from expensive metals such as platinum, ruthenium and iridium.
According to the researchers, about 96 percent of the world’s hydrogen is currently produced from fossil fuels. Producing one kilogram of conventional gray hydrogen releases about 22 pounds (10 kilograms) of carbon dioxide, while blue hydrogen releases about 13 pounds (6 kilograms).
To curb dependence on precious metals, the researchers used Ti₃C₂Tₓ MXene as a conductive scaffold and grew carbon nanofibers directly on its surface using chemical vapor deposition. Iron or nickel oxide particles formed at the fiber tips, creating two catalyst materials: FeO-CNF@MX and NiO-CNF@MX.
Microscopic and spectroscopic analyzes revealed that the carbon nanofibers successfully formed over the MXene layers while preserving the layered structure of the material. The nickel-based composite also produced a more graphitic and less defective carbon structure than the iron-derived version.
Iron outperforms nickel
The team evaluated both materials in an alkaline electrolyte used for water splitting.
For the hydrogen evolution reaction, the nickel-based catalyst required a surge voltage of 490 millivolts (mEV) to achieve a current density of 10 milliamperes per square centimeter, compared to 520 mEV for the iron version. The study showed that both outperformed similar catalysts that lacked MXene support.
The biggest improvement occurred during the oxygen evolution reaction – the nickel catalyst required only 300 mEV, compared to 360 mEV for the iron catalyst. Ruthenium oxide, one of the industry’s benchmark catalysts, required 250 mEV, leaving the nickel material behind by only 50 mEV despite using inexpensive metals.
The nickel composite also showed slightly lower charge transfer resistance, demonstrating more efficient electron movement during the reaction.
“By growing the fibers directly on the MXene sheets, we obtained a conductive backbone and many accessible active sites,” the researchers said.
In their study, the scientists assembled complete water-splitting cells using the same catalyst on both electrodes. They found that the iron-based material provided higher initial power, reaching the target current density at 2.2 volts, while the nickel catalyst required 2.7 volts. According to the researcher, iron helps to stabilize reaction intermediates during oxygen production, thereby improving the overall performance of the cell.
Both prototype electrolysers remained stable even during a 24-hour test. Cell voltage increased by only 0.2 to 0.3 volts, with the nickel catalyst showing slightly less performance drift over time, the study reported.
Although the new materials cannot yet compete with platinum catalysts, which only require about 70 millivolts for hydrogen production, the researchers say the work demonstrates a simple and scalable way to build efficient electrocatalysts from abundant, low-cost materials.
The results were recently published in ACS Applied Nanomaterials.
