Cheaper green hydrogen catalyst comes within 50 millivolts of costly ruthenium

Researchers have developed a low-cost catalyst for green hydrogen production that performed within 50 millivolts of a ruthenium-based benchmark during oxygen evolution, yielding a potential alternative to catalysts made from scarce and expensive precious metals. ​The team created catalysts using nickel and iron oxides anchored to carbon nanofibers grown on a conductive two-dimensional material known as MXene. The study suggests the approach may help lower the cost of water electrolysis, a process that produces hydrogen without carbon emissions. Carbon nanofiber catalysts for green hydrogen ​Green hydrogen is made by splitting water into hydrogen and oxygen using electricity. Unlike conventional hydrogen production, which largely depends on fossil fuels, the process emits no carbon dioxide when powered by renewable energy. However, efficient water splitting requires electrocatalysts, which are typically made from costly 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 roughly 22 pounds (10 kilograms) of carbon dioxide, while blue hydrogen produces about 13 pounds (6 kilograms). ​To curb reliance on precious metals, the researchers used Ti₃C₂Tₓ MXene as a conductive scaffold and grew carbon nanofibers directly on its surface through chemical vapor deposition. Iron or nickel oxide particles formed at the fiber tips, creating two catalyst materials: FeO-CNF@MX and NiO-CNF@MX. ​Microscopy and spectroscopy analyses established that the carbon nanofibers formed successfully across the MXene sheets while preserving the material’s layered structure. 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 an overpotential of 490 millivolts (mEV) to reach a current density of 10 milliamps per square centimeter, compared with 520 mEV for the iron version. Both outperformed similar catalysts that lacked the MXene support, the study demonstrated. ​The biggest improvement came during the oxygen evolution reaction—the nickel catalyst required just 300 mEV, compared with 360 mEV for the iron catalyst. Ruthenium oxide, one of the industry’s benchmark catalysts, required 250 mEV, leaving the nickel material only 50 mEV behind despite using inexpensive metals. ​The nickel composite also showed slightly lower charge-transfer resistance, demonstrating more efficient electron movement during the reaction. ​”Growing the fibers directly on the MXene sheets gave us a conductive backbone and a lot of accessible active sites,” the researchers said. In their study, scientists assembled complete water-splitting cells using the same catalyst on both electrodes. They found that the iron-based material delivered stronger initial performance and reached target current density at 2.2 volts while the nickel catalyst required 2.7 volts. According to the researcher, iron helps stabilize reaction intermediates during oxygen production, advancing overall cell performance. Both prototype electrolyzers also remained stable 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 do not yet match platinum catalysts, which require only about 70 millivolts for hydrogen production, the researchers said the work demonstrates a simple and scalable way to build efficient electrocatalysts from abundant, inexpensive materials. The findings were published recently in ACS Applied Nano Materials. Get the latest in engineering, tech, space & science - delivered daily to your inbox.