- UNIST team boosts performance and durability of manganese catalyst by adding neodymium

- Catalyst stable for more than 1,000 hours, raising hopes for lower green hydrogen production costs

An AI-generated image of a manganese-based water-splitting catalyst. [Provided by UNIST]
An AI-generated image of a manganese-based water-splitting catalyst. [Provided by UNIST]

Researchers have developed a high-performance water-splitting catalyst that uses abundant manganese in place of costly and scarce iridium to produce green hydrogen.

The Ulsan National Institute of Science and Technology (UNIST) announced Wednesday that a research team led by professors Ryu Jeong-gi and Lee Jun-hee of the Department of Energy and Chemical Engineering developed an oxygen evolution catalyst by adding neodymium (Nd), a rare-earth element, to manganese oxide, significantly improving its reaction performance and durability.

Water electrolysis splits water into hydrogen and oxygen using electricity to produce green hydrogen. Proton exchange membrane (PEM) water electrolysis, which is particularly well-suited for producing high-purity hydrogen, requires a catalyst that can withstand strongly acidic environments. Iridium is currently the material of choice for its superior performance and durability, but its high cost and limited reserves have been cited as major obstacles to large-scale deployment.

The research team turned to manganese, which is abundant in nature, as an alternative. Plants also rely on a manganese-based catalyst when breaking down water to produce oxygen during photosynthesis. Manganese, however, tends to dissolve or lose its structural integrity in acidic environments, limiting its practical use as a water-splitting catalyst.

The team overcame these weaknesses by incorporating neodymium into manganese oxide. The resulting catalyst operated stably for more than 1,000 hours under a current density of 200 milliamperes per square centimeter (mA/cm²) in a strongly acidic solution — a stark contrast to a catalyst without neodymium, which saw a sharp drop in performance after about 300 hours.

UNIST researchers who conducted the study. From left: Professor Ryu Jeong-gi, Professor Lee Jun-hee and researcher Kim Hyeon-gu. [Provided by UNIST]
UNIST researchers who conducted the study. From left: Professor Ryu Jeong-gi, Professor Lee Jun-hee and researcher Kim Hyeon-gu. [Provided by UNIST]

The catalyst also requires less additional voltage to generate the same amount of oxygen, improving energy efficiency. In tests on an actual water electrolysis device, it maintained stable performance for more than 600 hours at a current density of 100 mA/cm².

The key lies in neodymium's ability to stabilize both the electronic state and the structure of manganese at the same time. Manganese effectively promotes the oxygen evolution reaction in its trivalent ion (Mn³⁺) state, but tends to shift to divalent and tetravalent states in acidic environments. Divalent manganese in particular leaches into the electrolyte, degrading the catalyst's performance and lifespan.

Neodymium supplies electrons to the surrounding manganese atoms and regulates their bonding state, keeping them in the trivalent state favorable for the reaction. In this process, regions of manganese oxide (Mn₂O₃) containing trivalent manganese promote the oxygen evolution reaction, while regions of manganese dioxide (MnO₂) provide structural stability in the acidic environment. The team also confirmed the electron-supply and atomic-bond-strengthening effects through theoretical calculations.

The findings were published in Nature Communications on Sept. 11.


nbgkoo@heraldcorp.com