Korean researchers synthesize green ammonia using water instead of hydrogen gas

South Korean researchers have succeeded in electrochemically synthesizing ammonia using water as the hydrogen source, bypassing the need for hydrogen gas.

The Korea Institute of Energy Research said Tuesday that a research team led by Kim Jae-hyung of its Clean Fuel Research Laboratory had demonstrated that a palladium membrane can selectively transport hydrogen ions from water, and applied the finding to a green ammonia synthesis process.

In electrochemical devices, membranes keep reactants, products and solvents separated while allowing the necessary ions to pass through. Conventional devices have relied mainly on polymer-based membranes, such as ion-exchange membranes.

Polymer membranes contain narrow channels through which water flows, and ions travel along those channels. The problem is a phenomenon known as "crossover," in which unwanted molecules such as water pass through alongside the ions, degrading the performance and stability of the electrochemical device. Conventional membranes face an inherent trade-off: reducing crossover also slows ion transport, making it impossible to improve both properties at once.

The research team addressed the crossover problem by replacing the polymer membrane with a palladium membrane, which absorbs hydrogen atoms. Because palladium has virtually no gaps, it absorbs only hydrogen and carries it to the other side of the membrane, blocking everything else.

When an electric field is applied, hydrogen ions on one surface of the palladium membrane are converted into hydrogen atoms and absorbed into the metal. They then migrate through the palladium and emerge on the opposite side, where they revert to hydrogen ions and enter the solution. Throughout this process, the solvents, reactants and products on either side of the membrane remain fully separated, blocked by the palladium itself.

The team applied the palladium membrane to an electrochemical ammonia synthesis process through a joint study with a research group led by Professor Hwang Yun-jeong at Seoul National University. Electrochemical ammonia synthesis is a green technology that draws hydrogen ions — the raw material for synthesis — from water rather than fossil fuels, and uses renewable energy to power the process, reducing carbon emissions.

Experiments yielded a Faradaic efficiency of 51 percent for ammonia synthesis, and the team confirmed that the type of lithium salt anion dissolved in the organic solvent electrolyte significantly affects synthesis efficiency.

The water crossover problem that had plagued conventional ion-exchange membranes did not occur with the palladium membrane, allowing the system to maintain a stable Faradaic efficiency of around 50 percent over 12 hours.

"This result overcomes the longstanding limitation of polymer membranes, which struggled to simultaneously improve hydrogen ion transport and material blocking," Kim said. "Beyond ammonia synthesis, the technology can be applied to a wide range of electrochemical devices that require strict material separation, contributing to broader applicability."

The research, supported by the National Research Council of Science and Technology's Global TOP Strategic Research Institute program, was published in the June issue of the international journal Advanced Science.