For years, scientists have tried to make ammonia without relying on fossil-fuel-derived hydrogen, but they couldn’t figure out a way to move hydrogen ions into the reaction chamber without letting water come along with them.
A South Korean research team has now demonstrated a way around this problem using a dense palladium membrane that temporarily turns hydrogen ions into hydrogen atoms, moves them through the metal, and converts them back into ions on the other side.
This approach allowed the researchers to makeammonia using wateras the hydrogen source while keeping the water-sensitive reaction compartment largely dry.
“Our study introduces a new ion transport mechanism, expanding the design space for next-generation electrochemical systems that require strict compartmentalization,” the study authorsnote.
Why water is a problem
Electrochemical ammonia synthesis could use renewable electricity to produce ammonia from nitrogen and water rather than relying on fossil-fuel-derived hydrogen.
However, the researchers usedlithium-mediated nitrogen reduction, or Li-NRR, in which nitrogen reacts in a non-aqueous electrolyte.
Even small amounts of water entering this compartment can interfere with the lithium chemistry and form an unwanted solid-electrolyte interphase that eventually hurts the reaction.
The conventional solution is an ion-exchange membrane. These membranes contain water-filled pathways that allow protons to move between the two sides, but those same pathways can also allow water and other molecules to cross.
More from Science
See AllScience18-detector neutrino system probes rare particle interactions near nuclear reactorScienceA simple coating could make next-gen chips easier to manufactureScienceNew vertical quantum sensor works in magnetic fields 20,000 times stronger than EarthScience256-qubit quantum computer heads to Florida for research across health and energyScienceSuper rare radioactive element recovered at 99.93% purity from US nuclear wasteTrying to make them more selective generally compromises their ability to transport ions quickly, creating a long-standing conductivity-versus-selectivity trade-off. The researchers took a different approach, which is to make the metal itself carry the hydrogen.
The power of palladium
The researchers used a densepalladium foilas a membrane. When hydrogen ions reach one side, an applied electric field causes them to gain electrons and enter the palladium as hydrogen atoms.
Palladium can store hydrogen in its lattice, forming palladium hydride (PdHₓ), allowing those hydrogen atoms to diffuse through the metal. At the opposite surface, they are released as hydrogen ions again.
This hydrogen-storage property is crucial. Experiments with metals such as platinum and nickel did not produce the same proton-shuttling behavior because they cannot store hydrogen in the same way.
In other words, the membrane isn’t simply a dense metal barrier; its ability to temporarily absorb hydrogen is what makes the transport mechanism work.
“We demonstrate a unique proton shuttling mechanism of the bipolar palladium membrane that enables selective proton transport while suppressing molecular crossover,” the study authors added.
The researchers then connectedthe membraneto a continuous-flow ammonia electrolyzer. Water at the anode underwent the oxygen evolution reaction (OER), generating protons. The palladium membrane transported those protons into a separate, non-aqueous catholyte, where nitrogen underwent Li-NRR and was converted into ammonia.
This allowed water to provide the hydrogen source without exposing the lithium-mediated reaction to the aqueous compartment.
In a 12-hour continuous-flow test, the new system maintained its ammonia performance while the water content of the catholyte remained just 105 parts per million, far below previously reported water crossover through ion-exchange membranes.
“This achievement is significant in that our proposed novel ion-transport mechanism provides an effective solution to the crossover issue, which remains a primary barrier to implementing green ammonia synthesis through electrochemical devices,” Jae-Hyung Kim, one of the study authors and a senior researcher at Korea Institute of Energy Research (KIER), said.
The researchers also tested a less volatile diglyme-based electrolyte for longer operation. The system ran for approximately 79 hours, with ammonia Faradaic efficiency (the share of the electrical current that produced ammonia) still at 50 percent after 72 hours. The experiment eventually stopped when the catholyte gelled and blocked the flow channel.
A membrane with potential beyond ammonia
The results do not yet make the technology ready for industrialammonia production. The extended experiment revealed several obstacles, including catholyte degradation, changes to the palladium surface, and about 5 ppm of dissolved palladium after prolonged operation.
The researchers say future work will need to improve the electrolyte, flow-cell design, and stability of the palladium membrane.
Still, the significance of the work extends beyond ammonia. By moving hydrogen through a metal lattice instead of transporting hydrated protons through a water-filled polymer, the approach offers a new way to keep chemically incompatible environments separated inside electrochemical devices.
“The developed technology holds high potential for broader applications across various electrochemical devices that demand even stricter mass separation than ammonia synthesis,” Kim said.
Thestudyis published in the journalAdvanced Science.
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For years, scientists have tried to make ammonia without relying on fossil-fuel-derived hydrogen, but they couldn’t figure out a way to move hydrogen ions into the reaction chamber without letting water come along with them.
A South Korean research team has now demonstrated a way around this problem using a dense palladium membrane that temporarily turns hydrogen ions into hydrogen atoms, moves them through the metal, and converts them back into ions on the other side.
This approach allowed the researchers to makeammonia using wateras the hydrogen source while keeping the water-sensitive reaction compartment largely dry.
“Our study introduces a new ion transport mechanism, expanding the design space for next-generation electrochemical systems that require strict compartmentalization,” the study authorsnote.
Why water is a problem
Electrochemical ammonia synthesis could use renewable electricity to produce ammonia from nitrogen and water rather than relying on fossil-fuel-derived hydrogen.
However, the researchers usedlithium-mediated nitrogen reduction, or Li-NRR, in which nitrogen reacts in a non-aqueous electrolyte.
Even small amounts of water entering this compartment can interfere with the lithium chemistry and form an unwanted solid-electrolyte interphase that eventually hurts the reaction.
The conventional solution is an ion-exchange membrane. These membranes contain water-filled pathways that allow protons to move between the two sides, but those same pathways can also allow water and other molecules to cross.
More from Science
See AllScience18-detector neutrino system probes rare particle interactions near nuclear reactorScienceA simple coating could make next-gen chips easier to manufactureScienceNew vertical quantum sensor works in magnetic fields 20,000 times stronger than EarthScience256-qubit quantum computer heads to Florida for research across health and energyScienceSuper rare radioactive element recovered at 99.93% purity from US nuclear wasteTrying to make them more selective generally compromises their ability to transport ions quickly, creating a long-standing conductivity-versus-selectivity trade-off. The researchers took a different approach, which is to make the metal itself carry the hydrogen.
The power of palladium
The researchers used a densepalladium foilas a membrane. When hydrogen ions reach one side, an applied electric field causes them to gain electrons and enter the palladium as hydrogen atoms.
Palladium can store hydrogen in its lattice, forming palladium hydride (PdHₓ), allowing those hydrogen atoms to diffuse through the metal. At the opposite surface, they are released as hydrogen ions again.
This hydrogen-storage property is crucial. Experiments with metals such as platinum and nickel did not produce the same proton-shuttling behavior because they cannot store hydrogen in the same way.
In other words, the membrane isn’t simply a dense metal barrier; its ability to temporarily absorb hydrogen is what makes the transport mechanism work.
“We demonstrate a unique proton shuttling mechanism of the bipolar palladium membrane that enables selective proton transport while suppressing molecular crossover,” the study authors added.
The researchers then connectedthe membraneto a continuous-flow ammonia electrolyzer. Water at the anode underwent the oxygen evolution reaction (OER), generating protons. The palladium membrane transported those protons into a separate, non-aqueous catholyte, where nitrogen underwent Li-NRR and was converted into ammonia.
This allowed water to provide the hydrogen source without exposing the lithium-mediated reaction to the aqueous compartment.
In a 12-hour continuous-flow test, the new system maintained its ammonia performance while the water content of the catholyte remained just 105 parts per million, far below previously reported water crossover through ion-exchange membranes.
“This achievement is significant in that our proposed novel ion-transport mechanism provides an effective solution to the crossover issue, which remains a primary barrier to implementing green ammonia synthesis through electrochemical devices,” Jae-Hyung Kim, one of the study authors and a senior researcher at Korea Institute of Energy Research (KIER), said.
The researchers also tested a less volatile diglyme-based electrolyte for longer operation. The system ran for approximately 79 hours, with ammonia Faradaic efficiency (the share of the electrical current that produced ammonia) still at 50 percent after 72 hours. The experiment eventually stopped when the catholyte gelled and blocked the flow channel.
A membrane with potential beyond ammonia
The results do not yet make the technology ready for industrialammonia production. The extended experiment revealed several obstacles, including catholyte degradation, changes to the palladium surface, and about 5 ppm of dissolved palladium after prolonged operation.
The researchers say future work will need to improve the electrolyte, flow-cell design, and stability of the palladium membrane.
Still, the significance of the work extends beyond ammonia. By moving hydrogen through a metal lattice instead of transporting hydrated protons through a water-filled polymer, the approach offers a new way to keep chemically incompatible environments separated inside electrochemical devices.
“The developed technology holds high potential for broader applications across various electrochemical devices that demand even stricter mass separation than ammonia synthesis,” Kim said.
Thestudyis published in the journalAdvanced Science.
Get the latest in engineering, tech, space & science - delivered daily to your inbox.
By subscribing, you agree to our
Terms of Useand
PoliciesYou may unsubscribe at any time.
0
COMMENT
Subscribe to
Today!
Access to exclusive content, expert insights and a deeper dive into engineering and tech. No ads, no limits.
Explore Now!By
Rupendra BrahambhattRupendra Brahambhatt is an experienced writer, researcher, journalist, and filmmaker. With a B.Sc (Hons.) in Science and PGJMC in Mass Communications, he has been actively working with some of the most innovative brands, news agencies, digital magazines, documentary filmmakers, and nonprofits from different parts of the globe. As an author, he works with a vision to bring forward the right information and encourage a constructive mindset among the masses.
- 1Commercially viable fusion energy that delivers limitless clean power could be closer to reality
- 2Hafnium oxide stays stable at 1,562°F, boosting future capacitors, memory and cooling
- 318-detector neutrino system probes rare particle interactions near nuclear reactor
- 4Rugged 160W power supply handles -51°F to 140°F with 91% efficiency and IP67 rating
- 5Hydrogen fuel cell that works without air targets long-duration Moon missions
