Theoretical framework developed by University of Tartu researchers creates new opportunities for clean energy production
Estonian Research Council
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The AI image of the catalyst precision design was generated for illustrative purposes.
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An international study, involving researchers from the University of Tartu Institute of Chemistry, was recently published in Chemical Society Reviews. It provides the most comprehensive theoretical description to date of electrocatalysis and how its current limitations can be addressed. The research establishes a framework that helps design more efficient fuel cells, electrolysers, and other clean energy conversion devices.
Electrocatalysis is a process that enables to convert electrical energy into chemical energy and vice versa – for example, in hydrogen production or in fuel cells.
More specifically, the article explains so-called scaling relations. One of the authors of this study, Nadežda Kongi, Associate Professor in Colloidal and Environmental Chemistry at the University of Tartu, explained that these are the laws of nature that link the strengths of different reaction steps and determine how good a catalyst can ultimately be. A catalyst is a substance that accelerates chemical reactions without being consumed in the process. In electrocatalysis, it allows energy to be converted much more efficiently and with lower energy consumption.
The scaling relations have so far set limits to the efficiency of catalysts. “It means that when one reaction step is improved, another deteriorates. This, in turn, sets boundaries on how efficient the catalyst can be,” Kongi said. She explained that if it were possible to overcome scaling relations, hydrogen production, fuel cells, and battery performance could be made more efficient. This would be a major achievement in the energy sector, as these technologies play a key role in the green transition.
Five options to outsmart scaling relations
The authors of the article have created a theoretical framework for scientists, which integrates chemistry, energy, and geometry into a unified system. They define five general strategies that can be used to manipulate scaling relations in electrocatalysis: tuning, breaking, switching, pushing, and bypassing.
As an important new observation, Kongi pointed out that the geometry of the catalyst, for example, the arrangement of atoms, plays a significantly greater role than previously thought. “The distance between atoms on the catalyst’s surface determines both the rate and the pathway of the reaction,” Kongi said.
Two decades of knowledge combined into one
According to Nadežda Kongi, this research joins the theoretical and experimental understanding of the last twenty years into a single whole. “Our work provides a direction for developing a new generation of catalysts, which are crucial for creating clean energy solutions. The result is a practically applicable theory that guides the development of next-generation clean energy technologies.”
The article “Twenty years after: scaling relations in oxygen electrocatalysis and beyond” was published in Chemical Society Reviews, a top-tier journal of chemical sciences. The authors of the article from the University of Tartu are Nadežda Kongi, Associate Professor in Colloidal and Environmental Chemistry, and Vladislav Ivaništšev, Associate Professor in Physical and Electrochemistry.
https://pubs.rsc.org/en/content/articlehtml/2025/cs/d5cs00597c
Journal
Chemical Society Reviews
Method of Research
Literature review
Subject of Research
Not applicable
Article Title
Twenty years after: scaling relations in oxygen electrocatalysis and beyond
Article Publication Date
23-Nov-2025
Scientists unveil mechanism behind greener ammonia production
Cutting-edge X-ray techniques reveal how copper oxide catalyzes electrochemical reaction
Tokyo Metropolitan University
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(top) Proportion of copper (I) in copper oxide and copper (0) in metallic copper particles under different applied voltages. A more negative voltage correlates with the appearance of more Cu-Cu bonds. (lower left) Scanning electron microscopy (SEM) image of copper oxide particles mounted on carbon fiber. (lower mid) Production rate of nitrite and ammonium ions at different voltages, and efficiency of ammonium production. (lower right) SEM image of metallic copper particles on carbon fiber.
view moreCredit: Tokyo Metropolitan University
Tokyo, Japan – Researchers from Tokyo Metropolitan University have revealed how a catalyst in a promising chemical reaction for industry helps make ammonia, a major ingredient in fertilizer. Copper oxide is a key catalyst in the electrochemical nitrate reduction reaction, a greener alternative to the existing Haber-Bosch process. They discovered that copper particles are created mid-reaction, helping convert nitrite ions to ammonia. This insight into the underlying mechanisms promises leaps forward in developing new industrial chemistry.
As an ingredient in fertilizer, ammonia is an important chemical in industrial agriculture. The most widely adopted way to make ammonia is the Haber-Bosch process, where nitrogen and hydrogen are reacted at high temperature and pressure. This makes the process energy intensive; it is said to account for around 1.4% of global carbon dioxide emissions. As a chemical underpinning so much food production, the hunt is on for greener ways to make ammonia.
A team led by Professor Fumiaki Amano from Tokyo Metropolitan University has been studying the electrochemical nitrate reduction reaction, a promising alternative that can make ammonia from nitrates at room temperature and pressure. Electrochemical processes work by putting electrodes into a chemical mixture and applying a voltage to drive reactions. Despite numerous studies identifying specific reactions occurring at the electrodes as ammonia is produced, the exact mechanism has proven elusive.
Using cutting-edge techniques, the team gained unprecedented insight into how ammonia is produced in the presence of a copper oxide catalyst, one of the most effective electrocatalysts for this kind of reaction. They used operando X-ray absorption, a method combining insights into electronic states with knowledge of local bonding and structure. Mounting small particles of copper oxide onto carbon fibers, they succeeded in extracting how things change as the voltage is made more negative during the reaction. Under a positive voltage, it was shown that nitrate ions “passivate” the catalyst by absorbing onto them and preventing the conversion of copper oxide into metallic copper, making nitrite ions instead. As the voltage is made more negative, ammonia production is seen to ramp up abruptly. This happens at the same time as the appearance of metallic copper particles, evidenced by a dramatic increase in the number of copper-copper bonds. They discovered that the metallic copper is helping to add hydrogen to the nitrite ions to make ammonia.
The team’s measurements have shown how surface passivation affects the efficiency of the copper oxide catalyst, and how the production of metallic copper is crucial to the efficient production of ammonia. Their work highlights a broad class of strategies to optimize green ammonia production and design new electrochemical catalysts.
This work was supported by Tokyo Metropolitan University and the Tokyo Global Partner Scholarship Program and was based on results obtained from project JPNP14004 commissioned by the New Energy and Industrial Technology Development Organization (NEDO).
Journal
ChemSusChem
Article Title
Potential- and Time-Dependent Operando X-Ray Absorption Study of Cu2O Microcrystals Transformations during Nitrate Reduction to Ammonia
Efficient neutral nitrate-to-ammonia electrosynthesis using synergistic Ru-based nanoalloys on nitrogen-doped carbon
Shanghai Jiao Tong University Journal Center
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- A selective etching strategy was developed to construct a serious of RuM nanoalloys (M = Fe, Co, Ni, Cu) uniformly dispersed on porous nitrogen-doped carbon.
- It has been demonstrated that RuM nanoalloys would present the enhancement synergic effect on significantly improve the kinetic of *NO2 conversion to *HNO2, which achieves efficient neutral NH3 electrosynthesis at more positive potential.
Credit: Lisi Huang, Pingzhi Zhang, Xin Ge, Bingyu Wang, Jili Yuan*, Wei Li*, Jian Zhang*, Baohua Zhang, Ozge Hanay, Liang Wang*.
As fertilizer demand rises and nitrate pollution spreads, turning waste NO₃⁻ into green NH₃ has become urgent. Now, researchers from Guizhou University, Hunan Agricultural University and Shanghai University, led by Professor Jili Yuan, Professor Wei Li and Dr Liang Wang, report a selective-etching route to RuM (M = Fe, Co, Ni, Cu) nanoalloys that deliver 100 % Faradaic efficiency for neutral ammonia electro-synthesis at only −0.1 V vs RHE—outperforming most catalysts reported to date.
Why RuM Nanoalloys Matter
• Energy Efficiency: Alloying shifts the Ru d-band center upward, cutting the *NO2 → *HNO2 barrier to 0.46 eV and suppressing the hydrogen-evolution side-reaction that normally wastes electrons.
• In-Electrode Conversion: The porous nitrogen-doped carbon host ensures rapid proton/electron delivery, enabling 0.83 mg NH3 h-1 mgcat-1 at room temperature without external heat or pressure.
• Circular Nitrogen Economy: When assembled into a Zn–NO3⁻ battery the cathode produces 0.688 mg NH3 h-1 mgcat-1 while delivering 10.16 mW cm-2 power—turning nitrate remediation into a self-powered chemical plant.
Innovative Design and Features
• Nanoalloy Types: RuFe-NC, RuCo-NC, RuNi-NC and RuCu-NC (2–3 nm) are etched in molten urea/NaCl, yielding lattice-contracted (101) planes and uniform metal dispersion verified by HR-TEM, XRD and XPS.
• Functional Support: Chloride-assisted etching creates mesopores (20–50 nm) that triple the electrochemical surface area, while nitrogen dopants anchor alloys and lower the work function for faster electron injection.
• Device Architecture: Drop-cast on carbon paper, the catalysts serve as air-breathing cathodes in H-cells and coin-type Zn batteries, demonstrating scalability from 1 cm2 lab cells to 24 h continuous timers.
Applications and Future Outlook
• Multi-Level Selectivity: RuFe-NC reaches 100 % NH₃ FE at −0.1 V, while RuCo-NC maintains 98 % FE after 12 cycles and 96 % in 0.05 M NO3⁻—a tolerance window critical for real wastewater.
• Digital Logic Gates: The catalyst layer doubles as a low-potential sensor pixel; changes in NH3 FE are converted to voltage signals, offering a new route for nitrate-aware IoT nodes.
• Artificial Nitrogen Fixation: In-situ Raman, EPR and ATR-SEIRAS reveal *HNO₂ and *NH₂ intermediates, confirming a synergy-driven pathway that can be generalized to Co-, Ni- or Cu-based ternary alloys for urea, hydrazine or C–N bond construction.
• Challenges and Opportunities: The team highlights the need for roll-to-roll etching protocols, membrane-electrode assemblies that separate NH3 from the electrolyte, and life-cycle studies comparing energy input to Haber–Bosch. Future work will explore Ru–Co–Fe trimetallics and AI-guided composition tuning to push onset potentials above 0 V RHE.
This work provides materials chemists, environmental engineers and energy-storage designers with a universal alloying blueprint for turning nitrate waste into carbon-free ammonia while co-generating electricity. Stay tuned for more advances from Professor Jili Yuan, Professor Wei Li and Dr Liang Wang!
Journal
Nano-Micro Letters
Method of Research
Experimental study
Article Title
Efficient Neutral Nitrate to Ammonia Electrosynthesis Using Synergistic Ru Based Nanoalloys on Nitrogen Doped Carbon
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