04/11/2025
Ammonia production by selective nitrogen reduction reaction
Electrocatalytic reduction of dinitrogen is a promising route for sustainable production of ammonia, although the selectivity challenge of the competing nitrogen reduction and hydrogen evolution reactions in aqueous electrolytes has not yet been solved.
Single-atom catalysts (SACs) offer the hope of bridging this gap because they exhibit unique electronic structure and reactivity in catalytic transformations compared to conventional bulk materials.
In a recent article in the journal Materials Today, in-situ formed single-atom centers on Molybdenum-based MXenes were shown to direct the selectivity to the preferred product ammonia by pulsing the electrochemical potential, thus offering a new route to overcome selectivity in nitrogen reduction.
Single atom catalysts (SACs) have emerged as a new class of materials to create active and selective catalysts. Most often, this implies anchoring a - usually precious - transition metal on some kind of support.
Researchers led by CENIDE member Prof. Dr. Kai S. Exner, head of the Department of Theoretical Catalysis and Electrochemistry at the University of Duisburg-Essen (UDE), recently reported that MXenes - a class of two-dimensional materials that were only discovered in 2011 - are able to form SAC-like sites in-situ upon application of an anodic electrode potential. This discovery can greatly simplify the production of single-atom catalysts and eliminates the need for expensive precious metals.
Now, it has been shown by Exner and coworkers that the SAC-like sites of MXenes can also efficiently catalyze nitrogen reduction under cathodic conditions. 'We concluded that Molybdenum-based MXenes have the potential to direct selectivity toward the preferred product ammonia,' explains Exner. To reach this conclusion, Exner and his team modeled electrochemical pulse experiments, in which the applied electrode potential is circulated between a working potential and a resting state.
For archetypal SAC catalysts, the application of pulse experiments is critical because the SAC sites are often unstable in an electrochemical environment due to metal dissolution. A different situation is encountered with the in-situ formed SAC-like sites of MXenes: these sites are regenerated while the potential is maintained at an anodic resting state, whereas the conversion of nitrogen to ammonia takes place during the cathodic pulse.
"Our work provides a new line of thought of how to solve the associated challenges of low Faradaic efficiency in ammonia formation", concludes Exner. Further work is needed to develop smart materials with in-situ formed SAC-like sites coupled with electrochemical pulse experiments. These efforts could also be useful for catalytic processes beyond nitrogen reduction and relevant for energy conversion and storage.
Source: Center for Nanointegration Duisburg-Essen (CENIDE)