W3 3-364

+49 441 798 3727

E-Mail: bjoern.mueller2@uol.de

Research field: 

• Electrochemical catalysts for NRR

Research:

• Synthesis of VO_xN_y
• Electrocatalytic activity for NRR

Surface engineered metal Nitrides for genuine nitrogen Reduction – SuNRed

Ammonia (NH₃) is indispensable for today’s society and modern agriculture. The Haber-Bosch process has yielded enormous benefits throughout the world. However, its reliance on fossil fuels requiring around 2% of the global energy consumption have propelled efforts to explore alternatives. In light of climate change, interest in electrocatalytically nitrogen reduction reaction (NRR) has exploded as one of the more promising since it can use renewable energy sources.

The importance of NRR has led to an increase in research activity with many publications based on novel materials for the electrochemical nitrogen reduction reaction (NRR). On metals, NRR is proposed to follow an associative Heyrovsky mechanism: N₂ adsorbs on the surface and is through an alternating or distal reaction pathway dissociated, reduced and protonated to form NH₃Calculations indicate that weak nitrogen-fixing surfaces are limited by nitrogen activation, while strongly nitrogen-fixing surfaces are limited by intermediate reaction species. The hydrogen evolution reaction (HER) is kinetically favoured over the NRR and occurs at almost identical reversible cell potential. This leads to a low NH3 production rate and a low Faraday efficiency (FE). The currently low efficiency leads to a susceptibility to contamination. This makes the detection of NRR activity complicated and requires N15 measurements.

In addition to expensive noble metal catalysts, transition metal nitrides (TMN) are considered to be promising catalysts. These follow the Mars van Krevelen mechanism (MvK), which is known from the oxidative dehydrogenation of propane to propene. In the case of NRR: The MvK mechanism proceeds through addition of protons and electrons (H⁺ and e^-) to a lattice nitrogen atom at the catalyst surface to produce NH_3. The produced NH₃ desorbs and leaves a N-vacancy in the nitride surface. By introducing the N₂ dissolved in the electrolyte, the vacancy is filled with a nitrogen atom, while the other nitrogen atom is also protonated to form a second NH₃.