Nitrogen electrochemically reduced to ammonia with hematite: density-functional insights

Area of Science:

• Electrochemistry
• Materials Science
• Computational Chemistry

Background:

• Recent advancements propose synthesizing ammonia (NH3) via steam electrolysis using nano-iron(III) oxide (Fe2O3) suspensions.
• This method offers a promising route towards a carbon dioxide (CO2)-free and cost-effective ammonia industry.

Purpose of the Study:

• To elucidate the atomistic mechanisms of nitrogen (N2) reduction during electrochemical ammonia synthesis.
• To investigate the N2 reduction process on hematite (Fe2O3) surfaces at the density-functional theory (DFT) level.

Main Methods:

• Density-functional theory (DFT) calculations were employed to model the electrochemical formation of NH3.
• Both associative and dissociative reaction mechanisms for N2 reduction were considered.
• The energy landscape and required applied bias for proton transfer steps were analyzed.

Main Results:

• A viable reaction pathway for ammonia synthesis on the hematite(0001) surface was identified.
• An applied bias of -1.1 V was found to be necessary for downhill proton transfer processes.
• The initial protonation of adsorbed molecular nitrogen was determined to be the most energy-intensive step.

Conclusions:

• The computational findings align well with experimental electrolysis potentials that initiate electric current.
• This study provides crucial atomistic insights into the electrochemical reduction of N2 to NH3 on Fe2O3 surfaces.
• The identified reaction pathway and energy requirements offer guidance for optimizing CO2-free ammonia production technologies.