A Theoretical Perspective for Ammonia Synthesis: Nitric Oxide or Nitrate Electroreduction?

Area of Science:

• Green Chemistry
• Electrochemistry
• Catalysis

Background:

• Conventional ammonia synthesis is energy-intensive and generates significant greenhouse gases.
• Electrocatalytic reverse artificial nitrogen cycle (eRANC) presents a sustainable alternative powered by renewable electricity.
• Research focuses on overcoming challenges in eRANC for efficient ammonia production.

Purpose of the Study:

• To theoretically and computationally evaluate challenges and opportunities in eRANC routes for ammonia synthesis.
• To compare different eRANC pathways, including electrochemical reduction of nitrate (eNO3RR), nitrite (eNO2RR), and nitric oxide (eNORR).
• To identify the most promising eRANC strategies for sustainable ammonia production.

Main Methods:

• Theoretical and computational analysis of eRANC pathways.
• Comparison of experimental results with theoretical predictions.
• Evaluation of nitrogen fixation routes: N2→NO→NH3 and electrochemical reduction of nitrogen oxides.

Main Results:

• The N2→NO→NH3 route shows high ammonia production efficiency, contingent on solving nitric oxide (NO) solubility issues in reactor design.
• Electrochemical reduction of nitrate (eNO3RR) is a viable, non-toxic alternative, benefiting from efficient solid-liquid interfaces.
• Low selectivity at low overpotentials remains a challenge for eNO3RR.

Conclusions:

• eRANC routes hold significant potential for efficient and sustainable ammonia production.
• Reactor design to manage nitric oxide solubility is crucial for the N2→NO→NH3 pathway.
• Further optimization is needed to improve selectivity in eNO3RR, especially at lower overpotentials.