Emerging Electrochemical Routes for Green Ammonia Production: A Critical Review

Resumo

Ammonia (NH₃) is essential to the global chemical industry, primarily for fertilizer production, and is emerging as a promising carbon-neutral energy carrier. The conventional Haber–Bosch (HB) process, which supplies over 90% of global production, is energy-intensive and accounts for 1–2% of global energy use and up to 1.8% of CO₂ emissions. To meet carbon-neutrality goals, renewable electricity–based alternatives are under development. This review examines emerging electrochemical pathways for green ammonia synthesis, including electrochemical Haber–Bosch (e-HB), nitrogen reduction (eNRR), nitrate reduction (NO₃⁻RR), and nitrogen oxides reduction (NOₓRR). Advances (2020–2025) in catalysts, electrolytes, and cell design are highlighted, along with challenges such as low Faradaic efficiency (FE) and competition with hydrogen evolution. e-HB shows the highest maturity (FE up to 99%, TRL 8–9), while eNRR and Li-mediated NRR offer high selectivity but limited energy efficiency and scalability. NOₓRR stands out for its >90% selectivity and integration with waste treatment. Overall, e-HB remains the most viable near-term route, whereas eNRR and NOₓRR hold long-term potential for decentralized and sustainable production, contingent on efficiency gains, scalability, and supportive policy measures.