Towards sustainable ammonia synthesis: a critical review of alternative methods to the Haber-Bosch process

Abstract

Ammonia is indispensable for global agriculture, industry and its emerging role as an energy carrier. However, its production remains dominated by the century-old Haber-Bosch process which consumes 1-2% of the world’s total energy and contributes to 1.5-2% of global CO2 emissions. This review analyses the current industrial standard and its limitations, and assesses the technical feasibility and potential of alternative pathways. These include electrocatalytic nitrate reduction, direct electrochemical nitrogen reduction, a renewable-powered Haber-Bosch process, photocatalytic nitrogen reduction and biological nitrogen fixation. Such approaches operate under milder conditions, utilizing renewable energy to reduce the reliance on fossil fuels. Although no single technology can yet fully replace the conventional Haber-Bosch process, advancements in catalyst designs, process engineering and renewable energy integration could enable large-scale green ammonia production in the future. Such developments would enhance global food security, reduce the environmental impact of carbon emission and energy consumption, and would contribute significantly to achieving climate targets.