Strategies in cell design and operation for the electrosynthesis of ammonia: status and prospects

Abstract

Ammonia (NH₃) electrosynthesis directly from nitrogen at ambient temperature and pressure is a thermodynamically feasible yet a kinetically challenging route to address the energy and environmental concerns associated with the well-established Haber–Bosch process. Despite growing interest and progress boosted by innovative electrocatalyst development, this emerging field is still plagued by insufficient catalytic activities and low faradaic efficiencies to reach commercial relevance. Electrolytic cell design and operational conditions are two overlooked aspects, which offer important approaches along with advanced electrocatalysts to produce NH₃. This work provides a thorough and critical overview of a large number of published electrocatalysis results highlighting the analytical uncertainties associated with N-containing contaminants. Furthermore, it systematically summarizes the electrochemical cell designs, the choices of cell components, and key operational parameters for NH₃ electrosynthesis. Strategies to promote nitrogen mass transfer while controlling the proton access near reaction sites are highlighted, which include using gas-phase reactors, selecting a suitable membrane/electrolyte configuration, engineering the electrode's (electro)chemical and physical properties, and adjusting the operating conditions and flow configurations under kinetic and mass transfer limitation considerations.