Electrochemical ammonia synthesis: Mechanistic understanding and catalyst design

NH3 production is dependent on the century-old Haber-Bosch process, which is energy and capital intensive and relies on H-2 from steam reforming, hence, contributing to greenhouse gas emissions. Electrochemical NH3 synthesis can be realized by reaction of N-2 and a proton source under mild conditions powered by renewable electricity, which offers a promising carbon-neutral and sustainable strategy. However, N-2 has remarkable thermodynamic stability and requires high energy to be activated. Implementation of this "clean'' NH3 synthesis route therefore still requires significant enhancement in energy efficiency, conversion rate, and durability, which is only achievable through the design of efficient electrocatalysts. This article provides a timely theoretical and experimental overview of recent advances in the electrocatalytic conversion of N-2 to NH3 underlining the development of novel electrocatalysts. Advances of in situ and operando studies for mechanistic understanding of the reaction and the main challenges and strategies for improving electrocatalytic N-2 reduction are highlighted.