Towards sustainable electrochemical ammonia synthesis

Abstract

This perspective proposes feasible strategies to enhance the energy efficiency of electrochemical ammonia synthesis through electrocatalyst design and device optimization. Also, the challenges and prospects are evaluated for future development.

Ambient Electrochemical Ammonia Synthesis: From Theoretical Guidance to Catalyst Design

“…The U.S. Department of Energy has announced technical indicators for commercial electrochemical ammonia synthesis in 2016, including current density >300 mA cm −2 , Faradic efficiency >90%, energy efficiency >60%, and service lifespan >1000 h. Currently, the performance of electrochemical NRR from N 2 is far from meeting the commercial standard, thus a thorough investigation of the ammonia synthesis system is required, including electrocatalyst engineering (high activity, selectivity, and stability), electrolyte optimization (high Faradic efficiency), and electrocatalytic reaction cell design (high current density toward N 2 electroreduction). [ 115 ] Besides NRR, the electrochemical reduction of nitrate is an alternative approach for commercial ammonia production with extensive nitrogen‐containing industrial sewage, which significantly improves the ammonia yield rate and Faradic efficiency by transforming the gas‐liquid‐solid three‐phase reaction into a liquid‐solid two‐phase reaction.…”

Ammonia Energy: Synthesis and Utilization

“…Currently, widely accepted reaction mechanisms for the reduction of N 2 to NH 3 include dissociative mechanism, associative mechanism, and Mars-van Krevelen mechanism. In the electrochemical nitrogen reduction reaction process, the associative mechanism and Mars-van Krevelen mechanism may have higher energy efficiency and thermodynamic favorability than the dissociative mechanism, but depending on the adsorption characteristics of intermediates, different products (ammonia or hydrazine) may be generated …”

“…However, most NRR catalysts currently developed can only maintain stability for a few hours (<60 h) in stability tests, far from reaching commercial goals. According to the promotion strategies of industrial ammonia synthesis catalysts, selecting suitable supports and promoters can further improve the long-term stability of NRR electrodes and reduce their economic costs …”

Experimental discovery of novel ammonia synthesis catalysts via active learning

“…23 This has spurred research and development for sustainable synthesis of “green” ammonia to reduce the dependence on fossil fuels and mitigate climate change. 22,24,25…”