Advanced Ruthenium-Based Electrocatalysts for NOx Reduction to Ammonia

Ammonia (NH3) is widely recognized as a crucial raw material for nitrogen-based fertilizer production and eco-friendly hydrogen-rich fuels. Currently, the Haber-Bosch process still dominates the worldwide industrial NH3 production, which consumes substantial energy and contributes to enormous CO2 emission. As an alternative NH3 synthesis route, electrocatalytic reduction of NOx species (NO3-, NO2-, and NO) to NH3 has gained considerable attention due to its advantages such as flexibility, low power consumption, sustainability, and environmental friendliness. This review timely summarizes an updated and critical survey of mechanism, design, and application of Ru-based electrocatalysts for NOx reduction. First, the reason why the Ru-based catalysts are good choice for NOx reduction to NH3 is presented. Second, the reaction mechanism of NOx over Ru-based materials is succinctly summarized. Third, several typical in situ characterization techniques, theoretical calculations, and kinetics analysis are examined. Subsequently, the construction of each classification of the Ru-based electrocatalysts according to the size of particles and compositions is critically reviewed. Apart from these, examples are given on the applications in the production of valuable chemicals and Zn-NOx batteries. Finally, this review concludes with a summary highlighting the main practical challenges relevant to selectivity and efficiency in the broad range of NOx concentrations and the high currents, as well as the critical perspectives on the fronter of this exciting research area.