Selective NO_x^– Electroreduction to Ammonia on Isolated Ru Sites

Abstract

Nitrate and nitrite (NO x –) are widespread contaminants in industrial wastewater and groundwater. Sustainable ammonia (NH3) production via NO x – electroreduction provides a prospective alternative to the energy-intensive industrialized Haber–Bosch process. However, selectively regulating the reaction pathway, which involves complicated electron/proton transfer, toward NH3 generation relies on the robust catalyst. A specific consideration in designing selective NO x –-to-NH3 catalysts should meet the criteria to suppress competing hydrogen evolution and avoid the presence of neighboring active sites that are in favor of adverse N–N coupling. Nevertheless, efforts in this regard are still inadequate. Herein, we demonstrate that isolated ruthenium sites can selectively reduce NO x – into NH3, with maximal Faradaic efficiencies of 97.8% (NO2 – reduction) and 72.8% (NO3 – reduction) at −0.6 and −0.4 V, respectively. Density functional theory calculations simulated the reaction mechanisms and identified the *NO → *NOH as the potential rate-limiting step for NO x –-to-NH3 conversion on single-atom Ru sites.

Progress and prospects of electrochemical reduction of nitrate to restore the nitrogen cycle

“…[71][72][73] Consequently, single-atom catalysts have found widespread applications in nitrate reduction, beneting from their advantageous characteristics. Ke et al 74 developed atomically dispersed Ru catalysts supported on carbon nitride (Ru SA-NC). In comparison to Ru nanoparticles (NPs), the isolated Ru single-atoms demonstrated exceptional performance in nitrate reduction, achieving a remarkable nitrate removal efficiency of 78%.…”

Recent Advances in Electrocatalysts for Sustainable Electrosynthesis of Ammonia and Urea from Ambient Nitrite Reduction and C–N Coupling

“…Inspired by the rapid development of SACs with maximum atom utilization, superior activity, and distinct selectivity in the electrocatalytic fields, Ke et al synthesized nitrogenated carbon loaded with atomically dispersed Ru sites (Ru SA-NC) for NO 2 RR (Figure 6i). 144 Compared with Ru nanoparticles (Ru NPs), single-atom Ru sites featuring ideal electronic structure and coordination environments deliver superior activity and selectivity for NO x − reduction and exhibit higher NO 2 − reduction activity than NO 3 − reduction as suggested by DFT calculations (Figure 6j,k). Experimentally, the Ru SA-NC catalyst shows an FE of 97.8% and an NH 3 yield of 0.69 mmol h −1 cm −2 at −0.4 V vs RHE (Figure 6l,m).…”

“…(m) Ammonia yield rates and FEs during five successive electrolysis cycles. Reprinted from ref . Copyright 2023 American Chemical Society.…”

Sustainable Ammonia Electrosynthesis from Nitrate Wastewater Coupled to Electrocatalytic Upcycling of Polyethylene Terephthalate Plastic Waste

“…In conventional aqueous-based overall nitrate reduction electrolyzer, two half-reactions are involved: the NO 3 RR at the cathode and the oxygen evolution reaction (OER) at the anode. , Of these, the anodic OER is a relatively complicated four-electron transfer process with intrinsically sluggish reaction kinetics and high theoretical potential (1.23 V vs reversible hydrogen electrode, RHE), leading to low energy conversion efficiency and high energy consumption during nitrate upcycling. , Simultaneously, the market value of as-generated oxygen is not ideal . An effective strategy for improving energy efficiency and reducing energy input in the overall electrocatalytic process is to replace OER with other organic oxidation reactions that are thermodynamically more favorable, possess lower electrode potential, and can produce high value-added anode products. , Plastics are widely applied in various industries due to their advantages of lightweight, chemical stability, and low cost.…”