Efficient Electrocatalytic N₂ Reduction on Three-Phase Interface Coupled in a Three-Compartment Flow Reactor for the Ambient NH₃ Synthesis

Abstract

The electrochemical N2 reduction reaction (eNRR) represents a carbon-free alternative to the Haber–Bosch process for a sustainable NH3 synthesis powered by renewable energy under ambient conditions. Despite significant efforts to develop catalyst activity and selectivity toward eNRR, an appropriate electrochemical system to obstruct the drawback of low N2 solubility remains broadly unexplored. Here, we demonstrate an electrocatalytic system combining a ruthenium/carbon black gas diffusion electrode (Ru/CB GDE) with a three-compartment flow cell, enabling solid–liquid–gas catalytic interfaces for the highly efficient Ru-catalyzed eNRR. The electrolyte optimization and the Ru/CB GDE development through the hydrophobicity, the Ru/CB loading, and the post-treatment have revealed the crucial contribution of interfacial N2 transportation and local pH environment. The optimized hydrophobic Ru/CB GDE generated excellent eNRR performance, achieving a high NH3 yield rate of 9.9 × 10–10 mol/cm2 s at −0.1 V vs RHE, corresponding to the highest faradaic efficiency of 64.8% and a specific energy efficiency of 40.7%, exceeding the most reported system. This work highlights the critical role of design and optimization of the GDE-flow cell combination and provides a valuable practicable solution to enhance the electrochemical reaction involving gas-phase reactants with low solubility.

Interfacial wettability and mass transfer characterizations for gas–liquid–solid triple‐phase catalysis

“…On the contrary, surface ligands modification could deliver hydrophobic properties with different degrees according to the ligand's composition and coverage. [ 39,40 ] For copper dendrite nanoarray electrode, 1‐octadecanethiol modification dramatically increased its CA from 17° to 153°. [ 41 ] The better hydrophobicity contributed to the formation of abundant triple‐phase interfaces and reduced CO 2 reduction overpotential.…”

“…On the contrary, surface ligands modification could deliver hydrophobic properties with different degrees according to the ligand's composition and coverage. [39,40] For copper dendrite nanoarray F I G U R E  Experimental and computational strategies applied for triple-phase wettability and mass transfer characterization in the order of spatial resolution and analysis accuracy. Micro-computed tomography image is reproduced with permission.…”

Electrochemical Ammonia: Power to Ammonia Ratio and Balance of Plant Requirements for Two Different Electrolysis Approaches

“…The faradaic efficiency will also determine the amount of hydrogen needed initially through the water electrolysis unit operation, as well as the post-processing at the cathode since a low faradaic efficiency will result in an increased concentration of hydrogen at the cathode requiring processing and separation from the ammonia product regardless of the arrangement. 60% has been chosen as an optimistic starting point for the system, but does have some literature precedent demonstrating it is possible to achieve (Cong et al, 2019;Wei et al, 2021).…”

“…While half-cell and small scale electrochemical ammonia reactors have been investigated in detail, little focus has been FIGURE 2 | (A) Reported performance from selected studies (Kordali et al, 2000;Han et al, 2018;Qin et al, 2018;Yang et al, 2018;Cong et al, 2019;Tao et al, 2019;Nazemi et al, 2020;Wei et al, 2021) of faradaic efficiency and ammonia formation rate, (B) theoretical full cell potential for reported literature half-cell and relationship to ammonia formation rate [y-axis same as (A)] (C) schematic representation of cell potential calculation in impact of ammonia formation overpotential in V vs NHE (normal hydrogen electrode) where E t, H2O and E t,H2 represent the theoretical potential for a reaction generating ammonia from either water or hydrogen as the proton source while E cell,H2 and E cell,H2O represent the measured potential required for the full cell arrangement which has 'z V' overpotential. on the practical application and process integration of these units.…”

Connection of Ru nanoparticles with rich defects enables the enhanced electrochemical reduction of nitrogen

“…As an important chemical in agricultural, plastic, and textile industries, ammonia (NH 3 ) has played a vital role in economic development. [1][2][3] Moreover, NH 3 can serve as a stable hydrogen (H 2 ) carrier, which acts as a crucial intermediate in clean energy conversion. Although the air contains 78% nitrogen, the highly stable triple bonds in N 2 exhibit a bond energy as high as 940 kJ mol À1 , resulting in a large energy barrier to activate the inert N 2 .…”