Advances in Electrochemical Ammonia Synthesis Beyond the Use of Nitrogen Gas as a Source

Abstract

Electrocatalytic reduction of dinitrogen has emerged as a new strategy for ammonia synthesis. Despite being environmentally benign and energy‐saving, it suffers from low conversion efficiency and short yield of ammonia because of the challenges of activating the inert N≡N bond at room temperature and atmospheric pressure. As a result of this, researchers proposed to reduce the nitrogenous species, one category of air and water pollutants, into valuable ammonia. Although remaining largely underexplored, this alternative approach shows promising efficiency for ammonia synthesis, while achieving high catalytic activity and selectivity remains challenging. In this Minireview, we summarize recent electrocatalytic performances of denitrification with selective formation to ammonia in terms of proposed active sites and reaction mechanisms. Additionally, we discuss the common issues in the state‐of‐the‐art experimental tests and highlight the breakthroughs via computational screening of electrode materials. The aim of this is to steer the future research directions in the field, which is aiming for an optimal catalytic system with higher activity and selectivity for electrocatalytic denitrification.

Cu clusters/TiO2−x with abundant oxygen vacancies for enhanced electrocatalytic nitrate reduction to ammonia

“…[10][11][12][13] And the relatively low bond energy of NO 3 À (204 kJ mol À1 ) makes it a favorable alternative for the next conversion to other nitrogen-containing species compared with N 2 . 14 Thus, the electrochemical nitrate reduction reaction (NO 3 RR) has emerged as an ingenious approach which can realize not only a feasible treatment of the nitrate contaminant but also a carbon-free synthesis of value-added ammonia under mild conditions, especially driven by renewable energy sources (Fig. 1).…”

“…Fig.4(a) 1 H-NMR spectra of electrolytes after the NO 3 RR at À0.75 V for 2 h using14 NO 3 À and 15 NO 3 À as N sources. (b) The standard curve of the integral area ( 14 NH 4 + -14 N/C 4 H 4 O 4 and 15 NH 4 + -15 N/C 4 H 4 O 4 ) against the concentration of 14 NH 4 + -14 N and 15 NH 4 + -15 N, respectively.…”

Efficient nitric oxide electroreduction toward ambient ammonia synthesis catalyzed by a CoP nanoarray

“…3,9 Notably, ambient NO reduction by electrocatalysis is being investigated as a sustainable approach for NO hydrogenation to other harmless or valuable nitrogen species, using only water and electrical energy. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] Among these products, NH 3 as a critical chemical for producing fertilizers and a potential carbon-free energy carrier with high energy density is a notable target molecule. 24,25 Although NH 3 can be produced by N 2 electroreduction, [26][27][28][29] it is extremely challenging from both thermodynamic and kinetic points of view since N 2 is chemically inert and poorly dissolves in water.…”

“…24,25 Although NH 3 can be produced by N 2 electroreduction, [26][27][28][29] it is extremely challenging from both thermodynamic and kinetic points of view since N 2 is chemically inert and poorly dissolves in water. 30 Encouragingly, NO with an unpaired electron in the 2p* antibonding orbital is a highly reactive nitrogen source, 16,31 thus boosting reaction kinetics toward efficient NH 3 synthesis. Moreover, the study of electrocatalytic NO reduction reaction (NORR) is of fundamental scientific interest as this environmentally important reaction is viewed as the first step toward understanding denitrification electrochemistry as well as developing sufficient NH 3 production technologies.…”

Nickel nanoparticles wrapped in N-doped carbon nanostructures for efficient electrochemical reduction of NO to NH3

“…8 Other than abundant N 2 , few nitrogen-based oxides such as NO 2 , N 2 O, and NO can be used as a source of NH 3 production via the electrochemical reduction method. 9 NO is one of the major by-products of the high-temperature combustion engines and coal cracking process. 10 Since the lower concentration in the atmosphere, NO is not considered hazardous to health.…”