Graphene Derivatives and Graphene Composite Electrocatalysts for N₂ Reduction Reaction

Abstract

Ammonia (NH3) plays a key role in human society. The conventional Haber–Bosch process under high temperature and pressure is widely used to synthesize NH3, resulting in huge energy costs and serious environmental issues. At present, the electrochemical conversion of nitrogen (N2) and water (H2O) into NH3 at ambient conditions is considered as a promising and alternative method, and electrocatalysts are critical for nitrogen reduction reaction (NRR) to realize NH3 synthesis. Graphene as an emerging 2D material has received significant attention in electrocatalysis NRR due to its unique properties such as high conductivity, specific surface area, a distinct 2D structure, and simplicity for modification. Herein, the electrochemical basis for NRR is provided including reactions in the NRR system, NRR mechanisms, criteria for NRR electrocatalysts (density functional theory and experiments), and verifying the nitrogen source and electrolytes. Then, the effect of doping (nonmetallic elements and single/dual metal atoms) and intrinsic defects on the NRR performance for graphene derivatives is reviewed, and the graphene composite electrocatalysts for NRR are summarized. Furthermore, deep sights and existing issues toward the further development of graphene derivatives and graphene composite electrocatalysts on NRR are discussed.

Recent advances in material design and reactor engineering for electrocatalytic ambient nitrogen fixation

“…For accurate quantification, external and internal standard methods can be used. The former uses standard solutions containing different concentrations of 14 NH 3 or 15 NH 3 (such as 14 NH 4 Cl or 15 NH 4 Cl) and draws the standard curve using the corresponding peak area. The latter is the quantitative addition of internal standard compounds to 14 NH 3 or 15 NH 3 samples.…”

“…whereas the electrochemical process requires a fixed potential to drive the conversion of N 2 to NH 3 , which makes it superior to the photochemical process. 14,15 However, low NRR selectivity and weak catalytic activity in the system limit the application of electrocatalytic synthesis in the production of NH 3 from N 2 and H 2 O. 16 The synthesis of NH 3 in electrochemical cells has a variety of potential benefits, including the ability to work at low temperatures, decentralizing NH 3 production using renewable energy sources, use of water as a hydrogen source, and the ability to completely exploit membrane electrode assemblies developed for energy storage devices.…”

Green Synthesis of Nitrogen‐to‐Ammonia Fixation: Past, Present, and Future

“…Important milestones in the research and development of this emerging field are highlighted in Figure . 2. [21][22][23][24][25][26] The research activities in the green conversion of N 2 to NH 3 can be constructively divided into three major groups: (i) the selectivity and adjustment of various catalysts, [27][28][29][30] (ii) the type of electrolyte/solvent system, [23] and (iii) the investigation of reaction conditions. [26,31] Recently much effort and progress has been made in green NH 3 synthesis using photocatalytic and (photo-)electrochemical approaches, meanwhile, some questions that the detected NH 3 is derived from the extraneous contamination rather than N 2 have arisen among some researchers in this field (Figure .…”

Self‐Supporting Electrodes for Gas‐Involved Key Energy Reactions

“…Electrochemical reduction of nitrogen is one of the potential strategies for the production of ammonia. [235,236] It should be noted that with the extremely strong triple bond in a nitrogen molecule, it is very difficult to obtain ammonia relative to the HER and OER production. On the basis of the different properties of catalysts, the possible reaction mechanisms of electrochemical nitrogen [213] Copyright 2020, Wiley-VCH.…”