Layer structured materials for ambient nitrogen fixation

Recently, the research of nitrogen fixation at ambient conditions has attracted wide attention due to its potential of relatively low energy consumption and environmental friendliness. The rational design of catalysts is one of the pivotal factors to achieve high nitrogen fixation efficiency. On account of the large exposed surfaces areas, continuous conducting pathways, open shortened diffusion distances, stable in−plane chemical bonds, expanded interlayer spacing, as well as weak van der Waals interaction within layers, it has been an extensive option to choose layer structured materials as potential nitrogen fixation materials in recent years. Notably, compared to other nitrogen − fixation catalysts, layered materials not only reduce the migration distances between the reaction interface and charge carriers, inhibiting the possibility of charge carrier recombination, but also enrich low–coordinated surface atoms. Moreover, most of them belonging to p–block materials show excellent hydrophobicity, strong chemical interaction with N2 molecules, and low cost, which make them promising candidates for effectively limiting hydrogen evolution. Despite the favorable advantages of the layer structured materials on nitrogen fixation, more challenges and opportunities have arisen for the exploitation and fabrication of novel layered materials with unique properties and specific functions to achieve high selectivity and high yield. Up to now, although the research scope of layered structured materials has been expanded gradually and their structural feature supply an alternative way of improving nitrogen fixation properties while puting forwarding relative binding and effect mechanisms, the adsorption and catalysis mechanisms of these materials in nitrogen fixation are still controversial due to the lack of in situ/operando characterization and neglect of the complex reaction system and environment factors. In this review, we firstly summarize typical layered materials used in nitrogen fixation and categorize them into metal–containing and metal–free materials. The former includes transition metal dichalcogenides, MXenes, and metal–organic frameworks, as well as other emerging advanced materials such as layered double hydroxides, bismuth–based layered materials while the latter includes graphene, graphitic carbon nitride sheet, black phosphorus, boron–based layered materials, and covalent organic framework. Secondly, we briefly introduce the structural characteristics and the recently reported synthesis strategies based on the typical layer structured materials, and discuss their structure–performance relationship. Thirdly, insights into possible pathways, strategies, and products of nitrogen fixation are discussed to provide layer structured materials with corresponding suitable avenues in the future. More importantly, their up–to–date progress applied in photocatalytic, electrocatalytic, and photoelectrocatalytic nitrogen reduction reactions will be systematically presented, and the concomitant obstacles are also revealed. At last, the strategies, challenges, and prospects for future developments of nitrogen fixation materials at room temperature and pressure are summarized.