Abstract:

The development of highly efficient and low-cost electrocatalysts is important for both hydrogen- and carbon-based energy technologies. The electronic structure and coordination features, particularly the coordination environment and the amount of low-coordination atoms, of the catalyst are key factors that determine their catalytic activity and stability in a particular reaction. The regulation and rational design of catalytic materials at the molecular and atomic levels are crucial to achieving precise chemical synthesis at the atomic scale. Recently, significant efforts have been made to engineer coordination features and electronic structures by reducing the particle size, tuning the composition of the edges, and exposing specific planes of crystals. Among these representative strategies, the methods based on the confinement effect are most effective for achieving precise chemical synthesis with atomic precision at the molecular and atomic levels. Under molecular or atomic scale confinement, the physicochemical properties are largely altered, and the chemical reactions as well as the catalytic process are completely changed. The unique spatial and dimensional properties of the confinement regulate the molecular structure, atomic arrangement, electron transfer, and other properties of matter in space. It not only adjusts the coordination environments to control the formation mechanism of active centers, but also influences the structural and electronic properties of electrocatalysts. Therefore, the adsorption of catalytic intermediates is altered, and consequently, the catalytic activity and selectivity are changed. In a confined reaction, usually in suitable nano-reactors, the physicochemical properties of reaction products, such as the state of matter, solubility, dielectric constant, and molecular orbital, are finely modulated. Thus, the catalysts produced by confinement significantly differ from those produced in an open system. For example, atomic-layered metals with low coordination can be produced in a two-dimensional confined space. The nitrogen configurations of nitrogen-doped graphene can also be regulated in two-dimensional or three-dimensional confined systems. Herein, the confinement-induced methods, specifically the method used for atomic regulation, are reviewed, such as the control of molecular configuration, the modification of the coordination structure, and the alteration of charge transfer. Applications in the field of fuel cells and material energy conversion are also reviewed. In the next stage, it is important to conduct in-depth investigations of the constructed confinement environment by selecting different substrates for the regulation and rational design of confined catalytic materials. The investigation of the derived properties of the catalyst after release from the confinement is crucial for the development of uncommon catalytic properties.

Key words: Confinement, Electrocatalyst, Electronic structure, Coordinate feature, Molecular configuration