The coordination structure and the hydrophilic and hydrophobic microenvironment on the surface jointly improve the electrocatalytic performance of monoatomic particles.

First authors: Sun Jing, Xue Hui.

Correspondent: Zhang *, Wu Limin *, Qin Wang *

SETTING: Inner Mongolia University

Research background

In recent years, monoatomic catalysts have become a research hotspot because of their high metal utilization rate, unique structure and electronic characteristics. Due to the strong interaction between a single atom and its coordination atom, the local coordination environment of SACs, including the coordination number and the type of coordination atom, will have an important impact on the catalytic activity and stability of the single atom. In addition, in the process of electrocatalytic reaction, reactants, intermediates and products all diffuse to the catalyst surface or electrolyte through the interface microenvironment, and the interface microenvironment structure of the catalyst has a very important influence on its internal reaction and transfer process.

Article introduction

In view of this, the team of professors from Inner Mongolia University cooperated with researcher Zhang from Dalian Institute of Chemistry to develop a unique iron-based monoatomic catalyst with double coordination of N and P, which showed excellent electrocatalytic performance for oxygen reduction. In this paper, through the treatment of ionic liquids, secondary P atoms are introduced into the Fe-N4 structure to adjust the coordination structure and local electronic structure of Fe-N4 species. The introduction of ionic liquid can not only enhance the hydrophobicity of the catalyst surface, form an ionic liquid protective layer, effectively adjust the microenvironment of the catalyst reaction interface, but also significantly improve the catalytic activity and stability.

Figure 1. Synthesis methods and forms of catalysts.

The main points of this article

Point 1: The ORR activity can be effectively improved by adjusting the coordination environment of a single atom through heteroatom doping. At present, the common strategy to synthesize monoatomic atoms is to pyrolyze heteroatom-doped MOF precursors at high temperature. This method may affect the formation of single atoms, and its flexibility and universality are seriously restricted by pyrolysis temperature and metal loading. In this study, a simple ionic liquid treatment method was developed. The Fe-N4 SAC catalyst was immersed in hydrophobic ionic liquid, and the coordination environment of SACs was successfully adjusted to form Fe-N2P unsaturated coordination structure.

Figure 2. Analysis of coordination structure, bonding and vacancy of catalyst.

Point 2: The high solubility of O2 in ionic liquid layer is beneficial to drive O2 to diffuse to the active site of the catalyst, improve the utilization rate of the active site, and thus improve the ORR performance. Ionic liquid phase can replace water phase as reaction medium, which can protect the catalyst from external oxidation or poisoning and effectively improve the stability of the catalyst.

Figure 3. Study on electrocatalytic performance of catalyst.

Point 3: The calculation results of density functional theory show that the mixed coordination of Fe-N2P and the formation of N vacancy make more electrons concentrate around the active site of Fe single atom, which is beneficial to the formation of OOH* intermediates, thus improving the reaction kinetics of the catalyst.

Figure 4. Theoretical calculation of catalyst.

Article link

Research group website: /groups/ Qin Wang/