Axial coordinated iron-nitrogen-carbon as efficient electrocatalysts for hydrogen evolution and oxygen redox reactions

Designing highly active electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution and reduction reactions (OER and ORR) is pivotal to renewable energy technology. Herein, based on density functional theory (DFT) calculations, we systematically investigate the catalytic activity of iron-nitrogen-carbon based covalent organic frameworks (COF) monolayers with axially coordinated ligands (denotes as FeN4-X@COF, X refers to axial ligand, X= -SCN, -I, -H, -SH, -NO2, -Br, -ClO, -Cl, -HCO3, -NO, -ClO2, -OH, -CN and -F). The calculated results demonstrate that all the catalysts possess good thermodynamic and electrochemical stabilities. The different ligands axially ligated to the Fe active center could induce changes in the charge of the Fe center, which further regulates the interaction strength between intermediates and catalysts that governs the catalytic activity. Importantly, FeN4-SH@COF and FeN4-OH@COF are efficient bifunctional catalysts for HER and OER, FeN4-OH@COF and FeN4-I@COF are promising bifunctional catalysts for OER and ORR. These findings not only reveal promising bifunctional HER/OER and OER/ORR catalysts but also provide theoretical guidance for designing optimum iron-nitrogen-carbon based catalysts.