Metal complexes of bipyridine-functionalized covalent organic frameworks as efficient electrocatalysts for oxygen evolution reaction

Electrocatalytic water splitting is considered a clean and practic al method for producing energy.In this study,COF-Bpy,a bipyridine-functionalized covalent organic framework(COF),was prepared via post-synthetic modification,after which electrocatalysts for the oxygen evolution reactions(OER)were formed through coordination to single-or double-transition metals(Fe,Co,Ni,FeCo,FeNi or CoNi).COF-Bpy@FeNi delivered the best OER performance among the studied electrocatalysts,with an overpotential of 399 mV at 10 mA·cm^(-2)in an alkaline electrolyte(1.0 mol·L^(-1)KOH aqueous).Notably,the electrocatalytic performance of COF-Bpy@FeNi showed slight degradation during durability testing,which is ascribable to its irreversible benzoquinoline structure and strong metal coordination.As expected,COF-Bpy@FeNi exhibited a low overpotential of 347 mV at a turnover frequency(TOF)of 0.1 s^(-1),which suggests that COF-Bpy@FeNi possesses excellent intrinsic electroc atalytic OER activity.Finally,density functional theory(DFT)calculations reveal that the Ni site plays a major role,while the Fe site adjusts the electronic structure of the Ni ions,which rationalizes the excellent OER properties of COF-Bpy@FeNi.This study not only provides a simple and efficient method for complexing COFs with transition metals,but also offers a novel strategy for designing porous organic polymer electrocatalysts.