Interfacial Co–O–Fe bonding in novel amorphous NiCo-ZIF@MIL-100 as efficient active sites enabling electrocatalytic water oxidation

Abstract

Metal–organic frameworks (MOFs) have recently been reported as promising catalysts for the oxygen evolution reaction (OER). Hence, we chose hydroxyl-rich 2,5-dihydroxyterephthalic acid as the ligand to prepare a novel MIL-100 and wrapped it on the NiCo-ZIF-67 surface to obtain an amorphous hollow material (NiCo-ZIF-67@Fe-MIL-100, denoted as NiCo-ZIF@MIL). The composite material presents a low overpotential (η ≈ 139 mV @ 10 mA cm⁻²), a small Tafel slope (119 mV dec⁻¹) and great stability for the OER in 1 M KOH solution. Density Functional Theory (DFT) calculations show that the hydroxyl-rich structure, which accelerates OH⁻ transfer and promotes the formation of the Co–O–Fe bridge, effectively reduces the reaction energy barrier (from 2.67 eV for NiCo-ZIF-67 to 2.08 eV for NiCo-ZIF@MIL). This work provides an important reference for the development of double-MOF materials.