Double Perovskite-Type (NH4)3FeXCo1-XF6 Electrocatalyst for Efficient Water Oxidation

It is of great significance for the development of efficient nonprecious electrocatalysts to boost the sluggish oxygen evolution reaction (OER). Here, we propose that Fe cation-bound ammonium fluoride (NH4F) can serve as a structure-directing agent to replace the imidazole ligand in zeolitic imidazolate framework-67 (ZIF-67), thereby forming a bimetallic fluoride with a double-perovskite structure [(NH4)3FexCo1-xF6, NFCF]. This NFCF electrocatalyst has a unique open-frame structure, which can provide rich active sites, a large electrochemical surface area, and extra electrolyte diffusion channels. The calculation results of density functional theory (DFT) reveal that this NFCF electrocatalyst has a lower energy barrier of OOH* to O2 than that of the perovskite-type fluoride. The co-existence of Co and Fe in the NFCF is beneficial to weaken the OH* adsorption energy during OER catalysis. At current densities of 10 and 100 mA cm-2, the NFCF electrocatalyst only needs a low overpotential of 243 and 360 mV, respectively. In addition, it can maintain an operating stability for up to 100 h at a constant current of 100 mA cm-2. This study will help us to develop double-perovskite electrocatalysts for efficient water oxidation.