Controllable amorphization engineering on bimetallic metal–organic frameworks for ultrafast oxygen evolution reaction

Deliberate tailoring of the metal–organic frameworks (MOFs) composition and structure could provide limitless flexibility for the development of highly efficient electrocatalysts toward oxygen evolution reaction (OER). However, the changes in crystallinity of MOFs related to the composition manipulation have seldom been explored for the catalytic OER activity. Herein, we realize the controllable amorphization engineering on CoxFey-MOFs from crystalline to amorphous state by deliberately adjusting the ratio of Co/Fe precursors introduced within the MOFs. While crystalline MOFs are formed with initially dominating the contribution of Co ions, amorphous MOFs are obtained when the amount of Fe ions exceeds 60%. Theoretical findings propose that the defects formation energies of CoxFey-MOFs can be dramatically reduced with the decrease of Co/Fe ratio, which make the long-range disorder structure be readily formed with abundant defects. The disorder structure and the tunable ratio of Co/Fe enable to endow the bimetallic CoxFey-MOFs with abundant active sites and fast charge transfer, thus boosting the catalytic activity towards OER. It is found that the optimized amorphous Co4Fe6-MOF can deliver the current density of 10 mA cm−2 only at a low overpotential of 241 mV with extremely small Tafel slope of 30.1 mV dec-1. The present work enriches the understanding on the crystalline-to-amorphous transformations and sheds light on the way for the applications of amorphous MOFs nanomaterials in water splitting field.