Self-supported three-dimensional macroporous amorphous NiFe bimetallic-organic frameworks for enhanced water oxidation

Amorphous materials are attractive for their “dangling bonds” and more active than the crystalline counterparts in many applications. Metal-organic frameworks (MOFs) have emerged as an exciting class of porous materials that received considerable interest in many research fields including electrocatalysis. However, amorphous MOFs have been rarely investigated directly as electrocatalysts compared with crystalline ones. In this study, amorphous bimetallic NiFe-MOF with a three-dimensional (3D) macroporous structure was successfully prepared on nickel foam via one-step bottom-up solvothermal reactions and exhibited the potential as efficient OER (oxygen evolution reaction) electrocatalysts. The prepared self-supporting electrode can provide a 10 mA cm−2 current density at an overpotential of 211 mV, as well as remarkable operational stability and nearly 100% Faraday efficiency. This performance is superior to most previously reported MOF electrocatalysts and well exceeds the corresponding crystalline NiFe-MOF. The greatly enhanced activity of amorphous NiFe-MOF was originated from the abundant active metal sites and improved charge transfer due to unsaturated coordination as well as increased contact area with the electrolyte and good mass transfer benefitting from the unique 3D macroporous structure. This work will stimulate widespread interest in the study of amorphous MOF nanostructures with abundant active sites for improved electrocatalysts and beyond.