A Binder-Free Electrode with 2D NiFe MOF/rGO as Bifunctional Catalyst for Rechargeable Zinc Air Battery.

Zinc air batteries (ZAB) are regarded as a promising candidate for the next generation energy storage device due to its low-cost, high-energy density, and eco-friendliness. However, precious materials such as Pt and RuO₂ are commonly used as catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and it is important to find alternative catalysts with high stability, low cost, and outstanding catalytic activity to replace the precious metals. Metal organic framework (MOF) is a promising catalyst candidate which has high surface area and abundant active sites to react with air. MOF generally exhibits relatively low conductivity, which lowers the Coulombic efficiency of the batteries. To solve this problem, MOF is commonly grown on conductive substrates such as Ni foam, reduced graphene oxide (rGO), carbon nanotube (CNT), etc. Previous studies have shown high OER performance of the NiFe bimetallic MOF, which is rarely used for ZAB. Also, catalysts are usually coated on the current collector using binder, which may block the mass transport and decrease the rate of electrochemical reaction. Herein, we used rGO as a conductive substrate for the growth of 2D NiFe MOF to prepare a binder-free electrode and studied the impact of precursor concentrations, reaction temperatures, and reaction times on the growth of 2D NiFe MOF. The OER and ORR performances of the binder-free electrode are remarkably higher than those of the electrodes containing binder. We anticipate that these results could open a new direction for the use of 2D NiFe MOF/rGO for zinc air batteries.