Pyrolysis-free ZIF-67-graphene oxide composite films for improving the sluggish kinetics of the oxygen reduction reaction in a neutral medium

Abstract

In this work, a rational design of an efficient electrocatalyst containing metal–nitrogen–carbon linkage (M–N–C) has been demonstrated for the oxygen reduction reaction (ORR) in a neutral medium. M–N–C composite materials comprising transition metals are the most competitive catalysts for the ORR and have drawn extensive research interest due to their enhanced activity and low-cost. Herein, a facile electrochemical synthetic strategy is designed for the fabrication of free-standing electrocatalysts [abbreviated as TC-GO (GO-ZIF-67) and TC-GO (GO-ZIF67-Fe)] containing graphene oxide as a base layer and a composite layer consisting of GO and ZIF-67 (with and without Fe) on a Toray carbon (TC) electrode and demonstrated their application for the ORR at a neutral pH. The fabricated electrocatalysts display a large electrochemically active surface area (2.37 cm²) and good electrical conductivity and possess ideal structural and compositional features required for the ORR when compared with its parent material (ZIF-67). This work highlights the efficiency of the electrochemical method in preparing the freestanding films of a composite material consisting of GO and ZIF on a TC electrode rather than the usually followed chemical methods of synthesizing ZIF or its composites followed by high temperature pyrolysis. Such processes generally are energy intensive and affect the structural stability of the framework that also needs to be drop-cast onto the electrode surface. The electrochemically prepared composite material displays good electrochemical activity towards the ORR (E_onset = 0.654 V vs. RHE and E_1/2 = 0.361 V vs. RHE) at neutral pH. Thus, the proposed strategy has the potential to serve as a platform for designing non-precious, highly electroactive catalysts under neutral conditions with desirable activity towards the ORR which can be used in energy conversion technologies including fuel cells.