High performance oxygen reduction and evolution reactions by graphitization of nickel –cobalt framework system

Abstract

This study presents the successful synthesis of metal-organic frameworks (MOFs) via a simple one-pot method, followed by pyrolysis at 1000 °C to be used in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). A study utilizing various techniques, including field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD), investigated the properties of NiCo-MOF and its individual components before and after pyrolysis.The pristine MOFs exhibited limited electrochemical stability for both ORR and OER, while the pyrolyzed MOFs demonstrated a significant enhancement and excellent long-term stability in OER and ORR performance in alkaline media. Notably, the OER performance rivaled that of the benchmark IrO2 electrocatalyst, with similar onset potentials (1.48 V for IrO2, 1.52 V, 1.56 V, and 1.59 V for pyrolyzed NiCo-MOF, Co-MOF, and Ni-MOF, respectively). Furthermore, the pyrolyzed MOF catalysts displayed promising ORR activity in a 0.1 M KOH solution under O2 saturation, as evidenced by their onset potentials (around 0.615 V, 0.63 V, and 0.7 V vs. RHE) and favorable Tafel slopes (53, 84, and 154 mV dec⁻1, for graphitizated Ni-MOF, Co-MOF, and NiCo-MOF, respectively). These findings demonstrate the effectiveness of pyrolysis in engineering the MOF crystal structure for enhanced catalytic performance. This paves the way for further exploration of this synthesis method for the design of structurally optimized catalysts and applicable to a broad spectrum of energy technologies.