Tuning chemical and surface composition of nickel cobaltite-based nanocomposites through solvent and its impact on electrocatalytic activity for oxygen evolution

Recently, cobaltites derived from the Zeolitic Imidazolate Framework 67 (ZIF-67) have stood out as promising electrocatalysts for the oxygen evolution reaction (OER). However, it is still necessary to understand the experimental parameters in the synthesis of these materials and their impacts on electrocatalysis. Thus, this work reports the influence of the solvent on the impregnation of nickel ions into ZIF-67 for the obtention of nickel cobaltites and its impact on the electrocatalytic behavior. The impregnation process was conducted in methanol or ethanol and investigated via infrared spectroscopy, powder X-ray diffraction (XRD) and thermogravimetry, to understand the different mechanisms of interaction between nickel ions and ZIF- 67. Electrocatalysts were obtained after calcination of the precursors at 350 degrees C in air. Both solvents lead to the formation of nanocomposites. However, the experiments in methanol resulted in the formation of the nanocompouite NiCo2O4/C, while the use of ethanol led to an additional crystalline phase of nickel oxide (NiCo2O4/NiO/C). Measured overpotentials in the alkaline medium were 333 and 341 mV (in KOH 1 M, at j = 10 mA cm(-2)), respectively, for NiCo2O4/NiO/C and NiCo2O4/C. The material's high electrocatalytic performance is related to the high concentration of electroactive sites like Ni3+ and Co3+ ions and the presence of oxygen vacancies. Higher catalytic performance for the NiCo2O4/C nanocomposite was observed at high current densities, related to the low electrode resistance.

Automated summary

This study investigates the influence of solvents on the impregnation of nickel ions into ZIF-67 for the synthesis of cobaltites, and explores their impact on electrocatalytic behavior. Both methanol and ethanol can form nanocomposites, but methanol experiments result in the formation of NiCo2O4/C nanocomposites, while ethanol experiments lead to the additional crystalline phase of nickel oxide (NiCo2O4/NiO/C). The NiCo2O4/C nanocomposite shows higher catalytic performance at high current densities due to low electrode resistance.