Nanocompósito de CeO2/CO3O4 derivado de MOFs como eletrocatalisador aplicado à reação de evolução do oxigênio

Abstract

Hydrogen gas (H2) was pointed out as one of the great promises for replacing fossil fossils and for generating clean energy. Among several sustainable production methods, water breakdown via electrolysis stands out the most. However, for H2 to be produced by electrodecomposition on a large scale, it is necessary to use electrocatalysts to optimize as semi-reactions, in particular the oxygen evolution reaction (OER), as it has a slow kinetics and endergonic reaction. As an alternative to conventional metal-based catalysts (Pt, Pd, Ru and Ir), this work produced low-cost metal-based electrocatalysts such as cobalt and cerium, using Metal -Organic Frameworks (MOFs) as sacrificial materials. In this context, MOF-Ce was prepared from cerium (III) precursor and succinate ligand by the hydrothermal method, and ZIF -67 from cobalt (II) precursor and 2-methylimidazole ligand. The MOF-Ce@ZIF-67 system was heat treated to generate the composite of CeO2/Co3O4 oxides, which was structurally and chemically by X-ray diffraction, Rietveld refinement, infrared spectroscopy, and UV-vis, thermogravimetry and scanning electron microscopy coupled with energy dispersive. The diffraction patterns indicated the formation of the ceria/cobaltite phase, with cubic structures and crystal average size around 31 nm, also confirmed by the M-O vibrational absorption bands in the infrared spectrum. The UV-VIS spectrum shows bands related to charge transfer and d-d transitions of cerium and cobalt ions in CeO2/Co3O4, developing band energies in the values 250-350, 450 and 725-750 nm. SEM images revealed irregular morphologies, with distribution maps of homogeneous elements for cobalt and cerium atoms, indicating no phase segregation at the material. The electrochemical tests for a different OER reaction an excellent overpotential η = 366 mV and stability in 15 hours at j = 10 mA cm -2 and KOH electrolyte 1 mol L -1 , the Tafel slope was 92.6 mV dec -1 and the double-layer capacitance 3.19 mF. The results demonstrate a performance-like or superior to similar materials already reported in the literature