ACOPLAMENTO DE ÓXIDOS DE Ni E Zn ORIGINADOS DE ZIF8 COMO PROMISSOR ELETROCATALISADOR PARA A REAÇÃO DE DESPRENDIMENTO DE OXIGÊNIO

Abstract

Advances in the design of efficient and affordable electrocatalysts for oxygen evolution reaction (OER) have been interpreted as important steps towards the development and application of electrochemical technologies for production of green fuel and clean energy. Herein, we report the synthesis and characterization of efficient and stable electrocatalysts toward OER in alkaline medium based on Ni and/or Co oxides highly dispersed on Zn oxide originated from zeolitic imidazole framework (ZIF8) by using a combination of solvothermal and calcination methods. The calcination of solvothermal treated Ni/ZIF8, named Ni/ZIF8–900A composite, exhibited the most impressive OER active among the synthesized materials, showing a η at 10 mA cm−2 of 0.34 V, which was the same value performed by RuO2 and relatively close to the value obtained by the IrO2 (0.29 V), both state-of-art catalysts. Furthermore, in the face of the long-term electrochemical test, the minor electroactivity loss was registered for the Ni/ZIF8–900A composite, evincing its high electrocatalytic performance toward OER in alkaline medium. The physicochemical characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) mapping, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and elemental analysis (EA), thermogravimetry (TG) and Fourier-transform infrared spectroscopy (FTIR) revealed that Ni/ZIF8–900A consists of overlapping and merged structures (large blocks) with lattice finger of (101) plane of ZnO and (111) plane of Ni 0.8 Zn 0.2 O, with Ni enrichment on the catalyst’s surface of Ni/ZIF8–900A (Ni(1):Zn(2) in mass % in comparison with bulk composition (Ni(1):Zn(14) in mass %)). The large amount of Ni 3+ at the surface of Ni/ZIF8–900A (before and after stability tests) as well as N atoms bonded to the metals were responsible for its improved OER electrocatalytic activity. The electrochemical results revealed that the surface structure of Ni oxides-enriched Ni/ZIF8–900A catalyst are activated when exposed to oxidative potentials during OER experiments. This surface activation led to an expansion of the active surface area and an increase in the number of active sites due to the formation of oxides, in addition to the possibility of Ni3+ conversion to Ni4+ on the oxides formed, contributing to its impressive OER electrocatalytic activity. Furthermore, its low Tafel slope value (ca. 61 mV dec −1 ) suggests the OER involves 4 electrons with the formation of Ni oxyhydroxide, operating under high faradaic efficiency (98.4 % at 1.62 V) and turnover frequency (123.4 s −1 at 1.62 V).