Polimorfos de Ni(OH)2 e Materiais Mistos Eletroativos Baseados em Argilas Esmectitas: Caracterização Estrutural e Comportamento Eletroquímico

Abstract

This work presents a comparative study of structure and electrochemical behaviour of the alpha and beta phases of nickel hydroxide [Ni(OH)2] on different supporting electrolytes. The materials were prepared by sol-gel method, and precipitation in an alkaline medium. Electroactive mixed materials (EMM), obtained from the combination of colloids of Ni(OH)2 with natural smectite clays, with the aim of stabilizing the Ni(OH)2 by the clays were also prepared. The alpha and beta-phase Ni(OH)2 were characterized by X-ray diffraction with Synchrotron Light and showed indices Miller values (hkl) typical of the alpha phase (003), (006) and (101) planes of reflection characteristic of phase with the d (003) from 11,48 Å for [?1-Ni(OH)2] and 9,86 Å for [?2-Ni(OH)2]. XRD for phase ?Ni shows characteristic planes (001), (100), (101), (110), with the interlayer spacing (001) of 4,66 Å. The TG/DTA, SEM-EDS, EAA and Raman spectra data confirm the composition and properties showing the alpha and beta phases of nickel hydroxide according to the method of preparation. Platinum electrodes modified were with the gels alpha-Ni(OH)2, voltammetric cycles exhibit peak pair (anodic and cathodic) more acute and symmetrical in relation to the beta phase. Interestingly, for the NaOH and LiOH electrolyte, showed the best voltammetric profiles KOH electrolyte, which is commonly used. Furthermore, the cyclic voltammograms (CVs) for the phase ?1-Ni(OH)2 was found to be a combination of VCs ?2-Ni(OH)2 and beta-Ni(OH)2, suggesting that the electroactive material has alpha2 best electrochemical performance. The preparation of the mixed electroactive material (EMM) was obtained from the combination of alpha-nickel hydroxide colloidal with natural clays (Volclay and Argel ), which allows of being produced in large quantities. In the X-ray diffraction profile the presence of ?-Ni(OH)2 layer on the surface of the clay and the shift of the peak 001 was observed, indicating the interleaving by increasing the interlayer spacing of the clays. Data from thermogravimetric analysis (TG / DTA) show that Ni(OH)2 as the stabilized clay enhances the thermal stability at 100ºC, together with its decomposition. Images of scanning electron microscopy (SEM) and mapping by energy dispersive spectroscopy (EDS) confirm these features and the homogeneous distribution of nickel in the clay. The electrochemical activity was measured using chemically modified electrodes (CME). VCs have symmetric peaks characteristic redox Ni(II)/Ni(III). The EMM ?2Ni-Argel shows the ratio between the anodic and cathodic charge (Qpa/Qpc) ? 1, i.e., reversible and stable with a load capacity in the 1st cycle of 382 mAhg?¹, and increased the 500th cycle 489 mAhg?¹. The EMM ?2Ni-Volcaly has higher load carrying capacity, but appears anode coupled wave, which may be due to the formation of ?-Ni(OH)2 phase after successive cycling. In this regard, EMM present as good materials for energy storage and/or as non-enzymatic glucose sensor, electrocatalysis of alcohols and electrosynthesis.