Electrochemical and structural properties of Ni(II)-alumina composites as an annealing temperature function

Abstract

Alumina powders, pure and doped with nickel, were synthetized by sol-gel method and calcined at 500, 900 and 1100 o C in order to obtain mesoporous structures with a high specific surface area, well adapTab. to catalytic application. The characterization of samples was performed by XRD, EPR spectroscopy and electrochemical impedance spectroscopy (EIS). XRD analysis showed that the addition of Ni 2+ , as well as the annealing temperature, affects the structural properties of the obtained composites. EPR analysis revealed the traces of Fe 3+ impurities, the presence of oxy defects in alumina and Ni 2+ in tetrahedral position for samples calcined at 1100 o C. The impedance of the Nafion/alumina modified GCE depended on combined effect of porous structure and surface properties of alumina samples. The electrochemical behavior of a glassy carbon electrode modified with Ni (II)-doped aluminas was studied in 0.5 M NaOH solution, with and without methanol. The electrochemical activity of nickel-doped alumina composites was dictated by the amount of present NiO impurity.

Application of Ni(II)-alumina composites for electrocatalytic reduction of 4-nitrophenol

“…However, Tauc plots are characterized by the presence of additional transition at 3.9 eV, which probably originate from defect states placed in band gap of alumina matrix. This result is in accordance with XRD data [19], which confirmed defect spinel structure of γ-alumina, characterized with the presence of cation vacancies. Extrapolation of linear part of the Tauc's plot for A10-1100 sample gave value of 1.74 eV, which is close to value reported previously for NiAl 2 O 4 [24], but also at 3.6 eV, which corresponds to band-gap energy of NiO [25] Tauc's plot of A20-1100 sample revealed presence of alumina (5.0eV), NiAl 2 O 4 (1.8eV) and NiO (3.6eV), with additional transition placed at 3.1 eV, which can be attributed to oxygen vacancy with one electron [26].…”

“…Electrochemical response of GCE modified with different alumina samples toward 4-NP reduction was rather similar to each other. Bearing in mind that alumina samples investigated in this paper have rather different textural properties [18] and crystallographic structure [19] it can be concluded that apparent electrocatalytic effect probably originated from surface properties of alumina samples that were similar in all investigated samples. The highest currents for reversible redox peak were observed for alumina samples A10-1100.…”

“…Coordination states are relevant for the distribution of charge (acid-base character) of surfaceactive centers. Thermal decomposition of crystalline hydrated forms of aluminum oxide yielded gamma phase at 500 o C, delta phase at 900 o C and stable α-Al 2 O 3 at 1100 o C [19]. The amount of the surface hydroxyl groups is reduced with the increase of the calcination temperature.…”

“…The results obtained by characterization of samples by nitrogen adsorption-desorption isotherms and X-ray powder diffraction measurements are presented elsewhere [18,19].…”

“…PCA was performed with data that take into account only properties of alumina. The influence of nickel phases on the electrocatalytic activity was previously investigated [19] in the reaction of electrooxidation of methanol. The recorded electrocatalytic activity originated only from formed NiO and was directly proportional to its amount.…”