Kinetics of Redox Processes in the Polymer Films of Ni(II)SalenType Complexes

Abstract

Instruments.-Spectroelectrochemistry measurements were carried out by SPELEC DROPSENS with reflection probe UV-VIS.Cyclic voltammetry, chronocoulometry and chronopotentiometry measurements were performed using AUTOLAB PGSTAT 10 Eco Chemie in three-electrode system. A Pt disk electrode (from MIN-ERAL) modified with polymer nickel complexes (Ptpoly) were used as a working electrode. The surface area of the Pt disk electrode (0.1865 cm 2 ) was determined voltammetrically using potassium hexacyanoferrate(III) solution as a standard. 33 A Pt plate was used as a counter electrode and Ag/AgCl (1 mol•dm -3 NaCl) a reference electrode, was connected to the bulk of the solution by a Luggin capillary.Voltammograms were recorded in the potential range of 0 V to 2.1 V, at sweep rates between 0.01 and 2 V•s −1 .Chronocoulometry were carried out using two different potential steps, for different times of potential step (10 −3 ÷ 30 s). The first step

Electrocatalytic Properties of Ni(II) Schiff Base Complex Polymer Films

“…The observed difference of the anode peaks potentials was (Δ E II–I = 0.34 V). However, as the electroactive surface coverage increased, the potential of the first step of the process increased ( E I = 0.83 V) ( Figure 1 b, dashed line), and the differences of the anode peaks potentials decreased (Δ E II–I = 0.28 V) as a result of a decrease in relocation [ 43 ], caused by an increase in difficulties in the charge transfer [ 38 ]. However, in the films with the most concentration of active centers, the anode process became one-step and occurs at the potential corresponding to the peak potential of the second step of oxidation of poly [Ni(salcn)] ( E = 1.12 V) ( Figure 1 c, dashed line).…”

“…Limitations in delocalization, the number of steps in the anode process and in kinetics, proceeding with the increase in the electroactive surface coverage, are most likely related to the cross-linked structure of this polymer, as shown by FTIR ATR spectroscopy studies [ 35 ]. The measure of difficulties in charge transfer are lower values of cD 1/2 ( D —diffusion coefficient) for films of this polymer than for poly [Ni(salcn(Bu))] films, while the concentration of active surface centers ( Γ ) in poly [Ni(salcn(Bu))] are smaller than in the poly [Ni(salcn)] films (the comparison for polymers obtained by recording the same number of electropolymerization cycles and at the same electrode polarization rate) [ 38 ]. The poly [Ni(salcn)] polymer films underwent irreversible electrode processes ( Figure 1 a–c, dashed lines).…”

“…The kinetics of electrode processes occurring in the films of this polymer is the fastest. D values are higher than for poly [Ni(salcn)] polymers [ 38 ]. The reason is most likely the less compact structure of poly [Ni(salcn(Bu))], due to electropolymerization in one direction, forced by substituents in ortho - positions and the significant steric effect of tert -Bu substituents, facilitating the charge transfer, regardless of the electroactive surface coverage.…”

“…However, the electrocatalysis process occurred at a potential higher than the oxidation potential of the poly [Ni(salcn)] film, which most probably resulted from the nature of the polymer film. In the investigated film of medium electroactive surface coverage, charge transfer is more difficult than in a film with low electroactive surface coverage [ 38 ], and additionally the introduced catechol makes this process even more difficult. This was confirmed by tests carried out in a film with low electroactive surface coverage ( Figure S5, solid line, ESI , Γ = 4.97 × 10 −9 mol·cm −2 ), obtained as a result of recording one cycle at v = 0.05 V·s −1 .…”

“…They oxidize in two steps to the macro phenoxyl radical and macro bisphenoxyl radical [ 36 , 37 ]. The research also showed the influence of the substituent and the electroactive surface coverage on the kinetics of electrode processes [ 38 ].…”