Electrochemical and electron paramagnetic resonance study of the mechanism of oxidation of 2,3,5,6-tetra-Me-pyrazine-di-N-oxide as a mediator of electrocatalytic oxidation of isopropyl alcohol at glassy carbon and single-walled carbon nanotube electrodes

Comparative Electrochemical and Electron Paramagnetic Resonance Study of the Mechanism of Oxidation of 2,3,5,6-Tetra-Me-Pyrazine-Di-N-Oxide as a Mediator of Electrocatalytic Oxidation of Methanol at Glassy Carbon and Multi-Walled Carbon Nanotube Paper Electrodes

“…2d) exceeds by several times the diffusion current of oxidation of 1 mM ferrocene (as a reference current, we used the diffusion current of ferrocene oxidation which proceeds reversibly with the loss of one electron). These features of Pyr2 oxidation at MWCNT paper electrode are similar observed at SWCNT paper electrode [49] and correspond to the compounds adsorbed at the surface of electrode [55]. The shift of potential of Pyr2 oxidation at MWCNT paper electrode may be explained by necessity of overcoming adsorption forces at discharge of adsorbed particles.…”

“…The oxidation of Pyr2 at GC electrode by the method of cyclic voltammetry was studied early [49] in 0.1M LiClO4 solution in acetonitrile. It was found that the current of anodic peak of Pyr2 oxidation (1.4 V) is proportional to square root of the scan rate and concentration of Pyr2 indicating the diffusion character of the electrochemical process.…”

“…The process is irreversible and corresponds to EC process when the charge transfer is followed by irreversible chemical reaction. The rate of chemical reaction of radical cation Pyr2  with acetonitrile molecule 0.54 s -1 was estimated by Kulakovskaya et al [49] from the ratio of currents of cathodic to anodic peak as described in some studies [53,54]. At electrolysis at Pt electrode in 0.1 M LiClO4 solution in acetonitrile [49] was recorded the EPR spectrum of radical cation of Pyr2 at positive potential at decreasing temperature down to -45  С. Parameters of EPR spectrum of Pyr2: g-factor = 2.0089, Gaussian line of 1.45 mT width between extreme.…”

“…The rate of chemical reaction of radical cation Pyr2  with acetonitrile molecule 0.54 s -1 was estimated by Kulakovskaya et al [49] from the ratio of currents of cathodic to anodic peak as described in some studies [53,54]. At electrolysis at Pt electrode in 0.1 M LiClO4 solution in acetonitrile [49] was recorded the EPR spectrum of radical cation of Pyr2 at positive potential at decreasing temperature down to -45  С. Parameters of EPR spectrum of Pyr2: g-factor = 2.0089, Gaussian line of 1.45 mT width between extreme. The intensity of the EPR signal reached its maximum at 1.6 V and does not changed at further increasing the potential up to 2.4 V. This indicated that this radical cation is not further oxidized to a dication in this range of Е.…”

“…Therefore, it was reasonable to study the possibility of using such electrodes in the processes of electrocatalytic oxidation of organic compounds in the presence of electrochemically generated aromatic di-N-oxide radical cation. We studied the mechanism of oxidation of PhenDNO in the presence of cyclohexanol [47] and PhenDNO and Pyr2 in the presence isopropyl alcohol (i-PrOH) [48,49] by the methods of cyclic voltammetry, EPR electrolysis and the differential capacitance at GC and SWCNT paper (produced in our institute [47] and produced by "NanoLab's" firm (USA) [48,49]) electrodes in 0.1 M LiClO4 solutions in acetonitrile. It was found that the catalytic efficiency of oxidation of organic compounds at SWCNT electrodes in the presence of aromatic di-N-oxide increases several times as compared with oxidation at GC electrode.…”