ELECTROCATALYTIC OXIDATION OF STARCH IN TWO-CHAMBER CELL WITH REGENERATION OF OXIDANT IN SITU ON ELECTRODES FROM Pb/PbO2 AND GRAPHITE

Electrocatalytic oxidation of potato starch was investigated potassium iodate in a two-chamber electrolytic cell with in situ regeneration of the oxidant on Pb/PbO2 and graphite electrodes, depending on the current density, electrolyte pH and electrolysis time. To analyze the samples of the starting and oxidized starch, the methods of photometry, X-ray diffraction, gel permeation chromatography, and IR spectroscopy were used. The optimal conditions for starch dialdehyde production were determined: current density 50 mA/cm2, electrolyte pH 7, electrolysis time 80 min. and a temperature of 25 °С. The weight average molecular weights (Mw) of AIBN samples were determined, which are several orders of magnitude lower (104) than the average molecular weight of native starch (108).

Using pH dependence for understanding mechanisms in electrochemical CO reduction

Utilizing electrochemical conversion of CO(2) into hydrocarbons and oxygenates is envisioned as a promising path towards closing the carbon cycle in modern technology. To this day, however, the exact reaction mechanisms towards the plethora of single and multi-carbon products on Cu electrodes are still disputed. This uncertainty even extends to the rate-limiting step of the respective reactions. Since multi-carbon products do not show a dependence on the electrolyte pH in neutral and alkaline media, CO dimerization on the Cu surface has been proposed as the rate-limiting step. However, other elementary steps would lead to the same pH dependence, namely the proton-electron transfer to *CO followed by subsequent coupling or the protonation of the *OCCO dimer. The pH dependence of methane production on the other hand suggests that the rate limiting step is located beyond the first proton-electron transfer to *CO. In order to conclusively identify the rate limiting steps in CO reduction, we analyzed the mechanisms on the basis of constant potential DFT calculations, CO reduction experiments on Cu at varying pH values (3 - 13) and fundamental rate theory. We find that, even in acidic media, the reaction rate towards multi-carbon products is nearly unchanged on an SHE potential scale, which indicates that its rate limiting step does not involve a proton donor. Hence, we deduce that the rate limiting step can indeed only consist of the coupling of two CO molecules on the surface, both in acidic and alkaline conditions. For methane, on the other hand, the rate-limiting step changes with the electrolyte pH from the first protonation step in acidic/neutral conditions to a later step in alkaline conditions. Finally, based on an in-depth kinetic analysis, we conclude that the pathway towards CH4 involving a surface combination of *CO and *H is unlikely, since it is unable to reproduce the measured current densities and Tafel slopes.

Electrochemical implications of modulating the solvation shell around redox active organic species in aqueous organic redox flow batteries

Organic and organometallic reactants in aqueous electrolytes, being composed of earth-abundant elements, are promising redox active candidates for cost-effective organic redox flow batteries (ORFBs). Various compounds of ferrocene and methyl viologen have been examined as promising redox actives for this application. Herein, we examined the influence of the electrolyte pH and the salt anion on model redox active organic cations, bis((3-trimethylammonio) propyl)- ferrocene dichloride (BTMAP-Fc) and bis(3-trimethylammonio) propyl viologen tetrachloride (BTMAP-Vi), which have exhibited excellent cycling stability and capacity retention at ≥1.00 M concentration [E. S. Beh, et al. ACS Energy Lett. 2, 639–644 (2017)]. We examined the solvation shell around BTMAP-Fc and BTMAP-Vi at acidic and neutral pH with SO42-, Cl−, and CH3SO3− counterions and elucidated their impact on cation diffusion coefficient, first electron transfer rate constant, and thereby the electrochemical Thiele modulus. The electrochemical Thiele modulus was found to be exponentially correlated with the solvent reorganizational energy (λ) in both neutral and acidic pH. Thus, λ is proposed as a universal descriptor and selection criteria for organic redox flow battery electrolyte compositions. In the specific case of the BTMAP-Fc/BTMAP-Vi ORFB, low pH electrolytes with methanesulfonate or chloride counterions were identified as offering the best balance of transport and kinetic requirements.

Improving the Anticorrosion Characteristics of Polymer Coatings in the Case of Their Modification with Compositions Based on Organosilanes

The effect of a series of organosilanes and their mixtures with corrosion inhibitors on the anticorrosion properties of polymer and paint coatings on steel, namely, on the adhesive characteristics of the coatings and corrosion behavior of the metal in the presence of coatings modified with organosilanes, corrosion inhibitors, and their mixtures, is studied. It is shown that mixtures of 1,2,3-benzotriazole (BTA) with vinyltrimethoxysilane (VTMS) or aminoethylaminopropyltrimethoxysilane—diaminosilane (DAS) inhibit the local dissolution and underfilm corrosion of carbon steel, and the potential of local depassivation shifts by 0.3–0.4 V. Here, compact polymer-like layers that are strongly bound to the metal surface are formed on the surface of steel. Corrosion and mechanical tests of the samples of pipe steels with different types of inhibiting compositions are conducted. The effect of the inhibitors on the crack growth under static loading in a model soil electrolyte (pH of 5.5) and on the crack resistance of steel under slow tension in an NS-4 model underfilm electrolyte (pH of 7.0) is evaluated. The tests are performed in media free from and containing hydrogen sulfide. It is shown that the best inhibiting properties are manifested by the mixtures of corrosion inhibitors with organosilanes. Comparative laboratory and bench tests for the adhesive strength, water resistance, and resistance to cathodic detachment of the adhesive junctions obtained upon applying the modified polymer and paint coatings onto the surface of steel are performed. It is found that introducing a mixture of organosilane and a corrosion inhibitor improves the adhesive properties of polymer and paint coatings.