ON THE KINETICS OF ANODIC PROCESSES AT OXIDATION OF AQUEOUS SOLUTIONS OF DIMETHYL SULFOXIDE

Dimethyl sulfoxide is a feedstock for a large number of organic substances syntheses. Nowadays research is considerably focused on the production of general products of dimethyl sulfoxide oxidation – dimethyl sulfone and methane sulfonic acid. Dimethyl sulfone is well–known as a food supplement for the treating and strengthening of human joints and ligaments. dimethyl sulfone is basically synthesized by oxidation of dimethyl sulfoxide in hot 30 % hydrogen peroxide in glacial acetic acid. Synthesis is accompanied by significant losses of hydrogen peroxide, the target product has to be significantly purified. It becomes possible to control the synthesis of pure dimethyl sulfone and methane sulfonic acid when using the electrochemical method of oxidation of dimethyl sulfoxide in its aqueous solution with chemically resistant anode and high overvoltage of oxygen reaction Controlled synthesis is relevant because sulfur tends to change the oxidation rate. Study of kinetics of anodic processes at platinum electrode was performed in the dimethyl sulfoxide concentration range about 1.0…4.0 mol∙dm–3. Current raise was observed at potentials that are more positive than 1.3…1.4 V. This potential range corresponds to oxygen release. Dissolved sulfuric acid (0.2 mol∙dm–3) was added in order to inhibit the oxygen release and achieve the potential for the formation of peroxide radicals in aqueous solutions of dimethyl sulfoxide. It is known that sulfate ions are adsorbed on the surface of the platinum anode, displacing molecules of protonated water. This allows to shift the potentials and increase of the electrolysis current in 0.2 mol∙dm–3 H2SO4 to 1.7…1.9 V. It indicates the processes of formation of peroxide radicals on the surface of the platinum anode. Further shift of the anode potential into more positive area than 2.00…2.05 V leads to a rapid increase in current density. At such potentials, dimethyl sulfoxide and dimethyl sulfone are oxidized to methane sulfonic acid with a parallel oxygen and hydrogen peroxide release. Current–voltage study has shown that the oxidation of dimethyl sulfoxide in aqueous solutions runs through the formation of dimethyl sulfone. When conducting electrochemical synthesis with control of the anode potential, it is possible to produce dimethyl sulfone without further oxidation to methane sulfonic acid. The addition of 0.2 mol∙dm–3 H2SO4 to aqueous dimethyl sulfoxide solutions inhibits oxygen release and intensifies oxidation of dipole dimethyl sulfoxide molecules adsorbed on the platinum surface. The influence of adsorption processes on the kinetics of anode processes at the platinum anode in aqueous solutions of dimethyl sulfoxide at high anode potentials has been studied.

Electrochemical conversion pathways and existing morphology of arsenic(III) in anode-cathode separated electrolytic cells

To explore the electrochemical conversion of arsenic at different voltages and pH, an open separated electrolytic cell with a platinum anode and a graphite cathode was selected for this paper. The form and concentration of arsenic in the anodic cell and cathodic cell were detected. Experimental results proved that at 40.0 V, As(III) in an acid electrolyte in the cathodic cell was firstly mainly reduced to AsH3 with trace As(0) as intermediate. As the electrolysis time arrived at 27 min, pH in the cathodic cell jumped suddenly from acidity to alkalinity, accompanied by the majority of the remaining As(III) converting to As(V) for an instant. As time went on, As(III) and As(V) remained almost unchanged at the ratio of 1:3, and the reduction of As(III) became extremely weak in the alkaline environment. When pH in the cathodic tank was adjusted to keep it acid, As(III) was eventually converted to AsH3. Compared with high voltage, at a low voltage of 1.0 V the cathode failed to achieve the potential of As(III) reduction and As(III) was eventually oxidized to As(V) in the acid catholyte. Electrochemical oxidation of As(III) in the open cathodic cell was likely caused by in-situ generation of peroxide from electrochemical reduction of O2. Theoretical support for electrochemical oxidation of As(III) on a carbon cathode in neutral and weak alkaline media is provided in this study.

Space charge layer effect at the platinum anode/BaZr0.9Y0.1O3−δ electrolyte interface in proton ceramic fuel cells

Space charge layer model at the Pt anode/BZY10 proton conductor interface.

Tolerance and Recovery of Ultralow-Loaded Platinum Anode Electrodes upon Carbon Monoxide and Hydrogen Sulfide Exposure

The effects of carbon monoxide (CO) and hydrogen sulfide (H2S) in concentrations close to their respective limits in the Hydrogen Quality Standard ISO 14687-2:2012 on the performance of proton exchange membrane fuel cells (PEMFCs) with ultralow-loaded platinum anode catalyst layers (CLs) were investigated. The anodic loadings were 50, 25, and 15 µg/cm², which represent the current state-of-the-art, target, and stretch target, respectively, for future automotive PEMFCs. Additionally, the effect of shut-down and start-up (SD/SU) processes on recovery from sulfur poisoning was investigated. CO at an ISO concentration of 0.2 ppm caused severe voltage losses of ~40–50% for ultralow-loaded anode CLs. When H2S was in the fuel, these anode CLs exhibited both a nonlinear decrease in tolerance toward sulfur and an improved self-recovery during shut-down and start-up (SD/SU) processes. This observation was hypothesized to have resulted from the decrease in the ratio between CL thickness and geometric cell area, as interfacial effects of water in the pores increasingly impacted the performance of ultrathin CLs. The results indicate that during the next discussions on the Hydrogen Quality Standard, a reduction in the CO limit could be a reasonable alternative considering future PEMFC anodic loadings, while the H2S limit might not require modification.