Highly Efficient Electrochemical Production of Hydrogen Peroxide Using the GDE Technology.

This work examines the role of oxygen supply in the improvement of the hydrogen peroxide (H2O2) electrochemical production efficiency and the generation of high H2O2 concentrations in electrochemical processes operated in a discontinuous mode. To conduct this study, a highly efficient Printex L6 carbon-based gas diffusion electrode (GDE) as a cathode was employed for the electrogeneration of H2O2 in a flow-by reactor and evaluated the effects of lowering the operation temperature (to increase solubility) and increasing the air supply in the system on H2O2 electrogeneration. The results obtained in this study show that unlike what is expected in flow-through reactors, the efficiency in the H2O2 production is not affected by the solubility of oxygen when GDE is employed in the electrochemical process (using the flow-by reactor); i.e., the efficiency of H2O2 production is not significantly dependent on O2 solubility, temperature, and pressure. The application of the proposed PL6C-based GDE led to the generation of accumulated H2O2 of over 3 g L-1 at a high current density. It should be noted, however, that the application of the electrocatalyst at lower current densities resulted in higher energy efficiency in terms of H2O2 production. Precisely, a specific production of H2O2 as high as 131 g kWh-1 was obtained at 25 mA cm-2; the energy efficiency (in terms of H2O2 production) values obtained in this study based on the application of the proposed GDE in a flow-by reactor at low current densities were found to be within the range of values recorded for H2O2 production techniques that employ flow-through reactors.

One-step preparation of Co2V2O7: synthesis and application as a Fenton-like catalyst in a gas diffusion electrode.

Bimetallic oxides and MOFs have been used as catalysts for the ORR via two-electron and Fenton-based processes. This work reports the development of a new green one-step route for obtaining Co2V2O7. The Co2V2O7 oxide was immobilized on Printex-L6 carbon and used as a catalyst for the oxygen reduction reaction (ORR) and in heterogeneous Fenton-based processes. The PL6C/2.5% Co2V2O7 sample exhibited the best performance in the ORR via a two-electron pathway, increasing the selectivity for H2O2 generation. Electrochemical impedance spectroscopy analysis showed a decrease in charge transfer resistance in the Co2V2O7/PL6C matrix. The application of a gas diffusion electrode (GDE) modified with 2.5% Co2V2O7 resulted in a 30% increase in H2O2 production compared to the unmodified GDE. The unmodified GDE promoted methyl-paraben (MeP) removal of ∼80% after 90 min treatment, whereas the modified GDE promoted ∼90% of MeP removal in 30 min. The results obtained point to the potential of Co2V2O7 in improving the efficiency of GDE when applied for the treatment of organic pollutants.

Selective UV-filter detection with sensors based on stainless steel electrodes modified with polyaniline doped with metal tetrasulfonated phthalocyanine films.

This work describes the construction and application of two amperometric sensors for sensitive UV-filter determination. The sensors were prepared using stainless steel electrodes in which polyaniline (PANI) was electrochemically polymerized in the presence of nickel (NiPcTS) or iron (FePcTS) tetrasulfonated phthalocyanines. The sensor surface characterizations were carried out using atomic force microscopy (AFM). The PANI/NiPcTS sensor was selective for the chemical UV-filter p-aminobenzoic acid (PABA) and the PANI/FePcTS sensor was selective for octyldimethyl-PABA (ODP), both in a mixture of tetrahydrofuran (THF) and 0.1 mol L(-1) H2SO4 at a volume ratio of 30 : 70, and with an applied potential of 0.0 mV vs. Ag|AgCl. A detailed investigation of the selectivity was carried out for both sensors, in order to determine their responses for ten different UV filters. Finally, each sensor was successfully applied to PABA or ODP quantification in sunscreen formulations and water from swimming pools.