RESUMEN

Aqueous electrolytes used in CO2 electroreduction typically have a CO2 solubility of around 34 mM under ambient conditions, contributing to mass transfer limitations in the system. Non-aqueous electrolytes exhibit higher CO2 solubility (by 5-8-fold) and also provide possibilities to suppress the undesired hydrogen evolution reaction (HER). On the other hand, a proton donor is needed to produce many of the products commonly obtained with aqueous electrolytes. This work investigates the electrochemical CO2 reduction performance of copper in non-aqueous electrolytes based on dimethylformamide (DMF), n-methyl-2-pyrrolidone (NMP), and acetonitrile (ACN). The main objective is to analyze whether non-aqueous electrolytes are a viable alternative to aqueous electrolytes for hydrocarbon production. Additionally, the effects of aqueous/non-aqueous anolytes, membrane, and the selection of a potential window on the electrochemical CO2 reduction performance are addressed in this study. Experiments with pure DMF and NMP mainly produced oxalate with a faradaic efficiency (FE) reaching >80%; however, pure ACN mainly produced hydrogen and formate due to the presence of more residual water in the system. Addition of 5% (v/v) water to the non-aqueous electrolytes resulted in increased HER and formate production with negligible hydrocarbon production. Hence, we conclude that aqueous electrolytes remain a better choice for the production of hydrocarbons and alcohols on a copper electrode, while organic electrolytes based on DMF and NMP can be used to obtain a high selectivity toward oxalate and formate.

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In this study, we investigated the impact of a TiO2 nanotube (NT) interlayer on the electrochemical performance and service life of Sb and Bi-doped SnO2-coatings synthesized on a titanium mesh. Ti/SnO2-SbBi electrode was synthetized by a thermal decomposition method using ionic liquid as a precursor solvent. Ti/TiO2-NT/SnO2-SbBi electrode was obtained by a two-step electrochemical anodization, followed by the same process of thermal decomposition. The synthesized electrodes were electrochemically characterized and analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy. Terephthalic acid (TA) experiments showed that Ti/SnO2-SbBi and Ti/TiO2-NT/SnO2-SbBi electrodes formed somewhat higher amounts of hydroxyl radicals (HO) compared with the mesh boron doped diamond (BDD) anode. Electrochemical oxidation experiments were performed using iodinated contrast media (ICM) as model organic contaminants persistent to oxidation. At current density of 50 A m-2, BDD clearly outperformed the synthesized mixed metal oxide (MMO) electrodes, with 2 to 3-fold higher oxidation rates observed for ICM. However, at 100 and 150 A m-2, Ti/SnO2-SbBi had similar performance to BDD, whereas Ti/TiO2-NT/SnO2-SbBi yielded even higher oxidation rates. Disappearance of the target ICM was followed by up to 80% removal of adsorbable organic iodide (AOI) for all three materials, further demonstrating iodine cleavage and thus oxidative degradation of ICM mediated by HO. The presence of a TiO2 NT interlayer yielded nearly 4-fold increase in anode stability and dislocated the oxygen evolution reaction by +0.2 V. Thus, TiO2 NT interlayer enhanced electrode stability and service life, and the electrocatalytic activity for the degradation of persistent organic contaminants.

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Alternative routes to degrade dyes are of crucial importance for the environment. Hence, we report the electrochemical removal of indanthrene blue by using a boron-doped diamond anode, focusing on the toxicity of the treated solutions. Different operational conditions were studied, such as current density (5, 10, and 20 mA cm-2) and electrolyte composition (Na2SO4, Na2CO3, and NaNO3). Besides, the pH was monitored throughout the experiment to consider its direct influence on the ecotoxicity effects. The highest electrochemical oxidation efficiency, measured as color removal, was seen in the 180 min condition of electrolysis in 0.033 M Na2SO4, applying 20 mA cm-2, resulting in a color removal of nearly 91% and 40.51 kWh m-3 of energy consumption. The toxicity towards Lactuca sativa depends solely on pH variations being indifferent to color removal. While the inhibition concentration (IC50) for Raphidocelis subcapitata increases 20% after treatment (in optimized conditions), suggesting that the byproducts are more toxic for this specific organism. Our data highlight the importance of analyzing the toxicity towards various organisms to understand the toxic effect of the treatment applied.

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The electrochemical reduction of CO2 to fuels or commodity chemicals is a reaction of high interest for closing the anthropogenic carbon cycle. The role of the electrolyte is of particular interest, as the interplay between the electrocatalytic surface and the electrolyte plays an important role in determining the outcome of the CO2 reduction reaction. Therefore, insights on electrolyte effects on the electrochemical reduction of CO2 are pivotal in designing electrochemical devices that are able to efficiently and selectively convert CO2 into valuable products. Here, we provide an overview of recently obtained insights on electrolyte effects and we discuss how these insights can be used as design parameters for the construction of new electrocatalytic systems.

RESUMEN

The contamination of surface and ground water by antibiotics is of significant importance due to their potential chronic toxic effects to the aquatic and human lives. Thus, in this work, the electrochemical oxidation of cephalexin (CEX) was carried out in a one compartment filter-press flow cell using a boron-doped diamond (BDD) electrode as anode. During the electrolysis, the investigated variables were: supporting electrolyte (Na2SO4, NaCl, NaNO3, and Na2CO3) at constant ionic strength (0.1 M), pH (3, 7, 10, and without control), and current density (5, 10 and 20 mA cm-2). The oxidation and mineralization of CEX were assessed by high performance liquid chromatography, coupled to mass spectrometry and total organic carbon. The oxidation process of CEX was dependent on the type of electrolyte and on pH of the solution due to the distinct oxidant species electrogenerated; however, the conversion of CEX and its hydroxylated intermediates to CO2 depends only on their diffusion to the surface of the BDD. In the final stages of electrolysis, an accumulation of recalcitrant oxamic and oxalic carboxylic acids, was detected. Finally, the growth inhibition assay with Escherichia coli cells showed that the toxicity of CEX solution decreased along the electrochemical treatment due to the rupture of the ß-lactam ring of the antibiotic.

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