Oxidation of Chloride Ion on Platinum Electrode: Dynamics of Electrode Passivation and its Effect on Oxidation Kinetics

Quantitative Evaluations on Ozone Evolution Electrocatalysts by Scanning Electrochemical Microscopy for Oxidative Water Treatment

This study valorized scanning electrochemical microscopy (SECM) for the detection of dissolved O3, which is increasingly in demand for water treatment. Au ultramicroelectrodes biased at 0.62 V RHE provided superior activity and selectivity for O3 reduction, compared to Pt analogues. It allowed quantitative in situ interrogation of ozone evolution reaction (OZER) electrocatalysts with unprecedented estimations on the OZER overpotential. The difference in onset potentials between the OZER and the competing oxygen evolution reaction (OER) primarily accounted for the OZER current efficiency (CE) on boron-doped diamond (BDD, 1.4% at 10 mA cm-2 in 0.5 M H2SO4), Ni-Sb-doped SnO2 (NSS, 10.8%), and SiOx-coated NSS (NSS/SiOx, 34.4%). SECM areal scans in tandem with elemental mapping perspicuously visualized the improved OZER activity by the SiOx overlayer on NSS. A shift in the charge transfer coefficient further rationalized the elevated OZER selectivity on NSS/SiOx, in association with the weakened Sn-O bond strength confirmed by valence band X-ray photoelectron spectra. The invigorated OZER on NSS/SiOx effectively accelerated the degradation of a model aqueous pollutant (4-chlorophenol).

An electrogenetic interface to program mammalian gene expression by direct current

Wearable electronic devices are playing a rapidly expanding role in the acquisition of individuals' health data for personalized medical interventions; however, wearables cannot yet directly program gene-based therapies because of the lack of a direct electrogenetic interface. Here we provide the missing link by developing an electrogenetic interface that we call direct current (DC)-actuated regulation technology (DART), which enables electrode-mediated, time- and voltage-dependent transgene expression in human cells using DC from batteries. DART utilizes a DC supply to generate non-toxic levels of reactive oxygen species that act via a biosensor to reversibly fine-tune synthetic promoters. In a proof-of-concept study in a type 1 diabetic male mouse model, a once-daily transdermal stimulation of subcutaneously implanted microencapsulated engineered human cells by energized acupuncture needles (4.5 V DC for 10 s) stimulated insulin release and restored normoglycemia. We believe this technology will enable wearable electronic devices to directly program metabolic interventions.

Formation of Halogenated Byproducts upon Water Treatment with Peracetic Acid

Peracetic acid has quickly gained ground in water treatment over the last decade. Specifically, its disinfection efficacy toward a wide spectrum of microorganisms in wastewater is accompanied by the simplicity of its handling and use. Moreover, peracetic acid represents a promising option to achieve disinfection while reducing the concentration of typical chlorination byproducts in the final effluent. However, its chemical behavior is still amply debated. In this study, the reactivity of peracetic acid in the presence of halides, namely, chloride and bromide, was investigated in both synthetic waters and in a real contaminated water. While previous studies focused on the ability of this disinfectant to form halogenated byproducts in the presence of dissolved organic matter and halides, this work indicates that peracetic acid also contributes itself as a primary source in the formation of these potentially carcinogenic compounds. Specifically, this study suggests that 1.5 mM peracetic acid may form around 1-10 μg/L of bromoform when bromide is present. Bromoform formation reaches a maximum at near neutral pH, which is highly relevant for wastewater management.

Electrochemical deposition of nickel from aqueous electrolytic baths prepared by dissolution of metallic powder

A new method of preparation of aqueous electrolyte baths for electrochemical deposition of nickel targets for medical accelerators is presented. It starts with fast dissolution of metallic Ni powder in a HNO3-free solvent. Such obtained raw solution does not require additional treatment aimed to removal nitrates, such as the acid evaporation and Ni salt precipitation-dissolution. It is used directly for preparation of the nickel plating baths after dilution with water, setting up pH value and after possible addition of H3BO3. The pH of the baths ranges from alkaline to acidic. Deposition of 95% of ca. 50 mg of Ni dissolved in the bath takes ca. 3.5 h for the alkaline electrolyte while for the acidic solution it requires ca. 7 h. The Ni deposits obtained from the acidic bath are physically and chemically more stable and possess smoother and crack-free surfaces as compared to the coatings deposited from the alkaline bath. A method of estimation of concentration of H2O2 in the electrolytic bath is also proposed.

Descriptive Role of Pt/PtOx Ratio on the Selective Chlorine Evolution Reaction under Polarity Reversal as Studied by Scanning Electrochemical Microscopy

This study investigated competing chlorine evolution reaction (ClER) and oxygen evolution reaction (OER) on Pt electrodes under variable polarity reversal intervals (±16.7 mA cm^-2, 30-600 s) in the context of distinctive roles of Pt(0) and PtO_x on the surface in dilute (0.1 M) NaCl solutions. The substrate generation/tip collection mode of scanning electrochemical microscopy (SECM) quantified the current efficiency (CE) of ClER with a large tip-to-substrate distance (>500 μm) to avoid intervention of bubbles and spatial variations. Surface interrogation SECM using [Ru(NH₃)₆]^2+/3+ coupled with X-ray photoelectron spectroscopy (XPS) identified the Pt⁴⁺-enriched surface of PtO_x with a bilayer structure to give more efficient regeneration of Pt(0) under the shorter reversal interval. The in situ SECM complemented bulk electrolysis and XPS to demonstrate that ClER on Pt(0) and OER on PtO_x primarily determine the CE of ClER, in agreement with a kinetic model. The descriptive role of surface Pt/PtO_x ratio rationalized the enhanced selectivity for ClER upon the polarity switching, being independent on a scaling relationship. The current reversal (not allowed to IrO₂ electrodes) also alleviated calcareous scale deposit in the electrolyte with hardness.

Electrochemical deposition of nickel targets from aqueous electrolytes for medical radioisotope production in accelerators: a review

This paper reviews reported methods of the electrochemical deposition of nickel layers which are used as target materials for accelerator production of medical radioisotopes. The review focuses on the electrodeposition carried out from aqueous electrolytes. It describes the main challenges related to the preparation of suitable Ni target layers, such as work with limited amounts of expensive isotopically enriched nickel; electrodeposition of sufficiently thick, smooth and free of cracks layers; and recovery of unreacted Ni isotopes from the irradiated targets and from used electrolytic baths.

Electrochemical disinfection of irrigation water with a graphite electrode flow cell

In this work, we report experimental studies on the disinfection of irrigation water using a flow cell assembled with low-cost graphite plates as both anode and cathode. Natural irrigation waters collected from two irrigation locations (Reservoir 225 and Bott Well Pond) in Hawaii were used, and synthetic irrigation waters were prepared based on the chemical analysis of natural irrigation waters. The concentration of chloride was 10.2 mg/L in the synthetic Reservoir 225 water and 6.9 mg/L in the synthetic Bott Well pond water. Escherichia coli K12 ER2738 was selected as a model bacterium to evaluate the disinfection capability of the flow cell. Experiments performed in the synthetic irrigation waters showed that E. coli was inactivated by free chlorine species electro-generated from oxidation of chloride ions at the graphite anode. Complete removal of E. coli was achieved within 10 min in the synthetic irrigation waters. The disinfection of the natural irrigation waters took about four times longer than the disinfection of the synthetic irrigation waters. This result is most likely due to the presence of organic matter (and possibly other oxidizable species) in the natural irrigation waters. PRACTITIONER POINTS: Electrochemical flow cell disinfects to 99.9% with commercial graphite electrodes. E. coli is removed in 10 min from synthetic irrigation water by a flow cell. E. coli removal takes 4× longer in natural irrigation water. A minimum current density of ≥1 mA/cm² is required for disinfection. The primary disinfection mechanism is through chlorine generated from chloride ions.

Automated Electrochemical Glucose Biosensor Platform as an Efficient Tool Toward On-Line Fermentation Monitoring: Novel Application Approaches and Insights

Monitoring and control of fermentation processes remain a crucial challenge for both laboratory and industrial-scale experiments. Reliable identification and quantification of the key process parameters in on-line mode allow operation of the fermentation at optimal reactor efficiency, maximizing productivity while minimizing waste. However, state-of-the-art fermentation on-line monitoring is still limited to a number of standard measurements such as pH, temperature and dissolved oxygen, as well as off-gas analysis as an advanced possibility. Despite the availability of commercial biosensor-based platforms that have been established for continuous monitoring of glucose and various biological variables within healthcare, on-line glucose quantification in fermentation processes has not been implemented yet to a large degree. For the first time, this work presents a complete study of a commercial flow-through-cell with integrated electrochemical glucose biosensors (1^st generation) applied in different media, and importantly, at- and on-line during a yeast fed-batch fermentation process. Remarkably, the glucose biosensor–based platform combined with the developed methodology was able to detect glucose concentrations up to 150 mM in the complex fermentation broth, on both cell-free and cell-containing samples, when not compromised by oxygen limitations. This is four to six-fold higher than previously described in the literature presenting the application of biosensors predominately toward cell-free fermentation samples. The automated biosensor platform allowed reliable glucose quantification in a significantly less resource and time (<5 min) consuming manner compared to conventional HPLC analysis with a refractive index (RI) detector performed as reference measurement. Moreover, the presented biosensor platform demonstrated outstanding mechanical stability in direct contact with the fermentation medium and accurate glucose quantification in the presence of various electroactive species. Coupled with the developed methodology it can be readily considered as a simple, robust, accurate and inexpensive tool for real-time glucose monitoring in fermentation processes.

Electrochemical Synthesis of Hindered Primary and Secondary Amines via Proton-Coupled Electron Transfer

Accessing hindered amines, particularly primary amines α to a fully substituted carbon center, is synthetically challenging. We report an electrochemical method to access such hindered amines starting from benchtop-stable iminium salts and cyanoheteroarenes. A wide variety of substituted heterocycles (pyridine, pyrimidine, pyrazine, purine, azaindole) can be utilized in the cross-coupling reaction, including those substituted with a halide, trifluoromethyl, ester, amide, or ether group, a heterocycle, or an unprotected alcohol or alkyne. Mechanistic insight based on DFT data, as well as cyclic voltammetry and NMR spectroscopy, suggests that a proton-coupled electron-transfer mechanism is operational as part of a hetero-biradical cross-coupling of α-amino radicals and radicals derived from cyanoheteroarenes.

Electrochemical biofilm control: a review

One of the methods of controlling biofilms that has widely been discussed in the literature is to apply a potential or electrical current to a metal surface on which the biofilm is growing. Although electrochemical biofilm control has been studied for decades, the literature is often conflicting, as is detailed in this review. The goals of this review are: (1) to present the current status of knowledge regarding electrochemical biofilm control; (2) to establish a basis for a fundamental definition of electrochemical biofilm control and requirements for studying it; (3) to discuss current proposed mechanisms; and (4) to introduce future directions in the field. It is expected that the review will provide researchers with guidelines on comparing datasets across the literature and generating comparable datasets. The authors believe that, with the correct design, electrochemical biofilm control has great potential for industrial use.