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Defect‐engineering is a viable strategy to improve the activity of nanocatalysts for the oxygen evolution reaction (OER), whose slow kinetics still strongly limits the broad market penetration of electrochemical water splitting as a sustainable technology for large‐scale hydrogen production. High‐entropy spinel oxides (HESOs) are in focus due to their great potential as low‐cost OER electrocatalysts. In this work, electrospun HESO nanofibers (NFs), based on (Cr,Mn,Fe,Co,Ni), (Cr,Mn,Fe,Co,Zn) and (Cr,Mn,Fe,Ni,Zn) combinations, with granular architecture and oxygen‐deficient surface are produced by calcination at low temperature (600 or 500 °C), characterized by a combination of benchtop analytical techniques and evaluated as electrocatalysts for OER in alkaline medium. The variation of HESO composition and calcination temperature produces complex and interdependent changes in the morphology of the fibers, crystallinity and inversion degree of the spinel oxide, concentration of the oxygen‐vacancies, cation distribution in the lattice, which mirror on different electrochemical properties of the fibers. The best electrocatalytic performance (overpotential and Tafel slope at 10 mA cm−2: 360 mV and 41 mV dec−1, respectively) pertains to (Cr1/5Mn1/5Fe1/5Co1/5Ni1/5)3O4 NFs calcined at 500 °C and results from the lower outer 3d‐electron number, eg filling closer to its optimal value and higher occupation of 16d sites by the most redox‐active species. [ABSTRACT FROM AUTHOR]

A novel electrochemical sensor for the determination of nitrites based on the modified screen‐printed electrode (SPCE) by Zn‐bidentate Schiff base complexes (ZnLX2) is presented. ZnLX2 complexes have been synthesized and characterized using several morphological and microstructural techniques such as scanning electron microscopy (SEM), X‐ray powder diffraction (XRD), and fourier transformed‐infrared (FT‐IR) spectroscopy. Cyclic voltammetry (CVs) proved the good electrochemical performances of the ZnLX2/SPCE for nitrite ions determination. The influence of pH, scan rate, nitrite concentration, and interfering ions was investigated. After optimization of the operating parameters, the developed ZnLX2/SPCE sensor displayed two linear relationships between response current and nitrite concentration in the overall range 2–4838 μM and a lower detection limit estimated to be 0.78 μM based on 3σ/m. Finally, the analytical application of the developed sensor was evaluated to quantify nitrite in a real sample of mineral water. Results obtained demonstrate that the ZnLX2/SPCE electrochemical sensor provided an effective tool for the detection of nitrite ions. [ABSTRACT FROM AUTHOR]

We report CNT/Al2O3 core–shell nanostructures for the electrochemical detection of dihydroxybenzene (DHB) isomers. Amorphous films of Al2O3 (1.2–15.4 nm in thickness) are uniformly deposited onto the inner and outer walls of CNTs by atomic layer deposition. The effect of the Al2O3 shell thickness on the electrochemical detection of dihydroxybenzene isomers was explored using cyclic and square-wave voltammetry. The best sensing properties are found at a shell thickness of approx. 2.4 nm (CNT/Al2O3(9) sensor), where the oxidation peak currents (sensor-signal) increased ca. 10 times as compared to a sensor fabricated with non-coated CNTs. All of the three DHB isomers (hydroquinone, catechol and resorcinol) are independently detected in the concentration ranges of 2–1000 μmol L−1, 0.5–700 μmol L−1 and 3.5–500 μmol L−1, respectively. The sensors show reliable repeatability, reproducibility, long-term stability, and applicability in the analysis of real samples. Based on these findings, a plausible mechanism is proposed highlighting the role of the Al2O3–shell. [ABSTRACT FROM AUTHOR]

In this article, the electrochemical monitoring of phenol (Ph) in water by using a nanostructured MnO2-modified screen-printed carbon electrode (MnO2-SPCE) is reported. MnO2 nanoparticles were synthesized by the redox-precipitation method. Morphological, textural, and microstructural characteristics were investigated by scanning electron microscopy (SEM), X-ray diffraction, Raman, Brunauer–Emmett–Teller (BET) surface area, and pore volume analyses. Electrochemical properties of the modified MnO2-SPCE electrode have been investigated by cyclic voltammetry and linear sweep voltammetry. The detection of Ph in water by the developed sensor was exploited using square wave voltammetry and chronoamperometry. The sensor showed good characteristics, such as simple fabrication, low cost, good sensitivity, stability, reproducibility, and selectivity, against inorganic analytes and other phenolic compounds. The reported results demonstrated the great potential of nanostructured MnO2 in developing high performances electrochemical sensors to be utilized in the field of environmental pollution monitoring. [ABSTRACT FROM AUTHOR]

This article describes a simple though extremely effective sensor for acetone monitoring in the breath. The sensor is capable of monitoring the presence of acetone at parts per million (ppm) concentrations, thus being suitable for a diabetes diagnosis. It has a dimension of $3 {\,\,\mathrm {mm}} \times 6 {\,\,\mathrm {mm}}$ and a cost of less than one dollar. The small dimensions allow one to greatly limit the power required to increase its temperature, and its high selectivity with respect to other gases present in the breath reduces the risk of false-positive responses. The sensor is based on a thin alumina substrate on which platinum strips are deposited on both faces. A thin Nb2O5 layer with a nanometric thickness provides the required sensitivity and selectivity. Sensor prototypes have been characterized by field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) and proved an inherent linear response up to a few ppm of acetone. [ABSTRACT FROM AUTHOR]

The rapid growth of research in electrochemistry in the last decade has resulted in a significant advancement in exploiting electrochemical strategies for assessing biological substances. Among these, amino acids are of utmost interest due to their key role in human health. Indeed, an unbalanced amino acid level is the origin of several metabolic and genetic diseases, which has led to a great need for effective and reliable evaluation methods. This review is an effort to summarize and present both challenges and achievements in electrochemical amino acid sensing from the last decade (from 2010 onwards) to show where limitations and advantages stem from. In this review, we place special emphasis on five well-known electroactive amino acids, namely cysteine, tyrosine, tryptophan, methionine and histidine. The recent research and achievements in this area and significant performance metrics of the proposed electrochemical sensors, including the limit of detection, sensitivity, stability, linear dynamic range(s) and applicability in real sample analysis, are summarized and presented in separate sections. More than 400 recent scientific studies were included in this review to portray a rich set of ideas and exemplify the capabilities of the electrochemical strategies to detect these essential biomolecules at trace and even ultra-trace levels. Finally, we discuss, in the last section, the remaining issues and the opportunities to push the boundaries of our knowledge in amino acid electrochemistry even further. [ABSTRACT FROM AUTHOR]

We report CNT/Al2O3 core-shell nanostructures for the electrochemical detection of dihydroxybenzene (DHB) isomers. Amorphous films of Al2O3 (1.2-15.4 nm in thickness) are uniformly deposited onto the inner and outer walls of CNTs by atomic layer deposition. The effect of the Al2O3 shell thickness on the electrochemical detection of dihydroxybenzene isomers was explored using cyclic and square-wave voltammetry. The best sensing properties are found at a shell thickness of approx. 2.4 nm (CNT/Al2O3(9) sensor), where the oxidation peak currents (sensor-signal) increased ca. 10 times as compared to a sensor fabricated with non-coated CNTs. All of the three DHB isomers (hydroquinone, catechol and resorcinol) are independently detected in the concentration ranges of 2-1000 μmol L-1, 0.5-700 μmol L-1 and 3.5-500 μmol L-1, respectively. The sensors show reliable repeatability, reproducibility, long-term stability, and applicability in the analysis of real samples. Based on these findings, a plausible mechanism is proposed highlighting the role of the Al2O3-shell.