Redox Pair Research Articles

Fabrication of Cu0-composited CuFe2O4 magnetic nanoparticles on diatomite support for efficient degradation of tetracycline hydrochloride by a Fenton-like system

Paramagnetic Cu/CuFe2O4/DE composites were fabricated by a one-step solvothermal method to design a heterogeneous Fenton-like catalyst to degrade tetracycline hydrochloride (TC). The Cu/CuFe2O4/DE were characterized by SEM, TEM, XRD, BET, and XPS methods. The catalytic activity of CuFe2O4 was improved using diatomite and Cu0. Diatomite (DE) enhanced the dispersity of Cu/CuFe2O4, minimized metal ions leaching, and improved stability. The Cu0 is used for the regeneration of Fe3+. The synergy between Cu+/Cu2+ and Fe2+/Fe3+ redox pairs promotes hydroxyl radical production upon H2O2 decomposition. The synthesized materials were characterized by SEM, TEM, XRD, BET, and XPS, and their catalytic activities were discussed and analyzed. 95.5 % TC was degraded within 90 min (initial conditions, pH = 5.0 and [TC] 50 mg/L), and showing excellent anti-interference ability to the presence of SO42-, Cl-, NO3-, CO32- and humic acid (HA).The presence of active species, viz., •OH and •O2- radicals generated in the Cu/CuFe2O4/DE/H2O2 system were detected by ESR quenching measurements. The •OH and •O2- mediated TC degraded pathways were proposed using the intermediates identified by LC-MS data. The novel heterogeneous Fenton-like process developed using Cu/CuFe2O4/DE/H2O2 is robust for TC degradation as exemplified in its stability and reusability measurements.

Multiple Stroboscopic Detection of Long-Lived Nuclear Magnetization for Glutathione Oxidation Kinetics.

Imaging the molecular kinetics of antioxidants by magnetic resonance can contribute to the mechanistic understanding of therapeutic approaches. Magnetic resonance detection of the response to flashes of oxidative stress requires sequential spectroscopy on the same time scale on which reactive oxygen species are generated. To this effect, we propose a single-polarization multiple-detection stroboscopic experiment. We demonstrate this experiment for the follow-up of glutathione oxidation kinetics. On-the-fly stroboscopic detection minimizes the durations necessary for single acquisitions yet necessitates sustaining of magnetization lifetimes. Long-lived proton spin states (LLS) in the cysteine and glycine residues of glutathione with TLLS up to 16 s are reached. Based on 1H LLS, we followed fast oxidation kinetics in the glutathione redox pair GSH/GSSG. This new detection method allows sampling of long-lived spin order multiple times via small flip-angle excitations. This establishes the ground for the follow-up of redox processes detecting GSH/GSSG kinetics as magnetic-resonance biomarker of FLASH oxidative processes on time scales of tens of seconds.

Triple Tumor Microenvironment-Responsive Ferroptosis Pathways Induced by Manganese-Based Imageable Nanoenzymes for Enhanced Breast Cancer Theranostics.

Previous studies have found that activated CD8+ T cells secrete elevated levels of interferon-gamma (IFN-γ) to trigger ferroptosis in tumor cells. However, IFN-γ-mediated ferroptosis is induced at low levels in tumor cells because of the limited IFN-γ secreted by CD8+ T cells in the immunosuppressive tumor microenvironment. Recent studies have shown that manganese ion can activate the cyclic guanosine monophosphate-adenosine monophosphate (GMP-AMP) synthase/stimulator of interferon genes (cGAS-STING) pathway and support adaptive immune responses against tumors, which enhances the level of tumor-infiltrating CD8+ T cells. Therefore, tumor microenvironment-responsive Mn-based nanoenzymes (Mn-based NEs) that activated the cGAS-STING pathway are designed to amplify immune-driven ferroptosis. The multifunctional all-in-one nanoplatform is simply and mildly synthesized by the coordination between Mn3+ ions and 3,3'-dithiodipropionic acid. After intracellular delivery, each component of Mn-based NEs exerts its function. That is, glutathione is depleted through disulfide-thiol exchange and redox pair of Mn3+ /Mn2+ , a hydroxyl radical (·OH) is generated via the Fenton-like reaction to cause ferroptosis, and Mn2+ augments cGAS-STING activity to boost immune-driven ferroptosis. In addition, ferroptosis amplifies Mn2+ -induced immunogenic cell death and initiates the antitumor immune "closed loop" along with immune-driven ferroptosis. Notably, this multifunctional nanoplatform is effective in killing both primary and distant tumors.

Electrochemical Properties and Perspectives of Nickel(II) and Cobalt(II) Coordination Polymers-Aspects and an Application in Electrocatalytic Oxidation of Methanol

The electrochemical sensing potential of two isostructural one-dimensional nickel(II) and cobalt(II) coordination polymers with 4,4′-bipyridine (4,4′-bpy) and 6-oxonicotinate (6-Onic), namely, {[Ni(4,4′-bpy)(H2O)4](6-Onic)2×2H2O}n and {[Co(4,4′-bpy)(H2O)4](6-Onic)2×2H2O}n, was investigated along with the polymers’ potential applications in the catalytic oxidation of methanol. The highly oxidative species from redox pairs Ni(II)/Ni(III) and Co(II)/Co(III) in these compounds represent catalytically active centres for oxidation of small molecules. A glassy carbon electrode (GCE) modified with a Ni polymer showed stability and reproducibility in 0.1 M NaOH, while the oxidation current inc 2reased with the increasing methanol concentration, suggesting that the Ni-polymer-modified electrode possess good sensing ability with respect to methanol. The GC electrode modified with the Co polymer is not reproducible and cannot be used for electroanalytical purposes under these experimental conditions. The GC electrode modified with the Ni polymer was successfully applied in the determination of methanol. This method showed favourable linear concentration dependence with a good sensitivity of 2.65 and 11.0 mA mM−1, a wide concentration range (0.001–4 mM), and a detection limit of 0.8 μM, which indicates its excellent application potential for methanol oxidation and thus its determination.

Efficient Oxidative Dehydrogenation of Ethylbenzene over K/CeO2 with Exceptional Styrene Yield

Oxidative dehydrogenation (ODH) is an alternative for styrene (ST) production compared to the direct dehydrogenation process. However, ODH with O2 or CO2 suffers from either over-oxidation or endothermic property/low ethylbenzene conversion. Herein, we proposed an ODH process with a CO2-O2 mixture atmosphere for the efficient conversion of ethylbenzene (EB) into styrene. A thermoneutral ODH is possible by the rationalizing of CO2/O2 molar ratios from 0.65 to 0.66 in the temperature range of 300 to 650 °C. K modification is favorable for ethylbenzene dehydrogenation, and 10%K/CeO2 achieved the highest ethylbenzene dehydrogenation activity due to the enhanced oxygen mobility and CO2 adsorbability. The catalyst achieved 90.8% ethylbenzene conversion and 97.5% styrene selectivity under optimized conditions of CO2-4O2 oxidation atmosphere, a temperature of 500 °C, and a space velocity of 5.0 h−1. It exhibited excellent catalytic and structural stability during a 50 h long-term test. CO2 induces oxygen vacancies in ceria and promotes oxygen exchange between gaseous oxygen and ceria. The ethylbenzene dehydrogenation in CO2-O2 follows a Mars-van Krevelen (MvK) reaction mechanism via Ce3+/Ce4+ redox pairs. The proposed ODH strategy by using oxygen vacancies enriched catalysts offers an important insight into the efficient dehydrogenation of ethylbenzene at mild conditions.

Electronic structure regulation of an S-scheme CuBi2O4/Sr0.5NaTaO3 heterojunction with efficient carrier spatial transfer

The conduction/valence band (CB/VB) edge of perovskite-type ATaO3 largely straddles across the Fermi level, which endows it to be an attractive semiconductor with superior redox capacity. Nevertheless, the pristine ATaO3 suffers from the limited light responsive range and the low quantum efficiency. Herein, an S-scheme CuBi2O4/Sr0.5NaTaO3(CBSNT) heterostructure was firstly constructed, and being applied into the antibiotic water remediation. The kinetic constant for 40CBSNT composite (0.022 min−1) was 3.1 and 5.5 times higher than pristine SNTO (0.007 min−1) and CBO (0.004 min−1). h+ and ·O2– were proved as the dominant active radicals in CBSNT photocatalytic system. The reversible Cu+/Cu2+ redox pairs enables rapid hole extraction and efficient charge separation on the interface of CBSNT heterojunction. The synergistic effect of work function, Fermi energy level and the built-in electric field drive the electrons transfer from CBO to SNTO. The electrons flow trend on the heterojunction interface was jointly proved by XPS and DFT-calculated work function results. According to the DFT results, the photo-excited electrons was migrated from the Ta5d + O2p hybrid orbitals of SNTO's CB to recombine with the holes in the O2p orbital of CBO's VB in the S-type CBSNT heterostructure. The S-scheme pathway facilitated the carriers’ separation, and retained the strong redox capacity. Additionally, the AQE of the photodegradation system according to COD results was 0.15%. This work could layout some enlightenment for the efficient carrier spatial transfer implement in the heterojunction system design.

Constructing functional thermal-insulation-layer on Co3O4 nanosphere for reinforced local-microenvironment photothermal PMS activation in pollutant degradation

Photothermal catalysis of functional materials triggered by light-irradiation to local heating approach attracts growing attention, but one key detail affecting catalytic thermodynamic process was often ignored that thermal-conductive surface of functional materials directly contacting reaction solution easily delivers heat to the reaction system, leading to weakening heating effect in the interfacial local catalytic microenvironment. Herein, a functional low-thermal-conductivity layer that Mn-coupling porous SiO2 shell layer was constructed over the Co3O4 nanospheres. Specifically, SiO2 with porous channels introduced acts as the thermal-insulation layer to prevent the heat dissipation of the photo-heating core of Co3O4. More importantly, porous channel and inserted MnOx active species could further offer an additive special reaction microenvironment over the photo-heating core of Co3O4. Additionally, the introduction of Mn and structural remodeling through tailored annealing temperature (600–800 °C) can give improved catalytic hybrids abundant valence states and interfacial effects. A series of Co@Mn/m-SiO2 catalysts were fabricated based on the above control tactic. The Co@Mn/m-SiO2 catalysts exhibit superior activating ability for peroxymonosulfate (PMS) to degrade bisphenol A (BPA) and other pollutants including 2, 4-dichlorophenol (2, 4-DCP), phenol (PhOH), oxytetracycline (OTC), and tetracycline (TCN). Specifically, Co@Mn/m-SiO2-700 was shown to achieve complete degradation of 20 ppm BPA in less than 10 min under optimal conditions. In addition, we demonstrated that functional silica layer modified Co3O4 affords a better photo-heating effect compared to bare Co3O4 sphere in air or water, thereby contributing to a faster PMS activation efficiency. Besides, thermal treatment processing for Co@Mn/m-SiO2 catalyst makes the surface reactive species be optimized to generate more beneficial redox pairs and reach excellent photothermal catalytic efficiency in various pollutants treatment.

Design and fabrication of nickel lanthanum telluride microfibers for redox additive electrolyte-based flexible solid-state hybrid supercapacitor

In this article, we describe the design of a flexible solid-state hybrid supercapacitor (FSSHSC) using mixed metal telluride NiLaTe microfibers (MFs) atop Ni foam (NF). The goal of the study is to examine the effect of counter metal ions Ni and La, in addition to Te, in the formation of longer one-dimensional (1-D) architecture. The NiTe MFs and La2Te3 microrods (MRs) were synthesized and compared with bimetallic telluride. La exhibit's slower reaction kinetics than Ni when reacting with Te due to the different crystal structural stability of La2Te3 (cubic phase) and Te (hexagonal phase). Three-electrode investigations incorporating aqueous potassium ferrocyanide (KFC) reveal that the electrochemical performance of NiLaTe MFs is doubled compared to the typical aqueous KOH electrolyte alone. The presence of the redox pair [Fe(CN)6]3−/[Fe(CN)6]4− allows for faster ion transport inside the active electrode surface, which improves electrochemical performance. The FSSHSC device was fabricated, comprising NiLaTe as the positive, activated carbon (AC) as the negative electrode, and PVA-KOH-KFC gel, which acts as an electrolyte and a separator. The device performance was compared to that of a liquid system as well as one without a redox additive gel system. The significance of polymer-based gel and KFC for device construction is briefly reviewed. The final built device NiLaTe//AC in gel + KFC system has a maximum areal capacity of 65.6 μAh cm−2 (60.0 mA h g−1) at a current density of 2 mA cm−2, a maximum energy density of 45.5 Wh Kg−1 (52.36 μWh cm−2), and a maximum power density of 5488.7 W Kg−1(6312.0 μW cm−2). Furthermore, the device outperforms the cyclic stability for 10,000 cycles with an 80.1 % capacity retention and exhibits excellent flexibility at different bending angles. The assembled FSSHSCs device successfully illuminates an LED bulb for 70 s.

Comparative Study of Heat-Discharging Kinetics of Fe-Substituted Mn2O3/Mn3O4 Being Subjected to Long-Term Cycling for Thermochemical Energy Storage

The heat-discharging kinetics of an iron-substituted Mn2O3/Mn3O4 redox pair subjected to long-term thermal cycling tests using a temperature swing process at high temperatures was investigated for next-generation concentrated solar power plants equipped with thermochemical energy storage. The heat-discharge mode kinetics for long-term thermal-cycled samples have never been reported. Additionally, comparisons of the heat-discharge mode kinetics for both long-term thermal-cycled and as-prepared samples have never been discussed. In terms of the reproducibility and sustainability of thermochemical energy storage, kinetic evaluations of samples with thermally stable morphologies subjected to long-term thermal cycling at high temperatures are important for next-generation solar thermal power plants. For the long-term thermal-cycled sample, the A2 model based on the Avrami–Erofeev reaction describes the discharging mode behavior in a fractional conversion range of 0–0.24, the contracting area (R2) model best fits in a fractional conversion range of 0.24–0.50, and the third-order (F3) model matches in a fractional conversion range of 0.50–0.70. For the as-prepared sample, the power-law (P2) model describes the behavior of the first part of the discharging mode, whereas the Avrami–Erofeev (A4) model best fits the last half of the discharging mode. The predicted theoretical models for both samples were compared with previous kinetic data.

Heterostructure-strengthened metal-support interaction of single-atom Pd catalysts enabling efficient oxygen activation for CO and VOC oxidation

Catalytic oxidation of air pollutants depends on the active oxygen species, which requires a deep understanding of the active sites responsible for oxygen activation. In this study, we utilized a heterostructured support (ZnMn2O4@MnO2) to modulate the metal-support interactions (MSIs) in single-atom Pd catalysts, achieving efficient activation of both adsorbed oxygen (Oads) and lattice oxygen (Olatt). Specifically, the tailored MSIs induced an efficient redox pair for CO oxidation, i.e., Pd1O3 and Pd1O5, promoting the activation of O2 to Oads, which led to 90% CO conversion at room temperature and a novel “MvK-induced L-H” reaction mechanism. Moreover, the tailored MSIs induced the stretching of the Mn-O bond, facilitating the participation of Olatt in toluene oxidation. Our results demonstrate a novel approach to modulating MSIs in single-atom catalysts (SACs) and highlight the superiority of the strong MSIs introduced by heterostructured supports for oxygen activation.

Improving the Efficiency of Electrocatalysis of Cytochrome P450 3A4 by Modifying the Electrode with Membrane Protein Streptolysin O for Studying the Metabolic Transformations of Drugs.

In the present work, screen-printed electrodes (SPE) modified with a synthetic surfactant, didodecyldimethylammonium bromide (DDAB) and streptolysin O (SLO) were prepared for cytochrome P450 3A4 (CYP3A4) immobilization, direct non-catalytic and catalytic electrochemistry. The immobilized CYP3A4 demonstrated a pair of redox peaks with a formal potential of -0.325 ± 0.024 V (vs. the Ag/AgCl reference electrode). The electron transfer process showed a surface-controlled mechanism ("protein film voltammetry") with an electron transfer rate constant (ks) of 0.203 ± 0.038 s-1. Electrochemical CYP3A4-mediated reaction of N-demethylation of erythromycin was explored with the following parameters: an applied potential of -0.5 V and a duration time of 20 min. The system with DDAB/SLO as the electrode modifier showed conversion of erythromycin with an efficiency higher than the electrode modified with DDAB only. Confining CYP3A4 inside the protein frame of SLO accelerated the enzymatic reaction. The increases in product formation in the reaction of the electrochemical N-demethylation of erythromycin for SPE/DDAB/CYP3A4 and SPE/DDAB/SLO/CYP3A4 were equal to 100 ± 22% and 297 ± 7%, respectively. As revealed by AFM images, the SPE/DDAB/SLO possessed a more developed surface with protein cavities in comparison with SPE/DDAB for the effective immobilization of the CYP3A4 enzyme.

Kinetics and Structural Optimization of Cobalt-Oxide Honeycomb Structures Based on Thermochemical Heat Storage

Thermochemical heat storage is an important solar-heat-storage technology with a high temperature and high energy density, which has attracted increasing attention and research in recent years. The mono-metallic redox pair Co3O4/CoO realizes heat storage and exothermic process through a reversible redox reaction. Its basic principle is to store energy by heat absorption through a reduction reaction during high-irradiation hours (high temperature) and then release heat through an exothermic-oxidation reaction during low-irradiation hours (low temperature). This paper presents the design of a cobalt-oxide honeycomb structure, which is extruded from pure Co3O4, a porous media with a high heat-storage density and a high conversion rate. Based on the experimental data, a three-dimensional axisymmetric multi-physics numerical model was developed to simulate the flow, heat transfer, mass transfer, and chemical reaction in the thermochemical heat-storage reactor. Unlike the previous treatment approach of equating chemical reactions with surface reactions, the model in this paper considers the consumption and generation of solids and the diffusion and transfer of oxygen in the porous medium during the reaction process, which brings the simulation results closer to the real values. Finally, the influence of the physical parameters of the honeycomb-structured body on the storage and exothermic process is explored in a wide range. The simulation results show that the physical-parameter settings and structural design of the cobalt-oxide honeycomb structure used in this paper are reasonable, and are conducive to improving its charging/discharging performance.

Efficient emerging contaminants (EM) decomposition via peroxymonosulfate (PMS) activation by Co3O4/carbonized polyaniline (CPANI) composite: Characterization of tetracycline (TC) degradation property and application for the remediation of EM-polluted water body

Earth abundant transition metal-based materials are widely served as peroxymonosulfate (PMS) activators for degradation of emerging contaminants. However, the agglomeration of catalyst particles and metal ion leaching hinder their practical applications for pollutant decomposition. In this study, a Co3O4-carbonized polyaniline composite (Co3O4/CPANI) was implemented for PMS activation. The Co3O4/CPANI + PMS system exhibited high catalytic performance toward tetracycline (TC) degradation (degradation efficiency of 92.11%, initial TC level of 20 mg/L). Moreover, the practical application potential of Co3O4/CPANI + PMS system was well verified with three antibiotics (i.e., TC, doxycycline (DOX), and ciprofloxacin (CIP)) at highest actual aquatic environmental levels (1.0 and 0.5 mg/L). In the established Co3O4/CPANI + PMS system, both radicals (•O2−, •OH and SO4•-) and non-radical (1O2) contributed to TC degradation, and 1O2 was the dominant reactive oxygen species (ROS). CO groups, oxygen vacancies (OVS), redox pairs of Co2+/Co3+ species, and graphitic N all served as active sites in the PMS activation process, especially, OVS were crucial for the generation of 1O2. This study provides an efficient method for the synthesis of metal-based nanocatalysts with low nanoparticle aggregation and metal leaching which could act as a sustainable PMS activator for the remediation of TC-polluted water environment.

Anhydrous Thermogalvanic Gel for Simultaneous Waste Heat Recovery and Thermal Management of Electronics

Due to their distinctive characteristics of adequate flexibility, stability, and functional diversity, thermogalvanic gels have demonstrated tremendous promise in the area of renewable energy sources. However, their inability to adapt to low or high temperature environments greatly limits their practical applications. In this work, an anhydrous thermogalvanic gel prepared from dimethyl sulfoxide (DMSO)/ethylene glycol (EG) binary organic solvent is developed with Fe3+/2+ as a redox pair, which displays an exceptional temperature tolerance (−80 to 80 °C) and remarkable antidrying property (80% weight retention at 70 °C after 12 h), while maintaining stable mechanical flexibility and electrical conductivity over a wide temperature range. These merits result from the formation of numerous hydrogen bonds between DMSO and EG molecules, which prevent crystallization and hinder evaporation of the solvent simultaneously. As an applicative demonstration, by placing the thermogalvanic gel on the surface of a charging battery/charger/chip, it acts as a thermal-conductive network while performing the thermal-electric conversion, revealing a viable strategy for simultaneous waste heat recovery and thermal management. This research provides new insight into the creation of flexible thermoelectric materials for energy recovery and self-powered wearable electronics.

Improvement of surface properties of metal doped-CeO2 nanospindle catalysts for direct synthesis of dimethyl carbonate from CO2 and methanol

To utilize carbon dioxide (CO2) which is the main greenhouse gas, this study developed effective metal doped-CeO2 nanospindle catalysts for conversion of CO2 and methanol into dimethyl carbonate (DMC). Ce0.9M0.1O2 nanospindles (where M is a transition metal, i.e., Zr, Fe, Cu and Co) were prepared by a template-free hydrothermal method. The substitution of different valence and size cations, including Zr4+, Fe3+, Cu2+ and Co2+, for Ce4+ sites in the fluorite CeO2 lattice induced the defect formation of surface-active sites of exposed Ce3+ and oxygen vacancies through the charge compensation and redox pair reactions. Ce0.9Fe0.1O2 solid solution with well-preserved spindle shaped morphology showed the highest catalytic performance by giving DMC yield at 3.56 mmol.gcat−1 with 100% DMC selectivity. The improvement of catalytic activity was attributed to the higher proportion of surface defect sites and variation of acid-base properties caused by the integration of Fe dopants into CeO2 ionic system.

Galvanic Replacement Synthesis of Metal Nanostructures: Bridging the Gap between Chemical and Electrochemical Approaches

ConspectusGalvanic replacement synthesis involves oxidation and dissolution of atoms from a substrate while the salt precursor to another material with a higher reduction potential is reduced and deposited on the substrate. The driving force or spontaneity of such a synthesis comes from the difference in reduction potential between the redox pairs involved. Both bulk and micro/nanostructured materials have been explored as substrates for galvanic replacement synthesis. The use of micro/nanostructured materials can significantly increase the surface area, offering immediate advantages over the conventional electrosynthesis. The micro/nanostructured materials can also be intimately mixed with the salt precursor in a solution phase, resembling the setting of a typical chemical synthesis. The reduced material tends to be directly deposited on the surface of the substrate, just like the situation in an electrosynthesis. Different from an electrosynthesis where the two electrodes are spatially separated by an electrolyte solution, the cathodes and anodes are situated on the same surface, albeit at different sites, even for a micro/nanostructured substrate. Since the oxidation and dissolution reactions occur at sites different from those for reduction and deposition reactions, one can control the growth pattern of the newly deposited atoms on the same surface of a substrate to access nanostructured materials with diverse and controllable compositions, shapes, and morphologies in a single step. Galvanic replacement synthesis has been successfully applied to different types of substrates, including those made of crystalline and amorphous materials, as well as metallic and nonmetallic materials. Depending on the substrate involved, the deposited material can take different nucleation and growth patterns, resulting in diverse but well-controlled nanomaterials sought for a variety of studies and applications.In this Account, we recapitulate our efforts over the past two decades in fabricating metal nanostructures for a broad range of applications by leveraging the unique capability of galvanic replacement synthesis. We begin with a brief introduction to the fundamentals of galvanic replacement between metal nanocrystals and salt precursors, followed by a discussion of the roles played by surface capping agents in achieving site-selected carving and deposition for the fabrication of various bimetallic nanostructures. Two examples based on the Ag-Au and Pd-Pt systems are selected to illustrate the concept and mechanism. We then highlight our recent work on the galvanic replacement synthesis involving nonmetallic substrates, with a focus on the protocol, mechanistic understanding, and experimental control for the fabrication of Au- and Pt-based nanostructures with tunable morphologies. Finally, we showcase the unique properties and applications of nanostructured materials derived from galvanic replacement reactions for biomedicine and catalysis. We also offer some perspectives on the challenges and opportunities in this emerging field of research.

Direct Electrochemistry of Glucose Dehydrogenase-Functionalized Polymers on a Modified Glassy Carbon Electrode and Its Molecular Recognition of Glucose.

A glucose biosensor was layer-by-layer assembled on a modified glassy carbon electrode (GCE) from a nanocomposite of NAD(P)+-dependent glucose dehydrogenase, aminated polyethylene glycol (mPEG), carboxylic acid-functionalized multi-wall carbon nanotubes (fMWCNTs), and ionic liquid (IL) composite functional polymers. The electrochemical electrode was denoted as NF/IL/GDH/mPEG-fMWCNTs/GCE. The composite polymer membranes were characterized by cyclic voltammetry, ultraviolet-visible spectrophotometry, electrochemical impedance spectroscopy, scanning electron microscopy, and transmission electron microscopy. The cyclic voltammogram of the modified electrode had a pair of well-defined quasi-reversible redox peaks with a formal potential of -61 mV (vs. Ag/AgCl) at a scan rate of 0.05 V s-1. The heterogeneous electron transfer constant (ks) of GDH on the composite functional polymer-modified GCE was 6.5 s-1. The biosensor could sensitively recognize and detect glucose linearly from 0.8 to 100 µM with a detection limit down to 0.46 μM (S/N = 3) and a sensitivity of 29.1 nA μM-1. The apparent Michaelis-Menten constant (Kmapp) of the modified electrode was 0.21 mM. The constructed electrochemical sensor was compared with the high-performance liquid chromatography method for the determination of glucose in commercially available glucose injections. The results demonstrated that the sensor was highly accurate and could be used for the rapid and quantitative determination of glucose concentration.

Development of organic redox‐active materials in aqueous flow batteries: Current strategies and future perspectives

AbstractAqueous redox flow batteries, by using redox‐active molecules dissolved in nonflammable water solutions as electrolytes, are a promising technology for grid‐scale energy storage. Organic redox‐active materials offer a new opportunity for the construction of advanced flow batteries due to their advantages of potentially low cost, extensive structural diversity, tunable electrochemical properties, and high natural abundance. In this review, we present the emergence and development of organic redox‐active materials for aqueous organic redox flow batteries (AORFBs), in particular, molecular engineering concepts and strategies of organic redox‐active molecules. The typical design strategies based on organic redox species for high‐capacity, high‐stability, and high‐voltage AORFBs are outlined and discussed. Molecular engineering of organic redox‐active molecules for high aqueous solubility, high chemical/electrochemical stability, and multiple electron numbers as well as satisfactory redox potential gap between the redox pair is essential to realizing high‐performance AORFBs. Beyond molecular engineering, the redox‐targeting strategy is an effective way to obtain high‐capacity AORFBs. We further discuss and analyze the redox reaction mechanisms of organic redox species based on a series of electrochemical and spectroscopic approaches, and succinctly summarize the capacity degradation mechanisms of AORFBs. Furthermore, the current challenges, opportunities, and future directions of organic redox‐active materials for AORFBs are presented in detail.

Bare and Pt-loaded LaCo1-xFexO3 perovskites as catalysts for CO-PROX reaction

Perovskites based on cobalt and iron LaCo1-xFexO3 (x = 0, 0.1 and 1) and their behavior in the presence of platinum yPt/LaCo1-xFexO3 (y = 0.1, 0.5 and 2.5% wt.) were evaluated as catalysts in the preferential oxidation of carbon monoxide (CO-PROX). Perovskites (general formula ABO3) are alternative materials to conventional transition metal oxides, expanding the tunable redox properties according to the combination of elements. In CO-PROX, Co3O4 and Pt/Fe3O4 are well-studied systems. The superficial Co3+/Co2+ redox pair is highly active. Still, the Co3O4 is easily reduced at low temperatures under the reducing conditions of CO-PROX, forming less active phases enriched in Co2+ and Co0. On the other hand, Fe3O4 is not active but becomes highly reactive when associated with Pt through the redox mechanism intermediated by the Fe3+/Fe2+ pair created at the metal interface. Supported by in situ characterization under reducing conditions and complementary ex situ analyses, we found that the LaCoO3 resembles the Co3O4, and the addition of Fe forming LaCo0·9Fe0·1O3 induced higher stability of the perovskite structure under reducing conditions. The presence of Pt significantly impacted the stabilization of the active sites under CO-PROX conditions depending on the perovskite composition. Finally, the Pt/LaFeO3 catalyst combined the high activity of the Pt/Fe3O4 system with the thermal stability of the perovskite structure.

Selective Electroreduction of Oxalic Acid to Glycolic Acid by Mesoporous TiO2 Spheres

AbstractReducing oxalic acid to glycolic acid electrochemically remains a significant challenge due to the high overpotential and low selectivity and stability. This study uses mesoporous TiO2 spheres of anatase phase as catalysts to reduce oxalic acid to glycolic acid with low overpotential. The maximum Faradaic efficiency of glycolic acid reaches 73.9 % at −0.5 V vs RHE. The mesoporous structure not only increases the specific surface area, but also limits the escape of intermediate glyoxalic acid from the catalyst surface due to the space‐limiting effect of the mesoporous channel, such that oxalic acid can be deeply reduced to glycolic acid. Moreover, a mechanism for oxalic acid reduction is proposed, and the Ti3+/Ti4+ redox pair plays an important role in the reduction of oxalic acid.