Fast Electron Transfer Kinetics Research Articles

Sandwich-type electrochemical aptasensor based on hemin-graphite oxide as a signal label and rGO/MWCNTs/chitosan/carbon quantum dot modified electrode for sensitive detection of Acinetobacter baumannii bacteria

Acinetobacter baumannii (A. baumannii) is a pathogenic bacterium that causes severe infections and its rapid and reliable diagnosis is essential for effective control and treatment. In this study, we present an electrochemical aptasensor based on a signal amplification strategy for the detection of A. baumannii, the high specificity and affinity of the aptamer for the target make it favorable for signal amplification. This allows for a highly sensitive and selective detection of the target. The aptasensor is based on a carbon screen-printed electrode (CSPE) that has been modified with a nanocomposite consisting of multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), chitosan (CS), and a synthesized carbon quantum dot (CQD) from CS. Additionally, the self-assembled aptamers were immobilized on hemin-graphite oxide (H-GO) as a signal probe.The composition of the nanocomposite (rGO-MWCNT/CS/CQD) provides high conductivity and stability, facilitating the efficient capture of A. baumannii onto the surface of the aptasensor. Also, aptamer immobilized on Hemin-graphite oxide (H-GO/Aptamer) was utilized as an electrochemical signal reporter probe by H reduction. This approach improved the detection sensitivity and the aptamer surface density for detecting A. baumannii. Furthermore, under optimized experimental conditions, the aptasensor was demonstrated to be capable of detecting A. baumannii with a linear range of (10 – 1 × 107 Colony-forming unit (CFU)/mL) and a limit of detection (LOD) of 1 CFU/mL (σ = 3). One of the key features of this aptasensor is its ability to distinguish between live and dead bacteria cells, which is very important and critical for clinical applications. In addition, we have successfully detected A. baumannii bacteria in healthy human serum and skim milk powder samples provided using the prepared electrochemical aptasensor.The functional groups present in the synthetic CQD, rGO-MWCNT, and chitosan facilitate biomolecule immobilization and enhance stability and activity. The fast electron-transfer kinetics and high conductivity of these materials contribute to improved sensitivity and selectivity. Furthermore, The H-GO/Aptamer composite's large surface area increases the number of immobilized secondary aptamers and enables a more stable structure. This large surface area also facilitates more H loading, leading to signal amplification.

Strategically Designed Pd-Induced Changes in Alkaline Hydrogen Evolution Reaction and Oxygen Evolution Reaction Performances of Electrochemical Water Oxidation by the Galvanically Synthesized MoO2/MoO3 Composite Thin Film.

Electrochemical water oxidation is believed to be an effective pathway to produce clean, carbon-free, and environmentally sustainable green energy. In this work, we report a simple, easy-to-construct, facile, low-cost, and single-step galvanic technique to synthesize a Pd-supported temperature-assisted MoOx thin film nanocomposite for effective water oxidation. The most suitable nanocomposite exhibits very low overpotential at 10 mA/cm2 with smaller Tafel slope values for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) processes in an alkaline medium. The formation of a metal oxide-metal junction accelerates the growth of more active sites, promoting induced electronic synergism at the MoOx-Pd interface. This endows higher electrical conductivity and faster electron transfer kinetics, thus accelerating the faster water dissociation reaction following the Tafel-Volmer mechanism to boost the HER process in an alkaline medium. The excellent electrochemical HER and OER performances of our electrocatalyst even supersede the accomplishments of the benchmark catalysts Pt/C and RuO2. Moreover, neither of these two catalysts demonstrates both catalytic reactions, i.e., HER and OER at the same time, which have been observed for our synthesized catalyst. Our findings illustrate the potential of a thin-film MoOx-Pd nanocomposite to be an exceedingly effective electrocatalyst developed by interface engineering strategies. This also provides insight into designing several other semiconductor composite catalysts using simple synthesis techniques for highly efficient HER/OER processes that could be alternatives to benchmark electrocatalysts for water electrolysis.

Ruthenium nanoparticles embedded poly(4-aminodiphenylamine) nanocomposites based determination of guaifenesin in real samples

An efficient sensing surface is fabricated through incorporating ruthenium on electropolymerized poly-(4-aminodiphenylamine)(Padpa) film by potentiodynamic cycling of 4-aminodiphenylamine (4-adpa) in an acidic medium. The mechanism of electropolymerization comprises the conversion of protonated monomer to di-imine species and generates positively charged radical-intermediate via dimerization step. The surface morphology of deposited film on electrode surface is studied using SEM and XPS techniques. The electrocatalytic appraisal of constructed (Ru/Padpa/GCE) sensing interface is examined towards the electro-oxidation of guaifenesin (GUA) by differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and chronoamperometric (CA) methods. The Ru/Padpa/GCE sensing interface displayed a linear response of GUA from 1.5 to 45 µg/mL with the limit of detection (LOD) of 48.8 ng/mL (S/N = 3). The obtained higher activity of Ru/Padpa/GCE is mainly attributed to its larger active surface area, faster electron transfer kinetics, and higher catalytic sites from the interface. The Ru/Padpa/GCE sensing interface is further applied for the determination of GUA in pharmaceutical (cough syrup, and human urine) samples with a recovery of 97.1–101.0 %. The diffusion coefficient of GUA (1.51 × 10-6 cm2/s) is also obtained via theoretical electrochemical method, which ensures that Ru/Padpa/GCE sensing interface can be considered as a potential candidate for clinical diagnostic analysis.

Comparative electrochemical properties of polyaniline/carbon quantum dots nanocomposites modified screen-printed carbon and gold electrodes

In this study, carbon quantum dots (Cdots) synthesized from a pencil graphite precursor using a bottom-up method were incorporated into polyaniline (PANI) to form Cdots-PANI nanocomposite. Cdots, PANI and Cdots-PANI nanocomposites were characterized using the Fourier-Transform infrared spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The FT-IR spectra of graphene and Cdots show the emergence of a peak at 3500 cm−1, which was initially absent in graphene, after the formation of Cdots, among other peaks. The peak at 3500 cm−1 and the stretching vibration at 1647 cm−1 suggest the presence of –OH and C=C in the Cdots. The FT-IR spectra of PANI/Cdots and PANI show that the peaks in PANI shifted to higher wavenumbers after composite formation. Similarly, the UV–visible spectra of the PANI/Cdots composite revealed a hypsochromic shift of the characteristic PANI peaks at 320 and 600 nm to 300 and 560 nm, respectively. Electrochemical characterization of Cdots, PANI and Cdots-PANI nanocomposites was done with screen-printed carbon electrodes (SPCE) and screen-printed gold electrodes (SPAuE) modified with the nanomaterials and the nanocomposites. The electrochemical properties of the as-synthesized nanomaterials and the nanocomposite were investigated with Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) in 10 mM K3[Fe(CN)6] solution using the bare screen-printed electrodes and the modified electrodes. The modified electrodes gave higher anodic peak current (Ipa) responses and lower charge transfer resistance (Rct) values in the redox probe than the bare electrodes. The SPCE-Cdots-PANI nanocomposite-modified electrode exhibited better redox potentials, faster electron transfer kinetics, larger surface area, and greater stability than the bare electrodes and the other modified electrodes. The outstanding electrochemical properties of SPCE-Cdots/PANI underscores its potentials as a sensitive electrochemical sensor for a wide range of analytes.

Electrochemical Detection of Metol through the Cobalt Nickel Oxide Nanosheets Incorporated with MCM-41 Nanospheres Composites Modified Glassy Carbon Electrode

In this study, contaminations of metol (or Elon) in environmental water and industrial wastewater are the major causes of toxicity, which is very harmful to human health and other living things. Hence the determination of metol in high demand is more important. Further, the Mobil Composition of Matter (MCM-41) mesoporous silica nanoparticles incorporated with cobalt nickel oxide (CoNiO2) complex to form MCM-41/CoNiO2 composite modifying the glassy carbon electrode (GCE) used for metol detection. The MCM-41/CoNiO2 composite coated on the GCE surface exhibited fast electron transfer kinetics, improved conductivity, a large surface area, active stability, and improved catalytic efficiency. The structural morphology of the MCM-41/CoNiO2 composite was investigated using several spectroscopic and microscopic techniques. Here, the MCM-41/CoNiO2 composite was verified using different characterization studies such as Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, Energy Dispersive X-ray Analysis, X-ray Diffraction Analysis, and X-ray Photoelectron Spectroscopy. Additionally, the electrochemical investigations have included Electrochemical Impedance Spectroscopy, Cyclic Voltammetry, and Differential Pulse Voltammetry studies. The GCE/MCM-41/CoNiO2 electrode shows a low detection limit of 10 nM and the LOQ value is 0.1 μM with a broad linear response range of 0.1–750 μM, and greater sensitivity of 0.411 μA μM−1 cm−2 under optimal voltammetry.

Sulfanilamide Electrochemical Sensor Using Phenolic Substrates and CO2 Laser Pyrolysis.

The concentration of environmental pollutants needs to be monitored constantly by reliable analytical methods since they pose a public health risk. Developing simple and affordable sensors for such pollutants can allow for large-scale monitoring economically. Here, we develop a simple electrochemical sensor for sulfanilamide (SFD) quantification using a phenolic resin substrate and a CO2 laser to pyrolyze the sensor geometry over the substrate. The sensors are modified with carbon nanotubes via a simple drop-casting procedure. The carbon nanotube loading effect the electrochemical performance toward a redox probe and analytical performance for SFD detection is investigated, showing no net benefit beyond 1 mg L-1 of carbon nanotubes. The effects of the modification on the SFD oxidation are shown to be more than just an electrode area effect and possibly attributed to the fast electron transfer kinetics of the carbon nanotubes. SFD detection is performed at small solution volumes under static (800 μL) and hydrodynamic conditions (3 mL) in a fully integrated, miniaturized batch-injection analyses cell. Both methods have a similar linear range from 10.0 to 115.0 μmol L-1 and high selectivity for SFD determination. Both systems are used to quantify SFD in real samples as a proof of concept, showcasing the proposed device's applicability as a sensor for environmental and public health monitoring of SFD.

Pencil Graphite Electrocatalytic Sensors Modified by Pyrene Coated Reduced Graphene Oxide Decorated with Molybdenum Disulfide Nanoroses for Hydrazine and 4-Nitrophenol Detection in Real Water Samples.

Novel nanostructured platforms based on Pencil Graphite Electrodes (PGEs), modified with pyrene carboxylic acid (PCA) functionalized Reduced Graphene Oxide (rGO), and then decorated by chronoamperometry electrodeposition of MoS2 nanoroses (NRs) (MoS2NRs/PCA-rGO/PGEs) were manufactured for the electrocatalytic detection of hydrazine (N2H4) and 4-nitrophenol, pollutants highly hazardous for environment and human health. The surface morphology and chemistry of the MoS2NRs/PCA-rGO/PGEs were characterized by scanning electron microscopy (SEM), Raman, and X-ray photoelectron spectroscopy (XPS), assessing the coating of the PCA-rGO/PGEs by dense multilayers of NRs. N2H4 and 4-nitrophenol have been monitored by Differential Pulse Voltammetry (DPV), and the MoS2NRs/PCA-rGO/PGEs electroanalytical properties have been compared to the PGEs, as neat and modified by PCA-rGO. The MoS2NRs/PCA-rGO/PGEs demonstrated a higher electrochemical and electrocatalytic activity, due to their high surface area and conductivity, and very fast heterogeneous electron transfer kinetics at the interphase with the electrolyte. LODs lower than the U.S. EPA recommended concentration values in drinking water, namely 9.3 nM and 13.3 nM, were estimated for N2H4 and 4-nitrophenol, respectively and the MoS2NRs/PCA-rGO/PGEs showed good repeatability, reproducibility, storage stability, and selectivity. The effectiveness of the nanoplatforms for monitoring N2H4 and 4-nitrophenol in tap, river, and wastewater was addressed.

Recent Developments on Electroactive Organic Electrolytes for Non-Aqueous Redox Flow Batteries: Current Status, Challenges, and Prospects.

The ever-increasing threat of climate change and the depletion of fossil fuel resources necessitate the use of solar- and wind-based renewable energy sources. Large-scale energy storage technologies, such as redox flow batteries (RFBs), offer a continuous supply of energy. Depending on the nature of the electrolytes used, RFBs are broadly categorized into aqueous redox flow batteries (ARFBs) and non-aqueous redox flow batteries (NARFBs). ARFBs suffer from various problems, including low conductivity of electrolytes, inferior charge/discharge current densities, high-capacity fading, and lower energy densities. NARFBs offer a wider potential window and range of operating temperatures, faster electron transfer kinetics, and higher energy densities. In this review article, a critical analysis is provided on the design of organic electroactive molecules, their physiochemical/electrochemical properties, and various organic solvents used in NARFBs. Furthermore, various redox-active organic materials, such as metal-based coordination complexes, quinones, radicals, polymers, and miscellaneous electroactive species, explored for NARFBs during 2012-2023 are discussed. Finally, the current challenges and prospects of NARFBs are summarized.

In situ fabrication of copper oxide nanoparticles decorated carbon cloth for efficient electrocatalytic detection of nitrite

In this work, a simple and efficient electrochemical sensor for nitrite based on in situ fabrication of copper oxide nanoparticles decorated carbon cloth (CuO NPs/CC) has been fabricated by efficient electrodeposition and calcination route. Owing to the synergistic effect of high conductivity, fast electron transfer kinetics, excellent electrocatalytic activity and large electroactive specific surface area, the CuO NPs/CC electrode has exhibited brilliant ability in nitrite detection, including wide linear ranges of 0.5–3000 μM, low detection limit of 0.043 μM (S/N = 3), the fast response time of 0.9 s and high sensitivity of 1656 μA mM−1 cm−2. Additionally, CuO NPs/CC electrode has been successfully used to determine nitrite in real samples of drinking water and sauerkraut with satisfactory recoveries.

Microfluidic-Assisted Alignment of Graphene Nanosheets for Microfiber Formation

Recently, our lab developed graphene oxide microfibers for ultrasensitive neurochemical detection with fast-scan cyclic voltammetry (FSCV). Graphene-fiber microelectrodes provide a significant advance over traditional carbon-fiber microelectrodes due to their resistance to detrimental fouling, fast electron transfer kinetics, and frequency independent behavior. Despite our recent advancement, there still exists a gap in our understanding of how specific changes in the carbon chemical structure influences adsorption and interaction of various neurochemicals at the surface. Understanding the extent to which the carbon chemical structure influences electrochemical detection is critical for designing tailor-made electrodes for ultrasensitive analyte detection. From a molecular level point-of-view, the graphene sheet consists of two regions with different structure: i) the basal plane, consisting of conjugated sp2 hybridized carbon atoms, and characterized by an atomic flatness and low defect density; and ii) the edge plane, that forms sp3 sites with a high level of defects and a variety of functional groups and dangling bonds. It is generally believed that the electrochemical properties of the basal and edge plane are significantly different, however, there has been debate concerning the electrochemical activity at the basal and edge plane. The conventional consensus is that electron transfer kinetics is faster on the edge plane in comparison with the basal plane sites, while the opposite barrier of this debate provides evidence for fast electron transfer at pristine basal plane. Moreover, how these factors influence neurochemical detection, particularly at rapid scan rates, is still lacking due to the necessity of using microelectrodes with FSCV. To date, most studies analyzing the influence of basal vs. edge plane surfaces on electrochemical detection have used macroelectrodes like highly ordered pyrolytic graphite (HOPG) which are not amenable to FSCV detection due to the large capacitive currents obtained at macroelectrodes at scan rates consisting of hundreds of volts per second. Therefore, to address this existing knowledge gap in understanding how edge vs. basal planes influence subsecond neurochemical detection, the ability to develop microelectrodes with controlled surfaces is crucial. Here, I will discuss our labs latest effort in developing graphene oxide microfibers with controllable nanosheet alignment to study the influence of basal vs. edge plane availability on neurochemical detection at rapid scan rates. To assist in nanosheet alignment, we use microfluidic channels to assist in fluid-driven control of nanosheet orientation. Using microfluidics to help develop highly controllable electrode materials provides a critical advance in our ability to develop novel carbon surfaces for detection.

Inkjet Printing-Manufactured Boron-Doped Diamond Chip Electrodes for Electrochemical Sensing Purposes.

Fabrication of patterned boron-doped diamond (BDD) in an inexpensive and straightforward way is required for a variety of practical applications, including the development of BDD-based electrochemical sensors. This work describes a simplified and novel bottom-up fabrication approach for BDD-based three-electrode sensor chips utilizing direct inkjet printing of diamond nanoparticles on silicon-based substrates. The whole seeding process, accomplished by a commercial research inkjet printer with piezo-driven drop-on-demand printheads, was systematically examined. Optimized and continuous inkjet-printed features were obtained with glycerol-based diamond ink (0.4% vol/wt), silicon substrates pretreated by exposure to oxygen plasma and subsequently to air, and applying a dot density of 750 drops (volume 9 pL) per inch. Next, the dried micropatterned substrate was subjected to a chemical vapor deposition step to grow uniform thin-film BDD, which satisfied the function of both working and counter electrodes. Silver was inkjet-printed to complete the sensor chip with a reference electrode. Scanning electron micrographs showed a closed BDD layer with a typical polycrystalline structure and sharp and well-defined edges. Very good homogeneity in diamond layer composition and a high boron content (∼2 × 1021 atoms cm-3) was confirmed by Raman spectroscopy. Important electrochemical characteristics, including the width of the potential window (2.5 V) and double-layer capacitance (27 μF cm-2), were evaluated by cyclic voltammetry. Fast electron transfer kinetics was recognized for the [Ru(NH3)6]3+/2+ redox marker due to the high doping level, while somewhat hindered kinetics was observed for the surface-sensitive [Fe(CN)6]3-/4- probe. Furthermore, the ability to electrochemically detect organic compounds of different structural motifs, such as glucose, ascorbic acid, uric acid, tyrosine, and dopamine, was successfully verified and compared with commercially available screen-printed BDD electrodes. The newly developed chip-based manufacture method enables the rapid prototyping of different small-scale electrode designs and BDD microstructures, which can lead to enhanced sensor performance with capability of repeated use.

Bimetallic copper-cobalt MOFs anchored carbon nanofibers hybrid mat based electrode for simultaneous determination of dopamine and tyramine

Early monitoring of histamine and tyramine levels in foodstuffs could protect against several diseases. In the present study, a self-standing copper-cobalt(2-methylimidazole) MOF anchored carbon nanofiber hybrid mat (Cu-Co(2-Meim)MOF@CNF) was prepared for the simultaneous detection and quantification of dopamine and tyramine in cheese and banana samples. As-prepared Cu-Co(2-Meim)MOF@CNF hybrid mats are highly porous with a large surface area, and also possess excellent hydrophilicity, which allows the analyte molecules to easily access the redox-active metal sites of the MOF matrix and subsequently enhance the sensitivity. The functional groups within the MOF matrix can also function as active adsorption sites during electrocatalysis. At the acidic condition (pH = 5.0), the Cu-Co(2-Meim)MOF@CNF exhibited improved catalytic activity and strong electrochemical sensitivity toward dopamine (DA) and tyramine (TY) with faster electron transfer kinetics and significant fouling resistance. The oxidation reactions of dopamine and tyramine at the hybrid electrode were irreversible and diffusion-controlled. The Cu-Co(2-Meim)MOF@CNF/GCE sensor demonstrated a broad linear range from 5 to 800 µM along with a low LOD of 44.2 nM and 52.7 nM for dopamine and tyramine, respectively. The hybrid sensor exhibited excellent anti-interference properties and long-term storage stability for up to 30 days. It is noteworthy that the Cu-Co(2-Meim)MOF@CNF/GCE sensor has demonstrated the capability of detecting dopamine and tyramine in cheese and banana samples, respectively, which would be helpful for food analysis and food safety.

A pyramidal metal organic frameworks-derived FeP@CoP aluminium-ion battery cathode displaying low-temperature tolerance and fast electron transfer kinetics.

Engineering appropriate cathode materials is significant for the development of high-performance aluminum-ion (Al-ion) batteries. Here, a pyramidal metal organic frameworks (MOFs)-derived FeP@CoP composite is developed as cathode, which exhibits good stability and high capacity. FeP@CoP cathode remains a high capacity of 168 mAh g-1 after 200 cycles, and displays a stable rate-performance at both room and low temperatures of -10 °C. After three rounds of rate-performance cycling, the FeP@CoP composite recovers 178.2 mAh g-1 at 0.3 A g-1. Moreover, density functional theory (DFT) calculations verify improved electron-transfer kinetics with narrowed band gap and enhanced density of states. Those findings would inspire a broad set of studies on MOFs-derived composites for high-performance secondary batteries.

Carbon nanomaterials and their composites for electrochemical glucose biosensors: A review on fabrication and sensing properties

BackgroundWith the increasing prevalence of diabetes that increases the risk of cardiovascular diseases, kidney failure, nerve degeneration, eye damage, lower extremity amputations and birth defects, the demand for highly efficient glucose sensors has attracted significant attention worldwide. In this regard, carbon nanomaterials-based electrochemical glucose sensors have shown great potential in the detection and monitoring of glucose. MethodsDifferent forms of carbon such as carbon nanotubes, graphene, reduced graphene oxide, carbon nanofibers, activated and amorphous carbon, carbon spheres, carbon nanoparticles, carbon quantum dots, carbon nanorods, carbon nanocages etc. and their hybrids have been extensively researched for highly efficient glucose sensors due to their large surface area, porosity, lightweight, thermal stability, excellent mechanical properties, ease of fabrication, high electrical conductivity, excellent catalytic properties and fast electron transfer kinetics. Significant findingsDue to their large surface area and tunable porosity, carbon nanomaterials have been used as a scaffold for the immobilization of large quantities of bioreceptor units such as enzymes and highly catalytic metal or metal oxide nanostructures, which can enhance the electroanalytical properties of the biosensor. In this review paper, the fabrication and electroanalytical properties of carbon nanomaterials based enzymatic and nonenzymatic electrochemical glucose sensors have been reviewed and their sensing mechanisms are discussed.

Electrochemical surface rehydrogenation of boron-doped diamond electrodes after electrochemical polishing

Non-diamond carbon impurity and surface roughness are features that can affect the response of boron-doped diamond (BDD) electrodes. Herein, we report on the electropolishing of BDD electrodes carried out in the presence of acetic and sulfuric acid for different times (1, 2, and 4 h). The wet electrochemical treatment smooths the polycrystalline diamond surface and reduces the non-diamond sp2 carbon impurity content while increasing the surface oxygen content. Changes in surface texture and microstructure were revealed by atomic force microscopy, Raman spectroscopy, and cyclic voltammetry. Subsequently, the surface oxygen content was reduced by increasingly severe cathodic pretreatments (CPTs). This was revealed by changes in the voltametric response for the [Fe(CN)6]3−/4– and ascorbic acid (AA) redox systems, as both exhibit electron transfer kinetics sensitive to the level of oxidation of the BDD surface. For [Fe(CN)6]3−/4–, greater ∆Ep values were obtained for the electropolished (EP-BDD) electrodes, as compared to the as received (AR-BDD) electrode. However, after CPTs the EP-BDD electrodes exhibited smaller ∆Ep values (∼60 mV), which indicate significantly improved electrochemical reversibility and faster electron-transfer kinetics caused by the decreased level of surface oxidation (greater hydrogenation). The increased surface oxygen content brought on by the electropolishing process had also a significant effect on the AA oxidation peak potential (Eap), making it at least ∼140 mV more positive than that for the AR–BDD electrode. However, after CPTs the Eap values for the EP–BDD electrodes became at least ∼0.1 V less positive than that for the AR–BDD electrode, indicating that the surface of the EP-BDD electrodes possesses less surface carbon‑oxygen functional groups (i.e., it is more hydrogenated). The combination of electropolishing and cathodic pretreatment is a way to process the BDD electrode surface to create a smoother, low oxygen surface in much the same way as a hydrogen plasma treatment does.

Manganese cobalt-MOF@carbon nanofiber-based non-enzymatic histamine sensor for the determination of food freshness.

Early detection of histamine in foodstuffs/beverages could be useful in preventing various diseases. In this work, we have prepared a free-standing hybrid mat based on manganese cobalt (2-methylimodazole)-metal organic frameworks (Mn-Co(2-MeIm)MOF) and carbon nanofibers (CNFs) and explored as a non-enzymatic electrochemical sensor for determining the freshness of fish and bananas based on histamine estimation. As-developed hybrid mat possesses high porosity with a large specific surface area and excellent hydrophilicity those allow easy access of analyte molecules to the redox-active metal sites of MOF. Furthermore, the multiple functional groups of the MOF matrix can act as active adsorption sites for catalysis. The Mn-Co(2-MeIm)MOF@CNF mat-modified GC electrode demonstrated excellent electrocatalytic activities toward the oxidation of histamine under acidic conditions (pH = 5.0) with a faster electron transfer kinetics and superior fouling resistance. The Co(2-MeIm)MOF@CNF/GCE sensor exhibited a wide linear range from 10 to 1500µM with a low limit of detection (LOD) of 89.6nM and a high sensitivity of 107.3 µA mM-1cm-2. Importantly, as-developed Nb(BTC)MOF@CNF/GCE sensor is enabled to detect histamine in fish and banana samples stored for different periods of time, which thus indicates its practical viability as analytical histamine detector.

TiO2 nanotubes modified with cobalt oxyphosphide spheres for efficient electrocatalytic hydrogen evolution reaction in alkaline medium

Electronic and surface modulation through coupling between oxygen and phosphorous in cobalt oxyphosphide (CoOP) is identified as an effective approach to enhancing the electrocatalytic hydrogen evolution reaction (HER) in an alkaline medium. This work demonstrates a one-step and safe electrodeposition method to modify the surface of ordered titania nanotubes (TNTs) with CoOP spheres. The effect of electrodeposition charge density, pH of the electrodeposition bath, and presence of citric acid on the electrocatalytic HER performance of CoOP-modified TNTs was investigated. The Ti/TNTs/CoOP electrode requires only 130 mV overpotential to deliver 10 mA cm−2 in a 1.0 M KOH electrolyte. The Tafel slope is estimated to be 72.5 mV dec−1. Both the HER performance and Tafel value of Ti/TNTs/CoOP are superior to CoOP deposited on bare Ti foil (165 mV and 78.4 mV dec−1), FTO (185 mV; 88.1 mV dec−1), and glassy carbon (214 mV; 93 mV dec−1). The electrochemically active surface area (ECSA) and impedance spectroscopy findings revealed that the synergistic coupling between the CoOP and TNTs enhances the surface area and density of accessible active sites while reducing the charge transfer resistance at the electrode/electrolyte interface. Such a synergistic effect is ascribed to the effective electronic interaction between CoOP and TNTs, and the faster electron transfer kinetics because of the unidirectionality of the 1-D TNTs.

Simple and ultrasensitive self-supporting electrochemical sensor for nitrite based on cobalt oxide grafted carbon cloth

In this work, a simple and ultrasensitive self-supporting electrochemical sensor for nitrite based on Co3O4 decorated carbon cloth has been efficiently fabricated by using a facile one-pot hydrothermal approach. Due to the benefits of high conductivity, large electroactive specific surface area, fast electron transfer kinetics and superior electrocatalytic activity, the Co3O4/CC electrode has exhibited outstanding nitrite sensing performance, including broad detection ranges 1–4000 μM in three divisions with a detection limit of 0.12 μM (S/N = 3), the fast response time of 0.7 s and high sensitivity. Additionally, nitrite in drinking water and pickled cabbage was successfully measured with high recoveries using the Co3O4/CC electrode.

All-MXenes zinc ion hybrid micro-supercapacitor with wide voltage window based on V2CTx cathode and Ti3C2Tx anode

To further improve the electrochemical performance for the wearable and microelectronic devices, we reported an all-MXenes zinc ion hybrid micro-supercapacitor (ZIHMSC) with a wide voltage window (1.60 V) based on V2CTx as the cathode and Ti3C2Tx as the anode. The flexible V2CTx and Ti3C2Tx electrodes are fabricated by the electrophoretic deposition method, which is simple and conducive to the realization of positive and negative electrodes matching. Benefiting from the synergistic effect of the two MXenes and the unique configuration, our ZIHMSCs also achieve fast ion and electron transfer kinetics, showing better rate capability than the MXene/Zn system. And the ZIHMSCs achieve excellent electrochemical performance, with high area capacitance of 200.1 mF cm−2, well stability over 5,000 charge/discharge cycles, and high energy density of 71.6 μWh cm−2 at 400.7 μW cm−2. The reason for the wide voltage window of the ZIHMSC was well revealed by the large work function difference between the two electrode materials of V2CTx and Ti3C2Tx and the redox potential of the electrolyte. And the electrochemical energy storage mechanisms are well investigated by ex-situ XPS and XRD. In addition, the ZIHMSC displays well flexibility and mechanical property, suffering from 15,000 bending cycles under 90°. The ZIHMSCs can successfully drive digital tubes and meters and enable digital meters to operate for more than 600 s, proving their practical application potential.

N, S dual-doped carbon aerogels-supported Co9S8 nanoparticles as efficient oxygen reduction reaction electrocatalyst for zinc-air battery

The innovative design of highly active and noble-metal-free electrocatalysts for the oxygen reduction reaction (ORR) is urgently required for the widespread application of Zinc-air batteries (ZABs). This study presents a porous composite, Co9S8 @NSC, which integrates N and S co-doped carbon aerogels with Co9S8 nanoparticles to create ideal ORR electrocatalysts. The porous carbon aerogels posesess a high specific surface area, which offers abundant catalytic sites and efficient channels for the reactants and electrolytes, while maintaining a uniform distribution of nanoparticles during long-term operation. The collaboration of ORR-active Co9S8 nanoparticles and N and S co-doped carbon aerogels significantly improves ORR performance. Co9S8 @NSC demonstrates a competitive ORR activity, including a high half-wave potential (E1/2, 0.85 V), fast electron transfer kinetics (Tafel slop, 53.3 mV dec−1), and prominent long-term stability. When utilized as an air cathode catalyst in primary Zn-air batteries, the Co9S8 @NSC electrode displays a power density of 150.9 mW cm−2 and a specific capacity of 735 mAh gzn−1. Overall, this work presents a promising electrocatalyst design for ORR, which could greatly benefit the development of ZABs.