Surface Of Graphite Electrode Research Articles

Charged Microdroplets Deposition for Nanostructured-Based Electrode Surface Modification

Accelerated synthesis of gold nanoparticles (AuNPs) in charged microdroplets produced by electrospray ionization (ESI) was exploited to modify the surface of graphite screen-printed electrodes (GSPEs). The deposited AuNPs were then functionalized by the charged microdroplets deposition of 6-ferrocenyl-hexanethiol (6Fc-ht) solutions that act as reducing and stabilizing agents and provide electrochemical properties for the modified electrodes. The morphology and composition of the AuNPs were characterized by scanning electron microscopy (SEM). Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of the modified electrodes. The results showed that the ESI microdroplets deposition technique produces uniform and well-dispersed AuNPs on GSPE, and optimal conditions for deposition were identified, enhancing GSPE electrocatalytic performance. Further functionalization by ESI microdroplets of AuNPs with 6Fc-ht demonstrated improved redox properties compared with the conventional self-assembled monolayer (SAM) method, highlighting the technique’s potential for the easy and fast functionalization of electrochemical sensors.

A Novel, Selective, and Fast Electrochemical Sensor Based on an 8-Nitroquinoline-Coated Pencil Graphite Electrode for Rutin Determination in Orange Juice

In this study, we developed a facile and low-cost method to prepare a modified electrode by coating the pencil graphite electrode (PGE) surface with 8-nitroquinoline (8-NQ). The surface modification process was carried out by electrochemical reduction of 8-NQ on the PGE surface in ethanol solution. The optimum conditions were determined for the experimental studies. The differential pulse voltammetry was used to determine rutin with the modified electrode (8-NQ/PGE). The developed electrode showed excellent performance for rutin oxidation in a pH 3.0 Britton Robinson buffer (BR). In this media, linearly increasing anodic peak currents were observed with the concentration of rutin in two wide concentration ranges (i.e., 0.016–0.96 μM and 0.96‒19.73 μM), the sensor showed a low detection limit (i.e., 4.14 nM) (3 s m−1). It displayed good stability and selectivity. Also, it was used successfully for the determination of rutin in orange juice samples.

The development of a disposable voltammetric sensor based on two-dimensional leaf-like ZIF-L (Zn) modified screen-printed graphite electrode for the simultaneous analysis of uric acid, dopamine and theophylline

The two-dimensional)2D) leaf-like zeolitic imidazolate framework-L (Zn) (ZIF-L (Zn)) was synthesized using a simple method in this study. The ZIF-L (Zn) was characterized using various techniques, such as FE-SEM, XRD, and EDX. The ZIF-L (Zn) was utilized to modify the surface of screen-printed graphite electrode (ZIF-L (Zn)/SPGE) to detect uric acid (UA). The sensor exhibited electrocatalytic behavior for uric acid in phosphate buffer solutions (PBS, 0.1 M), with a linear dependence between the current response and uric acid concentration in the dynamic range from 0.1 μM to 900.0 μM, a low limit of detection (LOD) of 0.04 μM, and good sensitivity of 0.0393 μA/μM under optimized experimental conditions. The ZIF-L (Zn)/SPGE sensor was successfully applied for uric acid determination in the presence of dopamine (DA) and theophylline (Thp) without any interference. The proposed electrode exhibits well-separated oxidation peaks at potentials of 139, 260 and 900 mV for dopamine, uric acid, and theophylline, respectively. In addition, the practical application of the fabricated sensor was demonstrated by detecting dopamine, uric acid, and theophylline in real samples.

An Electrochemical Immuno-cytosensor Modified with Nanofibers for the Determination of a Carcinoembryonic Antigen

In this study, La0.25Fe0.75FeO3 (PNp)perovskite nanoparticle was synthesized using the sol–gel method. PNp-coated polyacrylonitrile (PAN) nanofibers were prepared by electrospinning on the pencil graphite electrode (PGE) surface. In another step, carcinoembryonic antigen (CEA) was loaded with CEA antibodies (Anti-CEA) as a biomarker receptor. Finally, PGE/PAN@PNp/Anti-CEA was used for CEA detection. Optimization steps and cell culture steps were performed using differential pulse voltammetry (DPV). The use of this composite system is a novel immunosensor development approach for label-free detection of CEA. Under optimum conditions, detection limit (LOD) of PGE/PAN@PNp/Anti-CEA immunosensor LOD 1.48 ng/mL, limit of quantification (LOQ) = 4.94 ng/mL, reproducibility 1.46% (n = 5) and R2 = 0.9984 for antigen concentration within a linear working range of 0.1–10 ng/mL. Also, immunosensor recovery in real serum samples containing dopamine and ascorbic acid was found as 98.94 ± 7.43. It has great potential in clinical screening of different cancer biomarkers. The number of cells attached to the PGE/PAN@PNp/Anti-CEA/BSA(bovine serum)/CEA surface decreased in RT-4(bladder cancer), MDA-MB-231 (triple-negative breast adenocarcinoma cell line), and T98G cells (glioblastoma multiforme cell line), which are known as CEA-negative cell lines, whereas the number of MCF-7 cells (estrogen-sensitive human breast cancer cell line, known to be CEA positive) attached to the PGE/PAN@PNp/Anti-CEA/BSA/CEA surface increased, indicating higher affinity to the immunosensor surface. As a result, while MCF-7, which is CEA positive, can be determined best when using an immune-cytosensor, the cell that can be best determined with cytosensors was found to be RT-4.

Impedimetric monitoring of microRNA-200c-3p using hydroxyapatite nanoparticles modified pencil graphite electrodes

It is important to monitor miRNA-200c-3p as it can potentially serve as an important biomarker for respiratory diseases including COVID-19 and cancer. Despite the importance of microRNA monitoring, there are few previous studies for miRNA-200c-3p monitoring, and the application of hydroxyapatite nanoparticles (HaNP) in miRNA biosensors is quite limited. This study aims to fill this gap by utilizing the advantageous properties of HaNPs to develop a powerful strategy to detect microRNA-200c-3p. First, HaNPs were modified on the surface of pencil graphite electrodes (PGEs). Subsequently, hybridization between a phosphate-labeled miRNA-200c-3p-specific DNA probe and its complementary RNA target was carried out in the solution phase. The DNA-RNA hybrid forms were immobilized on the surface of the HaNP-PGEs and the impedimetric measurements were performed. The changes at the charge transfer resistance value (Rct) were evaluated in terms of the hybridization and optimization of the experimental conditions. The detection limits (DLs) were calculated as 0.12 µg/mL (16.19 nM) in phosphate buffer solution (PBS, pH 7.40) and 0.31 µg/mL (41.82 nM) in synthetic plasma. The selectivity of the developed biosensor was tested against miRNA-200c-5p and miRNA-141-3p. The results promise a significant improvement in public health in terms of a leap forward in the early diagnosis of many serious diseases.

Targeted Formation of Biofilms on the Surface of Graphite Electrodes as an Effective Approach to the Development of Biosensors for Early Warning Systems.

Biofilms based on bacteria Pseudomonas veronii (Ps. veronii) and Escherichia coli (E. coli) and yeast Saccharomyces cerevisiae (S. cerevisiae) were used for novel biosensor creation for rapid biochemical oxygen demand (BOD) monitoring. Based on the electrochemical measurement results, it was shown that the endogenous mediator in the matrix of E. coli and Ps. veronii biofilms and ferrocene form a two-mediator system that improves electron transport in the system. Biofilms based on Ps. veronii and E. coli had a high biotechnological potential for BOD assessment; bioreceptors based on such biofilms had high sensitivity (the lower limits of detectable BOD5 concentrations were 0.61 (Ps. veronii) and 0.87 (E. coli) mg/dm3) and high efficiency of analysis (a measurement time 5-10 min). The maximum biosensor response based on bacterial biofilms has been observed in the pH range of 6.6-7.2. The greatest protective effect was found for biofilms based on E. coli, which has high long-term stability (151 days for Ps. veronii and 163 days for E. coli). The results of the BOD5 analysis of water samples obtained using the developed biosensors had a high correlation with the results of the standard 5-day method (R2 = 0.9820, number of tested samples is 10 for Ps. veronii, and R2 = 0.9862, number of tested samples is 10 for E. coli). Thus, biosensors based on Ps. veronii biofilms and E. coli biofilms could be a novel analytical system to give early warnings of pollution.

Bio-inspired pulsed power switch under shock wave

The spark gap switch is a crucial component in the primary energy drive system for large pulse power devices. The switch electrodes are composed of high-density artificial graphite, possessing excellent erosion resistance. However, insufficient mechanical strength in the graphite electrodes makes them especially susceptible to mechanical damage under the enormous impact force caused by the increasing arc current, which seriously affects the reliability and service life of the switch. The distribution of the shock wave overpressure on the graphite electrode surface is deduced and calculated, and the refraction and reflection process of the shock wave from the air to the graphite interface is analyzed based on the Huygens–Fresnel principle. Furthermore, the doubling of refracted shock wave intensity into the graphite electrode is a preliminary characterization. The propagation process of stress wave after the shock wave enters the electrode is investigated by establishing two conventional graphite electrode structure models, namely T-shape and reverse T-shape, which reveal that severe stress concentration occurs in both structures. Drawing inspiration from the physiological structure of the woodpecker’s head, renowned for its exceptional impact resistance, the macroscopic geometry of the graphite electrode and the assembly structure of the switch have been bionically designed. The simulation results demonstrate that, in comparison to the conventional electrode structure, the bionic electrode structure eliminates stress concentration at the bolt end and electrode corner, while significantly reducing maximum equivalent stress and the degree of the stress concentration on the bottom surface of the electrode. These features contribute to the enhancement of the current capacity and reliability of the spark gap switch.

Selective Amperometric Sensor for the Determination of Hydrazine at a Gold Nanoparticle Decorated Poly(Brilliant Blue) Modified Electrode

There is a pressing requirement to synthesize stable electrode components that possess enhanced capabilities for creating electrochemical sensors, which are sensitive and discerning, to swiftly detect dangerous noxious substances. A sensitive electrochemical sensor has been developed in this study for hydrazine (HY) oxidation, utilizing gold nanoparticles (AuNPs) and poly(brilliant blue) (p(BB)) modifiers on the surface of the pencil graphite electrode (PGE). The features of the sensor for detecting hydrazine were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). Additionally, when examined under optimal parameters using CV and amperometry, the proposed hydrazine sensor presents favorable electrochemical and analytical figures of merit. The AuNPs/p(BB)/PGE provides the determination of low levels of hydrazine in water samples with a detection limit of 0.14 µM. A wide linear range from 1.0 to 800 μM was obtained. The findings indicate that the AuNPs/p(BB)/PGE sensor exhibits good stability, repeatability, and reproducibility for hydrazine. The proposed sensor was effectively used to determine hydrazine in both water and mineral water samples.

Levan modified patulin specific impedimetric aptasensor with its application in food and biological fluids

In this study, a label-free impedimetric aptasensor was developed for the determination of patulin (PAT) mycotoxin. The pencil graphite electrode (PGE) surface was modified with the levan and then PAT-specific aptamer was immobilized onto the PGE surface. After the interaction of PAT with aptamer EIS measurements were performed. Under optimum conditions, the limit of detection (LOD) in buffer medium was calculated as 0.095 pg/mL in the concentration range of 10−1–105 pg/mL. The selectivity of the developed label-free impedimetric aptasensor was investigated against fumonisin B1 (FB1), ochratoxin A (OTA), and deoxynivalenol (DON) in buffer medium. The implementation of label-free impedimetric aptasensor to patulin determination was performed in apple juice samples as well as in fetal bovine serum (FBS) medium. Accordingly, the LOD of PAT was estimated as 3.27 pg/mL in apple juice and 0.41 pg/mL in the FBS medium. The selectivity of the aptasensor was also investigated in both mediums. It is predicted that the developed aptasensor will have an important place in the fields of food safety and health monitoring in the literature. Also, it is anticipated that the electrochemical determination of mycotoxins, especially in biological fluids, will be a role model for future studies.

Effect of the charge rate on the mechanical response of composite graphite electrodes: in situ experiment and mathematical analysis.

The cycling lifespan and coulombic efficiency of lithium-ion batteries are crucial to high C-rate applications. The Li-ion concentration is crucial in determining the mechanical integrity and structural stability of electrodes. In this work, graphite is selected as the working electrode due to its widespread use in the electric vehicle industry. The experimental data have shown that the electrodes with a mass loading of 6.54 mg cm-2 exhibited poor cycling performance and high charge transfer resistance at high charge rates. To explain this phenomenon, an in situ stress measurement system and a C-rate-dependent stress model are established to study the mechanical properties of the composite graphite electrode during the electrochemical process at various C-rates. Moreover, the effect of the Li-ion concentration-dependent modulus and C-rate-dependent partial molar volume is taken into account in the mathematical model. The computational curvature data fit well with the corresponding experimental data, highlighting the importance of considering lithium-ion concentration in mechanical stress. It has been found that stresses along the thickness of the active layer switch between compressive and tensile stresses due to the competition between bending stress and diffusion-induced stress. The stress at the outer surface of the composite graphite electrodes reaches a maximum magnitude of 27.5 MPa at a 1.5C-rate. In contrast, the stress at the interface of the active layer is maximum at a 0.5C-rate due to the existence of more lithium ions. Our study provides a direct insight into the quantitative analysis of electrode stresses at different C-rates.

The effect of gold nanostructure morphology on label-free electrochemical immunosensor design

In this research, various electrodeposition techniques were used to form gold nanostructures (AuNSs) on the surface of graphite rod electrode (GE). Three distinct AuNS morphologies on GE have been achieved based on the composition of electrodeposition solution. The use of H2SO4 as a supporting electrolyte resulted in the formation of smaller but more numerous AuNSI with a modified electrode’s electroactive surface area (EASA) of 0.213 cm2. Exchanging the supporting electrolyte to KNO3 and increasing HAuCl4 concentration facilitated the formation of bigger AuNSII particles with electrode EASA of 0.116 cm2. Finally, a partial coverage of GE by branched gold nanostructures (AuNSIII) was achieved with an estimated EASA of 0.110 cm2, when the HAuCl4 and KNO3 concentrations were increased. Estimated values of heterogeneous electron transfer rate constant did not depend on AuNS morphology. Electrode modified with AuNSI exhibited the highest bovine serum albumin (BSA) immobilization efficiency and the highest relative response for the detection of specific polyclonal antibodies against BSA (p-anti-BSA) compared to other modified electrodes. The limit of p-anti-BSA detection in PBS buffer was calculated as 0.63 nM, while in blood serum it was 0.71 nM. Linear ranges were from 1 to 7 nM and from 1 to 5 nM, respectively.

Electrochemical investigation of an anticancer drug 5-Fluorouracil in the presence of Theophylline using low-cost and disposable poly(GLY) modified pencil graphite electrode

Herein this study, a facile, efficient and disposable electrochemical sensor has been prepared by electropolymerization of glycine (poly(GLY)) on the surface of pencil graphite electrode (PGE). The surface topology of the equipped poly(GLY) modified pencil graphite electrode (poly(GLY)/PGE) and bare pencil graphite electrode (BPGE) has been characterized by the scanning electron microscopy (SEM) combined with energy dispersive x-ray analysis (EDX) and charge transfer behaviour was measured by electron impedance spectroscopy (EIS) method. The voltammetric behaviour of anticancer, 5-fluorouracil (5-FU) in the presence of theophylline (THP) has been carried out in 0.1 M phosphate buffer solution (PBS) of physiological pH 7.0 using different techniques such as cyclic voltammetry (CV), linear sweep voltammetry (LSV) and differential pulse voltammetry (DPV). The proposed poly(GLY)/PGE shows augmented peak current for 5-FU at lower potential side over the BPGE due to the electrocatalytic behaviour of modifier layers wrapped on the electrode surface. The kinetic behaviour of 5-FU at modified electrode surface was studied by varying different parameters such as pH, scan rate and concentration study in 0.1 M PBS used as a supporting electrolyte. The limit of detection (LOD) for 5-FU was attained using DPV method with different concentrations (1.0–13.0 μM) and it was found to be 0.012 μM. The possible electrochemical reaction of 5-FU was proposed and it was incorporated by two electrons and two protons mechanism at modified electrode surface. The voltammetric response of poly(GLY)/PGE towards the determination of 5-FU was unaffected in the presence of some excipients in addition to the remarkable stability and reproducibility. The applicability of the proposed sensor has been performed by real sample investigation of 5-FU with a substantial percentage of recovery results in all optimized conditions.

Reprint of “Characteristics and electrochemical performance of copper/graphite felt composite electrodes for vanadium redox flow battery”

BackgroundVanadium oxide is considered environmentally benign; however, its economic utilization is highly challenging due to the inability to control the size of etched holes. To address this limitation, it is crucial to regulate the depth of the hole by modifying the etching conditions. A controllable hole depth has the potential to enable its application in vanadium redox flow batteries (VRBs). MethodsIn this study, electrodeposition is used to deposit copper particles on the surface of graphite felt electrodes. The copper particles are then employed to etch the graphite felt surface under a reducing atmosphere, which produces porous copper/graphite felt composite electrodes that can be used in VRBs. The effect of etching temperature and time on the material characteristics and the electrochemical performance of this composite electrode were investigated. Significant FindingsThe holes on the graphite felt surface following a heat treatment are studied, especially as the temperature approaches 900 °C. The observed specific surface area is 16.59 m2/g. Upon grafting of oxygen functional groups, the O/C ratio of the composite electrodes reaches 0.12. After the annealing at 900 °C, the energy efficiency of the porous copper/graphite felt composite electrode is 67.40%, the voltage efficiency is 70.13%, and the current efficiency is 96.11%. Under long-term cyclic discharge, the composite electrode exhibits a good capacitance retention of 91% and a capacitance utilization of 63%.

MoS2 Quantum Dots-based Low-cost and Disposable Electrochemical Sensor for the Detection of Lead (II) Ions

After the discovery of graphene, two-dimensional (2D) nanomaterials have received great attention due to their excellent physico-chemical properties. Application of 2D-nanomaterials as receptors of a sensor can achieve high sensitivity and specificity as every atom of the material directly interacts with the analyte. In the present work, MoS2 quantum dots (MSQD) for the ultrasensitive electrochemical detection of lead (Pb2+) ions. MSQDs were prepared by mechanical shear exfoliation method. Size of the QDs and inter planar distance of the crystalline QDs were studied using transmission electron microscope (TEM). The prepared quantum dots were drop casted on a shiny surface of well-polished pencil graphite electrode (PGE). In order to obtain the highest sensitivity for Pb2+-ion sensing, anodic stripping DPV (ASDPV) was employed and consequently, the effect of pH, deposition potential and time were optimized. The sensor shows a linear range from 5.66 10−9 M to 491.93 10−9 M with a calculated detection limit 1.96 10−9 M for the detection of Pb2+-ion. The sensor’s response for Pb2+-ion was unaffected in the presence of any other metal ions. A remarkable average recovery percentage around 99.50% from the Pb2+-ion spiked agriculture soil and ground water samples proves the practical applicability of the sensor.

Innovative polymer engineering for the investigation of electrochemical properties and biosensing ability.

Subtle engineering for the generation of a biosensor from a conjugated polymer with the inclusion of fluorine-substituted benzothiadiazole and indole moieties is reported. The engineering includes the electrochemical copolymerization of the indole-6-carboxylic acid (M1) and 5-fluoro-4,7-bis(4-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (M2) on the indium tin oxide and graphite electrode surfaces for the investigation of both their electrochemical properties and biosensing abilities with their copolymer counterparts. The intermediates and final conjugated polymers, Poly(M1) [P-In6C], Poly(M2) [P-FBTz], and copoly(M1 and M2) [P-In6CFBTz], were entirely characterized by 1H NMR, 13C NMR, CV, UV-Vis-NIR spectrophotometry, and SEM techniques. HOMO energy levels of electrochemically obtained polymers were calculated from the oxidation onsets in anodic scans as -4.78 eV, -5.23 eV, and -4.89 eV, and optical bandgap (Egop) values were calculated from the onset of the lowest-energy π-π* transitions as 2.26 eV, 1.43 eV, and 1.59 eV for P-In6C, P-FBTz, and P-In6CFBTz, respectively. By incorporation of fluorine-substituted benzothiadiazole (M2) into the polymer backbone by electrochemical copolymerization, the poor electrochemical properties of P-In6C were remarkably improved. The polymer P-In6CFBTz demonstrated striking electrochemical properties such as a lower optical band gap, red-shifted absorption, multielectrochromic behavior, a lower switching time, and higher optical contrast. Overall, the newly developed copolymer, which combined the features of each monomer, showed superior electrochemical properties and was tested as a glucose-sensing framework, offering a low detection limit (0.011 mM) and a wide linear range (0.05-0.75 mM) with high sensitivity (44.056 μA mM-1 cm-2).

Publisher note

BackgroundVanadium oxide is considered environmentally benign; however, its economic utilization is highly challenging due to the inability to control the size of etched holes. To address this limitation, it is crucial to regulate the depth of the hole by modifying the etching conditions. A controllable hole depth has the potential to enable its application in vanadium redox flow batteries (VRBs). MethodsIn this study, electrodeposition is used to deposit copper particles on the surface of graphite felt electrodes. The copper particles are then employed to etch the graphite felt surface under a reducing atmosphere, which produces porous copper/graphite felt composite electrodes that can be used in VRBs. The effect of etching temperature and time on the material characteristics and the electrochemical performance of this composite electrode were investigated. Significant FindingsThe holes on the graphite felt surface following a heat treatment are studied, especially as the temperature approaches 900 °C. The observed specific surface area is 16.59 m2/g. Upon grafting of oxygen functional groups, the O/C ratio of the composite electrodes reaches 0.12. After the annealing at 900 °C, the energy efficiency of the porous copper/graphite felt composite electrode is 67.40 %, the voltage efficiency is 70.13 %, and the current efficiency is 96.11 %. Under long-term cyclic discharge, the composite electrode exhibits a good capacitance retention of 91 % and a capacitance utilization of 63 %.

Electrochemical DNA Sensor Designed Using the Pencil Graphite Electrode to Detect Listeria monocytogenes.

In the present work, a novel electrochemical DNA sensor was designed to detect L. monocytogenes. Two different gene fragments were selected for the sensor design. One is a 702bp long fragment of the hlyA gene, encoding the synthesis of listeriolysin O toxin, which is unique only to pathogenic strains of L. monocytogenes and is essential for pathogenicity. The other is a 209bp long fragment of the 16S RNA gene found in all species of the Listeria genus. As the working electrode, the pencil graphite electrode was modified in various ways (activated or covered with polypyrrole), and six different combinations were constituted using three types of the modified working electrode and two different gene fragments. The developed system is based on differential pulse voltammetric transduction of guanine oxidation after hybridization between the selected gene fragment (38µg/mL) and the selected fragment-specific inosine-modified probe (1.8 µmol/L) immobilized on a pencil graphite electrode surface. The comparison of all combinations demonstrates that the best results are obtained with the combination formed from a polypyrrole-coated pencil graphite electrode (prepared at 2 scans) and 702bp fragment of the hlyA gene. The analysis time is less than 1 hour, and the necessary DNA concentrations for the analysis have been determined as 8.2 × 10-11M DNA and 2.7 × 10-10M DNA respectively, for the hlyA gene and 16S RNA gene.

Using reactivity predictors for enhancing the electrocatalytic activity of MN4 molecular catalysts for the oxygen reduction reaction: The role of the N-pyridinium functional group in the porphyrazine-derivative ligands

Using reactivity predictors to enhance or control the electrocatalytic activity of materials is a fascinating concept. This is especially true for the development of alternative platinum metal group-free materials as it facilitates the rational design of active catalytic materials for the oxygen reduction reaction (ORR). In previous work, we have found that the peripheral and non-peripheral electron-withdrawing effects and the electron-pull effect from axial extraplanar ligand in iron-phthalocyanine (FePc) are key factors in improving the binding energy between the active Fe site and O2 resulting in an increase of the electrocatalytic activity of FePcs for the ORR. In this work, we have utilized fundamental principles of electrocatalysis and DFT calculations to design and synthesize FeN4 molecular catalysts to increase their catalytic performance for the ORR through the "pull" effect. To achieve this, by chemical synthesis, we have incorporated pyridinium functional groups (N+py) in peripheral and non-peripheral positions into the porphyrazine cyclic ligands. In this fashion we obtain the porphyrazinium molecular catalysts, [Fe(II)2,3-(TMe)TPyPz]4+ and [Fe(II)3,4-(TMe)TPyPz]4+. Because these new compounds are not commercially available and, to the best of our knowledge, they have not been tested for ORR. In order to determine their effectiveness, we have compared porphyrazinium with neutral analog porphyrazine compounds (Fe(II)TPyPz) and perfluorinated and perchlorinated iron phthalocyanines, which are currently the best molecular catalysts for ORR. The electrocatalytic activity was determined for each molecular catalyst deposited on the edge plane of a graphite electrode (EPG) surface in an alkaline medium. Only for the purpose of comparison we include two Fe porphyrins studied previously, which show low activity for ORR. Although the DFT theoretical analysis of porphyrazinium complexes suggests a high activity for these catalysts, our experimental findings revealed the opposite trend. Therefore, this finding makes us reconsider the interfacial effects, such as the counter-ions effects on N+py that could influence the electron-pull effect, opening new insights for designing molecular catalysts considering interface engineering. Moreover we report for the first time, the reactivity linear relationship between the metal-centered redox potential gap (E°Fe(III)/(II) – E°Fe(II)/(I))) with the electrocatalytic activity for ORR for all catalysts studied, emerging this potential gap as a possible and promising new reactivity descriptor for ORR in MN4 catalyst.

Edge and Basal Plane Anisotropy of a Preanodized Pencil Graphite Electrode Surface Revealed Using Scanning Electrochemical Microscopy and Electrocatalytic Dopamine Oxidation as a Molecular Probe.

Pencil graphite (PGE), an ultralow-cost and ready-to-use disposable-type electrode, has been used for various electrochemical and electroanalytical applications after its surface anodization (PGE*, * means preanodized surface). Indeed, systematic studies on mechanistic and surface features of PGE* have not yet been explored. Herein, we report anodized pencil graphite as a model system to study molecular level insights into the surface using a scanning electrochemical microscopy (SECM) technique and dopamine (DA) electrocatalytic oxidation reaction as a molecular probe. The as-prepared PGE* showed an appreciable electronic conductivity similar to the edge-plane graphitic sites (EPPG) of the highly pyrolytic graphitic electrode (HOPG) but without any surface deterioration that occurs with HOPG due to the instability of the EPPG. Physicochemical characterizations by FESEM, FTIR, Raman, and XPS techniques revealed a flake-like exfoliated PGE* surface with higher contents of carbon-oxygen especially phenolic/alcoholic functional groups than the PGE surface. Based on the chronocoulometric experiment, the number of functional groups formed on the PGE* was calculated as 10.9 × 10-10 mol cm-2. An independent SECM technique using ferricyanide as a redox probe showed the existence of a heterogeneous surface and exhibited an improved electron transfer activity due to the flake-like graphitic island on the PGE* surface. Investigated DA electrochemical oxidation on PGE* yielded about three times enhancement in the peak current signal and about 200 mV reduction in the oxidation potential over the PGE without any serious surface fouling feature that is related to the intermediate polydopamine formation on the basal-plane graphitic surface of the underlying electrode. As an independent electroanalytical study, a prototype electrochemical sensor using PGE* as a working electrode for instant detection of DA-containing pharmaceutical samples in a 1 mL Eppendorf vial has been demonstrated.

Construction of a logic gate sensitive monitoring system of Graphdiyne/Poly(N,N-dimethylacrylamide) binary structure films for environmental pollutant phenylhydrazine

In this work, binary hydrogel films based on Graphdiyne/Poly(N,N-dimethylacrylamide (GDY/PDEA) were successfully polymerized and assembled on pyrolytic graphite (PG) electrode surface. When phenylhydrazine (PHz) as an active electrochemical probe in solution exhibits reversible cyclic voltammetric (CV) behaviors in response to temperature, salt and pH at the membrane electrode. The CV signals of PHz were significantly enhanced by electrocatalysis of GDY layer of the films. And the mechanism of membrane reaction was discussed and studied. The presence of protonated PHz determines the pH-sensitive property of the system. During pH adjustment with esterase urease, in situ enzymatic electrocatalysis that may be accelerates the electron transfer rate at the electrode surface. The structural alterations of PDEA hydrogels under multiple conditions were attribute to the temperature response and salt concentration–response. GDY films can also have an effect on the CV response signals. In conclusion, a multi-stimulus response hydrogel film environmental sensor has been constructed, and a 5-input/5-output logic gate system including OR, AND and NOT has been successfully constructed. And constructed 2-to-4 decoder and 2-to-1 encoder two logic devices. It provides a new method to increase the complexity of the environmental pollutant monitoring calculation system.