Cyclic Voltammetry Curves Research Articles

Electrochemical Evaluation of Manganese Electrolytes for Redox Flow Batteries

Redox flow batteries (RFBs) are promising candidates for long-duration energy storage mainly due to the lower cost of improving the energy density compared to lithium-ion batteries. However, the full sustainability of RFBs has not been achieved yet, and there is a lot of room for further improvement. One of the main parameters showing a strong influence on the sustainability of RFBs is redox active materials. In this work, manganese was selected for electrochemical evaluation as it fulfills the sustainability requirements. Manganese is a non-toxic, low-cost and abundant material with sufficient aqueous solubility[1]. Moreover, the standard potential of manganese (1.51 V) is higher than that of vanadium (1.26 V).For electrochemical parameters, we have, through cyclic voltammetry (CVs) and polarization curves, estimated the diffusion coefficient (D0 ) and heterogeneous standard electron transfer rate (k 0) of manganese in an acidic electrolyte in the presence of titanium as an additive. In order to investigate the performance of an RFB system using a manganese electrolyte, a hybrid system was designed that uses hydrogen gas on the negative side and an acidic manganese electrolyte the positive side. We have studied the resistance behavior of the hybrid RFB through electrochemical impedance spectroscopy at different states of charge. From EIS data, cell ohmic resistance, and a general idea of the different processes taking place at different state of charge were obtained. Moreover, we studied the performance of the hybrid RFB during 70 cycles, obtaining an average coulombic efficiency of 98.1%, voltage efficiency of 77.8% and capacity retention of 97.7%. Carney, J.R., B.R. Dillon, and S.P. Thomas, Recent Advances of Manganese Catalysis for Organic Synthesis. European Journal of Organic Chemistry, 2016. 2016(23): p. 3912-3929.

Formation of the Heterojunction Based on Titania Modified with Ni and Ag Sulfide Via SILAR Method - Electrochemical and Photoelectrochemical Activity

The great interest of TiO2 nanotubes (TiNT) is justified by large surface area, high degree of ordering, facilitated charge transport along the nanotube, mechanical strength, strong UV absorption and light scattering due to the pore specific arrangement well as wide range of potential applications in solar cells, photocatalysis and sensors [1]. However, due to the wide energy band gap of TiO2 (3.2 eV) its photoactivity is limited and therefore titania based heterojunction are formed with the photoabsorber being active in the visible range [2]. In line with this strategy, we present electrochemical and photoelectrochemical activity of TiNT modified by NiS and AgS.The electrode is fabricated via electrochemical anodization of Ti foil, thermal annealing providing anatase phase and finally Successive Ionic Layer Adsorption and Reaction (SILAR) was carried out using silver, nickel and sulfur ions precursor and with different number of deposition cycles. The characteristic Ag-S, Ag-O and S-O peaks appearing on Raman spectra indicating successful SILAR modification. The cyclic voltammetry curves for TiNT, NiS/TiNT, AgS/TiNT and AgS/NiS/TiNT electrode were registered in 0.5 M Na2SO4 (Fig.1a). Peaks found on the anodic branch of the AgS/NiS/TiNT electrode at 0 V and +0.3 V vs. Ag/AgCl/0.1 M KCl are assigned to oxidation of Ag0 to Ag1+ and Ag1+ to Ag2+, respectively. When the scan went towards cathodic direction, peak located at +0.1 V and -0.1 V indicates reduction of Ag2+ to Ag1+ and Ag1+ to Ag0, respectively [3]. Furthermore, the linear voltammetry measurements performed under visible light illumination in 0.5 M Na2SO4 is presented in Fig.1b. The best photoactivity was reached for the AgS/NiS/TiNT electrode when only 5 deposition cycles for each metal precursor was applied. The photocurrent registered at +0.5 V reaches ca. 40 µA/cm2 which is 20 times higher than for pure TiNT.Summing up, modification of titania nanotubes by nickel and silver sulfides significantly enhanced material photoelectrochemical response under visible light. Moreover, it has been proved that this synergetic effect originated from the titania/metal sulphide heterojunction that can be achieved using SILAR method.Research is financed by National Science Centre (Poland): Grant no. 2020/39/I/ST5/01781[1] K. Siuzdak et al. RSC Advances, 5 (2015) 50379, DOI:10.1039/c5ra08407e[2] S. Chandrasekaran et al. Chemical Society Reviews, 48 (2019) 4178, DOI:10.1039/c8cs00664d[3] J.R.N. Santos et al. Electrocatalysis, 13 (2022) 713, DOI: 10.1007/s12678-022-00754-2 Figure 1

Engineered Conductive Proteins for Supercapacitors

Proteins can be used as building blocks of functional materials for electrochemical applications due to their structural properties and the possibility to tailor their ionic and electronic conductive properties.[1] One of the most attractive applications is in the bioelectronics field, for example as energy storage devices such as Electrical Double Layer Capacitors (EDLCs), due to the nontoxicity and biocompatibility of the materials.[2] EDLCs are primarily used for applications where high power is required during a short period of time. They present several advantages, such as fast charge-discharge cycling, high power density, and outstanding long-term stability.[3]Traditionally, the incorporation of biomaterials in EDCLs is limited because they can be denaturalized in contact with organic solvents or salts. In addition, they easily interact with other cell components resulting in parasitic reactions and their complex purification processes hinder their commercialization.[4] These drawbacks can be overcome by introducing engineered proteins, since their amino acid sequences can be tuned resulting in 3D structures with varying degrees of complexity. Based on this approach, engineered proteins with improved conductivity will be introduced as interlayers with good stability and wettability, to ensure that the ions can shuttle freely between the two electrodes.In our case, consensus tetratricopeptide repeat (CTPR) proteins have been chosen [5] and engineered with the aim of increasing the ionic conductivity of the resulting variants. CTPR variants have been mixed with 5% PEG solutions and drop cast to obtain self-standing films. After being cross-linked, the films have been sandwiched in a two electrodes Swagelok-cell configuration between two electrodes made of activated carbon. KCl (3M) aqueous solution has been used as electrolyte for evaluating the electrochemical performance of the devices.The electrochemical characterization of the EDLC devices has been carried out using cyclic voltammetry (CV) and galvanostatic cycling (GC) to study the effect of the of the engineering strategy of the CTPR proteins on the EDLC performances. The CV curves of the devices using thin films of proteins with distinct mutations show quadratic capacitive responses for all the assembled EDLCs, demonstrating both its ability to isolate the two electrodes and to allow the diffusion of ions. The EDLCs capacitances were calculated and analyzed from the GC characteristics at different charge-discharge currents and compared with commercial glass fiber separators confirming their feasibility as safe and environmentally friendly separators. The ionic diffusive behavior of the devices has been also studied by electrochemical impedance spectroscopy (EIS). Finally, the effect of the thickness, porosity, polarity, wettability, and ionic conductivity of the different protein separators has been addressed to explore the role of the engineered proteins in EDLC devices. Acknowledgements This abstract is part of R&D&I project TED2021-131641B-C44, funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGenerationEU/PRTR. This project has received funding from the European Union’s Horizon 2020 FET Open under the grant agreement No: 964593

Electrochemical Investigations of Ag and Bi in Choline Chloride-Ethylene Glycol DES Electrolyte

Electrodeposition for silver and bismuth is currently carried out in alkaline solutions, e.g., by use of cyanide, and by electroplating these metals, by themselves or together. The electroplated products have important uses, e.g., in semiconductors [1].Choline Chloride (ChCl)-Ethylene Glycol (EG) DES mixtures, often referred to as ethaline, have been shown to have superior electrochemical properties compared to many other DES systems [2]. This system is considered a green solvent [3]. In this work, the electrochemical behaviour of Ag and Bi in ethaline electrolyte has been investigated to obtain the necessary parameters to extract them by electrochemical methods, either separately or together, when both are present in the DES electrolyte. The presence of Cu and Sb in the electrolyte, has also been studied, and its effect in the metal obtained has been evaluated. Ethaline solutions were fabricated by mixing together ChCl and EG at 1:2 ChCl:EG molar ratio by stirring at 60 °C until a clear liquid was formed. Model electrolyte solutions were then produced by dissolving AgCl and BiCl3, as well as SbCl3 and CuCl2, in the DES. Electrochemical investigations were carried out at 60 °C by cyclic voltammetry (CV), chronoamperometry (CA) and potentiostatic electrolysis using a 3-electrode setup.The CVs obtained using Pt-wire or GC-rod as working electrodes in the DES with 10 mM Ag(I) and Bi(III), showed two distinguished peaks in the cathodic scan. The CV and CA results showed that the Bi deposition starts at approximately 0.15-0.20 V more cathodic than the Ag deposition. Two or more electrochemical signals were observed in the reverse anodic scan, correlating to the dissolution of the metals, alloys and possible electrolyte reactions. Example of CV curve obtained on a Pt wire at a scan rate of 200 mV/s is included.The results indicated that it could be possible to electrochemically extract only Ag or both Ag and Bi simultaneously, when present at identical concentrations in the DES electrolyte, by carefully choosing the deposition potential. This was confirmed after analysis of the cathodic deposits on Pt and stainless steel (316L) substrates by Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS).Experiments with Sb(III) and Cu(II), in addition to Ag(I) and Bi(III) present in the DES electrolyte showed that the cathodic deposition of the different metals appears in the order Ag<Sb<Bi<Cu. Significant co-deposition might occur, enhanced by favourable alloy formation, when metallic elements may deposit at activities lower than 1. Still, at 10 mM of each of the four metal salts present in the DES electrolyte, it was possible to obtain deposits with one, two, three or four metals present, by choosing the proper cathodic deposition potential.AcknowledgementsThis project has received funding from the EU’s Horizon 2020 research and innovation program under Grant Agreement 815748. The content in this presentation reflects only the views of the authors. The European Commission is not responsible for any use that may be made of the information it contains.

Electrochemical Properties of PEDOT:PSS/Graphene Conductive Layers in Artificial Sweat.

Electrodes based on PEDOT:PSS are gaining increasing importance as conductive electrodes and functional layers in various sensors and biosensors due to their easy processing and biocompatibility. This study investigates PEDOT:PSS/graphene layers deposited via spray coating on flexible PET substrates. The layers are characterized in terms of their morphology, roughness (via AFM and SEM), and electrochemical properties in artificial sweat using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The layers exhibit dominant capacitive behavior at low frequencies, with cut-off frequencies determined for thicker layers at 1 kHz. The equivalent circuit used to fit the EIS data reveals a resistance of about three orders of magnitude higher inside the layer compared to the charge transfer resistance at the solid/liquid interface. The capacitance values determined from the CV curves range from 54.3 to 122.0 mF m-2. After 500 CV cycles in a potential window of 1 V (from -0.3 to 0.7 V), capacitance retention for most layers is around 94%, with minimal surface changes being observed in the layers. The results suggest practical applications for PEDOT:PSS/graphene layers, both for high-frequency impedance measurements related to the functioning of individual organs and systems, such as impedance electrocardiography, impedance plethysmography, and respiratory monitoring, and as capacitive electrodes in the low-frequency range, realized as layered PEDOT:PSS/graphene conductive structures for biosignal recording.

Electrodeposition nanofabrication of carboxylated carbon nanotubes/α-MnO2 nanorods/ polypyrrole composites as high hybrid capacitance electrodes for efficient U(VI) electrosorption

The uranium-containing wastewater resourced from the nuclear fuel cycle presents serious harm to human health and ecological environment. Herein, carboxylated carbon nanotubes/α-MnO2 nanorods/polypyrrole (CMP) composite as high hybrid capacitance (EDL and pseudocapacitance) electrodes with good electrosorption performance for U(VI) were nanofabricated by the electrodeposition of polypyrrole (PPy) on the surface of carboxylated carbon nanotubes/α-MnO2 nanorods composites using potentiostatic method. The morphology and structure characteristics, electrochemical properties and electrosorption U(VI) properties of the CNT/α-MnO2/PPy composites were systematically investigated. The results show that among the CMP composites obtained at different pyrrole concentrations, CMP-0.10 has the highest specific capacitance (366.97F/g), and its electrosorption performance is also the best, which is due to its well balanced porous structure and high hybrid capacitance which favors U(VI) ions transfer and storage. Cyclic voltammetry (CV) curves with obvious redox peaks were observed at low sweep speeds, indicating its hybrid capacitance behavior of CMP composites in which the capacitance contribution can be quantified. The electrosorption experiments were performed in a capacitive deionaiztion (CDI) system in which different factors (voltage, pH, U(VI) concentration and contact time, etc.) on the electrosorption of U(VI) were investigated, which shows that high U(VI) removal could be achieved at a wide pH range. The theoretical simulation using different models shows the best fit of the Langmuir model for the electrosorption isotherms and PFO model for the kinetics. The U(VI) electrosorption capacity reaches 339.45 mg/g at 0.9 V and pH 4.5 for CMP-0.10, which is much higher that achieved at 0.0 V. The facile fabrication, excellent electrochemical and electrosorption performance as well as good cycling stability for the CMP composites highlight their potential application in radioactive wastewater treatment.

Electrochemical synthesis of conjugated copolymer poly(3-hexylthiophene-co-dithenopyrrole): Stepwise approach to enhance electro-optical properties

Electrochemical polymerisation of 3-hexylthiophene (3HT) and electrochemical copolymerisation of 3HT and N-benzoyl dithienopyrrole (BDP) were performed to prepare polymer and copolymer films using a linear sweep voltammetry potentiostatic technique with a voltage range from 1.7-1.8 V and a scan rate of 0.1 mV/s. Cyclic voltammetry (CV) curves, Fourier-transform infrared (FTIR) spectra, scanning electron microscope (SEM) images, and UV-Vis absorption spectra of the polymer and copolymer were recorded for analysis and comparison of the electropolymerisation process and properties of the resultant films. The SEM photographs of the copolymer base on 3HT and BDP exhibited a rigid structure with large spherical aggregates with an average size around 200 nm. The copolymer of 3HT and BDP exhibited the band gaps of 2.25 eV which was determined via electrochemical measurement that is higher than of band gaps of homopolymer poly(3-hexylthiophene) (P3HT). The copolymer’s energy bandgap HOMO-LUMO was enhanced compared to polymer P3HT. Moreover, the increased conjugation length significantly improved the morphology structure as well as the electrochemical stability of the conjugated copolymer.

Anodic oxidation of ciprofloxacin antibiotic and real pharmaceutical wastewater with Ti/PbO2 electrocatalyst: Influencing factors and degradation pathways

This study investigated the impact of operational variables including current density, solution pH, sodium sulfate electrolyte concentration, initial pollutant concentration, and reaction time on ciprofloxacin (CIP) anodic oxidation and its COD removal by Ti/PbO2 electrocatalyst. Ti/PbO2 anode was prepared by electrochemical method and its characteristics were determined using SEM, EDX-map, XRD, and linear sweep voltammetry (LSV) techniques. Under optimal conditions, the removal rate of CIP and COD at the initial concentration of 15 mg/L of the pollutant after 75 min of reaction was 92 % and 88.8 %, respectively. CIP mineralization was confirmed by evaluating its UV–vis spectra and cyclic voltammetry (CV) curves during the process. Considering the degradation intermediates identified by LC-MC analysis, the main reactions in CIP mineralization pathways were discussed in detail. Finally, the improvement of biodegradability of pharmaceutical wastewater during anodic oxidation treatment was evaluated. The results indicated that the biodegradability of wastewater significantly increased from BOD/COD = 0.18 for raw wastewater to BOD/COD = 0.42 for treated wastewater. The results showed that anodic oxidation with Ti/PbO2 electrocatalyst can be a practical method of treating wastewater that contains resistant and toxic pharmaceutical compounds.

Probing the Synergy of Ni(OH)2/NiO Nanoparticles Supported on rGO for Battery‐Type Supercapacitors

Herein, a direct hydrothermal protocol for the synthesis of nickel‐based hydroxide/oxide nanocomposites grown on reduced graphene oxide (rGO) is presented. The materials are employed as a high‐performance active layer for advanced supercapacitors. Ni(OH)2/rGO and NiO/rGO nanocomposites demonstrate a high specific capacitance of 1255.12 and 636.84 F g−1 at 10 mV s−1 obtained from cyclic voltammetry curves while 1092.5 and 1070 F g−1 are estimated from galvanostatic charge–discharge at 1 A g−1, respectively. Subsequently, symmetric devices with a broad potential window of 1.4 V for both the materials are also fabricated. Symmetric devices deliver maximum specific capacitance of 115.71 and 80.28 F g−1 at 1 A g−1 with an energy density of 31. 5 and 22 Wh kg−1 at power density of 1.4 kW kg−1, which indicates the high‐rate capability of the devices. The devices have maximum capacity retention of 81% and 93%, when tested for 1000 discharge cycles at 3 A g−1, showing high cycle stability. The superlative performance of nanocomposites can be attributed to the synergistic effects they exhibit, demonstrating that they are appealing electrode materials for supercapacitor applications.

Prominent Structural Dependence of Quantum Capacitance Unraveled by Nitrogen-Doped Graphene Mesosponge.

Porous carbons are important electrode materials for supercapacitors. One of the challenges associated with supercapacitors is improving their energy density without relying on pseudocapacitance, which is based on fast redox reactions that often shorten device lifetimes. A possible solution involves achieving high total capacitance (Ctot), which comprises Helmholtz capacitance (CH) and possibly quantum capacitance (CQ), in high-surface carbon materials comprising minimally stacked graphene walls. In this work, a templating method is used to synthesize 3D mesoporous graphenes with largely identical pore structures (≈2100 m2 g-1 with an average pore size of ≈7nm) but different concentrations of oxygen-containing functional groups (0.3-6.7 wt.%) and nitrogen dopants (0.1-4.5 wt.%). Thus, the impact of the heteroatom functionalities on Ctot is systematically investigated in an organic electrolyte excluding the effect of pore structures. It is found that heteroatom functionalities determine Ctot, resulting in the cyclic voltammetry curves being rectangular or butterfly-shaped. The nitrogen functionalities are found to significantly enhance Ctot owing to increased CQ.

Rational design of pyrene and thienyltriazine-based conjugated microporous polymers for high-performance energy storage and visible-light photocatalytic hydrogen evolution from water

Conjugated microporous polymers (CMPs) have found extensive applications in various fields such as optoelectronics, CO2 capture, and catalysis. However, their potential in electrochemical supercapacitors as energy storage and H2 production systems remains relatively unexplored. This limited exploration can be attributed to certain challenges, including issues related to structural and electrochemical stability, as well as the relatively modest specific capacitance. Additionally, many of the CMPs discovered thus far have exhibited lower energy densities, further contributing to this underexplored aspect of their utility. In this study, we prepared two different CMPs [TPET-TTh and PyT-TTh CMPs] containing thienyltriazine units (TTh) for the redox mechanism and constructed electrodes for supercapacitor applications. The synthesized TPET-TTh and PyT-TTh CMPs displayed exceptionally high specific surface areas of 545 and 528 m² g⁻¹, respectively. Furthermore, their pore sizes were very similar, centered at approximately 0.39 and 0.36 nm, respectively. To evaluate their electrochemical properties, the TTh-CMPs were examined using cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The resulting CV curves exhibited rectangular shapes, indicative of the characteristic behavior of electric double-layer capacitors, across a range of potential and scan rates. These TPET-TTh and PyT-TTh CMPs delivered nominal specific capacitances of 74 and 76 F g−1 at 0.5 A g−1, respectively. In addition, they exhibited outstanding capacity retentions of 95.2 and 97.30 % even after 2000 cycles [analyzed at 10 A g−1]. The TTh-CMPs also exhibited excellent light-capture capabilities. The PyT-TTh CMP has faster charge separation and lower charge recombination rates than TPET-TTh CMP. This results in a higher hydrogen evolution rate from the water decomposition reaction. The H2 production rate of PyT-TTh CMP could be as high as 18,533 μmol g−1 h−1, which is approximately 4-fold that of TPET-TTh CMP. This study offers a strategy for the design of TTh-containing CMPs that exhibit exceptional energy storage application and photocatalytic efficiency for H2 evolution.

N-doped carbon quantum dots as corrosion inhibitor for ultra-high voltage etched Al foil

In this work, the N-doped carbon quantum dots (N-CQDs) were synthesized by hydrothermal method, and introduced into the preparation process of ultra-high voltage etched Al foil as corrosion inhibitor, in order to alleviate its over-etching (tunnels clustering and overall thinning), thus to increase its specific capacitance. N-CQDs were characterized by ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS). The effects of N-CQDs on etched tunnels, cross section of tunnel tunnels and electrochemical behavior of etched Al foil were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), open circuit potential (OCP), cyclic voltammetry curve (CV), potentiodynamic polarization curves (PDP) and electrochemical impedance spectroscopy (EIS). As a result, when 100 mg·L−1 N-CQDs is added, the over-etching on etched Al foil surface is obviously modified, together with the extended depth, the relieved tunnels clustering, and the lowed Al foil weight loss ratio. Meanwhile, compared with the sample without N-CQDs, the specific capacitance of the ultra-high voltage formed foils prepared by anodizing at 600 V increased by 30 % from 0.49 μF·cm−2 to 0.64 μF·cm−2.

Green mediated sol-gel auto combustion and solution combustion synthesis of calcium magnesium aluminate (CMA) nanoparticles: Modified carbon paste and nickel mesh electrodes for supercapacitor and sensor applications

Calcium Magnesium Aluminate (CMA) nanomaterials (NMs) were designed using a density functional theory (DFT) based materials project. Sol-gel and combustion techniques were used to prepare CMA nanoparticles and compared with characteristics and electrochemical studies with different electrodes like modified carbon paste and nickel mesh in this article. Structural characterizations using X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectra were performed. Morphological characterizations using Scanning Electron Microscopy (SEM) and High-resolution Transmission Electron Microscopy (TEM) were carried out. Modified carbon paste electrodes and nickel mesh electrodes were developed using CMA NMs via sol-gel and combustion method, its electrochemical techniques such as Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV) were compared for the sensitive detection of biomonitoring samples (i.e. uric acid, creatinine, ascorbic acid, riboflavin) and environmental contaminants (i.e. Lead nitrate and Cadmium nitrate). Specific capacitance (Csp) was calculated using CV curves for both modified carbon paste and nickel mesh electrodes found that, prepared nickel mesh electrodes by CMA NMs via sol-gel method exhibits comparatively maximum Csp value. Nickel mesh electrodes were further analysed galvanometric charge-discharge process via sol-gel and combustion technique. This report paves the way for tri-metal aluminate (CMA) design and development for electrochemical applications such as supercapacitors and sensors for the detection of various analytes.

Interaction between bilirubin oxidase and Au nanoparticles distributed over dimpled titanium foil towards oxygen reduction reaction

Spatial distribution of enzymes on electrodes is a key point to understand and optimize bioelectrocatalysis, although not largely investigated. In this work, Ti nanodimples serve as a platform for getting a controlled spatial distribution of gold nanoparticles (AuNPs). By varying the thickness of the initial gold layer, AuNPs with average sizes ranging from 13±6, 46±12 to 81±13 nm are obtained. AFM and TEM allow to localize the AuNPs in the dimples. It is in particular highlighted that the smallest NPs are present not only at the bottom but also on the edges of the Ti dimple, with TiO2 layer in their close surrounding. Enzymatic O2 reduction by immobilized Myrothecium verrucaria bilirubin oxidase (Mv BOD) is then investigated on the different materials. After having demonstrated the occurrence of the bioelectrocatalytic reaction on AuNPs excluding the Ti surface, the efficiency of the catalysis is discussed as a function of the AuNP size. The shape and fitting of the cyclic voltammetry curves obtained with the smallest AuNPs suggest a decrease in the electron transfer rate as a consequence of the colocalization of AuNPs and semiconducting TiO2. Interestingly, high stability of the enzymatic current is obtained with the highest AuNPs even in the presence of high concentration of salts.

Reliably and accurately estimate energy in super-capacitor via a model of cyclic voltammetry

As effective energy storage device super-capacitors have been widely applied in energy storage field. Cyclic voltammetry (CV) test is utilized to characterize the electrochemical performance of super-capacitors. Even if there are basic formulas to estimate specific capacitance by integral of CV, the integrable model of CV was not given in these literatures. Meanwhile, storage energy during one CV has not been known up to now. Researchers are keen to be able to calculate energy from CV. However, most current studies have not already provided integrable model of CV which is in any shape. The establishment of the accurate CV model is an important basis to realize the reliable estimation of energy density in super-capacitors via CV measurement, and also a necessary work to develop the super-capacitors management system. To fill this gap of knowledge, correct basic formula for calculation energy (density) is provided in this work for the first time in this work. To reliably and accurately calculate energy (density), a novel equivalent circuit model as dynamic model in explicit functional form of quasi ellipse shape of CV is established in this work. This quasi ellipse shape model of CV was validated on a set of thirty-five experimental CV curves, the results calculated from quasi ellipse model agree well with the experimental data because the essential novelty of the proposed model is that it is from Kirchhoff's current law and this law tells us how to calculate the total current density of a parallel circuit. Because this quasi ellipse shape model of CV is confirmed through experimental results and the integral of the model is also in explicit functional form, reliable and accurate energy (density) of each CV curve was also obtained. As another essential innovation of the proposed methodology is that quantitative relationship between the scan rate, potential window, intrinsic performance parameters of super-capacitor, measurement temperature, bending angle and energy (density) is quantitatively searched, this work makes a significant practical contribution and it makes impact on the research work on the research community. Hence, more scientific and practical significance of CV can be gained from the passage of this article.

Supercritical fluid-assisted fabrication of CuxOSAS-based electrochemical sensor for cysteine detection with enhanced sensitivity and reduced oxidation potential

This work demonstrates a rapid and effective strategy to make a cysteine detection system with higher sensitivity and lower detection limit using an eco-friendly supercritical antisolvent (SAS) technology. Copper salt particles were prepared via SAS and transformed into copper(I/II) oxide (CuxOSAS) upon calcination at 400℃. The resulting calcinated product exhibited a significantly reduced particle size and the presence of mixed valence states. The fabricated CuxOSAS cysteine detection system demonstrated excellent performance, with a cyclic voltammetry (CV) curve displaying a low oxidative overpotential (∼0.1 V vs. Ag/AgCl). The linear detection range was 0.001 μM to 0.25 μM and 0.25 μM to 1000 μM, respectively, with corresponding sensitivity of 2447.1 μA·cm−2·μM−1 and 0.3714 μA·cm−2·μM−1, respectively. In conclusion, the SAS-prepared CuxOSAS hold great prospective for electro-sensing and biomolecular catalysis applications.

Microwave-assisted synthesis of P-doped and O-rich graphitic carbon catalyst for vanadium redox flow batteries

P-doped, O-rich graphitic carbon (POGC) was synthesized via an environmentally friendly, cost effective microwave (MW)-assisted treatment using a phytic acid precursor. The treatment facilitated the formation of coral-like clusters and barrel-like graphitic structures; the P-doped graphitic structures and P–C bonds increased with the increasing irradiation time. The irradiation process increased the graphitization degree of the P-doped structure, resulting in high catalytic activity toward vanadium ion redox reactions (VIRRs), as well as improved electrical conductivity. The optimal treatment time (60 s) for POGC (POGC-60) was determined by evaluating the cyclic voltammetry curves of VIRR using POGC. POGC-60 exhibited the highest peak current densities in the anolyte and catholyte, approximately three times higher than that of the control electrode. Additionally, POGC-60 significantly reduced the charge-transfer resistance, indicating a decrease in the overpotential of VIRR. Similar improvements (increased peak current densities, reduced potential differences, and reduced charge-transfer resistance) were observed when POGC was combined with commercial graphite felt (GF) electrodes, GF/POGC. The vanadium redox flow batteries (VRFBs) utilizing the GF/POGC electrodes demonstrated enhanced efficiencies and discharge capacities (even at high current densities), as well as exceptional long-cycle stability. These findings highlight MW irradiation as a commercially feasible option for achieving the facile manufacture of cost effective, outstanding, environmentally friendly catalysts for VRFBs.

INVESTIGATION OF THE MECHANISM OF LANTHANUM IONS ELECTROREDUCTION ON NICKEL ELECTRODE IN CHLORIDE MELT

The electrochemical behavior of lanthanum ions on a nickel electrode has been studied using various electrochemical methods such as cyclic voltammetry, chronopotentiometry, open circuit chronopotentiometry (on-off curves), and square wave voltammetry in an equimolar melt of potassium and sodium chlorides at 973 K. The cyclic voltammetry curves has several reduction waves on the cathodic branch and corresponding oxidation waves on the anodic branch. The first wave A is located in the potential region –(0.0–0.1) V, where the reduction of Ni2+ ions takes place. The second wave B is in the region of potentials –(1.72–1.77) V, on it occurs electroreduction of ions \({\text{LaCl}}_{6}^{{3 - }}\) on nickel electrode with certain depolarization with formation of intermetallide of lanthanum with nickel LaxNiy. The appearance of the third wave C in the potential region –(2.09–2.13) V, we associate with the electroreduction of chloride complexes \({\text{LaCl}}_{6}^{{3 - }}\) on intermetallide LaxNiy with the formation of metallic lanthanum. On the basis of the obtained data it is shown that during the electroreduction of lanthanum chloride complexes in KCl–NaCl melt at T = 973K the nickel electrode interacts with the released lanthanum, causing a significant depolarization of the process of electroreduction of the chloride complex, also formation of intermetallide with Ni electrode occurs.

NANOSTRUCTURED COMPOSITES BASED ON MATRICES OBTAINED FROM COAL RAW MATERIALS FOR DEVELOPMENT OF ELECTRODE MATERIALS FOR SUPERCAPACITORS

The article reports the results of the study of the morphology, porous structure and electrical capacitance characteristics of highly porous carbon matrices (HPCMs) obtained from coal raw materials with different degrees of metamorphism and nanostructured composites (NSCs) based on them, the surface of which is decorated with gold or manganese oxide nanosized particles (NP), accumulating electrical charge during polarization in the electrolyte via two mechanisms (formation of an electrical double layer (EDL) and involvement of pseudo-capacitance component during Red-Ox reactions on electrodes). The samples of HPCMs were obtained by high-temperature (800 °C) alkaline activation (the mass ratio KOH/C = 2 : 1) of fossil coal from the coal basins of the Kemerovo Region and the Republic of Sakha (Yakutia): CAK - based on anthracite of the Kiyzasskiy open-pit mine (Kuzbass), with the highest coalification degree; CBK - based on boghead (a kind of sapropel coal ) from the Taymylyr deposit (Yakutia) with the lowest degree of metamorphism; CDK - based on long-flame coal (Kuzbass) occupying an intermediate position in the metamorphism series. Results obtained by scanning electron microscopy, small-angle X-ray scattering in combination with sorptometry showed that the NSC morphology is largely determined (except for submicron aggregates) by the porous structure of the matrices. The shape of cyclic voltammetry (CVA) curves for HPCMs CDK, CBK and Au-NP filled NSC based on them indicated a significant contribution from EDL into capacitance; the contribution of pseudo-capacitance is observed for the composite MnOx/CDK electrode. The features of CVA curves for microporous CAK HPCM and NSC based on it are probably caused by hindered diffusion. The specific electrical capacitance is higher as a result of the polarization of CDK and CBK HPCM with large proportions of mesopores, as well as NSCs on their basis, than that resulting from the polarization of microporous CAK and the corresponding composites. For all three HPCMs, the introduction of fillers causes an increase in the electrode capacitance. The effect is more significant for NSCs obtained from hard coals with a low level of metamorphism (an increase up to 1.8 and 1.6 times with respect to the capacitance of initial matrices for NSCs based on CDK and CBK, respectively, according to the impedance measurement data), which is due to a decrease in the active resistance and the charge transfer resistance of the cells, and, in general, to the active component of the impedance.

The fabrication and in vitro bioactivity of HA/ZrO2/MgO gradient composite coatings

Hydroxyapatite (HA), chitosan (CS), ZrO2 and MgO suspensions were distributed by zonal electrophoresis (ZE), and then HA/CS/ZrO2/MgO composite coating on the surface of titanium substrate was fabricated by electrophoretic deposition (EPD) in a reverse electric field subsequently. An HA/ZrO2/MgO gradient composite coating (Z1) was fabricated by calcination at 700 °C for 120 min. At the same time, another HA/ZrO2/MgO composite coating (E1) was directly fabricated only by electrophoretic deposition for comparison, where ZrO2 and MgO were osteogenic trace element compounds (OTECs). The morphology, structure, composition, wettability, apatite-forming ability, antibacterial efficacy of the composite coating Z1 were investigated by XRD, FT-IR, FESEM, EDS, contact angle goniometry, Lloyd's universal testing machine, electrochemical workstation, immersing in simulated body fluid, and inhibition experiments. The results showed that the contents of Ca, Zr, and Mg elements had a gradient distribution in direction of coating thickness. With the addition of ZrO2 and MgO, the contact angle of Z1 is significantly reduced from 52.5° to 27.3°. Remarkably, Z1 has more improved properties than E1, mainly manifested in the bonding strength of Z1 and titanium substrate up to 29.3 MPa, exceeding the standard requirements for bonding strength of HA coating implants (15 Mpa, iso13779-2) and as can be observed from cyclic voltammetry (CV) curve and Tafel polarization curve, Z1 exhibit superior electrochemical stability and strong corrosion resistance when immersed in HEPES simulated body fluid (H–SBF). In addition, after immersing in H–SBF for 24 d, the surface of the Z1 was completely covered by carbonated hydroxyapatite (CHA) and the Ca/P of the coating increased from 1.67 to 1.99. Furthermore, the antibacterial effect test of Z1 showed that the antibacterial rates of Z1 against Escherichia coli and Staphylococcus aureus reached to 98.2 % and 86.3 %, respectively.