H2SO4 Electrolyte Solution Research Articles

Effect of charge-discharge with higher capacitance performance of Ni-substituted CoFe2O4 magnetic nanoparticles for energy storage

In this work, we synthesized NixCo1-xFe2O4 (0 ≤ x ≤ 0.8) magnetic nanoparticles (MNPs) by using ultrasonication-assisted reverse chemical co-precipitation method. The X-ray diffraction (XRD) patterns confirm the single-phase with mixed spinel structure of the NixCo1-xFe2O4 (0 ≤ x ≤ 0.8) MNPs with the crystallite size range between 12 nm - 17 nm. The molecular dynamics and oleic acid coated Ni-substituted CoFe2O4 magnetic nanoparticles were confirmed by FTIR measurements. The surface composition of NixCo1-xFe2O4 (0 ≤ x ≤ 0.8) MNPs (Ni, Co, Fe and O) and their oxidation states were estimated using X-ray photoelectron spectroscopy. The NixCo1-xFe2O4 (0 ≤ x ≤ 0.8) MNPs are spherical in shape and polycrystalline in nature, confirmed by FESEM and HRTEM measurements. The Ni-substituted CoFe2O4 MNPs with higher zeta potential (ζ) from −24 mV to -41 mV with an increase in Ni concentration, signifies the stable colloidal stability due to the electrostatic repulsion between MNPs. The DC magnetization (M-vs-H) measurements reveal the ferrimagnetic behavior of NixCo1-xFe2O4 (0 ≤ x ≤ 0.8) MNPs, which suppress the saturation magnetization (MS) from 48.6 emu/g to 5.3 emu/g with the enhanced coercivity (HC) from 335 Oe to 1700 Oe with the substitution of Ni2+ ions is in corroboration with electron paramagnetic resonance (EPR) measurements. The enhanced EPR resonance field (Hres = 2335 Oe - 3261 Oe) with the substitution of Ni2+ ions is attributed to the generation of oxygen vacancies and defects, which are predominant in Ni0.8Co0.2Fe2O4, resulting in significantly enhanced electrochemical performance. Therefore, the three-electrode system was utilized to investigate the electrochemical properties of NixCo1-xFe2O4 (0 ≤ x ≤ 0.8) MNPs. The Ni-substituted CoFe2O4 MNPs have demonstrated significantly enhanced capacity retention of 77 % even after 5000 cycles in 1 M H2SO4 electrolyte solution. NixCo1-xFe2O4 (0 ≤ x ≤ 0.8) MNPs exhibit an excellent specific capacity (Cs) of 794.5 F/g at a current density of 1 A/g, signifies the rate of redox reaction at surface electrolyte interface (SEI) is greatly influenced by the surface to volume ratio. Thus, with the enhancement of Ni2+ ions, redox reaction kinetics might become more efficient resulting in the enhanced charge storage capacity.

Interconnected hierarchical 3D porous carbon derived from Saccharum officinarum L. leaf based on the synergistic effect of KOH for high performance supercapacitor

ABSTRACT Porous carbon has continuously been explored based on biomass for green energy storage due to its abundant, renewable, environmentally friendly resource, economical features, and thermal-chemical stability. Therefore, this study aimed to present porous carbon derived from sugarcane or Saccharum officinarum L. leaf as a precursor, achieved through a KOH activation strategy that combines a two-step pyrolysis process. The synthesized material exhibited an interconnected 3D hierarchical structure, a high specific surface area of 752 m2/g, and a carbon purity of 91.38%. Supercapacitor cell electrode had the highest specific capacitance of 471 F/g induced by 0.5 M KOH. Furthermore, in the 1 M H2SO4 electrolyte solution, the symmetrical supercapacitor cell electrodes produced the highest specific energy of 65.55 Wh/Kg at a specific power output of 329 W/Kg. As a result, a sustainable green method was established by using a biomass energy source that is applied as high-performance supercapacitor cell material.

0D-3D Superstructure of Biocarbon with FeCl3-Assisted for Electrochemical Symmetrical Supercapacitor

Biomass materials exhibit a diversity of macrostructures that can be derived or developed into various 0D-3D nanoscale structural designs with various different dimensions such as spherical, nanofiber, tubular, nanosheet, hierarchical, nanosphere, and honeycomb structures, when converted into activated carbon. This research converts oil palm empty fruit bunch fiber biomass into supercapacitor carbon material by optimizing the chemical activation process by varying the activating reagent. The active carbon conversion process includes precarbonization stages, chemical activation (KOH, FeCl3, and ZnCl2), carbonization, and physical activation. The resulting electrode was confirmed to have a morphology with a 0D to 3D structure (nanosphere, nanofiber and nanopore) due to the FeCl3 activator, so the resulting surface area was high (517.998 m/g). Biomass was successfully converted into carbon which was confirmed through through the resulting physical and electrochemical properties. The electrochemical performance of the sample supercapacitor cell was analyzed in a symmetric two-electrode system in 1 M H2SO4 electrolyte solution. The FeCl3-activated samples shows the highest specific capacitance of 256 F/g at a scan rate of 1 mV/s. In addition, oil palm empty fruit bunch fiber biomass is a potential raw material, as a carbon material for supercapacitor cells with high performance.

Engineering 3D-interconnected graphene nanoplatelets and polyaniline nanocomposite for high energy density energy storage

A high-performance, seaweed-shaped 3D interconnected nanocomposite electrode comprising graphene nanoplatelets (GNP) and polyaniline (PANI) as an electrode material for supercapacitors is synthesized via conventional in-situ chemical oxidative polymerization. This research aims to enhance the electrochemical performance of the GNP/PANI nanocomposite electrode material by manipulating their shape and electroactive characteristics for greater optimization. While seaweed-shaped GNP/PANI nanocomposites have been reported previously, none have demonstrated high electrochemical performance with an optimized 40 wt% of GNP in GNP/PANI nanocomposite. This deficiency is attributed to the lack of 3D well-interconnected nanocomposite formation and the electroactivity of GNP/PANI when compared to individual PANI or GNP in H2SO4 electrolyte.The electrochemical study confirms an upward revision in specific capacitance, from 400 Fg−1 for GNP and 514 Fg−1 for PANI, to 1088 Fg−1 for the GNP/PANI electrode material in an aqueous 1 M H2SO4 electrolyte solution. It is envisioned that formation of such 3D interconnected GNP/PANI nanocomposite contributes in increasing the interplanar and interchain distances in the nanocomposite particularly in GNP layered structure. Additionally, it is observed that the electrochemical impedance parameters, such as charge transfer resistance Rct (0.12 Ω), high response frequency (1.367 Hz), and short relaxation time (τo ∼ 0.73 s) of the GNP/PANI nanocomposite electrode material, demonstrate excellent performance. The seaweed-shaped GNP/PANI nanocomposite exhibits promising potential as an electrode material for next-generation symmetric supercapacitors due to its high specific capacitance, low cost, and ease of fabrication.

Corrosion-Resistant and Electrically Conductive Oxide Coatings for Metal Bipolar Plates for PEM Electrolyzers

The PEM electrolyzers are considered a promising alternative to alkaline water electrolyzers, as the advantages of PEM technology are high efficiency, high power density, a wide range of power inputs, low operating temperatures, relatively quick start-up, and easy scale-up. The ability of PEM electrolyzers to function dynamically makes them particularly appealing in energy capture and storage systems where electrical energy is derived from renewable sources such as solar and wind power. The bipolar plates (BPPs) are essential components of the PEM electrolyzer stacks and account for the main fraction of the total weight and cost. The BPPs must be electrically conductive, highly corrosion-resistant, and maintain a low interface contact electrical resistance (ICR). The root causes of the BPPs corrosion issues are non-conductive oxides formation increasing electrical resistance, and metal ions out-diffusion poisoning the catalyst and electrolyte membrane. The US Department of Energy has set targets for bipolar plates in fuel cells, including corrosion current densities < 1 µA/cm2 and ICR < 10 mΩ·cm2. Even though these targets do not apply to BPPs in PEM electrolyzers, they provide an indication of acceptable values. The problems outlined above are being overcome or minimized by applying corrosion-resistant and simultaneously electrically conductive coatings.This work, therefore, investigates various corrosion-resistant and electrically conductive oxide coatings prepared by reactive high-power impulse magnetron sputtering (HiPIMS) on SS316L substrates. Reactive HiPIMS is an advanced and progressive magnetron sputter deposition technique suitable for preparing high-quality oxide coatings. The main advantage of HiPIMS is a high degree of ionization of sputtered particles in the discharge plasma and the associated high ion-to-atom ratio in particle flux toward the substrate. This allows one to achieve coating densification and crystallinity at low substrate temperature and without applying a substrate bias voltage. In our case, the native oxide on the SS316L substrate surface was removed by employing plasma etching prior to the coating deposition utilizing HiPIMS-generated ions accelerated towards the substrate by an applied bias voltage. The oxide coatings were deposited using an unbalanced magnetron with a directly water-cooled planar target with a diameter of 100 mm in argon-oxygen gas mixtures at the argon pressure of 1 Pa in an ultra-high vacuum chamber. The oxygen partial pressure was controlled by a PID regulator at a given power density in a pulse. This allowed the deposition of the coatings with different stoichiometries and, thus, different electrical conductivity and corrosion resistance.The electrical resistivity of oxide coatings was measured by a four-point probe system on a non-conductive glass substrate. The compaction pressure dependence of ICR between the test plate and a gas diffusion layer (GDL) was measured in a range from 0.3 to 2.0 MPa on a custom-designed device using gold-coated cylindrical copper electrodes. All electrochemical measurements were performed in an H2SO4 electrolyte solution with an acidity of pH 5.5, fluorine ions concentration of 5 ppm, and a temperature of 60 ℃ to simulate the PEM electrolyzer environment. Accelerated corrosion tests were carried out in extreme anodic conditions of the PEM electrolyzer via potentiostatic polarization at a potential of 2 V vs SHE. Open circuit potential, corrosion current, Tafel slopes, and polarization resistance were determined from potentiodynamic polarization curves measured from 0 to 2 V vs SHE recorded at a scan rate of 1 mV/s, this range should cover most of the potentials experienced inside a PEM electrolyzer. Potentiodynamic polarization and ICR versus compaction pressure were measured before and after the accelerated corrosion test.

SURFACE QUALITY AND CORROSION RESISTANCE OF 316L STAINLESS STEEL ELECTROPOLISHED USING PHOSPHORIC – SULFURIC ACIDS

Electropolishing is an electrochemical surface finishing technique. It is commonly applied to equipment that requires a gleaming finish. This surface property is frequently required in 316L stainless steel (SS) medical implants. Electropolishing removes a thin layer from the metal's surface through electrochemical processes. This results in a very clean, smooth, and bright metal surface. The process parameters, such as electrolyte solution, electrical current, and electropolishing time, influence surface roughness and glossiness. The dissolution of metallic ions during the process may also affect the corrosion resistance of the treated material in addition to producing a shiny surface. This study investigated the surface glossiness, surface roughness, and corrosion of electropolished 316L SS. Electropolishing experiments on 316 SS were carried out using various H3PO4 (50%) and H2SO4 (32%) electrolyte solution compositions. The influences of electrolyte solution composition, electric current, and electropolishing time were studied. The results showed that increasing the H2SO4 content of the mixture and electropolishing the 316L SS for a longer period of time improved the surface roughness and glossiness. Under 10 Amp electric currents, the best surface glossiness was discovered. A corrosion test revealed that the electropolishing produced a Cr and Ni-rich layer that improved the corrosion resistance of the samples.

Electrospun Carbon Nanofibre‐Based Catalysts Prepared with Co and Fe Phthalocyanine for Oxygen Reduction in Acidic Medium

AbstractA Pt‐free cathode catalyst is necessary for proton‐exchange membrane fuel cell (PEMFC) to enable the widespread use of these environmentally friendly energy conversion devices at affordable price. Herein, a pyrolyzed electrospun carbon nanofibre (CNF) catalyst is prepared embedded with cobalt(II) phthalocyanine and iron(II) phthalocyanine compounds to provide the transition metal N4‐macrocyclic complex‐derived sites (MNX) possessing better electrocatalytic oxygen reduction reaction (ORR) activity. The physical characterisation showed the nanofibrous structure of catalyst with rough surface texture and considerable amount of N, Fe, and Co. The D−MN4−CNF−IL−A catalyst prepared using ionic liquid as a porogen displayed the best electrocatalytic activity for O2 electroreduction proceeding via 4e− pathway in 0.5 M H2SO4 electrolyte solution with the ORR onset and half‐wave potential of 0.83 and 0.71 V vs reversible hydrogen electrode (RHE), respectively.

Enhanced electrochemical performance of oxygen, nitrogen, and sulfur trial-doped Nypa fruticans-based carbon nanofiber for high performance supercapacitors

The utilization of biomass-derived carbon materials, which exhibit nanofiber structures and possess advantageous properties such as porosity, abundant availability, heteroatom content, and high specific surface area, is important in the development of green energy technologies and sustainability. Therefore, this research focuses on the synthesis of Nypa Fruticans Fiber (NFF)-derived carbon nanofiber materials through activation and carbonization processes as well as doping of oxygen (O), nitrogen (N), and sulfur (S) heteroatoms. O doping was carried out internally (activation process) while N-S doping was carried out externally using thiourea (0.1, 0.3 and 0.5 g) which aims to produce high physical properties of carbon electrodes (crystallinity structure, surface morphology, surface area specific) related to the performance improvement of supercapacitor cells. Furthermore, the NFF electrode with O-N-S doping has the physical properties of a low crystallinity structure, a high specific surface area of 1230.05 m2g−1 and the formation of a large number of nanofiber structures. The electrochemical properties of the NFF-03 supercapacitor cell electrode had the highest specific capacitance, specific energy, and specific power values of 430 Fg−1, 248 Wkg−1, 64 Whkg−1, respectively, at a current density of 1 Ag−1 in 1 M H2SO4 electrolyte solution, at a voltage of 1 V with doped 0.3 g of thiourea. The results of this research provide a clear reference that the trial heteroatom (O-N-S) doping process can produce high physical properties of carbon electrodes leading to increased performance of biomass-derived supercapacitor cells with a simple, relevant and low-cost synthesis strategy.

Synthesis and characterization of cotton candy-PANI: Enhanced supercapacitance properties

Polyaniline (PANI) is a popular material for making supercapacitor electrodes due to its long-term cycle stability, specific capacitance, conductivity, mechanical robustness, scalability, and viability. All of these characteristics may be improved by introducing new architecture and employing alternative synthetic methods. The current study covers the synthesis and electrochemical performance of the protonated emeraldine salt of a newly architected PANI, which is referred in this article as cotton candy polyaniline (cc-PANI). It was found that the direct current (DC) conductivity and specific capacitance of PANI and cc-PANI electrodes are 1.21 × 10−4 Scm−1, 3.73 × 10−4 Scm−1 and 161.66 Fg-1, 203.33 Fg-1 at a current density of 1Ag-1 in a 1 M H2SO4 electrolyte solution respectively. Further, the static contact angle (CA) was found to be 38.3o and 32.6o for PANI and cc-PANI. Here, a novel designed cc-PANI was effectively synthesised and characterised. This strategy offers new hopes in the realm of PANI with improved supercapacitance qualities.

POROUS CARBON FROM PINEAPPLE PEEL AS ELECTRODE MATERIAL OF SUPERCAPACITOR

Porous carbon from biomass has a great potential to be developed. Biomass as a resource is renewable, abundantly available, and cheap. One application of porous carbon is as an electrode material of supercapacitor due to its advantageous pore properties such as high specific surface area and pore volume. This research prepared porous carbon material from pineapple peel waste and tested it as a supercapacitor electrode. The research steps were material preparation, conversion of pineapple peel to porous carbon, and characterization, including material characterization and electrochemical characterizations. Pineapple peel (under 80 mesh size) was pre-carbonized by hydrothermal method at 1900C for 2 hours under a subcritical condition. After that, biochar was pyrolyzed at 9000C and activated using CO2/N2 (KB-900-50). As a reference, biochar was also pyrolyzed under a nitrogen atmosphere at 9000C without activation (KB-900). Produced porous carbon was characterized (i) pore structures, e.g., specific surface area, average pore diameter, and total pore volume using N2-sorption analysis, and (ii) electrochemical performance, e.g., cyclic voltammetry and galvanostatic method using 1 M H2SO4 electrolyte solution. The result showed that the activation process effectively increased the porosity of porous carbon. Material (KB-900-50) possesses a high surface area of 648 m2/g and a high capacitance value of 78 F/g.

(Digital Presentation) A Study on the Poly(Amidoamine) Dendrimer Encapsulated Platinum Nanoparticles for Hydrogen Evolution Reaction in Proton Exchange Membrane Water Electrolyzer

Hydrogen is a non-polluting energy carrier being considered for use in many sectors, including transportation, chemical industry, as well as the energy storage. The main motivation is to reduce utilizing fossil fuels and thus to stop global warming. Hence, speeding up research and development efforts in hydrogen production is critical to ensuring a sufficient share of hydrogen to be used in the envisaged economy sectors in the coming decades. Proton exchange membrane water electrolyzis (PEM WE) is the perspective technology to supply, in combination with the renewable energy sources, so called green hydrogen connected with a zero carbon dioxide emissions. This technology is characterized by high process intensity, good faradaic efficiency, quick response time and the possibility of high-pressure operation [1]. Important aspect, however, represents improvement of its economic competitiveness to the alternative hydrogen production routes. Important aspect represents an effective electrocatalysis of the desired electrode reactions.Number of catalysts are being studied for the hydrogen evolution reaction (HER). However, to the date, Pt-based nanoparticular catalysts are still considered to be a state of the art, robust option for use as a cathode catalyst in PEM WE. But the high cost and limitted stability are still obstacle to use Pt based catalysts in PEM WE effectivelly [1]. Hence, the effort has to be made to improve the stability of Pt nanoparticles and thus to retain its catalytic activity even under reduced loads. Poly(amidoamine) dendrimer (PAMAM) encapsulation of the nanoparticles represents a promising approach to solve this issue. PAMAM works as a template, protecting encapsulated Pt nanoparticles without passivating their surface and preventing them from agglomeration. This approach has been validated by using dendrimer encapsulated Pt nanparticles (Dend-Pt) as an oxygen reduction reaction catalyst in the fuel cells [2]. The PAMAM are monodispersed macromolecules, having a three-dimensional structure. Typically, there are three types of PAMAM, namely cationic (-NH2), anionic (-COONa) and neutral (-OH). Thus, the charge of the surface groups determines the dendrimer type. Based on the size and molecular weight, each type of PAMAM dendrimers has been classified into different generation for example, G1 and G10 are denoted as 1st and 10th generations, respectively [2].The goal of this work is to reduce Pt load required for efficient and stable HER in a PEM WE. PAMAM encapsulated Dend-Pt incorporated into multilayer graphene oxide (MLG) are used for this purpose.At first, the most suitable dendrimer template for Pt encapsulation needs to be identified and an optimum loading improving its HER efficiency in PEM WE determined. Our previous communication has proved the excellent HER activity of the carbon supported Dend-Pt, revealing an important role of the various carbon supports in enhancing conductivity, stability and catalytic activity of the Dend-Pt for HER [3]. Thus, Dend-Pt were synthesized encapsulated within the different types of dendrimer templates with varying surface end groups (-NH2, -COONa and –OH). Different generations of each type of dendrimer were used. The synthesis method consists in a simple chemical reduction in an aqueous solvent at the room temperature. The encapsulated amount of Pt was fixed for the each dendrimer under study. Commercially available MLG was used as a carbon support. The Dend-Pt was incorporated into MLG through chemical covalent linkage using (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide) (EDC) and N-hydroxyl sulfoxuccinimide (NHS) as the cross-linking agents. The amount of the cross-linking agents (EDC and NHS) used was optimised as a the mass ratio of Dend-Pt and MLG with respect to the HER activity of the resulting catalyst. The formation of the zero-valent Dend-Pt was confirmed using UV-Vis absorption and XPS spectroscopy. The structure of Dend-Pt and MLG/Dend-Pt composites were determined using TEM. The loading of the Dend-Pt on MLG surface was determined using the ICP-OES spectrometry. The electrochemical HER catalysis by different catalysts was studied by means of voltammetric methods and electrochemical impedance spectroscopy in an environment of the 0.5 M H2SO4 electrolyte solution. As a proof of concept, the PEM water electrolysis in single-cell setup was perfomed using either a commercial catalyst (40% Pt/C) or Dend-Pt as a cathode catalyst. Iridium dioxide was used as an anode catalyst.AcknowledgementThe authors gratefully acknowledge financial support from “The Grant Agency of the Czech Republic” (GAČR) under project no. 20-21105Y.Reference:[1] M. Prokop, M. Drakselova, K. Bouzek, Curr Opin Electrochem, 20 (2020) 20-27.[2] B. Devadas, A.P. Periasamy, K. Bouzek, Coord. Chem. Rev, 444 (2021) 214062.[3] B. Devadas, T. Imae, Electrochem. Communications, 72 (2016) 135-139. Figure 1

Anodic Polarization Study of Step Pulse Waveform for Machining Accuracy in Electrochemical Micromachining

Electrochemical micromachining (EMM) shows promise as a versatile process for machining chemically resistant metallic materials in microsystems applications. A traditional rectangular pulse pattern has been modified into a step pulse waveform with a series of short rectangular pulses with different amplitudes. By establishing the experimental setup, anodic polarization behavior has been investigated throughout the dissolution process with 0.1 M H2SO4 electrolyte solution at different applied voltages under the application of rectangular and step pulse waveforms. Utilizing the step pulse waveform, oscillation of the anode potential and transpassive state have been obtained during machining. Thus, from polarization studies, it has been observed that at 13 V, the current density is accelerated in a moderate range, i.e., 0 to 33 A cm−2, which can reduce the anodic dissolution rate during the active state. Alternatively, the stray current effects and micro-sparks can be controlled because the duration of the passive state is very small and the RMS voltage can be reduced by 20.65% as compared to the rectangular pulse waveform. Further, overcut and tapering effects have been reduced by 83.99% to 51.39% and by 98.66% to 44.48% at the applied voltage of 13 to 17 V, respectively.

Highly Capacitive Mesoporous Polyaniline Spheres as Scalable and High Electrochemical Performance Supercapacitor Electrode

AbstractThis article demonstrates morphological based fabrication of Polyaniline mesopores (PANIMS) via the standard polymerization approach using Triton as an additive and 0.1 M H2SO4 as an electrolyte to achieve improved specific capacity (736 F g−1) in contrast to reported bulk PANI as well as PANI sphere morphologies. PANIMS1 exhibit long cyclic stability and capacitive retention ∼83 % in 0.1 M H2SO4 electrolyte after 5000 cycles. This easy and low‐cost fabrication of PANIMS was conducted by varying minimal amount of Triton in 0.1 M H2SO4 electrolyte solution to form mesopores. The adsorption and desorption isotherm of the mesopores suggests a specific surface area of 50.9 m2 g−1with a pore diameter of 2.2 nm. The protocol followed to form these PANIMS involves the variation of surfactant Triton to achieve sphere morphology thereby enhancing the charge storage property of PANI. These spheres also possess an enhanced electrical conductivity to be around ∼23 S/m than their bulk counterpart. The electrochemical assays show that there is excellent electrolyte ion penetration in the H2SO4 electrolyte which promotes a rapid ion transport to the PANIMS active sites. Also, a low value of Rct ∼2.17 Ω helps in giving a good capacitive performance of the PANIMS1 electrode. The electrochemical impedance spectroscopy (EIS) analysis shows a phase degree at 68°, response frequency at 0.38 Hz and time constant at 2.63 s. The study shows the present mesopores morphology of PANI projects to be one of the good electrode candidates for supercapacitor applications.

Graphene oxide-polyaniline conducting composite film deposited on platinum-iridium electrode by electrochemical polymerization of aniline: Synthesis and environmental electrochemistry application

Graphene oxide (GO) was synthesized by the modified Hummers method. Graphene oxide-polyaniline (GO-PANI) composite film was deposited on platinum-iridium (Pt-Ir) electrode by electrochemical polymerization of aniline in the solution of 0.5 M H2SO4 and 0.4 M aniline monomer with 4 mg/mL dispersed GO powder under constant potential. The structural and morphological properties of GO and GO-PANI composite film were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The electrochemical behavior of GO-PANI composite film was analyzed by cyclic voltammetry (CV) in terms of cycling stability and reusability. The characterization results confirmed the successful production of GO and the formation of GO-PANI composite film. GO-PANI deposited Pt-Ir electrode was further examined in electrochemical degradation of Reactive Blue 4 and Acid Red 97 textile dyes in 0.5 M H2SO4 electrolyte solution for the environmental electrochemistry application.

Improved electrochemical performance of symmetric polyaniline/activated carbon hybrid for high supercapacitance: Comparison with indirect capacitance

AbstractPolyaniline (PANI) chains doped with very small amount of Activated Carbon (AC) as an electrode material in aqueous H2SO4 electrolyte was successfully employed in this work to enhance the electrochemical capacitive properties of PANI. The aim of this research is to improve overall specific capacitance of PANI by incorporating only minute amount of AC as a PANI dopant. There are many reports available on PANI/AC but the use of such a minute amount of AC in H2SO4 electrolyte which enhances the overall specific capacity of the composite has not been reported elsewhere. An improvement in the specific capacitance from 763.44 to 897.50 F g−1 in aqueous 0.1 M H2SO4 electrolyte solution is observed by adding mere 0.04 g of AC. It is envisaged that AC enhances SO4−2 ion transportation, forwards a stable and fast surface redox reactions, hence collectively improving the overall capacitive performance of supercapacitor electrode. The charge/discharge measurements shows that AC particles stops the PANI chains degradation during charge/discharge cycle. Also, the retention rate (54%) of PANI1.0/AC0.04 indicates approximately 11% more stability than pure PANI (43%) electrode alone. It was further observed that the electrochemical impedance parameters viz., that charge transfer resistance (Rct) (0.79 Ω), response frequency (0.26 Hz), response time (3.84 s) and knee frequency (9.16 Hz) of PANI1.0/AC0.04 electrode material shows excellent performance of the PANI doped AC. Considering its high specific capacitance, low‐cost and ease of synthesis, PANI1.0/AC0.04 seems to be a promising electrode material for next generation symmetric supercapacitors.

FeNC Electrocatalysts with Densely Accessible FeN4 Sites for Efficient Oxygen Reduction Reaction

AbstractThe development of iron and nitrogen co‐doped carbon (FeNC) electrocatalysts for the oxygen reduction reaction (ORR) in proton‐exchange membrane fuel cells (PEMFCs) is a grand challenge due to the low density of accessible FeN4 sites. Here, an in situ trapping strategy using nitrogen‐rich molecules (e.g., melamine, MA) is demonstrated to enhance the amount of accessible FeN4 sites in FeNC electrocatalysts. The melamine molecules can participate in the coordination of Fe ions in zeolitic imidazolate frameworks to form FeN6 sites within precursors. These FeN6 sites are then converted into atomically dispersed FeN4 sites during a pyrolytic process. Remarkably, the FeNC/MA exhibits a high single‐atom Fe content (3.5 wt.%), a large surface area (1160 m2 g−1), and a high density of accessible FeN4 sites (45.7 × 1019 sites g−1). As a result, FeNC/MA shows a much enhanced ORR activity with a half‐wave potential of 0.83 V (vs the reversible hydrogen electrode) in a 0.5 m H2SO4 electrolyte solution and a good performance in a PEMFC system with an activity of 80 mA cm−2 at 0.8 V under 1.0 bar H2/air. This work offers a promising approach toward high‐performance carbon‐based ORR electrocatalysts.

Direct Exfoliation of Conductive MoS2 Using Peroxide for Solid State Sensor and Catalytic Applications

Two-dimensional (2D) materials have attracted much attention over the last decade due to their high performance in nanoelectronic devices. The discovery of graphene opened up many opportunities to investigate and explore other 2D materials. There has been a drive to expand the toolbox of 2D materials to also include insulators and semiconductors with a variety of bandgaps. As a result, a wide range of materials have been discovered or predicted, with molybdenum disulfide (MoS2) being particularly popular. Using the semiconducting phase of MoS2 (2H-MoS2) requires a relatively high voltage to get sufficient conductivity due to the presence of a band gap. However, for applications in batteries, supercapacitors, electrocatalysts and solar cells, a substantially increased conductivity is required in order to achieve reasonable currents.1 The most common source of conductive MoS2 is metallic MoS2 (1T-MoS2) that has been prepared via the lithium intercalation process, which requires inert atmosphere processing and safety procedures.2 Hence, there is a desire to develop a safer and more efficient process to yield conductive MoS2. Defects play a very important role in modulating the electrical properties of MoS2. Sonication of MoS2 in an appropriate solvent results in many disordered structural defects. The most common defects on MoS2 are sulfur defects. These defects increase the energy level of the gap state and eventually deteriorate the device performance. Thiol based molecules are commonly used to reduce the number of sulfur defects on MoS2. Other molecules such as oxygen or organic super acids like bis(trifluoromethane) sulfonamide (TFSI) have also been reported to passivate the surface defect.3 Past research has mainly focused on the theoretical study of defective MoS2 and how to utilize those defects for improving photoluminescent efficiency. However, those defects can also be utilized to improve the conductivity of MoS2 as a safer alternative for applications in batteries, supercapacitors, solar cells, electrocatalyst and sensors.Conductive MoS2 (c-MoS2) can be used as active material for low-cost solid-state chemiresistive pH sensors.4 In chemiresistive sensors, conductivity changes are observed based on direct interactions between the active material and the analyte.5 Even though chemiresistive pH sensors based on exfoliated graphene, carbon nanotubes, or graphitic materials are available, their sensing response is limited to less than 20%.6 On the other hand, MoS2 has attracted great attention as a promising electrocatalyst for the hydrogen evaluation reaction (HER) because of abundant active sites at edge sites and on the basal plane for facilitating hydrogen production. Water splitting is the simplest and most convenient method to generate hydrogen. In industrial applications, an electrocatalyst is commonly used to accelerate the HER and reduce the overpotential. Even though 2H-MoS2 has good catalytic activity at the edge sites, its low electrical conductivity limits the achievable current density, resulting in a high Tafel value and making it unsuitable for practical application in HER.In this work, we show a simple and effective way to prepare few layer c-MoS2 under ambient conditions using 0.06 vol% aqueous hydrogen peroxide. We have demonstrated that the bulk conductivity of the conductive MoS2 that we prepared is up to seven orders of magnitude higher than that of the semiconducting phase of MoS2. The samples were also characterized with Hall measurements, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy which showed that hydrogen molybdenum bronze (HxMoO3) and substoichiometric MoO3−y help tune the conductivity of the nanometer-scale thin films without impacting the sulfur-to-molybdenum ratio. C-MoS2 was further functionalized with thiols to determine the number of residual reactive sites. An important goal of our work is to control the conductivity of the MoS2 thin films in safe and facile ways that enable their application in low-cost chemiresistive sensors in liquid environments. We fabricated chemiresistive pH sensors with centimeter channel lengths while maintaining low measurement voltages. We further measured the catalytic activity of c-MoS2 films in 0.5 M H2SO4 electrolyte solution with three electrode systems using linear sweep voltammetry (LSV) which showed a lower Tafel value at 10 mA/cm2 current density. The lower Tafel value demonstrated that c-MoS2 has potential to use as catalyst for HER. Our study furthers the understanding of conductive forms of MoS2, and also opens up a new pathway for next generation electronic and energy conversion devices.

Microstructure, High-Temperature Wear Resistance, and Corrosion Resistance of Laser Cladded Co-Based Coating

Co-based coating has been fabricated on Ti-6Al-4V (TC4) titanium alloy by laser cladding. The phase composition and microstructure of the coating were analyzed using metallurgical microscope (MM), scanning electron microscope (SEM), x-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM), respectively. The microhardness, high temperature wear resistance and corrosion resistance of the coating were investigated by performance tests. The results show that the coating was mainly composed of CoTi, CoTi2 and Co0.5Cr1.5Ti crystalline phases and an amorphous phase. The microhardness of the coating was twice that of the titanium alloy substrate. The value of friction and wear coefficient of the coating was lower and more stable, and the wear mass loss decreased by 52% as compared with the substrate in the high-temperature friction and wear test. The oxidative wear mechanism in the condition of high temperature friction and wear was studied. Moreover, the coating exhibited better corrosion resistance than the substrate in both NaCl and H2SO4 electrolyte solutions.

Fabrication of NiS2 Nanomaterials for Cd2+ Sensing

Heavy metal Cadmium (Cd) will continuously pollute the atmosphere, soil and various water environments through material circulation, and even pose a threat to human safety. It has been designated as a first-class pollutant in sewage by China, therefore there is an urgent need to find new, more effective, and low-cost method to accurately detect Cadmium ion (Cd2+) concentration. We experimentally prepared a new Cd2+ sensor based on NiS2 nanomaterials capable of measuring Cd2+ concentration. The corresponding relationship between over potential of NiS2 nanomaterials in H2SO4 electrolyte solutions with different Cd2+ concentration and reduction peak with change of Cd2+ concentration was obtained by electrochemical method.

Silver nanoparticles decorated phthalocyanine doped polyaniline for the simultaneous electrochemical detection of hydroquinone and catechol

Abstract In this proposed study, the new electrocatalyst was synthesized by incorporating the supramolecular electrocatalyst tetra amino cobalt phthalocyanine (TACoPc) into the conducting polyaniline (PANI) and which was subsequently used to decorate silver nanoparticles (AgNPs) using Ag+ solution on the surface of TACoPc/PANI composite to form a supramolecular hybrid system. The decoration of AgNPs on the surface of TACoPc/PANI was carried out in an aqueous media at room temperature and which was confirmed by various spectroscopic techniques. The synthesized catalyst AgNPs decorated TACoPc doped PANI (TACoPc/PANI/AgNPs) modified the glassy carbon electrode (GCE) used to construct the electrochemical sensor for simultaneous detection of hydroquinone (HQ) and catechol (CC). The modified electrode showed the two distinct peaks for HQ and CC in CV analysis with a considerable potential difference of 0.080 V vs SHE. The presence of central cobalt metal in TACoPc macromolecular electrocatalyst mediates the oxidation of HQ and CC, which was successively enhanced by the incorporation of conducting PANI and AgNPs. The sensor exhibited excellent electrocatalytic activity with good stability, selectivity, reproducibility, and a very low limit of detection in the electrochemical sensing of HQ and CC in a 0.1 M H2SO4 electrolyte solution.