Chronopotentiometry Techniques Research Articles

Enhanced hydrogen storage performance of zinc and magnesium cobaltite nanocomposites

Renewable and sustainable energies are vital for the near future. Hydrogen, as a clean energy carrier, is a potential candidate for supplying energy in the foreseeable future. Nowadays, hydrogen storage technology has become a significant issue in the energy sector. In this study, ZnCo2O4/ZnO and MgCo2O4/MgO nanocomposites have been synthesized using the sol-gel method with stearic acid as a complexing agent. Different analyses were studied to examine the crystal structure, morphology, and physical properties of the as-prepared samples, including X-ray diffraction (XRD), Fourier transforms infrared (FT-IR), field emission scanning electron microscopy (FESEM), diffuse reflectance spectroscopy (DRS), and vibrating sample magnetometer (VSM). Various methods have been utilized for hydrogen storage technology. In a pioneering approach, the electrochemical hydrogen storage of samples was compared by the chronopotentiometry technique in KOH (4 M) electrolyte solution. The results reveal that ZnCo2O4/ZnO and MgCo2O4/MgO nanocomposites exhibit excellent discharge capacities of 4240 and 3529 mAh/g, respectively, after 11 cycles.

Design of a new nanocomposite based on Keggin-type [ZnW12O40]6− anionic cluster anchored on NiZn2O4 ceramics as a promising material towards the electrocatalytic hydrogen storage

Extensive research efforts have been dedicated to developing electrode materials with high capacity to address the increasing complexities arising from the energy crisis. Herein, a new nanocomposite was synthesized via the sol–gel method by immobilizing K6ZnW12O40 within the surface of NiZn2O4. ZnW12O40@NiZn2O4 was characterized by FT-IR, UV–Vis, XRD, SEM, EDX, BET, and TGA-DTG methods. The electrochemical characteristics of the materials were examined using cyclic voltammogram (CV) and charge–discharge chronopotentiometry (CHP) techniques. Multiple factors affecting the hydrogen storage capacity, including current density (j), surface area of the copper foam, and the consequences of repeated cycles of hydrogen adsorption–desorption were evaluated. The initial cycle led to an impressive hydrogen discharge capability of 340 mAh/g, which subsequently increased to 900 mAh/g after 20 cycles with a current density of 2 mA in 6.0 M KOH medium. The surface area and the electrocatalytic characteristics of the nanoparticles contribute to facilitate the formation of electrons and provide good diffusion channels for the movement of electrolyte ions throughout the charge–discharge procedure.

Fabrication and Investigation of a MoS2/Fe3O4/PANI Composite for Supercapacitor Applications

AbstractThis study investigates a successful fabrication of MoS2/Fe3O4/PANI composite by chemical co‐precipitation method. The facile hydrothermal approach was employed to synthesize a MoS2/Fe3O4 composite, followed by the utilization of a conventional chemical oxidation strategy to produce a PANI coating on the composite, thereby generating an active material for electrochemical reactions and a structure facilitating the transportation of ions via multiple pathways. The fabricated MoS2/Fe3O4/PANI composite was characterized by SEM, ICP, XRD, FT‐IR, and so on. In this study, we delved into the electrochemical charge storage feature of MoS2/Fe3O4/PANI. The electrochemical characteristics of the nanocomposite were assessed through the implementation of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry techniques in a 3 M KOH electrolytic solution, utilizing nickel foam as both a material support and current collector for two electrode configurations. The findings indicate that MoS2, as the support matrix, possesses notable attributes such as a substantial surface area, elevated electrical conductivity, and varied oxidation states. As a result, the electrical conductivity performance of the MoS2/Fe3O4/PANI composite, which includes well‐dispersed Fe3O4 nano‐cubes on the surfaces of MoS2, is significantly enhanced. In comparison to pure Fe3O4, the resultant composite revealed improved specific capacitances of 401 F/g at 1.25 A g−1, along with outstanding cyclic stability of 89.3 even after undergoing 5000 cycles. The superior electrochemical properties observed may be ascribed to both the proficient electrical conductivity of MoS2 and the incorporation of Fe3O4 particles, which are anchored onto the MoS2. The results prove that MoS2/Fe3O4/PANI hybrid composite holds as highly efficient electrode material for supercapacitor.

Parallel Amperometric and Potentiometric Multianalyte Detection in a Microfluidic System

The adoption of microfluidic technologies in electrochemical biosensor development has enabled quantitative biomarker monitoring that use significantly lower volumes of reagents and samples, miniaturized electrodes, and inexpensive fabrication techniques, while presenting opportunities for multianalyte detection. We describe the fabrication of amperometric and potentiometric biosensors on a multichannel, platinum screen-printed electrode (SPE) and demonstrate their operation in parallel on a microfluidic multianalyte electrochemical sensor array (µMESA) platform.Working electrodes (WEs) of an SPE were were modified with either enzymes or ion selective membranes (ISMs) for amperometric or potentiometric measurements respectively. Oxidase enzymes were dissolved in an osmium (II) bis(2,2'-bipyridine)chloride-poly(vinylimidazole-allylamine) redox polymer and immobilized on four WEs. The use of this osmium-based electron transfer mediator has been previously reported to lower the oxidation potential of analytes and to improve overall sensor performance. The remaining four WEs were modified by electrodeposition of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), an intrinsically conductive polymer. Solid contact ISMs were prepared by combining ionophores, lipophilic ion exchangers, and a fluorosilicone polymer, and drop casting the mixtures on PEDOT:PSS-coated WEs. Plasticizer-free ISMs improve sensor lifetime by lowering the glass transition temperature and eliminating leaching of plasticizers from the ISM. By utilizing these strategies, we fabricated amperometric sensors for glucose and lactate, and potentiometric sensors for K+ and Ca2+ ions. Glucose is a primary substrate for energy metabolism while lactate is a major metabolite and signaling molecule. K+ ions maintain cell membrane physiology and homeostasis whereas Ca2+ ions serve as messengers during muscle activity and neurotransmission.Sensor characteristics like sensitivity, selectivity, linear range, and operational longevity for each biosensor were assessed using chronoamperometry or chronopotentiometry techniques on a potentiostat/potentiometer instrument. The results indicate that the sensor fabrication strategies described, in combination with our µMESA platform, can be used to measure changes in metabolite concentrations under laminar flow. Ultimately, this versatile technology may provide novel insights into complex physiological and pathological processes in biological systems.

Sol-gel synthesis, characterization, and electrochemical evaluation of magnesium aluminate spinel nanoparticles for high-capacity hydrogen storage

In this research, we successfully synthesized magnesium aluminate (MgAl2O4) spinel nanoparticles using a sol-gel process, with stearic acid serving as a capping agent. The synthesis process involved calcination at 900 °C for 4 h, resulting in the formation of nanoparticles with an average crystallite size of approximately 12 nm, as determined through Debye–Scherrer analysis and X-ray diffraction (XRD) data. The optical band gap was measured as 2.84 eV using Diffuse Reflectance Spectroscopy (DRS) analysis. Additionally, we found the mean pore size of the nanoparticles to be 20.2 nm through Brunauer–Emmett–Teller (BET) analysis. We characterized the resulting powders using various techniques, including Fourier Transform Infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Vibrating Sample Magnetometry (VSM). We conducted electrochemical investigations utilizing the Chronopotentiometry (CP) technique. The electrochemical analysis demonstrated that MgAl2O4 spinel nanoparticles exhibit a noteworthy hydrogen storage capacity of 4000 mAh/g, highlighting their potential as promising candidates for hydrogen storage applications. This comprehensive study underscores the successful synthesis, thorough characterization, and exceptional electrochemical performance of MgAl2O4 spinel nanoparticles, firmly positioning them as valuable materials for advancing hydrogen storage technologies.Graphical

Excellent electrochemical hydrogen storage capabilities of green synthesized LiCoO2 nanoparticles

Nowadays, the consumption of fossil fuel resources and the enhancement of environmental pollution are serious problems. One of the best strategies for resolving this issue is to use sustainable and renewable energy sources. Hydrogen, as a clean energy carrier, is a suitable candidate to supply the energy demand in the future and achieve carbon neutrality. Today, storing hydrogen and applying it as a fuel is one of the most significant issues in the world. Hydrogen must be stored in a safe, economical, and reversible. Hydrogen can be stored using nanoparticles. In this study, for the first time, lithium cobalt oxide (LiCoO2) nanoparticles have been synthesized by a green method using Aloe vera leaves extract. The structure and morphology of the sample have been investigated by means of various techniques. The hydrogen storage capacity of the as-synthesized LiCoO2 nanoparticles has been measured in alkaline media using the chronopotentiometry technique. The obtained results show the high discharge capacity of 4858 mAh/g, after 11 cycles.

Synthesis, characterization, and hydrogen storage capacity of MgMn2O4 spinel nanostructures

Pure MgMn2O4 spinel nanostructures were synthesized by the sol-gel method using stearic acid as a reducing and complexing agent. Structural characterization performed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) with energy dispersive spectrometry (EDS) mapping, Diffuse reflectance spectroscopy (DRS), Vibrating sample magnetometer (VSM) and surface area analyses (Brauner–Emmett–Teller). In this work, the hydrogen storage capacity of MgMn2O4 nanostructures was studied by the chronopotentiometry (CP) technique for the first time. The discharge capacity of the Magnesium manganese oxide in 1 mA current and after five cycles achieved 2000 mAh/g. Therefore, MgMn2O4 spinel nanostructures could be suitable materials for energy storage applications.

Synthesis, characterization, and electrochemical evaluation of SnFe2O4@MWCNTS nanocomposite as a potential hydrogen storage material

The widespread use of hydrogen as a vehicle fuel has prompted us to develop a new nanocomposite by immobilizing of tin ferrite nanoparticles (SnFe2O4) on the surface of multi-walled carbon nanotubes (abbreviated as MWCNTS) for the first time. The prepared nanocomposite powder (SnFe2O4@MWCNTS) was investigated utilizing various microscopy and spectroscopy methods, such as FT-IR, XRD, SEM, EDX, and BET techniques. Moreover, the electrochemical property of SnFe2O4@MWCNTS nanocomposite was investigated by cyclic voltammogram (CV) and charge–discharge chronopotentiometry (CHP) techniques. A variety of factors on the hydrogen storage capacity, such as current density, surface area of the copper foam, and the influence of repeated hydrogen adsorption-desorption cycles were assessed. The electrochemical results indicated that the SnFe2O4@MWCNTS has high capability and excellent reversibility compared to SnFe2O4 nanoparticles (NPs) for hydrogen storage. The highest hydrogen discharge capability of SnFe2O4@MWCNTs was achieved ∼ 365 mAh/g during the 1st cycle, and the storage capacity enhanced to ∼ 2350 mAh/g at the end of 20 cycles using a current of 2 mA. Consequently, the SnFe2O4@MWCNTS illustrated great capacity as a prospective active material for hydrogen storage systems.

Electrodeposited Ni/C-SnO2 composite electrode materials for hydrogen evolution reaction in alkaline electrolyte

The high performance Ni/C-SnO2 composite electrodes were successfully prepared for hydrogen evolution reaction (HER) in alkaline media by an easy and low cost composite electrolytic deposition method. The Ni/C-SnO2 composite coating was physically examined by using various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive analysis of X-ray (EDX). The XRD and EDX results showed that C-SnO2 particles prepared by high temperature hydrolysis method were successfully incorporated in Ni coatings. The preferred orientation of Ni particle in composited coatings had been altered to (111) crystal plane which was more benefit for HER. The SEM and XRD results indicated that the addition of C-SnO2 particles refined Ni crystallization in composite coatings. The catalytic activity and stability of the composite coatings for hydrogen evolution reaction were examined by steady-state polarization, Tafel plots, electrochemical impedance spectroscopy (EIS) and chronopotentiometry technique. Compared to Ni coating, the Ni/C-SnO2 composite coatings exhibited higher hydrogen evolution performance. The abundant OHads on C-SnO2 surface accelerated the water molecular decomposition and Hads formation which determined the rate of HER (Volmer step). The carbon in C-SnO2 improved the conductivity of composite electrode, which was also helpful for HER.

A new approach to synthesize ammonium uranate decorated reduced graphene oxide nanosheets and their performance in electrochemical hydrogen storage

In this research, the ternary solid phase of UO3·NH3H2O has been successfully synthesized via a simple and novel hydrothermal method under ammonia atmosphere, and identified as an ammonium uranate. Moreover, the decorated reduced graphene oxide network with ammonium uranate, UO3/rGO nanocomposite, was prepared and used to hydrogen sorption and storage. On the other word, for the first time, the electrochemical hydrogen storage behavior of the uranium compounds was evaluated by chronopotentiometry technique. Additionally, in order to further investigate the effect of ammonium uranate nanoparticles on the hydrogen storage property of UO3/rGO, two ratios of UO3:rGO in the as-made nanocomposites, 1:3 (UrGO3) and 1:10 (UrGO10), were studied. On this basis, the maximum discharge capacity was observed for the UrGO3 at 16,343 mAh/g after 20 cycles. The FE-SEM images indicated the UrGO3 nanosheets consist of the hierarchical plate-like pores, in a good agreement with BET analysis. According to the results, UO3 is introduced as a good candidate to improve the performance of electrochemical hydrogen storage on the graphene surface.

Comparative study on the electrochemical synthesis of zinc oxide nanorods using chronoamperometry and chronopotentiometry and their application in inverted polymer solar cells

In this work, the influences of zinc oxide nanorods (ZnO NRs) arrangement, as the electron transport layer (ETL), on the photovoltaic performance of the inverted structure polymer solar cells (PSCs) were studied. Two arrangements of ZnO NRs were electrochemically synthesized on the indium tin oxide (ITO) electrode by chronoamperometry (CA) and chronopotentiometry (CP) techniques at 80 °C. Structural, morphological, optical, and electrochemical features of the prepared samples were compared using different techniques. Applying the CA technique resulted in the vertical growth of ZnO NRs on the ITO electrode. However, flower-like ZnO NRs were formed in the sample prepared by the CP method. The energy levels, charge transfer resistance, recombination resistance, and charge mobility of the prepared samples were evaluated using cyclic voltammetry and electrochemical impedance spectroscopy. Results revealed that the flower-like ZnO NRs prepared by the CP method enjoy a considerably higher (128%) charge mobility of 31.67 × 10−4 cm2/V, lower (17.6%) charge resistance of 32.82 Ω, and higher optical transparency of ∼75.52% at 550 nm. The PSC prepared based on the flower-like ZnO NRs provided a PCE of 4.45, which was about 230.57%, 145.42%, and 302.72% higher than that achieved for the ZnO nanoparticles-, and the vertical ZnO NRs-based devices, and the reference device containing no ETL. Moreover, the flower-like ZnO NRs-based PSC exhibited greater stability in the air and retained about 72% of its initial PCE after 450 h.

Structure and electrochemical hydrogen storage properties of spinel ferritesSmxZn1−xFe2O4alloys (x = 0,x = 0.2,x = 0.4, andx = 0.6) forNi‐MHaccumulator applications

AbstractIn this article, we examine the effects of Sm substitution by Zn on the structures and electrochemical characteristics of SmxZn1−xFe2O4alloys prepared by sol–gel technique. The structural properties of the electrodes are studied by X‐ray diffraction and scanning electron microscope (SEM). The structural properties of these alloy are well influenced by the substitution rate. The SEM images of the powder of all samples (x = 0, 0.2, 0.4, and 0.6) shows the presence of agglomerates in the powder particles. Moreover, EDX investigation demonstrates that the chemical and theoretical compositions of all the prepared alloys are almost the same. The electrochemical performance of the oxide electrodes was analyzed at temperature 298 K using chronopotentiometry, chronoamperometry, and cyclic voltammetry techniques. During the first cycles, the electrochemical discharge capacity increases for all alloys. Obviously, this evolution is rapid for the unsubstituted alloy, but it becomes slower by increasing the substitution rate. The highest discharge capacity value was obtained for the ZnFe2O4electrode of the order of 180 mAh/g while the highest retained capacity was observed for the Sm0.6Zn0.4Fe2O4electrode. The kinetic results showed that the exchange current densityI0and the hydrogen diffusion coefficientDHof the anodes increased with increasing substitution rate and the best values were obtained for the Sm0.6Zn0.4Fe2O4anode.

Development of Ni-Co-CNT composite coatings for corrosion protection of mild steel in 5% NaCl

In this report, corrosion resistance of Ni-Co-CNT composite coatings on mild steel was studied. The deposition step follows composite-electrodeposition technique. The effect of CNT nanoparticle on corrosion resistance behavior of Ni-Co alloy coatings on mild steel were studied. The Ni-Co bath contents such as electrolytes, stabilizer and additives were optimized by using Hull cell. The optimized amount of CNT particle in the bath was found to be 0.5g/L. The surface modification of Ni-Co alloy coatings in the presence of nanoparticle was studied interms of their corrosion resistance behavior. The Ni-Co-CNT composite coatings was developed at different current densities. The corrosion protection efficacy of the deposited coatings has been studied by using Tafel extrapolation and electrochemical impedance techniques. The Ni-Co-CNT coating was found to be more stable and results showed linear change of potential with time. The result depicted that deposited composite coating on mild steel at a current of 4.0Adm −2 was found to be more corrosion resistance as compared with other current density coatings. This was attributed to decrease of size of the particle with increase of current densities as confirmed by AFM analysis. The chronopotentiometry technique revealed that coating was found to be more stable for several hours at different current densities. The coating obtained at a c.d of 4.0A dm −2 was found be more stable towards corrosion and confirmed by Chrono potentiometric techniques.

Advanced strategies for hydrogen generation by rhodium metal catalysts coated by the electrodeposition method

The theory and kinetics of the hydrogen evolution reaction (HER) on electrodeposited rhodium in acidic media (0.5 M H2SO4 solution) were looked into. An electrodeposition approach using direct current (DC) and pulse current (PC) was used to deposit rhodium on a stainless steel 304 (SS304) substrate. Several parameters, including rhodium concentrations, current densities, temperature, pH, and coating duration, were used to optimise the rhodium bath. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) analyses were used to assess the change in surface shape and chemical composition. The best coating was demonstrated at PC 75% duty cycle with an optimised current density of 4.0 A/dm2, which was better than the remaining PC cycles and DC source coating, indicating the most productive activity for hydrogen production. The activity of Rh catalyst coatings resembled that of pure platinum metal. Cyclic voltammetry (CV), chronopotentiometry (CP), and potentiodynamic polarisation techniques were studied to determine the HER. The results obtained from the PC technique with a 75% duty cycle give more HER performance.

Morphology engineering of Ni6MnO8/NiMn2O4 nanostructures through in-situ solvothermal synthesis controlling for electrochemical hydrogen storage inquiries

Murdochite-type Ni6MnO8 based three-dimensional (3D) structures have been synthesized for electrochemical hydrogen storage. As a proof-of-concept experiment, a novel strategy is developed to fabricate the 3D hierarchical nano/microspheres Ni6MnO8/NiMn2O4 composite via a simplistic in-situ synthesis process in terms of solvothermal method. The synthesis of this type of materials was conducted in the presence of diverse of carboxylic acids such as trimesic acid, malonic acid, citric acid and succinic acid which affect on the morphology and phase structure. Different microspheres are provided by self-assembly of nano components including nanoparticles and nanorods to form microsphere, micro flower and hollow sphere. Correspondingly, changing the molar ratio of Ni:Mn led to formation of different products of Ni6MnO8 and Ni6MnO8/NiMn2O4. The resultant samples were characterized by several techniques such as XRD, EDS, FT-IR, FE-SEM, TEM, BET and VSM to better determination of purity, morphology and physical properties. The electrochemical behavior of resultant electrode materials was studied using cyclic voltammetry and chronopotentiometry technique to comparing the hydrogen storage ability. The presence of NiMn2O4 in the composite texture affects the physicochemical and electrochemical properties of Ni6MnO8 structures. The results show that hydrogen storage capacitance of hollow sphere Ni6MnO8/NiMn2O4 altered to 354 mAhg−1 after 16 cycles at 1 mA current density compared with pristine Ni6MnO8 microsphere (153 mAhg−1). Moreover, after optimizing the morphology and composition of synthesized products, the electrode materials based on Ni6MnO8/NiMn2O4 present optimistic potential for hydrogen storage application.

Moringa Oleifera leaf extract mediated synthesis of reduced graphene oxide-vanadium pentoxide nanocomposite for enhanced specific capacitance in supercapacitors

Moringa Oleifera leaf extract has been prepared and used as an environmental-friendly reducing agent. Reduced graphene oxide (RGO) has been decorated with vanadium pentoxide (V2O5) in presence of Moringa Oleifera leaf extract to generate a RGO/V2O5 nanocomposite. Analytical, spectroscopic, and electrochemical characterizations of synthesized V2O5, RGO, and RGO/V2O5nanocomposite have been used to evaluate its morphology and structure. The RGO production and recombination with V2O5 are confirmed by the Characterization result. RGO, V2O5, and RGO/V2O5 nanocomposite have been evaluated for their electrochemical performances in supercapacitor applications by using various electrochemical techniques. The enhanced specific capacitance of 906 Fg−1 has been accomplished for RGO/V2O5 nanocomposite compared to 146 and 535 Fg−1 for V2O5 and RGO, respectively, at 2 mVs−1 scan rate using cyclic voltammetry (CV) technique. Chronopotentiometry technique has also been evaluated and observed the specific capacitance of 380 Fg−1 at a current density of 0.5 Ag−1. RGO/V2O5 nanocomposite could be a choice of material in energy storage devices.

Electrochemical hydrogen storage capacities of sol-gel synthesized Dy3Fe5O12/DyFeO3 nanocomposites: Schiff-base ligand-assisted synthesis and characterization

The nanostructured multiferroic Dy-Fe-O electrode materials for hydrogen storage request are synthesized via H2Salbn assisted sol-gel procedure. H2Salbn Schiff-base ligand plays the dual role of capping agent and fuel. The synthesis parameters affect the purity of obtained samples to form pristine DyFeO3, DyFeO3/Dy3Fe5O12 and Dy3Fe5O12/DyFeO3 compounds. Electrochemical attributes of resulting products are discovered by CV and charge-discharge chronopotentiometry techniques. The discharge capacity for DyFeO3/Dy3Fe5O12 nanocomposites by a high amount of DyFeO3 in the composite texture measured 447 mAhg−1 at a current of 1 mA. However, the discharge capacity for nanocomposites of Dy3Fe5O12/DyFeO3 with a high amount of Dy3Fe5O12 in the composite texture is considered about 257 mAhg−1 at a current of 1 mA. According to the found consequences, the DyFeO3/Dy3Fe5O12 nanocomposites verify appropriate capacity as the probable and capable active material for hydrogen storage policies.

Facile Fabrication of Polyaniline/Pbs Nanocomposite for High-Performance Supercapacitor Application.

In this work, a polyaniline/lead sulfide (PANI/PbS) nanocomposite was prepared by combining the in situ oxidation polymerization method and the surface adsorption process. This nanocomposite was applied as a supercapacitor electrode. The crystal structure, nanomorphology, and optical analysis of PANI and PANI/PbS were investigated. The electrochemical performance of the designed PANI/PbS electrode-based supercapacitor was tested by using cyclic voltammetry (CV), chronopotentiometry (CP), and AC impedance techniques in HCl and Na2SO4 electrolytes. The average crystallite size of the PANI/PbS nanocomposite is about 43 nm. PANI/PbS possesses an agglomerated network related to PANI with additional spherical shapes from PbS nanoparticles. After the PANI/PbS nanocomposite formation, there are enhancements in their absorption intensities. At a current density of 0.4 A g−1, the specific capacitance of PANI/PbS in Na2SO4 and HCl was found to be 303 and 625 F g−1, respectively. In HCl (625 F g−1 and 1500 mF cm−2), the gravimetric and areal capacitances of the PANI/PbS electrode are nearly double those of the Na2SO4 electrolyte. Also, the average specific energy and specific power density values for the PANI/PbS electrode in HCl are 4.168 Wh kg−1 and 196.03 W kg−1, respectively. After 5000 cycles, the capacitance loses only 4.5% of its initial value. The results refer to the high stability and good performance of the designed PANI/PbS as a supercapacitor electrode.

Autogenous Oxidation/Reduction of Polyaniline in Aqueous Sulfuric Acid

In this work, we have shown through open circuit potential experiments that in aqueous sulfuric acid solutions, a thick polyaniline film undergoes autogenous oxidation when reduced below a threshold potential and autogenous reduction when oxidized above the threshold potential. This phenomenon is associated with the high resonance stability of polarons in long polyaniline chains present in thicker films. We have determined the rates of these reactions using a linear sweep chronopotentiometry technique. We propose that the oxidation reaction of polyaniline produces polarons with a concomitant reduction of hydrogen ions to hydrogen radicals, which further combine with each other to produce the hydrogen molecule in the absence of dissolved oxygen. On the other hand, at high potentials polarons are reduced with the concomitant oxidation of water to hydroxyl radicals. Both the radicals are stabilized due to the interaction of their unpaired electrons with pi-electrons of the aromatic rings of the polymer backbone. At the equilibrium value of the open circuit potential, both the hydrogen radicals and hydroxyl radicals are generated at equal rates and react with each other to form water.

Synthesis of strontium chromate-nitrogen and sulfur co-doped graphene and its potential for electrochemical hydrogen storage

In the present study, monazite-type strontium chromate (SrCrO4) as a ternary metal oxide was prepared by the sol-gel method. Nitrogen and sulfur co-doped graphene decorated with SrCrO4 nanocrystals was synthesized successfully, and the electrochemical hydrogen storage performance of the SrCrO4 and its relative nanocomposites also were investigated by chronopotentiometry (CHP) technique. The effect of doped graphene as a substrate of the SrCrO4 sample on the improvement of the electrochemical hydrogen storage performance was considered as well. The SrCrO4-nitrogen and sulfur co-doped graphene (SrCrO4/NSG) displayed the highest discharge capacity in comparison to SrCrO4-reduced graphene oxide (SrCrO4/rGO), SrCrO4 calcined at 1000 °C (SrCrO4 (1000)) and SrCrO4 calcined at 800 °C (SrCrO4 (800)). Also, increasing the hydrogen storage capacity of the samples by repeating the cycles indicated the excellent cycle stability of the nanoparticles. In monazite-type structures, oxygen vacancies can be created by thermal treatment. Creating oxygen vacancies can improve redox reactions, which increase the conductivity of the samples and hydrogen storage capacity.