Na2SO4 Aqueous Solution Research Articles

Experimental measurements and thermodynamic modeling of dissociation pressure of CO2 hydrate in sulfate solutions

Carbon capture and storage (CCS) has been a popular strategy to mitigate climate change and has attracted significant attention from both industry and academia. CO2 can be stored in the form of CO2 hydrate in deeper locations in an ocean, which makes it a potential option for CO2 sequestration. Dissolved salts in the ocean brine can significantly affect the dissociation pressure of CO2 hydrate. Sulfate salts are one of the most common salt species in the oceanic brine. Although various experimental studies have been conducted to investigate the phase behavior of CO2 hydrate in brine, few studies focus on the effect of sulfate salts on the dissociation pressure of CO2 hydrate. In this study, we build an in-house experimental setup to investigate the effect of monovalent and divalent sulfate salts on the dissociation pressure of CO2 hydrate. The dissociation pressure of CO2 hydrate in Na2SO4, K2SO4, MgSO4, and CuSO4 aqueous solutions is measured using the isochoric pressure search method at different concentrations over the temperature range of 274.36–––282.15 K and the pressure range of 1.50–––4.03 MPa. A hybrid methodology incorporating the Soave-Redlich-Kwong Equation of State (SRK EOS), the van der Waals-Platteeuw (vdW-P) model, and the Pitzer model is applied to predict the dissociation pressure of CO2 in sulfate solutions. In addition, the dissociation enthalpies of CO2 hydrate in these sulfate solutions are calculated using the Clausius-Clapeyron equation based on the measured dissociation points. The experimental results show that the dissociation pressure of CO2 hydrate in Na2SO4, K2SO4, and MgSO4 solutions is higher than that in pure water, and the dissociation pressure of CO2 hydrate in sulfate solutions increases with an increasing salt concentration. Conversely, CuSO4 barely affects the dissociation pressure of CO2 hydrate, which is mainly attributed to the lower molar concentration of the ions compared with the other salt solutions and the ion specificity of Cu2+. The prediction results are in alignment with the experimental data measured in this study, which proves the feasibility of the thermodynamic model in predicting the dissociation pressure of CO2 hydrate in sulfate solutions. Additionally, the calculated dissociation enthalpies of CO2 hydrate show a dependence on both temperature and salt concentration. It is also revealed that Cu2+ exhibits ion specificity in affecting the dissociation enthalpy of CO2 hydrate, likely due to its distinct ability to impact the cage occupancy of CO2 hydrate compared with the other ions. These findings enhance our understanding of the impact of sulfate salts on the dissociation behavior of CO2 hydrate and offer valuable insights for CO2 sequestration.

Fabrication of NiO/TiO2/rGO nanocomposites as a quasi-solid-state asymmetric supercapacitor: Paving the way for PhotoSupercapacitor application

In this present communication, a novel ternary nanocomposite, NiO/TiO2/rGO (NTG), was synthesised via a simple hydrothermal technique for photosupercapacitor application. The XRD pattern confirmed the crystalline nature and phase structure of the as-synthesised material. FE-SEM and HR-TEM analyses demonstrated the embellishment of NiO/TiO2 nanoparticles on the rGO sheets, which facilitates more voids and shorter diffusion paths. The electrochemical investigation of the prepared samples was assessed using 1 M Na2SO4 and Na2CO3 aqueous electrolyte solutions. Among the synthesised samples, NTG-2 carried out under 1 M Na2SO4 electrolyte exhibited a maximum specific capacitance of 1285 Fg-1 at 1 Ag-1, maintaining a capacitance retention of 94 % after 5000 cycles. The NTG-2 electrode was additionally utilised in the construction of an asymmetric supercapacitor that has an impressive specific capacitance of 478 Fg-1 at 1 Ag-1. This displays an intriguing performance in terms of energy and power density of 42.2 Wh Kg−1 at 0.5 kW kg−1. In PSC, the as-fabricated TiO2/N719/I−/I3−/Pt@NTG-2//AC architecture possessed a specific capacitance of 567.5 Fg-1 at 1 Ag-1, with an energy density of 50.4 Wh Kg−1 and a power density of 0.4 kW kg−1. As a result, it has been concluded that the novel NTG-2 device opens new opportunities to develop new architectures for efficient energy storage applications.

Tuning the surface charge of rice straw-derived cellulose nanofibril membrane separator for electrochemical performance enhancement of supercapacitors

The electrochemical performance of supercapacitors has often overlooked the effect of surface charge on cellulose-based separators. Cellulose nanofibrils (CNFs) produced by 2,2,6,6-tetramethylpipridine-1-oxyl (TEMPO) oxidation possess a high anionic surface charge due to the presence of carboxylate groups, which could affect the transport of electrolyte ions. In this work, the surface of CNFs is modified with a cationic polyelectrolyte, namely polydiallydimethylammonium chloride (PDADMAC), to yield a nearly-zero surface charge CNF membrane derived from rice straw. The surface modification of CNFs using 20 wt% PDADMAC results in CNF-M2, with a surface charge of +5.3 mV, notable porosity (64 %), excellent electrolyte uptake (225 %), and improved ionic conductivity (5.0 mS cm−1). A symmetric supercapacitor assembled with CNF-M2 as a separator, exhibits enhanced specific capacitance (185.3 F g−1 at 0.1 A g−1), energy density (37.1 Wh kg−1 at a power density of 0.24 kW kg−1), and is able to maintain 100 % capacitance retention over 10,000 cycles in 1.0 M Na2SO4 aqueous electrolyte solution. This surface modification leads to 1.2–1.4 times increase in energy and power densities compared to the unmodified CNF membrane. Thus, the nearly-zero surface charge of the modified CNF membrane holds promise as a separator that elevates the performance of supercapacitors.

Bi2Se3/ZnSe heterojunction on flexible Mo metal foil for photo electrolysis water splitting application

Abstract The green hydrogen generation by photoelectrochemical (PEC) process emerged as a viable approach to replace non-renewable energy sources, which is done by using semiconducting materials. Recently ZnSe-based heterostructure/junction promise a suitable approach to enhance the PEC performance of photoelectrode. Here we have grown Bi2Se3/ZnSe heterojunction on flexible Mo metal foil by using magnetron sputtering technique toward PEC water splitting application. The crystallinity, structural, and surface morphology of the deposited films were investigated by X-ray diffraction, Raman spectroscopy, and field emission scanning electron microscopy, respectively. The PEC measurements were performed under 100 mW/cm2 (AM = 1.5 G) simulated solar radiation in 0.5 M Na2SO4 aqueous electrolyte solution. The PEC measurements show that Bi2Se3/ZnSe photoelectrode performs better as a photocatalyst, with a photocurrent density of ∼96.4 μA/cm2 (at 0.4 V vs Ag/AgCl), which was found to be three times higher than pristine ZnSe film (∼32.4 μA/cm2). This work suggests the importance of heterojunction towards efficient photoelectrodes for green hydrogen generation.

Development of cellulose/ZnO based bioplastics with enhanced gas barrier, UV-shielding effect and antibacterial activity

Development of renewable and biodegradable plastics with good properties, such as the gas barrier, UV-shielding, solvent resistance, and antibacterial activity, remains a challenge. Herein, cellulose/ZnO based bioplastics were fabricated by dissolving cellulose carbamate in an aqueous solution of NaOH/Zn(OH)42−, followed by coagulation in aqueous Na2SO4 solution, and subsequent hot-pressing. The carbamate groups detached from cellulose, and ZnO which transformed from cosolvent to nanofiller was uniformly immobilized in the cellulose matrix during the dissolution/regeneration process. The appropriate addition of ZnO (below 10.67 wt%) not only improved the mechanical properties but also enhanced the water and oxygen barrier properties of the material. Additionally, our cellulose/ZnO based bioplastic demonstrated excellent UV-blocking capabilities, increased water contact angle, and enhanced antibacterial activity against S. aureus and E. coli, deriving from the incorporation of ZnO nanoparticles. Furthermore, the material exhibited resistance to organic solvents such as acetone, THF, and toluene. Indeed, the herein developed cellulose/ZnO based bioplastic presents a promising candidate to replace petrochemical plastics in various applications, such as plastic toys, anti-UV guardrails, window shades, and oil storage containers, offering a combination of favorable mechanical, gas barrier, UV-blocking, antibacterial, and solvent-resistant properties.

Theoretical and practical investigation of ion-ion association in electrolyte solutions.

In this study, we present a new equation of state for electrolyte solutions, integrating the statistical associating fluid theory for variable range interactions utilizing the generic Mie form and binding Debye-Hückel theories. This equation of state underscores the pivotal role of ion-ion association in determining the properties of electrolyte solutions. We propose a unified framework that simultaneously examines the thermodynamic properties of electrolyte solutions and their electrical conductivity, given the profound impact of ion pairing on this transport property. Using this equation of state, we predict the liquid density, mean ionic activity coefficient, and osmotic coefficient for binary NaCl, Na2SO4, and MgSO4 aqueous solutions at 298.15K. Additionally, we evaluate the molar conductivity of these systems by considering the fraction of free ions derived from our equation of state in conjunction with two advanced electrical conductivity models. Our results reveal that, while ion-ion association has a minimal influence on the modification of the predicted properties of sodium chloride solutions, their impact on sodium and magnesium sulfate solutions is considerably more noticeable.

Mott–Schottky Analysis of Historical and Archaeological Copper–based Objects

AbstractThe application of Mott–Schottky (M−S) analysis of impedance data to sub–micro samples extracted from the corrosion patina of copper, bronze, and brass archaeological artifacts attached to graphite electrodes is described. The corresponding theoretical approach is developed to account for the contribution of the composition and structure of the corrosion patina and the effect of the bare graphite substrate. Experimental data in contact with 0.10 M Na2SO4 aqueous solution at pH 6.28 are consistent with the p‐type semiconducting nature of the main copper corrosion products, cuprite, and tenorite. The values of the apparent flat band potential and the slope of the M−S plots allow archaeological samples to be grouped according to their M−S parameters (slopes and intercepts). Assuming equivalent conditions of corrosion, the resulting grouping is judged to be dependent on the composition, and/or method of manufacture, and/or age. Studied samples include Renaissance statues from the Hofkirche in Innsbruck and a variety of objects from museums and Archaeological Heritage Office (soprintendenza) in Austria (Bad Aussee, Johanneum Graz, and the Tyrolean State Museums), and Italy (Genoa and San Remo), dating from the Bronze Age to the 18th century. Complementary data are provided by voltammetry of immobilized particles.

CdS/ZnS core–shell nanorod heterostructures co-deposited with ultrathin MoS2 cocatalyst for competent hydrogen evolution under visible-light irradiation

Hydrogen generation via semiconductor photocatalysts has gained significant attention as a sustainable fuel generation process. To demonstrate the performance of nanoscale core–shell heterostructure in photocatalytic hydrogen production, we have fabricated CdS nanorods coated with ZnS photocatalyst via wet-chemical reaction followed by deposition of ultrathin MoS2 nanosheets by photo reduction process. The effect of ZnS content and suitable amount of MoS2 loading over the visible-light induced photocatalytic hydrogen evolution was examined in Na2S and Na2SO3 aqueous solutions. Interestingly, it is apparent that a close connection (or heterojunction) between CdS and ZnS is believed to easily tunnel the charge carriers to the surplus surface states, making its electrons and holes energetically favourable to transfer from ZnS to MoS2 for photocatalytic reactions and subsequently, enhances the H2 evolution activity in CdS/ZnS type I core–shell heterostructures. The optimal MoS2 concentration is resolved to be 7 mol% and the subsequent visible-light induced H2 generation rate was 13589 μmol h−1g−1, which is 19 and 158 fold higher than pristine CdS and ZnS respectively. The probable photocatalytic mechanism of CdS/ZnS type I core–shell heterostructure with MoS2 cocatalyst is proposed. Our inexpensive and convenient preparation strategy may offer novel prospects in the engineering of desirable nanoheterostructures with better performance.

Redox-active cerium-based metal–organic layers coordinated on carbon nanotubes as materials for supercapacitors

In this work, the redox-active, two-dimensional (2D), and highly dispersible metal–organic layers (MOLs) constructed from hexa-cerium(IV) clusters, CeBTB (BTB = 1,3,5-benzenetribenzoate), were directly coordinated onto the surface of carboxylic acid-functionalized multi-walled carbon nanotubes (CNTs) by utilizing a post-synthetically grafting approach. Nanocomposites with various MOL-to-CNT ratios can be synthesized. Crystallinity, porosity, morphology, electrical conductivity, and electrochemical behaviors of CeBTB and all nanocomposites as well as the chemical interaction between CeBTB and CNT in the composite are investigated. Thin films of materials with the same mass loading are then fabricated for measuring their capacitive performances in neutral aqueous solutions of Na2SO4. With the electrical conductivity provided by carbon nanotubes and the redox activity of CeBTB between Ce(IV) and Ce(III), the optimal CeBTB-CNT nanocomposite can show a better capacitive performance compared to the pristine CeBTB, pristine CNT, and the physical mixture of both of them with the same MOL-to-CNT ratio. With such a simple post-synthetically grafting approach that can precisely control the ratio between the 2D MOLs and CNTs, the findings here open opportunities for designing numerous composites composed of MOLs and nanocarbons with tunable conductivity, redox activity, and functionality, which are potential candidates for a range of applications.

B-site disorder driven Griffiths-like phase and electrochemical behavior in Y2NiCrO6 double perovskite

In this investigation, nanoparticles of B-site disordered Y2NiCrO6 (YNCO) double perovskite were synthesized by the facile sol–gel method to evaluate their magnetic and electrochemical properties. Their crystallographic structure is monoclinic and the average size of the particles is 79±16 nm. XPS analysis indicated a mixed oxidation states of B-site transition metals Ni2+/Ni3+ and Cr2+/Cr3+. The mixed valence states of Ni and Cr, along with the mixed magnetic phases of YNCO, constitute a signature of the B-site disorder. This antisite disorder contributed to the observation of a Griffiths-like phase arising from ferromagnetic short-range interactions above the magnetic transition up to the Griffiths temperature, T G = 137 K. The synthesized YNCO double perovskite demonstrated a promising behavior as an electrode material for electrochemical supercapacitors. In a three-electrode system, it displayed a specific capacitance of 270 F g−1 at a current density of 0.5 A g−1. In a symmetric two-electrode system, YNCO exhibited a specific capacitance of 180 F g−1 at 0.5 A g−1, alongside an energy density of 6.25 Wh kg−1 at 250 W kg−1 power density. In both cases, we employed a mild 0.5 M neutral aqueous Na2SO4 solution as the electrolyte, in contrast to the typically employed corrosive and concentrated alkaline aqueous solution. The fascinating magnetic and charge storage properties of the B-site disordered YNCO double perovskite indicate its potential for use in spintronic devices and as efficient electrodes in symmetric hybrid supercapacitors.

Charge Storage and Magnetic Properties Nitrogen-Containing Nanoporous Bio-Carbon

This article presents the technology for the preparation of a nitrogen-containing nanoporous bio-carbon and investigates its properties. It has been shown that the synthesised bio-carbon is characterised by a high degree of homogeneity, which has been confirmed by energy dispersive spectroscopy. The obtained bio-carbon has a micromesoporous structure, which has been confirmed by the results of studies using the method of low-temperature nitrogen adsorption and desorption. It was found that the specific surface area of biochar is 1247 m2/g. The data on nitrogen adsorption and desorption were compared with the data on small-angle X-ray scattering, and it was found that the micropores in the synthesised bio-carbon are open pores, while mesopores remain closed. The energy dispersion analysis showed that the structure of the bio-carbon does not contain ferromagnetic atoms, but due to the addition of nitrogen, the synthesised bio-carbon in a magnetic field has the properties of a ferromagnet with a characteristic hysteresis of the specific magnetisation. It was found that this material has a saturation magnetisation σs of 1.4 A∙m2∙kg−1 and a coercive force Hc of 10 kA/m. Symmetric supercapacitors were fabricated from the synthesised bio-carbon material with 30% aqueous KOH and 1 M Na2SO4 as electrolytes. It was found that for bio-carbon synthesised at 800 °C, the specific capacitance in a 30% aqueous solution of KOH is 180 F/g, and in a 1 M aqueous solution of Na2SO4, it is 124 F/g. The cyclic voltammetry of the fabricated supercapacitors at different rates of potential expansion was investigated and analysed. Impedance studies on these supercapacitors were carried out. The equivalent electrical circuits describing the electrochemical processes in the studied supercapacitors were constructed and characterised.

MoS2 thin film decorated TiO2 nanotube arrays on flexible Ti foil for solar water splitting application

MoS2/TiO2 nanostructure provides a lot of advantages in photoelectrochemical (PEC) applications due to the absorption of the wide spectrum solar radiation, more catalytically active sites, proper band alignment, and better separation of photogenerated charge carriers. Here we report PEC water splitting studies of MoS2 thin film grown by chemical vapor deposition on TiO2 nanotubes fabricated on flexible thin Ti foil. Raman and x-ray diffraction analysis confirmed the polycrystalline growth of a few layers MoS2 on TiO2/Ti through their characteristic peaks. Field emission scanning electron microscopy revealed the nanotube surface morphology of TiO2 having a diameter in the range of 200–300 nm. The chemical and electronic composition of MoS2 and TiO2 were investigated by x-ray photoelectron spectroscopy. PEC measurements performed in 0.5 M Na2SO4 aqueous electrolyte solution under 100 mW cm−2 (AM 1.5G) simulated sunlight revealed 2-fold improved photocurrent density for MoS2/TiO2 heterostructure (∼135.7 μA cm−2) compared to that of bare TiO2 (∼70 μA cm−2). This is attributed to extended light absorption and more catalytically active surface area resulting from MoS2 functionalization of the TiO2 nanotubes, which results in better PEC activity. This study provides a new insight to explore the performance of thin metal foil-based photoelectrode in PEC applications that can be beneficial to develop roll-to-roll device fabrication to advance futuristic flexible electronics.

Thermodynamics of the Eu(III)-Mg-SO4-H2O and Eu(III)-Na-SO4-H2O systems. Part I: solubility experiments and the full dissociation Pitzer model.

The solubility of Eu(III) was investigated under undersaturated conditions in acidic, dilute to concentrated MgSO4 and Na2SO4 solutions at T = (22 ± 2) °C. After attaining equilibrium conditions, solid phases were characterized by a multi-method approach, including X-ray diffraction (XRD), Raman and infrared (IR) spectroscopy, quantitative chemical analysis (ICP-OES) and thermogravimetric analysis (TG-DTA). A total of 45 solubility samples were investigated for the systems Eu2(SO4)3-MgSO4-H2O (19 samples) and Eu2(SO4)3-Na2SO4-H2O (26 samples). Eu2(SO4)3·8H2O(cr) was found to control the solubility of Eu(III) in all investigated MgSO4 solutions, as well as in dilute Na2SO4 systems. The transformation of Eu2(SO4)3·8H2O(cr) into the double salt Na2Eu2(SO4)4·2H2O(cr) was observed at mNa2SO4 > 0.01 mol kg-1. The latter phase is characterized by significantly lower solubility. Based on these experimental solubility measurements, thermodynamic and activity models were proposed based on the Pitzer equations considering the full dissociation of the Eu(III) species in MgSO4 and Na2SO4 aqueous solutions, i.e. deliberately excluding Eu(III)-sulfate complex formation. A combination of the geochemical calculation code PhreeSCALE and the parameter estimation code PEST was used to determine the values of solubility products and binary and ternary specific interaction parameters (β(0)ij, β(1)ij, Cϕij, θik, Ψijk).

Enhanced electrocatalytic activity in hydrogen evolution reaction using 2D/2D nanohybrids of ruthenate nanoflakes and graphitic carbon nitride.

Photoelectrochemical and electrochemical water splitting was examined using ruthenate nanoflake (RuNF) and graphitic carbon nitride (g-C3N4) hybrids. A two-dimensional and visible-light-responsive photocatalyst g-C3N4 was hybridized with the RuNFs that we recently synthesized via a bottom-up process in aqueous solution, yielding 2D/2D nanocomposites. The influence of the 2D/2D nanocomposites on oxygen and hydrogen evolution during photoelectrochemical and electrochemical water splitting was investigated. First, electrolysis of a Na2SO4 aqueous solution was conducted with intermittent photo-irradiation. Both the g-C3N4 electrode and the RuNF/g-C3N4 hybrid electrode provided anodic and cathodic photocurrents at high and low potentials, respectively; however, the copresence of RuNFs decreased the photocurrents, probably because the RuNFs retarded the light absorption by g-C3N4. Moreover, the use of RuNF/g-C3N4 hybrids as electrodes facilitated both the oxygen and hydrogen evolution reactions without photo-irradiation. However, for the oxygen evolution reaction, the effect of the RuNFs was similar to that of RuO2 nanoparticles, indicating that the influence of the type and morphology of ruthenium species on the oxygen evolution reaction was small. Conversely, irrespective of the pH of the aqueous solutions in an electrolytic bath, the 2D/2D nanostructure of RuNFs and g-C3N4 decreased the overpotential of the hydrogen evolution reaction. However, the use of RuO2 particles instead of RuNFs did not cause such a phenomenon. Thus, it was revealed that the RuNFs synthesized via a bottom-up process were useful as a co-catalyst for the hydrogen evolution reaction.

Charge particle dynamics and electrochemical behaviour of SrTiO3-δ as anode material for IT-SOFC applications

SrTiO3-δ is a well-known metal oxide with cubic perovskite structure. In this work, we have synthesized SrTiO3-δ via conventional solid-state reaction route (SSR) and studied its electrochemical behaviour in three different pH media viz. 1 M aqueous solution of Na2SO4, (pH 7, neutral medium), KOH (pH 14, basic medium) and 0.5 M solution of H2SO4 (pH 1, acidic medium). The cubic phase with lattice constant, a = 3.905 Å is confirmed through XRD measurements. The electrical characterization of the sample was done in the frequency range 1Hz to 1 MHz and temperature range 25 oC–700 oC. The dynamics of the charged particles in the sample was studied using Jonscher power law. The scaling behaviour of the system has been investigated to understand the conduction mechanism. Further, charge carrier kinetics was also studied to understand the ionic contribution. Electrocatalysis was studied by cyclic voltammetry confirming the redox process in neutral and basic media, which was further confirmed in the XPS study. A better redox coupling occurs that was related to the Ti d-orbital and the O p-orbital interaction. The conductivity and catalytic properties of these materials indicated their use in different applications such as in fuel cells, sensors as well as in electrochemical devices.

Conformal Coverage of ZnO Nanowire Arrays by ZnMnO3 : Room-temperature Photodeposition from Aqueous Solution.

Compositionally and structurally complex semiconductor oxide nanostructures gain importance in many energy-related applications. Simple and robust synthesis routes ideally complying with the principles of modern green chemistry are therefore urgently needed. Here we report on the one-step, room-temperature synthesis of a crystalline-amorphous biphasic ternary metal oxide at the ZnO surface using aqueous precursor solutions. More specifically, conformal and porous ZnMnO3 shells are photodeposited from KMnO4 solution onto immobilized ZnO nanowires acting not only as the substrate but also as the Zn precursor. This water-based, low temperature process yields ZnMnO3 /ZnO composite electrodes featuring in 1 M Na2 SO4 aqueous solution capacitance values of 80-160 F g-1 (as referred to the total mass of the porous film i. e. the electroactive ZnMnO3 phase and the ZnO nanowire array). Our results highlight the suitability of photodeposition as a simple and green route towards complex functional materials.

Low mass loading of graphene quantum dots on titanium nitride nanotube arrays for boosting capacity and operating voltage of symmetric supercapacitor in an aqueous electrolyte

Compared to other supercapacitors, aqueous supercapacitors offer reliability, a long lifecycle, and affordability. However, the significant challenge in advancing aqueous supercapacitors lies in their limited operating voltage window. This limitation has resulted in a notable reduction in energy density. Therefore, contemporary electrode materials exhibiting high electrochemical activity and wide operating potential windows are imperative. This study introduces a technique that not only boosts energy density but also signifies a significant breakthrough for metal nitride-based aqueous supercapacitors. This method broadens the operating voltage range and necessitates optimization of the heterostructure design. A distinctive titanium nitride/graphene quantum dot (TiN/GQD) heterostructure was synthesized through electrophoretic deposition of GQDs onto plasma-nitrided TiO2 nanotubes. This novel heterostructure demonstrates the capability to function across an extended voltage range of 2 V. It is noteworthy that the TiN/GQD nanocomposite has excellent bonding at the interface of TiOC and a large surface area, resulting in an exceptional areal capacitance of 190 mF cm−2 at a current density of 0.2 mA cm−2 in 0.5 M Na2SO4 aqueous solution. It also displays excellent cycle stability (91.5 % after 6000 galvanostatic charge-discharge cycles). Moreover, the optimum GQDs deposition time (15 min) was determined to achieve the most efficient electrochemical performance. Furthermore, a symmetric TiN/GQD-15 supercapacitor device was assembled, reaching a high energy density of 8.2 Wh kg−1 at a power density of 77 W kg−1.

Synergetic effect on enhanced electrochemical properties of MnO2 nanorods on g-C3N4/rGO nanosheet ternary composites for pouch-type flexible asymmetric supercapattery device

In this work, one-dimensional MnO2 nanorods are distributed evenly over two-dimensional g-C3N4/rGO nanosheets using a simple hydrothermal approach. The structure, functional group, morphologies, elemental analyses and surface area of prepared samples have been investigated. Moreover, the electrochemical performance of MnO2/g-C3N4/rGO in 1 M Na2SO4 aqueous electrolyte solution was tested using cyclic voltammetry (CV), galvanostatic charge and discharge (GCD), electrochemical impedance spectroscopy (EIS) and capacitance retention. The MnO2/g-C3N4/rGO material has superior electrochemical performance than pure and binary electrode materials due to the high surface area of ternary composite (469.26 m2/g) compared to pure (38.083 m2/g). The ternary MnO2/g-C3N4/rGO electrode obtained the high specific capacitance of 716.6 Fg−1 at 1 Ag−1 and kept 97 % capacitance retention after 10,000 cycles at a current density of 10 Ag−1. Since the synergistic effects of MnO2 and g-C3N4/rGO improve electrochemical performance, the ternary composite is an excellent option for high-performance supercapacitors. Moreover, the pouch-type supercapattery device was assembled using MnO2/g-C3N4/rGO and activated carbon electrodes. The supercapattery device exhibits a maximum specific capacitance of 108.5 Fg−1 with 91.5 % capacitance retention after 10,000 cycles at a high current density of 10 Ag−1. The device achieved a high energy density of 48.6 Wh kg−1 at a power density of 899.9 W kg−1 in the operating potential value of 0–1.8 V. The fabricated supercapattery device was tested for real practical application by charging 30 s and attained a self-discharging time of 5 min.

Molarity Influenced Interesting Electrochromic Optical Modulation Peak Shift in Nebulized Spray Deposited Mn3O4 Films

Herein, we report the investigations on the electrochromic properties of nebulized-spray deposited Mn3O4 thin films in Na2SO4 aqueous solution as a function of molar concentration, for the first time. Phase analysis reveals that the films possess a tetragonal structure. From the Raman study, strong Mn2+ breathing vibration (in Mn–O) occurred in tetrahedral sites (of spinel Mn3O4). At 0.02 M, the film surface is covered with very-tiny particles with 84% highest optical transparency average. Both transmittance and absorbance related properties of electrochromic states are consider here, while introducing the notions of transmittance modulation (ΔT), absorbance modulation (ΔA), transmittance modulation efficiency (TME) and absorbance modulation efficiency (AME (or) coloration efficiency). When the concentration increases, the red shift was occurred at highest peaks of ΔT, ΔA, TME and AME with respect to the decrease in optical band gap. The maximum AME and TME of 25.064 cm2 C−1 (at 369.1 nm) and 17.542 cm2 C−1 (at 438.6 nm) were obtained for prepared samples. After the 100th cycle, the average AME (and TME) values in the UV and visible regions are decreases from 18.910 to 2.783 cm2 C−1 (2.884 to 1.060 cm2 C−1) and from 11.089 to 4.772 cm2 C−1 (11.346 to 4.684 cm2 C−1), respectively, indicating that the film is electrochromically active in the visible region even after the 100th cycle.

Ultrasonic-assisted, rapid preparation of mesoporous MnCO3 for electrochemical supercapacitor applications: A novel approach

Accounting for the methods opted in the preparation of nanoscale materials with high surface rea, average pore size and volume needs high energy and time-consuming processes. This work discloses a quick, scalable, and simple co-precipitation method for synthesizing MnCO3 for use in supercapacitors as a working electrode using MnSO4 and (NH4)HCO3 as the manganese and carbonate sources, respectively. As-synthesized sample is subjected to sonication at different periods for evaluating the effect of capacitance and the size of MnCO3 particles. Investigations using X-ray diffraction and X-ray photoelectron spectroscopy proves that MnCO3 can form the rhodochrosite phase and microscopical analyses reveals that nanograins smaller than 10 nm aggregated into spherical particles that were submicron in size. N2 adsorption–desorption isotherm isotherms validates the mesoporosity of MnCO3. The Galvanostatic charge–discharge cycling and cyclic voltammetry techniques examine the capacitance characteristics of mesoporous MnCO3 in both 0.1 Mg(ClO4)2 and Na2SO4 aqueous solutions. Mesoporous MnCO3 delivers a specific capacitance of 188F g−1 and 124F g−1 at a specific current of 0.33 A g−1 in both Mg(ClO4)2 and Na2SO4 aqueous solutions with a loading level of 1.5 mg cm−2. Additionally, mesoporous MnCO3 shows strong rate capability and stable cycle-life over 10,000 cycles. These demonstrates the mesoporous nanomaterials with high surface area and volume can enhance the energy storage capacitance of a supercapacitor.