KOH Aqueous Solution Research Articles

FeCl3-modified carbon as an electrode material for supercapacitors: preparation, analysis, and electrochemical properties

The necessity to combat the effects of global warming has made the use of renewable energy sources essential. Much attention has been focused on utilizing various types of biomass that can provide high energy productivity and serve as an alternative to traditional fossil fuels. This study specifically aims to investigate the electrochemical properties of carbon materials obtained from plant-based raw materials after biofuel production by the carbonization of melon and citrus peels at 300 °C and chemical activation using FeCl3. It is established that chemical activation with FeCl3 at 700 °C has led to dehydration, degradation of the carbon matrix, and the development of a microporous surface. For a two-electrode electrochemical cell, the specific capacitance values at a discharge current of 50 mA are 196 F/g in an aqueous KOH solution and 78 F/g in TEABF4. Based on the impedance spectroscopy results, an equivalent electrical circuit has been modeled, revealing the energy storage mechanism at the carbon electrode-electrolyte interface, with a physical interpretation of each circuit element provided. Most importantly, the device remains stable with no capacitance loss after 1000 cycles. The research findings may contribute to expanding the use of biomass as a cost-effective electrode component for supercapacitors.

Modifying of magnetic UiO-66-NH2 as a new nanosorbent by thermo-alkali-hydrolysis technology for highly efficient enrichment and determination of quercetin in apple peel

For rapid separation of quercetin from apple peel, a novel magnetic nanomaterial was prepared by a simple and economical thermal alkaline hydrolysis method in this study. This magnetic nanomaterial was obtained by mixing and then heating magUiO-66-NH2 (magnetic University of Oslo 66-NH2) with 0.05 mol·L−1 KOH aqueous solution, and was named magUiO-66-NH2-MH0.05 (magUiO-66-NH2-mixed heating0.05), which has better magnetic properties, thermal stability, pore capacity and average pore size than magUiO-66-NH2. The obtained magUiO-66-NH2-MH0.05 had strong adsorption capacity for quercetin, and the maximum adsorption capacity was 65.30 mg·g−1. MagUiO-66-NH2-MH0.05 tends to be monolayer-layer adsorption for quercetin, and electron sharing or transfer may occur during the adsorption process. Compared with naringenin, naringin and gallic acid, magUiO-66-NH2-MH0.05 showed good recognition ability for quercetin, and the recovery rate was good. After 7 cycles, the removal rate of magUiO-66-NH2-MH0.05 for quercetin was 96.3 % of the initial adsorption capacity. A magnetic solid-phase extraction method coupled with High-Performance Liquid Chromatography based on magUiO-66-NH2-MH0.05 was successfully used for rapid separation and determination of quercetin in apple peel. This study will help to discover the experimental law of the treatment of UiO-66-NH2 nanomaterials by hot alkaline hydrolysis, reveal the reaction mechanism, and expand the application of UiO-66-NH2 nanomaterials in food analysis.

On the van der Waals Heteroepitaxy and Hydroxylation/Oxidation States of Au@Muscovite by Pulsed Laser Ablation in Water and Recovery in Aqueous KOH Solution

On the van der Waals Heteroepitaxy and Hydroxylation/Oxidation States of Au@Muscovite by Pulsed Laser Ablation in Water and Recovery in Aqueous KOH Solution

WITHDRAWN: Magnetic field-assisted electrodeposition of ZnCo2O4-rGo nanoelectrodes for enhanced supercapacitor performance

To investigate a convenient, rapid, and environmentally friendly method for the preparation of supercapacitor electrode materials to enhance supercapacitor performance, this study achieved the successful synthesis of ZnCo2O4-rGo (ZCG) nanomaterial electrodes on a nickel foam substrate. These electrodes were then assembled into supercapacitors using Magnetic field-assisted Electrodeposition (MFAED) technology. The surface morphology and structure characterization analysis revealed that the ZCG-4 material exhibited a mesoporous layered nanosheet structure. Moreover, they exhibited a significant specific active surface area of 155.7 m2/g and showed excellent adhesion to the nickel foam substrate. The electrochemical properties of the ZCG nanoelectrode material were studied in a 1 M KOH aqueous solution. The results revealed that the ZCG-4 nanoelectrode displayed low electrochemical impedance (Rs 0.23 Ω, Rct 1.36 Ω, and Zw 0.99 Ω) and a high specific capacitance of 2672 Fg−1. Furthermore, at a current density of 3 Ag−1, the electrode maintained good capacity retention (2672 Fg−1–2529 Fg−1, 94.6 %). Moreover, it retained a significantly high specific capacitance of 1339 Fg−1 even after 6000 cycles under a current density of 20 Ag−1. The supercapacitor assembled with ZCG-4 electrodes exhibits good electrochemical performance, possessing a high capacitance of 5.8F/cm2 at a current density of 1 mA/cm2. Moreover, the ZCG-4 supercapacitor demonstrates outstanding cyclic performance, maintaining 86 % capacity retention following 6000 charge–discharge cycles at a high current density of 30 mA/cm2. The mechanism of magnetic field electrodeposition for preparing ZCG has also been explained using magnetohydrodynamics theory. At a magnetic field strength of 6 T, the ion migration speed is 1.7 × 10−5 m/s, and the addition of the magnetic field effectively increases this speed. An effective magnetic field electrodeposition approach was thus proposed in this investigation to enable the synthesis of high-performance electrode materials and capacitors by combining metal oxide and rGo.

Nanoarchitectonics of bimodal porous carbon nanosheet with NiO/Ni nanoparticles derived from nitrile-functionalized benzoxazine for a supercapacitor electrode material

Nitrile-functionalized benzoxazine was successfully synthesized as a precursor for porous carbon. NH4Cl was used as a template to generate the nanosheet morphology and mesopore structure, while nickel(II) chloride in the hydrate form was used as a nickel source. The results showed that carbon samples based on pristine nitrile-functionalized benzoxazine revealed the standard isotherm of type I, representing a microporous nature. This isotherm was altered to type IV, indicating a mesoporous nature after adding the NH4Cl template, and the morphology of the carbon sample was also transformed into a more nanosheet-like structure with increasing NH4Cl loading. The specific surface area, mesoporosity and pore volume of the as-prepared samples tended to increase when increasing NH4Cl template loading, with Ni-PCN5 (5 g of NH4Cl template) having the maximum mesoporosity of 88.7%. The maximum specific surface area and pore volume are 556 m2 g−1 for Ni-PCN5–350 and 0.71 cm3 g−1 for Ni-PCN5, respectively. In addition, the metallic nickel nanoparticles were successfully embedded in the carbon structure, which were further transformed into nickel oxide nanoparticles after an annealing process. This annealing process also resulted in carbon samples with the standard isotherm of type I. For electrochemical performance, Ni-PCN-300 also showed the highest value of the specific capacitance, as high as 181 F g−1 measured at a current density of 0.1 A g−1 in a 1 mol L−1 KOH aqueous electrolyte solution, with an excellent cycling stability of 96.5% over 2000 testing cycles. In short, this work demonstrates a facile, inexpensive and eco-friendly approach to rationally design and synthesize nickel/nickel oxide nanoparticles-embedded porous carbon nanosheets with a micro- and mesoporous structure, as a promising candidate for a supercapacitor electrode material.

Synthesis of 3D rice-like BiOCl battery-type electrode material and evaluation of their electrochemical performance in a symmetrical supercapacitor device configuration

3D porous rice-like BiOCl nanostructure was prepared via solvothermal technique with sodium chlorate as a surfactant which serves as electrode material for the supercapacitor applications. The prepared nanoparticles supported on nickel foam textile exhibit high battery-type charge storage ability in a 3 M KOH aqueous electrolyte solution. The dominance of the battery-type charge storage mechanism of the BiOCl electrode was confirmed through the CV study. Furthermore, the GCD study revealed a good specific capacity of 501 C/g at 0.5 A/g current density and cycle stability of 80% over 2500 cycles. In the presence of a 3 M KOH electrolyte, a symmetric supercapacitor device was constructed with two identical 3D rice-like BiOCl electrodes. This configuration unveiled an impressive energy density of 21.8 Wh/kg at 772.5 W/kg power density. To illustrate its practical viability, two BiOCl/BiOCl symmetric devices were connected in series, successfully powering a red LED for approximately 50 s with high light intensity. This underscores the practical potential of the 3D rice-like BiOCl electrode in energy storage systems. In order to maximize the potential of BiOCl material in the future, the focus could be shifted towards mitigating the challenge of potential drop. This hurdle could be tackled by fabricating nanocomposites of BiOCl incorporated with conductive polymers and graphene oxide, thus elevating its overall performance.

Force Fields for High Concentration Aqueous KOH Solutions and Zincate Ions.

Motivated by increasing interest in electrochemical devices that include highly alkaline electrolytes, we investigated two force fields for potassium hydroxide (KOH) at high concentrations in water. The "FNB" model uses the SPC/E water model, while the "FHM" model uses the TIP4P/2005 water model. We also developed parameters to describe zincate ions in these solutions. The density and viscosity of KOH using the FHM model are in better agreement with experiment than the values from the FNB model. Comparing the properties of the zincate solutions to the available experimental data, we find that both force fields agree reasonably well, although the FHM parameters give a better prediction of the viscosity. The developed force field parameters can be used in future simulations of zincate/KOH solutions in combination with other species of interest.

Band Structure Tuning via Pt Single Atom Induced Rapid Hydroxyl Radical Generation toward Efficient Photocatalytic Reforming of Lignocellulose into H2.

Photocatalytic lignocellulose reforming for H2 production presents a compelling solution to solve environmental and energy issues. However, achieving scalable conversion under benign conditions faces consistent challenges including insufficient active sites for H2 evolution reaction (HER) and inefficient lignocellulose oxidation directly by photogenerated holes. Herein, it is found that Pt single atom-loaded CdS nanosheet (PtSA-CdS) would be an active photocatalyst for lignocellulose-to-H2 conversion. Theoretical and experimental analyses confirm that the valence band of CdS shifts downward after depositing isolated Pt atoms, and the slope of valence band potential on pH for PtSA-CdS is more positive than Nernstian equation. These characteristics allow PtSA-CdS to generate large amounts of •OH radicals even at pH 14, while the capacity is lacking with CdS alone. The employment of •OH/OH- redox shuttle succeeds in relaying photoexcited holes from the surface of photocatalyst, and the •OH radicals can diffuse away to decompose lignocellulose efficiently. Simultaneously, surface Pt atoms, featured with a thermoneutral , would collect electrons to expedite HER. Consequently, PtSA-CdS performs a H2 evolution rate of 10.14 µmol h-1 in 1m KOH aqueous solution, showcasing a remarkable 37.1-fold enhancement compared to CdS. This work provides a feasible approach to transform waste biomass into valuable sources.

Bifunctional nickel phosphide nanoparticle/nickel cobalt sulfide nanosheet framework for electrocatalytic simultaneous hydrogen evolution and 2,5-Furandicaroxylic acid production

Replacing the O2 evolution reaction of water splitting with a thermodynamically more favorable reaction has attracted considerable attention for simultaneous value-added feedstock formation coupled with H2 production. Herein, bifunctional nickel phosphide nanoparticle/nickel cobalt sulfide nanosheet framework (NCSP150) is constructed on Ni foam for electrocatalytic hydrogen evolution reaction (HER) and 5-hydroxymethyl furfural (HMF) oxidation reaction (HMFOR) to 2,5-furandicaroxylic acid (FDCA) in 0.1 M KOH where HMF degradation is negligible. NCSP150 respectively demonstrates a Faradaic efficiency of 98.5 % for H2 generation at 10 mA cm−2 in 0.1 M KOH aqueous solution and exhibits a Faradaic efficiency of 95.2 % for FDCA formation at 1.52 V vs. RHE in a 10 mM HMF/0.1 M KOH aqueous solution. Moreover, NCSP150 sustains superior electrocatalytic performances for at least 12 h in the 0.1 M KOH electrolyte. In a two-electrode H cell using NCSP150 as both cathode and anode, the cell voltage required to afford the current density of 10 mA cm−2 is less 153 mV than water electrolysis when adding 5 mM HMF in 0.1 M KOH. This work emphasizes bifunctional NCSP150 as a promising non-precious-metal electrocatalyst for simultaneous hydrogen evolution and FDCA production in 0.1 M KOH, suitable for scaling up industrial production.

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.

Investigation of the effect of carbonization temperature of plant biomass on the electrochemical properties of carbon material

Porous carbon materials (PСM) with different pore distributions in size and size of the specific surface area up to 250 m2/g were obtained by changing the carbonization temperature of plant biomass, namely walnut shells. The electrodes of electrochemical supercapacitors are formed based on the obtained carbon materials. The electrochemical behavior of PCM in 33% aqueous KOH solution has been studied by cyclic voltammetry and galvanostatic discharge-discharge methods and the value of their specific capacitance. The physicochemical processes occurring at the carbon electrode/electrolyte interface have been investigated by the method of impedance spectroscopy.

Ordered FeCo2O4 & polypyrrole particles/branch nanotrees arrays grown on carbon fiber cloth substrate for energy storage applications

Supercapacitors are being utilized in energy storage devices with increasing interest a reason of their characteristics, which include high specific power, rapid charge and discharge rates, and long-term cycle stability. Most recently, research has concentrated on creating nanostructures to improve supercapacitors capacitance. The enhanced specific surface area of a material facilitates rapid diffusion of electrolyte ions; carbon fiber cloth (CFC) has been specifically utilized as a templates, leading to theoretical and practical advantages. In addition, the FeCo2O4 (FCO) and polypyrrole (PPy) to the CFC substrate is believed to be significant in enhancing the electrochemical behavior of supercapacitors. This study investigates the design approach of nanotree, configurations, and electrochemical characteristics of FCO-PPy on CFC for utilization in supercapacitors. The results of this research offer promising prospects for the advancement of future technologies to store energy. Porous FeCo2O4–polypyrrole (FCO-PPy) nanostructured arrays on CFC have been synthesis by a simple hydrothermal process with addition annealing process. The present research exhibits a unique nanostructure that exhibits exceptional electrochemical performance, characterized by a high capacitance and a desirable cycle life even under high rates of operation. The FCO-PPy nanowire arrays supported by CFC demonstrated a high specific capacitance of 1070 F g−1 at current densities of 2 A g−1 in a 2 M KOH aqueous solution when tested as an electrode in a system of supercapacitors. In addition, the FCO,CFC&PPy nanocomposite electrode shows excellent performance and long-term cyclic stability (90% capacitance retention after 10,000 cycles). The fabrication method presented here is cost-effective, facile, and scalable, which can open a new pathway for real device applications. Utilizing energy storage sustainability goods in business, adopting environmentally friendly chemicals, and being cost-conscious can considerably extend battery life. This includes breakthrough technology to mix modern materials, new electrode materials, new battery designs, and supercapacitors to revolutionize energy storage.

Overall collaborative contribution of electrodeposited NiFe2O4@Ni0.75Fe0.25S2 composites for high performance supercapacitors

In this work, a three-dimensional layered NiFe2O4@Ni0.75Fe0.25S2 composite has been synthesised by a two-step electrodeposition process. In the 3 M KOH aqueous solution system, the NiFe2O4@Ni0.75Fe0.25S2 composite exhibits good electrochemical properties due to the overall synergistic effect of the two components. The layered nanostructures provide a high surface area, which increases the specific capacity of NiFe2O4@Ni0.75Fe0.25S2@NF. The current density is 1 A g−1 and the maximum specific electrostatic capacity is 734 C g−1. The construction of an asymmetric supercapacitor (ASC) involves the assembly of NiFe2O4@Ni0.75Fe0.25S2@NF//AC@NF. Operating at a current density of 1 A g−1, this ASC achieves an impressive maximum specific electrostatic capacity of 734 C g−1. In particular, the assembled NiFe2O4@Ni0.75Fe0.25S2 @NF//AC@NF ASC exhibits exceptional electrochemical performance. In particular, it demonstrates an ultra-high specific capacitance of 463 C g−1 at a current density of 1 A g−1, coupled with excellent cycle stability. Even after 10,000 charge-discharge cycles at a current density of 10 A g−1, only 3.6 % of the initial specific capacitance is lost. These impressive results show that NiFe2O4@Ni0.75Fe0.25S2@NF electrodes offer a new solution for the design of high performance aqueous supercapacitors.

Copious Dislocations Defect in Amorphous/Crystalline/Amorphous Sandwiched Structure P-NiMoO4 Electrocatalyst toward Enhanced Hydrogen Evolution Reaction.

The design and synthesis of efficient, inexpensive, and long-term stable heterostructured electrocatalysts with high-density dislocations for hydrogen evolution reaction in alkaline media and seawater are still a great challenge. An amorphous/crystalline/amorphous sandwiched structure with abundant dislocations were synthesized through thermal phosphidation strategies. The dislocations play an important role in the hydrogen evolution reactions. Copious dislocation defects, combined with cracks, and the synergistic interfacial effect between crystalline phase and amorphous phase regulate the electronic structure of electrocatalyst, provide more active sites, and thus endow the electrocatalysts with excellent catalytic activity under alkaline water and seawater. The overpotentials of P-NiMoO4 at 10 mA/cm2 in 1 M KOH aqueous solution and seawater are 45 and 75 mV, respectively. Additionally, the P-NiMoO4 electrocatalyst exhibits long-term stability over 100 h. This study provides a simple approach for synthesizing amorphous/crystalline/amorphous sandwiched non-noble-metal electrocatalysts with abundant dislocations for hydrogen evolution reaction.

Enhanced Oxygen Reduction Activity of Platinum Micropore

AbstractThe high overpotential of oxygen reduction reaction (ORR) prevents the wide commercialization of fuel cells and metal‐air batteries. To accelerate the reaction rate, porous electrocatalysts draw attention to obtain a higher specific surface area. However, the effect of micropores on ORR kinetics has not been understood because of the non‐uniform pore sizes, length, and tortuosity of practical electrocatalysts. In this study, we evaluate ORR activity in a micropore using platinum model electrodes with arrays of cylindrical pores with a uniform pore diameter of 1.8 nm. The model electrodes having pore lengths of 45, 100, and 380 nm are fabricated, and their ORR performances are examined by electrochemical measurements and numerical simulations in 0.1 mol dm−3 KOH aqueous solution. The intrinsic ORR activity of the micropore is successfully obtained with the electrode having a pore length of 45 nm, where oxygen transport resistance in the micropore has little effect on ORR. It is found that the intrinsic ORR activity of the micropore is higher than that of a planar Pt surface. X‐ray photoelectron spectroscopy and CO stripping voltammetry indicate a downshift of the d‐band center, which can be the origin of the high intrinsic ORR activity.

In-situ fabrication of Cr doped FeNi LDH on commercial stainless steel for oxygen evolution reaction

Commercial stainless steel has attracted increasing interest due to their rich content in transition metal elements and corrosion resistance properties. In this work, we design a facile and rapid route to in-situ fabricate the Cr doped FeNi layered double hydroxides nanosheets (LDHs) on modified stainless steel (Cr–FeNi LDH @ ESS) under ambient condition.The ultra small scaled 2D structure only around 20 nm diameter and metal ions with multivalent oxidation state were observed on the in situ fabricated LDHs, which provides high active area and active sites and thus promote excellent oxygen evolution reaction (OER). The Cr–FeNi LDH @ESS electrocatalysts exhibit an over potential of 280 mV at 10 mA cm−2 and achieves a Tafel slope of 44 mV dec−1 for OER in the 1.0 M KOH aqueous solution. We anticipate that the operating strategy of our system may promote the development of commercial non-precious productions as the efficient electrocatalysts for energy storage and conversion.

THERMOCHEMISTRY OF THE DISSOLUTION OF 5,10,15,20-TETRAKIS(1'-CARBOXYMETHYL-PYRID-4-YL)PORPHYRIN TETRACHLORIDE AND 5,10,15,20-TETRAKIS(1'- CARBOXYMETHYL -PYRID-4-YL)PORPHYRIN TETRABROMIDE AT 298.15 K

5,10,15,20-tetrakis(1'-carboxymethylpyrid-4-yl)porphyrin tetrachloride (1) and 5,10,15,20-tetrakis(1'-carboxymethylpyrid-4-yl)porphyrin tetrabromide (2) were synthesized. Water-soluble tetrapyridylporphine derivatives are salts of halides with multicharged cations with a complex aromatic structure. Thermal effects of dissolution of crystalline tetrapyridylporphins (1) and (2) in water and in aqueous solutions of KOH at 298.15 K were determined by direct calorimetric method. The integral enthalpies of dissolution were measured on a variable temperature calorimeter with an isothermal shell that we designed. The reaction part of the calorimeter and all internal parts in contact with the solution are made of titanium alloy VT-1. The volume of the calorimetric cell was ~60 cm3. The stability of the thermostating system during calorimetric measurements was maintained with an accuracy of 10–3 K. The standard enthalpies of formation of compounds were calculated using the additive group method. This method takes into account the influence of the primary environment for atoms. The values of the standard enthalpy of tetrapyridylporphine formation and its dissociation products in an aqueous solution were obtained for the first time. They are key quantities in the thermochemistry of this compound, open up the possibility of conducting rigorous thermodynamic calculations in systems with tetrapyridylporphine. The differences in thermochemistry of porphyrins (1) and (2) related to different counter-ion (chloride or bromide) opens a possibility to use solution calorimetry for distinguishing between these ions, which can be useful in some industrial applications.

Nucleophilic hydrolysis enables HF-etched MXene kilofarad specific capacitance and excellent rate performance.

Here, an unusual MXene with a high ratio of oxygen functional groups was prepared by hydrothermal treatment of HF-etched MXene in aqueous KOH solution. The prepared MXene (H-220) exhibits ultrahigh specific capacitance (1030 F g-1 in a potential window of 0.85 V), and excellent rate and cycling performance simultaneously in a sulfuric acid electrolyte, and can act as an anode material of proton batteries.

A benzoquinone-imidazole hybrid organic anolyte for aqueous redox flow batteries.

A benzoquinone derivative annelated by two imidazole rings was investigated as an organic anolyte of aqueous redox flow batteries. The anolyte showed a high solubility of 0.18 M in 1 M KOH aqueous solution and exhibited a one-step two-electron reversible redox wave with a half-wave potential of -0.59 V VS. SHE. An aqueous redox flow cell comprising the benzoquinone-imidazole hybrid as the anolyte and potassium ferrocyanide as the catholyte showed an operating voltage of ∼1.1 V and minimum capacity fading of over 220 cycles.

Easy conversion perovskite fluorides KCo1-xFexF3 for efficient oxygen evolution reaction.

Herein, we report an easily oxidized Co-Fe perovskite fluoride as an efficient catalyst for the oxygen evolution reaction (OER). In situ Raman spectroscopy showed that the presence of F promotes reconstruction to form highly active (Co3+Fe3+)OOH, and the current density of 10 mA cm-2 can be achieved at the overpotential of only 118 mV in 1 M KOH aqueous solution. This work helps to understand the role of fluoride during the OER.