KOH Electrolyte Research Articles

Unlocking the potential of lattice oxygen evolution in stainless steel to achieve efficient OER catalytic performance

Excellent OER catalysts can enhance the efficiency of hydrogen production from electrolytic water. The development of low-cost, abundant, and highly efficient catalysts remains crucial for the electrolytic hydrogen production industry. In this work, we have developed a highly efficient and cost-effective stainless steel-based OER catalyst using a strategy combining anodic corrosion and structural reconstruction. This approach is not only simple and easy to scale up production, but more importantly, it can also achieve controllable switching of lattice oxygen evolution mechanism (LOM). Specifically, in a 1 M KOH electrolyte, this catalyst achieves current densities of 500 mA/cm² and 1000 mA/cm² with remarkably low overpotentials of only 347 mV and 382 mV, respectively. Moreover, the catalyst exhibits exceptional stability even under high industrial current densities. In-situ differential electrochemical mass spectrometry (DEMS) experiments provide direct evidence of the transition from the adsorbate evolution mechanism (AEM) to the LOM. Through comprehensive characterizations and density functional theory (DFT) calculations, we have elucidated the underlying mechanism responsible for the improved performance and identified key factors influencing the induction of the LOM. This work provides support and new insights for the design and preparation of high-performance steel-based electrolytic water catalysts.

Employing shielding effect of intercalated cinnamate anion in NiFe LDH for stable and efficient seawater oxidation

Seawater electrolysis is a valuable and promising method for clean hydrogen generation. The corrosion induced from active anions in seawater and the competition between oxygen evolution reaction (OER) and chloride evolution reaction (CER) limit the overall efficiency of seawater electrolysis. Herein, shielding strategy was introduced with cinnamate anion (CNA) intercalated in NiFe LDHs (NiFe LDHCNAs) for efficient alkaline seawater oxidation. It displays an outstanding OER performance with 247 mV and 258 mV to achieve the current density of 50 mA/cm2 in 1 M KOH electrolyte and alkaline seawater (1 M KOH + real seawater), respectively. Meanwhile, CNA-NiFe LDH presents excellent durability (over 72 h at 100 mA/cm2) in 1 M KOH electrolyte and alkaline seawater. The enhanced catalytic performance and durability can ascribe to the enlarged interlayer spacing by CNA intercalation and shielding effect of CNA against chlorine corrosion. This research offers a novel approach to the design of efficient electrocatalysts for hydrogen production from seawater electrolysis.

Highly porous carbon with selective transformation of nitrogen groups boosts the capacitive performance through boric acid template assisted strategy

To address the extensive demand for energy storage, the development of unique carbon-based supercapacitors represents a viable solution. We successfully synthesize the unique boron (B), nitrogen (N)-containing porous carbon (denoted as BNPC) from reed biomass through one-step boric acid templated carbonization method, which are used as high-performance carbon electrode for electric double-layer capacitor (EDLC). By the synergistic effects of boric acid template and N-rich melamine, a well-balanced micro‐/meso-porous structure and abundant N and oxygen (O) heteroatoms within BNPC are readily obtained, exhibiting an ultrahigh specific surface area of 2619 m2·g−1. These distinctive natures endow BNPC electrode with the excellent capacitive behaviors, affording an outstanding specific capacitance of 396.8 F·g−1 at a three-electrode (3E) system with KOH electrolyte. Density functional theory (DFT) method is utilized to further clarify the interaction mechanism between K and designed graphene with various N configurations, revealing the significant roles of Pyridinc-N and Graphitic-N. The two-electrode (2E) symmetric supercapacitor assembled by BNPC electrodes in TEABF4 electrolyte demonstrates an extremely high energy density of 51.82 Wh·kg−1 at a power density of 375 W·kg−1 and great capacitance retention of 91 % after 6000 cycles. This reed-derived highly porous carbons display superior electrochemical performance, making it the ideal candidates for large capacity supercapacitors in practice.

Surfactant-free CuPd nano-alloy for N2H4 oxidation-assisted H2 evolution and H2O2 detection

The utilization of hydrazine oxidation reaction (HzOR) with a lower thermodynamic oxidation potential has been regarded as an efficient strategy for H2 generation through electrolysis. However, a highly efficient and stable bifunctional electrocatalyst for overall hydrazine (N2H4) splitting was scarce. This work verified promising CuPd nano-alloy as a bifunctional electrocatalys for energy-efficient electrolytic hydrogen production, with hydrazine assistance. It is demonstrated that the CuPd nano-alloy exhibited enhanced electrocatalytic activity for both cathodic and anodic reactions compared to pure Cu and Pd nanocrystals, benefiting from its favorable electronic structure. Under 1.0 M KOH electrolyte with 0.1 M N2H4, the surfactant-free CuPd nano-alloy only required a potential of 0.648 V to achieve the N2H4 splitting (OHzS). The surfactant-free surface maximized exposed active sites, which facilitated the adsorption and desorption of reactants, resulting in enhanced electrocatalytic activity. And working potential for HzOR by surfactant-free CuPd was only 50.4 % compared to the CuPd nano-alloy with surfactant. This work provided an efficient electrocatalyst for OHzS. The enhanced electro-catalytic performances resulting from the electronic structure of alloy and the surfactant-free interface effect have been thoroughly discussed and verified, which would be invaluable for the design of efficient electrocatalysts for H2 production.

Cr-doping promoted surface reconstruction of Ni3N electrocatalysts toward efficient overall water splitting

Understanding and utilizing the dynamic changes of electrocatalysts under working conditions are important for advancing the sustainable hydrogen production. Here, we for the first time report that Cr-doping can promote the in situ reconstruction of a self-supported Ni3N electrocatalyst (Cr-Ni3N/NF) during oxygen and hydrogen evolution reactions (OER and HER), and therefore improve the electrocatalytic water splitting performance. As identified by in situ measurements and theoretical calculations, Cr-doping enhances OH– adsorption during OER at anode and thereby boosts the transformation of Ni3N pre-catalysts to defect-rich nickel oxyhydroxide (NiOOH) active species. Meanwhile, it facilitates the generation of Ni3N/Ni(OH)2 at cathodes due to effective H2O activation, leading to the fast HER kinetics on the Ni3N/Ni(OH)2 interfaces. Notably, the optimal Cr-Ni3N/NF displays good OER and HER performance in 1.0 M KOH electrolytes, with low overpotentials of 316 and 188 mV to achieve the current density of ± 100 mA cm−2, respectively. Benefiting from its bi-functionality and self-supporting property, an alkaline electrolyzer equipped with Cr-Ni3N/NF as both anode and cathode affords a small voltage of 1.72 V at 100 mA cm−2, along with 100 h operation stability. Elucidating that Cr-doping can boost in situ reconfiguration and consequently the electrocatalytic activity, this work would shed new light on the rational design and synthesis of electrocatalysts via directional reconstructions.

FeMnO3/CNT as a synergistic bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions in alkaline medium

The development of highly effective and low-cost electrocatalysts for energy conversion and storage devices is triggered by the sluggish kinetics of oxygen reduction and evolution reactions. Perovskite-based oxides are identified as potential ORR and OER electrocatalysts in an alkaline medium. Thus, the present study discusses the synthesis and characterization of FeMnO3/CNT as a bifunctional catalyst with a low potential gap of 0.89 V. The FeMnO3/CNT composite was synthesized by the solution combustion method and characterized using spectroscopic and electron microscopic techniques. The increase in the ID/IG ratio obtained from the Raman spectra of the FeMnO3/CNT composite with respect to bare CNT indicates the functionalization of CNT. The ORR and OER characteristics of the FeMnO3/CNT composite were analyzed with rotating ring disc electrode and rotating disc electrode measurements. The LSV curve of the FeMnO3/CNT composite synthesized with 0.3g of CNT show better ORR and OER activity. The ORR activity measurements of the composite done in 0.1 M KOH electrolyte show a good onset potential of 0.95 V vs. RHE and a half-wave potential of 0.74 V. The HPRR studies show that the ORR reaction mechanism follows a 2e− + 2e− reduction pathway. The OER measurements in an alkaline medium show an onset potential of 1.63 V vs. RHE with a Tafel slope of 115.3 mV dec−1. Also, this work gives an insight into the fundamental understanding of the synergy between the perovskite and CNT, leading to an enhanced ORR and OER catalytic activity. In addition, the material exhibits good stability for ORR and OER stability studies.

Pt atomic clusters/MoS2 nanosheets/Co-doped hollow carbon nanofibers for high-current–density alkaline hydrogen production

The application of layered molybdenum disulfide (MoS2) in catalytic hydrogen production has attracted great interest, while their catalytic properties are limited by poor electron conductivity and a few catalytically active sites. In this work, we demonstrated a highly active electrocatalyst for large-scale hydrogen production, consisting of two-dimensional (2D) Pt-MoS2 nanosheets along one-dimensional (1D) cobalt nanoparticle integrated carbon hollow nanofibers (Co@CHNF). The as-prepared Pt-MoS2-Co@CHNF had a large specific surface area (44.5 m2 g−1). X-ray photoelectron spectrometer (XPS) and spherical aberration corrected transmission electron microscope (AC-STEM) demonstrated that Pt atomic clusters (Pt ACs) were doped on MoS2 nanosheets by thermodynamically induced spontaneous interfacial redox between MoS2 and H₂PtCl₆. The Pt-MoS2-Co@CHNF based catalysts exhibited an overpotential as low as 91 mV for 10 mA cm−2 and 258 mV for 200 mA cm−2 in 1 M KOH electrolyte, and there is no significant floating for catalytic active with 14 h continuous operation, which demonstrates its excellent long-term operation durability, significantly superior to the previously reported state-of-the-art Co-based or Mo-based catalysts. In particular, the self-supporting binder-free Pt-MoS2-Co@CHNF catalyst-based electrode showed an ultra-high current density of 500 mA cm−2 at a low overpotential of 301 mV, without any decrease after 24 h operation at 500 mA cm−2 in 1 M KOH seawater electrolyte, representing a great potential for large-scale seawater hydrogen production.

Experimental investigation on accelerated generation of HHO gas using titanium electrodes with platinum and mixed metal oxide coating - A comparative study

HHO gas is an alternate source of fuel that can be used in automobiles as a clean fuel with reduced carbon emissions, replacing the conventional hydrocarbon fuels being used today. Many different methods are involved in the production of this gas. Among these methods, alkaline water electrolysis is one of the easiest and most reliable methods for production. Though there are many limitations in the storage of Hydrogen, the HHO gas has been produced on-site using alkaline water electrolysis. This article mainly focuses on the production of HHO gas for different operating parameters and conditions, such as change of electrolyte, electrode material coating, effect of temperature and the surface area of the electrode. The electrolytes used in the electrolyser are sodium hydroxide (NaOH) and potassium hydroxide (KOH). The electrode material is titanium coated with two different materials namely Mixed Metal Oxide (MMO) and Platinum (Pt) respectively. A maximum yield of 0.9 LPM of HHO gas has been generated when supplying 40 amps of current to the electrolyser unit coated with MMO and KOH as electrolyte. Use of KOH electrolyte results in higher production rate when compared to NaOH. MMO coated titanium electrode produces more HHO gas when compared to platinum coated electrode.

CoFe hydroxide towards CoP2-FeP4 heterojunction for efficient and long-term stable water oxidation

Electrochemical water splitting stands out as a promising avenue for green hydrogen production, yet its efficiency is fundamentally governed by the oxygen evolution reaction (OER). In this work, we investigated the growth mechanism of CoFe hydroxide formed by in situ self-corrosion of iron foam for the first time and the significant influence of dissolved oxygen in the immersion solution on this process. Based on this, the CoP2-FeP4/IF heterostructure catalytic electrode demonstrates exceptional OER activity in a 1 M KOH electrolyte, with an overpotential of only 253 ± 4 mV (@10 mA cm−2), along with durability exceeding 1000 h. Density functional theory calculations indicate that constructing heterojunction interfaces promotes the redistribution of interface electrons, optimizing the free energy of adsorbed intermediate during the water oxidation process. This research highlights the importance of integrating self-corroding in-situ growth with interface engineering techniques to develop efficient water splitting materials.

Three-Dimensional Modeling of Anion Exchange Membrane Electrolysis: A Two-Phase Flow Approach

Anion exchange membrane water electrolyzers (AEMWEs) are attracting growing interest as a green hydrogen production technology. Unlike proton exchange membrane (PEM) systems, AEMWEs operate in an alkaline environment, allowing one to use less expensive, non-noble materials as catalysts for the reactions and non-fluorinated anion exchange polymer membranes. However, the performance and stability of AEMWEs strongly depend on the alkaline electrolyte concentration. In this work, a three-dimensional multi-physics model considering two-phase flow effects is applied to understand the impact of KOH electrolyte concentration and its flow rate on AEMWE performance, as well as on the current and gas volume fraction distributions. The numerical results were compared to experimental data published in the literature. For current densities above 1 A/cm2, a strongly non-uniform H2 and O2 gas volume distribution could be evidenced by the 3D simulations. Increasing the KOH electrolyte flow rate from 10 to 100 mL/min noticeably improves cell performance for current densities above 1 A/cm2. These results show the importance of accounting for the three-dimensional geometry of an AEMWE and two-phase flow effects to accurately describe its operation and performance.

Synergistic Advancements in Battery-Grade Energy Storage: AgCoS@MXene@AC Hybrid Electrode Material as an Enhanced Electrocatalyst for Oxygen Reduction Reaction

The extreme usage of fossil fuels and the rising conservation deterioration have made developing clean, renewable energy essential. Among the most promising methods for addressing the world’s energy dilemma are electrochemical energy storage devices (EES); batteries and supercapacitors (SCs) are two typical components in this class. Supercapacitors are incredibly impressive since they can store energy remarkably in seconds. In this work, we present a highly effective electrode material (AgCoS@MXene) for supercapattery device application that is produced hydrothermally. We examined the morphology and crystallinity of the synthesized materials using SEM and XRD studies. The synthesized compounds were subjected to a thorough electrochemical performance study employing a three-electrode configuration in a 1 M KOH electrolyte. AgCoS@MXene demonstrated an exceptional Qs of 943.22 C g−1 at a current density of 2.0 A g−1. We formed a supercapattery device (AgCoS@MXene//AC) with AgCoS@MXene as the positive electrode and activated carbon (AC) as the negative electrode. The supercapattery device was demonstrated to have a high specific capacity of 315.22 C g−1, a power density of 1275 W kg−1, and an energy density of 35.94 Wh kg−1. In addition, 5000 charging and discharging cycles were used to assess the device’s long-term longevity. The findings indicated that the device preserved nearly 82% of its initial capacity. Besides, the hybrid electrode is used for the electrocatalytic activity for the oxygen reduction reaction. These promising findings imply that AgCoS@MXene is a beneficial electrode material for upcoming energy storage devices to enhance the electrocatalytic activity for the oxygen reduction reaction.

Fe-NiO/MoO2 and in-situ reconstructed Fe, Mo-NiOOH with enhanced negatively charges of oxygen atoms on the surface for salinity tolerance seawater splitting

Seawater electrolysis is a promising technique for H2 production on a large scale. However, the electrocatalytic activity and stability will be deteriorated as the increase of salt concentrations which happened in the seawater splitting. Herein, through the electrodeposition and rapid Joule heating method, the Fe-NiO/MoO2 heterostructure is designed as a highly active bifunctional electrocatalyst. During the OER possess, Fe-NiO/MoO2 is reconstructed to the Fe, Mo-NiOOH with Fe and Mo co-doping. Based on the theoretical analysis, more electrons were transferred to the O atoms on the surface of Fe, Mo-NiOOH, thereby forming a more negatively charged surface. Moreover, that surface is found to repel Cl− ions while enriching H2O molecules to form a thin water layer on Fe, Mo-NiOOH surface based on molecule dynamics (MD) simulation, thereby improving the anti-corrosion capacity of Fe, Mo-NiOOH. The reconstructed Fe, Mo-NiOOH achieved an overpotential of 399 mV at 1000 mA cm−2 in alkaline seawater, and the increase of overpotential for Fe, Mo-NiOOH was about 0.02 V at 500 mA cm−2 from 0 M to 3 M NaCl in 1 M KOH electrolyte. For the HER, Fe-NiO/MoO2 achieved an overpotential of 169 mV and 417 mV at 100 and 1000 mA cm−2 in alkaline seawater, respectively, and the increase of overpotential for Fe-NiO/MoO2 was about 0 mV at 500 mA cm−2 from 0 M to 3 M NaCl in 1 M KOH electrolyte. This work sheds fresh light into the development of efficient electrocatalysts for salinity tolerance seawater splitting.

From barley straw biomass to N/S co-doped as electrode material for high-performance supercapacitor applications

An innovative and cost-efficient methodology is proposed for developing porous carbon materials from barley straw biomass waste using thiourea as dopant and FeCl3 as activator. By varying precursor ratio and activation, porous carbon frameworks (BCF-Ts) with tailored porosity and N/S-doping were synthesized. BCF-Ts showed remarkable pore size distribution and high surface area responsible for enhanced electrochemical performance by enabling efficient ion transmission. The optimized N/S-doped activated carbon (BCF-T) exhibited high specific surface area of 938.7 m2 g−1. As supercapacitor electrode, BCF-T displayed exceptional performance including high specific capacitance of 496 F g−1, power density of 500.95 Wkg-1, and energy density of 42.02 Whkg−1 in KOH electrolyte. Moreover, BCF-T showed impressive cyclic stability, retaining 90.13 % capacitance after 2000 cycles. The tailored porosity, heteroatom doping, large surface area, and proper graphitization of BCF-T facilitated rapid ion diffusion, sufficient charge storage, and pseudocapacitance. This work provides valuable guidance on synthesizing high-performance porous carbon materials from biomass waste for supercapacitor applications.

Iron-Cobalt Phosphide Encapsulated in a N-Doped Carbon Framework as a Promising Low-Cost Oxygen Reduction Electrocatalyst for Zinc-Air Batteries.

The oxygen reduction reaction (ORR) plays a vital role in many next-generation electrochemical energy conversion and storage devices, motivating the search for low-cost ORR electrocatalysts possessing high activity and excellent durability. In this work, we demonstrate that iron-cobalt phosphide (FeCoP) nanoparticles encapsulated in a N-doped carbon framework (FeCoP@NC) represent a very promising catalyst for the ORR in alkaline media. The core-shell structured FeCoP@NC catalyst offered outstanding ORR activity with a half-wave potential (E1/2) of 0.86 V vs reversible hydrogen electrode (RHE) and excellent stability in a 0.1 M KOH electrolyte, outperforming commercial Pt/C and many recently reported noble-metal-free ORR electrocatalysts. The superiority of FeCoP@NC as an ORR electrocatalyst relative to Pt/C was further verified in prototype zinc-air batteries (ZABs), with the aqueous and flexible ZABs prepared using FeCoP@NC offering excellent stability, impressive open circuit voltages (1.56 and 1.44 V, respectively), and high maximum power densities (183.5 and 69.7 mW cm-2, respectively). Density functional theory calculations revealed that encapsulating FeCoP nanoparticles in N-doped carbon shells resulted in favorable electron penetration effects, which synergistically regulated the adsorption/desorption of ORR intermediates for optimal ORR performance while also boosting the electronic conductivity. Our findings offer valuable new insights for rational design of transition metal phosphide-based catalysts for the ORR and other electrochemical applications.

Highly Porous Ni Electrode Decorated with Fe<sub>3</sub>O<sub>4 </sub>for Oxygen Evolution Reaction(OER)

Hydrogen is an environmentally friendly energy source that can be extracted from water through electrolysis. However, the slow oxygen evolution reaction (OER) at the anode side is the main obstacle to the widespread use of water-splitting devices. This study used self-developed highly porous nickel structures (SMNF) and commercial nickel foam (CNF) as working electrodes in the electrolysis process. Iron (II, III) Oxide (Fe3O4) as a catalyst is coated with a dip coating technique on the Ni porous structure and then calcined using a laser process to produce a Ni-Fe3O4-based electrode. Electrochemical test results show that the presence of Fe3O4 significantly impacts high reaction kinetics. The SMNF-Fe3O4 demonstrated an overpotential of 217,3 mV at 1 M KOH electrolyte, at a current density of 10 mA, lower to SMNF electrode without Fe3O4 with an overpotential of 361,4 mV under the same conditions. In addition, the difference in porosity less significantly affects the electrode's effectiveness due to the slight difference in mass loading, which is only < 5 mg. However, electro-impedance spectroscopy (EIS) testing shows better performance on SMNF-Fe3O4 with a smaller electrical series resistance (ESR), around 0.638 Ω, compared to CNF-Fe3O4, which is 0.767 Ω. Overall, observations by chronoamperometry test at an overpotential of 155 mV at 5 hrs show stable performance of SMNF-Fe3O4 electrodes.

Honeycomb-structured S and N-codoped highly graphitized carbon as a catalyst support for Rh nanoparticles: A new benchmark electrocatalyst for hydrogen evolution reaction

State-of-the-art electrocatalysts are based on catalytically active metal deposited on conductive porous carbon. Herein, we report a new strategy of engineering of a honeycomb-structured S and N dual-doped graphene-like carbon (SNG) as a supporting material for Rh catalysts by a simple low-temperature (850 °C) pyrolysis of S-doped carbon nitride (S-CN) in the presence of Mg. Interestingly, here Mg plays a marvelous dual role not only as a reducing agent for graphitizing the S-CN but also as a precursor for new Mg3N2 and MgS products, which play as pore-generating templates for honeycomb-like structures. This features highly robust graphitized carbon with excellent electrical conductivity, proper S and N content, and porosity, making it highly desirable as catalyst support. Supporting Rh (5.2 wt.%) on SNG outperforms state-of-the-art commercial Pt/C electrodes for hydrogen evolution reaction (HER) under alkaline settings (1.0 M KOH) with an extremely lower overpotential of 13 mV at 10 mA cm−2, a lower Tafel value, and a higher turnover frequency. In addition, Rh/SNG as the cathode for industrial water electrolysis in 6.0 M KOH electrolyte at 70 °C shows excellent performance with only 1.76 Vcell to achieve 500 mA cm−2 and maintains long-term durability with negligible decay. The distinctive properties of SNG, including S and N dual doping, high graphiticity, superior electrical conductivity, and honeycomb-like hierarchical meso‑ and macropore structure, are credited with this remarkable HER performance. The S and N dopants in the SNG framework optimize the electronic structure of the Rh by synergistic interaction between them as illustrated by first-principal density functional theory calculations and electronic structure analysis.

Assessing the dynamics of O2 desorption from cobalt phthalocyanine by in situ electrochemical scanning tunneling microscopy

We report here the in situ electrochemical scanning tunneling microscopy (ECSTM) study of cobalt phthalocyanine (CoPc)-catalyzed O2 evolution reaction (OER) and the dynamics of CoPc-O2 dissociation. The self-assembled CoPc monolayer is fabricated on Au(111) substrate and resolved by ECSTM in 0.1 M KOH electrolyte. The OH− adsorption on CoPc prior to OER is observed in ECSTM images. During OER, the generated O2 adsorbed on CoPc is observed in the CoPc monolayer. Potential step experiment is employed to monitor the desorption of OER-generated O2 from CoPc, which results in the decreasing surface coverage of CoPc-O2 with time. The rate constant of O2 desorption is evaluated through data fitting. The insights into the dynamics of Co-O2 dissociation at the molecular level via in situ imaging help understand the role of Co-O2 in oxygen reduction reaction (ORR) and OER.

Synergistic performance of co-precipitated CoCuFe Prussian blue analogue and hydrothermally synthesized V₂C MXene in a solid-state asymmetric supercapacitor

Asymmetric supercapacitors (ASCs) have gained significant attention for their high energy density and extended potential window, ensuring optimal power density. This study presents a solid-state ASC using CoCuFe Prussian blue analogue (PBA) as the positive electrode and hydrothermally grown Vanadium MXene (V2C) as the negative electrode. SEM analysis reveals CoCuFe PBA's coagulated skeleton-like structure and V2C MXene's nanosheet-like morphology. In a three-electrode configuration, CoCuFe PBA shows a specific capacitance of 441 F/g at 0.8 A/g (0 to 0.5 V), while V2C MXene achieves 243 F/g at −1 to 0 V with a 2 M KOH electrolyte. The CoCuFe PBA//V2C ASC device achieves 185 F/g at 1 A/g with a PVA-KOH electrolyte at 1.5 V. This combination facilitates rapid ion diffusion, yielding an energy density of 57.8 Wh/kg and a power density of 1500 W/kg. The device also retains 82 % of its capacitance after 10,000 charge-discharge cycles at 6 A/g, demonstrating excellent stability and potential for high-performance supercapacitors.

Supercapacitor properties of Ni2+ incrementally substituted with Co2+ in cubic spinel NixCo1-xFe2O4 nanoparticles by sol-gel auto combustion method

The nanoparticle powder of Ni1-xCoxFe2O4 (x = 0.00, 0.25, 0.50, 0.75, 1.00) spinel ferrite was successfully prepared by the sol-gel auto-combustion method. The synthesized nanomaterials were used to prepare spinel ferrite supercapacitor electrode material. The structured phase of prepared nanoparticle powders was studied using XRD which shows the prepared sample consists of nanocrystalline single phase, with cubic spinel ferrite. Furthermore, using FESEM surface morphology of prepared samples was investigated. Ni1-xCoxFe2O4 nanoparticles spinel ferrite structure was verified by FT-IR, which detected distinctive vibrational bands at octahedral and tetrahedral locations.The spinel ferrite type materials are good active electrode materials. In this study, the prepared Ni1-xCoxFe2O4 electrode material is used as cathode material for supercapacitor. The electrochemical behavior of prepared samples was studied and compared by using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in 1 M KOH electrolyte. An electrochemical measurement study of prepared samples shows excellent performance and desirable cycling stability for supercapacitors. The prepared Ni0.5Co0.5Fe2O4 spinel ferrite gives the highest specific capacitance of 1282 F/g at a current density of 5 mA/cm2 with corresponding energy density of 30 Wh/kg and power density of 301 W/kg. Also, they exhibited outstanding cycling stability for 5000 cycles with 91.24 % capacity retention.

Preparation of manganese/nitrogen-sulfur carbon electrodes from black liquor of bamboo pulp for supercapacitors

Biomass-derived porous carbons from low-cost lignin are the promising candidate electrode for aqueous supercapacitors. Notably, the poor charge storage ability severely hinders the industrial production. The sodium lignosulphonate was firstly prepared by methylsulfonation with formaldehyde (HCHO) and sodium sulfite (Na2SO3). Then, lignin-based N-S co-doped porous carbon materials (LNSC) were prepared via one-step carbonization with sodium lignosulphonate as raw material and urea as a nitrogen source dopant and mild activator. And, MnCO3 nanowires were prepared and loaded on LNSC to fabricate manganese/nitrogen-sulfur carbon composites (LNSC/Mn-x) with high electrochemical performance. The prepared LNSC/Mn-40 was dominated by micro-mesopores with a total pore volume of 1.01 cm3 g−1 and a specific surface area of up to 770.68 m2 g−1. In a three-electrode system, LNSC/Mn-40 showed a specific capacitance of 234.92 F g−1 at 0.5 A g−1 in 6 M KOH electrolyte, greatly better than LNSC (151.98 F g−1 at 0.5 A g−1), while the symmetric supercapacitor demonstrated a maximum energy density of 7.21 Wh kg−1 at a power density of 5765 W kg−1 along with good cycling stability of 69.77 % capacitance retention for up to 10,000 cycles. The results suggested that lignin can be considered as an ideal candidate for porous carbon electrode for supercapacitors and reduce industrial production cost.