MnCo2 O4 Research Articles

Fabrication of MnCo2O4@PANI nanocomposites as electrode material for high-energy density asymmetric supercapacitor

In this work, the co-precipitation method has been utilized to synthesize MnCo2O4 (MCO) and MnCo2O4@Polyaniline (PMCO) nanocomposites. The wt% of polyaniline (PANI) has been varied from 0 to 30 %, keeping the MnCo2O4 precursor quantity constant. The nanocomposite with 20 wt% PANI (P20MCO) exhibits better electrochemical properties compared to other synthesized nanocomposite samples. The P20MCO nanocomposite exhibits specific capacitances of 765 F g−1 at 0.5 A g−1 and 88.13 % capacitance retention over 10,000 consecutive cycles. An asymmetric supercapacitor (ASC) has been constructed using P20MCO as cathode and commercially activated carbon as anode. The fabricated ASC device exhibits outstanding cycling stability with 91.48 % capacitance retention for 45,000 cycles at 12 A g−1. The ASC has the highest power density of 14.3 kW kg−1 and specific energy density of 58 Wh kg−1. Moreover, a red LED is illuminated by a single device and putting two devices in series light the blue, green, and white LEDs. These ASCs glow a red LED for more than 13 min. Our results suggest that the P20MCO nanocomposite-based supercapacitor devices will be promising for energy storage applications because of their easy production approach and good electrochemical performance.

Type-II heterojunction Se-g-C3N4/ZnO coupled MnCo2O4 photocatalyst for enhanced levofloxacin hydrochloride degradation activated by peroxymonosulfate

The advanced oxidation process induced by photocatalysis under visible light undoubtedly possesses greater application potential and cost-effectiveness due to the high excitation energy supply costs. Here, we proposed a novel Type-II heterojunction Se-g-C3N4/ZnO (Se-CN/ZnO) and MnCo2O4 (MCO) photocatalyst for the efficient degradation of levofloxacin hydrochloride (LEV) activated by peroxymonosulfate (PMS) under sunlight. Analysis results confirmed the oxidation process was executed by Se-CN/ZnO synergistic MCO-activated PMS for the responsive degradation of LEV, achieving a removal efficiency greater than 98.6 % within 15 min (kinetic rate constant Kobs = 0.299 min−1), under optimal conditions ([Se-CN/ZnO (300 °C)]0 = 46 mg, [MCO]0 = 1.6 mg, [PMS]0 = 0.27 mM, [Aeration rate]0 = 146 mL/min, pH = 5.5). Effective interfacial transfer and spatial segregation of the photogenerated electron-hole were attributed to the stabilized Type-II energy band structure of Se-CN/ZnO, the rapid cyclic redox of metal ions Mnn+(n = 2,3,4) and Com+(m = 2,3) promoted the activation of PMS reduction of LEV through synergistic action of various endogenous substances. Analysis of the contribution of reactive oxygen species by electron paramagnetic resonance substantiated the dominant role of ·OH and O2·-, and the superiority of the degradation process was further validated with the analysis of the non-toxic and ecological safety characteristics of intermediates. The recommended method of eco-friendly and stable catalytic performance of LEV has engineering application prospects that are incomparable to many publicly available treatment methods.

MnCo2O4 Spinel Nanorods for Highly Sensitive Electrochemical Detection of Nitrite.

The rational design of nitrite sensors has attracted significant research interest due to their widespread use and the associated risks of methemoglobinemia and carcinogenicity. The undisclosed nitrite-sensing performance of the spinel cobaltite MnCo2O4 (MCO) prepared by an oxalate-assisted coprecipitation method is reported in this study. Spectroscopy and microscopy investigations revealed the formation of uniform MCO nanorods with a high aspect ratio. The electrocatalytic nitrite oxidation at the MCO-coated glassy carbon electrode (MCO/GCE) indicated the promising performance of the synthesized material for nitrite sensing. MCO/GCE detects nitrite in a concentration range of 5 μM to 3 mM and has a limit of detection of 0.95 μM with a higher sensitivity of 857 μA mM-1 cm-2 in a response time of 4 s. In MCO, the mixed-valence states of Co2+/Co3+ confer a high electrical conductivity, and higher valent redox couples of Mn and Co impart remarkable electrocatalytic activity toward nitrite oxidation. MCO spinel undergoes facile and ultrafast faradaic reactions to mediate nitrite oxidation. Additionally, the mesopores of MCO nanorods facilitate the rapid diffusion of electrolyte and nitrite ions. Employing the electrode in sensing nitrite in milk, lake, and tap water samples further validates its potential application in real-life testing. MCO spinel nanorods showcase promising scope for utilization in the electrochemical sensing of nitrite and inspire further exploration of transition-metal oxide-based mixed-spinel materials.

Ce-doping at Mn site to enhance resistive switching performance of spinel MnCo2O4 resistive random access memory devices

The spinel Ce-doping MnCo2O4 (MCO) thin films were fabricated on Pt/Ti/SiO2/Si substrates for resistive switching (RS) layer using sol-gel spin-coating deposition method. The Pt/Mn0.925Ce0.075Co2O4/Pt (Pt/7.5MCC/Pt) device exhibits stabler and superior bipolar RS performance, the concentrated distribution of Reset/Set voltage as low as – 0.62/1.175 V, good cycle endurance and excellent time retention capability. The improvement in the RS performance of the Pt/7.5MCC/Pt devices can be attributable to the effective limitation of the random formation and rupture of conductive filaments by appropriate Ce doping. The carrier transport mechanism of the device at high resistance state can be dominated by the Schottky emission, whereas the carrier transport mechanism at low resistance state consistent with the Ohmic conduction. This work provides a potential performance improvement approach to design the resistive memory devices for data storage applications.

Influence of conductive carbon and MnCo2O4 on morphological and electrical properties of hydrogels for electrochemical energy conversion.

In this work, a strategy for one-stage synthesis of polymer composites based on PNIPAAm hydrogel was presented. Both conductive particles in the form of conductive carbon black (cCB) and MnCo2O4 (MCO) spinel particles were suspended in the three-dimensional structure of the hydrogel. The MCO particles in the resulting hydrogel composite acted as an electrocatalyst in the oxygen evolution reaction. Morphological studies confirmed that the added particles were incorporated and, in the case of a higher concentration of cCB particles, also bound to the surface of the structure of the hydrogel matrix. The produced composite materials were tested in terms of their electrical properties, showing that an increase in the concentration of conductive particles in the hydrogel structure translates into a lowering of the impedance modulus and an increase in the double-layer capacitance of the electrode. This, in turn, resulted in a higher catalytic activity of the electrode in the oxygen evolution reaction. The use of a hydrogel as a matrix to suspend the catalyst particles, and thus increase their availability through the electrolyte, seems to be an interesting and promising application approach.

Synthesis of mesoporous Zn-doped MnCo2O4 nanoparticles for high-energy density solid-state asymmetric supercapacitor

This study aims to determine how Zn doping at the cobalt site of MnCo2O4 (MCO) affects its electrochemical properties. Synthesized MnZn0.4Co1.6O4 (0.4ZMCO) sample's electrode provides an enormous improvement in electrochemical characteristics as compared to that of MCO because of its higher BET surface area (74 m2/ g) and mesoporous distribution of pore sizes. The 0.4ZMCO exhibits specific capacitances of 720 F g−1 at 0.5 A g−1, along with satisfactory rate capability. In addition, this electrode exhibits outstanding cyclability, maintaining a capacitance retention of 91 % and a coulombic efficiency of 99.78 % throughout 10,000 continuous cycles, even under high current density of 10 A g−1. An asymmetric supercapacitor (ASC) device is constructed using 0.4ZMCO as the cathode and activated carbon as the anode electrode. This ASC device performs with a good specific energy density of 49 Wh kg−1 and a power density of 8.64 kW kg−1. Furthermore, the ASC device exhibits 99.40 % coulombic efficiency and 91.84 % capacitance retention up to 30,000 GCD cycles in PVA/KOH gel electrolyte at a specific current density of 8 A g−1. Additionally, a single device illuminates a red LED, while connecting two devices in series illuminates red and green LED for more than 15 and 12 min, respectively. We believe Zn-doped MCO has great potential in constructing higher-performance supercapacitor devices due to its straightforward synthesis process and excellent electrochemical properties.

Scalable synthesis of binder-free hierarchical MnCo2O4 nanospikes/Ni(OH)2 nanosheets composite electrodes for high-capacity supercapatteries

Supercapatteries have received great attention in recent years due to its excellent charging storage capabilities. The effective electrochemically active surface area of the electrode is crucial in obtaining high capacity in supercapatteries. Herein, we present a scalable synthesis of binder-free hierarchical MnCo2O4 (MCO) nanospikes/Ni(OH)2 (NiOH) nanosheets (MCO/NiOH) nanocomposites for supercapattery electrode application. The MCO/NiOH nanocomposites are synthesized by the two-step hydrothermal method at low-cost without affecting nanostructures and further used as electrodes in fabricating a supercapattery. The synergistic effect of the NiOH nanosheets and MCO nanospikes helps to enhance the electrochemical charge storage performance when compared to their counterparts. The growth of NiOH nanosheets over the MCO nanospikes helps to suppress the self-discharge nature of MCO nanospikes otherwise. The MCO/NiOH//activated carbon supercapattery fabricated in the asymmetric configuration delivers a maximum specific capacity of 890C/g with a high energy density of 75.2 Wh/kg. The MCO/NiOH//activated carbon supercapattery exhibits a capacity retention of 86 % after completing 5000 charge/discharge cycles. Therefore, MCO/NiOH nanocomposite electrodes are capable candidates for the next-generation electrochemical energy storage systems.

A new and robust MnCo1.9Sb0.1O4 spinel cathode for proton-conducting solid oxide fuel cells

As a cathode material for proton-conducting SOFCs (H–SOFCs), a novel MnCo1.9Sb0.1O4 (MCSO) spinel material was suggested. The MCSO material was effectively produced, and it demonstrated excellent phase stability at elevated temperatures and chemical stability against CO2 and H2O. Doping Sb into the MnCo2O4 (MCO) allowed for enhanced proton diffusion and surface exchange, as evidenced by electrical conductivity relaxation tests. In addition, an oxygen-vacancy-rich surface was developed for the MCSO material, resulting in the possibility of a high cathode oxygen reduction reaction activity. The MCSO material was examined in the H–SOFC application, and the fuel cell with an MCSO cathode attained a high power density of 1380 mW cm−2 at 700 °C. At 700 °C, the cell employing the Sb-free MCO cathode, which had a comparable cell microstructure to the MCSO cell, only obtained a peak power density of 836 mW cm−2. The higher cell performance resulted from the Sb-modified MCO cathode's increased catalytic activity. In addition, the MCSO cell displayed excellent operational stability under fuel cell operating conditions, indicating that MCSO is a novel and effective spinel cathode for H–SOFCs.

Interaction between SOFCs interconnect Cr-free multicomponent spinel coating materials and chromia

Excellent Cr diffusion resistance and interface stability is essential for coatings applied on the surface of ferrite stainless steel interconnect for SOFCs. Four kinds of materials, the equimolar (MnFeCoNiCu)3O4 (Eq), non-equimolar (Mn0·272Fe0·272Co0·272Ni0·092Cu0.092)3O4 (Non-Eq), MnCo2O4 (MC) and the Quaternary (MnFeCoNi)3O4 (Quaternary), are combined with chromium oxide to form diffusion couples in order to study the interfacial reaction mechanism. The constitutes and morphologies of the samples are tested. Two different composition reaction layers are found in equimolar/Cr2O3 diffusion couple. A slight Cr inward diffusion is detected in Quaternary/Cr2O3 diffusion couple.

The Polysulfide-Cathode Binding Energy Landscape for Lithium Sulfide Growth in Lithium-Sulfur Batteries.

A cathode substrate with strong adsorption of lithium polysulfides (LiPSs) has been preferred for lithium-sulfur(Li-S) batteries. However, the recent finding that controlled growth of lithiumsulfides(Li2 S) during discharge is crucial forS utilization stimulates improvement of this preference. Here, the Li2 S growth and cell capacity in the LiPS binding energy landscape of cathode substrates are investigated. Specifically, Co-based ternary oxides are employed to obtain binding energies in the range of 4.0-7.4eV. Of these substrates, only the MnCo2 O4 substrate with moderate LiPS affinity exhibits 3D Li2 S growth. The MnCo2 O4 cells achieve high sulfur utilization up to 84% at 0.2C and excellent performance even under high sulfur loading/lean electrolyte conditions. In contrast, weak affinity substrates such as ZnCo2 O4 and strong affinity substrates such as NiCo2 O4 and CuCo2 O4 exhibit low discharge capacity with 2D Li2 S growth. For optimal LiPS affinity driving 3D growth, a balance between promoting LiPS adsorption and diffusion limitation in the LiPS adsorption layer is suggested.

Tailoring a low-energy ball milled MnCo2O4 spinel catalyst to boost oxygen evolution reaction performance

The development of cost-efficient oxygen evolution reaction (OER) catalysts is one of the most important tasks facing modern techniques for hydrogen production. In this work, for the first time, a low-energy ball milling process of MnCo2O4 (MCO) spinel powders, with a mechanical modification time exceeding 1 day was used. After 6 days of ball-milling, the obtained overpotential of the electrocatalyst reached the value of 375 mV at 10 mA cm−2, which is a relatively low value obtained for this type of compound. The studies showed how the mechanical (low-energy long-term milling process) and chemical modification of the fragmented spinel powder nanoparticle surfaces affects the increase of the electrocatalytic properties. The addition of the appropriate amount of conductive carbon black (cCB) and Nafion ionomer to the ink of the MCO spinel also has a significant effect on the improvement of the catalytic performance of the manganese-cobalt oxide during the milling process. By reducing the amount of Nafion to 10 % of its initial value, the overpotential dropped to 352 mV at 10 mA cm−2 after 30 days of ball-milling. This shows that catalyst ink and layer composition are important factors influencing the catalyst’s efficiency in the OER.

Enhanced resistive switching performance of spinel MnCo2O4 resistive random access memory devices: Effects of annealing temperatures and annealing atmospheres

The spinel MnCo2O4 (MCO) thin films were fabricated on Pt/Ti/SiO2/Si substrates for resistive memories via sol-gel spin-coating deposition method under different annealing temperatures and annealing atmospheres. The 650oC-annealing Pt/MCO/Pt device shows better bipolar resistance switching parameters than the devices annealed at 600 °C and 700 °C. The nitrogen-annealing Pt/MCO/Pt device exhibits optimum resistance switching parameters due to increasing of the oxygen-vacancies proportion, formation of confined and stable conductive filaments, and suppressing of the randomness of oxygen vacancies. The carrier transportation mechanisms of the devices with numerous oxygen-vacancies content in low resistance state (LRS) and high resistance state (HRS) are dominated by Ohmic conduction and Schottky emission, respectively. For the devices with fewer oxygen-vacancies content, the conduction mechanisms at LRS and HRS can be described by nearest-neighboring hopping conduction and space-charge-limited current model, respectively. This work indicates that the spinel MCO films have good potential application in resistive random access memory.

Facile synthesis of mesoporous MnCo2O4@MoS2 nanocomposites for asymmetric supercapacitor application with excellent prolonged cycling stability

A synergistic effect occurs in material science when a composite material's physical and chemical properties increase significantly as compared to its individual components. In the present work, MnCo2O4 (MCO) and MnCo2O4@MoS2 (MCOS) nanocomposites have been synthesized using the co-precipitation synthesis process. The main focus of the present research is to observe the impact of MoS2 on the electrochemical characteristics of the nanocomposites while keeping the MCO precursor quantity constant. The MCOS nanocomposite was synthesized with a homogeneous dispersion of 20 % MoS2 (MCOS20). It has the most significant enhancement in electrochemical properties due to its larger specific surface area (44 m2g−1) and mesoporous distribution of pore size. The MCOS20 nanocomposite as a single electrode possesses larger specific capacitances of 512 F g−1 at 0.5 A g−1 and exhibits a good rate capability. Besides that, the electrode exhibits excellent cycling stability of 91.87 % along with the coulombic efficiency of 99.57 % up to 5000 consecutive cycles, even at a high current density of 8 A g−1. An asymmetric supercapacitor (ASC) device has been fabricated with the MCOS20 nanocomposite as a cathode and commercially purchased activated carbon as an anode electrode to examine the practical utility of synthesized composite material. The device displays the highest specific energy density and power density of 36 Wh kg−1 and 19 kW kg−1, respectively. The device shows excellent stability up to 20,000 cycles at 3.5 A g−1 with a coulombic efficiency of 98.85 % and capacitance retention of 94.28 % in 6 M KOH gel electrolyte. Furthermore, the two devices illuminate red, blue, and yellow LEDs. It lights up for more than 3 min a red LED. We believe that our proposed MCOS20 nanocomposite has potential for use as electrodes in the fabrication of high-performance supercapacitor devices, owing to its simple manufacturing method and good electrochemical performance.

Tailoring Oxygen Reduction Reaction Pathway on Spinel Oxides via Surficial Geometrical-Site Occupation Modification Driven by the Oxygen Evolution Reaction.

The oxygen reduction reaction (ORR) has been demonstrated as a critical technology for both energy conversion technologies and hydrogen peroxide intermediate production. Herein, an in situ oxygen evolution reaction (OER) surface evolution strategy is applied for changing the surface structure of MnCo2 O4 oxide with tetrahedral and octahedral cations vacancies to realize reaction pathway switching from 2e- ORR and 4e- ORR. Interestingly, the as-synthesized MnCo2 O4 -pristine (MnCo2 O4 -P) with the highest surficial Mn/Co octahedron occupation favors two electrons reaction routes exhibiting high H2 O2 selectivity (≈80% and reaches nearly 100% at 0.75V vs RHE); after surface atoms reconstruction, MnCo2 O4 -activation (MnCo2 O4 -A) with the largest Mn/Co tetrahedron occupation present excellent ORR performance through the four-electron pathway with an ultrahigh onset potential and half-wave potential of 0.78 and 0.92V, ideal mass activity (MA), and turnover frequencies (TOF) values. Density functional theory (DFT) calculations reveal the concurrent modulations of both Co and Mn by the surface reconstructions, which improve the electroactivity of MnCo2 O4 -A toward the 4e- pathway. This work provides a new perspective to building correlation of OER activation-ORR property, bringing detailed understating for reaction route transformation, and thus guiding the development of certain electrocatalysts with specific purposes.

Catalytic combustion of lean methane over MnCo2O4/SiC catalysts: Enhanced activity and sulfur resistance

The simultaneous control of catalytic activity and sulfur resistance is a challenging task for non-noble metal catalysts in the domain of heterogenous catalysis. Herein, by dispersing MnCo2O4 (MCO) nanoparticles on a SiC substrate, we develop a novel catalyst for methane combustion that exhibits excellent low-temperature catalytic activity as well as high sulfur resistance. Strong interactions between SiC and MCO reduce the crystallite size of MCO and increase the specific surface area of the catalyst and the concentration of the active species, namely, Co3+ and surface oxygen species. The 60%MCO/SiC sample shows the highest catalytic activity, with T10, T50, and T90 values of 335, 375, and 444 °C, respectively, at a space velocity of 45,000 mL∙g−1∙h−1. In-situ diffuse reflectance infrared spectroscopy experiments and physicochemical characterizations indicate that the enhancement of catalytic activity is mainly attributed to the abundant adsorbed oxygen and surface Co3+ species in the catalysts that accelerate the formation of carbonate and formic acid species during methane conversion. The 60%MCO/SiC sample also exhibits high sulfur resistance, which is mainly attributed to the inhibiting effect of SiC on the catalyst for bulk sulfate formation. The findings of this study provide insights for the fabrication of catalysts with high activity as well as high sulfur resistance.

Cation-Tuning Induced d-Band Center Modulation on Co-Based Spinel Oxide for Oxygen Reduction/Evolution Reaction.

Atomic substitutions at the tetrahedral site (ATd ) could theoretically achieve an efficient optimization of the charge at the octahedral site (BOh ) through the ATd -O-BOh interactions in the spinel oxides (AB2 O4 ). Despite substantial progress having been made, the precise control and adjustment of the spinel oxides are still challenging owing to the complexity of their crystal structure. In this work, we demonstrate a simple solvent method to tailor the structures of spinel oxides and use the spinel oxide composites (ACo2 O4 /NCNTs, A=Mn, Co, Ni, Cu, Zn) for oxygen electrocatalysis. The optimized MnCo2 O4 /NCNTs exhibit high activity and excellent durability for oxygen reduction/evolution reactions. Remarkably, the rechargeable liquid Zn-air battery equipped with a MnCo2 O4 /NCNTs cathode affords a specific capacity of 827 mAh gZn -1 with a high power density of 74.63 mW cm-2 and no voltage degradation after 300 cycles at a high charging-discharging rate (5 mA cm-2 ). The density functional theory (DFT) calculations reveal that the substitution could regulate the ratio of Co3+ /Co2+ and thereby lead to the modulation of the electronic structure accompanied with the movement of the d-band center. The tetrahedral and octahedral sites interact through the Mn-O-Co, and the Co3+ Oh of MnCo2 O4 with the optimal charge structure allows a more suitable binding interaction between the active center and the oxygenated species, resulting in superior oxygen electrocatalytic performance.

Fe-doped (Ni,Mn)Co2O4 nanorod arrays on Ni foam as highly efficient electrocatalyst for oxygen evolution reaction in alkaline and neutral conditions with superb long-term stability

It is drawing increased interest to exploit highly active and durable electrocatalysts based on earth-abundant elements for oxygen evolution reaction (OER). In this work, we successfully synthesized Fe-doped (Ni,Mn)Co2O4 nanorod arrays on nickel foam (labeled as FNMCO/NF) via a anion-exchange route with subsequent annealing process. Experiments showed that the initial concentration of [Fe(CN)6]3- anions could affect the electrocatalytic activity of the as-synthesized FNMCO/NF integral electrode. The FNMCO-6/NF prepared from 6 mM of K3[Fe(CN)6] solution presented the strongest OER electrocatalytic activity. Only overpotential of 242 mV or 449 mV was required to reach the current density of 10 mA cm−2 in 1 M KOH solution or 0.1 M phosphate buffer solution (PBS). Also, after continuously catalyzing for 155 h at 100 mA cm−2 in 1 M KOH solution or 150 h at 20 mA cm−2 in 0.1 M PBS, the overpotential of the as-obtained FNMCO-6/NF electrode rarely varied, implying its superb durability.

Ultrahigh Rate Capability and Lifespan MnCo2 O4 /Ni-MOF Electrode for High Performance Battery-Type Supercapacitor.

MnCo2 O4 is derived from a Co/Mn bimetallic metal-organic framework (MOF). Then Ni-MOF is directly grown on the surface of the obtained MnCo2 O4 to form a nano-flower structure with small balls. A large surface area, abundant active sites of MnCo2 O4 and porosity of Ni-MOF allow the prepared MnCo2 O4 /Ni-MOF composite material to deliver an excellent electrochemical performance. At the same time, an appropriate thermal treatment temperature of the MnCo2 O4 precursor is also very important for controlling the morphology of the obtained MnCo2 O4 and electrochemical performances of the resulted composite material including electric conductivity, specific capacitance and rate performance. The prepared MnCo2 O4 -600/Ni-MOF shows an ultrahigh rate performance (when the current density increases from 1 to 10 A g-1 , the capacitance retention rate is as high as 93.41 %) and good cycle stability (the assembled asymmetric supercapacitor advice delivers a capacitance retention rate of 94.74 % after 20 000 charge and discharge cycles) as well as a relatively high specific capacitance. These excellent electrochemical properties indicate that MnCo2 O4 /Ni-MOF has a good application prospect in the market.

Simple strategy synthesis of manganese cobalt oxide anchored on graphene oxide composite as an efficient electrocatalyst for hazardous 4-nitrophenol detection in toxic tannery waste

Hazardous 4-nitrophenol (4-NP) and its isomers are very harmful to humans, plants, and animals even at very low concentrations. Consequently, it is very urgent and essential to identify 4-NP in the environment with a simple and accurate method. Herein, MnCo2O4 (MCO) nanosphere was synthesized by simple co-precipitation process using sodium hydroxide as a precipitating agent and subsequent elimination by calcination. The MCO@GO is prepared by ultrasound irradiation at room temperature. Graphene oxide was anchored with MCO nanospheres were performed excellent electrocatalytic activity owing to their Mn2+/Mn3+ and Co2+/Co3+ have an impressive synergistic effect (MCO) and large active surface area (GO). The prepared MCO@GO nanocomposite was characterized by different analytical techniques namely XRD (crystal nature), FTIR (functional group), FESEM, TEM (morphological analysis), XPS (elemental state). The electrochemical characterization was monitored by CV and DPV. The MCO@GO nanocomposite was drop cast on a glassy carbon electrode is referred to as MCO@GO/GCE for the electrochemical determination of 4-NP with good practical applicability. The peak current was increased while increasing the concentration of 4-NP from 0.5 µM to 151.5 µM with a regression equation y = 0.4952(µM) + 3.092 and correlation coefficient R2 = 0.9921. From this slope value, the LOD and sensitivity were determined to be 0.012 µM and 6.868 μA μM−1 cm−2. The sensor was successfully used for practical application of the 4-NP determination in toxic tannery wastes with a strong agreement with the added value and the recovery results. The objective of our work has afforded to readers a thorough understanding of the synthesis and electrochemical sensing applications of MCO@GO and some guidance in future research.

Filling the Charge-Discharge Voltage Gap in Flexible Hybrid Zinc-Based Batteries by Utilizing a Pseudocapacitive Material.

The high charge-discharge voltage gap is one of the main bottlenecks of zinc-air batteries (ZABs) because of the kinetically sluggish oxygen reduction/evolution reactions (ORR/OER) on the oxygen electrode side. Thus, an efficient bifunctional catalyst for ORR and OER is highly desired. Herein, honeycomb-like MnCo2 O4.5 spheres were used as an efficient bifunctional electrocatalyst. It was demonstrated that both ORR and OER catalytic activity are promoted by MnIV -induced oxygen vacancy defects and multiple active sites. Importantly, the multivalent ions present in the material and its defect structure endow stable pseudocapacitance within the inactive region of ORR and OER; as a result, a low charge-discharge voltage gap (0.43 V at 10 mA cm-2 ) was achieved when it was employed in a flexible hybrid Zn-based battery. This mechanism provides unprecedented and valuable insights for the development of next-generation metal-air batteries.