Electrochemical behavior of manganese dioxide on a gold electrode

Zero Voltage-Degradation of Li2MnO3 with Ultrathin Amorphous Li─Mn─O Coating

Manganese-based lithium-rich layered oxides (Mn-LLOs) are promising candidate cathode materials for lithium-ion batteries, however, the severe voltage decay during cycling is the most concern for their practical applications. Herein, an Mn-based composite nanostructure constructed Li2MnO3 (LMO@Li2MnO3) is developed via an ultrathin amorphous functional oxide LixMnOy coating at the grain surface. Due to the thin and universal LMO amorphous surface layer etched from the lithiation process by the high-concentration alkaline solution, the structural and interfacial stability of Li2MnO3 are enhanced apparently, showing the significantly improved voltage maintenance, cycle stability, and energy density. In particular, the LMO@Li2MnO3 cathode exhibits zero voltage decay over 200 cycles. Combining with ex situ spectroscopic and microscopic techniques, the Mn2+/4+ coexisted behavior of the amorphous LMO is revealed, which enables the stable electrochemistry of Li2MnO3. This work provides new possible routes for suppressing the voltage decay of Mn-LLOs by modifying with the composite functional unit construction.

Embeddable Chloride Sensor for Monitoring Chloride Penetration into Cement Mortar

A composite solid chloride sensor consisting of two single sensors, i.e., Ag/AgCl working electrode and Mn/MnO2 reference electrode, was developed. The Ag/AgCl electrode was prepared by the anodic polarization method, while the Mn/MnO2 reference electrode was prepared using the powder compaction technique. Then, the electrochemical performances such as stability, reproducibility, and sensitivity of the composite and single sensors were investigated in a saturated Ca(OH)2 solution and mortar specimen. A current density of 0.5 mA/cm2 and polarization time of 2.5 h were the optimal preparation parameters of the Ag/AgCl selective electrode. The Ag/AgCl selective electrode showed a linear potential response with the logarithm of chloride ion content in solution and had good stability, reproducibility, and anti-polarization performances. In addition, the Mn/MnO2 electrode exhibited potential stability after being activated in an alkaline solution for 60 days. The composite sensor demonstrated exceptional sensitivity to the Cl- content, boasting a slope of approximately 51.1 mV/decade, and showcased excellent stability in both solution and mortar specimens. In every measurement, the time needed for the potential of a composite sensor to become stable was less than 30 s. The sensor enables non-destructive in situ monitoring of the chloride ion content in cement mortar, thus realizing early warning of deterioration of reinforcement and guaranteeing long service life of the structure.

Porosity evolution and oxide formation in bulk nanoporous copper dealloyed from a copper-manganese alloy studied by in situ resistometry

The synthesis of bulk nanoporous copper (npCu) from a copper-manganese alloy by electrochemical dealloying and free corrosion as well as the electrochemical behaviour of the dealloyed structures is investigated by in situ resistometry. In comparison to the well-established nanoporous gold (npAu) system, npCu shows strongly suppressed reordering processes in the porous structure (behind the etch front), which can be attributed to pronounced manganese oxide formation. Characteristic variations with the electrolyte concentration and potential applied for dealloying could be observed. Cyclic voltammetry was used to clarify the electrochemical behaviour of npCu. Oxide formation is further investigated by SEM and EDX revealing a hybrid composite of copper and manganese oxide on the surface of a metallic copper skeleton. Platelet-like structures embedded in the porous structure are identified which are rich in manganese oxide after prolonged dealloying. As an outlook, this unique heterogeneous structure with a large surface area and the inherent properties of manganese and copper oxides may offer application potential for the development of electrodes for energy storage and catalysis.

Corrosion Diagnostics Performed on Cores Drilled from Concrete Structures, Using the Laboratory Simulation of Temperature and Relative Humidity Impact

This paper presents an improved procedure for conducting diagnostics tests on corrosion in reinforced concrete structures. This method consists in drilling cylindrical concrete cores with fragments of secondary steel reinforcement (e.g., spacer bars, stirrups, binders) from the selected areas of the structure. Then, a three-electrode system is arranged on those cylindrical cores under laboratory conditions. The fragment of steel rebar with concrete is used as the working electrode. Using the counter electrode in the form of a patented conductive coating applied on the core side wall with painting techniques and the graphite reference electrode placed in an opening made in the core near the reinforcement was the novelty of this method. Following the procedure, the occurrence of minimum and maximum corrosion rates in concrete is simulated in the climate chamber after determining, on the basis of historical weather data, extreme combinations of temperature, and relative humidity for a given structure. This method was verified in the diagnostics testing of two large reinforced concrete tanks for fresh water, and cement storage silos.

Construction of manganese oxide nanowire-like cluster arrays on a DNA template: Application to detection of hydrogen peroxide

Improved electron transfer properties and catalytic activity of manganese oxide (MnOx) was demonstrated following its electrochemical deposition on a deoxyribonucleic acid (DNA) modified glassy carbon electrode. The MnOx showed different morphologies, electrocatalytic properties and electrochemical kinetics. Scanning electron microscopy showed that electrodeposition of MnOx on a bare glassy carbon electrode led to the formation of irregular-shapes while a nanowire cluster (NWC) was formed on a GCE/DNA due to the DNA serving as a template. Electrochemical impedance spectroscopy (EIS) revealed lower charge transfer resistance of the MnOxNWC compared with MnOx. A new mechanism is presented for the electrodeposition of MnOx on the surface of a GC/DNA electrode. An electrochemical biosensor was fabricated based on depositing MnOx onto a glassy carbon /DNA electrode (GCE/DNA/MnOxNWC) and was used to detect hydrogen peroxide (H₂O₂). The MnOx nanowire cluster and DNA exhibited significant electrocatalytic activity for simultaneous electrocatalytic oxidation at two oxidation potentials (0.6 V and 0.98 V vs Ag/AgCl) and one reduction potential (-0.5 V vs Ag/AgCl) for H₂O₂ at pH 6.0. A new mechanism for the detection of H₂O₂ is presented. Excellent electrocatalytic activity, stability and facility for simultaneous detection of H₂O₂ at different of applied potentials are proposed advantages of the proposed electrochemical biosensor.

Fabrication of a 1D Mn3O4 nano-rod electrode for aqueous asymmetric supercapacitors and capacitive deionization

The Mn₃O₄ nano-rods & rGO system realizes the utilization of energy effectively for asymmetric supercapacitors and capacitive deionization.

MnOx/IrOx as Selective Oxygen Evolution Electrocatalyst in Acidic Chloride Solution

The oxygen evolution reaction (OER) and chlorine evolution reaction (CER) are electrochemical processes with high relevance to water splitting for (solar) energy conversion and industrial production of commodity chemicals, respectively. Carrying out the two reactions separately is challenging, since the catalytic intermediates are linked by scaling relations. Optimizing the efficiency of OER over CER in acidic media has proven especially difficult. In this regard, we have investigated the OER versus CER selectivity of manganese oxide (MnO_x), a known OER catalyst. Thin films (∼5–20 nm) of MnO_x were electrodeposited on glassy carbon-supported hydrous iridium oxide (IrO_x/GC) in aqueous chloride solutions of pH ∼0.9. Using rotating ring–disk electrode voltammetry and online electrochemical mass spectrometry, it was found that deposition of MnO_x onto IrO_x decreases the CER selectivity of the system in the presence of 30 mM Cl^– from 86% to less than 7%, making it a highly OER-selective catalyst. Detailed studies of the CER mechanism and ex-situ structure studies using SEM, TEM, and XPS suggest that the MnO_x film is in fact not a catalytically active phase, but functions as a permeable overlayer that disfavors the transport of chloride ions.

Performance enhancement of asymmetric supercapacitors with bud-like Cu-doped Mn3O4 hollow and porous structures on nickel foam as positive electrodes

Cu-doped Mn₃O₄ hollow nanostructures supported on Ni foams as high-performance electrode materials for supercapacitors were successfully synthesized through a facile hydrothermal method and subsequent calcination. The morphology, structure, and electrochemical performance of the as-prepared Mn₃O₄ nanostructures can be tuned just by varying the Cu doping content. Benefiting from the unique bud-like hollow structure, the 1.5 at% Cu-doped Mn₃O₄ sample has a high specific capacitance of 257.6 F g⁻¹ at 1 A g⁻¹ and remarkable stability (about 90.6% retention of its initial capacitance after 6000 electrochemical cycles). Besides, an asymmetric supercapacitor (ASC) cell based on the 1.5 at% Cu-doped Mn₃O₄ exhibits a high specific capacitance of 305.6 F g⁻¹ at 1 A g⁻¹ and an energy density of 108.6 W h kg⁻¹ at a power density of 799.9 W kg⁻¹. More importantly, the ASC shows good long-term stability with 86.9% capacity retention after charging/discharging for 6000 cycles at a high current density of 5 A g⁻¹.

The effect of Cu doping on the electrochemical performance of bud-like Mn₃O₄ nanostructures for supercapacitor application was comparatively investigated.

Autocatalytic and Non-Catalytic Oxidation of Manganese(II) on a Platinum Electrode in Acetic Buffer

The influence of acetate on Mn

Use of manganese dioxide as oxidant in polymerization of aniline on carbon black for supercapacitor performance

α-Manganese dioxide (MnO2) and β-MnO2 have been prepared by a simple one-step hydrothermal synthesis method. Polyaniline (PANI)/carbon black composites were synthesized in acidic medium by an in situ polymerization method using α-MnO2, β-MnO2, and ammonium peroxydisulfate (APS) as chemical oxidant. The morphology, structure, and electrochemical performances are characterized by X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, cyclic voltammetry, charge–discharge test, and electrochemical impedance measurements. The PANI/carbon black composite (PANI/C-2) prepared using β-MnO2 as oxidant shows significantly better specific capacity performance compared with those prepared using α-MnO2 and APS as oxidant. Addition of carbon black into the PANI composites prepared via the conventional polymerization method showed improved specific capacitance.

Nucleation and growth of electrodeposited Mn oxide rods for supercapacitor electrodes

The nucleation and growth of electrodeposited Mn oxide rods has been investigated by preparing deposits on Au coated Si at varying deposition times between 0.5 s and 10 min. The deposits were investigated using high resolution scanning and transmission electron microscopy. A model for the nucleation and growth of Mn oxide rods has been proposed. Nucleation begins as thin sheets along Au grain boundaries and triple points. As these nucleation sites are consumed, nucleation spreads across the grains. Nucleation of sheets in close proximity causes agglomeration and the formation of rounded particles. Some of these rounded particles then accelerate in growth, initially in all directions and then primarily in the direction normal to the sample surface. Accelerated growth normal to the sample surface leads to the formation of rods. As rods grow, the growth of other particles accelerates and they become rods themselves. Eventually the entire sample surface is covered with rods 15-20 μm long and about 2 μm wide. The sheet-like morphology of the deposits is retained at all stages of deposition. Electron diffraction analysis of 3 s and 6 s deposits shows that the sheets are initially amorphous and then begin to crystallize into a cubic spinel Mn3O4 crystal structure. High resolution imaging of the 6 s sample shows small crystalline regions (∼5 nm in size) within an amorphous matrix.

Low-temperature synthesis of Mn(3)O(4) nanoparticles loaded on multi-walled carbon nanotubes and their application in electrochemical capacitors

A low-temperature, efficient and one-step deposition method, in which Mn(CH(3)COO)(2)·4H(2)O serves as precursor and O(2) as oxidant, was employed to deposit Mn(3)O(4) nanoparticles on multi-walled carbon nanotubes (MWCNTs) in ethanol solution at 150 and 200 °C. The resulting Mn(3)O(4)/MWCNT composites were characterized by means of different techniques including x-ray diffraction, x-ray photoelectron spectroscopy and transmission electron microscopy. It was indicated that the Mn(3)O(4) nanoparticles were attached uniformly on MWCNTs with sizes less than 10 nm, and the loading amount of Mn(3)O(4) could be tuned by changing the initial weight ratio of Mn(CH(3)COO)(2)·4H(2)O/MWCNT. The electrochemical behavior of the Mn(3)O(4)/MWCNT composites was examined by cyclic voltammetry, and the result indicated the specific capacitance of the composite electrode was 330 F g(-1), nearly 18 times higher than that of the pure MWCNT electrode. The good performance of the as-prepared composites as electrode material may be attributed to the synergistic effects of the Mn(3)O(4) nanoparticles and the MWCNTs.

Preparation and characterization of polyaniline/manganese dioxide composites and their catalytic activity

This paper is devoted to the preparation of polyaniline/MnO2 (PANI/MnO2) composites via chemical oxidation of aniline in H2SO4 medium using beta-MnO2 as an oxidant. The parameters affecting the polymerization reaction are considered. These parameters are [aniline], amount of beta-MnO2, stirring time, and polymerization temperature. SEM, FT-IR, XRD, and TGA techniques are used to characterize the resulting composites. XRD measurements reveal the distortion of the crystal structure of beta-MnO2 after the polymerization reaction. Thus, the XRD pattern of PANI is predominating. The crystalline composites are obtained using higher molar ratio of [Ox]/[ANI] and at higher temperature. Increasing the amount of beta-MnO2 led to an increase in the acidic character of the obtained composites due to adsorption of excess H+ on the oxide surface. The thermal stability of the composites decreased with increasing both [aniline] and stirring time, while it increased with increasing amount of beta-MnO2. The applications of the composites in the oxidative degradation of Direct Red 81, Acid Blue 92, and Indigo Carmine dyes exhibited good catalytic activity in the presence of H2O2 as an oxidant. The reactions followed first-order kinetics and the rate constants were determined. The degradation reaction involved the catalytic action of the PANI counterpart of the composite toward H2O2 decomposition, which can lead to the generation of HO radicals as a highly efficient oxidant attacking the target dyes. The detailed kinetic studies and the mechanism of these catalytic reactions are under consideration in our group.