Engineering nanostructured Ag doped α-MnO2 electrocatalyst for highly efficient rechargeable zinc-air batteries

Engineering of highly active, and non-precious electrocatalysts are vital to enhance the air-electrodes of rechargeable zinc-air batteries (ZABs). We report a facile co-precipitation technique to develop Ag doped α-MnO₂ nanoparticles (NPs) and investigate their application as cathode materials for ZABs. The electrochemical and physical characteristics of α-MnO₂ and Ag doped α-MnO₂ NPs were compared and examined via CP, CV, TGA/DTA, FT-IR, EIS, and XRD analysis. CV result displayed higher potential and current for ORR in Ag doped α-MnO₂ NPs than α-MnO₂; but, ORR performance decreased when the Ag doping was raised from 7.5 to10 mmol. Moreover, α-MnO₂ and Ag doped α-MnO₂ NPs showed 2.1 and 3.8 electron transfer pathway, respectively, showing Ag doped α-MnO₂ performance to act as an active ORR electrocatalyst for ZABs. The EIS investigation exhibited that charge-transfer resistance for Ag doped α-MnO₂ was extremely lower associated to the MnO₂ demonstrating that the successful loading of Ag in α-MnO₂. A homemade ZAB based on Ag–MnO₂-7.5 showed a high open circuit potential, low ohmic resistances, and excellent discharge profile at a constant current density of 1 mA/g. Moreover, Ag–MnO₂-7.5 show a specific capacity of 795 mA h g⁻¹ with corresponding high energy density ∼875 Wh kg⁻¹ at 1 mA cm⁻² discharging conditions.

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Ag doped α-MnO₂ electrode for rechargeable zinc–air battery was prepared via a facile co-precipitation technique.

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Ag doped α-MnO₂ electrode shows lower charge transfer resistance associated to un-doped MnO₂ electrode.

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Ag doped α-MnO₂ shows enhanced ORR kinetics in oxygen electrode potential.

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The capacitance performance of Ag doped α-MnO₂ electrodes was highly improved.

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Ag doped α-MnO₂ electrode showed energy density of 69.3 W h kg−1 and power density of 722.9 W kg−1.

Highly efficient Ag doped δ-MnO2 decorated graphene: Comparison and application in electrochemical detection of H2O2

Cytotoxic H₂O₂ is an inevitable part of our life, even during this contemporary pandemic COVID-19. Personal protective equipment of the front line fighter against coronavirus could be sterilized easily by H₂O₂ for reuse. In this study, Ag doped δ-MnO₂ nanorods supported graphene nanocomposite (denoted as Ag@δ-MnO₂/G) was synthesized as a nonenzymatic electrochemical sensor for the sensitive detection of H₂O₂. The ternary nanocomposite has overcome the poor electrical conductivity of δ-MnO₂ and also the severe aggregation of Ag NPs. Furthermore, δ-MnO₂/G provided a rougher surface and large numbers of functional groups for doping more numbers of Ag atoms, which effectively modulate the electronic properties of the nanocomposite. As a result, electroactive surface area and electrical conductivity of Ag@δ-MnO₂/G increased remarkably as well as excellent catalytic activity observed towards H₂O₂ reduction. The modified glassy carbon electrode exhibited fast amperometric response time (<2 s) in H₂O₂ determination. The limit of detection was calculated as 68 nM in the broad linear range (0.005-90.64 mM) with high sensitivity of 104.43 µA mM^-1 cm^-2. No significant interference, long-term stability, excellent reproducibility, satisfactory repeatability, practical applicability towards food samples and wastewater proved the efficiency of the proposed sensor.

An Enzyme-Based Interdigitated Electrode-Type Biosensor for Detecting Low Concentrations of H2O2 Vapor/Aerosol

This work introduces a novel method for the detection of H2O2 vapor/aerosol of low concentrations, which is mainly applied in the sterilization of equipment in medical industry. Interdigitated electrode (IDE) structures have been fabricated by means of microfabrication techniques. A differential setup of IDEs was prepared, containing an active sensor element (active IDE) and a passive sensor element (passive IDE), where the former was immobilized with an enzymatic membrane of horseradish peroxidase that is selective towards H2O2. Changes in the IDEs’ capacitance values (active sensor element versus passive sensor element) under H2O2 vapor/aerosol atmosphere proved the detection in the concentration range up to 630 ppm with a fast response time (<60 s). The influence of relative humidity was also tested with regard to the sensor signal, showing no cross-sensitivity. The repeatability assessment of the IDE biosensors confirmed their stable capacitive signal in eight subsequent cycles of exposure to H2O2 vapor/aerosol. Room-temperature detection of H2O2 vapor/aerosol with such miniaturized biosensors will allow a future three-dimensional, flexible mapping of aseptic chambers and help to evaluate sterilization assurance in medical industry.

Oxygenated functional group-engaged electroless deposition of ligand-free silver nanoparticles on porous carbon for efficient electrochemical non-enzymatic H2O2 detection

The construction of metal-carbon nanostructures with enhanced performances using traditional methods, such as pyrolysis, photolysis, impregnation-reduction, etc., generally requires additional energy input, reducing agents and capping ligands, which inevitably increase the manufacturing cost and environmental pollution. Herein, a novel one-step substrate-induced electroless deposition (SIED) strategy is developed to synthesize ligand-free Ag NPs supported on porous carbon (PC) (Ag/PC). The PC matrix enriched with oxygenated functional groups has a low work function and thus a low redox potential compared to that of Ag+ ions, which induces the auto-reduction of Ag+ ions to Ag NPs. The as-synthesized Ag/PC-6 modified electrode can be used as an excellent nonenzymatic H2O2 sensor with a broad linear range of 0.001-20 mM, a low detection limit of 0.729 μM (S/N = 3), and a high response sensitivity of 226.9 μA mM-1 cm-2, outperforming most of the reported sensor materials. Moreover, this electrode can be applied to detect trace amounts of H2O2 in juice and milk samples below the permitted residual level in food packaging and the recovery of H2O2 is 99.6% in blood serum (10%) with good reproducibility. This study proposes an efficient approach for synthesizing a highly active supported Ag electrocatalyst, which shows significant potential for practical applications.

Flexible Active-Site Engineering of Monometallic Co-Layered Double Hydroxides for Achieving High-Performance Bifunctional Electrocatalyst toward Oxygen Evolution and H2O2 Reduction

It is highly desirable but challenging to develop a facile and scalable strategy to synthesize efficient bifunctional electrocatalysts for oxygen evolution and H₂O₂ reduction by engineering the active site of monometallic-layered double hydroxides (LDHs). Herein, we developed a convenient, efficient, and scalable method for the construction of monometallic Co-LDHs with tunable Coⁿ⁺ (n = 2, 3) concentration by a one-pot solvothermal reaction in a short time (e.g., 2 and 4 h) using only cobalt nitrate and hexamine as raw materials. The catalytic performance of Co-LDHs was mainly determined by the Coⁿ⁺ (n = 2, 3) concentration, which could be simply regulated by tuning the solvothermal time. Combining the joint merits of three-dimensional flowerlike architecture (abundant accessible active sites and a fast electron/mass transport), Co-LDHs-4 with abundant Co³⁺ species exhibited an excellent electrocatalytic activity for oxygen evolution reaction in terms of a low overpotential at 10 mA cm^-2 (η₁₀ = 241 mV) and long-term durability for 70 h at 100 mA cm^-2, better than the state-of-the-art IrO₂ and most of the reported analogues. Besides, Co-LDHs-2 enriched in Co²⁺ displayed a superior electrochemical activity for H₂O₂ detection with a broad linear range (0.002-20 mM), a low detection limit (0.002 mM), and a high response sensitivity (272.02 μA mM^-1 cm^-2). Therefore, this work opens a new horizon for the rational development of a highly active electrocatalyst with tunable concentrations of active components.

Facile Synthesis of ZnMn2O4@rGO Microspheres for Ultrasensitive Electrochemical Detection of Hydrogen Peroxide from Human Breast Cancer Cells

Mixed transition-metal oxides have witnessed increasing attention in catalysts and electrocatalysts. Herein, reduced graphene oxide-wrapped ZnMn₂O₄ microspheres (ZnMn₂O₄@rGO) were facilely synthesized through the solvothermal technique. The microstructure and morphology of ZnMn₂O₄@rGO microspheres were analyzed under Raman, X-ray photoelectron, X-ray diffraction, and energy-dispersive spectroscopies and scanning electron microscopy. The synthesized ZnMn₂O₄@rGO was employed as an excellent electrocatalyst for the reduction of hydrogen peroxide (H₂O₂). The ZnMn₂O₄@rGO-modified glassy carbon electrode (ZnMn₂O₄@rGO/GCE) exhibited a linear detection to H₂O₂ in a wide concentration range of 0.03-6000 μM with a detection limit of 0.012 μM. The biosensor was evaluated to determine H₂O₂ secreted by human breast cancer cells (MCF-7), indicating its promising applications in physiology and diagnosis.

A novel non-enzymatic H2O2 sensor using ZnMn2O4 microspheres modified glassy carbon electrode

With a facile solvothermal technique, ZnMn₂O₄ microspheres were synthesized in this work, which were used as enzyme mimics for the electrocatalytic reduction of H₂O₂. The morphology, crystal phase and structure of the ZnMn₂O₄ microspheres underwent characterization under X-ray diffraction spectroscopy, Raman spectroscopy, energy-dispersive spectroscopy, and scanning electron microscopy. The synthesized ZnMn₂O₄ microspheres showed an average diameter of 2 μm with great crystallinity, and exhibited excellent catalytical activity towards H₂O₂ electroreduction in alkaline media. The glassy carbon electrode modified by ZnMn₂O₄ microspheres showed a linear amperometric response for H₂O₂ in a wide concentration range of 0.02 ˜ 15 mM with detection limit of 0.13 μM under the optimized conditions. Besides, the sensor proposed here was successfully used to determine H₂O₂ in milk, suggesting that ZnMn₂O₄ microspheres can be used for non-enzymatic electrochemical sensor applications.