| Nano metal oxide materials have long been studied as potential electrode materials for energy storage devices, electrochemical supercapacitor and electrochemical sensors due to the ease of large-scale fabrication and high electrochemical activity. Among various metal oxides, lead dioxide is a fascinating oxide, and its high electrical conductivity and good chemical stability enable it to have unique properties and extensive applications in lead-acid batteries, hybrid supercapacitors, wastewater treatment and electrocatalytic processes. However, as the positive active materials of lead-acid battery, the utilization of PbO2active materials is very low; therefore it can not meet the requirement of high specific energy for lead-acid battery in practical application. It is therefore urgent to improve their overall performance. A good path is the development of the nanostructured PbO2materials with high specific surface area. Hence, the aim of this paper is to fabricate the nanostructured PbO2materials using electrochemical and chemical method and study the effect of surface morphology and crystal structure of PbO2on their electrochemical properties. In order to increase the utilization of the positive active materials, it is necessary to construct the PbO2nanoparticle aggregates with hierarchical structures, which can increase the contact area between active materials and electrolyte, thereby improving the connection between PbO2particles. Besides, the nanostructured PbO2with defined morphology can be used to construct the electrochemical sensor of glucose, which provide a feasible strategy for enhancing the properties of electrochemical sensor due to the high conductivity and fast charge transfer rate. The main contents of this paper include:(1) Effects of surface morphology of nanostructured PbO2thin films on their electrochemical propertiesThe advantages of lead-acid battery include low cost, high safety and good abilities in high discharge rate; however, except for the polluting nature of Pb and its compounds in the production process, its biggest drawback is the low energy density of the whole battery system, which mainly results from poor utilization of active materials, especially that of the positive active material, PbO2. The microstructure and surface morphology of PbO2have a strong influence on the overall performance of lead-acid battery, and the methods for preparing the PbO2materials also affect the discharge property of batteries. Therefore, we fabricated a series of PbO2thin films on the pure Pb surface by means of the electrochemical oxidation of Pb substrate and used the as-fabricated Pb electrodes coated with different PbO2thin films as the model electrodes to study the dependence of electrochemical properties of PbO2materials on their microstructure and morphology, thereby providing necessary technical basis for the improvement of electrochemical performance of PbO2active materials. The electrochemical properties of the PbO2films with different structure and morphology were investigated by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and constant current charge/discharge methods. The results demonstrated that the PbO2layer formed at a current density of10mA cm-2possessed the higher reduction peak current, the smaller ohmic resistance and charge-transfer resistance, the higher discharge capacity and better cycle performance than the other PbO2layers, due to high surface area, relatively small and uniform size, and especially good connectivity between PbO2nanoparticles. Meanwhile, the surface morphology of PbO2thin film electrode formed at a current density of10mA cm-2was observed after cycling, there was no obvious agglomeration between particles. The results help us to ensure that the PbO2active materials with nanostructured and uniform particles can improve the discharge performance of lead-acid battery.(2) Increasing the utilization of positive active materials of lead-acid battery by using nanostructured PbO2microspheresBecause the nanostructured PbO2materials paly an important role in enhancing the discharge performance, it is very important to fabricate these nanostructured materials and use them as positive active materials. Nowadays, the synthesis of PbO2powder materials with various forms has been reported, but their corresponding electrochemical properties as the positive electrode have not been investigated owing to many restrictions from the preparation procedures of electrodes. Therefore, herein we fabricated a thin film electrode by pressing the PbO2materials onto a conductive current collector for the convenience of the connection among the particles and between the particles and the current collector. This kind of thin flim electrode can be tested as the positive electrode of lead-acid battery.For the first time, using cetyltrimethylammonium bromide (CTAB) as a structure-directing agent in the alkaline media (pH=13.5), we fabricated the nanostructured PbO2microspheres (Nano-PbO2microspheres) with good crystalline structures and homogeneous through a simple liquid-phase oxidation method of Pb2+ions. Meanwhile, the Bulk-PbO2particles were prepared in the absence of CTAB. Both of them were pressed onto the different current collector (lead alloy sheet or Pt sheet) and tested in the concentrated H2SO4solution. The as-prepared thin positive electrode, which was composed of Nano-PbO2microspheres as active materials and lead alloy sheet as current collector, delivered a discharge capacity of101.8mAh/g (45%of active material utilization) and displayed a good cycle life (capacity retention was about90%after100cycles). The reasons of the good discharge behavior are interpreted as follows:(i) the specific surface area of Nano-PbO2microspheres was6times as much as that of Bulk-PbO2, leading to significant increase of the electrochemical active area,(ii) the charge-transfer resistance of Nano-PbO2microspheres was smaller than that Bulk-PbO2, and (iii) formation of "intermediate layer" between the PbO2nanoparticles and lead alloy sheet greatly improved the connection between the active materials and current collector. Besides, the presence of free surfaces and grain boundaries in the Nano-PbO2microspheres were in favor of the electron transfer rate and the H+, SO42-ions adsorption on the electrode surface, which made the discharge reaction proceed quickly and result in the better discharge performance of the Nano-PbO2microspheres. The use of nano PbO2materials chemically synthesized provides a feasible way to increase the utilization of positive active materials of lead-acid battery.(3) Construction of the carbon cloth-supported Co3O4/PbO2nanorod array electrode and its electrochemical sensing of glucoseNanostructured metal oxides are more applicable to the fabrication of non-enzymatic electrochemical sensors because of the unique electrocatalytic properties, but some problems may be encountered in the actual application because of the variation of local pH and the adsorption of intermediates. However, PbO2materials with the high electrical conductivity and good stability can help us to construct a novel sensor and improve the ability for glucose sensing.A novel electrochemical sensor for the detection of glucose was constructed based on the use of CO3O4/PbO2core-shell nanorod arrays as electrocatalysts. Firstly, the CO3O4nanowire arrays grew directly on a flexible carbon cloth substrate by the hydrothermal synthesis, and then PbO2nanoparticles were coated on the CO3O4nanowire to form a core-shell structure by using the electrochemical deposition method. Compared with the carbon cloth-supported pure CO3O4nanowire array electrode, the carbon cloth-supported CO3O4/PbO2nanorod array electrode exhibited higher sensitivity (460.3μAmM-1cm-2) and lower detection limit (0.31μM, S/N=3). The PbO2shell could offer the higher specific surface area and act as a stable, conducting matrix to encapsulate the core CO3O4nanowires. Due to the excellent repeatability and anti-interference ability, the carbon cloth-supported Co3O4/PbO2nanorod array electrode was very effective and sensitive for the determination of glucose in actual samples. |
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