Shasha Zhu

Photochemical fabrication of 3D hierarchical Mn3O4/H-TiO2 composite films with excellent electrochemical capacitance performance

We herein report a novel, energy-saving and environmentally benign photodeposition approach to fabricate a manganese oxide film on hydrogenated TiO2 (H-TiO2) nanotube arrays using a Mn(2+)-containing solution as a precursor. Mn(2+) ions are oxidized to Mn3O4 by the photogenerated holes during the photodeposition. The preferential growth of Mn3O4 on the nucleation sites leads to the formation of Mn3O4 nanorods on each H-TiO2 nanotube, forming a 3D hierarchical Mn3O4/H-TiO2 composite film. The as-fabricated 3D hierarchical Mn3O4/H-TiO2 composite film electrode delivers a high specific capacitance of 508 F g(-1) at a current of 0.7 A g(-1). The composite film electrode still shows a specific capacitance of 228 F g(-1) even at a high rate of 35.7 A g(-1), demonstrating its prominent rate capability. Remarkably, the composite film electrode shows no obvious capacitance decay after 10,000 charge/discharge cycles at a current density of 3.6 A g(-1), revealing its superior electrochemical cycling stability. The prominent pseudocapacitive performance of the composite film electrode can be attributed to its unique structure characteristics. The as-constructed energy-saving and environmentally benign photodeposition method can be used as a general and efficient route to prepare other composite materials with controlled morphologies and dimensions.

Hierarchical CoO microflower film with excellent electrochemical lithium/sodium storage performance

Hierarchically nanostructured transition metal oxides are very attractive for electrochemical energy storage systems owing to the enhanced electrochemical performance induced by their unique microstructures. Herein, a hierarchical CoO microflower film is prepared by a low-temperature solvothermal method with subsequent annealing treatment. The CoO microflowers with an average size of about 6 μm consist of hexagonal nanosheets with a loose exterior layer, exhibiting a unique hierarchical micro–nanostructure. The hierarchical CoO microflower film electrode delivers a high capacity of 1297.9 mA h g−1 after 500 cycles at 454.5 mA g−1, manifesting superior lithium storage performance. The phenomenon of the lithium storage capacity increase during the initial 150 cycles is analyzed by comparing the galvanostatic discharge/charge voltage profiles at different cycles. For sodium storage, the CoO microflower film electrode shows a larger capacity of 277.8 mA h g−1 after 100 cycles at a current density of 90.9 mA g−1. Based on the physical characterization results of the cycled film electrodes, the sodium storage mechanism of CoO is clarified.

NiO@MnO2 core–shell composite microtube arrays for high-performance lithium ion batteries

Tubular array structures are very attractive for electrochemical energy storage and conversion systems due to their unique physicochemical properties. Herein, a NiO microtube array is fabricated via a facile oxalic acid corrosion method followed by heat treatment. A NiO@MnO2 core–shell composite microtube array is further achieved by the anodic electrodeposition using the NiO microtube array as substrate. When applied as self-supported electrode for lithium ion batteries (LIBs), the NiO@MnO2 core–shell composite microtube array electrode shows excellent lithium storage properties. The electrode delivers a reversible capacity of 510 mA h g−1 at a high rate of 5.1 A g−1, showing its good rate capability. In particular, a reversible capacity of 1573 mA h g−1 is observed after 500 cycles at a current density of 0.53 A g−1, demonstrating the superior cycling performance of the electrode. The electrodeposited MnO2 layer as a protective shell prevents the NiO microtubes from deformation during electrochemical cycling, responsible for the superior cycle stability of the NiO@MnO2 core–shell composite microtube array electrode. The prominent lithium storage performance of the composite microtube array electrode can be attributed to its unique structure characteristics.

Facile morphology controlled synthesis of nanostructured Co3O4 films on nickel foam and their pseudocapacitive performance

Nanostructured transition metal oxides are a current investigation focus for supercapacitors. We herein report a facile solvothermal synthesis of nanostructured Co3O4 films on nickel foam. The morphologies and dimensions of the Co3O4 films can be effectively tuned by tailoring the solvent compositions in the solvothermal reaction solutions. The effect of solvent composition on the morphologies of nanostructured Co3O4 films is analyzed. The 3D hierarchically porous Co3O4 network film, which is synthesized in the solvothermal reaction solution with an intermediate ethylene glycol/water volume ratio (1 : 29), shows a markedly enhanced pseudocapacitive performance. The specific capacitances of the Co3O4 network film electrode at the current densities of 0.870 and 17.391 A g−1 are 2817 and 1948 F g−1, respectively, revealing its large specific capacitance and excellent rate capability. Furthermore, the Co3O4 network film electrode exhibits good electrochemical cycling stability with a specific capacitance of 1628 F g−1 after 3500 cycles at a current density of 4.348 A g−1. The prominent pseudocapacitive performance of the Co3O4 network film electrode can be attributed to its unique structural characteristics. The as-synthesized 3D hierarchically porous Co3O4 network film with excellent pseudocapacitive performance demonstrates promising potential as a high-performance electrode for supercapacitors.

MOF-Derived Hierarchical MnO-Doped Fe3O4@C Composite Nanospheres with Enhanced Lithium Storage

Hierarchically nanostructured binary/multiple transition-metal oxides with electrically conductive coatings are very attractive for lithium-ion batteries owing to their excellent electrochemical properties induced by their unique compositions and microstructures. Herein, hierarchical MnO-doped Fe3O4@C composite nanospheres are prepared by a simple one-step annealing in Ar atmosphere, using Mn-doped Fe-based metal-organic frameworks (Mn-doped MIL-53(Fe)) as precursor. The MnO-doped Fe3O4@C composite particles have a uniform nanosphere structure with a diameter of ∼100 nm, and each nanosphere is composed of clustered primary nanoparticles with an amorphous carbon shell, forming a unique hierarchical nanoarchitecture. The as-prepared hierarchical MnO-doped Fe3O4@C composite nanospheres exhibit markedly enhanced lithium-storage performance, with a large capacity of 1297.5 mAh g-1 after 200 cycles at 200 mA g-1. The cycling performance is clarified through analyzing the galvanostatic discharge/charge voltage profiles and electrochemical impedance spectra at different cycles. The unique microstructures and Mn element doping of the hierarchical MnO-doped Fe3O4@C composite nanospheres lead to their enhanced lithium-storage performance.