Zhishun He

Surfactant-assisted photochemical deposition of three-dimensional nanoporous nickel oxyhydroxide films and their energy storage and conversion properties

Three-dimensional (3D) nanoporous nickel oxyhydroxide (NiOOH) films were prepared on a TiO2 nanoarray substrate by a novel surfactant-assisted photodeposition method using Ni2+-containing solutions as precursors, and their energy storage and conversion behaviors were investigated. In the photodeposition process, photogenerated holes were used to oxidize Ni2+ ions to Ni3+ ions, resulting in the precipitation of NiOOH onto the TiO2 nanoarray substrate. The amount of photochemically deposited NiOOH increased with an increase in the surfactant (sodium lauryl sulfate, SDS) concentration in the deposition solution. If the SDS concentration did not surpass 0.3 wt%, the photochemically deposited NiOOH composite film exhibited a 3D nanoporous structure, and the pore size decreased with an increase in the SDS concentration. The 3D nanoporous NiOOH composite film which was prepared by photodeposition for 5 h in the presence of 0.3 wt% SDS presented the largest discharge capacity in our experimental range, implying enhanced UV-induced oxidative energy storage. The as-photodeposited NiOOH nanoflakes with a quasi two-dimensional structure exhibited close contact with TiO2 nanorods, originating from the fact that NiOOH was deposited at the sites where the photogenerated holes were available. It was demonstrated that the as-photodeposited 3D nanoporous NiOOH composite film could be used for the removal of trace amounts of indoor formaldehyde gas, which was mainly due to the stored oxidative energy. The photodeposition method demonstrated here can be used as a general route to fabricate photocatalyst-based composite materials.

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.

Hierarchically porous CoNiO2 nanosheet array films with superior sodium storage performance

Nanostructured transition metal oxides are considered as some of the promising anode materials for rapidly emerging sodium ion batteries. Herein, a hierarchically porous CoNiO2 nanosheet array film is prepared via a low-temperature solvothermal method with subsequent annealing treatment. As a self-supported anode for sodium ion batteries (SIBs), the as-prepared hierarchically porous CoNiO2 nanosheet array film manifests superior sodium storage performance. The film electrode delivers a large reversible capacity of 746.6 mA h g−1 after 100 cycles at 200 mA g−1. In particular, a capacity of 419 mA h g−1 is achieved at a high current density of 1600 mA g−1, demonstrating a good rate capability.

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.