Preparation Of Transition Metal Oxide Micro-/Nanostructured Arrays On Metal Substrates And Their Lithium Storage Properties

Transition metal oxides such as iron oxides, cobalt oxides, nickel oxides, etc., are considered to be fascinating functional materials and have been widely exploited in various fields, including energy conversion or storage, sensing, catalysis, optical, electrical or optoelectronics applications. In order to integrate nanostructures into modern electronic devices, considerable efforts have been devoted to designing and assembling building blocks into highly organized 2D or 3D structures, especially into well-ordered arrays on functional substrates.For the ever-growing demand of high-performance devices, it is highly desirable to grow self-supported transition metal oxide micro-/nanostructured arrays on conducting substrates which function as electrodes directly. The integration of hierarchical micro-/nanostructures with well-ordered arrays on conducting substrates enables the synergy and integration of multi-functionalities into various electronic devices, such as lithium-ion batteries (LIBs), supercapacitors (SCs), solar cells, electrochromic devices and light-emitting diodes. The hierarchical micro-/nanostructures endow abundant electrode/electrolyte interfaces and reduce diffusion distance to the interior surface, leading to kinetic acceleration of the electrochemical reactions. Moreover, the well-ordered arrays closely connected to the current collectors can provide direct electron transport pathways, favoring the enhanced performances of the electronic devices. Additionally, the in-situ growth of active materials on the conducting substrates greatly simplifies the electrode fabrication process without using any binders or conductive additives.Here a novel self-sustained cycle of hydrolysis and etching (SCHE) is exploited to successfully synthesize 1D Ni(S04)0.3(OH)i.4 nanobelt arrays. The formation mechanism is as follows. When external Ni2+ ions in the aqueous solution started to hydrolyze under hydrothermal conditions, the hydrolysis products and H+ ions generated correspondingly. The H+ ions were then consumed by etching the nickel substrate to produce Ni2+ ions and H2, which in turn accelerated the hydrolysis of Ni2+ ions in an autocatalytic fashion, leading to a preferential hydrolysis on the surface of the nickel substrate. With the reaction continuing, the Ni2+ ions released from the Ni substrate supplemented the starting Ni2+ ions in the solution, establishing a self-sustained cycle of hydrolysis, etching and deposition occurring near and on the substrate surface. At last, the corresponding NiO film composed of porous nanobelt array could be obtained by post-heat treatment of the Ni(S04)0.3(OH)1.4 precursor film. The obtained NiO porous nanobelt arrays for lithium ion batteries exhibit excellent cycling stability and good rate capability:Cycling at current densities of 1 C and 10C for 100 cycles with high capacity retentions (almost 100%) and delivering capacities of 330 and 290mAhg-1 at a high current density of 20 and 30 C, respectively.We also proved that the self-sustained cycle of hydrolysis and etching (SCHE) strategy is an in-situ approach to selectively grow single or binary component micro-/nanostructured array films of metal oxides or their precursors onto metal substrates. This general method can be employed to produce a variety of hierarchical micro-/nanostructured arrays (Ti-, Ni-, Co-, Mn-, Fe-, Zn-, Cd-based precursors/oxides, etc.) on various metal substrates (like Ti, Al, Ni, Co, Zn, Cd foils) by tuning the cycle parameters, which implies the generality and efficacy of the strategy. We show that our delicate strategy provides a simple and convenient route to assemble a variety of ordered building blocks on metal substrates (current collectors) with novel micro-/nanostructures, which function as electrodes in lithium-ion batteries and may also find potential application in electronic devices.We report a cosurfactant-mediated microemulsion synthetic procedure to produce free-standing CuO arrays with hierarchical micro-cog architectures on copper substrates. Introducing of n-butanol as a cosurfactant into the ternary AOT/isooctane/water system increases the rigidity of reverse micelles, which can be selectively adsorbed on particular crystal faces, leading to well-aligned arrays and enlarged aspect ratio with average heights of over 6μm and diameters of 1 to 2μm. The CuO cog-array films were obtained from the thermal dehydration of Cu(OH)2 arrays on copper substrate, which exhibit excellent electrochemical performance when directly employed as anode electrodes in lithium ion batteries, including long cycling life (with capacity retention of 91.6% at 1 C over 300 cycles) and outstanding rate capability even at high current rates (about 466 and 418mAhg-1 at high rate of 12 and 15 C, respectively).Finally, a special polymeric nanopillar array, containing polyurethane acrylate (PU) and NOA63 adhesive, on a transparent plastic sheet, was used as a three-dimensional (3D) substrate. After coating the 3D nanopillar arrays with a hydrophobic agent (1H,1H, 2H,2H-perfluorooctyltrichlorosilane), these 3D nanopillar array substrates became superhydrophobic while still keeping optical transparency. Then, the LBL deposition was applied to the 3D superhydrophobic nanopillar arrays by dipping into 1% w/v poly (sodium 4-styrenesulfonate) (PSS) and 1% w/v poly (diallyldimethylammonium) chloride (PDDA) solutions alternatively for several times. During each dipping cycle, instead of traditional growth of monolayer film, novel and uniform nanobridges can be formed between the nanopillars. Interstingly, the direction of these nanobridges can be well controlled, by simply changing the LBL dip-coating direction with respect to the initial orientation of the nanopillar arrays. We can get the nanopillars connected to each other with parallel LBL nanobridges in the same direction.