We report a novel “sacrificial template-accelerated hydrolysis” (STAH) approach to the synthesis of iron oxide-based nanotube arrays including hematite α-Fe2O3 and magnetite Fe3O4 on centimeter-scale conducting alloy substrates. ZnO nanowire arrays are chosen as the inexpensive and sacrificial templates that do not contribute to the component of final iron oxide nanotubes but can be in situ dissolved by the acid produced from the Fe3+ precursor hydrolysis. Interestingly, the ZnO template dissolution in turn accelerates the Fe3+ hydrolysis, which is essential to initiating the nanotube formation. Such a STAH approach provides a morphology-reservation transformation, when various shaped ZnO templates are adopted. Moreover, by introducing glucose into the precursor solution, we also successfully obtain carbon/hematite(C/α-Fe2O3) composite nanotube arrays on large-area flexible alloy substrate, with a large number of pores and uniform carbon distribution at a nanoscale in the nanotube walls. These arrays have been demonstrated as excellent additive-free anode materials for lithium ion batteries in terms of good cycling performance up to 150 times (659 mA h g−1) and outstanding rate capability. Our result presents not only a new route for inorganic nanotube formation but also an insight for rational design of advanced electrode materials for electrochemical batteries and sensors.

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Carbon/ZnO nanorod arrays on nickel substrate have been fabricated over a large area by the simple carbonization of preadsorbed glucose on ZnO arrays at 500 °C in argon gas. The uniform coating of average 6 nm carbon shell on ZnO nanorod surface is confirmed. The novel array architecture possesses both the electroactivity of carbon and the electrochemical advantages of array structure on conductive substrate. When used as anode for Li ion batteries, it displays significantly improved performance in terms of cycling stability and rate capability. The observed lithium storage ability ranges among the best reported to date for ZnObased anode. We believe that the novel carbon-coating route is general and can be extendable to other metal oxide nanoarray electrodes.

We report for the first time a facile and direct synthesis of large-scale cobalt monoxide (CoO) porous nanowire arrays (NWAs) with robust mechanical adhesion to flexible conductive substrate (Ti foil) by a two-step method. Significantly raw salt cubic CoO of high quality from the complete pyrolysis of cobalt-hydroxide-carbonate (precursor) is achieved. When serving as lithium-ion battery electrodes in the absence of any ancillary materials (carbon black and binder), the as-obtained well-aligned CoO NWAs, possessing both the completely reversible electrochemical properties and unique advantages originating from integrated one-dimensional (1D) nanostructured architecture, exhibit good high-rate capability at a rate of 1 C (716 mA/g), 2 C (1432 mA/g), 4 C (2864 mA/g), and 6 C (4296 mA/g), respectively.

We have developed a general two-step synthesis of large-scale arrays of one-dimensional (1D) nanostructured Co3O4 directly on various substrates. Throughout a controllable hydrothermal process using urea as mineralizer and hereafter with a postcalcination process under air atmosphere, Co3O4 1D nanostructure arrays have been grown firmly on insulating substrates, such as glass slides and ceramics, which is quite convenient for the construction of gas sensor devices without any extra electrode preparation process. Furthermore, this direct-growth approach can be readily extended to conductive substrates (ITO, Ti, Fe−Co−Ni alloy), and meanwhile due to the robust mechanical adhesion and one-dimensional carrier transportation architecture firmly contacted to the metal, the metal substrate-supported Co3O4 arrays could act as a promising electrode material and be straightforwardly integrated into electronic and electrochemical nanodevices.

Large-scale uniform α-Co(OH)₂ nanowire arrays (NWAs) with an average length of ∼20 μm grown on pyrolytic graphite (PG) were successfully synthesized by a hydrothermal method at 120 °C. Ultrasonication test was carried out toward the as-made nanoarray products and the result demonstrated their robust adhesion to graphitic substrate. After 300 s of sonication testing, α-Co(OH)₂ NWAs could still possess both integrated one-dimensional (1D) nanoarray architecture and good electronic connections with current collector. When investigated as electrochemical pseudocapacitor electrodes, α-Co(OH)₂ NWAs exhibited good energy-storage performance in terms of high specific capacitance of 642.5 F/g, good rate capability, and excellent capacity retention. Our work not only presents a cost-effective and scale-up synthetic method for α-Co(OH)₂ NWAs but also holds promise in general synthesis of long arrays of other metal hydroxides/oxide (TiO₂, Fe₂O₃, SnO₂, etc.) nanostructures on PG substrate by using α-Co(OH)₂ NWAs as sacrificial templates.

Co-Fe layered double hydroxide (LDH) nanowall arrays (NWAs) have been grown directly from a flexible alloy substrate by a facile hydrothermal method. An ultrasonication test of 30 min towards the as-made Co-Fe LDH NWAs has demonstrated their ultra-robust mechanical adhesion to the substrate. In particular, an in situ carbon-source coating (ISCC) on the Co-Fe LDH NWAs was achieved during their in situ growing process conducted in a glucose-containing reaction solution. After annealing treatment in an argon atmosphere, carbon coated Co-Fe mixed oxide NWAs were evolved from thermal decomposition of LDH precursors and carbonization of glucose, and further investigated as anode materials for lithium-ion batteries (LIBs). When tested, the obtained carbon coated Co-Fe mixed oxide NWAs with improved electrical conductivity exhibited superior electrochemical performance in terms of specific capacity and cyclability as compared to a carbon-free sample and a sample made by the previous carbon-coating method. Our work presents an alternative way to fabricate in situ mixed transition metal oxide nanostructures for high-performance LIBs.

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