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Schematic of the electro-oxidation reaction process of NiCo2O4 nanocloth arrays on nickel foam. The unique morphological features can afford efficient 3D electron transport during the redox reaction.

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In this paper, for the first time, we report on the growth of ultrathin Ni(OH) 2 nanosheet arrays on a nickel foam (NF) via a novel pH-driven dissolution-precipitation route, carried out by a hydrothermal treatment of the NF in an acidic medium without the introduction of other nickel sources. Acid etching of the NF surface leads to nano-pits and produces Ni(H 2 O) n 2+ ions at the early stage of the reaction. With the elapsed time, an increase in the pH level occurs and the Ni(H 2 O) n 2+ ions gradually hydrolyze and preferentially precipitate on the nano-pits, serving as nucleation sites and leading to ultrathin Ni(OH) 2 nanosheet arrays on an NF. The effects of the experimental parameters, such as reaction time, acid type and starting pH value, on the Ni(OH) 2 growth are also investigated. Because the nano-pits are integrated parts of the NF and the deposition of Ni(OH) 2 nanosheets on such nano-pits ensures intimate contact between them, the Ni(OH) 2 /NF is robust enough to withstand a violent sonication process and efficient and rapid electron transfer is achieved. As a binder-free anode for Li-ion batteries, the Ni(OH) 2 /NF exhibits an unexpected ultrahigh capacity of 1689 mA h g −1 and excellent cycling stability.

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