In situ preparation of flower-like α-Ni(OH)2 and NiO from nickel formate with excellent capacitive properties as electrode materials for supercapacitors

• Flowerlike nickel formate-based precursor is obtained using hydrothermal method.
• Nickel formate can transform into α-Ni(OH)2 instead of Ni when heating at 210 °C.
• α-Ni(OH)2 and NiO are capable of inheriting the architecture of the precursor.
• α-Ni(OH)2 shows better capacitive properties than the precursor and NiO.

Flower-like precursor with coexisting nickel formate and α-Ni(OH)2 was synthesized via a template-free and cost effective hydrothermal method. It is found for the first time that the decomposition behavior of nickel formate in the presence of α-Ni(OH)2 is completely different from that of pure nickel formate. At a heating temperature of 210 °C, α-Ni(OH)2, which is originally inside the precursor, serving as crystal nucleus could induce nickel formate to transform into α-Ni(OH)2 instead of previously reported highly active metallic Ni. After elevating the heating temperature to 250 °C, single-phase NiO, which well inherited the flower-like morphology of the precursor, was obtained. Electrochemical properties of the precursor, α-Ni(OH)2 and NiO were investigated systematically to provide deep insight into their differences in supercapacitor applications. The precursor shows a relatively high specific capacitance of 923 F g−1 at 1 A g−1 but a poor capacitance retention of ∼50% after 600 cycles. Both the flower-like α-Ni(OH)2 and NiO electrodes exhibit excellent long cycling lives with capacitance retention of 89% and 86% after 1000 cycles, respectively. More importantly, the specific capacitance of α-Ni(OH)2 electrode, which is as large as 810.4 F g−1 at 1 A g−1, is very outstanding.

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