Facilely synthesized α phase nickel–cobalt bimetallic hydroxides: Tuning the composition for high pseudocapacitance

• α phase Ni–Co hydroxides have been synthesized via a precursor conversion method.
• The method is robust to synthesis α phase hydroxides with different Ni and Co ratios.
• Electrochemical properties can be improved by tuning the Ni and Co content.
• Bimetallic Ni–Co hydroxides exhibit excellent supercapacitive performance.
• The mechanism that the interlayer species are beneficial to the cycling stability is proposed.

A facile and novel precursor conversion method is successfully developed to grow Ni–Co hydroxides with α phase structure. The method is robust and versatile enough to be employed to prepare α phase Ni–Co hydroxides with similar interconnected flower-like nanostructures even at different Ni and Co contents. When used as the electroactive materials for supercapacitors, the bimetallic Ni–Co hydroxides deliver much higher specific capacitance with improved rate capability and cycling stability than monometallic Ni hydroxide. Especially, the Ni0.5Co0.5 hydroxide exhibits the highest specific capacitance of 1600 F g−1 at a current density of 1 A g−1. Meanwhile, the mechanism for better cycling stability of the bimetallic Ni–Co hydroxides is studied by FT-IR measurement. It is found that the introduction of Co ions contributes to the stable existence of ethylene glycol molecules in the interlayer space of the α phase Ni–Co hydroxides, resulting in superior cycling stability of the bimetallic Ni–Co hydroxides.