Unveiling the key factors affecting the grain size of NiCo2O4 during electrodeposition

The electrodeposition rate ratio of Co 2+ and Ni 2+ as a decisive factor influencing the nucleation and growth of NiCo 2 O 4 is temperature dependent. • In the synthesis of NiCo 2 O 4 by electrodeposition, with the increasement of the temperature, the grain size decreases first and then increases, which rule is in consistent with the deposition rate ratio of Co 2+ and Ni 2+ . • At 10 ℃, the deposition rate ratio of Co 2+ and Ni 2+ is approach to 2.5 : 1, when the synthesized NiCo 2 O 4 nanosheets are the smallest. • The assembled NiCo 2 O 4 (10 ℃) electrode is able to deliver an ultrahigh specific capacitance of 1590 and 1080 F·g −1 at current densities of 1 and 20 A·g −1 , respectively, with excellent cycling stability. NiCo 2 O 4 bimetallic oxides are extraordinary ideal choice for supercapacitor electrode materials. As is widely known, the electrochemical properties of NiCo 2 O 4 are strongly affected by its morphology. Then, how to obtain NiCo 2 O 4 with ideal morphology has become a hot topic. In this paper, we found that the deposition rate ratio of Co 2+ and Ni 2+ is a decisive factor influencing the nucleation and growth of NiCo 2 O 4 by the electrodeposition synthesis. When the deposition ratio of Co 2+ and Ni 2+ is close to 2.5:1, the nucleation rate of NiCo 2 O 4 increases. NiCo 2 O 4 nanoflakes with thinner and smaller morphology can be obtained. What’s more, we found that the deposition rate ratio of Co 2+ and Ni 2+ depends on the temperatures. Especially, the deposition rate ratio of Co 2+ and Ni 2+ can approach 2.5:1, when the electrodeposition temperature is 10 ℃. The obtained NiCo 2 O 4 flower cluster nanosheets exhibited an outstanding capacitance of 1590 F·g −1 at the current of 1 A·g −1 and 1080 F·g −1 at the current of 20 A·g −1 . More importantly, a large reversible capacitance of 1288 F·g −1 with a capacitance retention of 81.0% can be obtained after 10000 cycles at 1 A·g −1 .