Understanding the electrochemical activation behavior of Co(OH)2 nanotubes during the ion-exchange process

In this work, a Co(OH)2 nanotube array is grown on Ni foam by an electrochemically induced ion-exchange approach. These arrays can be applied in supercapacitors as electrode materials. In the cyclic voltammetry (CV) charging process, the CO32- in Co(CO3)0.5(OH)·0.11H2O is replaced by OH− in the electrolyte, leading to structural transformation from nanowire to nanotube due to Kirkendall effect. Electrochemical tests reveal that the as-prepared Co(OH)2 nanotubes array on Ni foam show low specific capacitance in the initial cycles. After activation of electrode materials, the delivered specific capacitance is significantly increased. X-ray diffraction and Fourier transform infrared techniques (FTIR) are used to study the activation mechanism of the Co(OH)2 nanotube array upon CV cycling. With the continuous cycling, phase transformation occurred, in which synthesized Co(OH)2 bonds are completely converted to CoOOH after 150 cycles.