Enhanced electrochemical performance of the cobalt chloride carbonate hydroxide hydrate via micromorphology and phase transformation.

Micromorphology and conductivity are two vital factors for the practical capacitance of the electrode materials for supercapacitors. In this work, a novel two-step electrochemical activation method involving a cyclic voltammetry (CV) treatment within 0-0.7 V followed by a CV treatment within -1.2-0 V is explored to induce the micromorphology and phase transformation of the cobalt chloride carbonate hydroxide hydrate (CCCH) nanoneedle arrays. The first-step activation transforms the CCCH to Co(OH) and then the reversible transformation between Co(OH) and CoOOH generates plenty of pores in the sample, thereby increasing the specific capacitance from 0.54 to 1.74 F cm at the current density of 10 mA cm. The second-step activation inducing the reversible transformation between Co(OH) and Co not only endows the final sample with a nanosheets-assembled fasciculate structure but also decreases the internal resistance via generating Co in the final sample (CCCH-P75N50). Consequently, the CCCH-P75N50 shows a high specific capacitance of 3.83 F cm at the current density of 10 mA cm. Besides, the aqueous asymmetric supercapacitor assembled with CCCH-P75N50 and commercial conductive carbon cloth (CC) delivers a high energy density of 2.75 mWh cm at a power density of 37.5 mW cm. This work provides a novel, facile and promising method to optimize the micromorphology and conductivity of Co-based electrodes.