Phosphate ion functionalization of Co(OH)2 nanosheets by a simple immersion method

Recently, surface engineering has attracted immense interest to improve the electrochemical performance of electrode materials. In this work, a simple method is presented to functionalize the surface of the electrode materials for supercapacitors. The functionalized process can be described that the Co(OH)2 nanosheets are electrodeposited on nickel substrate, followed by immersed in the phosphate ion solution. The structures, morphologies and electrochemical properties of the functionalized Co(OH)2 nanosheets are investigated. XRD, EDX and FTIR analysis indicate that the phosphate ion has successfully been adsorbed on the surface of the Co(OH)2 nanosheets. And the electrochemical tests show that through the phosphate ion functionalization, the Co(OH)2 nanosheets exhibit the remarkably enhanced supercapacitive performance with a specific capacitance of 740 F/g at a current density of 1 A/g in 6 M KOH as compared to the bare Co(OH)2 (433 F/g). In particular, the functionalized Co(OH)2 electrode has an excellent long-term cycling stability with 82.7% capacitance retention after 10000 cycles. In addition, further analysis shows that the enhanced electrochemical performance can be attributed to the functionalized Co(OH)2 nanosheets providing large reaction surface area, more active sites, and fast ion and electron transfer.