Morphology regulation of conductive metal-organic frameworks grown on graphene oxide for high-performance supercapacitors.

In this work, nickel-catecholate (Ni-CAT) nanorods were compounded on graphene oxide (GO) to form a composite Ni-CAT@GO (NCG) with a special "blanket-shape" structure, which was used as an electrode material for supercapacitors. The morphology of Ni-CATs grown on GO was modulated by introducing various contents of GO. With increasing GO, the length of nanorods of Ni-CATs is obviously shortened, and the charge transfer resistance of NCG is significantly reduced as the GO content is relatively low while it increases with further addition of GO, because excessive GO in NCG results in smaller crystal sizes accompanied by smaller stacking pores. Both the over-long Ni-CAT nanorods and the smaller stacking pores can restrict the accessible surface areas for the electrolyte. Optimal nanorod sizes are crucial to achieve good electrochemical performance for electrode materials. Galvanostatic charge-discharge analysis of NCG electrodes shows that their capacity initially increases and then decreases with the addition of more and more GO, and Ni-CAT@GO-0.5 (NCG0.5) with minimal charge transfer resistance exhibits the best electrochemical performance. The results demonstrate that the NCG0.5 electrode with optimal morphology possesses an excellent capacitance of 563.8 F g at 0.5 A g and a good rate performance of 61.9% at 10 A g, indicating that Ni-CAT@GO is a new type of promising electrode material for supercapacitors based on conductive metal-organic frameworks.