Shape-controlled synthesis of Ni-based metal-organic frameworks with albizia flower-like spheres@nanosheets structure for high performance supercapacitors.

Metal organic frameworks (MOFs) are considered as very promising positive electrode materials for supercapacitors. To achieve good electrochemical performance, in this work, we report a mixed-ligand approach to prepare modified Ni-MOF by using trimesic acid (BTC) as the modulator to partially replace the terephthalic acid (PTA) ligands. The introduction of BTC can induce the formation of nanosheets with inserted albizia flower-like spheres, where the nanowires on the albizia flower-like spheres can provide rich redox reaction sites and the "spacer" spheres between the layers can hinder the aggregation of the 2D nanosheets to provide fast transport pathways. Moreover, adsorption simulation shows that the adsorption energy of OH- on the mixed organic ligands is increased after introducing the BTC ligands, which may improve the reversible redox reaction kinetics in the electrode materials. The as-obtained albizia flower-like spheres@nanosheets structured Ni-MOF with the optimized amount of BTC exhibits a high capacitance of 920 F g-1 at 1 A g-1, good rate capability of 61% at 20 A g-1, and an excellent cycling stability in 6 M KOH electrolyte. This work may provide helpful guidance for controlling the structure and surface property of MOFs to improve the electrochemical performance for supercapacitors.