Tailoring Electronic Structure and Size of Ultrastable Metalated Metal-Organic Frameworks with Enhanced Electroconductivity for High-Performance Supercapacitors

摘要

Utilization of metal-organic frameworks (MOFs) as electrodes for energy storage/conversion is challenging because of the low chemical stability and poor electrical conductivity of MOFs in electrolytes. A nanoscale MOF, Co0.24Ni0.76-bpa-200, possessing ultrahigh stability with uncommon semiconductor behavior (sigma=4.2x10(-3) S m(-1)) was fabricated. The MOF comprises a robust hydrophobic paddlewheel and an optimized Co/Ni ratio, with consequent control over MOF size and the degree of conjugation of the coligand. A DFT study revealed that appropriate Ni2+ doping reduces the activation energy of the system, thus providing a higher carrier concentration, and the strongly delocalized N-donor ligand notably increases the metal-ligand orbital overlap to achieve efficient charge migration, leading to continuous through-bond (-CoNi-N-CoNi-)(infinity) conduction paths. These structural features endow the MOF with a good cycling stability of 86.5 % (10 000 cycles) and a high specific capacitance of 1927.14 F g(-1) among pristine MOF-based electrodes.