Fully-Packed Ultrasmall Au Nanoclusters in Covalent Organic Frameworks as Positive Electrodes for Supercapacitors

Abstract

Supported metal nanoclusters have emerged as highly promising class of materials with great potential across a wide range of applications including electrochemistry. However, fully-metal-loading of supports with ultrasmall pore structures, such as covalent organic frameworks (COFs), which might yield new performances, remains a challenge. Learning from the synthetic strategy of atomically-precise Au nanoclusters, Au elements are first complexed with alkynyl-modified building blocks prior to synthesis of COFs and a subsequent in-situ reduction then allows the size-focused formation of Au nanoclusters within each pore. With a partially-reduced Au content as high as ~50.8 wt %, the composites of Au nanocluster-filled COFs surprisingly exhibit a remarkable decrease in resistance as low as 80.16 Ω compared to their parent COFs, i.e. 4341 Ω for the pristine COFs and 3328 Ω for the Au(I) complex-tethered COFs, this dramatic reduction in resistance opens up the possibility for the construction of supercapacitors. The composites show impressive specific capacitance of 241.4 F·g-1 at a current density of 0.1 A·g-1 along with excellent rate capability at high scan rate of 200 mV·s-1. This work can be expanded to a general strategy for molecularly designing COFs with various metal NCs, potentially endowing the composites with novel application possibilities.