Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Nat Mater. 2017 Feb;16(2):220-224. doi: 10.1038/nmat4766. Epub 2016 Oct 10.
Owing to their high power density and superior cyclability relative to batteries, electrochemical double layer capacitors (EDLCs) have emerged as an important electrical energy storage technology that will play a critical role in the large-scale deployment of intermittent renewable energy sources, smart power grids, and electrical vehicles. Because the capacitance and charge-discharge rates of EDLCs scale with surface area and electrical conductivity, respectively, porous carbons such as activated carbon, carbon nanotubes and crosslinked or holey graphenes are used exclusively as the active electrode materials in EDLCs. One class of materials whose surface area far exceeds that of activated carbons, potentially allowing them to challenge the dominance of carbon electrodes in EDLCs, is metal-organic frameworks (MOFs). The high porosity of MOFs, however, is conventionally coupled to very poor electrical conductivity, which has thus far prevented the use of these materials as active electrodes in EDLCs. Here, we show that Ni(2,3,6,7,10,11-hexaiminotriphenylene) (Ni(HITP)), a MOF with high electrical conductivity, can serve as the sole electrode material in an EDLC. This is the first example of a supercapacitor made entirely from neat MOFs as active materials, without conductive additives or other binders. The MOF-based device shows an areal capacitance that exceeds those of most carbon-based materials and capacity retention greater than 90% over 10,000 cycles, in line with commercial devices. Given the established structural and compositional tunability of MOFs, these results herald the advent of a new generation of supercapacitors whose active electrode materials can be tuned rationally, at the molecular level.
由于电化学双层电容器 (EDLC) 的功率密度高、循环寿命优于电池，因此它已成为一种重要的电能存储技术，在间歇性可再生能源的大规模部署、智能电网和电动汽车中发挥着关键作用。由于 EDLC 的电容和充放电速率分别与表面积和电导率成正比，因此多孔碳如活性炭、碳纳米管和交联或多孔石墨烯被专门用作 EDLC 的活性电极材料。一类比活性炭表面积大得多的材料，有可能挑战碳电极在 EDLC 中的主导地位，这就是金属有机骨架 (MOF)。然而，MOF 的高孔隙率通常伴随着非常差的电导率，这使得这些材料迄今为止无法用作 EDLC 的活性电极。在这里，我们表明具有高导电性的 Ni(2,3,6,7,10,11-hexaiminotriphenylene) (Ni(HITP)) 可以作为 EDLC 的唯一电极材料。这是首例完全由纯 MOF 作为活性材料制成的超级电容器的例子，没有使用导电添加剂或其他粘合剂。基于 MOF 的器件的比表面积电容超过了大多数碳基材料，并且在 10,000 次循环中容量保持率超过 90%，与商业器件相当。鉴于 MOF 的结构和组成可调节性，这些结果预示着新一代超级电容器的出现，其活性电极材料可以在分子水平上进行合理的调节。
