New graphene-like two-dimensional material could improve energy storage

May 18, 2015

Porous, layered structure of highly conductive powder Ni3(HITP)2 (credit: Mircea Dinca, MIT)

MIT and Harvard University researchers have created a graphene-like electrically conductive. porous, layered material as possible new tool for storing energy and investigating the physics of unusual materials.

They synthesized the material using an organic molecule called HITP and nickel ions, forming a new compound: Ni3(HITP)2.

The new porous material is a crystalline, structurally tunable electrical conductor with a high surface area — features that are ideal for supercapacitors, which could extend the range of electric vehicles by capturing and storing the energy that would normally be wasted when brakes slow down a vehicle.

The new material is composed of stacks of unlimited numbers of two-dimensional sheets resembling graphite, with a room temperature electrical conductivity of ~40 S/cm (Siemens per centimeter). The conductivity of this material is comparable to that of bulk graphite and among the highest for any conducting Metal-organic frameworks (MOFs)* reported to date.

Also, the temperature-dependence of its conductivity linear at temperatures between 100 K (Kelvin) and 500 K, suggesting an unusual charge transport mechanism that has not been previously observed in any organic semiconductors, and thus remains to be investigated.

In bulk form, the material could be used for electrocatalysis applications (modifying the rate of chemical reactions) similar to how platinum works (but at lower cost). Upon exfoliation (peeling off of successive layers), the material is expected to behave similar to graphene, but with tunable bandgap and electromagnetic properties, suggesting new uses in electronic circuits and new exotic quantum properties in solid-state physics.

* MOFs are hybrid organic-inorganic materials that have traditionally been studied for gas storage or separation applications owing to their high surface area. Making good electrical conductors out of these normally insulating materials has been a long-standing challenge, as highly porous intrinsic conductors could be used for a range of applications, including energy storage.


Abstract of High Electrical Conductivity in Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2, a Semiconducting Metal–Organic Graphene Analogue

Reaction of 2,3,6,7,10,11-hexaaminotriphenylene with Ni2+ in aqueous NH3 solution under aerobic conditions produces Ni3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), a new two-dimensional metal–organic framework (MOF). The new material can be isolated as a highly conductive black powder or dark blue-violet films. Two-probe and van der Pauw electrical measurements reveal bulk (pellet) and surface (film) conductivity values of 2 and 40 S·cm–1, respectively, both records for MOFs and among the best for any coordination polymer.