Electrically conductive coals in nature: Their traits, whereabouts, green-exploitations and impacts

Amid the global advocation of carbon-neutrality, high-carbon-footprint-combustion is still catastrophically depleting the natural coal-reserves. Parallelly, high-value graphitic nanomaterials, from low-end graphitic-nano grains known as carbon black to high-end polymorphs of carbon nanofiber, carbon nanotube and graphene, have been invented to fuel an emerging economy with innovations emphasizing profitability instead of sustainability. Here, by analyzing the coal-traits and the relevant geological metamorphisms, we adopt the portrait of coal as a carbonaceous composite comprising graphitic nano-grains, typically merely 1-2 nm in size and not more than 20 % in concentration, in a matrix of amorphous carbonaceous macromolecules high in aromaticity, dusted by mineral-specks, with weak intermolecular links among all constituents. At the proximity of geological faults, metamorphism, carbonization and graphitization were once accelerated to form more graphitic nano-grains with crystallinity and electrical conductivity enhanced. Thus, coal-seams near such fault-dikes likely have electrically conductive coals full of percolated graphitic nano-grains with weak grain-boundary-links such that coal can be comminuted to graphitic nanomaterials without any chemical etch, with little loss, low cost and minimal environmental-load. Empowered by these views, we have found over twenty coal-fields in China and many more elsewhere having such conductive coals, with trials from lattice-imaging characterization to ton-scale production to validate our predictions. We trust that sharing such concepts and experimental findings promises new vehicles embracing sustainability to vitalize the coal-industry.