A high yield, low energy synthesis of carbon nano‐onions (CNOs) by electrolysis of CO2 in molten carbonate is presented. Carbon nano‐onions are a recently recognized, less studied morphology of carbon nanomaterials consisting of nested concentric carbon spheroids. Previously, a high yield growth of carbon nanotubes by CO2 electrolysis in molten carbonate was achieved through transition metal nucleation points on the electrolysis cathode. Here, effective low energy CNO synthesis from CO2 is achieved instead by excluding those nucleating agents from the molten carbonate growth medium resulting in a profusion of uniform CNOs, with an increasing diameter correlated to increasing growth time. CO2 transformation to valuable materials, such as CNOs, adds value to CO2 to incentivize consumption of this greenhouse pollutant. For example, CNOs are currently valued 20 000 times higher than coal.
This SEM, TEM and Raman Spectra and economic calculations data provides a benchmark for carbon nanotubes synthesized via molten electrolyte via the carbon dioxide to carbon nanotube (C2CNT) process useful for comparison to other data on longer length C2CNT wools; specifically: (I) C2CNT electrosynthesis with bare (uncoated) cathodes and without pre-electrolysis low current activation. (II) C2CNT Intermediate length CNTs with intermediate integrated electrolysis charge transfer. (III) C2CNT Admixing of sulfur, nitrogen and phosphorous (in addition to boron) to carbon nanotubes, and (IV) Scalability of the C2CNT process. This data presented in this article are related to the research article entitled “Carbon Nanotube Wools Made Directly from CO2 by Molten Electrolysis: Value Driven Pathways to Carbon Dioxide Greenhouse Gas Mitigation” (Johnson et al., 2017) [1].
An electrosynthesis is presented to transform CO2 into an unusual nano and micron dimensioned morphology of carbon, termed Carbon Nano-Scaffold (CNS) with wide a range of high surface area graphene potential usages including batteries, supercapacitors, compression devices, electromagnetic wave shielding and sensors. Current CNS value is over $323 per milligram. The morphology consists of a series of asymmetric 20 to 100 nm thick flat multilayer graphene platelets 2 to 20 µm long orthogonally oriented in a 3D neoplasticism-like geometry, and appears distinct from the honeycomb, foam, or balsa wood cell structures previously attributed to carbon scaffolds. The CNS synthesis splits CO2 by electrolysis in molten carbonate and has a carbon negative footprint. It is observed that transition metal nucleated, high yield growth of carbon nanotubes (CNTs) is inhibited in electrolytes containing over 50 wt% of sodium or 30 wt% of potassium carbonate, or at electrolysis temperatures less than 700 °C. Here, it is found that a lower temperature of synthesis, lower concentrations of lithium carbonate, and higher current density promotes CNS growth while suppressing CNT growth. Electrolyte conditions of 50 wt% sodium carbonate relative to lithium carbonate at an electrolysis temperature of 670 °C produced over 80% of the CNS desired product at 85% faradaic efficiency with a Muntz brass cathode and an Inconel anode.
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