Carbon Nano‐Onions Made Directly from CO₂ by Molten Electrolysis for Greenhouse Gas Mitigation

Abstract 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.