Electrosynthetic control of CNT conductivity & morphology: Scale-up of the transformation of the greenhouse gas CO2 into carbon nanotubes by molten carbonate electrolysis

TL;DR

This paper demonstrates a scalable electrochemical method to convert CO2 into various morphologies and conductivities of carbon nanotubes using molten carbonate electrolysis, with enhanced properties through electrolyte modifications.

Contribution

It introduces a scalable one-pot electrolysis process to produce diverse CNT morphologies and conductivities from CO2, with electrolyte doping to improve properties.

Findings

Electrolysis conditions control CNT morphology and conductivity.

Boron doping significantly enhances CNT conductivity.

Adding CaCO3 yields straight, thin-walled CNTs.

Abstract

Transformation of carbon dioxide into carbon nanotubes, CNTs, by electrolysis in molten carbonates provides a low cost route to extract and store this greenhouse gas. CNTs are more stable, compact and valuable than fuels or other CO2 conversion products, providing an incentive to remove CO2 for climate mitigation. Previously, solid core carbon nanofibers, CNFs were formed with C-13 isotope CO2, whereas hollow core fibers - carbon nanotubes, CNTs, were formed with natural isotope CO2 splitting in molten lithium carbonate. Here we demonstrate the extraordinary range of specific morphologies and conductivities of CNTs that can be achieved through control of the electrolysis conditions in a one pot-synthesis, and scale-up of this process by which the greenhouse gas CO2 is transformed into carbon nanotubes by molten carbonate electrolysis. Addition of Li2BO3, boron dopes and greatly enhances CNT conductivity formed at the galvanized steel cathode. Addition of CaCO3 to the Li2CO3 electrolyte, decreases oxide solubility in the region of CNT growth, producing straight thin-walled CNTs.