Exploration of alkali cation variation on the synthesis of carbon nanotubes by electrolysis of CO2 in molten carbonates

Abstract

The electrochemical splitting of CO2 in molten carbonate salt electrolytes can form a valuable product, carbon nanotubes, and with this product a value-incentivized pathway of climate change mitigation by transforming CO2 from a greenhouse gas pollutant into a useful resource. Instability of the anode can provide a challenge for a commercialization of this electrochemical technology. A nickel superalloy (Inconel 718) anode is shown to be highly stable for the scalable controllable, electrosynthesis of nano-carbons from CO2 in molten carbonates salts. Unlike pure nickel anodes that degrade (corrode) in the presence of potassium carbonate containing molten electrolytes, Inconel is stable as an anode even in these electrolytes. This opens up more cost-effective electrolytes (less expensive than lithium carbonate), and the systematic variation of alkali cation carbonates is explored. Coupled with a brass cathode, uniform carbon nanotubes (CNT) are efficiently synthesized by electrolysis of CO2 in either pure Li2CO3 or in ternary electrolytes, Li2CO3-Na2CO3-LiBO2 or Li2CO3-K2CO3-LiBO2. These results increase the foundation of understanding of the electrolytic splitting of carbon dioxide and provide the data for developing a high-efficiency CO2 electroreduction for the production of carbon nanotubes.