A new electrolyte for molten carbonate decarbonization

Abstract

The molten Li2CO3 transformation of CO2 to oxygen and graphene nanocarbons (GNCs), such as carbon nanotubes, is a large scale process of CO2 removal to mitigate climate change. Sustainability benefits include the stability and storage of the products, and the GNC product value is an incentive for carbon removal. However, high Li2CO3 cost and its competitive use as the primary raw material for EV batteries are obstacles. Common alternative alkali or alkali earth carbonates are ineffective substitutes due to impure GNC products or high energy limitations. A new decarbonization chemistry utilizing a majority of SrCO3 is investigated. SrCO3 is much more abundant, and an order of magnitude less expensive, than Li2CO3. The equivalent affinities of SrCO3 and Li2CO3 for absorbing and releasing CO2 are demonstrated to be comparable, and are unlike all the other alkali and alkali earth carbonates. The temperature domain in which the CO2 transformation to GNCs can be effective is <800 °C. Although the solidus temperature of SrCO3 is 1494 °C, it is remarkably soluble in Li2CO3 at temperatures less than 800 °C, and the electrolysis energy is low. High purity CNTs are synthesized from CO2 respectively in SrCO3 based electrolytes containing 30% or less Li2CO3. The transformation of CO2 to oxygen and graphene nanocarbons using lithium carbonate as an electrolyte is a promising, large-scale process for CO2 removal and valorization, but lithium carbonate is already in high demand as an important battery material. Here, the authors report the use of strontium carbonate as an alternative electrolyte in the electrochemical reduction of CO2 to carbon nanotubes.