Molten salt CO₂capture and electro-transformation (MSCC-ET) into capacitive carbon at medium temperature: effect of the electrolyte composition

Abstract

Electrochemical transformation of CO2 into functional materials or fuels (i.e., carbon, CO) in high temperature molten salts has been demonstrated as a promising way of carbon capture, utilisation and storage (CCUS) in recent years. In a view of continuous operation, the electrolysis process should match very well with the CO2 absorption kinetics. At the same time, in consideration of the energy efficiency, a molten salt electrochemical cell running at lower temperature is more beneficial to a process powered by the fluctuating renewable electricity from solar/wind farms. Ternary carbonates (Li : Na : K = 43.5 : 31.5 : 25.0) and binary chlorides (Li : K = 58.5 : 41.5), two typical kinds of eutectic melt with low melting points and a wide electrochemical potential window, could be the ideal supporting electrolyte for the molten salt CO2 capture and electro-transformation (MSCC-ET) process. In this work, the CO2 absorption behaviour in Li2O/CaO containing carbonates and chlorides were investigated on a home-made gas absorption testing system. The electrode processes as well as the morphology and properties of carbon obtained in different salts are compared to each other. It was found that the composition of molten salts significantly affects the absorption of CO2, electrode processes and performance of the product. Furthermore, the relationship between the absorption and electro-transformation kinetics are discussed based on the findings.

Chronopotentiometric Approach of CO2Reduction in Molten Carbonates

“…Consequently, molten carbonate electrolysis cells could be more competitive than other conversion technologies such as hydrogenation and electrochemical reduction in chlorides or ionic liquids. 8 Several studies [9][10][11][12] have been carried out on CO 2 reduction but its specific mechanism in molten carbonate is not fully justified yet. It has been suggested that CO 2 can be reduced indirectly through the reduction of carbonates and their regeneration by absorption of CO 2 .…”

Capture and electro-splitting of CO2 in molten salts

“…2 a), providing evidence for the presence of reaction (1) . Deng et al [2,17] observed mass gain when CO 2 was injected into the Li 2 O-containing molten salts ( Fig. 2 b), indicating that CO 2 can be captured by reaction (2) .…”

“…Both reaction (2) and (3) contribute to the CO 2 capture, however, understanding the main contributing factor is beneficial to maximize the capture capacity of molten salts. Deng et al [2,17] compared the amounts of absorbed CO 2 in carbonate molten salts containing different Li 2 O concentrations. As shown in Fig.…”

“…Molten salt CO 2 capture and electrochemical transformation (MSCC-ET) process is a preferable method for the conversion of CO 2 to advanced carbon materials [1,[16][17][18] . Electrons are the strongest reducing agent, guaranteeing a fast electrochemical reaction at mild conditions.…”

Effect of molten carbonate composition on the generation of carbon material

“…15,16 With the aid of eutectic salts electrolyte, CO 2 can be captured and subsequently converted into carbon monoxide (CO), 17 solid carbon 18,19 and even valuable chemicals of carbon nanobers (CNFs) or their hollow form of carbon nanotubes (CNTs) 20,21 that are widely applied in the manufacture of reinforced composites due to outstanding mechanical properties. Presently, carbonates, especially alkali carbonates of Li 2 CO 3 , Na 2 CO 3 and K 2 CO 3 , are widely recognised as the optimum choice for CO 2 capture and conversion, but to the best of our knowledge, rare work is dedicated to investigate the effect of carbonates composition on carbon production.…”