Electro-deposition and re-oxidation of carbon in carbonate-containing molten salts

Abstract

The electrochemical deposition and re-oxidation of solid carbon were studied in CO3(2-) ion-containing molten salts (e.g. CaCl2-CaCO3-LiCl-KCl and Li2CO3-K2CO3) at temperatures between 500 and 800 °C under Ar, CO2 or N2-CO2 atmospheres. The electrode reactions were investigated by thermodynamic analysis, cyclic voltammetry and chronopotentiometry in a three-electrode cell under various conditions. The findings suggest that the electro-reduction of CO3(2-) is dominated by carbon deposition on all three tested working electrodes (Ni, Pt and mild steel), but partial reduction to CO can also occur. Electro-re-oxidation of the deposited carbon in the same molten salts was investigated for potential applications in, for example, direct carbon fuel cells. A brief energy and cost analysis is given based on results from constant voltage electrolysis in a two-electrode cell.

Electrolytes for electrochemical energy storage

“…355 More importantly, it was confirmed that Li + ions play an essential role for carbon electro-deposition in carbonate-only electrolytes. 355,356 Electrochemical oxidation of the deposited carbon was also investigated, 355 and preliminary findings, as shown in Fig. 41, indicate two plateaux on the potential-time profiles related to the anodic oxidation of the deposited carbon.…”

“…graphite rod. 355 Although there are many similarities between DCFCs and MCFCs, the DCFC is the only type of fuel cell that uses a solid fuel (i.e., various forms of solid carbon) instead of using gaseous fuels, such as hydrogen gas and coal gas. Another distinctive characteristic of the DCFC is the fixed chemical potentials of both reactant (carbon) and the product (carbon dioxide), which are irrelevant to the fuel conversion rate or position within the cell.…”

“…[348][349][350] However, the research has remained fairly quiet until recent consideration of the process for capture and utilisation of CO2. [351][352][353][354][355][356][357][358][359][360] Particularly, electrodeposition and re-oxidation of carbon in molten carbonate salts under the CO2 atmosphere have been investigated in order to close the loop of CO2-carbon cycles via the combination of molten salt electrolysis and DCFCs for energy storage. 355,356 To help understand the carbon deposition process, different salt compositions have been used to investigate the electrochemical deposition and re-oxidation of solid carbon, which are CaCl2-CaCO3-LiCl-KCl (molar ratio of 0.30:0.17:0.43:0.10) and Li2CO3-K2CO3 (molar ratio of 0.62:0.38) at different temperatures and atmospheres.…”

“…355,356 To help understand the carbon deposition process, different salt compositions have been used to investigate the electrochemical deposition and re-oxidation of solid carbon, which are CaCl2-CaCO3-LiCl-KCl (molar ratio of 0.30:0.17:0.43:0.10) and Li2CO3-K2CO3 (molar ratio of 0.62:0.38) at different temperatures and atmospheres. 355 More importantly, it was confirmed that Li + ions play an essential role for carbon electro-deposition in carbonate-only electrolytes. 355,356 Electrochemical oxidation of the deposited carbon was also investigated, 355 and preliminary findings, as shown in Fig.…”

Review—Electrochemical Growth of Carbon Nanotubes and Graphene from Ambient Carbon Dioxide: Synergy with Conventional Gas-Phase Growth Mechanisms

“…8 This method relies on the decomposition of dissolved CO 2 between two biased electrodes, where elemental carbon is captured at the cathode, and the resulting structures of the deposited carbons are largely dependent on process parameters including electrolyte, current density, and electrode materials. [9][10][11][12][13][14][15][16] The equations that govern this process are:…”