Electrochemical formation of carbon nano-powders with various porosities in molten alkali carbonates

Physical characteristics of capacitive carbons derived from the electrolytic reduction of alkali metal carbonate molten salts

Carbons have been synthesized through the reduction of molten carbonate systems under varied conditions. The mechanism and kinetics of carbon electrodeposition has been investigated. Carbon morphologies include amorphous, graphite-like, and spherical aggregate phases. Increased graphitic character is observed in carbons electrodeposited at more cathodic potentials, particularly at higher temperatures. Bonding has been investigated and oxygen functionalised sp2 and sp3 structures have been identified. The level of functionalization decreases in carbons with reduced amorphous and increased graphitic character. Thermal decomposition of electrodepositied carbons has been investigated and zero order kinetics have been identified. A relationship has been identified between elevated oxygen functionalization and increased pseudo-capacitance, with carbons deposited at 0.15 A cm-2 showing capacitances of 400 F g-1 in 0.5 M H2SO4 at sweep rates of 10 mV s-1.

Use of inorganic fluorinated materials in lithium batteries and in energy conversion systems

After a review on the wide variety of inorganic fluorinated components in modern technologies, in particular for energy conversion/storage systems, the use of fluorinated carbons as electrodes for primary lithium batteries will be highlighted; in particular conventional graphite fluorides will be compared to recently investigated fluorinated carbon nanoparticles (F-CNPs) prepared from electrochemical reduction of molten carbonates.

Toward Small-Diameter Carbon Nanotubes Synthesized from Captured Carbon Dioxide: Critical Role of Catalyst Coarsening

Small-diameter carbon nanotubes (CNTs) often require increased sophistication and control in synthesis processes, but exhibit improved physical properties and greater economic value over their larger-diameter counterparts. Here, we study mechanisms controlling the electrochemical synthesis of CNTs from the capture and conversion of ambient CO₂ in molten salts and leverage this understanding to achieve the smallest-diameter CNTs ever reported in the literature from sustainable electrochemical synthesis routes, including some few-walled CNTs. Here, Fe catalyst layers are deposited at different thicknesses onto stainless steel to produce cathodes, and atomic layer deposition of Al₂O₃ is performed on Ni to produce a corrosion-resistant anode. Our findings indicate a correlation between the CNT diameter and Fe metal layer thickness following electrochemical catalyst reduction at the cathode-molten salt interface. Further, catalyst coarsening during long duration synthesis experiments leads to a 2× increase in average diameters from 3 to 60 min durations, with CNTs produced after 3 min exhibiting a tight diameter distribution centered near ∼10 nm. Energy consumption analysis for the conversion of CO₂ into CNTs demonstrates energy input costs much lower than the value of CNTs-a concept that strictly requires and motivates small-diameter CNTs-and is more favorable compared to other costly CO₂ conversion techniques that produce lower-value materials and products.

Effect of BaCO3 addition on the CO2-derived carbon deposition in molten carbonates electrolyzer

Atmospheric carbon dioxide is facilely transformed into carbon materials in Ba-containing or Ba-free carbonates eutectic.

Kinetic and Thermodynamic Characterization of Enhanced Carbon Dioxide Absorption Process with Lithium Oxide-Containing Ternary Molten Carbonate

Efficient and high-flux capture of CO₂ is the prerequisite of its utilization. Static absorption of CO₂ with solid Li₂O and molten salts (Li₂O-free and Li₂O-containing Li-Na-K carbonates) was investigated using a reactor with in situ pressure monitoring. The absorption capacity of dissolved Li₂O was 0.835 mol_CO2/mol_Li2O at 723 K, larger than that of solid Li₂O. For the solid Li₂O absorbents, formation of solid Li₂CO₃ on the surface can retard the further reactions between Li₂O and CO₂, whereas the dissociation/dissolution effect of molten carbonate on Li₂O improved the mass-specific absorption capacity of liquid Li₂O. In Li₂O-containing Li-Na-K molten carbonate, CO₂ was mostly absorbed by alkaline oxide ions (O^2-). The chemical interactions between CO₂ and CO₃^2- contributed to CO₂ uptake via formation of multiple carbonate ions. The mass transfer of these absorbing ions was found as the dominating factor governing the rate of static absorption. Higher temperatures reduced the thermodynamic tendency of CO₂ absorption, but a lower viscosity at elevated temperature was conducive to absorption kinetics. Compared with the commonly used CaO absorbent, Li₂O was much more dissolvable in molten carbonate. The Li₂O-containing molten carbonate is potentially a promising medium for industrial carbon capture and electrochemical transformation process.

An investigation into the carbon nucleation and growth on a nickel substrate in LiCl-Li2CO3 melts

The electrochemical deposition of carbon materials has been performed in LiCl-Li2CO3 melts using a Pt anode and a nickel cathode. Cyclic voltammetry and constant voltage electrolysis are conducted to investigate the electrode reactions, and the results prove that solid carbon is the only product from the cathodic reduction. Short-term electrolysis at 750 °C for 3, 10 and 20 s has been applied to study the formation and growth of the varied carbon microstructures. All of the results demonstrate that the morphologies of the deposited carbon are significantly affected by the cathode substrates, which may show different catalyzing effects on carbon nucleation. Two primary morphologies, quasi-spherical and nanofiber structures are observed at the nickel plate cathodes during the electrolysis and the formation and growth of carbon nanofibers are easily enhanced by using a high cell voltage. However, only a quasi-spherical structure is found on the molybdenum cathode substrate.

Direct Conversion of Greenhouse Gas CO2 into Graphene via Molten Salts Electrolysis

Producing graphene through the electrochemical reduction of CO2 remains a great challenge, which requires precise control of the reaction kinetics, such as diffusivities of multiple ions, solubility of various gases, and the nucleation/growth of carbon on a surface. Here, graphene was successfully created from the greenhouse gas CO2 using molten salts. The results showed that CO2 could be effectively fixed by oxygen ions in CaCl2-NaCl-CaO melts to form carbonate ions, and subsequently electrochemically split into graphene on a stainless steel cathode; O2 gas was produced at the RuO2-TiO2 inert anode. The formation of graphene in this manner can be ascribed to the catalysis of active Fe, Ni, and Cu atoms at the surface of the cathode and the microexplosion effect through evolution of CO in between graphite layers. This finding may lead to a new generation of proceedures for the synthesis of high value-added products from CO2, which may also contribute to the establishment of a low-carbon and sustainable world.

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

Electrochemical transformation of CO₂into 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 CO₂absorption 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 CO₂capture and electro-transformation (MSCC-ET) process. In this work, the CO₂absorption 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.

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

The electrochemical deposition and re-oxidation of solid carbon were studied in CO₃²⁻ 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 CO₃²⁻ 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.

Carbon electrodeposition in molten salts: electrode reactions and applications

Carbon dioxide can be electrochemically reduced to carbon in molten carbonate salts, promising affordable energy, materials and environmental explorations.