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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.

The CO 2 gas was utilised as a source of carbon for electro-carburisation of mild steel in carbonate containing molten salts at 800 • C. In the process, the mild steel to be carburised was made the cathode. An inert anode of SnO 2 was used to ensure oxygen gas as the by-product. Two molten salt baths, i.e. Na 2 CO 3 -NaCl (molar ratio = 4:1) and Li 2 CO 3 -K 2 CO 3 (molar ratio = 1:1), were investigated as the electrolyte and also the medium for CO 2 absorption. Microstructural changes in the electro-carburised samples, as revealed by either optical or scanning electron microscopy, were featured by the increase of the carbon rich cementite phase (Fe 3 C) at the expense of the original ferrite phase near the surface of the samples. Micro-hardness profiles measured from the surface to the centre of the electro-carburised sample presented clear evidence of carbon penetration as a function of the electrolysis voltage, and the activity of carbonate ions in the molten salts. The carbon-hardened case was up to 0.60 mm in thickness with the carbon content in the near surface region reaching saturation (Fe 3 C, 6.69 wt.%). The current efficiency of electro-carburisation depended on the cell voltage, and possible causes are discussed with the aid of a simple model correlating the hardness and carbon content.

The production of continuous carbon nanotube (CNT) fibers and films has paved the way to leverage the superior properties of individual carbon nanotubes for novel macroscale applications such as electronic cables and multifunctional composites. In this manuscript, we synthesize fibers and films from CNT aerogels that are continuously grown by floating catalyst chemical vapor deposition (FCCVD) and measure thermal conductivity and natural convective heat transfer coefficient from the fiber and film. To probe the mechanisms of heat transfer, we develop a new, robust, steady-state thermal characterization technique that enables measurement of the intrinsic fiber thermal conductivity and the convective heat transfer coefficient from the fiber to the surrounding air. The thermal conductivity of the as-prepared fiber ranges from 4.7 ± 0.3 to 28.0 ± 2.4 W m(-1) K(-1) and depends on fiber volume fraction and diameter. A simple nitric acid treatment increases the thermal conductivity by as much as a factor of ∼3 for the fibers and ∼6.7 for the thin films. These acid-treated CNT materials demonstrate specific thermal conductivities significantly higher than common metals with the same absolute thermal conductivity, which means they are comparatively lightweight, thermally conductive fibers and films. Beyond thermal conductivity, the acid treatment enhances electrical conductivity by a factor of ∼2.3. Further, the measured convective heat transfer coefficients range from 25 to 200 W m(-2) K(-1) for all fibers, which is higher than expected for macroscale materials and demonstrates the impact of the nanoscale CNT features on convective heat losses from the fibers. The measured thermal and electrical performance demonstrates the promise for using these fibers and films in macroscale applications requiring effective heat dissipation.

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Three dimensional manganese oxide on a CNT hydrogel has been developed with a satisfactory electrochemical performance.