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Nano Letters Letter Figure 3. Zn effect (without Ni, Co, or Cu) on SEM of the carbon product formed at the cathode following electrolysis in Li2CO3 (without added Li2O) between a planar, square 2.5 by 2.5 cm iridium anode and a coiled wire 10 cm2 galvanized (Zn coated) steel cathode. Each electrolysis is conducted at a low initial (0.05A) current to initiate any metal nucleation at the cathode followed by a 1 A electrolysis for 2 h (2 Ah). The observed product is the same without (left side) and with (right side) 0.06 m ZnO added to the 770 °C molten Li2CO3 electrolyte. Figure 4. Cu or Co effect (without Ni) on SEM of the carbon product formed at the cathode following electrolysis in Li2CO3 (without added Li2O) between a planar, square 2.5 by 2.5 cm iridium anode and a coiled wire 10 cm2 galvanized (Zn coated) steel cathode. Top: with 0.06 m CuO; bottom right: with 0.06 m CoO added to the 770 °C molten Li2CO3 electrolyte. Bottom: left EDS analysis of spot shown from the CuO cathode product. Each electrolysis is conducted at a low initial (0.05) current to initiate any metal nucleation at the cathode followed by a 1 A electrolysis for 2 h (2 Ah). concentration, and we see no evidence that Li ion intercalation interferes with the CNF growth. Li intercalation can still occur, but not the explosive exfoliation of the graphite associated with lithium metal deposition (the applied potential is too low to allow Li metal growth). Rather than the straight, uniform diameter CNFs observed in Figure 1, when Li2O is added to the molten Li2CO3 electrolyte the electrolysis product is a proliferation of tangled CNFs of a wide variety of diameters as shown in the Supporting Information. Evidently, high concentrations of oxide localized in the CNF formation region leads to torsional effects (tangling). The cathode consists of galvanized (zinc coated steel. This zinc metal is a critical activator to the observed high-yield CNF production but acts in a manner different than the nickel metal type of nucleation. Unlike Ni, Zn melts at 420 °C and is a liquid at the electrolysis temperature. Figure 3 presents the action of Zn (in the absence of nickel), whether present only as zinc metal on the galvanized steel cathode surface, or additionally as 6146 added as 0.06 m ZnO to the molten Li2CO3 electrolyte on the carbon nanostructures formed at the cathode. In either case, carbon is formed on a 10 cm2 cathode as photographed in the top left of Figure 1, but the anode instead of nickel is a planar 6.3 cm2 square iridium electrode. The observed cathode product conformation consists of spherical ∼1 μm carbon structures gathered in 3 to 6 μm clusters. In addition, a small fraction (<10%) of the washed product is seen to contain CNFs. In the absence of zinc (using either iron or nongalvanized steel cathodes) but in the presence of nickel, produced amorphous graphites and uncontrolled nanofiber structures with diameters ranging from 0.2 to 4 μm and either circular or rectangular duct-like cross sections as shown in the Supporting Information. Figure 4 presents evidence that in addition to Ni, Cu and Co can also act as nucleation sites in the high yield formation of CNFs at the cathode during electrolysis of molten carbonates. Each electrolyte yields CNFs. In the top SEM of the CuO cathode product, EDS analysis of the bright spot shown at the DOI: 10.1021/acs.nanolett.5b02427 Nano Lett. 2015, 15, 6142−6148PDF Image | One-Pot Synthesis of Carbon Nanofibers from CO2
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Sulfur Deposition on Carbon Nanofibers using Supercritical CO2 Sulfur Deposition on Carbon Nanofibers using Supercritical CO2. Gamma sulfur also known as mother of pearl sulfur and nacreous sulfur... More Info
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