*2.5. The Diverse Range of Carbon Allotropes Formed by Molten Electrolysis*

The top row and middle row of Figure 14 compares microscopy of this study's new carbon allotropes to those structures in the second row that were previously formed by molten electrolysis. The new electrolysis synthesis structures shown are conical CNF, nano-bamboo, nano-pearl, Ni coated CNT, nano-flower, nano-dragon, nano-rod, nano belt, nano-onion (also previously synthesized by alternative methodology in [25]), hollow nano-onion, and nano-tree. The previous distinct nanocarbon structures synthesized were carbon nanotubes ([11], and onward), nano-platelet [28], graphene (a two-step synthesis of CO2 molten electrolysis followed by exfoliation) [27] and nano-helices [20].

Annual anthropogenic emissions of carbon amount to about 7 Gigatons. Can molten carbon splitting of CO2 occur at a sufficient level to mitigate this anthropogenic carbon and mitigate global warming? Yes, but at a massive scale, as previously described [69].

Rather, than building stockpiles of CNMs to mitigate climate change, we put forth that the collective physical chemical properties of graphitic nanocarbon allotropes (including highest strength, high thermal and electrical conductivities, electronic and electrical storage properties, lubrication, medical applications, durable textiles, etc., and properties yet to be discovered) are greatly preferred over conventional materials and provide an incentive for their replacement by CNMs. Coupled with the very low cost of inorganic molten electrolysis (a low cost analogous to the industrial cost of aluminum production by splitting of aluminum oxide, but instead nanocarbon production by splitting of carbon dioxide), these new CNMs provide a value-added logical choice for replacement of these conventional materials, while eliminating CO2. Collectively, replacement of today's annual 9 Gigaton (Gt) usage of these conventional materials (including, annually, production of cement = 4 Gt, steel = 1.6 Gt, aluminum = 0.058 Gt, plastics = 0.37 Gt, wood construction = 2.0 Gt, cotton and wool = 0.1 Gt, paper and cardboard = 0.4 Gt) provides the opportunity to eliminate net anthropogenic CO2 and mitigate climate change.

**Figure 14.** SEM of nanocarbon allotropes synthesized by the electrolytic splitting of CO2 in molten carbonate. Top and middle row: nanocarbon allotropes as introduced and synthesized in this study. Bottom row: as previously synthesized. Top row (from left to right): (**A**): conical CNF, (**B**): nano-bamboo, (**C**): nano-pearl, (**D**): Ni-coated CNT, (**E**): nano-flower, (**F**): nano-dragon. Middle row: (**G**): nano-rod, (**H**): nano-belt, (**I**): nano-onion (also previously synthesized by alternative methodology in [25]), (**J**): hollow nano-onion, and (**K**): nano-tree. Bottom row (from left to right) (**L**): Carbon nanotube ([9]), (**M**): nano-scaffold ([28]), (**N**): nano-platelet ([27]), (**O**): graphene (2 step process, [27]), (**P**,**Q**): nano-helices ([20]).

#### *2.6. Raman and XRD of the New Structures Formed by Molten Electrolysis*

Figure 15 presents the effect of variation of the electrolysis conditions on the Raman spectra and XRD of the new carbon products of CO2 electrolysis in 770 ◦C Li2CO3. For comparison purposes, also included are the Raman spectra of the CNTs [29,38]. The graphitic fingerprints lie in the 1880–2300 cm−<sup>1</sup> and are related to different collective vibrations of sp-hybridized C-C bonds. The tangential G-band (at ~1580 cm−1) is derived from the graphite-like in-plane mode of E2G symmetry, and can be split into several modes, two of which are most distinct: the G1 (1577 cm−1) and G2 (1610 cm−1). The Raman spectrum exhibits two sharp peaks ~1350 and ~1580 cm<sup>−</sup>1, which correspond to the disorder-induced mode (D band) and the high frequency E2G first order mode (G band),

respectively, and an additional peak, the 2D band, at 2700 cm−1. The G' peak at ~2300, is related to the collective stretching vibrations of sp-hybridized C–C bonds.

**Figure 15.** Raman of the synthesis product consists of various labeled CNMs and packed carbon nanotube assemblies synthesized by the electrolytic splitting of CO2 in 770 ◦C Li2CO3 with a variety of systematically varied electrochemical conditions.

The intensity ratio between D band and G band (ID/IG) is a useful parameter to evaluate the relative number of defects and degree of graphitization. Table 4 summarizes Raman band peak locations and includes calculated (ID/IG) and (I2D/IG) peak ratios for the various carbon allotropes. A higher ratio ID/IG or a shift in IG frequency15 is a measure of increased defects in the carbon graphitic structure [70]. Defects that can occur in the graphitic structure include replacement of carbon sp<sup>2</sup> bonds, typical of the hexagonal carbon configuration in the graphene layers comprising the structures, with sp3, increase in pores or missing carbon in the graphene, and enhancement of defects that cause formation of heptagonal and pentagonal, rather than the conventional hexagonal, graphene building blocks of graphene [71].

Typically, ID/IG for multi-walled carbon nanotubes is in the range of 0.2 to 06. Compared to these values, with the exception of the hollow nano-onions, the new carbon allotropes generally exhibit a higher than 0.6 ID/IG, evidence of a higher number of defects and perhaps consistent with the greater morphological complexity of these new allotropes. The nanocarbon bamboo, pearl, annular and belts each exhibit a relatively high level of defect, often associated with greater pores and twists and turns in the structure due to the higher presence of sp<sup>3</sup> carbons. As observed from Table 4, the order of the increasing ID/IG ratio is

CNT < hollow nano-onion < dragon < flower < trees < bamboo < pearl < rod < CNF < belt.

The shift to higher frequencies of the frequency, ν, of the G band generally correlates with the observed ID/IG variation, with variations due to near lying ratios, and with the exception of an unusually large shift for nano-bamboo.

High levels of Ni, Cr or Co added to the electrolyte (nano-bamboo, nano-pearl and nano-flower allotropes) also appear to correlate with an increase in defects, and the very high added Ni powder used in the nano-rod synthesis correlates with a very high level of defects as indicated by the shift in IG frequency and an increase in ID/IG. Previously, increased concentrations of iron oxide added to the Li2CO3 electrolyte correlated with an increasing degree of disorder in the graphitic structure [20,21]. Interestingly, it is the synthesis with a low level of added iron oxide powder (but only added prior to the 24 h aging of the electrolyte) that results in the CNMs with the highest level of defects, the nano-belt CNM.

Lower defects are associated with applications which require high electrical conductivity and strength, while high defects are associated with applications which permit high diffusivity through the structure, such as those associated with increased intercalation and higher anodic capacity in Li-ion batteries and higher charge super capacitor.

Along with the XRD library of relevant compound spectra, XRD is presented in Figure 16 of the new nanocarbon morphologies products, prepared as summarized in Tables 2 and 3, and with SEM in Figures 2, 7 and 8. Each of the spectra exhibit the strong, sharp diffraction peak at 2*θ* = 27◦ characteristic of graphitic structures, and no indication of the broad peak indicative of amorphous carbon. In addition to graphite, the products XRD are grouped by which metal salts are present. Nano-bamboo exhibits the simplest composition with only a lithiated nickel salt present. The next most complex compositions, seen in the middle of Figure 16, are nano-dragons, nano-flowers and nano-trees, which also include the iron carbide salt Fe3C. The next most complex composition is exhibited in the figure in the lower left hand corner, for hollow nano-onions, which exhibit each of those previous metal salts as well as a lithiated chromium(III) salt. Finally, both nano-belt and nano-pearls include an additional lithiated copper salt, and it may be noted that they were respectively synthesized with a Muntz brass and a Monel cathode which contain copper. However, the source of the copper requires further investigation. To enter the nanocarbon, the copper may need to dissolve from the cathode, which is under cathodic bias. This did not occur with the other CNM products. The nano-belt XRD spectra is distinct from the others having a dominant peak at 2*θ* = 43◦, reflecting a higher concentration of metals than in the other products. The diminished presence of defects previously noted by the Raman spectra for the hollow nano-onion morphology, along with the XRD presence of Li2Ni8O10, LiCrO2 and Fe3C provide evidence that the co-presence of Ni, Cr and Fe as nucleating agents can diminish defects in the structure compared to Ni. On the other hand, the enhanced presence of defects previously noted by the Raman spectra for the nano-belt and nano-pearl morphologies, along with the XRD presence of LiCuO2, provide evidence that the copper salt increases defects in the structure compared to Ni, Fe or Cr as transition meal nucleating agents. Finally, it should be noted that the singular (amongst all the electrolyses) addition of cobalt powder to Electrolyses XIV and XV must be correlated

with the subsequent observed formation of the nano-flower allotrope. However, this cobalt does not make its way into the product as analyzed by XRD in Figure 16, is observed only in trace quantities by HAADF TEM (to be delineated and probed in future studies) and presumably has another role in promoting formation of this unusual products.

**Figure 16.** XRD of the synthesis product consisting of various labeled unusual nanocarbon morphologies synthesized by the electrolytic splitting of CO2 in 770 ◦C Li2CO3 with a variety of systematically varied electrochemical conditions. (**A**,**A-1**,**A-2**): XRD over various ranges of 2*θ*.
