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This paper demonstrates a highly favored route for the synthesis of controlled nanostructures at high rate, high yield, and low cost by molten carbonate electrolysis splitting of CO2. We show the wide, portfolio of carbon nanotubes (CNTs) that can be produced by controlling the electrolysis conditions in this one-pot synthesis. For example solid core carbon nanofibers are formed with C-13 isotope CO2, whereas hollow core CNTs are formed with natural abundance CO2 (which contains 99% C-12 and 1% C-13). Shown are the first doped electrosynthesized carbon nanotubes, prepared with added electrolytic LiBO2 for boron doping, and salts for phosphorous, nitrogen or sulfur CNT doping are probed. Boron doping greatly enhances conductivity of the CNTs. Electrolytic CaCO3 produces thin-walled CNTs, while excess electrolytic oxide yields tangled CNTs. Addition of up to 50 mol% Na2CO3 to a Li2CO3 electrolyte, decreases electrolyte costs and improves conditions for intercalation in Na-ion CNT anodes. Addition of BaCO3 increases electrolyte density. Longer electrolysis time leads to proportionally wider diameter CNTs. Synthetic components (steel cathode, nickel anode and inorganic carbonate electrolyte) are available and inexpensive. Advantages include (1) production is limited only by the cost of electrons (electricity) providing a substantial cost reduction compared to conventional CVD and polymer spinning syntheses and (2) the only reactant consumed in the formation of the CNTs is CO2, transforming this greenhouse gas into a stable, valuable product and providing an economic incentive to the removal of anthropogenic CO2 from flue gas or from the atmosphere.

This SEM, TEM and Raman Spectra and economic calculations data provides a benchmark for carbon nanotubes synthesized via molten electrolyte via the carbon dioxide to carbon nanotube (C2CNT) process useful for comparison to other data on longer length C2CNT wools; specifically: (I) C2CNT electrosynthesis with bare (uncoated) cathodes and without pre-electrolysis low current activation. (II) C2CNT Intermediate length CNTs with intermediate integrated electrolysis charge transfer. (III) C2CNT Admixing of sulfur, nitrogen and phosphorous (in addition to boron) to carbon nanotubes, and (IV) Scalability of the C2CNT process. This data presented in this article are related to the research article entitled “Carbon Nanotube Wools Made Directly from CO2 by Molten Electrolysis: Value Driven Pathways to Carbon Dioxide Greenhouse Gas Mitigation” (Johnson et al., 2017) [1].

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In the solar thermal electrochemical process (STEP), sunlight is split into visible (for photovoltaic electricity) and thermal (unused, sub-bandgap) radiation using the full solar spectrum to efficiently drive high temperature electrolyzes. Electrolysis conditions for STEP ammonia are investigated. A mixed molten carbonate/hydroxide electrolyte with iron oxide catalyzes ammonia formation from water (steam) and air (nitrogen) via an iron intermediate.The higher temperature required for effective iron formation needs to be balanced by the lower temperature for effective hydration of the electrolyte. STEP ammonia is illustrated at a nickel anode and steel cathode at 650 °C in Li 1.6 Ba 0.3 Ca 0.1 CO 3 with 6m LiOH and 1.5mThe Haber-Bosch ammonia process uses H 2 as a reactant, principally produced by natural gas steam reformation (CH 4 + 2H 2 O → 4H 2 + CO 2 ). Ammonia production was 1.45x10 8 tons in 2014; 1 emitting 2x10 8 tonnes of the greenhouse gas CO 2 . Ammonia is a critical resource to produce the world's fertilizer. 2 CO 2 -free alternatives are needed to synthesize ammonia directly from air and water. [3][4][5][6][7][8][9] We utilized Fe 2 O 3 as an electrocatalyst in molten hydroxides for such an electrolysis. 4 Metallic iron was determined as the chemical intermediate, 8 and the Fe 2 O 3 ammonia electrocatalyst can be isolated on activated carbon. 9We introduced an alternative solar energy conversion, STEP (solar thermal electrochemical process) to drive CO 2 -free chemical syntheses. 10-12 For example, STEP cement converts limestone to lime without CO 2 emission, 12,13 similarly STEP fuels, 14-18 STEP iron, 19-23 STEP carbon, 14,24-33 etc. 34,35 STEP uses full insolation, including solar thermal, driving hot electrolyses to desired products. Solar to chemical efficiencies as high as 50%have been observed for CO 2 splitting using photovoltaics and applying their (unused) solar thermal lowering the electrolysis potential. 14 STEP ammonia combines our previous STEP iron (electrolysis of iron oxide to iron in molten salts) and ammonia (electrolysis of air, N 2 , and water to ammonia) chemistries as illustrated in Figure 1. Incident sunlight is split into PV visible and thermal (unused, sub-bandgap) radiation. The solar thermal component heats the electrochemical couple, while the solar PV visible component generates electronic charge to drive electrolysis of the heated electrochemical redox couple. The electrolysis forms anodic oxygen, and cathodic iron (from Fe 2 O 3 ) which reacts with water and nitrogen to form ammonia (and Fe 2 O 3 , renewed to iron in the next cycle).In this communication, we focus on the electrolysis component for STEP ammonia. STEP requires high temperature with molten carbonate to deposit and reform the iron catalyst necessary for sustainable iron. [19][20][21][22][23] Molten hydroxide can be added to establish a foundation for proton availability (2MOH ⇌ M 2 O + H 2 O). However, high temperature dehydrates the electrolyte. Here, a "goldilocks" intermediate temperature range is esta...