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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...

Displaying superior strength, conductivity, flexibility and durability, carbon nanotube (CNT) applications had been limited due to the cost intensive complexities of their synthesis. We present an inexpensive, high-yield and scale-able synthesis of CNTs. We show that common metals act as CNT nucleation sites in molten media to efficiently drive the unexpected, high yield electrolytic conversion of CO2 dissolved in molten carbonates to CNTs. We accomplish this by electrochemically reducing CO2 on steel electrodes in a molten carbonate electrolyte. The CNT structure is tuned by controlling the electrolysis conditions, such as the addition of trace common metals to act as CNF nucleation sites, the concentration of added oxide, the addition of initiators and the control of current density. The process can be driven by efficient solar, as well as conventional, energy. Scalability of the process is demonstrated from 1 A to 100A. An inexpensive source of CNTs made from carbon dioxide will facilitate the rate of its adoption as an important societal resource for the building, aerospace, transportation, renewable energy, sporting and consumer electronics industries, while concurrently consuming carbon dioxide. As the levels of carbon dioxide (CO2) increase in the Earth’s atmosphere, the effects on climate change become increasingly apparent. An incentive to remove the greenhouse gas carbon dioxide is provided by its low energy, low cost, high yield conversion to valuable products such as carbon nanotubes. We've previously shown that carbon dioxide can be captured directly from the air at solar efficiencies as high as 50%, and that carbon dioxide associated with cement formation and the production of other commodities, such as ammonia and iron, can be electrochemically avoided in the STEP process.1-6 Here we show the effective capture of CO2 and its conversion at high yield to carbon nanotubes at low energy and high yield by dissolution in molten carbonates and splitting by electrolysis in molten carbonate to carbon nanotubes and oxygen.9-15 References 1Licht, STEP generation of energetic molecules: A solar chemical process to end anthropogenic global warming, J. Phys. Chem. , C, 113, 16283 (2009). 2Licht, Wang, Ghosh, Ayub, Jiang, Ganley, New Solar Carbon Capture Process: Solar Thermal Electrochemical Photo (STEP) Carbon Capture J. Phys. Chem. Lett ,1, 2363 (2010). 3Licht, Efficient Solar-Driven Synthesis, Carbon Capture, and Desalinization, STEP: Solar Thermal Electrochemical Production of Fuels, Metals, Bleach Advanced Materials ,47, 5592 (2011). 4Licht, Wu, Hettige, Wang, Lau, Asercion, Stuart, STEP Cement: Solar Thermal Electrochemical Production of CaO without CO2emission, Chemical Communications , 48, 6019 (2012). 5Licht, Cui, Wang, STEP Carbon Capture: the barium advantage, J. CO 2 Utilization , 1, 58 (2013). 6Licht, Cui, Wang, Li, Lau, Liu, Ammonia synthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3, Science, 345, 637 (2014). 7Cui,  Zhang, Liu, Liu, Xiang,  Liu, Xin, Lefler, Licht, Electrochemical synthesis of ammonia directly from N2 and water over iron-based catalysts supported on activated carbons, Green Chemistry , 2 DOI: 10.1039/C6GC02386J (2016). 8Li, Wang, Licht, Sustainable Electrochemical Synthesis of large grain or catalyst sized iron , J. Sustainable Metallurgy , 2, 405 (2016). 9Ren, Li, Lau, Gonzalez-Urbina, Licht, One-pot synthesis of carbon nanofibers from CO2, Nano Letters , 15, 6142 (2015). 10Ren, Lau, Lefler, S. Licht, The minimum electrolytic energy needed to convert carbon dioxide by electrolysis in carbonate melts, J. Phys. Chem. , C, 119, 23342 (2015). 11Licht, Douglas, Ren, Carter, Lefler, Pint, Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes, ACS Central Science , 2, 162 (2015). 12Ren, Lau, Lefler, Licht, The minimum electrolytic energy needed to convert carbon dioxide by electrolysis in carbonate melts, J. Phys. Chem. , C, 119, 23342 (2015). 13Lau, Dey, Licht, Thermodynamic assessment of CO2to carbon nanofiber transformation for carbon sequestration in a combined cycle gas or a coal power plant, Energy Conservation and Management , 122, 400 (2016). 14Wu, Li, Ji, Liu, Li, Yuan, Zhang, Ren, Lefler, Wang, Licht, One-Pot Synthesis of Nanostructured Carbon Material from Carbon Dioxide via Electrolysis in Molten Carbonate Salts, Carbon , 6, 27760 (2016). 15Ren, Licht, Tracking airborne CO2mitigation and low cost transformation into valuable carbon nanotubes, Scientific Reports , 106, 208 (2016). Figure: Molten carbonate electrolysis pathways converting CO2 leading to a high yield, uniform CNF product. Figure 1

As the levels of carbon dioxide (CO2) increase in the Earth’s atmosphere, the effects on climate change become increasingly apparent. With the demand to reduce our dependence on fossils fuels and lower our carbon emissions, a transition to renewable energy sources is necessary. Cost effective large-scale electrical energy storage must be established for renewable energy to become a sustainable option for the future. We've previously shown that carbon dioxide can be captured directly from the air at solar efficiencies as high as 50%, and that carbon dioxide associated with cement formation and the production of other commodities, such as ammonia and iron, can be electrochemically avoided in the STEP process.1-6 The carbon molten air battery, presented by our group in late 2013,7 as one of a new class of rechargeable “molten air” batteries that utilize a molten electrolyte and a quasi-reversible air electrode,7-10 is attractive due to its scalability, location flexibility, and construction from readily available resources, providing a battery that can be useful for large scale applications, such as the storage of renewable electricity. Uncommonly, the carbon molten air battery can utilize carbon dioxide directly from the air:7,11-18 charging: CO2(g) → C(solid) + O2(g) (1) discharging: C(solid) + O2(g) → CO2(g) (2) More specifically, in a molten carbonate electrolyte containing added oxide, such as lithium carbonate with lithium oxide, the 4 electron charging reaction eq. 1 approaches 100% faradic efficiency and can be described as the following two equations: O2- (dissolved) + CO2(g) → CO3 2- (molten) (1a) CO3 2- (molten) → C(solid) + O2(g) + O2- (dissolved) (1b) Using carbon formed directly from the CO2in our earth’s atmosphere, the carbon molten air battery is a viable system to provide large-scale energy storage. References 1Licht, STEP generation of energetic molecules: A solar chemical process to end anthropogenic global warming, J. Phys. Chem., C, 113, 16283 (2009). 2Licht, Efficient Solar-Driven Synthesis, Carbon Capture, and Desalinization, STEP: Solar Thermal Electrochemical Production of Fuels, Metals, Bleach Advanced Materials ,47, 5592 (2011). 3Licht, Wu, Hettige, Wang, Lau, Asercion, Stuart, STEP Cement: Solar Thermal Electrochemical Production of CaO without CO2emission, Chemical Communications , 48, 6019 (2012). 4Licht, Cui, Wang, Li, Lau, Liu, Ammonia synthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3, Science, 345, 637 (2014). 5Cui,  Zhang, Liu, Liu, Xiang,  Liu, Xin, Lefler, Licht, Electrochemical synthesis of ammonia directly from N2 and water over iron-based catalysts supported on activated carbons, Green Chemistry ,2 DOI: 10.1039/C6GC02386J (2016). 6Li, Wang, Licht, Sustainable Electrochemical Synthesis of large grain or catalyst sized iron , J. Sustainable Metallurgy ,2, 405 (2016). 7Licht, Cui, Stuart, Wang, Lau, Molten Air Batteries - A new, highest energy class of rechargeable batteries, Energy & Environmental Science ,6, 3646 (2013). 8Liu, Li, Cui, Liu , Hao, Guo, Pe. Xu, Licht, Critical advances for the iron molten air battery: A new lowest temperature, rechargeable, ternary electrolyte domain, J. Materials Chemistry, A ,3, 21039 (2015); ibid, 2, 10577 (2014). 9Cui,  Xin, Liu,  Liu,  Hao,  Guo, Licht, Improved cycle iron molten air battery performance using a robust fin air electrode,” J. Electrochem. Soc. ,in press (2016). 10Cui, Xiang, Liu,  Xin, Liu Licht, A novel rechargeable zinc-air battery with molten salt electrolyte, J. Power. Sources ,in press (2017). 11Licht, Cui, Wang, STEP Carbon Capture: the barium advantage, J. CO2 Utilization ,1, 58 (2013). 12Ren, Li, Lau, Gonzalez-Urbina, Licht, One-pot synthesis of carbon nanofibers from CO2, Nano Letters , 15, 6142 (2015). 13Ren, Lau, Lefler, S. Licht, The minimum electrolytic energy needed to convert carbon dioxide by electrolysis in carbonate melts, J. Phys. Chem. , C, 119, 23342 (2015). 14Licht, Douglas, Ren, Carter, Lefler, Pint, Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes, ACS Central Science , 2, 162 (2015). 15Ren, Lau, Lefler, Licht, The minimum electrolytic energy needed to convert carbon dioxide by electrolysis in carbonate melts, J. Phys. Chem. , C, 119, 23342 (2015). 16Lau, Dey, Licht, Thermodynamic assessment of CO2to carbon nanofiber transformation for carbon sequestration in a combined cycle gas or a coal power plant, Energy Conservation and Management , 122, 400 (2016). 17Wu, Li, Ji, Liu, Li, Yuan, Zhang, Ren, Lefler, Wang, Licht, One-Pot Synthesis of Nanostructured Carbon Material from Carbon Dioxide via Electrolysis in Molten Carbonate Salts, Carbon , 6, 27760 (2016). 18Ren, Licht, Tracking airborne CO2mitigation and low cost transformation into valuable carbon nanotubes, Scientific Reports , 106, 208 (2016). Figure: Variations of the Molten Battery. Figure 1

We’ve demonstrated multiple electron per molecule processes yield higher battery storage capacity, introducing a variety of novel storage chemistries including high efficiency in-situ photoelectrochemical solar cells,1,2 aluminum sulfur battery,3 super-iron battery,4 ammonia useful for fuel cells,5 and zirconia on VB2 batteries.6 Unusual multiple electron opportunities abound. For example, not only redox active oxygen from air, but also redox active carbon dioxide from air can be utilized for charge storage.7,8 The Licht group has recently introduced a new class of multiple electrons per molecule battery: Molten Air Batteries.9-14 These new batteries use multi-electron charge storage, a molten electrolyte, are quasi-reversible (rechargeable), and have amongst the highest intrinsic battery storage capacities. This talk will focus on advances in the molten air class of rechargeable batteries including carbon (4 electron storage), iron (3 electron storage) and VB2 (11 electron storage). For example, uncommonly, the carbon molten air battery can utilize carbon dioxide directly from the air or from industrial smoke stacks: charging: CO2(g) -> C(solid) + O2(g) (1) discharging: C(solid) + O2(g) -> CO2(g) (2) 1) S. Licht, G. Hodes, R. Tenne, J. Manassen, A Light Variation Insensitive High Efficiency Solar Cell" Nature , 326, 863-864 (1987). 2) S. Licht, "A Description of Energy Conversion in Photoelectrochemical Solar Cells" Nature , 330, 148-151 (1987). 3) D. Peramunage, S. Licht, "A Novel Solid Sulfur Cathode for Aqueous Batteries" Science , 261, 1029-1032 (1993). 4) S. Licht, B. Wang, S. Ghosh, "Energetic Iron(VI) Chemistry: The Super-Iron Battery," Science , 285, 1039-1042 (1999). 5) S. Licht, B. Cui, B, Wang, F.-F. Li, J. Lau, S, Liu, "Ammonia synthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3," Science, 345 , 637-640, (2014). 6) S. Licht, H. Wu, X. Yu, Y. Wang, "Renewable Highest Capacity VB2/Air Energy Storage," Chemical Communication , 2008, 3257-3259 (2008). 7) S. Licht, A. Douglas, R. Carter, M. Lefler, C. L. Pint, C. “Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes,” ACS Central Science , 2, 162-168 (2015). 8)J. Ren, S. Licht, “Tracking airborne CO2 mitigation and low cost transormation into valuable carbon nanotubes,” Scientific Reports, 6, 27760-1-11 (2016). 9) S. Licht, B. Cui, J. Stuart, B. Wang, J. Lau, "Molten Air Batteries - A new, highest energy class of rechargeable batteries," Energy & Environmental Science ,6, 3646-3657, with 2 pages supplementary information (2013). 10) B. Cui, S. Licht, "A Low Temperature Iron Molten Air Battery," Journal of Materials Chemistry A , 2, 10577-10580, with 3 pages supplementary (2014). 11) S. Liu, X. Li, B. Cui, X. Liu , Y. Hao, Q. Guo, P. Xu, S. Licht, "Critical advances for the iron molten air battery: A new lowest temperature, rechargeable, ternary electrolyte domain," Journal of Materials Chemistry A, 3, 21039-21043, with 2 page Supplementary Info (2015). 12) B. Cui, X. Xiang, S. Liu, H. Xin, X. Liu, and Stuart Licht, "A novel rechargeable zinc-air battery with molten salt electrolyte," Journal of Power Sources, 342, 435-441. (2017). 13) B. Cui, H. Xin, S. Liu, Xianjun Liu, Y. Hao, Q. Guo, and S. Licht, "Improved cycle iron molten air battery performance using a robust fin air electrode," Journal of the Electrochemical Society , 164, A88-A92 (2017). 14) Baochen Cui, Wei , Xiang, Shuzhi Liu, Hongyu Xin, Xianjun Liu, and Stuart Licht, "A long cycle life, high coulombic iron molten air battery," Sustainable Energy & Fuels , cover article, in press (2017).