Transformation of the greenhouse gas CO2 by molten electrolysis into a wide controlled selection of carbon nanotubes

Abstract

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.

Optimized Electrolytic Carbon and Electrolyte Systems for Electrochemical Capacitors

“…In more recent years this understanding of the molten carbonate system has paved the way for an increased understanding of both the mechanism of carbon formation from molten carbonate salts, [39][40][41] and for the application of molten carbonate reduction in attempts to produce carbons with specific properties or morphologies. [31,39,42,43] The research presented here continues from the work of this group, [27,28] which has shown how temperature, current density, substrate, and electrolyte variation influences the morphology of carbonate derived carbons, and how these morphological changes relate to aqueous supercapacitive performance in the materials. [27,28] This has indicated that electrochemical performance in aqueous systems is at its highest for materials showing elevated amorphous character, which contributes to increased double layer formation, [28] and high oxygen functionalization, which leads to high pseudo-capacitance.…”

Carbon Nano‐Onions Made Directly from CO2 by Molten Electrolysis for Greenhouse Gas Mitigation

“…[1,[29][30][31][32][33][37][38][39] Nickel and nickel alloys form a thin, stabilizing oxide layer when used as an anode, and the net reaction is the four electron reduction of CO 2 to form the building block carbons of CNTs. In the presence of transition metal nucleation agents such as nickel and chromium, we have demonstrated the controlled growth of carbon nanotubes from CO 2 as it is dissolved in a molten carbonate electrolyte.…”

“…[23] Carbon nano-onions can also be synthesized using arc discharge, laser ablation and plasma processes, shock compression techniques, autoclave processes (catalytic and noncatalytic), and by carbonization routes, [24] thermal pyrolysis of alcohol at high 2700 K, [25] and high fluence 120 keV implantation of carbon ions into copper and silver. In 2015 we introduced a chemistry to synthesize CNTs at high yield by electrolysis of CO 2 , [1,[29][30][31][32][33][35][36][37][38][39] rather than their conventional CVD synthesis from organometallics. [6] Challenges to the bulk production of bulk carbon nano-onions has limited their commercial availability.…”

“…[35,36] High yield, low electrolysis voltage, and high uniformity CNTs were demonstrated to be produced from dissolved CO 2 in a variety of alkali and alkali-earth carbonate electrolytes, [32,33] and straight (low defect) or tangled (high defect) were controlled through the addition or exclusion of oxide added to the molten carbonate electrolyte. [35,36] High yield, low electrolysis voltage, and high uniformity CNTs were demonstrated to be produced from dissolved CO 2 in a variety of alkali and alkali-earth carbonate electrolytes, [32,33] and straight (low defect) or tangled (high defect) were controlled through the addition or exclusion of oxide added to the molten carbonate electrolyte.…”

“…[35,36] High yield, low electrolysis voltage, and high uniformity CNTs were demonstrated to be produced from dissolved CO 2 in a variety of alkali and alkali-earth carbonate electrolytes, [32,33] and straight (low defect) or tangled (high defect) were controlled through the addition or exclusion of oxide added to the molten carbonate electrolyte. [1,33,38] In this study we provide for the first time an exploration of the initial phases of molten carbonate electrolysis CNT growth showing their relevance to discovery and introduction here of an alternative high yield carbon nano-onion synthesis: www.advsustainsys.com [1,33,38] In this study we provide for the first time an exploration of the initial phases of molten carbonate electrolysis CNT growth showing their relevance to discovery and introduction here of an alternative high yield carbon nano-onion synthesis: www.advsustainsys.com…”