Sustainable Carbons and Fuels: Recent Advances of CO₂ Conversion in Molten Salts

Abstract

Dedicated to Prof. Mingyuan He on the occasion of his 80th birthday. The massive release of the greenhouse gas CO 2 has resulted in numerous environmental issues. In searching for advanced technologies for CO 2 capture/conversions, recent advances in electrochemical reduction of CO 2 in molten salts shed a light on potential solutions to CO 2 mitigation. Electro-reduction of CO 2 in molten salts exhibits features like high selectivity and efficiency towards sustainable carbons and fuels, low toxicity, and possibility to combine with in situ CO 2 capture. In this Minireview, we highlight the tuning of the products in this process and mainly discuss two categories of electrolyte, carbonate-based molten salts (CMS) and those based on halides (HMS). Depending on the synthetic conditions, fuels such as CO or hydrocarbons (in the presence of hydrogen source, i. e., LiOH, NaOH, or KOH in the electrolyte) as well as high-value nanostructured carbons including carbon nanotubes, carbon nanofibers, carbon nano-onions, and graphene can be obtained with high efficiency. The synthesis parameters are compared, and the applications of as-obtained carbons are briefly summarized. Additionally, some perspectives on this technology are also discussed. 2. CO 2 Conversion in Carbonate-Based Molten Salts 2.1. Fundamentals of carbonate molten salts Molten carbonates, including alkali metal and alkali earth metal carbonates, are commonly used as electrolytes for electrolysis [a] A

A MnOx–graphitic carbon composite from CO2 for sustainable Li-ion battery anodes

“…One proposed method for splitting CO 2 is the molten salt CO 2 capture and electrochemical transformation (MSCC-ET) method [3,4] . With this method, the CO 2 molecule is transformed into solid carbon and gaseous oxygen via a molten salt intermediate with efficiency typically > 90 % [5] . Various carbon products, such as carbon nanofibers (CNF), carbon nanotubes (CNT), graphite and graphene, have been successfully prepared in molten salts via the MSCC-ET method [6] .…”

Bio‐inspired and Eco‐friendly Synthesis of 3D Spongy Meso‐Microporous Carbons from CO2 for Supercapacitors

“…Carbon nanotubes, [7] carbon nanofibers, [8] carbon nano‐onions, [9] carbon nanosheets, [10] graphene, [11] heteroatom‐doped carbons [12] etc. have been successfully synthesized by electrochemical reduction of CO 2 in molten salts [13] . Moreover, the structures of the CO 2 ‐derived products can be tuned by electrolysis conditions [13–14] …”

“…have been successfully synthesized by electrochemical reduction of CO 2 in molten salts [13] . Moreover, the structures of the CO 2 ‐derived products can be tuned by electrolysis conditions [13–14] …”

“…have been successfully synthesized by electrochemical reduction of CO 2 in molten salts. [13] Moreover, the structures of the CO 2 -derived products can be tuned by electrolysis conditions. [13][14] Herein, inspired by the spongy bone structure, 3D spongy meso-microporous carbon (SPC) is successfully prepared by one-step electro-reduction of the dissolved CO 2 in the molten eutectic carbonates Li 2 CO 3 À Na 2 CO 3 À K 2 CO 3 .…”

“…[13] Moreover, the structures of the CO 2 -derived products can be tuned by electrolysis conditions. [13][14] Herein, inspired by the spongy bone structure, 3D spongy meso-microporous carbon (SPC) is successfully prepared by one-step electro-reduction of the dissolved CO 2 in the molten eutectic carbonates Li 2 CO 3 À Na 2 CO 3 À K 2 CO 3 . The synthesized SPC4-0.5 shows uniform 3D sponge-like structure with mesomicropores.…”