Modulating carbon growth kinetics enables electrosynthesis of graphite derived from CO2 via a liquid–solid–solid process

Abstract

Highly graphitic carbon materials have gained considerable interests in practical applications, however, an efficient and cost-effective synthesis strategy using low-grade carbonaceous precursors is still in urgent need. In this work, we successfully synthesize well-crystalline graphite derived from CO2 by molten carbonate electrolysis under a mild operating temperature, where the as-formed carbon atoms follow a “dissolution–precipitation” process on a Ni cathode. Attributed to that Ni cathode can in situ act as a solid solvent for periodically accommodating/dissolving the as-formed carbon atoms, deliberately coordinating carbon formation flux with carbon dissolution flux can lead to the consecutive production of highly crystalline graphite, without contamination of transition metal catalyst. It was found that a low carbon deposition current density and a relatively high operating temperature (650–750 °C) both facilitate the growth of graphite structures, because a moderate current density enables a suitable carbon flux originating from the electro-reduction of the captured CO2 (in the form of CO32− in molten salts), which can more accessibly match the carbon dissolution flux in Ni substrate at an elevated temperature. The thickness of graphite can be easily controlled by electrolysis durations. This work provides a simple strategy to convert CO2 into graphitic carbon products with both promising purity and crystallinity.