Molten tin-salt liquid–liquid interfaces for graphite synthesis

Abstract

Graphite is a critical mineral facing supply chain risks and growing demand that drives the need for reliable synthetic production methods. This study demonstrates a scalable approach for advanced graphite synthesis through carbonate electrolysis on molten tin-salt liquid–liquid interfaces. These interfaces offer unique physicochemical characteristics that can facilitate the layered sp² carbon growth. Owing to its atomically smooth surface, molten tin suppresses step-edge pinning and defect-mediated nucleation of carbon atoms, while its minimal to no adhesion with carbon facilitates the release of thin carbon layers. Our results indicate that the presence of Co²⁺, Co³⁺ and Ni²⁺ ions at the liquid tin surface can significantly enhance the sp² carbon growth into ultrathin graphitic carbon. The study also demonstrates graphite production at the gram-scale, using custom-designed electrochemical reactor prototypes based on molten tin cathodes. These reactors achieved a low onset cell potential of approximately 1.7–2.0 V, high faradaic efficiencies of up to 96%, current densities exceeding 450 mA cm⁻² and a high carbon production rate of around 0.7 kg m⁻² h⁻¹. This study provides important insights into molten carbonate electrolysis and demonstrates its potential for the scalable CO₂ valorisation into a high-value energy material.