Room temperature conversion of CO2 to graphene allotropes in low-melting-point liquid metal electrocatalytic reactor – hydrodynamics control through inverted gas bubbler design

• Diffuser design minimizes coalescence, improving CO₂ delivery to catalytic sites. • A ca. 15-fold increase in current density at -1.6 V vs. RHE achieved through optimized CO₂ bubbling. • Demonstrated 24-h stable electrocatalysis without catalyst deactivation. • CO₂ reduction produced carbon black, graphene, and graphitic carbon. • Galinstan gained 3 × more carbon with graphitic ordering. Electrochemical carbon dioxide (CO₂) reduction presents a promising route for CO₂ utilization into high-value carbon-based products but is often hindered by inefficient gas diffusion towards, and product transport from, the electrochemically active surface area (ECSA) of porous electrodes. This study employs a room-temperature liquid metal (RTLM) electro-catalyst combined with controlled CO₂ bubbling to enhance the production of solid carbon materials, including carbon black, graphene sheets, and graphitic structures under ambient conditions. A custom-designed electrochemical cell was employed to address mass-transport limitations commonly encountered in conventional CO₂ purging configurations. The cell incorporates 3D-printed bubblers positioned to generate an inverted (i.e., positive) CO₂ concentration gradient. As a result, the local CO₂ concentration is highest at the liquid metal | electrolyte interface, thereby improving CO₂ availability at the electrochemically active region and mitigating diffusion-related limitations. This setup increases current densities at low potentials, reaching a ca. 15-fold increase in current density was observed at -1.6 V vs. RHE. Additionally, using RTLM with a nonaqueous electrolyte presented a way to suppress significant side reactions, such as hydrogen evolution reaction (HER), while favoring carbon-based species precipitation