Quantitative Insight into the Critical Role of Exchange Current Density on the Electrodeposition of Nano-Carbon

Molten salt electrochemical CO₂ conversion offers a promising route to close the carbon cycle by producing functional carbon materials and O₂. However, insufficient understanding of the mechanisms governing electrodeposited carbon microstructure and crystallinity hinders its tailored synthesis for energy storage and catalysis. This study reveals how electrode exchange current density (<i>i</i>₀) regulates deposition through coupled flow-field modeling, phase-field modeling, and experiments. We demonstrate accelerated kinetics on high-<i>i</i>₀ electrodes (stainless steel > tungsten > glassy carbon), driving thicker deposits though simultaneously inducing a kinetic-transport paradox: enhanced charge transfer triggers dense carbon layers that block O^2- diffusion. This is evidenced by morphological transitions (carbon nanotubes → spheres) and increased Raman D/G ratios (0.98 → 1.19), establishing an oxygen-retention-mediated graphitization compromise mechanism that guides electrode design for carbon capture technologies.