Critical Role of Carbon Electrode Properties in Submerged Arc Plasma Behavior and Resulting Nanocarbon Particle Morphology

This study investigates the influence of carbon electrode properties on plasma behavior and morphology of nanocarbon in submerged arc discharge (SAD) synthesis. Two commercially available graphite rods with contrasting physical and electrical properties-fine-grained, low-resistivity Rod 1 and coarse-grained, high-resistivity Rod 2-were employed as anodes in a dc arc configuration submerged in deionized water. Time-synchronized currentvoltage ( $I$ – $V$ ) and optical emission spectroscopy (OES) diagnostics were used to derive plasma ionization energy distributions, which were further correlated with the morphology of synthesized nanocarbons via high-resolution transmission electron microscopy (HRTEM). Rod 1 consistently produced a lower voltage arc with greater stability and a narrower ionization energy spectrum, concentrated below 4 eV, leading to the formation of spherical carbon nano-onions (CNOs) due to rapid quenching and shell closure dynamics. In contrast, Rod 2 exhibited a broader energy distribution extending beyond 10 eV, associated with a hotter, less stable arc and increased production of multiwalled carbon nanotubes (MWCNTs) and few-layer graphene sheets. The findings reveal that microstructural parameters, such as grain size, porosity, and resistivity, critically influence arc ignition, plasma energetics, and product selectivity. These insights demonstrate the utility of integrated electrical and spectroscopic diagnostics in tailoring SAD conditions for tunable nanomaterial synthesis and highlight electrode engineering as a key parameter for directing carbon nanostructure growth in plasma-based processes.