“…Depending on the synthesis method and processing parameters, the size of carbon onions may range from around 2-50 nm [5,6]. So far, carbon onions have been synthesized by several techniques, such as arc discharge [7][8][9], electron beam irradiation [2,10], catalytic decomposition of carbon-containing precursors [11][12][13][14], heat treatment of nanodiamonds [15][16][17], mechanical milling [18], carbon ion beam implantation [19,20], and detonation reactions [21]. Due to their nanoscopic size and facile fabrication, carbon onions have attracted significant interest for various applications, such as a conductive additive [22], solid state lubricant [23], field emitters [24,25], in polymer composites for electromagnetic shielding [26], or as electrode material for supercapacitors with high power density [5,27].…”