Waste tire heat treatment to prepare sulfur self-doped char via pyrolysis and K2FeO4-assisted activation methods

Waste tire was heat-treated to prepare sulfur self-doped chars via pyrolysis and activation processes. Pyrolytic waste tire chars were activated at different temperatures (600 ?C, 800 ?C, 1000 ?C, and 1200 ?C) with K2FeO4 additive ratios (mass ratio of K2FeO4 to char) being 0.5, 1, 2, and 3, respectively. The effective activation occurred over 600 ?C with K2FeO4 additive ratios over 0.5. The strongest activation occurred at 1000 ?C with K2FeO4 additive ratio of 3, and the specific capacitance increased to 129.5 F/g at 1 A/g, which was six times higher than that without K2FeO4. The activation mechanism revealed that higher K2FeO4 additive ratio promoted the transformation of large aromatic ring systems (>6 rings) to small ones and smaller pores formation. When K2FeO4 additive ratio was less than 2, high ratio not only promoted alkyl-aryl C-C bonds formation, but also inhibited sulfur enrichment with S 2p3/2 (sulphide bridge) converting to S 2p5/2 (sulphone bridge). But when the ratio was further increased, slight decomposition of alkyl-aryl C-C bonds with the promoted conversion of S 2p5/2 to S 2p3/2 was witnessed. Furthermore, higher activation temperature promoted the conversion of aromatic ring systems and alkylaryl C-C bonds to form ordered graphitic structures. S 2p3/2 was enriched before 800 ?C, but both S 2p3/2 and S 2p5/2 were released at higher temperature. Formation of smaller pores was promoted before 1000 ?C, but the char structure was then destroyed to form larger pores when temperature was further increased.