Transformation of Waste Coca-Cola® and Pepsi® into Activated Carbons with Enhanced Electrocatalytic Performance for Oxygen Reduction in Alkaline Media

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Abstract
This study investigates the morphological, compositional, and electrochemical properties of carbon materials derived from Pepsi (P) and Coca-Cola (CC) precursors, before and after chemical activation with ZnCl2. Scanning electron microscopy revealed a lower density of surface cracks in non-activated hydrothermal carbon (NAHC) samples compared to activated carbons (ACs), indicating structural changes induced by the corrosive activation process. Particle size analysis showed an increase in average diameter after activation, particularly pronounced in CC-derived samples, which also exhibited a broader particle size distribution. Elemental mapping confirmed carbon as the dominant and homogeneously distributed element, while oxygen-containing functional groups decreased significantly after activation. Oxygen reduction reaction investigation demonstrated that all synthesized non-activated and activated samples are electrocatalytically active in alkaline solution. CC-NAHC demonstrated the lowest Tafel slope (99 mV dec−1), while activated samples showed higher values, indicating slower kinetics and increased reaction limitations. Despite this, activated carbons—particularly CC-AC—displayed significantly higher diffusion-limited current densities (~−4.8 mA cm−2 at 1600 rpm), suggesting improved mass transport and conductivity. Furthermore, electron transfer number (n) analysis indicated that P-NAHC and CC-AC follow a near four-electron ORR pathway (n ≈ 3.6–3.9).
Funding Information
  • Ministry of Science, Technological Development and Innovation of the Republic of Serbia (451-03-34/2026-03/200146)
  • Ministry of Science, Technological Development and Innovation of the Republic of Serbia (451-03-33/2026-03/200146)
  • Foundation for Science and Technology, FCT, Portugal (LA/P/0095/2020)
  • Foundation for Science and Technology, FCT, Portugal (UID/PRR2/04540/2025)

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