The production of H₂O₂ via two-electron oxygen reduction reaction (ORR) is foreseen as a greener and decentralized alternative to the industrially dominant anthraquinone process. [1] This has been particularly promoted in the water treatment sector, owing to the high effectiveness of H₂O₂-based electrochemical advanced oxidation processes (EAOPs) to degrade water contaminants. [2] The use of carbonaceous air-diffusion cathodes appears as a suitable choice for this purpose due to their low cost and high activity/selectivity. On the other hand, mesoporous carbon supports are needed to both reduce the amount of noble metals employed as electrocatalysts in proton-exchange fuel cells (PEMFCs) and enhance the accessibility of reactants to the active sites. For both applications, our groups are developing mesoporous carbons obtained from abundant biomass resources such as chitosan and agarose, thereby fostering a circular economy approach. First, the excellent electrocatalytic performance of N-doped chitosan-derived carbons and large surface area agarose-derived carbons (Fig. 1a) is discussed, showing that current efficiencies above 95% (> 10 mM H₂O₂) can be achieved at 10 mA/cm², allowing the fast destruction of a pharmaceutical residue in electro-Fenton treatment (Fe²⁺ + H₂O₂ at acidic pH). [3] Second, chitosan-derived mesoporous carbons served as optimal supports for PtCu electrocatalysts, evidencing an increased activity of both the four-electron ORR (Fig. 1b) and the methanol oxidation reaction as compared to commercial supported Pt and PtCu catalysts, which is attributed to the good balance between micro/mesoporosity.[4]