Microbial fuel cells (MFCs) represent a sustainable alternative to generate energy from wastewater treatment, reducing the consumption and pollution of fossil fuels, which are used in traditional technologies. An effective way to improve the performance of MFCs is the use metal-free carbon-based anode catalysts, which have shown high catalytic activity with significantly lower cost than noble metals. In this study, the synthesis and characterization of methanol-functionalized carbon catalysts is reported. Onion waste has been thermochemically treated via carbonization, chemical activation with ZnCl₂ and pyrolysis at 400, 600 and 800 ºC (named CCA4, CCA6 and CCA8, respectively). Graphite flakes have been ball milled in the presence of thiourea and ZnCl₂, followed by pyrolysis at a 500 ºC in order to obtain the graphene catalyst (named GNS). Subsequently, the carbons have been submitted to surface functionalization with methanol using the intermittent microwave heating technique to produce the CCA4f, CCA6f, CCA8f and GNSf catalysts. Anodes have been fabricated by depositing catalytic layers (separately) of CCA4f, CCA6f, CCA8f and GNSf on gas diffusion electrodes. The catalytic activity of the anodes has been evaluated by cyclic voltammetry (VC) in a three electrodes half-cell, using Pharmaceutical Wastewater (PWW) as electrolyte, and compared to that of a gas diffusion electrode without catalyst. The results show that the mechanochemical treatment of graphite in the presence of thiourea modifies its crystalline structure producing the heteroatoms-doped GNS. Meanwhile, CCA4, CCA6 and CCA8 have an amorphous structure self-doped with the N and S heteroatoms. The catalysts are thermally stable at 700 ºC and exhibit a highly heterogeneous morphology. Nitrogen adsorption-desorption and BET analyses indicate that the activation with ZnCl₂ promotes the formation of mesoporous structures with average pore size ranging from 11.38 (GNSf) to around 2 nm (CCA4f, CCA6f and CCA8f). Moreover, the specific surface areas of CCA4f, CCA6f and CCA8f (1468, 1611 and 1269 m² g^-1, respectively) are approximately 20 times higher than that of GNSf (69.7 m² g^-1). The electrochemical characterization demonstrates that the increase in activation temperature improves the catalytic activity of the CCAf series of catalysts for the oxidation of organic matter in the PWW electrolyte. The current density (j) decreases in the order CCA8f>CCA6f>CCA4f. On the other hand, the catalytic activity of GNSf is less than those of CCA8f and CCA6f, but similar to CCA4f. The results show that the metal-free CCAf carbons have the potential to be used as anode catalysts in MFCs.