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Activated carbon (AC) is a low‐cost and effective catalyst for oxygen reduction in air cathodes of microbial fuel cells (MFCs), but its performance must be maintained over time. AC was modified by three methods: 1) pyrolysis with iron ethylenediaminetetraacetic acid (AC‐Fe), 2) heat treatment (AC‐heat), and 3) mixing with carbon black (AC‐CB). The maximum power densities after one month with these AC cathodes were 35 % higher with AC‐Fe (1410±50 mW m⁻²) and AC‐heat (1400±20 mW m⁻²), and 16 % higher with AC‐CB (1210±30 mW m⁻²) than for plain AC (1040±20 mW m⁻²), versus 1270±50 mW m⁻² for a Pt control. After 16 months, the Pt cathodes produced only 250±10 mW m⁻². However, the AC‐heat and AC‐CB cathodes still produced 960–970 mW m⁻², whereas plain AC produced 860±60 mW m⁻². The performance of the AC cathodes was restored to >85 % of the …