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Biodegradation of oil-contaminated sediments (OCS) in sediment microbial fuel cells (SMFC) is limited by several factors such as adapted microorganisms to degrade OCS, low conductivity and organic matter content, sluggish cathodic O2 reduction reaction (ORR), among others. The use of a birnessite/Carbon Fabric (CF) cathode improves the O2 reduction in SMFC. Oil-contaminated sediments amended with chitin (commercial analytical grade (CC) and dried natural shrimp shells (NC)) allows faster anaerobic biodegradation in the anolyte by the indigenous bacteria coming in the initial OCS, without further growth media. The SMFC containing the unmodified OCS produces a maximum power output of 5 mW m−2 in contrast to 62 mW m−2 and 178 mW m−2 of that SMFC containing CC and NC, respectively. High-power output of SMFC is the result of minimizing internal resistance by combining the following key factors: a) saturated air 0.8 M Na2SO4 catholyte at pH 2, b) the use of a birnessite/CF-cathode, and c) the presence of bacterial groups enriched on the anode biofilm as Deltaproteobacteria and Bacteroidetes, additional to other groups such as Aminocenantia depending on the source of chitin. The pH of the catholyte strongly modifies the power production of SMFC; a detailed discussion is included in this paper.