High materials costs and low performance are the persisting bottlenecks that significantly affect the microbial fuel cells (MFCs) applications. The membraneless single-chamber MFC with an air-breathing cathode is a simple configuration where the bacteria play a role in both the anodic and cathodic processes. However, the microbial cathodic semi-reaction is the rate-determining step that can impair the advantage of the natural availability of oxygen in the air. In this work, the microbial catalysis was improved adding cerium oxide nanoparticles (nanoceria) in carbon-based cathodes of air-breathing MFCs, boosting their performance. Two kinds of nanoparticles were tested: CeO₂ and Sm-doped CeO₂ (Sm-CeO₂) on carbon powder, using pristine carbon powder cathodes as a control. The energy generated was 113, 65 and 31 mWh m⁻², for Sm-CeO₂, CeO₂ and control MFCs, respectively, during four subsequent fed cycles of 0.036 mol L⁻¹ Na-acetate in carbonate buffer solution. The better performance of MFCs was correlated to the oxygen preferential and controlled entrapping and release via Ce^4+/3+ redox reaction at the carbon particle surface, as well as to the increased cathode active specific surface area. The achieved results suggest that nanoceria can act as oxygen storage for bacteria in the anaerobic biofilm colonizing the cathode.