Enhanced Power Generation of Oxygen-Reducing Biocathode with an Alternating Hydrophobic and Hydrophilic Surface

Most oxygen-reducing biocathodes for microbial electrochemical systems (MESs) require energy-intensive aeration of the catholyte, which negates the energy-saving benefits of MESs. To avoid aeration and enhance oxygen-utilization efficiency, columnar activated carbon with half of its surface coated by polytetrafluoroethylene (PTFE-coated CAC) was fabricated as biocathode material, and its performance was investigated using a tide-type biocathode MES (TBMES). The TBMES with PTFE-coated biocathode achieved a maximum power density of 8.2 ± 0.8 W m^-3, which was 39% higher than that of the untreated control (CAC biocathode). The PTFE-coated biocathode was able to store a cumulative total charge (Q_m) of (10.8 ± 0.2) × 10⁴ C m^-3 during one charge-discharge cycle, whereas the Q_m of CAC biocathode was only (6.9 ± 0.1) × 10⁴ C m^-3, demonstrating that the oxygen entrapment capability of PTFE-coated biocathode was 54 ± 3.8% higher than that of the control. Internal resistance analysis under both oxygen sufficient and reoxygenation conditions suggested the oxygen entrapped by this surface-hydrophobic biocathode was basically sufficient for cathodic oxygen reduction reaction. The slight difference in cathodic microbial communities of the two biocathodes further indicated that the higher accessibility of oxygen due to the hydrophobic surface was the primary cause for the better performance of the PTFE-coated biocathode, while the higher biocatalytic activity of the cathodic biofilm was a minor factor.