The　usage　time　of　air-cathode　microbial　fuel　cells　(MFCs)　is　significantly　influenced　by　the　moisture　content　within　the　proton　exchange　membrane　(PEM).　Therefore,　enhancing　the　water　retention　capability　of　the　PEM　by　applying　a　hydrophobic　polymer　coating　to　its　surface　has　extended　the　PEM＇s　usage　time　by　three　times　and　increased　MFCs＇　operational　duration　by　66%.　Moreover,　the　hydrophobic　nature　of　the　polymer　coating　reduces　contamination　on　the　PEM　and　prevents　anode　liquid　from　permeating　into　the　air　cathode.　Towards　the　end　of　MFC　operation,　the　internal　resistance　of　the　MFC　is　reduced　by　45%.　The　polymer　coating　effectively　maintained　the　oxygen　reduction　reaction　activity　in　the　cathode.　The　polymer　coating＇s　ability　to　restrict　oxygen　transmembrane　diffusion　is　demonstrated　by　experimental　data　showing　a　significant　decrease　in　oxygen　diffusion　coefficient　due　to　its　presence.　The　degradation　efficiency　of　the　chemical　oxygen　demand　from　16%　to　35%　increased　by　a　factor　of　one.