Medium-chain-length polyhydroxyalkanoates- co -polyhydroxybutyrate composited with carbon nanotubes as a proton exchange membrane in microbial fuel cells

Abstract The study investigated medium-chain-length polyhydroxyalkanoates- co -polyhydroxybutyrate (PHA/PHB) membranes integrated with carbon nanotubes (CNTs) as proton exchange membrane in microbial fuel cells (MFCs). Membranes composited with varying CNT concentrations (0.5-3 % w/w ) were characterized and compared against Nafion and PHA/PHB membranes. The CNT3% composite membrane demonstrated optimal properties, with ion exchange capacity (1.17 meq/g), water conductivity (18.51 µS/cm) approaching commercial Nafion performance (22.10 µS/cm) concurrently exhibiting lower oxygen crossover (6.6 % vs. 9.4 %). Electrochemical analyses revealed a maximum voltage of 574 mV and internal resistance of 642 Ω for the CNT3 % membrane, significantly outperforming lower CNT loadings and PHA/PHB membrane (11 mV, 266090 Ω). Although Nafion 117 showed 617 mV maximum voltage and 50 Ω overall internal resistance, the CNT3% membrane attained comparable voltage output with superior oxygen barrier properties. The enhanced performance of CNT-incorporated membranes is attributed to improved proton conduction mechanism and augmented porosity. The CNT-reinforced PHA/PHB membranes are strong candidates for replacing fluorinated membranes, providing a sustainable option with customizable electrochemical properties tailored to enhance MFC efficiency.