Eco-friendly composite of mcl-PHA with oyster shell powder and carbon nanotubes as proton exchange membrane boosts microbial fuel cells performance

This study presents a novel, sustainable proton exchange membrane (PEM) for microbial fuel cells (MFC) by reinforcing medium-chain-length polyhydroxyalkanoates (mcl-PHA) with oyster shell powder (OSP) and carbon nanotubes (CNT). Structural and morphological analyses confirmed successful filler integration, enhancing crystallinity, micro-porosity, and proton transport pathways. The composite membrane (OS30%CNT2%) demonstrated exceptional properties, including an ion exchange capacity of 1.10 ± 0.10 meq/g and porosity of 52.9 ± 1.3%, rivaling commercial Nafion. Thermal analysis confirmed retained membrane integrity despite multi-phase degradation, demonstrating structural stability under typical MFC operating conditions. The optimized formulation exhibited superior hydrophilicity (8.3% water uptake) and oxygen barrier performance (4.6 ± 0.2% diffusion), critical for MFC efficiency. In operational tests, OS30%CNT2% achieved a peak power density of 205 ± 6 mW/m², surpassing Nafion (175 ± 5 mW/m²), despite higher internal resistance (2,337 Ω). Notably, cost analysis revealed a significantly lower fabrication cost at $5.93 – $8.36 vs. $50.06 for Nafion, and superior cost-performance efficiency, with OS30%CNT2% achieving 18 × 103 $/W compared to 146 × 103 $/W for Nafion. These findings highlight the synergistic benefits of OSP and CNT, and demonstrate a cost-effective, sustainable alternative to conventional PEMs, promoting waste valorization and green energy advancement.