Synergistic medium-chain-length polyhydroxyalkanoate-hydrochar composite anodes for stable, high-power microbial fuel...

The advancement of sustainable bioelectrochemical systems requires anode materials that simultaneously deliver high power output, structural robustness, and controlled biodegradability. This study develops a new class of composite bioanodes by integrating biosynthesized medium-chain-length polyhydroxyalkanoates (mcl-PHA) with sugarcane bagasse-derived hydrochars possessing tailored surface chemistries namely raw (PHA-R), phosphate (PHA-P), and sulfonated (PHA-S), and compares their performance to a carbon-nanotube equivalent (PHA-C). The biocompatible mcl-PHA matrix acts as a multifunctional binder that improves electrode cohesion and ion transport, while hydrochar porosity and functional groups regulate interfacial charge transfer and microbial adhesion. Polarization analysis shows that the PHA-R composite achieves an average open-circuit voltage (OCV) of 938 ± 4 mV with a maximum power density of 1.5 ± 0.1 W/m² and current density of 3.2 ± 0.2 A/m², outperforming its non-polymeric counterpart. PHA-P and PHA-S composites also enhance power output up to 1.4 ± 0.1 W/m², and current generation up to 3.6 ± 0.1 A/m² relative to their respective pristine hydrochar MFC setups, highlighting strong polymer-carbon synergy. The PHA-C control MFC set up recorded the lowest power output exhibiting 901 ± 4 mV, 0.4 ± 0.0 W/m² and 1.7 ± 0.1 A/m². Electrochemical impedance spectroscopy (EIS) reveals that PHA-R and PHA-P composites substantially lower charge-transfer resistance compared with the control (PHA-C). Post-MFC operation, PHA-P and PHA-R retained the highest electrochemical activities, with specific capacitances of 26.3 and 16.9 F/g respectively, while PHA-S showed minimal capacitance of 4.6 F/g. Gel permeation chromatography further indicates reductions in mcl-PHA molecular weight, suggesting that biodegradation behavior can be modulated, although swelling and degradation should be carefully managed to maintain long-term anode stability.