Synergistic acceleration of proton migration in osmotic microbial fuel cell: hydrophilic nanochannels coupling acid-base pairs created by functionalized metal-organic frameworks in forward osmosis membrane.

The sluggish migration of proton from anode to cathode poses a significant challenge in osmotic microbial fuel cell (OsMFC), leading to a pH imbalance that impairs overall performance. Forward osmosis (FO) membrane provides a possibility to solve this issue by designing proton-conducting channels. Herein, we proposed a novel idea of synergistic acceleration of proton migration by constructing hydrophilic nanochannels and assembling acid-base pairs in FO membrane. It was realized by incorporating heterogenic functionalized metal-organic frameworks (MOFs) into a polyamide layer to fabricate thin film nanocomposite (TFN) FO membrane. The formation of acid-base pairs (S-O···HN) between NH-MIL-101(Cr) and SOH-MIL-101(Cr) significantly reduced proton migration energy barrier as revealed by density functional theory analysis. As a result, the synergistic effect of hydrophilic nanochannels and acid-base pairs created by the heterogenic MOFs significantly boosted proton transport. The OsMFC employing the as-prepared membrane (FO-3) achieved a peak power density of 9.80 ± 0.52 W·m. Additionally, the volume of pure water extracted was approximately 1.45 times greater than that of the control, and the average chemical oxygen demand (COD) removal efficiency increased by 10.64 %. This innovative protocol of fabricating highly proton-conducting MOFs-TFN FO membranes creates a unique perspective for effectively regulating pH imbalance in OsMFC for large-scale applications.