Electrostatic self-assembled nickel cobalt sulfide/Ti3C2 Mxene as a bio-capacitive anode for specific attracting sulfur-cycling bacteria and regulating extracellular electron transfer efficiency

Microbial fuel cells have been proposed as one of the sustainable and potential technologies for treating contaminants and synchronously producing green energy. However, the poor performance of the anode is a major obstacle in the practical application of MFCs. To address this challenge, the rational design of anode materials with enhanced biocatalytic and biocompatible properties has been considered as an effective approach to improve extracellular electron transfer (EET) processes and general MFC performance. Herein, in light of the interaction between the transition metal and exoelectrogens, nickel-cobalt sulfide/Ti3C2 Mxene (NiCo2S4/Mxene) is prepared by electrostatic assembly, which combined positively charged sea-urchin-like NiCo2S4 with negatively charged Mxene. This not only prevents the stacking of NiCo2S4 and Mxene but also accelerates the EET process by harnessing their biocompatibility and biocatalyst. As expected, the MFC with NiCo2S4/Mxene harvested higher electricity energy (9.66 ± 0.28 W/m3), significantly exceeded those of plain carbon felt (CF, 1.68 ± 0.13 W/m3), Mxene (4.32 ± 0.20 W/m3) and NiCo2S4 (5.41 ± 0.22 W/m3). Moreover, the microbial community analysis further revealed that the sulfide composite attracts a higher percentage of sulfur-cycling exoelectrogens (Desulfuromonas (24.25%) and Marinobacterium (15.75%)), motivating associated metabolic pathways with more efficient electricity generation processes. Such commendable performances are mainly attributed to the synergistic effect between NiCo2S4 and Mxene, which confers the bioanode with good biocompatibility and biocatalyst for biofilm adhesion and colonization, as well as providing abundant transition metals and sulfide active sites for the EET process. Our finding provides a facile routine for developing sulfide with appropriate modification as anode material for favorable performance of MFC, providing insights for sustainable and cleaner energy production in the future.