Facet-engineered hematite boosts microbial electrogenesis by synergy of promoting electroactive biofilm formation and extracellular electron transfer

Hematite has been proven to be an excellent material for enhancing extracellular electron transfer (EET) in microbial bioelectrochemical systems (BESs). However, the effect of hematite with different exposed facets on microbial EET remains unclear. Here, we synthesized two types of hematite nanoparticles with high {100} and {001} facet exposure (Hem_{100} and Hem_{001}), respectively, which were coated on ITO electrode to stimulate the microbial EET in the BESs. The results showed that the maximum biocurrent density of commercial hematite nanoparticles (Hem_NPs), Hem_{100} and Hem_{001} electrodes reached 73.33 ± 5.68, 129.33 ± 9.12 and 287.00 ± 19.89 μA cm^-2 from three replicates of each treatment, respectively. The current generation achieved from the Hem_{001} electrode was nearly 199-times higher than that of the blank ITO electrode (1.44 ± 0.10 μA cm^-2). The electrochemical measurements showed that the lowest charge transfer resistance (R_ct) was observed for the Hem_{001}, and the promoted biofilm formation and EPS secretion on the Hem_{001} electrode were also revealed, which could contribute the high performance of this electrode. Moreover, metagenomic analysis revealed that Hem_{001} might facilitate the microbial EET by stimulating the expression of genes related to cytochrome c and conductive nanowires. This study not only provides a new strategy to enhance microbial electrogenesis but also expands the knowledge of the effect of facet on microbial EET, helping to develop more efficient electrode materials in the future.