Biogenic Hematite from Bacteria: Facile Synthesis of Secondary Nanoclusters for Lithium Storage Capacity

Ferrihydrite, or iron(III) (oxyhydr)oxide (Fe(OH)₃), a representative scavenger of environmentally relevant toxic elements, has been repurposed as a low-cost and scalable precursor of well-developed hematite (α-Fe₂O₃) secondary nanoclusters with a hierarchically structured morphology for lithium-ion anode materials. Here, we report that the bacteria Clostridium sp. C8, isolated from a methane-gas-producing consortium, can synthesize self-assembled secondary hematite nanoclusters (∼150 nm) composed of small nanoparticles (∼15 nm) through the molecular structural rearrangement of amorphous ferrihydrite under mild conditions. The biogenic hematite particles, wrapped with graphene oxide reduced in situ by the reducing bacteria Shewanella sp. HN-41 via one-pot synthesis, deliver an excellent reversible capacity of ∼1000 mA h g^-1 after 100 cycles at a current density of 1 A g^-1. Furthermore, the heat-treated hematite/rGO exhibits a capacity of 820 mA h g^-1 at a high current density of 5 A g^-1 and a reversible capacity of up to 1635 mA h g^-1 at a current density of 100 mA g^-1. This study provides an easy, eco-efficient, and scalable microbiological synthetic route to produce hierarchical hematite/rGO secondary nanoclusters with potential as high-performance Li-ion anode materials.