Improved biofilm adhesion and electrochemical properties of a graphite-cement composite with silica nanoflowers versus two benchmark carbon felts

Low cost graphite-cement composite (GC70S) is prepared by blending graphite, cement and fumed SiO₂ to obtain nanoflowers and proposed as an alternative to common carbon-based materials in the anode of biodevices with biofilm growth. The selected anodic benchmarks are carbon felt (CF) that is cheap, flexible, porous, and conductive three-dimensional support and a modified CF with polyethyleneimine (CF-PEI), where PEI is used to coat the carbon fibers. In spite of such advantages, CF has drawbacks, such as deformation by pore compression, hydrophobicity, low biofilm adhesion, and easy fragility by aging. Compared to these benchmarks, the GC70S has a multi-modal pore size distribution with micro (1–7 μm) and nano (20 nm) pores, whereas CF and CF-PEI only show macroscopic (55–60 μm) pores. The comparative results also show that the new composite provides better wettability, higher specific surface area (4.53·10⁷ m²·m⁻³), and good electrical conductivity (2.04 ± 0.18 S·m⁻¹). In half-cell tests, the yeast biofilm is firmly attached to GC70S anode, while its charge transfer resistance is greatly reduced. From the biofilm resistance contribution, the inhabitancy appears more abundant than in CF or CF-PEI.