Anodized TiO2 nanotubes arrays as microbial fuel cell (MFC) electrodes for wastewater treatment: An overview

This review discusses the main advances in electrodes based on TiO2 nanotube arrays (TNA) to improve the performance of microbial fuel cells (MFC), a sustainable technology for wastewater treatment and bioelectricity generation. The properties and synthesis of anodized TNA films are well-established in the literature. Contrary to the dye-sensitized solar cells, photoelectrochemical water-splitting, photocatalysts, biosensors, and implant ap-plications, where they are widely explored, TNAs are still in the exploratory stage in fuel cells. The precise morphology control by the anodizing conditions, high surface area, low cost, chemical stability, and unidirec-tional orientation are their attractive properties. TNA-based electrodes have been explored mainly as bioanodes in conventional MFCs, and photoanodes in hybrid MFC systems and evaluated in terms of power and current generation and compared with Ti and carbon-based electrodes. The effects of nanotubular morphology, heat treatment conditions, and surface modification of TNA electrodes are addressed. Its utilization as a photoanode in photo-assisted MFCs is discussed as the strategies for improving MFC performance and turning it cost-effective by coupling other functions, like H2 production and CO2 conversion.