A Self-Sustained Photocatalytic Fuel Cell with N-Doped TiO₂ Photoanode for Decentralized Wastewater Remediation and Power Supply

Abstract

The practical deployment of photocatalytic fuel cells (PFCs) for real wastewater treatment is hindered by the ultraviolet-limited activity of TiO2 photoanodes and their reliance on external electrolyte replenishment. To overcome these dual constraints, we engineer a self-contained PFC system based on N-doped TiO2 (N-TiO2) nanorod arrays synthesized via a scalable hydrothermal urea-assisted route. The optimized N-TiO2 photoanode (3 mg urea) achieves a visible-light photocurrent density of 1.82 mA/cm2 (0 V vs. Ag/AgCl) in 0.5 M Na2SO4 representing a 7.5-fold enhancement over pristine TiO2. When integrated into a compact PFC, it enables simultaneous degradation of methyl orange and rhodamine B with concurrent power generation (4.8 and 12.5 μW/cm2, respectively). Critically, the device operates stably in synthetic urine as the sole electrolyte—without any external ion supplementation—delivering a photocurrent of 0.32 mA/cm2 and a maximum power density of 0.36 mW/cm2. This demonstrates its viability for decentralized applications where complex, real waste streams like human urine are prevalent. Combined experimental and DFT analyses reveal that N 2p states above the O 2p valence band edge narrow the effective bandgap and enhance visible-light-driven charge separation. This work establishes not only a scalable materials strategy but also a practical, self-sustained device architecture for portable PFC systems targeting integrated environmental remediation and energy recovery in off-grid settings.