Self-powered paper-based photo-microfluidic fuel cell stacks tested with physiological fluids

The autonomy of paper-based sensors that use the same physiological sample fluid to generate their own electrical energy has been of interest in recent years. In this work, we evaluated a paper-based photo-microfluidic fuel cell (paper-based photo-µFC) assembled in a square stacked configuration using four different physiological human fluids, each evaluated separately as the fuel (urine, blood serum, sweat, and saliva) and a ZnO-Pr (ZnO-Praseodymium) composite as anode and, Pt/C as cathode. In all four cases, it was observed that visible light increased the open circuit voltage, current density, and power density compared to dark conditions. Among the physiological fluids evaluated, the highest power density ( W ) under visible light irradiation was obtained when human blood serum was used as fuel (serum 2.6634 mW cm −2 > urine 2.1083 mW cm −2 > sweat 0 .2 489 cm −2 > saliva 0.0814 mW cm −2 ). This improved performance is ascribed to the generation and accumulation of photogenerated electrons in the conduction band, combined with a simultaneous increase in oxidizing holes at the valence band, which collectively shift the electrode potential to more positive values. The results demonstrate that physiological fluids are viable fuels for paper-based photo-µFC, highlighting their potential use as power sources in paper-based sensors.