The low electron–hole separation in the photoanode generally restricts the visible light response of photocatalytic fuel cell (PFCs). In this study, 5% NH₂-MIL-125/g-C₃N₄/Bi₂O₃/Ti photoanode was synthesized and assembled with a PFC with Cu cathode to degrade rhodamine B and generate electricity. With visible light irritation, the maximum photocurrent density, maximum power density, and degradation rate of the PFC were 0.59 mA cm⁻², 29.88 μW cm⁻², and 97.48% (1 h), respectively. The major active species in the PFC were h⁺, ˙O₂⁻, and ˙OH. The good performance of the PFC was ascribed to the formation of a double Z-type heterojunction in the 5% NH₂-MIL-125/g-C₃N₄/Bi₂O₃/Ti photoanode so that the photoelectrons of NH₂-MIL-125 and Bi₂O₃ directly combine with the photoholes of g-C₃N₄, making the photoholes of NH₂-MIL-125 and Bi₂O₃ and the photoelectrons of g-C₃N₄ directly or indirectly involved in the RhB degradation process and generating electricity. Thus, the separation rate of the e⁻–h⁺ pairs in the photoanode and the capability of the PFC are greatly improved.