<p>The photoelectrochemical (PEC) conversion of carbon dioxide (CO₂) into valuable chemicals and fuels offers a promising strategy to address global challenges such as climate change and glacier retreat. However, developing high-performance photocathodes for the CO₂ reduction reaction (CO₂RR) is challenging, particularly in optimizing the surface morphology and active site distribution of the electrodes. In this study, we propose a CuBi₂O₄ (CBO)-based photocathode capable of gas-phase CO₂RR through hybridization with cellulose nanofiber (CNF). Our results reveal that the CBO-CNF membrane exhibits inherent hydrophilicity and significantly larger active sites compared to a CBO film prepared with a Nafion binder, leading to reduced charge transfer resistance on the photocathode surface. Moreover, the simultaneous hydrothermal synthesis of the CBO-CNF composite precursor solution effectively inhibits the formation of undesirable CuO nanoparticles on the surface, which would otherwise increase charge transport resistance within the photocathode bulk. Consequently, the CBO-CNF membrane demonstrates superior PEC activities for CO₂RR, achieving a photocurrent density of − 5.69&#xa0;mA/cm² at − 0.4 V_RHE and an onset potential of 0.015 V_RHE. Furthermore, the incorporation of CNF improves the long-term PEC stability of the photocathode by promoting charge carrier participation in CO₂RR rather than undesired self-reduction reaction. This enhanced stability, coupled with the improved PEC performance, highlights the potential of CNF to replace existing polymer binder materials. These results suggest the feasibility of developing a new type of CBO photocathode with a porous membrane structure suitable for gas-phase PEC cells, marking a significant step forward in PEC technology for CO₂ conversion.</p>