<i>In Situ</i> Fabrication of Nanohybrid Heterojunction Thin-Film Photoanode of Co, Mo-Doped BiVO ₄ /NiFeOOH/MOF-ZIF-8/g-C ₃ N ₄ for Enhanced Photoelectrochemical Seawater Splitting

Direct photoelectrochemical (PEC) seawater splitting offers a sustainable pathway for green hydrogen (H2) fuel production, addressing critical global challenges related to energy and environment pollution. In this work, we report the successful fabrication of a multilayered Co,Mo-doped BiVO4/NiFeOOH/ZIF-8/g-C3N4 heterojunction photoanode using a combination of microwave-assisted hydro/solvothermal synthesis and doctor-blade coating techniques. The synergetic surface modification of the Co,Mo-BiVO4 film with NiFeOOH, ZIF-8, and g-C3N4 significantly enhances the PEC performance, achieving a high photocurrent density of 7.21 mA cm–2 at 1.23 V vs RHE, 5.2-fold greater than that of pristine BiVO4. Correspondingly, the photoanode exhibits an improved incident photon-to-current efficiency (IPCE) of 13.24% and absorbed photon-to-current efficiency (APCE) of 31.45% at 1.23 V vs RHE at 450 nm under AM 1.5G illumination in a 0.5 M Na2SO4 solution. To evaluate the practical performance in seawater splitting, we developed a compartmentalized, 3D-printed, membrane-less prototype continuous-flow PEC device for scalable H2 generation. Remarkably, the device achieved a photocurrent density of 4.03 mA cm–2 with sustained stability over 12 h. This enhanced performance is attributed to the increase in the number of active sites, improved photogenerated hole injection into the electrolyte, and suppressed charge recombination. This study demonstrates the potential of in-situ engineered heterojunction photoanodes comprising Co,Mo-BiVO4, NiFeOOH, porous ZIF-8, and g-C3N4 with strong π–π conjugation for efficient interfacial charge transfer and electronic structure modulation, advancing the design of next-generation photoanodes for sustainable solar-driven seawater splitting.