Large area ternary TiO2/CdS/g-C3N4 photoanode for hydrogen evolution by photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is a key technology for sustainable hydrogen production, yet most studies focus on small-scale photoelectrodes. While some have developed large-area photoelectrodes, they primarily use single-material systems rather than heterojunction structures. Here, we present a large-area heterojunction-based photoanode with an optimized design for improved performance and scalability. Optimization begins at small scale (1 cm2) using a synergistic combination of TiO2/CdS/g-C3N4 ternary heterojunction and mesoporous architecture strategies. CdS enables substantial charge generation through efficient light absorption and separation, while integration of TiO2 and g-C3N4 form type-II heterojunction that promotes directional charge transfer. Mesoporous TiO2 scaffold further boosts the PEC performance by facilitating CdS deposition, where an optimized four-layer thickness balances light absorption and minimizes recombination losses. The photoanode achieves a photocurrent density of 2.38 mA/cm2 at 1.23 VRHE and an applied bias photon-to-current efficiency of 1.46 %. Scaling up to 16 cm2 yields a high photocurrent of 21.3 mA, corresponding to 56 % of the photocurrent density of the best-performing 1 cm2 photoanode. This is enabled by employing cost-effective dynamic dispensing method for depositing mesoporous TiO2, which in turn allows uniform CdS growth. The outcome of this work provides a valuable framework for advancing large-scale PEC technology toward commercial applications.