S-scheme-mediated Ce-NSO/Ce-gCN heterostructure for enhanced photocatalytic hydrogen evolution via sea water splitting

Abstract

Developing stable and cost-effective photocatalysts that operate without precious metals or sacrificial agents is essential for practical and sustainable hydrogen production. In this study, a rare-earth cerium-doped S-scheme heterostructure was rationally designed and synthesized to achieve enhanced photocatalytic hydrogen evolution from seawater without the use of any hole scavenger. The direct use of seawater for photocatalytic hydrogen evolution is highly desirable because it constitutes nearly 97% of the Earth's water resources and eliminates the energy-intensive purification steps required for deionized water, thereby offering a more sustainable and economically viable pathway for large-scale hydrogen production. The incorporation of Ce in both NiSnO₃ (NSO) and graphitic carbon nitride (gCN) significantly improved interfacial coupling between NSO and gCN, charge carrier separation, and light-harvesting capability. Structural, optical, and photoelectrochemical studies confirmed an efficient S-scheme charge transfer mechanism. The 4% (w/w) Ce-doped photocatalyst delivered a hydrogen evolution rate of 1510 µmol (g h)⁻¹, which is twice the value of NSO/gCN and six times that of gCN, demonstrating the strong synergistic effect of Ce-doping and heterojunction design. Radical trapping studies, EPR and XPS analysis further verified that the enhanced activity was because of the generation of highly reductive electrons with prolonged carrier lifetime. Moreover, the Ce-NSO/Ce-gCN composite exhibited excellent stability with minimal activity loss over multiple cycles. These findings demonstrate that rare-earth doping is a key strategy for optimizing both the efficiency and durability of S-scheme heterostructures, offering a promising route toward sustainable, seawater-based photocatalytic hydrogen production.