The role of an ultra-thin carbon layer in enhancing solar water-splitting performance of Z-scheme ZnO@MOF-5/C photoanodes

In this study, we successfully synthesized core-shell ZnO@MOF-5/C ternary heterostructures as visible light-responsive photocatalysts for highly efficient photoelectrochemical (PEC) water splitting. A bioinspired poly-dopamine (PDA) shell was calcined to form a conductive N-doped graphitic carbon layer on ZnO@MOF-5, preserving its star-shaped morphology while significantly enhancing electron transport. As a result, the ZnO@MOF-5/C photoanode achieved an impressive photocurrent density of 3.41 mA/cm2 at 2.50 V vs. RHE under Xenon (Xe) illumination, surpassing pristine ZnO by 3.35 times and dark-state ZnO@MOF-5/C by 12.5 times. This enhancement is attributed to the efficient separation and transfer of photogenerated charge carriers. Additionally, the ZnO@MOF-5/C system exhibited a notable incident photon-to-current conversion efficiency (IPCE) of 24 % at 490 nm, highlighting its superior light-harvesting capability. To elucidate the underlying charge transfer mechanism, radical scavenging experiments and X-ray photoelectron spectroscopy (XPS) confirmed a Z-scheme charge separation pathway. These findings introduce a novel semiconductor-MOF heterojunction design with exceptional visible-light sensitivity, paving the way for advanced PEC applications.