Engineering an effective noble-metal-free photocatalyst for hydrogen evolution: hollow hexagonal porous micro-rods assembled from In2O3@carbon core–shell nanoparticles

It is desirable but challenging to design noble-metal-free photocatalysts with improved activity for hydrogen (H2) evolution. In this study, we fabricated hollow hexagonal porous micro-rods assembled from core–shell In2O3@carbon nanoparticles (PHIC) via one-step thermal decomposition of the In-MIL-68 precursor. Under simulated sun-light illumination, the final H2 yield rate of PHIC is comparable to that of Pt/PHI (PHI, hollow hexagonal micro-rods assembled from In2O3 nanoparticles without a carbon layer), indicating that the continuous carbon layer coating on In2O3 nanoparticles has a Pt-like effect on improving the photocatalytic activity. Our experimental results indicated that the improved photocatalytic H2 evolution of PHIC is attributed to the synergistic effect of efficient separation of photo-generated electron–hole pairs caused by the coating carbon layer, the enhanced optical absorption of the hollow structure, and the improved accessibility provided by the porous structure. Among them, efficient separation of photo-generated electron–hole pairs plays the main role. Furthermore, we reveal the microscopic charge carrier migration path via In2O3/graphite interfaces, meaning that the photo-generated electrons from In2O3 O2p orbitals transfer into the carbon C2p orbitals, leaving the photo-generated holes in In2O3 O2p orbitals, which is beneficial to improve the separation of photo-generated electron–hole pairs.