Nd2O3/TiO2 Nanotube Array Heterojunctions: Rare Earth Modification Driven Efficient Photoelectrochemical Water Splitting for Hydrogen Production

The photoelectrochemical water-splitting process for hydrogen production is limited by the large bandgap of semiconductor titanium dioxide (TiO2) and by interfacial recombination at particle interfaces. The technique used in this paper is that of electrochemical anodization to produce robust, ordered TiO2 nanotube arrays (TiO2 nanorod arrays denoted as TNTAs). Using the immersion-annealing method, Nd2O3 nanoparticles can be immobilized in situ, and Nd2O3/TNTAs composite photoanodes are fabricated. The heterointerface caused between the Nd2O3 nanoparticles and TiO2 results in the alignment of the Fermi levels and the formation of band bending and an internal electric field at the interface. It allows rapid photo-generated electron-hole (e−/h+) separation at the interface and, simultaneously, introduces novel localized electron states of Nd3+ within the TiO2 bandgap. This triggers hybridisation between the 3d orbitals of Ti and the 2p orbitals of O, thereby altering the band structure of TiO2. The best-performing Nd2O3/TNTAs photoelectrode outperforms pure TNTAs, with a photocurrent density of 1.59 mA·cm−2 at 1.23 V vs. RHE. It produces 162.6 μmol·cm−2 of hydrogen in a 3 h photocatalytic hydrogen production experiment, which is about 12.2 times that of pure TNTAs. This approach highlights the unique benefits and creative opportunities of applying rare-earth elements to address the critical issues of photocatalysts, such as significant band gaps and rapid recombination.