Heterogeneous p-n Junction CdS/Cu₂O Nanorod Arrays: Synthesis and Superior Visible-Light-Driven Photoelectrochemical Performance for Hydrogen Evolution

Heterogeneous p-n junction CdS/Cu₂O nanorod arrays have been fabricated by using a facile successive ionic-layer adsorption and reaction process to grow Cu₂O nanoparticles on the surface of ordered CdS nanorod arrays. The heterogeneous p-n junction nanorod arrays exhibit superior photoelectrochemical performance for hydrogen (H₂) generation and high stability under visible-light irradiation. The highest photocurrent density achieved by heterogeneous nanorod array photoelectrode is 4.2 mA cm^-2 in a sacrificial Na₂S and Na₂SO₃ mixture electrolyte solution at 0 V versus Ag/AgCl, which is 4 times higher than that of a pure CdS nanorod array photoelectrode. In addition, the heterogeneous nanorod array photoelectrode achieves an incident photon conversion efficiency value of 40.5% at 470 nm. The photocatalytic hydrogen generation rate of the heterogeneous nanorod array photoelectrode reaches up to 161.2 μmol h^-1, around 3-fold increase compared to that of a bare CdS photoelectrode. Furthermore, the heterogeneous p-n junction CdS/Cu₂O nanorod arrays show an excellent stability under long light illumination of 7200 s. The improved photoelectrochemical performance, photocatalytic activity, and excellent stability of the heterogeneous nanorod array photoelectrode resulted from the efficient separation of photoinduced electron-hole pairs, which is achieved by the synergistic effects of CdS, Cu₂O, p-n junction, and an inner electric field in the photoelectrode. The present work provides a new strategy to fabricate a heterogeneous photoelectrode. This facile strategy is expected to be utilized to fabricate electrodes of other materials for highly efficient solar-driven water splitting application.