Highly conversion efficiency of solar water splitting over p-Cu2O/ZnO photocatalyst grown on a metallic substrate

Abstract

Earth-abundant Cu2O-based photocatalysts are promising light absorbing materials for highly efficient solar hydrogen production through a photoelectrochemical (PEC) water splitting system. However, growth of these structures over incompatible and low conductive substrates hinders the interfacial charge transport kinetics of photo-generated carriers, which severely reduces PEC performance. Herein, we report a Cu2O photocathode directly grown on a metallic Ti coated on Mo-glass substrate with a ZnO protective nanolayer, to reduce the interfacial transport resistance of photo-generated charge carriers (holes) at the electrode–substrate interface, as well as to improve the separation and extraction efficiency at the electrode–electolyte interface, compared to that grown on a conventional FTO substrate. The morphological, structural, and optical characterization of all structures were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Bare Cu2O and Cu2O/ZnO photocathodes fabricated on Ti-substrate achieved efficient light harvesting with photocurrent densities (Jph) of ∼−3.03 and −7.23 mA cm−2 at 0 V, and photocurrent onsets over +0.69 and +0.83 V versus the reversible hydrogen electrode (RHE), respectively, which are approximately 10.45 and 24.93 times higher than that of the pristine Cu2O photocathode grown on a FTO substrate (Jph ∼−0.29 mA cm−2). Interestingly, the Cu2O/ZnO photocathode on Ti-substarte showed an impressive solar conversion efficiency of 1.77% at 0 V vs. RHE. The interfacial transport resistance was also reduced significantly after using this approach, which emphasizes the role of metallic substrate in enhancing the overall PEC performance.