Anatomy of a Visible Light Activated Photocatalyst for Water Splitting

Abstract

The supported mixed oxide (Rh 2−y Cr y O 3 )/(Ga 1−x Zn x )(N 1−x O x ) photocatalyst, highly active for splitting of H 2 O, was extensively characterized for its bulk and surface properties with the objective of developing fundamental structure−photoactivity relationships. Raman and UV−vis spectroscopy revealed that the molecular and electronic structures, respectively, of the oxynitride (Ga 1−x Zn x )(N 1−x O x ) support are not perturbed by the deposition of the (Rh 2−y Cr y O 3 ) NPs. Photoluminescence (PL) spectroscopy, however, showed that the oxynitride (Ga 1−x Zn x )(N 1−x O x ) support is the source of excited electrons/holes and the (Rh 2−y Cr y O 3 ) NPs greatly reduce the undesirable recombination of photoexcited electron/holes by acting as efficient electron traps as well as increase the lifetimes of the excitons. High Resolution-XPS and High Sensitivity-LEIS surface analyses reveal that the surfaces of the (Rh 2−y Cr y O 3 ) NPs consist of Rh 3+ and Cr 3+ mixed oxide species. In situ AP-XPS help to reveal that the Rh 3+ and surface N atoms are involved in water splitting. Dispersed RhO x species on the (Ga 1−x Zn x )(N 1−x O x ) support and on CrO x NPs were found to be the photocatalytic active sites for H 2 generation and N and Zn sites from the (Ga 1−x Zn x )(N 1−x O x ) support are the photocatalytic active site for O 2 generation. The current investigation establishes the fundamental structure−photoactivity relationships of these visible light activated photocatalysts.

Time-resolved infrared spectroscopic investigation of Ga2O3 photocatalysts loaded with Cr2O3-Rh cocatalysts for photocatalytic water splitting

“…Moreover, the trapped electrons in Cr2O3 may transfer to the Rh nanoparticles, either directly or indirectly by transferring back to Ga2O3 and then transfer to Rh eventually. The promotion of electron transfer from (Ga1-xZnx)(N1-xOx) to RhOx species by Cr2O3 in the (Rh2-yCryO3)/(Ga1-xZnx)(N1-xOx) photocatalyst was reported by Phivilay et al [38], and a similar mechanism for the Ni-NiSx/TiO2 photocatalysts that the Ni cocatalyst mediates the electron transfer from TiO2 to NiSx was also proposed [54]. The initial absorbance reduced further with the introduction of water or oxygen by 14.2% or 17.2%, respectively, than that in vacuum, which may be attributed to electron capture by water vapor and oxygen in the pre-microsecond timescale.…”

“…Maeda et al [37] proposed that the co-loading of Cr2O3 with Rh2O3 presumably changes the electronic state and chemical properties of the Rh2O3 cocatalyst, and the migration of the photogenerated electrons to the Rh2O3 cocatalyst and/or the reduction of surface-adsorbed H + followed by H2 formation proceed more smoothly. Recently, Phivilay et al [38] reported that the dispersed RhOx species (H2 evolution center) exists on both the (Ga1-xZnx)(N1-xOx) support and the CrOx nanoparticles in the (Rh2-yCryO3)/(Ga1-xZnx)(N1-xOx) photocatalyst, and the CrOx species appears to facilitate electron transfer from the (Ga1-xZnx)(N1-xOx) support to the RhOx species. Considerable efforts have been invested in revealing the roles of Rh-Cr oxide cocatalysts for photocatalytic water splitting; however, their nature is still not fully understood.…”

1D/2D Heterostructured Photocatalysts: From Design and Unique Properties to Their Environmental Applications

“…Nowadays, the top objectives of human development policy are to achieve sustainable production of clean energy and protect the ecological environment. [1][2][3][4][5][6] In the past few years, 1D nanowires/ nanotubes and 2D nanosheets have been extensively investigated as photocatalysts in the field of environmental protection and sustainable energy development due to their interesting…”

“…Nowadays, the top objectives of human development policy are to achieve sustainable production of clean energy and protect the ecological environment. [ 1–6 ] In the past few years, 1D nanowires/nanotubes and 2D nanosheets have been extensively investigated as photocatalysts in the field of environmental protection and sustainable energy development due to their interesting functions in nanoelectronics and optoelectronics. [ 7–14 ] 1D nanostructures could provide quick charge transfer along their axes, whereas 2D nanostructures (contain layered metal chalcogenides and MXenes) could confine electrons in their unique atomic layers.…”

Electrospinning Preparation of GaN:ZnO Solid Solution Nanorods with Visible-Light-Driven Photocatalytic Activity toward H2 Production

“…However, as for GaN:ZnO solid solution, due to the lack of H 2 evolution sites, it is necessary to employ a cocatalyst that plays a vital role in providing active sites and improving the charge separation for photocatalytic redox reactions [26][27][28]. Rh 2−y Cr y O 3 , as a traditional cocatalyst, has been found to be capable of promoting the realization of the photocatalytic water splitting [29,30]. Therefore, high-efficiency GaN:ZnO solid solutions decorated with cocatalyst of Rh 2−y Cr y O 3 were designed and prepared.…”