Synthesis of Narrow-Band-Gap GaN:ZnO Solid Solution for Photocatalytic Overall Water Splitting

Abstract

The solid solution of GaN and ZnO (GaN:ZnO) is a promising photocatalyst applicable to visible-light-driven overall water splitting. However, the band gap of active GaN:ZnO remains as large as ca. 2.7 eV because of the loss of ZnO during the widely applied NH 3 nitridation process. Herein, particulate GaN:ZnO exhibiting a band gap of 2.3 eV was synthesized via calcination of a mixture of Ga 2 O 3 , Zn, and NH 4 Cl in a sealed evacuated tube. The synthesis method was also featured with a high nitrogen utilization rate of 87%. The prepared narrow-band-gap GaN:ZnO was active in the overall water-splitting reaction. In the presence of sacrificial reagents, the apparent quantum yields of GaN:ZnO at 420 nm for H 2 and O 2 generation were 5.1 and 14.3%, respectively. GaN:ZnO was applied as an oxygen evolution photocatalyst to construct a Z-scheme overall water-splitting system with SrTiO 3 :Rh as a hydrogen evolution photocatalyst, which achieved a solar-to-hydrogen energy conversion efficiency of 3.7 × 10 −2 % and a remarkable photochemical stability up to 100 h. This work provides an approach to the synthesis of narrow-band-gap GaN:ZnO solid solution and shows the potential of this material in H 2 production from water under long-wavelength visible light.

Alcoholamine-Grafted Zinc Oxide Enhances CO2 Electroreduction at Elevated Temperatures

“…From the high-resolution transmission electron microscopy (HRTEM) images of TEA-ZnO and ZnO (Figure e,g), streaks with a lattice spacing of 0.28 nm can be assigned to the (100) crystallographic plane of hexagonal phase ZnO (PDF no. 36-1451) . EDX elemental mapping (Figure h–l) and EDX spectra (Figure S2) show a uniform distribution of Zn, O, N, and C elements on the surface of TEA-ZnO, indicating that the alkanolamine has been grafted onto the ZnO surface.…”

A perspective on two pathways of photocatalytic water splitting and their practical application systems

“…A Z-scheme system was then constructed by using the prepared GaN:ZnO as the OEP and SrTiO 3 :Rh as the HEP in combination with Fe 3+ /Fe 2+ as the electron mediator. The STH efficiency of 3.7 × 10 −2 % was achieved with remarkable stability up to 100 h. 107 Cooper's group explored a range of conjugated polymer photocatalysts for the hydrogen evolution half-reaction and various metal oxide materials as photocatalysts for oxygen production. It was found that P10 (homopolymer of dibenzo[ b , d ]thiophene sulfone) and BiVO 4 showed the highest activity in the presence of FeCl 2 and FeCl 3 aqueous solution, respectively, for H 2 and O 2 half-reactions.…”

Recent advances in photocatalyst sheet development and challenges for cost-effective solar hydrogen production

“…19 Moreover, highly crystalline GaN:ZnO with a narrow bandgap energy of 2.3 eV was recently synthesized using an ammonium salt as a nitriding reagent in a sealed evacuated tube. 20 This method prevented loss of ZnO during nitridation of the starting materials to form GaN:ZnO. Some non-oxide photocatalysts with bandgap energy smaller than 3.0 eV, such as Y 2 Ti 2 S 2 O 7 , SrTaO 2 N and TaON having a bandgap energy of 1.9, 2.1 and 2.5 eV, respectively, are active and stable in the OWS reaction via one-step photoexcitation.…”

“…It is noteworthy that in a recent study, narrow-bandgap GaN:ZnO synthesized in a sealed evacuated tube and loaded with IrO 2 (IrO 2 /GaN:ZnO) exhibited a relatively negative photoanodic current onset (+0.3 V vs. RHE) compared to CoO x / LaTiO 2 N (+0.75 V vs. RHE) when studied as a photoanode for photoelectrochemical oxygen evolution. 20 Therefore, IrO 2 / GaN:ZnO would be an interesting candidate of the OEP to replace CoO x /BiVO 4 :Mo and CoO x /LaTiO 2 N in the photocatalyst sheet, which may allow to improve the ZOWS performance.…”