Oriented p–n Heterojunction Ag₂O/Zn(O,S) Nanodiodes on Mesoporous SiO₂ for Photocatalytic Hydrogen Production

Abstract

Hydrogen is a great candidate fuel to replace fossil fuels in the future since it has high energy density, zero-emission, and renewability. Here, we report our design with p-type Ag2O and n-type Zn­(O,S) loaded on mesoporous silica to form SiO2/Ag2O/Zn­(O,S) with the nano p–n heterojunction to improve the efficiency of photocatalytic hydrogen evolution reaction (HER). The photocatalysts were systematically characterized to identify their properties. Through the optimization of the Zn­(O,S)-loaded amount and position of p-Ag2O, the highest hydrogen production rate of 9200 μmol·g–1·cat·h–1 was achieved by SiO2/Ag2O/Zn­(O,S)-0.6 catalyst with corresponding apparent quantum yield of 10.3%, which was about 2.7 times higher than pure Zn­(O,S). By placing n-Zn­(O,S) of diodes outward was proposed for the electron-rich part to enhance the reduction reaction, while placing p-Ag2O inward for the hole-rich part to modulate the electron concentration and establish the built-in electrical nanofield. The relative mechanism for improving the efficiency of HER has been investigated in this Article.

Amorphous-Ni(OH)2 on a Vertically Grown Lamellar Ag-Modified MoSx Thin-Film Electrode with Surface Defects for Hydrogen Production in Alkaline Solutions

“…The Mo 4+ , Mo 6+ , and Mo defect ratios are 35.7, 49.4, and 14.9%, respectively. Figure c reveals the existence of Ag + in NAM-1 with Ag 3d 5/2 and 3d 3/2 orbitals at 363.9 and 369.9 eV, respectively, which are consistent with previous works. ,, Figure d indicates that the orbitals of Ni 2+ 2p 3/2 and 2p 1/2 are located at 856.4 and 874.3 eV, respectively, with a spin-energy separation of ∼17.7 eV and two satellite peaks. − The oxygen analysis with high-resolution XPS shows three states of oxygen in chemisorbed water, hydroxides, and oxides bonded to nickel. The oxygen 1s orbitals after deconvolution revealed oxide, hydroxide, and chemisorbed oxygen, which were noticed at 529, 531, and 532.2 eV, respectively, as indicated in Figure e, agreed well with the previous work on Ni­(OH) 2 .…”

Morphology-Governed Performance of Multi-Dimensional Photocatalysts for Hydrogen Generation

“…It has been proposed that the combined effects of enhanced light harvesting, enlarged specific surface area (129 m 2 /g), hindered recombination of charge carriers, negatively shifted CB position, and an efficient exposure of active sites, are responsible for high photocatalytic activity (Figure 18). Another specific 3D structure has been presented by Gultom et al; a nanodiode of Ag2O and Zn(O,S), deposited on the surface of mesoporous silica to form the p-n heterojunction SiO2/Ag2O/Zn(O,S), as illustrated in Figure 19 [147]. It was found that the photocatalytic hydrogen generation has been obviously enhanced for the composite of n-Zn(O,S) with p-Ag2O (outward for improvement of reduction reactions, and inward for modulating the built-in electrical nanofield).…”

“…The remarkable enhancement of activity has been ascribed to the synergy between components via the following: (i) three-dimensional multi-bandgap quantum-well (3D MQW) band structure, (ii) improved photoabsorption, (iii) activity of surface oxygen, (iv) separation of charge carriers, (v) longer lifetime of charges, (vi) low charge transfer resistance, and (vii) the p-n heterojunction in the photocatalyst. Another specific 3D structure has been presented by Gultom et al; a nanodiode of Ag2O and Zn(O,S), deposited on the surface of mesoporous silica to form the p-n heterojunction SiO2/Ag2O/Zn(O,S), as illustrated in Figure 19 [147]. It was found that the photocatalytic hydrogen generation has been obviously enhanced for the composite of n-Zn(O,S) with p-Ag2O (outward for improvement of reduction reactions, and inward for modulating the built-in electrical nanofield).…”

“…Copyrights 2020 Elsevier [146]. Another specific 3D structure has been presented by Gultom et al; a nanodiode of Ag 2 O and Zn(O,S), deposited on the surface of mesoporous silica to form the p-n heterojunction SiO 2 /Ag 2 O/Zn(O,S), as illustrated in Figure 19[147]. It was found that the photocatalytic hydrogen generation has been obviously enhanced for the composite of n-Zn(O,S) with p-Ag 2 O (outward for improvement of reduction reactions, and inward for modulating the built-in electrical nanofield).…”

A molybdenum sulfo-oxide/cobalt oxysulfide Z-scheme heterojunction catalyst for efficient photocatalytic hydrogen production and pollutant reduction

“…In order to improve the preparation of heterojunction photocatalysts, it is of great signicance to design a heterojunction photocatalyst which can adjust the heterojunction two-phase energy band structure. On the basis of research by the same research group, 55,56 MoCoOS, a Z-scheme heterojunction catalyst prepared by simple hydrolysis of molybdenum and cobalt, has better hydrogen production capacity and excellent pollutant reduction capacity compared with other catalysts.…”