scholarly journals Dual promotional effect of CuxO clusters grown with atomic layer deposition on TiO2 for photocatalytic hydrogen production

2021 ◽  
Author(s):  
Saeed Saedy ◽  
Nico Hiemstra ◽  
Dominik Benz ◽  
Hao van Bui ◽  
Michael Nolan ◽  
...  
Keyword(s):  
Hydrogen Production ◽  
Atomic Layer Deposition ◽  
Density Functional ◽  
Atomic Layer ◽  
Active Area ◽  
Content Increase ◽  
Tio2 Photocatalysts ◽  
Photocatalytic Hydrogen Production ◽  
Promotional Effect ◽  
Layer Deposition

The promotional effects on photocatalytic hydrogen production of CuxO clusters deposited using atomic layer deposition (ALD) on P25 TiO2 are presented. The structural and surface chemistry study of CuxO/TiO2 samples, along with first principles Density Functional Theory simulations, reveal the strong interaction of ALD deposited CuxO with TiO2, leading to the stabilization of CuxO clusters on the surface; it also demonstrated substantial reduction of Ti4+ to Ti3+ on the surface of CuxO/TiO2 samples after CuxO ALD. The CuxO/TiO2 photocatalysts showed remarkable improvement in hydrogen productivity, with 11 times greater hydrogen production for the optimum sample compared to unmodified P25. With the combination of the hydrogen production data and characterization of CuxO/TiO2 photocatalysts, we inferred that ALD deposited CuxO clusters have a dual promotional effect: increased charge carrier separation and improved light absorption, consistent with known copper promoted TiO2 photocatalysts and generation of a substantial amount of surface Ti3+ which results in self-doping of TiO2 and improves its photo-activity for hydrogen production. The obtained data were also employed to modify the previously proposed expanding photocatalytic area and overlap model to describe the effect of cocatalyst size and weight loading on photocatalyst activity. Comparing the trend of surface Ti3+ content increase and the photocatalytically promoted area, calculated with our model, suggests that the depletion zone formed around the heterojunction of CuxO-TiO2 is the main active area for hydrogen production, and the hydrogen productivity of the photocatalyst depends on the surface coverage by this active area. However, the overlap of these areas initiates the deactivation of the photocatalyst.

An ultrathin Al2O3 bridging layer between CdS and ZnO boosts photocatalytic hydrogen production

2020 ◽  
Vol 8 (21) ◽  
pp. 11031-11042 ◽  
Author(s):  
Dandan Ma ◽  
Zhenyu Wang ◽  
Jian-Wen Shi ◽  
Yajun Zou ◽  
Yixuan Lv ◽  
...  
Keyword(s):  
Hydrogen Production ◽  
Atomic Layer Deposition ◽  
Atomic Layer ◽  
Evolution Rate ◽  
Deposition Method ◽  
Photocatalytic Hydrogen Production ◽  
Layer Deposition ◽  
Atomic Layer Deposition Method

An ultrathin Al2O3 bridging layer is intentionally introduced into the interface between CdS and ZnO by using an atomic layer deposition method, and the resultant CdS@Al2O3@ZnO catalyst exhibits a significantly enhanced H2 evolution rate.

scholarly journals Synthesis and Thermal Study of Hexacoordinated Aluminum(III) Triazenides for Use in Atomic Layer Deposition

2020 ◽  
Author(s):  
Rouzbeh Samii ◽  
David Zanders ◽  
Sydney Buttera ◽  
Vadim Kessler ◽  
Lars Ojamäe ◽  
...  
Keyword(s):  
Atomic Layer Deposition ◽  
Density Functional ◽  
Atomic Layer ◽  
Single Step ◽  
Vapor Pressures ◽  
Scanning Calorimetry ◽  
Layer Deposition ◽  
Ligand Interactions ◽  
Deposition Processes ◽  
Decomposition Pathway

<p>Amidinate and guanidinate ligands have been used extensively to produce volatile and thermally stable precursors for atomic layer deposition. The triazenide ligand is relatively unexplored as an alternative ligand system. Herein, we present six new Al(III) complexes bearing three sets of a 1,3-dialkyltriazenide ligand. These complexes volatilize quantitatively in a single step with onset volatilization temperatures of ~150 °C and 1 Torr vapor pressures of ~134 °C. Differential scanning calorimetry revealed these Al(III) complexes exhibited exothermic events that overlapped with the temperatures of their mass loss events in thermogravimetric analysis. Using quantum chemical density functional theory computations, we found a decomposition pathway transforming the relatively large hexacoordinated Al(III) precursor into a smaller dicoordinated complex. The pathway relies on previously unexplored inter-ligand interactions, in which protons migrate between the triazenide ligands. These new Al(III) triazenides provides a series of alternative precursors with unique thermal properties that could be highly advantageous for vapor deposition processes of Al containing materials.</p>

scholarly journals First Principles Mechanistic Study of Self-Limiting Oxidative Adsorption of Remote Oxygen Plasma During the Atomic Layer Deposition of Alumina

2018 ◽  
Author(s):  
Glen N. Fomengia ◽  
Michael Nolan ◽  
Simon D. Elliott
Keyword(s):  
Atomic Layer Deposition ◽  
First Principles ◽  
Density Functional ◽  
Atomic Layer ◽  
Molecular Water ◽  
Mechanistic Study ◽  
Hydroxyl Groups ◽  
Layer Deposition ◽  
Surface Intermediates ◽  
By Products

Plasma-enhanced atomic layer deposition (ALD) of metal oxides is a rapidly gaining interest especially in the electronics industry because of its numerous advantages over the thermal process. However, the underlying reaction mechanism is not sufficiently understood, particularly regarding saturation of the reaction and densification of the film. In this work, we employ first principles density functional theory (DFT) to determine the predominant reaction pathways, surface intermediates and by-products formed when constituents of O<sub>2</sub>-plasma or O<sub>3</sub> adsorb onto a methylated surface typical of TMA-based alumina ALD. The main outcomes are that a wide variety of barrierless and highly exothermic reactions can take place. This leads to the spontaneous production of various by-products with low desorption energies and also of surface intermediates from the incomplete combustion of –CH<sub>3</sub> ligands. Surface hydroxyl groups are the most frequently observed intermediate and are formed as a consequence of the conservation of atoms and charge when methyl ligands are initially oxidized (rather than from subsequent re-adsorption of molecular water). Anionic intermediates such as formates are also commonly observed at the surface in the simulations. Formaldehyde, CH<sub>2</sub>O, is the most frequently observed gaseous by-product. Desorption of this by-product leads to saturation of the redox reaction at the level of two singlet oxygen atoms per CH<sub>3</sub> group, where the oxidation state of C is zero, rather than further reaction with oxygen to higher oxidation states. We conclude that the self-limiting chemistry that defines ALD comes about in this case through the desorption by-products with partially-oxidised carbon. The simulations also show that densification occurs when ligands are removed or oxidised to intermediates, indicating that there may be an inverse relationship between Al/O coordination numbers in the final film and the concentration of chemically-bound ligands or intermediate fragments covering the surface during each ALD pulse. Therefore reactions that generate a bare surface Al will produce denser films in metal oxide ALD.

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