scholarly journals Stability and Degradation Mechanismof Si-based Photocathodes for Water Splitting with Ultrathin TiO2 Protection Layer

2019 ◽  
Vol 0 (0) ◽  
Author(s):  
Emanuel Ronge ◽  
Thorsten Cottre ◽  
Katharina Welter ◽  
Vladimir Smirnov ◽  
Natalie Jacqueline Ottinger ◽  
...  
Keyword(s):  
Water Splitting ◽  
Atomic Layer ◽  
Degradation Process ◽  
Alkaline Media ◽  
Semiconductor Surface ◽  
Nucleation Sites ◽  
Enhanced Solubility ◽  
High Structural Perfection ◽  
Protection Layer ◽  
The Stability

Abstract Using transmission and scanning electron microscopy, we study mechanisms which determine the stability of Silicon photocathodes for solar driven water splitting. Such tandem or triple devices can show a promising stability as photocathodes if the semiconductor surface is protected by an ultrathin TiO2 protection layer. Using atomic layer deposition (ALD) with Cl-precursors, 4–7 nm thick TiO2 layers can be grown with high structural perfection. The layer can be electrochemically covered by Pt nanoparticels serving as electro-catalysts. However, Cl-remnants which are typically present in such layers due to incomplete oxidation, are the origin of an electrochemical degradation process. After 1 h AM1.5G illumination in alkaline media, circular shaped corrosion craters appear in the topmost Si layer, although the TiO2 layer is intact in most parts of the crater. The crater development is stopped at local inhomogenities with a higher Pt coverage. The observations suggests that reduced Titanium species due to Cl−/O2− substitution are nucleation sites of the initial corrosion steps due to enhanced solubility of reduced Ti in the electrolyte. This process is followed by electrochemical dissolution of Si, after direct contact between the electrolyte and the top Si layer surface. To increase the stability of TiO2 protected photocathodes, formation of reduced Ti species must be avoided.

Coverage and Stability of NHx Terminated Cobalt and Ruthenium Surfaces: a First Principles Investigation

2019 ◽  
Author(s):  
Ji Liu ◽  
Michael Nolan
Keyword(s):  
Metal Surfaces ◽  
High Vacuum ◽  
Atomic Layer ◽  
Nitrogen Plasma ◽  
Operating Conditions ◽  
Ultra High Vacuum ◽  
Bridge Site ◽  
Stable Surface ◽  
Saturation Coverage ◽  
The Stability

<div>In the atomic layer deposition (ALD) of Cobalt (Co) and Ruthenium (Ru) metal using nitrogen plasma, the structure and composition of the post N-plasma NHx terminated (x = 1 or 2) metal surfaces are not well known but are important in the subsequent metal containing pulse. In this paper, we use the low-index (001) and (100) surfaces of Co and Ru as models of the metal polycrystalline thin films. The (001) surface with a hexagonal surface structure is the most stable surface and the (100) surface with a zigzag structure is the least stable surface but has high reactivity. We investigate the stability of NH and NH2 terminations on these surfaces to determine the saturation coverage of NHx on Co and Ru. NH is most stable in the hollow hcp site on (001) surface and the bridge site on the (100) surface, while NH2 prefers the bridge site on both (001) and (100) surfaces. The differential energy is calculated to find the saturation coverage of NH and NH2. We also present results on mixed NH/NH2-terminations. The results are analyzed by thermodynamics using Gibbs free energies (ΔG) to reveal temperature effects on the stability of NH and NH2 terminations. Ultra-high vacuum (UHV) and standard ALD</div><div>operating conditions are considered. Under typical ALD operating conditions we find that the most stable NHx terminated metal surfaces are 1 ML NH on Ru (001) surface (350K-550K), 5/9 ML NH on Co (001) surface (400K-650K) and a mixture of NH and NH2 on both Ru (100) and Co (100) surfaces.</div>

One-Dimensional TiO2@GaON Core-Shell Nanowires with Controlled Shell Thickness from Atomic Layer Deposition for Stable and Efficient Photoelectrochemical Water Splitting

2019 ◽  
Author(s):  
Jiajia Tao ◽  
Hong-Ping Ma ◽  
Kaiping Yuan ◽  
Yang Gu ◽  
Jianwei Lian ◽  
...  
Keyword(s):  
Atomic Layer Deposition ◽  
Band Gap ◽  
Water Splitting ◽  
Atomic Layer ◽  
Photoelectrochemical Water Splitting ◽  
Core Shell ◽  
Photoelectrochemical Performance ◽  
Highly Efficient ◽  
Layer Deposition ◽  
Shell Nanowires

<div>As a promising oxygen evolution reaction semiconductor, TiO2 has been extensively investigated for solar photoelectrochemical water splitting. Here, a highly efficient and stable strategy for rationally preparing GaON cocatalysts on TiO2 by atomic layer deposition is demonstrated, which we show significantly enhances the</div><div>photoelectrochemical performance compared to TiO2-based photoanodes. For TiO2@20 nm-GaON core-shell nanowires a photocurrent density up to 1.10 mA cm-2 (1.23 V vs RHE) under AM 1.5 G irradiation (100 mW cm-2) has been achieved, which is 14 times higher than that of TiO2 NWs. Furthermore, the oxygen vacancy formation on GaON as well as the band gap matching with TiO2 not only provides more active sites for water oxidation but also enhances light absorption to promote interfacial charge separation and migration. Density functional theory studies of model systems of GaON-modified TiO2 confirm the band gap reduction, high reducibility and ability to activate water. The highly efficient and stable systems of TiO2@GaON core-shell nanowires provide a deeper understanding and universal strategy for enhancing photoelectrochemical performance of photoanodes now available. </div>

scholarly journals Stabilized Hydroxide-Mediated Nickel-Based Electrocatalysts for High-Current-Density Hydrogen Evolution in Alkaline Media

2021 ◽  
Author(s):  
Yuting Luo ◽  
Zhiyuan Zhang ◽  
Fengning Yang ◽  
Jiong Li ◽  
Zhibo Liu ◽  
...  
Keyword(s):  
Water Splitting ◽  
Large Scale ◽  
Fossil Fuels ◽  
High Current Density ◽  
Critical Energy ◽  
Alkaline Media ◽  
Scale Production ◽  
High Current ◽  
Large Scale Production ◽  
Electrochemical Water Splitting

Large-scale production of green hydrogen by electrochemical water splitting is considered as a promising technology to address critical energy challenges caused by the extensive use of fossil fuels. Although nonprecious...

scholarly journals Superior FexN electrocatalyst derived from 1,1′-diacetylferrocene for oxygen reduction reaction in alkaline and acidic media

2020 ◽  
Vol 9 (1) ◽  
pp. 843-852
Author(s):  
Hunan Jiang ◽  
Jinyang Li ◽  
Mengni Liang ◽  
Hanpeng Deng ◽  
Zuowan Zhou
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Current Density ◽  
Active Sites ◽  
Reduction Reaction ◽  
Alkaline Media ◽  
Acidic Media ◽  
Onset Potential ◽  
Acidic And Alkaline Media ◽  
The Stability

AbstractAlthough Fe–N/C catalysts have received increasing attention in recent years for oxygen reduction reaction (ORR), it is still challenging to precisely control the active sites during the preparation. Herein, we report FexN@RGO catalysts with the size of 2–6 nm derived from the pyrolysis of graphene oxide and 1,1′-diacetylferrocene as C and Fe precursors under the NH3/Ar atmosphere as N source. The 1,1′-diacetylferrocene transforms to Fe3O4 at 600°C and transforms to Fe3N and Fe2N at 700°C and 800°C, respectively. The as-prepared FexN@RGO catalysts exhibited superior electrocatalytic activities in acidic and alkaline media compared with the commercial 10% Pt/C, in terms of electrochemical surface area, onset potential, half-wave potential, number of electrons transferred, kinetic current density, and exchange current density. In addition, the stability of FGN-8 also outperformed commercial 10% Pt/C after 10000 cycles, which demonstrates the as-prepared FexN@RGO as durable and active ORR catalysts in acidic media.

Distribution of Acidity and Alkalinity on Degraded Manuscripts Containing Iron Gall Ink

2015 ◽  
Vol 36 (3) ◽  
Author(s):  
Eva Marín ◽  
Maria Carme Sistach ◽  
Jessica Jiménez ◽  
Miguel Clemente ◽  
Guillem Garcia ◽  
...  
Keyword(s):  
Good Condition ◽  
Degradation Process ◽  
Degradation Processes ◽  
Alkaline Reserve ◽  
Hydrolysis Of Cellulose ◽  
Relevant Variables ◽  
Long Time ◽  
Iron Gall ◽  
The Stability

AbstractLong-time preservation of manuscripts depends on the stability of their support. One of the most important degradation processes of paper manuscripts containing iron gall ink is the acid hydrolysis of cellulose. The heterogeneity of the distribution of their constituent materials, together with the defined position of ink as a source of degradation agents, makes it difficult to obtain reliable and detailed information about degradation processes. The aim of this study is to contribute to the knowledge of the acid degradation process by looking at the distribution of relevant variables (pH, acidity and alkaline reserve) on real untreated iron gall ink containing manuscripts at different degradation stages. The study discusses the well-known differences between surface and cold extraction pH determination. It corroborates the relationship between pH, acidity and alkalinity and degradation stages, pointing out that acidity values for some manuscripts in apparent good condition are not far from those obtained for degraded manuscripts. The results indicate that in some partially degraded manuscripts, the coexistence of acid areas and areas with an alkaline reserve which do not participate in the neutralization process is possible. The role of water as a solvent for this equilibrium has also been evaluated.

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