scholarly journals Sputtered highly effective iridium catalysts: a new approach for green satellite propulsion

2021 ◽  
Vol 56 (16) ◽  
pp. 9974-9984
Author(s):  
Manfred Stollenwerk ◽  
Tobias Schäfer ◽  
Johannes Stadtmüller ◽  
Thorsten Döhring ◽  
Dominic Freudenmann ◽  
...  
Keyword(s):  
First Generation ◽  
Active Surface ◽  
Open Shell ◽  
Process Conditions ◽  
Active Surface Area ◽  
Zone Model ◽  
Space Propulsion ◽  
Iridium Catalysts ◽  
New Approach ◽  
Process Pressure

AbstractThis work demonstrated the large potential of sputtered iridium metal for catalytic reactions shown by the example of decomposition of hydrogen peroxide (H2O2) for space propulsion systems. For this purpose, iridium was coated onto Al2O3 pellets by a sputter process under varied process parameters. Depending on previously selected parameters, the obtained metal-loaded pellets offer closed- and/or open-shell structures. Catalytic productivity of these first-generation iridium-sputtered catalysts was estimated in laboratory experiments and compared to platinum-loaded pellets. Under optimized sputter-process conditions, the reactivity is significantly improved compared to the platinum-impregnated pellets. The better catalytic productivity can be explained by the increased active surface area of the iridium layers on the pellets. The surface morphology and the microstructure of the iridium coating can be actively controlled by the sputter pressure. The results are in accordance with the sputtering process pressure tendency described by the Thornton Structure–Zone Model. Graphical abstract

scholarly journals Synthesis of MWCNT Forests with Alumina-Supported Fe2O3 Catalyst by Using a Floating Catalyst Chemical Vapor Deposition Technique

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Shazia Shukrullah ◽  
Muhammad Y. Naz ◽  
Norani M. Mohamed ◽  
Khalid A. Ibrahim ◽  
Abdul Ghaffar ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Active Surface ◽  
Metal Catalyst ◽  
Process Conditions ◽  
Active Surface Area ◽  
Alumina Support ◽  
Vapor Deposition Technique ◽  
Catalyst Chemical Vapor Deposition

In this study, multiwalled CNT bundles were synthesized with an alumina-supported Fe2O3 catalyst by using a floating catalyst chemical vapor deposition (FCCVD) technique. The metal catalyst was synthesized by dispersing Fe2O3 on alumina support. Ethylene molecules were decomposed over different amounts of metal nanoparticles in a FCCVD reactor. The CVD temperature was elevated from 600°C to 1000°C. The large active surface area of the metal nanobuds promoted the decomposition of a carbon precursor and the fast growth of CNT bundles. Least dense bundles of varying heights were observed at lower CVD temperatures of 600°C and 700°C. At 800°C, CVD process conditions were found suitable for the fast decomposition of hydrocarbon. The relatively better yield of well-structured CNTs was obtained with a catalyst weight of 0.3 g at 800°C. Above 800°C, CNT forests start losing alignment and height. The forest density was also decreased at temperatures above the optimum. The elemental composition of CNT bundles revealed the presence of carbon, aluminium, oxygen, and iron in percentages of 91%, 0.76%, 8.2%, and 0.04%, respectively. A very small ID to IG ratio of 0.22 was calculated for CNTs grown under optimized conditions.

scholarly journals Electrochemical CO2 Reduction on Nanostructured Metal Electrodes: Fact or Defect?

2019 ◽  
Author(s):  
Recep Kas ◽  
Kailun Yang ◽  
Divya Bohra ◽  
Ruud Kortlever ◽  
Thomas Burdyny ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Structural Changes ◽  
Co2 Reduction ◽  
Catalyst Layer ◽  
Active Surface ◽  
Process Conditions ◽  
Active Surface Area ◽  
Catalytic Layer ◽  
Nanostructured Electrodes ◽  
Electrochemical Co2 Reduction

<div> <p>Electrochemical CO<sub>2</sub> reduction has received an increased amount of interest in the last decade as a promising avenue for storing renewable electricity in chemical bonds. Despite considerable progress on catalyst performance using nanostructured electrodes, the sensitivity of the reaction to process conditions has led to debate on the origin of the activity and high selectivity. Additionally, this raises questions on the transferability of the performance and knowledge to other electrochemical systems. At its core, the discrepancy is primarily a result of the highly porous nature of nanostructured electrodes, which are vulnerable to both mass transport effects and structural changes during the electrolysis. Both effects are not straightforward to identify and difficult to decouple. Despite the susceptibility of nanostructured electrodes to mass transfer limitations, we highlight that nanostructured silver electrodes exhibit considerably higher activity when normalized to the electrochemically active surface in contrast to gold and copper electrodes. Alongside, we provide a discussion on how active surface area and thickness of the catalytic layer itself can influence the selectivity, stability, activity and mass transfer inside and outside of the three dimensional catalyst layer. Key parameters and potential solutions are highlighted to decouple mass transfer effects from the measured activity in electrochemical cells utilizing CO<sub>2</sub> saturated aqueous solutions. </p> </div> <br>

scholarly journals Electrochemical CO2 Reduction on Nanostructured Metal Electrodes: Fact or Defect?

2019 ◽  
Author(s):  
Recep Kas ◽  
Kailun Yang ◽  
Divya Bohra ◽  
Ruud Kortlever ◽  
Thomas Burdyny ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Structural Changes ◽  
Co2 Reduction ◽  
Catalyst Layer ◽  
Active Surface ◽  
Process Conditions ◽  
Active Surface Area ◽  
Catalytic Layer ◽  
Nanostructured Electrodes ◽  
Electrochemical Co2 Reduction

<div> <p>Electrochemical CO<sub>2</sub> reduction has received an increased amount of interest in the last decade as a promising avenue for storing renewable electricity in chemical bonds. Despite considerable progress on catalyst performance using nanostructured electrodes, the sensitivity of the reaction to process conditions has led to debate on the origin of the activity and high selectivity. Additionally, this raises questions on the transferability of the performance and knowledge to other electrochemical systems. At its core, the discrepancy is primarily a result of the highly porous nature of nanostructured electrodes, which are vulnerable to both mass transport effects and structural changes during the electrolysis. Both effects are not straightforward to identify and difficult to decouple. Despite the susceptibility of nanostructured electrodes to mass transfer limitations, we highlight that nanostructured silver electrodes exhibit considerably higher activity when normalized to the electrochemically active surface in contrast to gold and copper electrodes. Alongside, we provide a discussion on how active surface area and thickness of the catalytic layer itself can influence the selectivity, stability, activity and mass transfer inside and outside of the three dimensional catalyst layer. Key parameters and potential solutions are highlighted to decouple mass transfer effects from the measured activity in electrochemical cells utilizing CO<sub>2</sub> saturated aqueous solutions. </p> </div> <br>

Tenacious Mass Transfer Limitations Drive Catalytic Selectivity during Electrochemical Carbon Dioxide Reduction

2019 ◽  
Author(s):  
Kailun Yang ◽  
Recep Kas ◽  
Wilson A. Smith
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Catalyst Layer ◽  
Active Surface ◽  
Active Surface Area ◽  
High Concentration ◽  
Copper Electrodes ◽  
Surface Enhanced ◽  
Local Current

<p>This study evaluated the performance of the commonly used strong buffer electrolytes, i.e. phosphate buffers, during CO<sub>2</sub> electroreduction in neutral pH conditions by using in-situ surface enhanced infrared absorption spectroscopy (SEIRAS). Unfortunately, the buffers break down a lot faster than anticipated which has serious implications on many studies in the literature such as selectivity and kinetic analysis of the electrocatalysts. Increasing electrolyte concentration, surprisingly, did not extend the potential window of the phosphate buffers due to dramatic increase in hydrogen evolution reaction. Even high concentration phosphate buffers (1 M) break down within the potentials (-1 V vs RHE) where hydrocarbons are formed on copper electrodes. We have extended the discussion to high surface area electrodes by evaluating electrodes composed of copper nanowires. We would like highlight that it is not possible to cope with high local current densities on these high surface area electrodes by using high buffer capacity solutions and the CO<sub>2</sub> electrocatalysts are needed to be evaluated by casting thin nanoparticle films onto inert substrates as commonly employed in fuel cell reactions and up to now scarcely employed in CO<sub>2</sub> electroreduction. In addition, we underscore that normalization of the electrocatalytic activity to the electrochemical active surface area is not the ultimate solution due to concentration gradient along the catalyst layer.This will “underestimate” the activity of high surface electrocatalyst and the degree of underestimation will depend on the thickness, porosity and morphology of the catalyst layer. </p> <p> </p>

scholarly journals High-Performance Lead-Acid Batteries Enabled by Pb and PbO2 Nanostructured Electrodes: Effect of Operating Temperature

2021 ◽  
Vol 11 (14) ◽  
pp. 6357
Author(s):  
Roberto Luigi Oliveri ◽  
Maria Grazia Insinga ◽  
Simone Pisana ◽  
Bernardo Patella ◽  
Giuseppe Aiello ◽  
...  
Keyword(s):  
High Performance ◽  
Active Material ◽  
Active Surface ◽  
Effect Of Temperature ◽  
Active Surface Area ◽  
Polycarbonate Membrane ◽  
Nanostructured Electrodes ◽  
Lead Acid Batteries ◽  
Improved Stability ◽  
Lead Acid

Lead-acid batteries are now widely used for energy storage, as result of an established and reliable technology. In the last decade, several studies have been carried out to improve the performance of this type of batteries, with the main objective to replace the conventional plates with innovative electrodes with improved stability, increased capacity and a larger active surface. Such studies ultimately aim to improve the kinetics of electrochemical conversion reactions at the electrode-solution interface and to guarantee a good electrical continuity during the repeated charge/discharge cycles. To achieve these objectives, our contribution focuses on the employment of nanostructured electrodes. In particular, we have obtained nanostructured electrodes in Pb and PbO2 through electrosynthesis in a template consisting of a nanoporous polycarbonate membrane. These electrodes are characterized by a wider active surface area, which allows for a better use of the active material, and for a consequent increased specific energy compared to traditional batteries. In this research, the performance of lead-acid batteries with nanostructured electrodes was studied at 10 C at temperatures of 25, −20 and 40 °C in order to evaluate the efficiency and the effect of temperature on electrode morphology. The batteries were assembled using both nanostructured electrodes and an AGM-type separator used in commercial batteries.

Hollow structure engineering of FeCo alloy nanoparticles electrospun in nitrogen-doped carbon enables high performance flexible all-solid-state zinc–air batteries

2020 ◽  
Vol 4 (4) ◽  
pp. 1747-1753 ◽  
Author(s):  
Yuanyuan Ma ◽  
Wenjie Zang ◽  
Afriyanti Sumboja ◽  
Lu Mao ◽  
Ximeng Liu ◽  
...  
Keyword(s):  
Active Sites ◽  
High Performance ◽  
Hollow Structure ◽  
Active Surface ◽  
Oxygen Electrode ◽  
Active Surface Area ◽  
Active Components ◽  
Nitrogen Doped Carbon ◽  
Structure Engineering ◽  
Kinetics Of

Hollow structuring of active components is an effective strategy to improve the kinetics of oxygen electrode catalysts, arising from the increased the active surface area, the defects on the exposed surface, and the accessible active sites.

scholarly journals Biofilm on the polymer composites - qualitative and quantitative microbiological analysis

2021 ◽  
Author(s):  
Dobrochna Ginter-Kramarczyk ◽  
Izabela Kruszelnicka ◽  
Michał Michałkiewicz ◽  
Przemysław Muszyński ◽  
Stanisław Zajchowski ◽  
...  
Keyword(s):  
Polymer Composites ◽  
Wood Flour ◽  
Biological Membrane ◽  
Polymeric Materials ◽  
Active Surface ◽  
Modern Technology ◽  
Biofilm Reactor ◽  
Active Surface Area ◽  
Microbiological Analysis ◽  
Wood Polymer

Abstract Background Modern technology, which has been getting more and more recognition in the world for the last several years, is the moving bed biofilm reactor (MBBR) technology. Currently, movable biofilters made of basic polymeric materials, polyethylene and polypropylene. Methods An innovative solution in the field, mainly because of the large active surface area for biological membrane can be wood polymer composites (WPC). In the research polypropylene (PP) and polyvinyl chloride (PVC) was used as the matrix. Two types of commercial wood flour also, selected from conifers, were selected for the study: Lignocel C 120 with particle sizes in the range of 70 μm–150 μm and L9 with dimensions of 0.8–1.1 mm and wood chips, which are used on an industrial scale for the production of chipboards, were used as a filler. A quantitative and qualitative analysis of newly formed biofilms was performed. Results The study showed a direct effect of the filler and its particle size on the susceptibility to the formation of the biofilm of on the composites surface. Conclusions Polypropylene PPH 648 T and 40% wt. of L9 type wood flour was the most susceptible to biofilm formation. Pure polypropylene PPH 648 T was the least susceptible material.

Increasing Active Surface Area to Fabricate Ultra-Hydrophobic Surface by Using “Black Silicon” with Bosch Etching Process

2012 ◽  
Vol 12 (6) ◽  
pp. 4919-4927 ◽  
Author(s):  
Nithi Atthi ◽  
Jakrapong Supadech ◽  
Gaetan Dupuy ◽  
On-uma Nimittrakoolchai ◽  
Apirak Pankiew ◽  
...  
Keyword(s):  
Surface Area ◽  
Hydrophobic Surface ◽  
Active Surface ◽  
Etching Process ◽  
Black Silicon ◽  
Active Surface Area

scholarly journals Preparation and Electrocatalytic Characteristics Research of Pd/C Catalyst for Direct Ethanol Fuel Cell

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Qiao Xia Li ◽  
Ming Shuang Liu ◽  
Qun Jie Xu ◽  
Hong Min Mao
Keyword(s):  
Fuel Cell ◽  
Average Particle Size ◽  
Active Surface ◽  
Carbon Support ◽  
Catalytic Performance ◽  
Active Surface Area ◽  
Average Particle ◽  
Ethanol Fuel ◽  
Direct Ethanol Fuel Cell ◽  
Electrochemical Active Surface Area

Two kinds of carbon-support 20% Pd/C catalysts for use in direct ethanol fuel cell (DEFC) have been prepared by an impregnation reduction method using NaBH4and NaH2PO2as reductants, respectively, in this study. The catalysts were characterized by XRD and TEM. The results show that the catalysts had been completely reduced, and the catalysts are spherical and homogeneously dispersed on carbon. The electrocatalytic activity of the catalysts was investigated by electrochemical measurements. The results indicate that the catalysts had an average particle size of 3.3 nm and showed the better catalytic performance, when NaBH4was used as the reducing agent. The electrochemical active surface area of Pd/C (NaBH4) was 56.4 m2·g−1. The electrochemical activity of the Pd/C (NaBH4) was much higher than that of Pd/C (NaH2PO2).

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