scholarly journals Highly Durable Graphene Monolayer Electrode on Insulating Substrate under Long-term Hydrogen Evolution Cycling

2022 ◽  
Author(s):  
Michel Wehrhold ◽  
Tilmann J Neubert ◽  
Tobias Grosser ◽  
Kannan Balasubramanian
Keyword(s):  
Chemical Modification ◽  
Hydrogen Evolution ◽  
Graphene Sheets ◽  
Graphene Monolayer ◽  
Force Microscopy ◽  
Long Term Stability ◽  
Atomic Force ◽  
Carbon Framework ◽  
Important Challenge

Electrochemical hydrogen evolution reaction (HER) at single graphene sheets has been investigated widely either in its pristine form or after chemical modification. One important challenge is the long-term stability of single graphene sheets on Si/SiO2 substrates under HER. Previous reports have found that due to stress developing under gas evolution, the sheets tend to break apart, with a very low lifetime limited to just a few cycles of HER. Here, we show through appropriate electrode preparation that it is possible to achieve highly durable single graphene electrodes on insulating substrates, which can survive several hundreds of HER cycles with virtually no damage to the sp2-carbon framework. Through systematic investigations including atomic force microscopy, Raman spectroscopy and electroanalysis, we show that even after so many cycles, the sheet is physically intact and the electron transfer capability of the electrodes remain unaffected. This extremely high stability of a single atomic sheet of carbon, when combined with appropriate chemical modification strategies, will pave way for the realization of novel 2D electrocatalysts.

Long-term stability and tree-ring oxidation of WSe2 using phase-contrast AFM

Nanoscale ◽  
2021 ◽  
Author(s):  
Lene Gammelgaard ◽  
Patrick Rebsdorf Whelan ◽  
Timothy J Booth ◽  
Peter Bøggild
Keyword(s):  
Atomic Force Microscopy ◽  
Tree Ring ◽  
Phase Contrast ◽  
Ambient Conditions ◽  
Force Microscopy ◽  
Long Term Stability ◽  
Atomic Force ◽  
Term Evolution ◽  
Ring Oxidation

In this work, we use atomic force microscopy (AFM) to investigate the long-term evolution of oxidative defects of tungsten diselenide (WSe2) in ambient conditions over a period of 75 months,...

scholarly journals Graphene Langmuir-Schaefer films Decorated by Pd Nanoparticles for NO2 and H2 Gas Sensors

2019 ◽  
Vol 19 (2) ◽  
pp. 64-69 ◽  
Author(s):  
Dmytro Kostiuk ◽  
Stefan Luby ◽  
Peter Siffalovic ◽  
Monika Benkovicova ◽  
Jan Ivanco ◽  
...  
Keyword(s):  
Gas Sensing ◽  
Pd Nanoparticles ◽  
X Ray Diffraction ◽  
X Ray ◽  
Force Microscopy ◽  
Si Substrates ◽  
Long Term Stability ◽  
Atomic Force ◽  
Few Layer Graphene

Abstract NO2 and H2 gas sensing by few-layer graphene (FLG) were studied in dependence on the annealing and decoration of graphene by palladium nanoparticles (NPs). Graphene was deposited onto SiO2 (500 nm)/Si substrates by a modified Langmuir-Schaefer technique. A solution of FLG flakes in 1-methyl-2-pyrrolidone was obtained by a mild sonication of the expanded milled graphite. FLG films were characterized by atomic force microscopy, X-ray diffraction, Raman spectroscopy, and the Brunnauer-Emmett-Teller method. Average FLG flake thickness and lateral dimension were 5 nm and 300 nm, respectively. Drop casting of Pd NP (6–7 nm) solution onto FLG film was applied to decorate graphene by Pd. The room temperature (RT) resistance of the samples was stabilized at 15 kΩ by vacuum annealing. Heating cycles of FLG film revealed its semiconducting character. The gas sensing was tested in the mixtures of dry air with H2 gas (10 to 10 000 ppm) and NO2 gas (2 to 200 ppm) between RT and 200 °C. The response of 26 % to H2 was achieved by FLG with Pd decoration at 70 °C and 10 000 ppm of H2 in the mixture. Pure FLG film did not show any response to H2. The response of FLG with Pd to 6 ppm of NO2 at RT was ≥ 23 %. It is 2 times larger than that of the pure FLG sample. Long term stability of sensors was studied.

scholarly journals Structure-Properties Correlation of Cross-Linked Penicillin G Acylase Crystals

Crystals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 451
Author(s):  
Marta Kubiak ◽  
Janine Mayer ◽  
Ingo Kampen ◽  
Carsten Schilde ◽  
Rebekka Biedendieck
Keyword(s):  
Mechanical Stability ◽  
Structural Characteristics ◽  
Penicillin G ◽  
Bacillus Species ◽  
Diffusion Limitations ◽  
Small Water ◽  
Long Term Stability ◽  
Atomic Force ◽  
First Time

In biocatalytic processes, the use of free enzymes is often limited due to the lack of long-term stability and reusability. To counteract this, enzymes can be crystallized and then immobilized, generating cross-linked enzyme crystals (CLECs). As mechanical stability and activity of CLECs are crucial, different penicillin G acylases (PGAs) from Gram-positive organisms have proven to be promising candidates for industrial production of new semisynthetic antibiotics, which can be crystallized and cross-linked to characterize the resulting CLECs regarding their mechanical and catalytic properties. The greatest hardness and Young’s modulus determined by indentation with an atomic force microscope were observed for CLECs of Bacillus species FJAT-PGA CLECs (26 MPa/1450 MPa), followed by BmPGA (Priestia megaterium PGA, 23 MPa/1170 MPa) and BtPGA CLECs (Bacillus thermotolerans PGA, 11 MPa/614 MPa). In addition, FJAT- and BtPGA CLECs showed up to 20-fold higher volumetric activities compared to BmPGA CLECs. Correlation to structural characteristics indicated that a high solvent content and low number of cross-linking residues might lead to reduced stability. Furthermore, activity seems to be restricted by small water channels due to severe diffusion limitations. To the best of our knowledge, we show for the first time in this study that the entire process chain for the characterization of diverse industrially relevant enzymes can be performed at the microliter scale to discover the most important relationships and limitations.

scholarly journals Wittichenite semiconductor of Cu3BiS3 films for efficient hydrogen evolution from solar driven photoelectrochemical water splitting

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Dingwang Huang ◽  
Lintao Li ◽  
Kang Wang ◽  
Yan Li ◽  
Kuang Feng ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Water Splitting ◽  
Low Cost ◽  
Solar Hydrogen ◽  
Onset Potential ◽  
Term Stability ◽  
Long Term Stability ◽  
Solar Water Splitting ◽  
Current Densities

AbstractA highly efficient, low-cost and environmentally friendly photocathode with long-term stability is the goal of practical solar hydrogen evolution applications. Here, we found that the Cu3BiS3 film-based photocathode meets the abovementioned requirements. The Cu3BiS3-based photocathode presents a remarkable onset potential over 0.9 VRHE with excellent photoelectrochemical current densities (~7 mA/cm2 under 0 VRHE) and appreciable 10-hour long-term stability in neutral water solutions. This high onset potential of the Cu3BiS3-based photocathode directly results in a good unbiased operating photocurrent of ~1.6 mA/cm2 assisted by the BiVO4 photoanode. A tandem device of Cu3BiS3-BiVO4 with an unbiased solar-to-hydrogen conversion efficiency of 2.04% is presented. This tandem device also presents high stability over 20 hours. Ultimately, a 5 × 5 cm2 large Cu3BiS3-BiVO4 tandem device module is fabricated for standalone overall solar water splitting with a long-term stability of 60 hours.

scholarly journals Strategy For Cellulase Immobilization And Its Partial Purification And Characterization

2021 ◽  
Author(s):  
Karina Komarova
Keyword(s):  
Active Site ◽  
Partial Purification ◽  
Purification Step ◽  
Purification And Characterization ◽  
Force Microscopy ◽  
Glycosidic Bonds ◽  
Atomic Force ◽  
Lower Glucose ◽  
Force Profile

Conversion of cellulose to glucose units by cellulases, called hydrolysis, is a very complex step in ethanol production. It requires the mixing of aqueous suspensions of cellulose/cellulases so that cellulases (majority composed of the active site domain and the binding site domain) can attach to cellulose chains, cut or hydrolyze ß(1-4) glycosidic bonds between glucose units, de-attach and move to another location. Mixing extent (insufficient or excessive agitation) might influence the attachment of cellulases and possibly lead to lower glucose yields. A long-term goal of this research is to determine the strength of mixing required to be applied during the cellulose-cellulase mixing cycle. For that purpose, one of the objectives was to purify CBH I exocellulase from the commercial cellulase mixture. A partial purification of the CBH I that was performed on a much smaller scale with uncontrolled flow rate was successful. Another objective was to propose a scheme that would covalently immobilize CBH I exoceullase via its active site domain (ASD) on an atomic force microscopy-compatible support, a silicon support. A theoretically-developed hypothetical scheme was constructed (with the provided detailed procedure). The approach of immobilizing the inhibitor specific to the ASD of CBH I enzyme led to the possibility that no purification of CBH I could be required. Skipping CBH I purification step would save time and hassle associated with purification step. Once the ASD of CBH I is immobilized on a silicon support, the AFM force profile between the free-floating CDB and substrate cellulose could be established.

Nanostructured molybdenum phosphide/N,P dual-doped carbon nanotube composite as electrocatalysts for hydrogen evolution

RSC Advances ◽  
2016 ◽  
Vol 6 (9) ◽  
pp. 7370-7377 ◽  
Author(s):  
Yang Zhao ◽  
Shuo Wang ◽  
Chunyan Li ◽  
Xianbo Yu ◽  
Chunling Zhu ◽  
...  
Keyword(s):  
Carbon Nanotube ◽  
Hydrogen Evolution ◽  
Alkaline Media ◽  
Term Stability ◽  
Long Term Stability ◽  
Excellent Activity ◽  
Molybdenum Phosphide ◽  
Carbon Nanotube Composite ◽  
Acidic And Alkaline Media

MoP/N,P dual-doped carbon nanotube composite exhibited excellent activity and long-term stability toward HER both in acidic and alkaline media, superior to most of catalysts reported previously.

scholarly journals Variation of Burkholderia cenocepacia cell wall morphology and mechanical properties during cystic fibrosis lung infection, assessed by atomic force microscopy

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
A. Amir Hassan ◽  
Miguel V. Vitorino ◽  
Tiago Robalo ◽  
Mário S. Rodrigues ◽  
Isabel Sá-Correia
Keyword(s):  
Mechanical Properties ◽  
Cystic Fibrosis ◽  
Atomic Force Microscopy ◽  
Cell Wall ◽  
Adaptive Evolution ◽  
Burkholderia Cenocepacia ◽  
Force Microscopy ◽  
Atomic Force ◽  
Morphology And Mechanical Properties

Abstract The influence that Burkholderia cenocepacia adaptive evolution during long-term infection in cystic fibrosis (CF) patients has on cell wall morphology and mechanical properties is poorly understood despite their crucial role in cell physiology, persistent infection and pathogenesis. Cell wall morphology and physical properties of three B. cenocepacia isolates collected from a CF patient over a period of 3.5 years were compared using atomic force microscopy (AFM). These serial clonal variants include the first isolate retrieved from the patient and two late isolates obtained after three years of infection and before the patient’s death with cepacia syndrome. A consistent and progressive decrease of cell height and a cell shape evolution during infection, from the typical rods to morphology closer to cocci, were observed. The images of cells grown in biofilms showed an identical cell size reduction pattern. Additionally, the apparent elasticity modulus significantly decreases from the early isolate to the last clonal variant retrieved from the patient but the intermediary highly antibiotic resistant clonal isolate showed the highest elasticity values. Concerning the adhesion of bacteria surface to the AFM tip, the first isolate was found to adhere better than the late isolates whose lipopolysaccharide (LPS) structure loss the O-antigen (OAg) during CF infection. The OAg is known to influence Gram-negative bacteria adhesion and be an important factor in B. cenocepacia adaptation to chronic infection. Results reinforce the concept of the occurrence of phenotypic heterogeneity and adaptive evolution, also at the level of cell size, form, envelope topography and physical properties during long-term infection.

Ta2O5-Incorporated WO3 Nanocomposite Film for Improved Electrochromic Performance in an Acidic Condition

2006 ◽  
Vol 6 (11) ◽  
pp. 3572-3576 ◽  
Author(s):  
Hee-Sang Shim ◽  
Hyo-Jin Ahn ◽  
Youn-Su Kim ◽  
Yung-Eun Sung ◽  
Won Bae Kim
Keyword(s):  
Surface Roughness ◽  
Photoelectron Spectroscopy ◽  
Potential Cycling ◽  
Force Microscopy ◽  
Atomic Force ◽  
Transmission Electron ◽  
Continuous Potential ◽  
Chemical States ◽  
The Stability

We report electrochromic and electrochemical properties of a WO3-Ta2O5 nanocomposite electrode that was fabricated from co-sputtering. Transmission electron microscopy (TEM)images of the WO3-Ta2O5 nanocomposite electrode revealed that morphology of the WO3 film was changed by incorporation of Ta2O5 nanoparticles, and their chemical states were confirmed to be W6+ and Ta5+ oxides from X-ray photoelectron spectroscopy (XPS). The introduction of Ta2O5 to the WO3 film played a role in alleviating surface roughness increase during continuous potential cycling; whereas the surface roughness of the WO3 film was increased from ca. 3.0 nm to ca. 13.4 nm after 400 cycles, the roughness increase on the WO3-Ta2O5 was significantly reduced to 4.2 nm after 400 cycles, as investigated by atomic force microscopy (AFM). This improvement of the stability by adding Ta2O5 may be responsible for the enhanced electrochemical and optical properties over long-term cycling with the WO3-Ta2O5 nanocomposite electrode.

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