bluuebunny/crossref_metadata_2025_split huggingface dataset:
Graphene Ring Nanoelectrodes (GRiNs): Application As an Electroanalytical Sensor
Authors: Ferrer-Huerta Miriam , Boxall Colin , Dickinson James William , Andrieux Fabrice , Freeman Neville J 
Published: February 2020

We present the fabrication and characterisation of Graphene Ring Nanoelectrodes (GRiNs) at size ranges below 10 nm. Graphene was obtained from chemically exfoliated graphite oxide (GO) prepared by a modified Hummers’ method. GO was dip coated from colloidal solution onto optical fibre and the consequential GO layer was reduced to graphene by both chemical (hydrazine) and thermal treatments. Subsequent electrical connections and isolation of the optical fibre were carried out.
In an attempt to reduce the thickness of the ring electrodes, mechanical exfoliation of the graphene layer was conducted using an adaptation of the classic Scotch tape method. This approach stripped off all the graphene layers from the optical fibre and was abandoned because it was not conducive to achieving GRiNs in the sub-5 nm domain. The lower limit for electrode thickness is 0.335 nm corresponding to a single layer of graphene.
In light of this previous trial, it was proven that the concentration of GO suspension and its viscosity governs the thickness of the graphene layer. Results show that previously used GO suspension concentrations of 10 wt% yield a thick fluid with non-newtonian rheological properties that result in GRiNs with micrometer range ring electrode thicknesses. Thinner, newtonian fluids are obtained at 1, 1.5, 2, 2.5, 4, 6, 8 and 8.5 wt%. Non-newtonian fluids are obtained at 8.6 wt%. GRINs fabricated using 4 wt% GO solution are found to be conducting and, through the application of electrochemical sizing methods, were proven to have ring electrode thicknesses in the sub-10 nm range.
The resultant nanoelectrodes are highly reliable, the nanoring design allows for efficient utilisation of electrochemically active edge sites. The behaviour of the so-formed graphene ring nanoelectrodes was studied using the well-known electrochemically reversible system of Fe(CN)6
4/3- with GRiNs of ring thicknesses 5-75 nm. Test results revealed that at thicknesses sub-10 nm, electron transfer rate constants are one order of magnitude larger than those obtained using macroelectrodes. Further, such GRiNs exhibit specific capacitances of two orders of magnitude greater than those reported for equivalent macroelectrodes.
These nanometer dimensions result in: increased densities of charge, and thus energy storage at the electrode surface compared to macroscopic systems; and enhanced rates of reactant mass transport to, and electron transfer across, the electrode/electrolyte interface (due to the more rapid potential drop within the diffusion double layer). These effects are especially enhanced at critical electrode dimensions of below 10 nm. Thus, their study consequently provides molecular level insight into nanoelectrochemistry application areas such as energy storage systems and environmental monitoring.
(Invited) Self-Assembly on Graphene and 2D Materials
Authors: De Feyter Steven 
Published: February 2020

Nanostructured monolayers of molecules can be formed at a variety of interfaces. At a liquid-solid interface, such two-dimensional (2D) molecular assemblies can be created by depositing a solution of the compound of interest on top of the substrate (drop casting) or by immersing the substrate into a solution (dip coating). Very often, only weak non-covalent interactions govern the interplay between molecules and molecules and substrate.
Advanced interface specific methods such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM) provide structural and other types of information at the nanoscopic level.
In this presentation, we focus on several aspects of molecular self-assembly at the interface between a liquid or air, and substrates such as highly oriented pyrolytic graphite and graphene. Highly oriented pyrolytic graphite can be considered as an excellent model surface for adsorption and self-assembly of molecules on graphene.
We will discuss the concept of 2D crystal engineering and the effect of solvent, solute concentration and temperature, bringing insight into thermodynamic and kinetics aspects of the self-assembly process at the interface between a liquid and graphite or graphene.1,2

Based on these insights, we will demonstrate molecular self-assembly based functionalization of graphite and graphene.3

Various applications will be presented,4 including tunable doping of graphene based field effect transistors5.
(1) De Feyter, S.; De Schryver, F. C. Chem.Soc.Rev. 2003, 32, 139.
(2) Mali, K. S.; Adisoejoso, J.; Ghijsens, E.; De Cat, I.; De Feyter, S. Acc.Chem.Res. 2012, 45, 1309.
(3) Li, B.; Tahara, K.; Adisoejoso, J.; Vanderlinden, W.; Mali, K. S.; De Gendt, S.; Tobe, Y.; De Feyter, S. ACS Nano 2014, 7, 10764.
(4) Xu, H.; Saletra, W. J.; Iavicoli, P.; Van Averbeke, B.; Schenning, A. P. H. J.; Beljonne, D.; Lazzaroni, R.; Amabilino, D. B.; De Feyter, S. Angew. Chem. Int. Ed. 2012, 51, 11981.
(5) Li, B.; Klekachev, A.; Cantoro, M.; Huyghebaert, C.; Stesmans, A.; Asselberghs, I.; De Gendt, S.; De Feyter, S. Nanoscale 2013, 5, 9640.

Figure 1
Material Deposition into Porous Silicon Template
Authors: Harraz Farid A. , Ismail Adel A. , Al-Sayari Saleh A. , Al-Hajry Ali , Al-Assiri Mohammad S. 
Published: February 2020

Porous silicon (PSi) is often fabricated by the electrochemical etching of silicon in a fluoride-based solution [1-4]. One of the unique properties of PSi layer is the ability to precisely tune the pore size and morphology through the variation of the silicon dopant type and level and controlling the applied anodic current and etching time. The compatibility of PSi with existing silicon processing technology adds another advantage. A wide range of materials including metals, conducting polymers, oxides, magnetic alloys and semiconductors can be deposited inside the pores of PSi templates by different techniques including; the electrochemical deposition, immersion plating and electroless deposition, sol-gel and chemical vapor deposition. Such deposition strategies would lead to various surface morphologies such as nanowires or nanorods, nanotubes, nanorings, nanodots and heterogeneous nano-macrostructures. The dimensions of as-formed hybrid structures can be controlled by regulating the shape and pore size of PSi template as well as the deposition conditions.
In this work, we used PSi as a template-directing synthesis of various metallic and polymeric nano-macrostructures. Firstly, preparation of various shapes and morphologies of PSi templates are given. Examples of chemical and electrochemical deposition of metals and conducting polymers are provided. We then focus on understanding of the mechanism of Cu deposition by the immersion plating method using the XPS sputter depth profiling into PSi template as a case study and discuss the processing issues associated with its deposition inside the nanoscale pores under the open-circuit condition.
Various pore diameters ranging from < 5 nm up to > 1 µm are accessible in PSi layers. Typical examples of SEM images of PSi templates, mainly ordered 5 µm macropores, 120 nm medium-sized pores and 20 nm mesopores are presented in Fig.1 [5]. Results of the synthesis and characterization of the obtained PSi-deposited materials will be presented and thoroughly discussed during the conference.

Keywords: Porous silicon; electrochemical deposition; immersion plating; Cu deposition; conducting polymer
References

F.A. Harraz, J. Sasano, T. Sakka, Y.H. Ogata, J. Electrochem. Soc., 149 (2002) C456.

F. A. Harraz, A. M. Salem, B. A. Mohamed, A. Kandil, I. A. Ibrahim. Appl. Surf. Sci., 264, (2013) 391.

F. A. Harraz. Appl. Sur. Sci., 287, (2013) 203.

F. A. Harraz, S. M. El-Sheikh, T. Sakka, Y. H. Ogata, Electrochim. Acta, 53, (2008) 6444.

K. Fukami, F. A. Harraz, T. Yamauchi, T. Sakka, Y. H. Ogata. Electrochem. Commun., 10, (2008) 56.

Figure 1
A Biomolecular Eco-Friendly Catalyst for Lithium-Oxygen Batteries
Authors: Ryu Won-Hee , Gittleson Forrest S , Taylor André D. 
Published: February 2020

In recent years lithium-oxygen (Li-O2) batteries have drawn much attention due to their exceptionally high energy density, which could exceed the capable value of conventional Li-ion batteries.1, 2 Li-O2 batteries operate via surface reactions that form (discharging) and evolve (charging) solid oxide products.3, 4 To facilitate reaction reversibility, the oxygen electrode for Li-O2 cells often requires an efficient catalyst. Yet insulating solid products formed during discharging often deactivate the catalyst surface, making product evolution difficult.5 Soluble catalysts have recently been shown to improve charge transfer with isolated or poorly conductive products near the electrode/electrolyte interface.6 Choosing proper catalytic molecules is essential to reduce the barrier to oxygen evolution in the Li-O2 cell. The redox molecules directly transport the generated electrons to/from the electrode substrate, consequently lowering overpotential. While a few redox molecules (e.g. Li iodide (LiI), tetrathiafulvalene (TTF), iron phthalocyanine (FePc), and 2,2,6,6-tetramethylpinperdinyloxyl (TEMPO)) have been investigated so far,6-9 seeking a low cost and environmentally friendly alternative is desirable.
In this presentation, we report the use of a common biomolecule as a soluble, eco-friendly catalyst to promote Li-O2 reactions with reduced overpotentials. We also elucidate the chemical reaction mechanism of its operation during oxide formation and evolution. In situ observations of chemical structure in the redox molecule are essential to establish the catalytic function and further design molecules for high performance Li-O2 battery systems. Here, we discuss the catalytic effects of the redox biomolecule on the significantly improved electrochemical characteristics of a practical Li-O2 battery.
1. D. G. Kwabi, N. Ortiz-Vitoriano, S. A. Freunberger, Y. Chen, N. Imanishi, P. G. Bruce and Y. Shao-Horn, Mrs Bull, 2014, 39, 443-452.
2. K. G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu and V. Srinivasan, Energy & Environmental Science, 2014, 7, 1555-1563.
3. W. H. Ryu, F. S. Gittleson, M. Schwab, T. Goh and A. D. Taylor, Nano Lett, 2015, 15, 434-441.
4. W. H. Ryu, T. H. Yoon, S. H. Song, S. Jeon, Y. J. Park and I. D. Kim, Nano Lett, 2013, 13, 4190-4197.
5. F. S. Gittleson, W. H. Ryu and A. D. Taylor, ACS Appl Mater Interfaces, 2014, 6, 19017-19025.
6. Y. H. Chen, S. A. Freunberger, Z. Q. Peng, O. Fontaine and P. G. Bruce, Nat Chem, 2013, 5, 489-494.
7. H. D. Lim, H. Song, J. Kim, H. Gwon, Y. Bae, K. Y. Park, J. Hong, H. Kim, T. Kim, Y. H. Kim, X. Lepro, R. Ovalle-Robles, R. H. Baughman and K. Kang, Angew Chem Int Edit, 2014, 53, 3926-3931.
8. B. J. Bergner, A. Schurmann, K. Peppler, A. Garsuch and J. Janek, J Am Chem Soc, 2014, 136, 15054-15064.
9. D. Sun, Y. Shen, W. Zhang, L. Yu, Z. Q. Yi, W. Yin, D. Wang, Y. H. Huang, J. Wang, D. L. Wang and J. B. Goodenough, Journal of the American Chemical Society, 2014, 136, 8941-8946.
Various Scales of Aging Heterogeneities upon PEMFC Operation – A Link between Local MEA Materials Degradation and the Cell Performance
Authors: Dubau Laetitia , Durst Julien , Castanheira Luis , Maillard Frederic , Lamibrac Adrien , Dillet Jérôme , Maranzana Gaël , Lottin Olivier , El Kaddouri Assma , De Moor Gilles , Bas Corine , Flandin Lionel , Rossinot Elisabeth , Caqué Nicolas , Chatenet Marian 
Published: February 2020

It is no secret that PEMFC performances decay upon operation, owing to the degradation of their core materials 1. Refining the data obtained from several experimental campaigns made in close collaboration between Axane and academic laboratories, it soon appeared that the materials degradations were not homogeneous within a PEMFC, whatever its operating conditions (stationary on the field or accelerated stress test at the laboratory scale) and their constitutive materials.
If one limits to the cathode active layer, there are three distinct levels of degradation heterogeneities. (i) At the scale of the MEA, the degradations are neither homogeneous along the gas channels of the bipolar plates (BP, from the inlet to the outlet, Figure 1) 2, nor along the active layer thickness (from the membrane interface to the diffusion layer interface) 2,3. (ii) The BP geometry also matters, since in the particular case of repeated start/stop and associated fuel-starvation events, harsher degradation was observed for the cathode regions facing the anode regions located under the land of the BP (Figure 2) 4. (iii) Finally, not all the cells operate and age in the same manner at the stack level (Figure 3) 5.
In any case, the degradations are strongly linked to the materials composing the MEA, but also depend on the fluidics of the cell (e.g. design of the bipolar plates and stack), which renders difficult any generalization of the conclusions obtained for a particular test.

References

(1) Gasteiger, H. A.; Vielstich, W.; Yokokawa, H. Handbook of Fuel Cells; John Wiley & Sons Ltd: Chichester, 2009; Vol. 5-6.
(2) Dubau, L.; Durst, J.; Maillard, F.; Chatenet, M.; Guétaz, L.; André, J.; Rossinot, E. Fuel Cells
2012, 12, 188.
(3) Ferreira, P. J.; la O', G. J.; Shao-Horn, Y.; Morgan, D.; Makharia, R.; Kocha, S.; Gasteiger, H. A. J. Electrochem. Soc.
2005, 152, A2256.
(4) Durst, J.; Lamibrac, A.; Charlot, F.; Dillet, J.; Castanheira, L. F.; Maranzana, G.; Dubau, L.; Maillard, F.; Chatenet, M.; Lottin, O. Appl. Catal. B: Environmental
2013, 138-139, 416.
(5) Dubau, L.; Castanheira, L.; Maillard, F.; Chatenet, M.; Lottin, O.; Maranzana, G.; Dillet, J.; ElKaddouri, A.; Basu, S.; De Moor, G.; Flandin, L.; Caqué, N. Int. J. Hydrogen Energy
2014, 39 21902

Figure 1
Effects of Repeated Feed-Gas Exchange Processes on Degradation Processes of Pt-Based PEFC Cathode Catalysts Studied by In-situ XAFS, STEM-EDS and Electrochemical Methods
Authors: Samjeské Gabor , Higashi Kotaro , Takao Shinobu , Sekizawa Oki , Kaneko Takuma , Nagamatsu Shinichi , Nagasawa Kensaku , Uruga Tomoya , Iwasawa Yasuhiro 
Published: February 2020

Start-up/shut-down procedures of polymer electrolyte fuel cells (PEFCs) result in temporal intermediate states of the anode Pt/C catalyst at the partial surface by exposing to both hydrogen and oxygen (air) in the feed-gas exchange processes of either air or H2 into the anode compartment. The inhomogeneous gas mixing in the anode leads to oxygen reduction reaction (ORR) at a part of the anode surfaces, which causes the corresponding cathode potential to spike up to about 1.6 V and hence carbon corrosion and Pt dissolution to deteriorate MEA performances. Recently, we reported the behavior of Pt/C cathode catalysts in MEAs during anode gas exchange cycles (AGEX )1,2 and cathode gas exchange cycles (CGEX)2 as characterized by in-situ time-resolved XAFS and STEM-EDS. Further investigations in this study have been done with an MEA Pt3Co/C cathode catalyst.
The Pt3Co/C cathode catalyst gave different results from those for the Pt/C cathode catalyst under both AGEX and CGEX conditions. While both performance and ECSA of the Pt/C cathode decreased with increasing AGEX cycles, only the performance decreased with the Pt3Co/C cathode. In the degradation process by the CGEX cycles neither performance nor ECSA decreased with the Pt3Co/C, while only the ECSA decreased with the Pt/C. Pt LIII-edge white line peak intensities for the Pt3Co/C showed a larger decrease under the AGEX conditions, but less under the CGEX conditions, comparable to the results obtained for the Pt/C as shown in Figure 1.
Figure1. Mass-activities (left axis) and averaged Pt LIII WL peak heights (right axis) for Pt/C (black) and Pt3Co/C (orange and green) during AGEX (left figure) and CGEX (right figure). The in-situ XAFS were measured at top (squares, open star for Pt3Co/C), middle (triangle), and bottom (circle) positions of the MEA.
(1) G. Samjeské et al., ECS Transactions,
64, 113-119 (2014)
(2) G. Samjeské et al., ChemElectroChem, DOI: 10.1002/celc.201500099

Figure 1
Impact of Cell Compression on Resistance, Mass Transport, and Ultimate PEMFC Performance
Authors: Sassin Megan B. , Garsany Yannick , Gould Benjamin D. , Swider-Lyons Karen 
Published: February 2020

The gas diffusion layer (GDL) plays multiple roles in the performance of a PEMFC: it provides pathways for fuel transport to and water away from the catalyst layer via the tortuous void/pore structure and it ensures a good electronic contact between the catalyst layer and the current collector of the PEMFC stack. A balancing act in cell assembly must be struck for the GDL to simultaneously offer the best transport pathways and electronic contact; different PEMFC operating conditions can require different assembly in terms of compression. To gain a better understanding of this balancing act and to optimize the performance of the PEMFC, we systematically varied the compression of a single cell PEMFC and evaluated it under different operating conditions to extract the impact on contact resistance and mass transport. Scanning electron microscopy of the GDL and catalyst layers post mortem reveal changes in the overall pore/void structure and provide further clues on the implications of compression on performance.
Silicon-Indium Tin Oxide Schottky Junction with Nickel Oxide Catalyst for Water Oxidation
Authors: Yoon Sanghwa , Lim Jae-Hong , Yoo Bongyoung 
Published: February 2020

The sunlight assisted water splitting using a photoelectrochemical (PEC) cell is an attractive approach to generate pure H2 and O2 without environmental pollution. The products by PEC solar fuel conversion can be separated, stored and transported, easily. To achieve high performance of PEC cell, the photoelectrode has several considerations such as efficient light absorption, catalysts and stability under aqueous solution. While hydrogen evolution reaction is simple electrochemical reaction and fast, oxygen evolution reaction (OER) is kinetically sluggish and includes multistep proton-coupled electron transfer.1-3 Therefore, effective catalysts are vital to be high efficiency of photoanode with OER. Recently, nickel oxide (NiO) receives attention as alternative OER catalyst of RuO2 or IrO2, because of low cost and high activity. Silicon (Si) with 1.1eV band gap and wide light absorption of the solar specturm is promising materials for water splitting. However, in alkaline electrolyte, the long-term stability of Si without passivation layer is poor and there cannot be formed photovoltage between Si and electrolyte. For effective PEC water oxidation of Si, it is necessary to select suitable protection layer, effective catalyst and generate large photovoltage.4

In this research, schottky junction between n-Si and ultrathin indium tin oxide (ITO) with high work function was fabricated for water oxidation by sputtering of ITO and the NiO nanoparticles were deposited by spray deposition method at relative low temperature of 260oC. A photocurrent density of 27.4mA/cm2 at 1.23V vs RHE, saturation current density of 37mA/cm2, and photovoltage as high as 545mV were achieved under solar illumination with 100mW/cm2(Fig. 1). In the high pH (1M KOH) electrolyte, the long-term stability of PEC water oxidation at 1.23V vs REH was observed with degradation of 34.23% for 96 hrs (Fig. 2). This work suggests the great approach to generate high voltage without n-p junction using doping process of Si and improve the performance and stability of Si photoanodes.
Reference

M. W. Kanan and D. G. Nocera, Science, 2008, 321, 1072-1075

M. Gratzel, Nature, 2001, 414, 338-344

O. Khaselev and J. A. Turner, Science, 1998, 280

J. Yang, K. Walczak, E. Anzenberg, F. M. Toma, G. Yuan, J. Beeman, A. Schwartzberg, Y. Lin, M. Hettick, A. Javey, J. W. Ager, J. Yano, H. Frei and I. D. Sharp, J. Am. Chem. Soc., 2014, 136, 6191-6194

Figure 1
Spray Pyrolyzed TiO2 / Sol Gel Dip Coated NiO Dye Sensitized Solar Cells
Authors: Murali Kollegal Ramakrishna 
Published: February 2020

TiO2 films were deposited on ITO coated glass substrates using spray pyrolysis technique. 0.1 M of Ti(acac) was dissolved in ethanol and sprayed onto indium tin oxide (ITO) substrates with dimensions of 75x25 mm2 at different substrate temperatures (T=375, 400, 425 and 450ºC) and annealed at 500 ºC for 1h in air. The substrates were first cleaned with water, followed by dipping in con.HCl, acetone and ethanol successively. Finally the substrates were rinsed in deionised water and allowed to dry in a hot air oven. NiO films of different thickness were deposited by sol gel dip coating adopting the following procedure. 20 ml of 0.1 M of nickel nitrate was taken in a beaker, to this acrylamide, n,n, bis acrylamide solution was added. The pH was adjusted to 9 and a few drops of ammonium persulphate was added, just before gellation, ITO substrate coated with TiO2 films were immersed in the above mixture and withdrawn at a slow rate. The coated film was dried for 15 min and then post heat vtreated in air at different temperatures ( T = 475,500 and 525°C) for 1 hour. For characterization of the films, individual films of TiO2 and NiO films deposited under identical conditions and of the same thickness were used. With increase of heat treatment temperature, the thickness decreased and the crystallinity improved.
The XRD profiles of the annealed TiO2 film is polycrystalline in nature and oriented along A (101) and A (200) planes, A (101) being the predominant peak. The films exhibited tetragonal crystal structure and the peak intensities are in agreement with the JCPDS data (No. 21-1272). The heat treatment NiO films indicated that the patterns show (1 1 1), (2 0 0) and (2 2 0) crystal planes of bulk NiO. For dense films obtained from Et/Bu, all peaks exhibit only cubic NiO structure from JCPDS 04-0835 with (1 1 1) preferential orientation.
The optical transmittance of NiO films increased with annealing temperature due to the increase in crystallite size and decrease in defects. At a wavelength of 550 nm. The Eg
value reduced from 3.76 to 3.56 eV with increasing heat treatment temperature. Band gap of the TiO2 films was calculated from the Tauc’s plot, the band gap decreased from 3.45 eV to 3.20 eV with increase of substrate temperature.
TiO2 and TiO2/NiO electrodes were immersed in an N719 solution for 24 h to adsorb sufficient dye. Pt was used as the cathode of the DSSC, and clamped together with the TiO2/NiO anode for cell testing. The electrolyte solution was dropped between the electrodes. The I-V characteristics was measured at 100 mW cm-2
illumination. LiI and Iodine was used as electrolyte. Bare TiO2 based DSSC cells exhibited a Voc of 450 mV and Jsc of 3.2 mA cm-2, these values increased to 690 mV and 7.0 mA cm-2 for the TiO2/NiO electrode post heat treated at 525°C. For the TiO2/NiO electrodes post heat treated at lower temperatures the values decreased.