bluuebunny/crossref_metadata_2025 huggingface dataset:
The Impact of Exposed Surface Area on the Response of SWCNT Optical Sensors
Authors: Gillen Alice Judith , Siefman Daniel Jerome , Wu Shang-Jung , Bourmaud Claire , Lambert Benjamin Paul , Boghossian Ardemis Anoush
Published: February 2020

Due to their distinct and advantageous fluorescence properties, semiconducting single-walled carbon nanotubes (SWCNTs) are being applied to a variety of optical sensing applications. Limitations in solubility and biocompatibility have been overcome by non-covalently functionalizing the surface of the SWCNT with wrappings using techniques that retain its inherent fluorescence. Though wrappings based on surfactants and single-stranded DNA (ssDNA) have been extensively studied for this purpose, they are limited by factors such as lack of selectivity and lower fluorescence quantum yield, respectively.

In this study, we take advantage of the higher fluorescence emission of surfactant-coated SWCNTs and focus on new approaches that can tune their selectivity as sensors. Through the concomitant monitoring of both the fluorescence intensity and wavelength position of emission peaks, we demonstrate the ability to increase the selectivity of sensors based on surfactant-suspended SWCNTs while retaining their higher fluorescence intensity. These results provide not only a promising avenue for rationally designing SWCNT sensors, but also insight on the mechanisms governing the selectivity of existing SWCNT-based optical sensors.
Controlling Doping Profiles in Enriched Semiconducting Carbon Nanotube Networks for Novel Energy Harvesting Electronic Devices
Authors: Hao Ji , Ferguson Andrew John , Blackburn Jeffrey L.
Published: February 2020

Carbon nanotubes have drawn lots of interest due to their unique chemical structure, which confers excellent thermal, mechanical and electronic properties. In particular, semiconducting single-walled carbon nanotubes (s-SWCNTs) are being seen as the most promising candidate for future optical, electronic, and energy conversion applications, due to their structure-tunable electronic bandgap. The demand for high-performance, flexibility, and low weight miniaturized and portable electronic devices and power sources, suggest s-SWCNTs as a strong candidate for such applications. However, the ability to exert fine control over the optical and electronic performance of s-SWCNT components in these devices is critical to their widespread applicability. One strategy toward achieving this control is through manipulation of the Fermi level of the semiconducting single-walled carbon nanotubes through various doping approaches. In this presentation, we will first illustrate the strategies we have developed to create controlled charge-carrier doping profiles in highly pure s-SWCNT networks. And we characterize the spatial distribution of the charge-carrier doping profile using confocal resonant Raman microscopy and probe the resulting variation in the electronic transport properties using field effect transistor measurements. We will subsequently discuss the incorporation of these tailored spatial charge-carrier doping profiles into energy harvesting device architectures and discuss the various factors that determine the observed device performance.
The Effect of Catalyst Thickness and the Hydrogen Annealing Time on Spin Capability of Carbon Nanotube Forest with a Fast Temperature Ramping Rate CVD System
Authors: Choi Ye Il , Dousti Behnoush , Jung Daewoong , Lee Gil Sik
Published: February 2020

In this paper, we report the effects of iron (Fe) thickness and the hydrogen (H2) annealing time on the spin-capability of vertically aligned carbon nanotube (CNT) forest. Using a chemical vapor deposition chamber with a magnetic arm and mobile furnace, quick heating and cooling were done on the sample. For the growth process of carbon nanotube forest, the sample was moved from room temperature to 780 °C in 3 seconds in helium (He) environment, and H2 and acetylene (C2H2) were used as annealing gas and carbon source, respectively. To study the effect of Fe thickness on spin-capability, 1.5, 2.5, and 3.5 nm of Fe thin film was deposited using e-beam deposition tool on top of a thin aluminum oxide (Al2O3) layer. Also, the duration of hydrogen annealing time for the Fe film to form Fe nanoparticles were varied from 10 ~ 60 seconds. Fe film thickness of 2.5 nm and 30 seconds of H2 annealing time resulted in well-spinning vertically aligned carbon nanotube forest.
(Invited) Control of Diazonium Chemistry Defects on Nanocarbon Field-Effect Transistors
Authors: Bouilly Delphine , Bazan Claudia Marcela , Beraud Anouk , Bencherif Amira
Published: February 2020

Field-effect transistors made of carbon nanotubes or graphene can be used as electronic sensors, by functionalizing the nanocarbon surface to ensure specific binding with a target analyte. Among functionalization strategies, aryldiazonium salts are often chosen to form stable covalent adducts, but this reaction is challenging to control in terms of density and position of the grafts. In this presentation, I will describe recent developments in understanding and controlling the formation of diazonium-induced defects on nanocarbon materials, using electrical measurements in field-effect transistor devices. In particular, I will present recent developments on mechanical and electrochemical approaches to control such defects on carbon nanotube and graphene devices, as well as applications in electronic sensors and single-molecule experiments.
Functionalized Carbon Nanotube Phototransistors with Sub-Femtowatt Sensitivity at Room Temperature
Authors: Bergemann Kevin Joseph , Léonard François
Published: February 2020

Detecting low intensity light requires photodetectors with high gain. Carbon nanotube (CNT) transistors functionalized with light absorbers have emerged as a promising approach to realize photodetectors that could approach single photon sensitivity at room temperature. Our previous work demonstrated high sensitivity for CNT transistors functionalized with C60, with modeling indicating that electron-donating sensitizers could lead to even better performance. Here we explore this concept and present a P3HT-functionalized CNT phototransistor capable of detecting 500 aW of visible light at room temperature, corresponding to a responsivity of 2e9 A/W (Gain > 4e9). Furthermore, the dynamical processes lead to a significantly improved response time down to the millisecond range.

Combined, these factors suggest that functionalized quasi-one-dimensional channels are a promising path for next-generation room temperature photodetectors.
Decay Dynamics and Diffusion Lengths of Bright and Dark Excitons in Air-Suspended Carbon Nanotubes
Authors: Ishii Akihiro , Machiya Hidenori , Kato Yuichiro K
Published: February 2020

As excitonic states play an important role in optical phenomena [1] in carbon nanotubes, their fundamental properties such as emission lifetime and diffusion length have been studied by various optical techniques [2]. In the lowest lying states of excitons, however, there exist other “dark” states, whose properties are not well understood yet because they are not optically accessible. Here we separately investigate exciton dynamics of parity-odd bright state and parity-even dark state by performing time-resolved photoluminescence measurements on defect-free as-grown carbon nanotubes. The emission decay curves exhibit bi-exponential behavior, where the fast and slow decay components arise from the dynamics of bright and dark excitons, respectively. We analyze such exciton dynamics using a three-level model including the effects of end quenching by measuring chirality-identified nanotubes with different suspended lengths [Fig. 1]. We find that bright excitons have lifetimes of ~70 ps and diffusion lengths of several hundred nanometers, consistent with the known values. In comparison, dark excitons have much longer lifetimes in the order of nanoseconds and diffusion lengths longer than 3 μm. We also observe a tendency that nanotubes with larger diameter have higher bright-dark transition rate, which is likely due to the diameter dependence of the splitting energy between bright and dark states.

Work supported by JSPS (KAKENHI JP16K13613 and JP17H07359), MEXT (Nanotechnology Platform), and RIKEN (Incentive Research Project). H.M. acknowledges support by RIKEN Junior Research Associate Program.

[1] A. Ishii, T. Uda, Y. K. Kato, Phys. Rev. Appl. 8, 054039 (2017).

[2] A. Ishii, M. Yoshida, Y. K. Kato, Phys. Rev. B 91, 125427 (2015).

Fig.1 Emission decay curves obtained from (9,8) nanotubes with various lengths ranging from 0.5 μm (purple) to 4.2 μm (red). The gray line indicates the instrument response function. (inset) Schematic of the three-level model for exciton decay dynamics.

Figure 1
Bispyridinylidenes: Tunable Anolytes for Organic Redox Flow Batteries
Authors: Alkhayri Fahad , Dyker C. Adam
Published: February 2020

Redox flow batteries (RFBs) are highly promising systems for large scale energy storage applications. Whereas most redox flow cells are based on metallic active species in aqueous media, there has been increasing interest in developing flow batteries based on solutions of redox active organic compounds in organic solvents in order to achieve higher energy density. Organic compounds with high redox potentials, which can be used for catholyte solutions, are available, but in order to take advantage of the high cell potentials that are possible in organic solvents, new organic anolyte materials with lower redox potentials are needed. This presentation will outline our assessment of bispyridinylidene-based anolytes. These compounds are low potential two-electron donors that can be modified to improve solubility, cell voltage, and to limit diffusion through the ion exchange membrane.
(Invited) The Complementarity of Cr and Mo in Reinforcing Oxide Protectiveness on Ni-Cr-Mo Alloys.
Authors: Henderson Jeffrey D. , Ebrahimi Nafiseh , Li Xuejie , Ogle Kevin , Noel James J.
Published: February 2020

Ni-Cr-Mo alloys are extremely corrosion resistant as a result of the passive oxide film that spontaneously develops on the alloy surface upon exposure to the environment. We report on investigations of the influence of the oxide film composition on the susceptibility of the alloy to crevice corrosion, the rate, morphology and extent of crevice corrosion damage, and the tendency to stifle or repassivate the crevice. Chromium oxides are well known to provide a strong barrier to corrosion in solutions of moderate pH, over a wide range of oxidizing conditions. The corrosion susceptibility, however, can be decreased by alloying additions of Mo, which permit the deposition of Mo-rich corrosion products in response to the failure or partial failure of the Cr oxide barrier in acidic solution or crevice corrosion -a kind of “back-up plan” for the workhorse Cr. Mo can also help to defend against transpassive dissolution of Ni-based alloys, although this influence seems to be a transient effect that is dependent on the local pH. Here we report the results of galvanostatically driven crevice corrosion experiments, online analysis of dissolved corrosion products by atomic emission spectroelectrochemistry (AESEC) during transpassive polarization, and immersion testing in strong acid solution.
Characterizing Stainless Steel Oxides Under Oxygen Reduction Reaction Conditions
Authors: Anderson Rachel M , Hangarter Carlos M , Policastro Steven A
Published: February 2020

The oxygen reduction reaction (ORR) on stainless steel oxides is a complex process that can drive galvanic corrosion on more electrochemically active materials such as aluminum, as well as drive localized corrosion. The local structure of the oxide, including defects and variations in composition and microstructure, determines the catalytic properties of the surface, and importantly this structure changes with potential. At more negative potentials, the partially-reduced surface changes the properties of the oxide. Electrochemical studies of both a stainless steel alloy as well as pure Fe, Cr, and Ni samples are compared to discern the surface species present and their impact on the kinetics for the ORR. Electrochemical impedance spectroscopy is used to probe the changing oxide properties with applied potential. These measurements are supported by surface analytical techniques including X-ray photoelectron spectroscopy to determine oxidation states and composition of the initial oxide and after potential holds, as well as glow-discharge optical emission spectroscopy to depth-profile the distribution of elements at the surface.
Further Developments of a Modular One-Dimensional Analytical Galvanic Corrosion Model
Authors: Tan Yong Teck , Blackwood Daniel John
Published: February 2020

Galvanic corrosion is an important topic in corrosion research and modelling can help us better understand this phenomena, especially at the joint interface between dissimilar metals. The objective of this work is to provide a simple to use and easily accessible one-dimensional analytical modelling tool that can be implemented within a spreadsheet program.

This work is a further development of the modular analytical modelling approach introduced by G.L. Song in 2010.1 Three new types of building blocks (an “inert” block, a “linear transition” building block and a “sigmoid transition” building block) are introduced to the original set of three types of building blocks (a “left” building block, a “bridge” building block and a “right” building block) for this analytical modelling approach. This enhanced model also takes into account electrical resistivity of the electronic current path through the substrate material, which is important for materials that can have significant electrical resistivity, such as carbon composite materials and zinc-rich paints. With these new developments, this one-dimensional analytical modelling approach is now able to model a greater range of corrosion phenomena than previously possible, as the restrictions of having a constant solution resistivity and zero substrate electrical resistivity across all building blocks are removed.

Case studies published in the corrosion literature are analyzed with this model to examine its validity and accuracy. An experimental system of zinc-rich paint on carbon steel was also investigated and analyzed with this model. The benefits and limitations of this approach will be discussed and possible techniques to improve the analytical model accuracy by judicious selection of input values and generation of “performance envelopes” shared.

Reference:

G. L. Song, Corros. Sci., 52, 455–480 (2010).
Dielectric Properties of Silica-Based Nanoscale Organic-Inorganic Hybrid Materials (NOHMs)
Authors: Mapesa Emmanuel Urandu , Cantillo Nelly M. , Hamilton Sara Triana , Park Ah-Hyung , Zawodzinski Thomas A. , Sangoro Joshua R
Published: February 2020

Broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC) and Raman spectroscopy are employed to study a series of nanoscale organic-inorganic hybrid materials (NOHMs) comprising 20 wt% silica nanoparticles and either covalently or ionically-bonded polymer canopies. By comparing the NOHMs to the neat polymers used as canopies in their synthesis, we find that timescales characterizing molecular dynamics in the NOHMs largely depend on the interaction between the inorganic cores and the organic canopies. Interestingly, the NOHM materials retain liquid-like behavior, very much unlike conventional polymer nanocomposites. These findings demonstrate the potential of achieving unique and desired material properties via NOHMs by informed choice of the canopy material.
CO2electrolyzer Development: Preliminary Results from a Bipolar-Membrane-Based Flow Cell for Electrocatalytic Reduction of Carbon Dioxide
Authors: Deutsch Todd G , Chen Yingying , Vise Ashlee , Mooney Mason , Bender Guido , Klein Ellis , Neyerlin K C
Published: February 2020

The electrocatalytic reduction of carbon dioxide (CO2) to useful chemicals and fuels is an area of great importance and interest. However, the 10’s of mA/cm2 current densities in aqueous-based reactors must be scaled up one or two orders of magnitude for it to be integrated in to industrial processes. Several groups have shown this is possible by introducing CO2 to the cathode in the gas-phase via a gas diffusion electrode. Through a robust fuel cell research program, NREL has developed considerable expertise in manipulating gas-phase reactions from the material to device level. That expertise has recently been leveraged to develop CO2 electrolyzers that use a gas-phase cathode for CO2 reduction, water oxidation in alkaline aqueous electrolyte as the proton and electron source, separated by a bipolar membrane with an engineered 3-D interfacial layer. In this talk, we will describe the details of our device design and show initial results from runs on our first reactor iteration. We will also describe our progress in designing and fabricating new automated test stands, with real-time online reduction product analysis, capable of performing in-situ electrochemical diagnostics on dynamic processes in these complex systems. The ultimate goal of this project is to establish a platform to evaluate and benchmark promising CO2 electrocatalysts under conditions relevant to their incorporation in to a tangible solution to the problem for which they are intended to address.
Critical Parameters and Their Influence on Hybrid Supercapacitor with Silicon Based Anode
Authors: Dai Fang , Lapierre Robert , Cai Mei
Published: February 2020

Development of novel energy storage systems with high energy and power is highly demanded due to the rapid growing commercial electrical device market. Among many electrochemical energy storage systems, supercapacitor has been recognized as promising system for power-based applications. A hybrid structure using lithium-ion battery electrode paring with conventional electric double-layer electrode has drawn attention in recent years, as it provides higher energy and power density than traditional EDLC type capacitors.

Here we report a summary of our recent investigation on some critical parameters and their influence on the hybrid type supercapacitor using silicon based anode material. The study focused on the N/P ratio, electrode areal loading, prelithation of silicon based anode, electrolyte selection, etc. Besides ordinary chemical and electrochemical characterizations, we also utilized a modified 3-electrode setup to study the electrochemical behavior on both electrodes. Further analysis reveals the relationship between the full-cell voltage and electrode voltage. The impact of the critical parameters as mentioned above on the cycling stability and energy/power density will be discussed with the experiment result analysis. We’ll also share some principles for the active material screening, electrode fabrication and cell design targeting desired applications.
(Invited) Storing Electrons and Holes in the Electrolyte - a New Opportunity for Supercapacitors
Authors: Bodin Charlotte , Le Vot Steven , Taberna Pierre-Louis , Simon Patrice , Favier Frederic , Fontaine Olivier
Published: February 2020

Electrolytes are at the heart of batteries and supercapacitors and their primary role is always to conduct ions, even if their specifications are actually more complex: chemical stability, large cell voltage, high conductivity. However, depending on the design of the molecules that compose the cation and/or the anion, their function could be extending.

In the field of supercapacitors, energy density is a technological limitation. The main orientation is to manufacture new electrode materials, with a purely capacitive character (EDLC) or with a pseudocapacitive character (i.e. a Faradaic phenomenon with a supercapacitor signature). In an innovative way, approaches are beginning to appear in the literature that consists in adding redox molecules to the electrolyte to participate to the charge storage. Despite this promise to increase energy densities (or apparent capacities), two limits are clearly identified: (1) self-discharge is important and (2) shuttle effects decrease Coulombic efficiency.

We have recently shown that one of the opportunities is to use biredox ionic liquids. These molecules whose anion and cation are functionalized by redox molecules so that the cation and anion of the electrolyte contribute to charges storing. The announced advantage of this approach is that redox ionic liquid molecules are bulky molecules for which mass transfer becomes difficult after charging. This approach of inhibiting self-discharge and shuttle effects, through ion confinement, is interesting and represents a real alternative to storage using electro-actives electrolyte. However, achieving this confinement effect in a usual organic electrolyte such as acetonitrile is the real challenge. Moreover, studying the impact of the environment is fundamental to address this challenge. Indeed, succeeding in maintaining high performance but in an acetonitrile electrolyte (used in commercial devices) would allow these redox ionic liquids to be a credible alternative to the development of EDLC supercapacitors, while increasing their energy density (their apparent capacity). It is to this problem that we have addressed in this work: to find an alternative to redox electrolyte in supercapacitors by understanding the confinement of redox ionic liquid in pores.
Creating Scalable Faradaic Carbon Nanotube Electrodes with Mild Chemical Oxidation
Authors: Emmett Robert K , Kowalske Michael J , Mou Hansen , Grady Mikaela , Roberts Mark E.
Published: February 2020

The advancement of novel materials to ameliorate interfacial charge transfer properties will drastically improve energy storage, heterogeneous catalysis, and various other electrochemical applications. Here we discuss a facile method that can utilize the Faradaic capabilities of residual iron nanoparticle catalysts that are captured within Multi-walled Carbon Nanotubes (MWNT) post-synthesis, thereby correcting the difficulties associated with creating hybrid nanocomposite electrodes. Non-purified MWNTs, experience a chemical oxidation procedure in an acidic environment with KMnO4 to partly “unzip” the MWNTs and reveal the redox-active iron nanoparticles to the electrolyte. A consistent redox peak affiliated with the Fe2+/3+ transition is achieved during the MWNT oxidation procedure yielding a ~350% improvement in capacitance (>300 F g-1) when compared to purified MWNT electrodes (70 F g-1). While these materials solely may be applicable as energy storage electrodes, the integration of redox species within an inert carbon electrode will also provide new opportunities to accelerate heterogeneous charge transfer reactions.
Using Hmpa As an Additive in Sodium Supercapacitor Electrolyte to Increase Thermal Stability
Authors: Tyler Jameson Landon , Delnick Frank M. , Yang Guang , Nanda Jagjit
Published: February 2020

The development of hybrid electric vehicles (HEV) and portable electronic devices has caused greater demand for high energy and power density devices typically in the form of batteries, but supercapacitors are being integrated into these devices. Supercapacitors boast high power densities (104 W/kg), long cycle lives (>100,000), and simplicity in fabrication. One issue that arises in the practical use of supercapacitors in HEVs is the instability of the electrolyte at elevated temperatures (above 60° C) in the working environment. A number of these sytems use electrolyte systems are unstable at elevated temperaturesr have high vapor pressures that can lead to dangerous conditions for devices.

Another concern of supercapacitors is their narrow voltage window that directly affects the overall power density. One novel electrolyte has been discovered that contains sodium hexafluorophosphate (NaPF6) in dimethoxyethane (DME) that boasts a 4V voltage window. The issue arises when this electrolyte is placed at elevated temperatures. PF6
-based salts are well known for quick and irreversible thermal degradation that leads to device failure. This degradation is due to an equilibrium that forms between PF6
- and PF5
-
that occurs at elevated temperatures. PF5
- is unstable and will begin to decompose and react with the solvent, impurities, or the electrolyte itself which leads to an autocatalytic degradation reaction. In lithium ion batteries, this issue can be alleviated by the addition of hexamethylphosphoramide (HMPA). HMPA acts as a complexing agent with PF5
-, the thermal decomposition product of NaPF6. This complexing inhibits further decomposition of PF6
- which ultimately increases the thermal stability of the electrolyte.

Our work investigates the limitations and advantages of using HMPA as an additive in NAPF6
in DME. A combination of electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR) provides enough evidence to prove that NaPF6 in DME does not degrade at elevated temperatures.
(Invited) The Intersection of Battery and Capacitor Function in Nanostructured Manganese Oxides for Zinc-Ion Cells: Insights from 2D Interfaces to 3D Architectures
Authors: Long Jeffrey W. , Sassin Megan B. , So Christopher R , Ko Jesse S. , Jeon Seokmin , Parker Joseph F. , Chervin Christopher N. , Rolison Debra R.
Published: February 2020

The primary alkaline Zn/MnO2 battery remains a ubiquitous energy-storage solution for many consumer uses, though its application space is narrowing due to limited rechargeability. The inherent cost and safety benefits of the Zn/MnO2 pairing electrodes can be translated to a new class of rechargeable “zinc-ion” batteries that are enabled by specific nanostructured manganese oxides that undergo reversible redox reactions in mild-pH Zn2+-based electrolytes. We are exploring two such MnOx polymorphs—layered, birnessite-type and cubic-spinel ZnMn2O4—for zinc-ion storage, where the oxide is expressed as a nanoscale coating on carbon nanofoam (CNF) paper substrates. The optimized electron/ion transport characteristics of MnOx–CNF electrode architectures ensures high oxide-normalized capacity delivered at moderate-to-high rates and over hundreds of charge–discharge cycles. Pseudocapacitive reactions at the MnOx are also activated when Na+ or Li+ salts are added to the Zn2+-based aqueous electrolyte, enabling pulse-power functionality at time scales approaching those for electrochemical capacitors [1]. Redox reactions at MnOx zinc-ion electrolytes may follow multiple pathways that including direct Zn2+ insertion/association and proton-insertion processes that shift local pH to induce the precipitation of Znx(OH)y(SO4)z at the MnOx surface. Ex situ characterization by diffraction, spectroscopy, and microscopy confirms that the latter process is dominant with birnessite-MnOx–CNF electrodes, with the reversibility of this complex precipitation/dissolution process promoted by the pore–solid architecture of the CNF [2]. To further unravel the mechanisms of Zn-ion storage, we examine 2D-planar MnOx–carbon electrodes that mimic the surfaces of their 3D counterparts, applying such in situ techniques as scanning-probe microscopy and quartz-crystal microbalance measurements. Insights from these investigations inform the design of advanced electrode architectures for high-performance, rechargeable zinc-ion batteries.

[1] “Combining Battery-Like and Pseudocapacitive Charge Storage in 3D MnOx@Carbon Electrode Architectures in Zinc-Ion Cells.” J.S. Ko, M.B. Sassin, J.F. Parker, D.R. Rolison, and J.W. Long, Sustain. Energy Fuels, 2 (2018) 626–636.

[2] J.S. Ko, M.D. Donakowski, M.B. Sassin, J.F. Parker, D.R. Rolison, and J.W. Long, MRS Comm., 9 (2019) 99–106.
(Invited) Factors Affecting Electrochemical Capacitor Performance
Authors: Donne Scott W
Published: February 2020

Electrochemical capacitors are an emerging technology suited for high power pulse applications. The performance of these devices is dependent on their composite materials, including the electroactive materials, conductive additives and electrolyte, as well as the electrode substrates and separators, as well as cell engineering, which includes factors such as anode-to-cathode ratio and the amount of conductor added to each electrode. The combination of each of these factors leads to the overall performance of the device.

Many electrochemical methods have been used to explore the behaviour of electrochemical capacitors, with techniques such as cyclic voltammetry and galvanostatic charge-discharge cycling providing information on material performance. Other methods such as electrochemical impedance spectroscopy and potential floating measurements have also been used to provide performance, conductivity and stability information. We have also contributed to the development of electrochemical methods with the application of step potential electrochemical spectroscopy (SPECS) to a variety of electrochemical capacitor systems.

Here we will present a range of outcomes arising from the application of SPECS to explore the effects of electrolyte, charge storage mechanism, and conductivity on elctrochemical capacitor performance.
(Invited) A Versatile Approach for Pre-Lithiation of LIC and Increase of Their Energy Density Via Pyrene Chemistry
Authors: Gaubicher Joël , Anothumakkool Bihag , Ahmad-Baraza Yuman Sayed , Wiemers-Meyer Simon , Taberna Pierre-Louis , Daffos Barbara , Simon Patrice , Ewels Chris , Guyomard Dominique , Winter Martin , Brousse Thierry
Published: February 2020

Double-layer capacitors (EDLC) [1-2] show superior power density, excellent shelf life, high coulombic efficiency, which make them ideal candidates for high-power applications. However, their use remains hindered because of their relatively low energy density in comparison to batteries. Molecular redox grafting[3,4] is one of the two main strategies being currently considered to enable higher energy performance, the other one consisting in tailoring micropore size[5].

The first part of this talk will show based on Raman and XPS analysis as well as theoretical calculations (DFT), that appropriate coupling of pyrene derivatives and carbons allows to increase significantly both the storage capability and average potential of the positive electrode while keeping outstanding retention of both the initial capacity for more than 4000 cycles, and the power characteristics of full cells [6].

The second part of this presentation will show how this pyrene chemistry can advantageously be used to enable a novel and industry relevant-approach for pre-lithiation of lithium-ion capacitors (LIC) full cells [7]. Interestingly, the versatility of this approach makes it of interest not only of Li-ion but also Na-ion batteries.

References

[1] B. E. Conway, Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications, Springer (1999).

[2] P. Simon and Y. Gogotsi, Nat. Mater., 7 (2008) 845-854.

[3] D. Belanger and J. Pinson, Chem. Soc. Rev., 40 (2011), 3995-4048.

[4] L. Madec, A. Bouvree, P. Blanchard, C. Cougnon, T. Brousse, B. Lestriez, D. Guyomard and J. Gaubicher, Energy & Environmental Science, 5 (2012) 5379-5386.

[5] J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon and P. L. Taberna, Science, 313 (2006) 1760-1763.

[6] B. Anothumakkool, P.-L. Taberna, B. Daffos, P. Simon, Y-S.-Ahmad-Baraza, C. Ewels, T. Brousse and J. Gaubicher , J. Mater. Chem. A, 5 (2017) 1488-1494.

[7] B. Anothumakkool, S. Wiemers-Meyer, D. Guyomard, M. Winter, T. Brousse, and J. Gaubicher,
Advanced Energy Materials, in press.
Relationship between Basal Plane Dislocation and Local Basal Plane Bending in PVT-Grown 4H-SiC Crystals
Authors: Ailihumaer Tuerxun , Raghothamachar Balaji , Dudley Michael
Published: February 2020

Efforts to improve the quality and size of 4H-SiC wafers have resulted in size of 6” and dislocation densities of the order of 103 cm-2. The presence of significant quantities of crystallographic defects in bulk 4H-SiC crystals continues to be a major obstacle for achieving high-quality 4H-SiC substrates. Of particular note is the nucleation and distribution of basal plane dislocations (BPDs). BPDs are deformation-induced and are mostly generated during post-crystal growth cooling or high temperature annealing processes. BPDs have been associated with the formation of Shockley stacking fault leading to an increase in forward voltage degradation and are undesirable. Depending on the PVT growth conditions, internal stresses due to non-uniformity of temperature field cause lattice plane bending. During cooldown, this bending is accommodated by the inhomogeneous distribution of BPDs in a PVT grown 4H-SiC boule and persists in wafers sliced from the boule. Crystal bending affects subsequent wafer processing especially polishing and device fabrication. Therefore, analysis of the BPD distribution (sign and density) enables us to better understand basal plane bending, which provides insight into further improvement of the crystal growth process. Synchrotron Monochromatic Beam X-ray Topography (SMBXT) studies in grazing incidence geometry reveal the appearance of black and white contrast of BPDs which are associated with opposite sign of Burgers vectors. Based on the principle of ray tracing, black contrast BPDs are generated by focusing of diffracted X-rays when the extra half plane is extending away from the imaged surface, while defocusing of X-rays contribute to the generation of white contrast BPDs due to the extra half plane extending towards the surface [1]. The inhomogeneous distribution of the two types of BPD contrast will thus result in concave/convex shape of the basal planes. In our study, we have evaluated the ratio of the black/white contrast of BPDs along 11-20 direction across multiple 6-inch diameter 4H-SiC substrates sliced from the same and different boules and predicted how the lattice is tilted in different substrate wafers. High resolution X-ray diffraction measurements are currently underway to investigate the variation of rocking curve peak shift along 11-20 direction and thus to further verify our result.
Combining Pore-Scale Liquid Water Visualization and Modeling to Understand Water Transport in Operating Fuel Cells
Authors: Shrestha Pranay , Lee ChungHyuk , Fahy Kieran F. , Balakrishnan Manojkumar , Ge Nan , Bazylak Aimy
Published: February 2020

An in-depth understanding of liquid water transport in fuel cell gas diffusion layers (GDLs) has the potential to inform the development of novel water management strategies that lead to improved fuel cell performance at high current densities. Several visualization (1-4) and modeling (5, 6) studies have shed light into some of these mechanisms of liquid water transport. However, due to the heterogenous nature of porous materials within the fuel cells, pore-scale modeling and simulations are required for in-depth analysis.

Due to recent advancements in visualization techniques, particularly high-resolution synchrotron X-ray (1-4) and neutron (7) micro-computed tomography, the spatial distribution of liquid water within individual GDL pores during fuel cell operation can be resolved. In addition, pore network modeling (8) has been used to simulate and examine pore-to-pore water transport behavior within a wide range of GDL materials. However, we need to combine pore-network simulations with experimental data of realistic fuel cell conditions to study water transport in representative operating conditions in greater detail.

In this study, we combined 3-D computed tomography and pore network modeling to expand on our understanding of liquid water transport within gas diffusion layers of operating fuel cells. First, we used synchrotron X-ray tomography to examine the micron-scale GDL porous structure and in-operando 3-D liquid water distribution using a custom fuel cell specialized for imaging. Then, we simulated water transport within the examined GDL structure using pore network modelling. We then compared the 3-D experimental results to our simulations to gain a deeper understanding of realistic inlet conditions for liquid water transport within the GDL. The study demonstrates a robust strategy to probe, understand, and predict liquid water transport within the complex porous structures in PEM fuel cells.

References

S. J. Normile, D. C. Sabarirajan, O. Calzada, V. De Andrade, X. Xiao, P. Mandal, D. Y. Parkinson, A. Serov, P. Atanassov and I. V. Zenyuk, Meter. Today Energy.,
9 (2018).

J. Eller, J. Roth, F. Marone, M. Stampanoni and F. N. Büchi, J. Electrochem. Soc.,
164, 2 (2017).

S. S. Alrwashdeh, I. Manke, H. Markötter, M. Klages, M. Göbel, J. Haußmann, J. Scholta and J. Banhart, ACS Nano.,
11, 6 (2017).

P. Krüger, H. Markötter, J. Haußmann, M. Klages, T. Arlt, J. Banhart, C. Hartnig, I. Manke and J. Scholta, J.Power Sources.,
196, 12 (2011).

C. Y. Wang, Chem. Rev.,
104 (2004).

P. P. Mukherjee, Q. J. Kang and C. Y. Wang, Energy Environ. Sci.,
4, 2 (2011).

J. M. LaManna, Y. Yue, T. A. Trabold, J. D. Fairweather, D. S. Hussey, E. Baltic and D. L. Jacobson, Meet. Abstr. - Electrochem.Soc., 32 (2017).

J. Gostick, M. Aghighi, J. Hinebaugh, T. Tranter, M. A. Hoeh, H. Day, B. Spellacy, M. H. Sharqawy, A. Bazylak, A. Burns, W. Lehnert and A. Putz, Comput. Sci. Eng.,
18, 4 (2016).
Comparing Different Cross-Section Cutting Methods for SEM Analysis of Membrane-Electrodes Assemblies
Authors: Merino Susana , Novillo Carlos , de Diego Gonzalo , Conde Julio J , Folgado María Antonia , Ferreira-Aparicio Paloma , Chaparro Antonio M
Published: February 2020

The observation of membrane-electrodes assemblies (MEAs) in cross-section is a basic tool for their morphological characterization, and the study of changes occurring in the different layers by operation in a fuel cell. But the preparation of a well-defined and representative cross-section plane in the MEAs is difficult due to a layered structure with very different mechanical properties among the layers, including a Nafion membrane, two catalyst layers, and two gas diffusion layers. For this reason, the preparation of samples for cross-sectional observation requires appropriate cutting techniques able to leave a cross-sectional plane showing the morphology of each layer with minor changes, ie. avoiding uneven surfaces, mixing of layers, porosity and morphology alterations, and/or delamination. It is possible that no single method may accomplish with all requirements, so different cross sectioning procedures must be used to have a complete characterization. With this aim, different preparation methods for cross-section analysis of MEAs have been tested in order to make a comparative analysis, showing advantages and disadvantages for each of the methods.

The preparation procedures analyzed are cutting with sharp-edge, laser-cutting, embedded-mechanical polishing, and focused ion beam (FIB). Results are shown in the figure. Cutting with a sharp edge (Fig. a) is a quick and easy method that may provide good cross-sectional observation and morphology preservation if an appropriate tool is used and careful handling. However, the probability for a successful preparation is not high due to frequent intermixing of layers, delamination, and uneven surface. Laser-cutting with a CO2 laser (Fig. b)) occurs by burning and vaporization of the material, leaving a plane with a clear damage at a micrometric scale. Especially Nafion membranes and carbon clothes showed severe alteration of the phases in the cutting plane, so this method cannot be used for a micrometric study of the morphology of the layers. Mechanical polishing of an embedded MEA a resin (Fig.c) provides, on the other hand, better preserved layers and more reproducible results; the morphology of powder layers, like the catalyst layer and microporous layer, may be altered because of the rearrangement of particles during the polishing process. Better preservation of multilayered samples can be obtained with the FIB technique (Fig.d), although the observation profile cannot be extended beyond a few millimeters. The FIB cross-cutting technique, that may be combined with a cross section polishing with argon gas, appears to better preserve the morphology of the layers and in a reproducible way.

Acknowledgements.

This work was supported by the Ministerio de Economía y Competitividad of Spain, and Fondo Europeo de Desarrollo Regional (FEDER), Project E-LIG-E, ENE2015-70417-P (MINECO/FEDER).

Figure 1
Advanced Electron Microscopy Methods to Evaluate Thin Ionomer Films in PEM Fuel Cell Catalyst Layers
Authors: More Karren L. , Cullen David A.
Published: February 2020

The ability to characterize the structure and chemistry of ionomer films within the catalyst layers in membrane electrode assemblies (MEAs) at the Å-scale via analytical electron microscopy presents many challenges. The ionomer degrades rapidly during analysis with high-current electron beams, which can be mitigated to some extent when experiments are conducted using higher operating voltages and under cryogenic temperatures.1These microscopy operational parameters have proven most useful for imaging, mapping, and analyzing ionomer aggregates that are typically tens-to-hundreds of nms in size but have not been particularly useful for understanding the nature of thin ionomer films that percolate through the thickness of the catalysts layers.

Recently, Oak Ridge National Laboratory has acquired a new aberration-(probe)-corrected analytical scanning transmission electron microscope (STEM) that can be operated under conditions significantly more favorable for interrogating “soft matter” at very high resolution, e.g., structure and chemistry of the nm-scale thin ionomer films within intact catalyst layers. This new STEM, the JEOL-NEOARM, can be operated between 30kV-200kV under low-electron-dose conditions. The NEOARM is equipped with state-of-the-art analytical capabilities for the simultaneous acquisition of electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDS). Most notably, the new STEM is equipped with a novel pixelated detector that enables ultrafast image/diffraction (ptychographic) data acquisition that will minimize exposure of the ionomer films to the electron beam, preventing damage accumulation, and allowing for complete data reconstruction following data collection.

We will present imaging and spectroscopic results obtained by varying the STEM operating conditions on the NEOARM (voltage, electron dose, sample temperature, ptychography reconstruction methods) and exploiting its unique combination of low-dose and ultrafast capabilities. The high-resolution structural and chemical information will provide new insight regarding thin ionomer films within MEA catalyst layers

Research supported by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy, as part of the Fuel Cell Performance and Durability (FC-PAD) Consortium. Microscopy research performed as part of a user project at the Center for Nanophase Materials Sciences, which is a U. S. Department of Energy, Office of Science User Facility.

References

D.A. Cullen, R. Koestner, R.S. Kukreja, Z.Y. Liu, S. Minko, O. Trotsenko, A. Tokarev, L. Guetaz, H.M. Meyer, C.M. Parish, and K.L. More, “Imaging and Microanalysis of Thin Ionomer Layers by STEM,” Journal of The Electrochemical Society
161F1111-17 (2014).
Adsorption Behavior of Perfluorosulfonic Acid Ionomers on a Pt(111) Surface Observed By Atomic Force Microscopy
Authors: Devivaraprasad Ruttala , Masuda Takuya
Published: February 2020

Understanding of the adsorbed structure of ionomers on the Pt electrocatalyst and carbon support surfaces are very important to improve the cell performance of polymer electrolyte membrane fuel cells (PEMFCs). The effect of the solvent composition and temperature on the adsorbed structure of ionomers have been studied by using various techniques, such as 19F nuclear magnetic resonance (19F NMR) spectroscopy, cryogenic scanning electron microscopy (cryo-SEM), dynamic light scattering (DLS), small angle X-ray scattering (SAXS), small angle neutron scattering (SANS), and electron spin resonance (ESR) techniques. However, it has not been fully clarified yet, due to the complexity of the system composed of a variety of ingredients including the Pt electrocatalyst, carbon support, ionomers, solvent and other contaminants. Thus, we have investigated the adsorbed structure of ionomers on the Pt(111) surface as a model of an electrocatalyst by using atomic force microscopy (AFM) at various solvent compositions.

A droplet of aqueous solutions of Nafion was placed on Pt (111) surfaces mounted on the AFM sample holder. AFM measurements were performed with Acoustic AC mode AFM using Agilent 5500 AFM microscope (Agilent Technologies, USA) with a silicon nitride cantilever. The images were recorded over a period of ~30 minutes with a scanning area of 1 µm × 1 µm.

In a 2 wt% aqueous solution of Nafion, relatively small aggregates of Nafion ionomers with a height of ~2-3 nm were observed at the Pt(111) surface. Amount of adsorption increased with time and, eventually, the surface was entirely covered by randomly oriented aggregates with a thickness of ~4 nm. In a 0.2 wt% aqueous solution, aggregates larger than those observed in the 2 wt% aqueous solution were imaged, suggesting that larger aggregates were formed in the lower concentration solution. Such a concentration-dependent adsorption behavior is further discussed on the basis of solvent composition and conformation of Nafion ionomers in liquid phase.

References

Masuda, H. Naohara, S. Takakusagi, P. R. Singh, K. Uosaki: Chemistry Letters, 38, 884 (2009).

Masuda, S. Faridah, P. Singh, H. Naohara, K. Uosaki, Journal of Physical Chemistry C, 117, 15704 (2013).

Masuda, K. Ikeda, K. Uosaki, Langmuir, 29, 2420 (2013).
Influence of Pore Size Distribution on Operando Gas Diffusion Layer Liquid Saturation
Authors: Xu Hong , Bührer Minna , Marone Federica , Schmidt Thomas J. , Büchi Felix N. , Eller Jens
Published: February 2020

Hydrogen fed polymer electrolyte fuel cells (PEFCs) have drawn attention as key technology for future decarbonized energy systems [1], in particular in the mobility sector, due to their high current density at low operating temperatures and rapid start-up [2]. The liquid water generated during high current density operation may saturate the pores of gas diffusion layers (GDLs), hence impede the gas transport to the catalyst layer, leading to performance losses. Higher performance requires, improved water management in GDLs. In this work, the liquid water distribution in GDLs has been studied with an operando X-ray tomographic microscopy (XTM) setup at the TOMCAT beamline of the Swiss Light Source (SLS) at Paul Scherrer Institut (PSI) [3,4]. XTM scans with a duration of 0.1 s and a voxel edge length of 2.75 um were employed to investigate PEFCs assembled with three types of GDL materials (Freudenberg I6, Toray TGPH-060 and SGL 24BA) with increasing pore size (see Figure 1). Properties of the operando liquid saturation were determined between OCV and 1.25 A/cm2 at current steps of 0.25 A/cm2 under H2/air operation with 100%/0% and 100%/100% humidified gases at start-up temperature of 25 oC. The influence of the GDL substrate pore size, current density and gas humidity on liquid water saturation and connectivity in the GDL will be presented.

References:

[1] Int. Energy Agency, Advanced Fuel Cells Implementing Agreement Annual Report (2009).

[2] J. W. Pratt, L. E. Klebanoff, K. Munoz-Ramos et al., Sandia Report, SAND2011-3119 (2011).

[3] J. Eller, F. Marone, F. N. Büchi, ECS Trans. 69(17), 523–531 (2015).

[4] J. Eller, J. Roth, F. Marone, M. Stampanoni, F. N. Büchi, J. Electrochem. Soc. 164(2), 115-126 (2017).

Figure 1