bluuebunny/crossref_metadata_2025_split huggingface dataset:
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
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).
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.
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.
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.
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