bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fighting the Noise: Towards the Limits of Subsecond X-ray Tomographic Microscopy of PEFC
Authors: Xu Hong , Bührer Minna , Marone Federica , Schmidt Thomas J. , Büchi Felix N , Eller Jens 
Published: February 2020

Management and removal of liquid water is essential to maintain and improve the overall performance of polymer electrolyte fuel cells (PEFC). X-ray tomographic microscopy (XTM) of PEFCs has been proven as a valuable tool in order to understand accumulation of liquid water in the gas diffusion layer (GDL), both with in-situ [1-3] and operando setups [4-8]. Progress in operando XTM of PEFCs has paved the way for 4D imaging studies of the water distribution in the GDL [9]. In order to capture the water dynamics at high current density operation a further decrease of the scan time towards 0.1 s is aspired and the consequences of the reduced signal to noise ratio in the XTM data on water detectability need to be quantified.
In this work different imaging parameters and their consequences on the contrast-to-noise ratio (CNR) of water versus void have been studied with an ex-situ XTM experiment at the TOMCAT beamline of the Swiss Light Source (SLS) at Paul Scherrer Institut (PSI). The cathode channels of a double channel XTM cell [8] have been filled with liquid water, while keeping the anode channels empty, as shown in Figure 1. The CNR(H2O/Void) in the gas channels serves as an indicator for contrast between liquid water and void in the GDL to derive optimized imaging parameters for operando conditions. Over a range of monochromatic beam energies (13.5 – 21 keV) and scan times (0.2 – 10 s) a beam energy of 13.5 keV was found to be mostly appropriate as it provides the highest CNR value. The presentation will focus on the consequences of sub-second XTM acquisition time on the image processing pipeline for the detectability of small water droplets and their connecting paths.
References
[1] R. Flückiger, F. Marone, M. Stampanoni, A. Wokaun, F. N. Büchi., Electrochim. Acta, 56, 2254-2262, 2011.
[2] A. Lamibrac, J. Roth, M. Toulec, F. Marone, M. Stampanoni, F. N. Büchi, J. Electrochem. Soc., 163, F202-F209, 2016.
[3] I. V. Zenyuk, D.Y. Parkinson, G. Hwang, A.Z. Weber,, Electrochem. Comm., 53, 24-28, 2015.
[4] A. Schneider, C. Wieser, J. Roth, L. Helfen, J. Power Sources, 195, 6349-6355, 2010.
[5] P. Krüger, H. Markötter, J. Haussmann, M. Klages, T. Arlt, J. Banhart, Ch. Hartnig, I. Manke, J. Scholta, J. Power Sources, 196, 5250-5255, 2011.
[6] J. Eller T. Rosén, F. Marone, M. Stampanoni, A. Wokaun, F. N. Büchi, J. Electrochem. Soc., 158, B963-B970
2011.
[7] T. Rosén, J. Eller, J. Kang, N. I. Prasianakis, J. Mantzaras, F. N. Büchi, J. Electrochem. Soc., 159, F536-F544 2012.
[8] J. Eller, J. Roth, F. Marone, M. Stampanoni, F. N. Büchi, J. Electrochem. Soc., 164, F115-F126, 2017.
[9] J. Eller, F. Marone, F. N. Büchi, ECS Trans., 69, 523-531, 2015.
Figure 1: Quantitative comparison of the contrast-to-noise ratio (CNR) between water and void for different beam energies and scan times (middle); qualitative through-plane slices are given for 0.5 s (left) and 10 s scan time (right).

Figure 1
Investigation of Hydrogen Starvation of Polymer Electrolyte Fuel Cells in Freezing Condition Using Reference Electrode
Authors: Hu Leiming , Hong Bo Ki , Oh Jong-Gil , Litster Shawn 
Published: February 2020

For vehicles using polymer electrolyte fuel cells (PEFCs) to be commercially competitive with conventional internal combustion engine vehicles, three major challenges must be resolved, i.e., cost, performance and durability (1). The durability of a PEFC system can be largely affected by hydrogen starvation. During the startup/shut down process (2) of the fuel cell system, or when the flow channel is blocked by water or ice, local hydrogen starvation arises within one or many of the cells in the fuel cell stack. When this happens, hydrogen oxidation reaction (HOR) on the anode side cannot support the current imposed by the other cells. In that case, the anode half-cell potential increases relative to the cathode potential, and the cell voltage reverses. The high anode half-cell potential during cell reversal leads to water electrolysis and carbon corrosion reaction, the latter of which causes damage to the carbon support in the catalyst layer and leads to severe cell performance degradation. Hydrogen starvation in normal operating condition has been extensively investigated (3-5). However, little research has been conducted on cell reversal at sub-zero temperatures.
In past work on studying cell reversal, the anode potential and the corresponding reactions are estimated from the fuel cell voltage assuming a stable cathode potential. However, at sub-zero temperatures, ice formation affects both the anode and cathode potentials, which makes it difficult to evaluate the cell reversal origin and the anode half-cell potential. To better understand hydrogen starvation and cell reversal behavior of PEFCs sub-zero temperatures, a specially designed, easy-handling reference electrode has been developed and integrated with the membrane electrode assembly (MEA) in order to separate anode and cathode potentials, as shown in Fig. 1. The external hydrogen reference electrode is attached to the MEA through a thin polymer electrolyte bridge. With the reference electrode installed, the cell reversal behavior is investigated for both the typical operating temperatures (65-80 oC) and the sub-zero temperatures (e.g., -15 oC). At 65 oC, the cell voltage change during hydrogen starvation is mainly affected by anode potential change, which shows the potential plateau for water electrolysis and carbon corrosion. In contrast, the cell voltage experiences several transient states at -15 oC. Using the reference electrode, we identify that only one of the potential plateaus in caused by changes in the anode potential and the remainder are a result of phenomena related to ice formation in the cathode. Herein, we present several unique aspects related to hydrogen starvation cell reversal at sub-zero temperatures that are identified using the reference electrode.

Figure 1
Strategies to Improve PFSA Membrane Durability: Benefits and Challenges
Authors: Zaton Marta , Donzel Nicolas , Pasquini Luca , Cavaliere Sara , Rozière Jacques , Jones Deborah J. 
Published: February 2020

The durability of ionomer membranes is an important factor affecting the lifetime of proton exchange membrane fuel cells. Degradation of ionomer membrane causes performance losses that accelerate with time and result in catastrophic MEA failure. Membrane instability has two main origins mechanical fatigue and chemical degradation. Both modes strongly depend on the operating conditions applied: temperature, relative humidity, humidity cycling, reactant pressure, applied voltage and properties of the membrane, mainly the ionomer type and equivalent weight (EW), and membrane thickness. Thin membranes (<<20 µm) with low equivalent weight (<<800 EW) are required to achieve industry targets for FCEV however they are also more prone to undergo accelerated degradation.
This work focuses on the development and evaluation of different methods to increase durability through the development of a highly heterogeneous membrane system comprising a reinforcing component, radical scavenger and/or hydrogen peroxide decomposition catalyst and in which the architecture of the membrane is designed at the nano- to micro-metric length scales, the latter facilitated by the use of solution casting processes. Electrospun nanofibres provide mechanical strength, ensure low membrane swelling when exposed to humidity cycles, and also provide an appropriate distribution medium for radical scavenging species. This presentation will discuss benefits and remaining challenges associated with efficiency and stability of mechanical and chemical reinforcements.
Acknowledgement: This project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 671465 VOLUMETRIQ. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme.
Titanium Oxide-Supported Electrocatalysts for Polymer Electrolyte Fuel Cells
Authors: Ioroi Tsutomu 
Published: February 2020

Durability of the catalyst materials is one of the issue hindering widespread commercialization of fuel cell vehicles because durability is the problem not only for the product life, but also for product cost. Carbon corrosion of the electrode materials such as catalyst support and MPL is one of the causes of performance fading, so that much more stable catalyst support material is indispensable to improve the durability [1]. So far we have developed Magneli-phase titanium oxide supported Pt catalysts as corrosion-resistant PEFC electrocatalysts at higher potentials, however catalyst activity was unsatisfactory [2]. To improve ORR activity of Pt/Ti4O7 catalysts further, alloying Pt with transition metal such as Ni and Co is effective and commonly used way for carbon-supported catalysts. In this work, we report Pt-Ni or Co alloy catalysts deposited on the corrosion-resistant Ti4O7 supports. Sub-stoichiometric titanium oxide was prepared by pulsed UV laser technique [2], and Pt-alloy catalyst particles were prepared by conventional impregnation/reduction method. From SEM and XRD results, it was found that deposited alloy particles were ordered Pt3Ni/Pt3Co phase with particle diameter of 5-20 nm. Half-cell study revealed that Pt3Ni/Ti4O7 shows increased ORR activity (0.80 mA cm-2
Pt @0.9 V in 0.1 M HClO4, 25oC) compared to commercial Pt/C catalyst (TKK TEC10V40E, 0.36 mA cm-2
Pt). MEA with Pt3Ni/Ti4O7 cathode was also examined, and confirmed the improved ORR activity. To examine the stability against higher potentials under MEA condition, accelerated stress test (AST) for start-up/shut-down was conducted according to FCCJ protocol. Similar to the Pt/Ti4O7 catalysts [2], improved stability of Ti4O7-supported Pt3Ni was also demonstrated. Detailed physicochemical properties of the prepared catalyst and stability of the cell performance will be discussed at the meeting.
Reference
1) T. Arai, T. Ozaki, K. Amemiya, T. Takahashi, SAE International Journal of Alternative Powertrains, Vol. 6(1), (2017).
2) T. Ioroi, T. Akita, M. Asahi, Y. Yamazaki, Z. Siroma, N. Fujiwara, K. Yasuda, J. Power Sources, 223, 183 (2013).
(Invited) Mapping Internal Polarization in YSZ Electrolytes Using Grain Size
Authors: Chen I-Wei , Dong Yanhao 
Published: February 2020

Polarization development near the electrodes is important for the performance of YSZ devices. However, there are very difficult to measure experimentally. Embedded electrodes have been used to obtain a few readings across the electrolyte thickness, but so far there has been no report that provides a continuous mapping of the electrolyte polarization. Here we demonstrate that grain growth provides a means for such mapping. The method is based on the observation that cation mobility in YSZ (as well as other fluorite structured oxides) increases rapidly with decreasing oxygen potential.
Placing YSZ under a large current in various atmospheres between electrodes of various configurations, we have created many grain size distributions that vary continuously or discontinuously between the cathode and anode. Aided by the correlation between grain boundary mobility and non-stoichiometry, the grain size map can be converted to a polarization map. Such mapping allows us to quantitatively assess the influence of electrode kinetics and atmosphere on internal polarization under large current conditions.
Under the same conditions of enhanced grain growth, we have observed widespread cavitation throughout YSZ in nearly all the samples tested in a reducing atmosphere. This is surprising since the prevailing theory attributes cavitation to oxygen bubbles, and it predicts oxygen bubbles to form inside the YSZ electrolyte only under a large positive oxygen potential. Yet the large grain size in our cavitated samples clearly indicates a large negative oxygen potential. Therefore, we must rule out the oxygen bubble model. Instead, we propose that cavitation in these samples is in the form of voids, which come from condensation of supersaturated oxygen vacancies.
These results further suggest strong electronic conduction in the electrolyte. Indeed, the observation of cavitation implies internal reactions between electronic defects and ionic defects, rendering the latter no longer fully ionized. These reactions have the effect of buffering the oxygen potential inside the electrolyte. The observed oxygen potential and grain size transition can only be successfully modeled by taking into account such internal reactions.
Strain-Based Scanning Probe Techniques for Imaging Space Charge Regions in Sm-Doped Ceria
Authors: Gerwe Brian S , Adler Stuart B. , Esfahani Ehsan N , Wang Peiqi , Chen Qian Nataly , Li Jiangyu 
Published: February 2020

Widespread implementation of renewable, but intermittent, energy sources is contingent upon a new generation of high performance batteries and electrolysis devices to store and convert energy chemically. However, development efforts are hindered by limited knowledge of kinetic and transport properties at the nanoscale, which often differ substantially from bulk properties. A deeper understanding of localized properties and their impact on material and device performance would facilitate further advancements in electrode materials which could lead to more cost effective energy storage and conversion devices.
Traditional characterization techniques, such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), can probe kinetic and transport rates as functions of applied potential and timescale, but cannot resolve spatial variations. To elucidate localized response under dynamic polarization, we are currently developing scanning probe techniques that will act as a nanoscale witness of local response in operando during EIS measurements. These techniques include electrochemical strain microscopy (ESM) and, more recently, scanning thermionic microscopy (STIM). In ESM a potential is applied to a conductive atomic force microscopy (AFM) tip, thus generating an electric field in a sample to drive ionic motion. This causes a strain in the material, often interpreted as Vegard strain, which is detected as a deflection of the AFM tip1. STIM functions by applying a periodic temperature perturbation from a heating element located on top of the AFM tip, inducing ionic motion by thermal stress. Again, material strain is detected by deflection of the tip, from which the fourth harmonic of the input frequency is related to shifts in chemical composition2.
We are currently applying these methods to two model systems: Gd-doped CeO2 , a common solid oxide fuel cell electrolyte, and Li1-xCoO2 ,often used as a positive electrode material in solid state lithium-ion batteries.
References:
1. Balke, N. et al. Nanoscale mapping of ion diffusion in a lithium-ion battery cathode. Nat. Nanotechnol.
5,749–754 (2010).
2. Eshghinejad, A. et al. Scanning thermo-ionic microscopy for probing local electrochemistry at the nanoscale. J. Appl. Phys.
119, 205110 (2016).
Bis(2-chloroethyl) ether-1,3-bis[3-(Dimethylamino)propyl]urea copolymer -Chitosan–Poly(acrylamide-co-diallyldimethylammonium chloride) blends as membranes For Alkaline Anion-exchange Membranes
Authors: Ao Bei , Wei Ya Nan , Qiao Jin Li 
Published: February 2020

Solid, thin, and flexible energy storage devices are required to power flexible and wearable technologies which are rapidly growing in importance. One of the key components for solid-state energy storage is a polymer electrolyte which eliminates liquid electrolyte leakage and minimizes bulky packaging. An ideal polymer electrolyte for supercapacitors should exhibit the following properties: (a) high ionic conductivity; (b) a wide electrochemical stability window for maximum cell voltage; and (c) high environmental and temperature stability for device safety and long service life[1-3].
In this paper, the novel, low-cost alkaline anion-exchange membranes (CS/PDDA), made from Chitosan and poly(diallyldimethylammonium chloride) blends, are successfully synthesized by a combined thermal and chemical cross-linking technique. The hydroxide conductivity (OH-), water uptake, ion exchange capacity (IEC), thermal stability, oxidative stability and alkaline stability of CS/PDDA membranes are measured to evaluate their applicability in electrochemical capacitors. The effects of membrane composition on OH- conductivity are studied using AC impedance technique. It is found that by cross-linking modifications, the membranes exhibit high OH- conductivity of 0.0162S cm-1 is achieved at m (CS) : m (PDDA)=1:0.5. The CS/PDDA membranes as electrode materials for supercapacitor demonstrated a wide voltage window (1.5 V), and exhibit high specific capacitance of 27.6 mF cm-2 at 100 mV s-1.
References
[1] H. Gao, K. Lian, RSC Advances, 4,33091(2014) .
[2] H. Gao, J. Li, K. Lian, RSC Advances, 4,21332(2014).
[3] M. Kaempgen, C.K. Chan, J. Ma, Y. Cui, G. Gruner, Nano Letters, 9,1872(2009).
Solid Acid Proton Conductors: Insights into Proton Conduction Mechanisms and Advances in Electrode Architectures
Authors: Elgammal Ramez Ahmed , Zawodzinski Thomas A. 
Published: February 2020

Intermediate-temperature fuel cell (ITFC) systems have recently received significant interest for stationary distributed generation applications. As opposed to high-temperature (> 650 °C) solid-oxide fuel cells (SOFCs), intermediate-temperature systems (200-500 °C) may be capable of reaching cost targets by relaxing material re­quirements for interconnects and systems-level requirements for insulation, heat exchangers, and other balance-of-plant elements. ITFCs may operate on minimally-processed fossil fuels such as natural gas, rather than the ultra-purified hydrogen required for low-temperature (< 100 °C) polymer electrolyte membrane fuel cells (PEMFCs), a feature that could possibly accelerate adoption due to the existence of established distribution networks for these fuels.
Various proton conducting solid acids of the general formula MHxXO4 (M = K, Cs, Nd; x = 0-2; X = S, P) have attracted considerable interest as electrolytes for ITFCs. We will present an overview of distinguishing structural features of these solid acids, temperature induced phase transitions, and comment on the varying mechanisms of proton conduction using studies from NMR, XRD, FT-IR, Raman microscopy, and AC impedance spectroscopy.
The most promising candidate for solid acid fuel cells (SAFCs) is CsH2PO4 (CDP). The current state-of-the-art SAFC utilizes thin films of platinum nanoparticles on a porous framework of CDP electrolyte. Our methodology to improve Pt utilization, increase electrode surface area, and electrical interconnectivity was achieved by using carbon-based supports for the electrocatalyst and homogenizing framework with CDP. Using a combination of chemical functionalization of nanostructured carbon and infiltration of CDP, we fabricated nanocomposite electrodes that demonstrated vastly superior performance. For example, at 0.8V and 250 °C, a hydrogen-air SAFC using this new electrode architecture we found an improvement in power density by almost a factor of 2, with a decrease in Pt loading of a factor of 15. Furthermore, with Pt loadings of 0.18 mgPt cm-2 we observed peak power densities of in excess of 300 mW cm-2. We will present a detailed account of these effects, comment on improved stability and durability of these electrodes, and illustrate using a combination of SEM and TEM that nanoconfined CDP exists within the electrode. Finally, we will discuss future directions including advanced manufacturing enabled by the nanocomposite structure.

Acknowledgements

This work is supported by ARPA-E under Cooperative Agreement Number DE-AR0000499.
Thermodynamics and Kinetics of Alkali Insertion in VOPO4 Polymorphs
Authors: Lin Yuh-Chieh , Hidalgo Marc Francis , Chu Iek-Heng , Chernova Natasha , Whittingham M. Stanley , Ong Shyue Ping 
Published: February 2020

Multi-electron polyanion cathodes offer the potential for achieving both high voltage and high capacity in rechargeable alkali-ion batteries. Among the few materials known to exhibit multi-electron cycling, the polymorphs of VOPO4 , which operate on the V3+«V4+«V5+ redox couples, are particularly promising due to the high gravimetric capacities that have been achieved and the high voltage of the V4+/
5+ couple. In this talk, we will provide an integrated computational and experimental study of the thermodynamics and kinetics of alkali (Li/Na) insertion into the α-I, β and ε polymorphs of VOPO4. We show that differences in voltage and rate capability of these different polymorphs for Li and Na insertion can be traced back to their fundamentally different VO6-PO4 frameworks. We will also provide an overview of the different contributions to the thermodynamic stability of the different polymorphs. This work was supported as part of the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012583.
Analysis of Charge / Discharge Behavior Using Simple and High-Precision Capacity Measurement: Application to Commercially Available Large-Format Lithium-Ion Batteries
Authors: Yamazaki Atsuko , Kobayashi Yo , Mita Yuichi , Miyashiro Hajime 
Published: February 2020

Lithium-ion batteries are adopted as stationary applications because of their high voltage, high-energy density and high efficiency properties. The batteries for stationary use are expected for long-term operation more than 20 years with 80 % capacity retention. Therefore suitable estimation of the operation period of the lithium-ion batteries are required. High-precision charge / discharge measurement is proposed to estimate an effective life time within short test periods [1]. Then, we developed a simple and high-precision charge / discharge capacity measurement system for large-format cells and determined the capacity fade of 20Ah class battery (SCiBTM by TOSHIBA Corp.). Cells were charged and discharged at 10A(C/2) constant current between 2.7 and 1.5 V at 45(±0.3) °C. The sampling rate of current and voltage during charge / discharge was 100 ms to minimize the counting error of integrated capacity. Figure 1 shows the capacity trends with cycle operation at above condition. The capacity decreased linearly with cycles within the measurement period. The capacity loss per cycle was estimated as 3.4 mAh/cyc by averaging 35 cycles according to the linear approximation as shown in Fig.1. The coulombic loss per cycle was about 8.1 mAh/cyc which was defined as the difference between charge and discharge capacity. This value was more than two times as large as the capacity loss per cycle. The difference between them is probably due to internal reaction without direct involvement of capacity loss during operation. This result suggested that chemical self-discharge process such as shuttle mechanism may be a dominant factor of the estimated coulombic loss.
[1] A. J. Smith, J.C. Burns, S. Trussler, and J. R. Dahn, J. Electrochem. Soc.,
157, A196-A202 (2010).

Figure 1