bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Electrolyte Concentration on the Electrochromic Properties of Tungsten Oxide Thin Films
Authors: Dzakpasu Cyril Bubu , Appiah Williams Agyei , Ryou Myung-Hyun , Lee Yong Min 
Published: December 2020

The worldwide energy crisis has drawn the attention of researchers to energy saving, energy-storing, and energy converting devices. Among them, electrochromic devices (ECDs) are being extensively studied to reduce energy consumption. Electrochromism refers to the persistent and reversible change of optical properties by an applied voltage pulse. Electrochromism has been proposed for many applications such as smart windows, rear-view mirrors, electrochromic displays, sensors, etc. The electrolyte is an indispensable component in the ECDs which strongly affects the electrochromic performance. The transport mechanism for the ions depends on the type and components of the electrolyte. Liquid electrolyte has been the electrolyte of choice owing to its high ionic conductivity. However, due to leakage issues, other alternatives such as gel-polymer electrolytes and solid electrolytes are being employed.
In this study, we evaluate the effect of LiClO4 in PC having different concentrations on the electrochromic performance of RF sputtered tungsten oxide (WO3) thin films. The effect of the electrolyte concentration was characterized by cyclic voltammetry (CV), chronoamperometry, potentiostatic measurement, electrochemical impedance spectroscopy (EIS), and transmittance measurements. In addition, mathematical modeling and simulation is adopted to enhance the understanding of the different salt concentration on the electrochemical performance. The model predictions are in good agreement with experimental cyclic voltammogram and transmittance data obtained from a three-electrode cell with WO3, Pt, and Ag/AgCl as the working, counter, and reference electrode, respectively. From the model predictions, the electrolyte with lower salt concentration exhibits higher coloring efficiency while the electrolyte with higher salt concentration exhibits higher switching speed.
Towards Systematic Understandings and Designs of Electrolyte/Electrode Interfaces By Computational Physics Approaches
Authors: Jinnouchi Ryosuki , Kodama Kensaku , Shinohara Akihiro , Kudo Kenji , Kitano Naoki , Suzuki Takahisa , Hasegawa Naoki , Morimoto Yu 
Published: December 2020

Reducing the amount of platinum group metals (PGMs) in catalyst layers is one of major issues in developments of polymer electrolyte fuel cells (PEFCs). Obviously, the mass activity of oxygen reduction reaction (ORR) needs to be enhanced to reduce the PGM-loading. Specific surface area of PGMs also needs to be large enough to decrease the local oxygen transport loss near the catalyst surface [1]. In addition, the catalysts need to be stable enough to ensure long-term operations of PEFCs [2]. To satisfy all these requirements, extensive studies have been carried out on explorations of optimal composition, size and shape of PGM nanoparticles [3] as well as desired controls of catalyst and ionomer distributions [4,5], and remarkable progresses have been achieved in past decades. In those studies, atomistic simulations have made significant contributions on revealing mechanisms underlying experimental observations and designing new materials. Electronic structure calculations adopting density functional theory (DFT), for example, have been utilized as a standard tool to predict the catalytic activity since the first successful reproduction of the volcano plot of ORR [6]. Molecular dynamics (MD) simulations using semi-empirical force fields have been successfully utilized to predict structures and transport properties of ionomer, too [7-9]. In this presentation, we will show results of our applications of DFT and MD simulations to cathode catalysts and ionomer thin films on catalyst surfaces [8,10]. After discussing the power of the conventional methods as well as their limitations, we will discuss recent progresses in state-of-the-art machine-learning methodologies [11-14] as a promising theoretical tool to examine complex finite-temperature properties of electrode/electrolyte interfaces.
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152, A2256 (2005).
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[4] S. Lister and G. McLean J. Power Sources
130, 61 (2004).
[5] S. Ott et al. Nature Mateir.
19, 77 (2019).
[6] Nørskov et al. J. Phys. Chem. B
108, 17886 (2004).
[7] S. S. Jang et al. J. Phys. Chem. B
108, 3149 (2004).
[8] R. Jinnouchi et al. Electrochim. Acta
188, 767 (2016).
[9] Y. Kurihara et al. J. Electrochem. Soc.
164, F628 (2017).
[10] R. Jinnouchi et al. Phys. Chem. Chem. Phys.
13, 21070 (2011).
[11] R. Jinnouchi and R. Asahi J. Phys. Chem. Lett.
8, 4279 (2017).
[12] R. Jinnouchi et al. Phys. Rev. Lett.
122, 225701 (2019).
[13] R. Jinnouchi et al. Phys. Rev. B
100, 014105 (2019).
[14] R. Jinnouchi et al. Phys. Rev. B
101 060201 (2020).
Parametric Modeling Study of PEM Fuel Cell with Platinum Group Metal -Free Cathode Catalyst Layer
Authors: Dunsmore Lisa , Litster Shawn 
Published: December 2020

Polymer electrolyte fuel cells offer zero-emissions energy conversion but are commercially limited by cost and durability. Stack cost can be reduced by using platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR). PGM-free catalysts have lower volumetric activity relative to PGM catalysts and consequently require thicker catalyst layers. Thicker catalyst layers result in increased oxygen transport resistance and flooding in the cathode, which must be considered to accurately model PGM-free fuel cells and quantify the distinct transport resistance. For this purpose, we have developed a well validated model to elucidate relative contributions to oxygen transport resistance. This two-phase, transient, non-isothermal, channel-to-channel model contains cathode catalyst layer morphology informed by plasma-focused ion beam (P-FIB) SEM. Furthermore, the model includes agglomerate treatment of volumetrically active catalyst primary particles coated by ionomer. The structure of the agglomerate model is well suited for describing the catalyst layers containing metal organic framework (MOF) derived metal-nitrogen-carbon catalysts that are roughly spherical and volumetrically active for ORR. The MOF-derived Fe-N-C catalyst used in this study’s experiments contains atomically dispersed active sites and uniform, tunable primary particle size. In this presentation, we will report on our investigation of the performance sensitivity to a wide variety of operating conditions and MEA design specificiation, including cell temperature, gas pressures, cathode thickness, hydrophobic pore fractions and wettability, catalyst primary particle size, ionomer content, and ionomer equivalent weight. Non-dimensional characteristic parameter analysis on the model results is used to distinguish the transition between proton conductivity limited and oxygen transport limited performance, and indicate critical values that affect the the through plane ultilization of the catalyst. This information and studies on the impact of active site density help us set catalyst-specific targets for meeting fuel cell performance goals. With highly active PGM-free catalysts, we can model the impact of parameter changes on transport with experimental validation.
DOE ACKNOWLEDGEMENT
This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office (FCTO) under award number DE-EE0008076. The authors gratefully acknowledge research support from the Electrocatalysis Consortium (ElectroCat), established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under contract number DEEE0008076.
Coarse-Grained Molecular Dynamics Simulation of Perfluorosulfonic Acid Dispersion in Mixtures of Water and Ethanol
Authors: Kuo An-Tsung , Nakabayashi Kazuhiro , Urata Shingo , Watabe Hiroyuki , Hommura Satoru 
Published: December 2020

Coarse-grained molecular dynamics simulation was used to investigate the aggregation behavior of perfluorosulfonic acid (PFSA) ionomers with equivalent weight (EW) of 844 in the dilute mixed water and ethanol solutions. Four different chain lengths (10, 20, 60, and 200 repeat units) of PFSA were studies. It was found that the shorter (10 and 20 repeat units) ionomers form spherical aggregates, whereas the longer (60 and 200 repeat units) ones form cylindrical-like aggregates in pure water and in the mixed water/ethanol solvents at ethanol contents ≤ 50 wt%. The aggregated structures become loose when ethanol content is increased to 50 wt%. With further increasing the ethanol content, the PFSA ionomers gradually uncoil their aggregated structures and extend the chains in the solution. The variation of aggregate structure with the ethanol content was consistent with our experimental observation. The finding will be useful for designing ionomer dispersed solution for thin film and catalyst ink fabrication.
Figure caption: EW844 PFSA polymers form cylindrical-like aggregates a low ethanol contents and random coil conformations at high ethanol contents.

Figure 1
Investigation of Liquid Water Distribution under Temperature Gradient in PEFC Using in-situ X-ray Visualization
Authors: Komiyama Takahiro , Sasabe Takashi , Naito Hiroshi , Kawamura Katsuyuki , Suzuki Toshiyuki , Hirai Shuichiro 
Published: December 2020

Polymer electrolyte fuel cells (PEFCs) are expected to be applied in wider range of applications including automobiles, and the operation at higher current density has been required. However, in the operation at high current densities, the performance of PEFCs is degraded due to liquid water accumulation in the gas diffusion layers (GDLs) which prevents the supply of oxygen to the catalyst. Furthermore, heat is generated in catalyst layer due to electrochemical reaction, leading temperature rise inside PEFCs. Since liquid water accumulation is closely related to temperature distribution, it is expected that temperature distribution alters the spots of liquid water accumulation. Therefore, it is necessary to understand the relationships between the liquid water distribution and the temperature distribution in the GDLs to improve the performance at high current density. This study intended to investigate the effects of temperature distribution on liquid water accumulation by in-situ X-ray visualization.
Liquid water distribution of 60, 70, and 80 ℃ cell temperature cases were measured by X-ray radiography, and current density was kept 1.5 A/cm2 in all cases. We used a serpentine type cell with ribs and flow channels of 300 µm width with 1.5 x 3.0 mm2 active area. As for GDLs, SIGRACET 29BC was used. The humidity of hydrogen in the anode was fixed at 100%. While, the humidity of air in the cathode was adjusted so that the gap between water vapor pressure and saturation pressure becomes 4.0 kPa.
Fig. 1 (a), (b) and (c) shows the liquid water distribution of the 60 ℃, 70 ℃, 80 ℃ cases. It is shown that the liquid water distribution in a region near the MPL/substrate boundary is clearly altered by the cell temperature. This effect is also observed in the averaged profiles of liquid water volume under rib areas (Fig. 1(d)). In Fig. 1(d), liquid water volume in the region near the MPL/substrate boundary (the region between 50 µm to 80 µm) of the 70 and 80 ℃ cases are clearly reduced compared to the 60 ℃ case. Since the overvoltage of each case is almost the same, the resultant temperature gradient inside GDLs due to the heat production is considered to be the same. Meanwhile, the saturated vapor pressure increases more abruptly at higher temperature, since the saturated vapor pressure is more affected by the initial cell temperature. The saturated vapor pressure of the 80 ℃ case is much larger than the other cases, therefore it is suggested that the lower amount of liquid water accumulation of the 80 ℃ case is caused by the larger saturated vapor pressure.

Figure 1
Measurement and Analysis of Gas Transport Properties in Catalyst Layers of Polymer Electrolyte Fuel Cells with Different Ionomer to Carbon Ratio
Authors: Tsutsui Fumiaki , Suzuki Takahiro , Tsushima Shohji 
Published: December 2020

Catalyst layers of polymer electrolyte fuel cells are electrochemical reaction fields with complicated porous structures. Catalyst layers are composed of carbon particles supporting platinum catalyst (Pt/C), ionomers and micropores. Gas transport properties in catalyst layers are key factors for improving cell performance. It is necessary to clarify the relationship between the gas transport properties and the microstructure. The authors reported that ionomer in the catalyst layer affects the porous structure and resultant cell performance [1]. Therefore, the objective of this study is to investigate the effects of ionomer to carbon ratio (I/C) of the catalyst layer on the porous structure formation and gas transfer.
In this study, gas transport properties in catalyst layers with different I/C were evaluated by the measurement of gas transfer through thin porous media operated under a micro-channel apparatus (Gas-TOUCA) [2]. The porous structures of catalyst layers were evaluated by the nitrogen adsorption method and the observation using a Field-emission scanning electron microscope (FE-SEM).
Typical experimental results of the measurement of Gas-TOUCA are shown in Figure 1. The measurement was carried out for the catalyst layers under the four conditions of I/C 0.1, 0.3, 0.5 and 1.0. The effective diffusion coefficient in the catalyst layer with I/C 0.5 was the largest, and that in the catalyst layer with I/C 1.0 was the smallest of the four conditions. The tortuosity factor of the catalyst layers with I/C 0.1, 0.3 and 1.0 was approximately 3. However, the tortuosity factor of catalyst layers with I/C 0.5 was approximately 2. Segregation of ionomer was observed in the catalyst layers with I/C 0.5 and 1.0 by SEM. On the other hand, there was no ionomer segregation in the catalyst layers with I/C 0.1 and 0.3, and most of the ionomer could have adsorbed on the Pt/C particles. Ionomer works as a dispersant in electrode slurries [3]. Less amount of ionomer leads to large attractive interaction of particles in the slurry, whereas an excessive amount of ionomer leads to deposition to pores in the catalyst layer. Therefore, the experimental results indicated that there is an optimum I/C ratio for gas transport.
References
[1] T. Suzuki, S. Tsushima and S. Hirai, Int. J. Hydrogen Energy, 36, 12361 (2011).
[2] T. Suzuki, Y. Nakata and S. Tsushima, ECS Trans., 92, 175 (2019).
[3] T. Suzuki, S. Okada and S. Tsushima, ECS Trans., 86, 193 (2018).
Acknowledgments
This work was financially supported by JSPS KAKENHI Grant Number 18K13702 and 18H01383. A part of this study was supported by the Osaka University Nanofabrication Platform [F-19-OS-0016] and [S-19-OS-0011] in the Nanotechnology Platform Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

Figure 1
Understanding Pyrolysis: Operandoand in Situcharacterization of Morphology and Composition Changes during Synthesis of M-N-C Electrocatalysts
Authors: Chen Yechuan , Huang Ying , Asset Tristan , Kulkarni Devashish Shashikant , Xu Mingjie , Tieu Peter , Pan Xiaoqing , Zenyuk Iryna V. , Atanassov Plamen 
Published: December 2020

Transition metal-nitrogen-carbon (M-N-C) materials have been continuously reported to be one of most promising platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR)/cathode in low-temperature polymer electrolyte fuel cells (PEFC) and other emerging areas (such as carbon dioxide reduction reaction and nitrogen reduction reaction). They are usually obtained through pyrolysis of low molecular weight (organic) or polymetric precursors. The pyrolysis consists of heat treatment in inert (or reductive) atmosphere. Through the decades of practice, this pyrolysis process has been optimized intuitively and empirically with little-to-no knowledge of the explicit sequence of transformations. Morphological, structural, interfacial and chemical changes during pyrolysis enable the emergence of the new material with atomically dispersed transition metal ions. These ions are incorporated in the graphene-like carbonaceous matrix, doped with nitrogen and forming various Fe-Nxcatalytically active sites. Often, a secondary pyrolysis process is being carries out, after the completion of the initial one, resulting in better defined, and in many cases, more active and stable catalysts (a.k.a. “re-pyrolysis”).
Our team have investigated both stages of the pyrolytic synthesis via in situXPS, TEM, EDS, XRD and nano- and micro-XCT methods in two separate studies dedicated to (i) pyrolysis of charge-transfer organic salt (nicarbazin) when mixed with silica template (a.k.a. “sacrificial support method” of M-N-C catalyst synthesis) and (ii) re-pyrolysis (secondary, “purification” pyrolysis) of the M-N-C material as a path to obtain atomically dispersed PGM-free catalyst.
During the first pyrolysis we have observed for the first time the explicit melting of the precursor (at exact thermal signature), wetting of the hard template and followed major transformation in morphology: pore structure evolution, initial graphitization, metal and metal carbide phase formation, secondary graphitization templated on the transition metal nanoparticles and secondary micro-pores formation. All these observations have been interpreted through cross-referencing tomography, crystallography, microscopy and spectroscopy in situdata streams.
We established that the re-pyrolysis of M-N-C materials could result in the amorphization of carbon, the rearrangement of multitudinous N-containing moieties, and increased content and a more uniform distribution of Fe-Nxsites, yet without major morphology changes in carbonaceous framework. In summary, the re-pyrolysis has multiple advantages and is recommended for all M-N-C electrocatalysts, no matter what precursors and parameters are set for their synthesis.
Double Point Temperature Measurements Under Rib and Channel in an Operating PEFC Using MEMS Sensors
Authors: Shigemasa Kaito , Otsuki Yota , Kurosu Masato , Sato Hayate , Araki Takuto 
Published: December 2020

Introduction

For more spread of polymer electrolyte fuel cells (PEFCs), investigating the temperature distribution inside an operating PEFC is important. Last year, correlation between local through-thickness temperature gradient and the PEFC performance was investigated [1]. In this case, temperature gradient was critical to the PEFC performance under certain operating conditions. Moreover, local in-plane temperature gradient should be suggested as an important factor to the PEFC performance. Therefore, in this study, two local temperature measurement on the interface of the cathode catalyst layer (CL) and the microporous layer (MPL) in a PEFC was performed while it was operated.

Experimental method

Thin-Film Thermocouple (TFTC)
For the local temperature measurement inside a PEFC, in-house thin-film thermocouple (TFTC) was fabricated using micro electromechanical system (MEMS). The thermocouple was made from Au and Ni. Its measurement point was about 30 µm width and about 6 µm thick, which was so fine and thin that it wouldn’t disturb a reaction inside a PEFC.
Cell Configuration
An active area of 1 cm2 PEFC cell was used, and is has five 1mm width gas channels and five 1mm width ribs with parallel flow configuration. 15 µm thick reinforces type PEM was used. TGP-H-060 (with MPL 2.0 mg/cm2) was used and in both anode and cathode side. TFTCs were inserted between interface of cathode CL/MPL, and two TFTCs were set on rib and channel, respectively.
Operation Conditions
Power generation was performed by sweeping the cell voltage from OCV to 0 V at a rate of 1 mV/s. K-type thermocouples were used to measure the bi-polar plates with gas channels and sensor terminal temperatures. An impedance analyzer was used to measure the cell resistance. O2 and air were used as a cathode supply gas, respectively. Pure H2 was used as an anode supply gas. The flow rates of anode gas / cathode gas were set in two conditions, 500/500 mL/min, and 30/75 mL/min.

Results and Discussion

Here, results in one operating condition is being shown, when the high flow rate has been chosen, and O2 has been chosen as a cathode supply gas. Fig.1 (a) shows the cell voltage and cell resistance transition with current density. In this case, the cell voltage decrease due to diffusion overvoltage didn’t occur. And Fig.1 (b) shows the temperature increase from the beginning operating the PEFC on the CL/MPL interface under rib and channel. The temperature on the channel was higher than that on the rib. Due to the condensed water which was generated with the PEFC operation, the effective thermal conductivity got decreased. The amount of the condensed water on the rib was larger than that on the channel. Therefore, total amount of the condensed water might affect on the effective thermal conductivity and caused the temperature difference on the rib and channel.

Reference

[1] K. Shigemasa, et al., ECS Trans., 92(8),161-4 (2019)

Figure 1