bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhanced Electrochromic Performances of Polyhedral Oligomeric Silsesquioxane (POSS) Modified Viologen Derivatives
Authors: Park Jong Seung , Pande Gaurav K. , Choi Jun Hong , Han Seong-Hun 
Published: December 2020

Polyhedral oligomeric silsesquioxane (POSS) is an inorganic silica nanocage surrounded by organic functional groups. Due to the presence of organic peripheries around the rigid case, functionalized POSS has often exhibited outstanding properties, thus finding useful for constructing porous inorganic-organic hybrid networks.
The electrochromic devices (ECDs) offer noticeable color changes due to the electron transfer and redox reaction. The electrochromic materials play a critical role in determining the optical response and absorption intensity of the ECDs. Various electrochromic materials have been investigated, including inorganic metal oxides, viologens, and conducting polymers. Among these, viologen derivatives have been studied in depth owing to high electron-accepting capability and facile synthetic routes. Besides, viologen based ECDs have found various applications, such as smart windows, electronic paper, and the famous antiglare rearview mirrors developed by Gentex. However, critical weaknesses of viologens include low coloration efficiency, slow switching speed, and reduced long-term stability. Furthermore, the durability in the repeated operation of ECDs is limited in non-complementary device structures.
Herein, we present the modification of viologen derivatives with the incorporation of POSS, in which the structural rigidity of POSS fillers and the synthetic versatility of viologen compounds are combined to ensure improved electrochromic performances. The solid-state ECDs are fabricated by sandwiching the single-layered ion gel containing POSS-modified viologens between two transparent electrodes. The resulting electrochromic behaviors are compared with those of conventional viologens, in terms of cyclic voltammetry, spectroelectrochemistry, and kinetic stability. Furthermore, the preparation of flexible ECDs using silver nanowire-PEDOT:PSS composite electrode is presented, and stable electrochromic operation in the repeated redox transitions is demonstrated on various plastic substrates.
Two-Dimensional, Two-Phase, Non-Isothermal Model Ofproton Exchange Membrane Fuel Cell
Authors: Monteverde Videla Alessandro Hugo Antonio , Rizvandi Omir Babaie , Fino Debora 
Published: December 2020

Fuel cells are part of the environmental and transportation solution of our future. With the creation of new performant catalysts [1], the use of less noble metals in the catalyst layer [2] and possible replacement of the Pt [3], it is essential to develop multiphysic models with high degree of detail for a complete optimization of the system. In this work, we develop a simple and accurate two-dimensional model for the resolution of the effects of anode and cathode flows and GDLs, catalyst layers and membrane. Brinkman equations are used to model flow distribution in GDLs and CLs. Maxwell-Stefan equations are used to model transport of gas species in GDLs and CLs by advection and diffusion mechanisms, and electrochemical reactions in the CL interfaces are modeled by modified Butler-Volmer equations. Furthemore liquid water, and dissolved water are included in the model. Conservation of liquid saturation is included in the cathode layers because of its effect on the gas transport and the cell performance
due to flooding specially at high current densities. Equations are solved numerically with the commercial finite element package, COMSOL Multiphysics v5.5. Fully-coupled solution is used with Newton iterations and direct MUMPS solver.

Figure 1a. Polarization curve computed by the model. Figure 1b. Distributions of liquid water saturation at cell voltage 0.4 V; anode and cathode sides are at the top and bottom, respectively.

Keywords

: PEM, Fuel Cell, CFD, Two-phase, Saturation, FEM, flooding

Stamenkovic, V. R.; Mun, B. S.; Mayrhofer, K. J.; Ross, P. N.; Markovic, N. M. J. Am. Chem. Soc. 2006, 128 (27), 8813−8819.

Thompson, S.T., James, B.D., Huya-Kouadio, J.M., Houchins, C., DeSantis, D.A., Ahluwalia, R., Wilson, A.R., Kleen, G., Papageorgopoulos, D.. J. Power Sources 399, 304–313 (2018)

H.A. Monteverde Videla, S. Ban, S. Specchia, L. Zhang, J. Zhang. Carbon, 76 (2014), pp. 386-400

Figure 1
Carbon Nano-Tube Based Nano-Porous Layer in Membrane-Electrode Assemblies for Polymer Electrolyte Membrane Fuel Cells
Authors: Kim Jaeyeon , Kim Hyeok , Song Hyeonjun , Im Dasom , Jeong Youngjin , Park Taehyun 
Published: December 2020

In the membrane-electrode assemblies(MEAs) for polymer electrolyte membrane fuel cells(PEMFCs), there is a micro-porous layer(MPL) which is placed between gas-diffusion layer(GDL) and catalyst-coated layer(CCL). It roles as a buffer layer between GDL and CCL, where it helps removing the byproduct (Water) and connects electrically to conduct the generated electrons outside of the electrochemical reaction sites. However, commercial MPLs are normally composed of nano-particulated bulk carbon, which are hot-pressed in the manufacturing process. Therefore it is normally brittle and their thickness is micro-scale. This feature sometimes causes the structural breakdown by the byproduct or cracked by repeated pressurization of hydrogen or air. In addition, the micro-thick layer is not proper to remove the byproduct because such thick structure would rather disturb removing the byproduct water from the inside of the CCL.
This study therefore developed the alternative of the conventional MPL. It is called “carbon nano-tube sheet” which is composed of well-networked multi-walled carbon nano-tubes. Thus it shows higher electrical conductivity, mechanically stronger, and thinner than conventional MPLs. It was employed as a new MPL and the thickness effect on the electrochemical performance was explored. As a result, the MPL thickness of 0, 15, 30, 100 μm was investigated. The electrochemical polarization characteristics showed that the 15 μm thick MPL has the highest performance, meaning it is the optimized thickness. 0 thick (No MPL) and 100 μm thick MPL showed lower electrochemical performance than that of 15 μm thick MPL. For no MPL case, it is attributed that the contact between CCL and GDL was poor because of no buffer layer, while the case of thicker MPL is attributed to the disturbance of the water removal and poor diffusivity of the reactant into the CCL. Their corresponding electrochemical impedance spectra were also investigated and the results also showed the same effects (Electrical connection and removal of water).
Towards Gas Distribution Layers
Authors: Csoklich Christoph , Steim Roland , Schmidt Thomas J. , Buechi Felix N. 
Published: December 2020

Today, gas diffusion layers (GDLs) are stochastic, carbon based porous materials consisting of carbon fibres (~ 10 µm Ø) in which diffusion is the dominating transport mode for the gas phase. The stochastic nature of these materials requires bulk descriptors for (anisotropic) pore/throat size distributions, bulk electronic/thermal conductivity, tortuosity, effective diffusion coefficients asf.1
,
2 Here, we introduce a novel two-layered structure that not only offers unique design possibilities but also exceeds in performance tests conventional GDL materials under various operating conditions.
The investigated GDL material consists of a gold-coated PET fabric (Sefar). Its two-layered design resembles a combination of GDL and microporous layer (MPL). The simpler, regular structure (Fig. 1) increases the effective diffusivity – both in-plane and through-plane - as compared to Toray 60 carbon paper and shows no notable local variation. Furthermore, only one layer of throats exists for product water to emerge, thus lowering the required break through pressure and leading to faster water removal. The structure and transport properties can be finely adjusted to the fuel cell geometry or the desired operating conditions.
The material and structural properties were investigated ex situ as well as for fuel cell operation. The electrochemical performance was compared to commercial Toray 60 carbon paper (with and without wet proofing/with and without MPL) in a wide parameter range (50-80°C TCell, 60-100 % RHCath, 1.5-2 bar).
Especially at high cathode gas humidity and colder operating temperatures, the new material outperforms the conventional GDL material and reaches higher current densities (up to 200 mA/cm2 or 100 mV gain, cf. Fig. 2). It seems that this structure still distributes the feed gas well enough across the catalyst layer and removes product water straight to the channel. The detailed water transport modes were investigated by operando 4D-X-ray tomographic microscopy. The results show a dry structure over a wide range of current densities, and the crucial alignment between fibres and ribs: only in closed off pores below a rib, water accumulated.
These new, woven GDL materials show the possibilities of deterministic, designed structures to controllably tune single transport properties and improve water management in PEFC GDLs. Furthermore, transport properties as e.g. the electrical conductivity are adjustable even locally. The simpler structure might also narrow the gap between modelling and validation due to the regular structure and easy accessible material properties.
References
[1] Mathias, M. F., Roth, J., et al, Handbook of Fuel Cells, 3, 517–537 (2010).
[2] Rosen, T., Eller, J., et al, J. Electrochem. Soc., 159, F536-F544 (2012).

Figure 1
Understanding Degradation Phenomena in HT-PEM Fuel Cells Using Micro-Computed Tomography
Authors: Schmies Henrike , Schonvogel Dana , Büsselmann Julian , Wagner Peter , Dyck Alexander 
Published: December 2020

In times of transition from conventional energy-converting techniques to new technologies for the generation of power and electricity, polymer electrolyte membrane fuel cells (PEMFC) play a crucial role. Especially high temperature (HT)-PEMFCs are operated at around 160 °C and can be fuelled using reformate gas from methanol or natural gas reformers allowing to be used for both, mobile and stationary applications. Typically combined heat and power systems or range extenders are in the current focus of the industry.
While the HT-PEMFC technology has made great progression in the last decades and started its way into commercialization, it still has to undergo more stages of advancement in order to become a real alternative for power supply in various sectors. One major hindrance of the technology is their insufficient lifetime accompanied by a lack of knowledge about external factors causing system degradation. Therefore, all cell components need a detailed degradation analysis which contributes to fundamental understanding.1-3

In this work, we investigate the components of the HT-PEMFC such as the bipolar plates (BPPs) and the membrane electrode assembly (MEA) regarding degradation phenomena during cell operation with use of contaminated air. By applying µ-computed tomography
(µ-CT), these components are analysed in detail with the aim to reveal structural and morphological changes on the micro meter scale that occur during the life time.
If the cell is operated with traces of contaminants (e. g. 10 ppm ammonia in the cathodic air stream) for a certain time period under constant load conditions, µ-CT investigation helps to identify degradation of the individual components. Figure 1 shows a reconstructed µ-CT image of a typical MEA with the gas diffusion layers (GDL) and the anode and cathode separated by the membrane. Analysis of thicknesses using single cross-sectional images of the MEA reveals that the catalyst layers do not change, while the membrane thickness decreased around 15 µm after operation with trace amounts of NH3. While this study shows local degradation of the MEA, we will investigate the BPP and its porosity after application in single cell HT-PEMFC under various operating conditions using µ-CT in another study. In combination we aim to present the opportunities of employing µ-CT as a technique to visualize and better understand degradation phenomena in HT-PEM fuel cell components.

Søndergaard, T.; Cleemann, L. N.; Becker, H.; Steenberg, T.; Hjuler, H. A.; Seerup, L.; Li, Q.; Jensen, J. O., Journal of The Electrochemical Society
2018,
165, (6), F3053-F3062.

Büsselmann, J.; Rastedt, M.; Klicpera, T.; Reinwald, K.; Schmies, H.; Dyck, A.; Wagner, P., Energies (Open Access Journal)
2020,
13, (3), 567.

Kannan, A.; Li, Q.; Cleemann, L. N.; Jensen, J. O., Fuel Cells
2018,
18, (2), 103-112.

Figure 1
Water Balance Measurements for a Single Proton Exchange Membrane Fuel Cell Using a Hot Wire Anemometer
Authors: Al Shakhshir Saher , Berning Torsten 
Published: December 2020

Water balance data for a single proton exchange membrane fuel cell with an active area of 50 cm2 were measured with a hot wire anemometer, placed in the anode outlet stream. The measured hot wire voltage, E, is divided by the calibration signal, E_0, that was taken for a dry hydrogen stream of the same molar flow as the anode outlet at the same temperature. Because water vapor has a much lower thermal conductivity than hydrogen, the recorded hot wire voltage is always lower than the calibration signal, and there is a clear correlation between the relative voltage signal E/E0 and the fuel cell water balance. The relative voltage single can be easily computed at any point in time to thus provide a real-time signal of the fuel cell water balance.
This data was for a variety of operating conditions. The results show the same trends that were observed by other researchers who used the water knock-out method, only with higher accuracy. A decrease in the anode inlet relative humidity decreases the water balance value, rd
, significantly while the cathode inlet relative humidity only slightly affects the measured water balance. The membrane-electrode-assembly in this work was provided by Hydrogen South Africa – Catalysis (HySA Catalysis).

Figure 1
High O2 Permeability Ionomers for Improved Fuel Cell Performance
Authors: Macauley Natalia , Spinetta Magali , Zhong Sichen , Yang Fan , Lousenberg Robert D , Zenyuk Iryna V. , Qi Yongzhen , Jankovic Jasna , Pedram Sara , Xu Hui 
Published: December 2020

In a proton exchange membrane (PEM) fuel cell, the local oxygen transport across the ionomer film in the catalyst layer has a significant impact on electrode performance especially at high current density.1 It is therefore crucial to use ionomers that have higher oxygen permeability than the baseline Nafion. In this work, novel ionomers with increased oxygen permeability have been synthesized by copolymerization of perfluoro-2,2-dimethyl-1,3-dioxole (PDD) with perfluoro(4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSVE) and a ter-monomer. PDD is the main source of higher permeability due to its bulky structure, PFSVE provides ionic conductivity and the amount of the ter-monomer is adjusted to achieve high yields without compromising the equivalent weight (EW). The ring structure of PDD creates additional open space within the ionomer structure for improved gas permeability. Some of the newly developed ionomers have up to five times higher permeability than Nafion, which should result in a significant improvement of fuel cell performance, mainly at high current densities. Ionomers with different PDD content and equivalent weight have been studied to establish the correlation between ionomer properties and MEA performance. Local oxygen resistance, ionomer sheet resistance, ionomer coverage, and SO3
- group coverage will be evaluated and correlated to electrode performance. The performance and durability of the electrodes using high permeability ionomer will be correlated to the ionomer interaction with catalyst particle.
This work will provide a comprehensive understanding of interactions among Pt, carbon, ionomer and their impact on the electrode structure and fuel cell performance and durability. The attained information will be used to improve fuel cell electrode design.
Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-SC0018597.
References:
1. Baker et al, J. Electrochem. Soc. 156, B991 (2014).
Power Generation Characteristics of PEFCs Using Heteropolyacids As Anode Redox Mediators
Authors: Naruse Shinji , Muroyama Hiroki , Matsui Toshiaki , Eguchi Koichi 
Published: December 2020

Polymer electrolyte fuel cells (PEFCs) have attracted much attention as clean power generation systems. PEFCs have been employed for residential cogeneration systems, fuel cell vehicles and spaceships due to short startup/shutdown times, small size, and low weight, compared to high– temperature FCs. Because precious metals such as Pt are utilized for electrocatalysts in order to obtain high power generation efficiency, high cost of the system is one of the issues in the spread period. In addition, hydrogen fuel has problems in safety and transportation.
Therefore, in recent years, PEFC using heteropolyacid (HPA) as a mediator has been reported for the solution of these problems [1]. In this system, reduced HPA is supplied to the anode, and is converted to oxidized HPA over the electrode via the following reaction.

[H
nXM
V

nM
VI
12–n
O40]
z

– → [XM
VI
12O40]
z

– + ne– + nH+

(1)

where X = Si, P and M = W, Mo, V

On the other hand, oxygen is reduced to produce water on the cathode, as in the case of general PEFCs. This PEFC system can be continuously operated by reducing the oxidized HPA and supplying it to the anode again. Electrochemical methods and addition of reducing agents can be considered for reducing oxidized HPA [2]. However, more effective reduction methods have been needed to achieve high performance and long-term operation.
In this study, various metal pieces were utilized for the reduction of oxidized HPA in order to establish an effective method. The effect of metal pieces on the power generation performance and long-term operation of PEFC was evaluated. H3PW12O40·28H2O (PW12) and H2SO4 were added to ultrapure water to prepare an oxidized PW12 solution (0.01 M PW12–0.5 M H2SO4). This solution was subjected to a constant current electrolysis (1.00 mA cm–2) or an addition of metal pieces (Al, Ni, Fe, Co) to obtain the reduced PW12. A membrane–electrode assembly was prepared using Nafion® membrane as an electrolyte, carbon black as an anode, and Pt/C as a cathode. The operating temperature was 80 ºC, and O2 (relative humidity: 100%) was supplied to the cathode. The reduced PW12 solution bubbled with Ar gas was supplied to the anode by a liquid feed pump. Current–voltage (I–V) measurements and galvanostatic operation tests (5.00 mA cm–2) were performed using this single cell. As a result, the addition of Co pieces achieved the high reduction degree of HPA and the superior cell characteristics. The suppression of the side reactions such as hydrogen generation and the increase of the output power were necessary for the improvement of PEFC system using HPA as the anode redox mediator.
[1] R. Singh, A. A. Shah, A. Potter, B. Clarkson, A. Creeth, C. Downs, F. C. Walsh, J. Power Sources, 201 (2012) 159–163.
[2] S. Nakada, E. Morikawa, T. Okanishi, H. Muroyama, T. Matsui, Y. Hirao, K. Eguchi, Abstract of 82th Meeting of Electrochem. Soc. Jpn., 3B09 (2015).
Development of Electrochemically-Driven CO2 Separator for Hydroxide Exchange Membrane Fuel Cells in Transportation Applications
Authors: Matz Stephanie , Setzler Brian , Weiss Catherine M. , Shi Lin , Gottesfeld Shimshon , Yan Yushan 
Published: December 2020

Hydrogen fuel cell vehicles are a promising, emerging alternative to the internal combustion engine but the commercialized proton exchange membrane fuel cells (PEMFCs) are comparatively expensive. Hydroxide exchange membrane fuel cells (HEMFCs) are a potentially lower cost hydrogen fuel cell technology under development; unfortunately, ambient levels of CO2 in air reduce HEMFC performance and impede HEMFCs from becoming competitive with the incumbent fuel cell technology.1 Current levels of atmospheric CO2 have been shown to decrease fuel cell performance up to 200 mV.2 The hydroxide produced during the electrochemical reaction in a HEMFC reacts readily with CO2 in air at the cathode due to its acid-base reaction and transports CO2 across the hydroxide exchange membrane. At the anode, the bicarbonates build up lowering the local pH until CO2 evolution is favorable, concurrently the pH gradient saps cell voltage. However, this transport results in the effective separation of CO2 from air. By optimizing a HEMFC for CO2 capture, rather than power production, an electrochemically-driven CO2 separator (EDCS) was developed using a poly(aryl piperidinium) membrane.3 The continuous and compact EDCS has the potential to enable HEMFCs to operate efficiently with ambient air in automotive applications.
This work will demonstrate the ability of the EDCS to effectively and continuously remove CO2 from air at ambient levels using minimal hydrogen flow to power the separation. This work will explore the effect of operating conditions such as flow rates, current density, and relative humidity on CO2 separation performance with the innovative EDCS. A carbon-ionomer interlayer between the catalyst layer and membrane was added to improve CO2 capture by creating an accessible volume for hydroxide and CO2 gas to react. Additionally, various design features of the cell were investigated to improve the mass transport such as flow fields and gas diffusion layers. The CO2 removal performance of a single-cell 25 cm2
EDCS is shown in Figure 1. Currently, the optimal design configuration of the EDCS has achieved 98% CO2 removal for 100 hours (Figure 2) with the potential to improve CO2 removal as well as processed gas throughput by further development of the module’s design.
References:

B.P. Setzler et al., Nature Nanotechnology 11, 12, 1020-1025 (2016).

N. Ziv et al., Chemsuschem, 11, 7, 1136-1150 (2018).

J. Wang et al., Nature Energy, 4, 5, 392-398 (2019).

Figure 1
In-Situ High-Temperature X-Ray Absorption Spectroscopy of Fe-N-C Electrocatalysts during Pyrolysis
Authors: Mufundirwa Albert , Yoshioka Satoru , Sugiyama Takeharu , Harrington George Frederick , Hayashi Akari , Sasaki Kazunari , Lyth Stephen Matthew 
Published: December 2020

Deeper understanding of the formation of active sites during the pyrolysis of iron-nitrogen-carbon (Fe-N-C) electrocatalysts for the oxygen reduction reaction (ORR) is required. Here, we present a nitrogen-doped carbon foam support treated at high temperature (1600 °C) to stabilise the material properties. Iron-containing precursors are then adsorbed onto the surface, followed by heat treatment. This changes the chemical state of the adsorbed iron, whilst the material properties of the support are effectively unchanged. The two-step synthesis method used to create these model electrocatalysts decouples porosity, microstructure, and conductivity from the electrochemistry, which can instead be attributed mainly to changes in the chemical environment of iron.
Advanced characterisation techniques such as in-situ high-temperature X-ray absorption spectroscopy (HT-XAS) and high-temperature near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) are employed to gain insights into the state of the adsorbed iron as it decomposes during pyrolysis to form active sites. Transmission electron microscopy (TEM) is used to track the microstructure for different types of precursor heated at different temperatures. Meanwhile, in-situ electrochemical XAS is used to understand how the chemical environment of the catalysts change during the ORR.
The results are discussed by relating different chemical environment with the electrochemical ORR activity. Despite the two-step synthesis technique, these model Fe-N-C electrocatalysts are highly active. The load-cycling durability and start-stop durability are measured, and the degradation mechanisms are discussed.