bluuebunny/crossref_metadata_2025 huggingface dataset:
Impedance Analysis of High Capacity Manganese Rich Cathode in Lithium Ion Batteries
Authors: Mao Wen-feng , Fu Yanbao , Battaglia Vince
Published: February 2020

The high capacity manganese rich (HCMR) cathode material (xLi2MnO3• (1-x)LiMO2, M = Ni, Co, Mn) demonstrates the highest discharge capacity (~250 mAh g-1) along with potential cost reduction and safety enhancement among all the high energy cathode materials considered for lithium ion batteries (LIBs).. However, the practical application of HCMR is prohibited due to, among other things, the high impedence at low states of charge (SOC), as shown in the PITT test in Fig. 1. The purpose of this study is to investigate the source of the high impedence for HCMR cathode materials.

HCMR electrodes were prepared with active material (85 wt%), acetylene black conductive additive (7 wt%), and PVdF binder (8 wt%). The loading of HCMR in the cathode is 1.1 mAh/cm2. 2325 coin cell hardware was used for electrochemical measurements, assembled with Celgard 2400 as separator and lithium metal as counter electrode. EIS tests were performed using a VMP3 electrochemical workstation. The EIS results are shown in Fig. 2, and the results of detailed impedance analysis are shown in Fig. 3. At lower SOCs, the HCMR exhibits a greater diffusion impedance (Rdiff), while the charge transfer impedance (Rct) rises quickly and then decreases. Both sources of resistance are much higher than the ohmic impedance (RL) and the another high-frequency source associated with wither the anode or an SEI on the cathode, (RSEI).

In all, we can conclude that both the solid state ionic diffusion and electrochemical charge transfer offer nearly equal contribution to the high impedance of HCMR at low SOCs (between 3.6 and 3.2 V). Therefore, stratagies that may increase the ionic diffusion coefficient (e.g. chemical doping), decrease the ionic diffusion length, or increase the rate of electrochemical reaction must be adopted to solve the high impedance issue at low SOC. Reducing the particle size would have the effect of simultaneously reducing the solid state transport length and increasing the area for charge transfer, but may come at the expense of increased dissolution of the transition metals (not studied here) from the active material.

Figure 1
Synthesis Technology of Nano-Crystalline LVP/C Cathode Materials for Lithium Ion Batteries
Authors: Choi Seung-Woo , Kim Min-Young , Yang Seung-Hoon , Kim Da-Hye , Noh Tae-Hyoung , Lee Moo-Sung , Kim Ho-Sung
Published: February 2020

It is reported that LVP(Li3V2(PO4)3) material has a good advantage for safety property, but this material showed low electric conductivity. Therefore, many researches have been performed to improve the electrochemical properties of LVP material by reducing of particle size with cation doping and carbon coating, etc. In here, we prepared nano-sized LVP/C composite materials with a high purity using a sol-gel method including a carbon coating and heat treatment process. As a result, nano LVP/C powders were obtained with calcination temperature of 750 ~ 900 °C. and the LVP/C material cells showed about 130 mAh/g in the range of 3.0 V to 4.3 V and 170 mAh/g in the range of 3.0 V to 4.8 V, approaching to the theoretical capacity.
Enhanced Electrochemical Performance of Ni-Rich Cathode Surface Modified with Double Layer
Authors: Lee Jun Won , Park Yong Joon
Published: February 2020

Recently, the Ni-rich cathode materials (such as Li[Ni0.8Co0.15Al0.05]O2) have attracted a lot of attention because of their high specific discharge capacity. However, they have several challenges such as insufficient rate capability, cyclic performance and thermal stability to be overcome. As an approach to address these issues, surface modification with stable materials has been applied to various cathode materials. In this study, the surface of the Li[Ni0.8Co0.15Al0.05]O2 was double coated with stable oxide (Li2ZrO3) and carbon having a high electronic conductivity. Surface coating with Li2ZrO3 can improve the cyclic performance and thermal stability of Ni-rich cathode because the coating layer can prevent from unwanted reaction between cathode and electrolyte. Moreover, Li2ZrO3 is not only stable oxide, but also Li ion conductor with suitable structure for Li ion transportation, which can enhance rate capability of Ni-rich cathode. The carbon with high electronic conductivity was also coated to compensate for low conductivity of oxide cathode. So, the double coating layer composed of Li2ZrO3 and carbon may lead to enhanced electrochemical performance of Ni-rich cathode.
An Optimized Carbon Matrix for Negative Lithium-Ion Battery Electrodes Based on Silicon and Carbon
Authors: Ulmann Pirmin A. , Pacheco Sergio B. , Mombelli Eddie , Leone Antonio
Published: February 2020

Since decades, attempts have been made to incorporate silicon into Li-ion battery anodes in order to improve the energy density beyond the theoretical limit of graphite (372 mAh/g).1 These efforts have frequently been hampered by poor cycling stability resulting from the substantial volume change of silicon during lithiation/de-lithiation cycles. It has recently been demonstrated that careful selection of conductive graphite and carbon black additives leads to significantly reduced aging phenomena in silicon-based composite electrodes.2

Electrochemical results will be presented for an optimized surface-modified carbon matrix that leads to highly favorable cycling stability in combination with commercially available silicon-based active materials. Bulk and surface properties of these composite electrodes will be discussed.

References:

1a) Besenhard, J. O.; Komenda, P.; Paxinos, A.; Wudy, E. Solid State Ionics 
1986, 18-19 (2), 823; b) Wilson, A. M.; Dahn, J. R. J. Electrochem. Soc.
1995, 142, 2, 326; c) Son, I. H.; Park, J. H.; Kwon, S.; Park, S.; Rümmeli, M. H.; Bachmatiuk, A.; Song, H. J.; Ku, J.; Choi, J. W.; Choi, J.; Doo, S.; Chang, H. Nature Commun. 
2015, 6, 7393.

2a) Du, Z.; Dunlap, R. A.; Obrovac, M. N. J. Electrochem. Soc.
2014, 161 (10), A1698; b) Petibon, R.; Chevrier, V. L.; Aiken, C. P.; Hall, D. S.; Hyatt, S. R.; Shunmugasundaram, R.; Dahn, J. R. J. Electrochem. Soc.
2016, 163 (7), A1146.
Synthesis and Electrochemical Properties of Li2MnO3 Li4Mn5O12 Binary System As Positive Electrode Materials for Lithium Ion Battery
Authors: Okada Masaki
Published: February 2020

Synthesis and Electrochemical Properties of Li2MnO3―Li4Mn5O12 Binary System as Positive Electrode Materials for Lithium Ion Battery

Masaki Okada and Yuya Sakaguchi

Inorganic Materials Research Laboratory, TOSOH CORPORATION

Lithium ion batteries are their high energy density compared with other batteries, progressed recently applied to applications requiring large capacity like for electric power storage system and electric vehicle. The positive electrode materials for a lithium ion battery, lithium metal oxide containing a large amount of rare metallic element such as cobalt or nickel are mainly investigated. Positive electrode material containing a large amount of these rare elements is very difficult to achieve both high energy density and low cost. As a positive electrode material that does not contain a rare metallic element, it is being studied of Li2MnO3 with a layered rock-salt structure. Li2MnO3 shows a large discharge capacity of more than 250mAh/g in the first cycle, but the capacity decreases with charge and discharge cycles. [1-3] In this work, we studied the Li2MnO3―Li4Mn5O12 binary system (Li4/3-4X/5Mn2/3O2-2X/5, 0<X<1) of the positive electrode materials based on Li2MnO3. Li4/3-4X/5Mn2/3O2-2X/5 can be suppressed capacity fading as compared with the conventional Li2MnO3. It may be able to achieve both low cost and high energy density.

Li4/3-4X/5Mn2/3O2-2X/5 was prepared by reacting of mixture of MnCO3･0.5H2O and LiOH･H2O as raw material. The mixture was fired at 400～600ºC for 32h in air stream. Crystal structure and multilayered particle structure were investigated through TEM and N2adsorption-desorption isotherm analysis, respectively. The electrochemical characterization of positive electrode material was performed on CR2032 coin type cells. From the TEM images of the prepared samples, the presence of two crystal phases was observed. In addition, the electron diffraction pattern is attributed to the rock salt and the spinel phase, the possibility of a two-phase coexistence structure of Li2MnO3 and Li4Mn5O12 having a twin structure has been suggested. The initial charge and discharge capacity of Li4/3-4X/5Mn2/3O2-2X/5 was reduced as compared with Li2MnO3, but cycle stability was improved (X=0.36, 170mAh/g@50th, 50mA/g, RT). In additionally, capacity fading is suppressed by magnesium substitution of a part of manganese, the substituted sample showed stable cycling at about 200mAh/g (X=0.36, Mg 8mol %). In the viewpoint of the crystal structure and multilayered particle structure, the effect of the characters on capacity and cycle ability will be discussed.

[1] Denis Y.W. Yu et.al., J. Electrochem. Soc. 2009 156(6) A417-A424

[2] Denis Y.W. Yu et.al. J. Electrochem. Soc. 2010 157(11) A1177-A1182

[3] Denis Y.W. Yu et.al., J. Electrochem. Soc. 2011 158(9) A1015-A1022
An Self-Healing Effective Binder for Silicon Anodes in Lithium Ion Batteries
Authors: Yu Bing , Wu Zhaohui , Yang Juanyu , Wang Han , Shi Bimeng
Published: February 2020

Unexpected electrochemical performance of the high-capacity silicon (Si) anode materials has been shown, due to severe capacity fading caused by enormous substantial volume change of Si during cycling. In an effort to find efficient polymer binder that could mitigate such capacity fading, alginate-carboxymethyl chitosan(Alg-C-chitosan) composite polymer is investigated as a low-cost water soluble binder for silicon anodes in lithium-ion batteries. The electrostatic interaction between carboxylate(-COO-) of Alg and protonated amines(-NH3+) of C-chitosan leads to the formation of a self-healing porous scaffold structure. Synergistic effect on the enhanced porous scaffold structure and self-healing electrostatic interaction of Alg-C-chitosan binder, effectively tolerate the tremendous volume change of Si and maintain an integrated electrode structure during cycling process. The Si nanopowder electrodes with Alg-C-chitosan composite binder exhibit an excellent cycling stability, with a capacity of 750 mAh g-1 remaining after 100 cycles. In addition, an extraordinary areal capacity of 3.76mAh cm-2 is achieved for Si-based anodes with Alg-C-chitosan binder.
Development of a Water Based Process for Stable Conversion Cathodes on the Basis of FeF3
Authors: Pohl Alexander Herald , Faraz Mohammadkazem , Schröder Andreas , Baunach Michael , Schabel Wilhelm , Guda Alexander , Shapovalov Viktor , Soldatov Alexander , Chakravadhanula Venkata Sai Kiran , Kübel Christian , Witte Ralf , Hahn Horst , Diemant Thomas , Behm Rolf Jürgen , Emerich Hermann , Fichtner Maximilian
Published: February 2020

A facile water based synthesis method for HTB-FeF3/rGO and r-FeF3/rGO composites was developed using FeF3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF3/rGO were cast in ambient air and the calendered electrode shows a stable specific energy of 470 Wh kg–1 (210 mAh g–1, 12 mA g−1) after 100 cycles in the range 4.3–1.3 V with very little capacity fading. The good cycle stability is attributed to the intimate contact of FeF3 nanoparticles with reduced graphene oxide carbon surrounding. Using a combination of in situ XRD, XAS and ex situ Mössbauer spectroscopy, we show that during discharge of HTB-FeF3/rGO composite Li is intercalated fast into the tunnels of the HTB-FeF3 structure up to x = 0.92 Li. The Li intercalation is followed by slow conversion of HTB-LixFeF3 to LiF and Fe nanoparticles below 2.0 V. During charge, the LiF and Fe phases are slowly transformed to amorphous FeF2 and FeF3 phases without reformation of the HTB-FeF3 framework structure. At an elevated temperature of 55 °C a much higher specific energy of 780 Wh kg−1 was obtained.

Figure 1
Synthesis, Characterization and Electrochemical Properties of Germanium@Multiwalled Carbon Nanotubes Composite As Anode in Lithium Ion Batteries
Authors: Goriparti Subrahmanyam , Zaccaria Remo Proietti , Capiglia Claudio
Published: February 2020

Rechargeable lithium ion batteries have been in use in portable appliances like laptops, cameras and cellular phones due to high gravimetric energy together with long cycle life [1-3]. However, the deployment of lithium ion batteries in applications like hybrid electric vehicles, plug in hybrid electric vehicles and smart grids needs improvements in terms of energy and power densities along with reducing the cost [1-2]. Nanostructured electrode active materials have attracted much attention because of their potential to provide higher energy and power densities than bulk materials. In Particularly anodes such as silicon, germanium, tin, metal oxides and carbonaceous are the most promising materials [2-3].

Germanium (Ge) nanocrystals with size of 5 nm and their composites of multiwalled carbon nanotubes (MWCNTs) were synthesized via solvothermal method. Ge and Ge@MWCNTs have been characterized through X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy. Furthermore, electrochemical studies have been carried out with cyclic voltammetry, galvanostatic charging and discharging test, and impedance spectroscopy. The results show that as prepared Ge-MWCNTs nanocomposite exhibits improved cycling performance with higher capacity retention with respect to pure Ge electrode. In fact, Ge-MWCNTs nanocomposite shown a discharge capacity of 1160 mAh g-1 at current rate of 0.1C after 60 cycles as well as an excellent discharge capacity of 406 mAh g-1 at a current rate of 5C even after 400 cycles.References

1. J. B. Goodenough et. al., J. Am. Chem. Soc., 135 (2013) 1167

2. S.Goriparti et.al., J. Power Sources, 257 (2014) 421

3. S.Goriparti et.al., ACS Appl.
Mater. Interfaces, 7, (2015) 25146

Figure 1
Template-Free Electrochemical Synthesis of Selenium Nanowires
Authors: Seyedmahmoudbaraghani Saba , Myung Nosang Vincent
Published: February 2020

During past years, one-dimensional nanostructures such as nanotubes and nanowires have drown much attention due to the possibility of their application in nanodevices. This is due to their size-dependent physical properties. Selenium is known to be an important elemental semiconductor which has been widely studied because of the exhibition of so many appealing properties such as high photoconductivity and low photomelting temperature, high piezoelectric, thermoelectricity, and non-linear optical responses. There has been extensive research on Selenium nanowires and nanorods among all Se nanostructures. Se nanowires can be fabricated by using solution-phase method, chemical vapor deposition method, and electrodeposition. The electrodeposition technique is more promising due its simplicity, cost-effectiveness, and low growth temperature.

In the present work, we are looking forward to fabricating one-dimensional trigonal Selenium nanowires using electrodeposition. The morphology is controlled as a function of applied potential and pH in the electrolytes. The temperature-dependent annealing will also be performed. The morphology and crystallinity of the Se nanostructures are characterized by Raman spectra, TEM, SEM, and XRD. The electrodeposition of trigonal Selenium nanostructures is demonstrated based on an analysis of linear sweep voltammetry and pH-Eh (pourbaix) diagram.
A New Membrane Electrode Assembly Structure with Novel Flow Fields for Polymer Electrolyte Fuel Cells
Authors: Park Jaehyung , Pasaogullari Ugur , Bonville Leonard J.
Published: February 2020

A conventional polymer electrolyte fuel cell (PEFC) incorporates a membrane electrode assembly (MEA) which is comprised of the anode catalyst layer-polymer electrolyte -cathode catalyst layer sandwiched between two gas diffusion layers (GDLs), and bipolar plates. Conventional GDL is typically comprised of highly porous carbon paper or cloth to help diffuse the reactant gases onto the electrode, which is coated with a thin micro-porous layer (MPL). At high current densities, mass transport limitations of fuel or oxidizer in the PEFC occur in porous structures of the GDL, particularly at the cathode, which result in a sharp drop in the output voltage. The key to minimizing mass-transport losses is effective water management in the cell. Liquid water in macro-pores of GDL decreases the fuel cell performance at high current density due to the lack of oxygen reaching the catalyst layer.

A new MEA structure is recently introduced, where the carbon paper backing layer is eliminated and the entire gas diffusion layer consists of only the MPL [1]. We have further improved on this concept by directly depositing the MPL onto the CCM, resulting in an improvement in the interfacial contact between the MPL and the catalyst layer, as well as a simplified fabrication and assembly process. Spray deposition method was used for depositing this MPL onto a commercial CCM [2]. This concept was proven to work and perform better than a conventional cell with a micro-channel flow field used to provide the desired pathway for the reactant gases throughout the cell substituting for the macro porous carbon paper and the millimeter sized flow field.

In this work, a porous foam is utilized as the flow field to distribute the reactant gases over the micro-porous layer instead of the micro-channel flow field. Various pore sizes of the foam, i.e. 60-100 PPI, are used to compare with the conventional micro channel flow field. Contact resistance, permeability, electrochemical impedance spectroscopy, and mechanical properties are used to further characterize the new MEA structure incorporating the porous foam flow field. This method can be an effective way of enabling very high power density operation by reducing the mass transport limitations, and provides an improvement in the interfacial contact between the MEA and the flow field as well as improved mechanical properties.

[1] T. Kotaka, Y. Tabuchi, U. Pasaogullari, and C. Y. Wang, Electrochim. Acta, 146, 618 (2014).

[2] J. Park, U. Pasaogullari, L. J. Bonville, ECS Transactions, 69, 1355-1362 (2015).
Electrochemical Characterization of PEMECs Operating at Various Current Densities
Authors: Elsoee Katrine , Madsen Laila G.- , Scherer Guenther G. , Hjelm Johan , Mogensen Mogens Bjerg
Published: February 2020

This conference contribution touches upon electrochemical characterization of operating polymer electrolyte membrane electrolysis cells (PEMECs) by the application of electrochemical impedance spectroscopy (EIS). Analysis of differences in impedance spectra (ADIS) (Jensen et al., 2007) can be applied to gain insight into the relative magnitudes of resistance contributions from the two electrodes, the electrolyte and of mass transfer limitations and can help identifying the time scale of the respective processes. The gained knowledge may facilitate further development of the PEMECs.

A state-of-the-art PEMEC obtained from IRD with a 2.9 cm2 active electrode area and loaded with 0.3 mg/cm2 IrO2 on the anode and 0.5 mg/cm2 Pt on the cathode was operated at current densities ranging from 0.07 to 1 A/cm2 while examined with EIS. The cell temperature at operation was 61 ˚C at all current densities, and the cell was conditioned for 20 minutes at each current step prior to EIS measurements. A Solartron 1260 was used for the data acquisition, the frequency range was 100 kHz - 0.01 Hz, the amplitude was 17.3 A/cm2 and 12 points were measured per decade. Nyquist plots of the EIS results are shown in the upper graph in the figure. One arc is evident in the spectrum at 0.07 A/cm2, whereas the spectra at 0.35 and 0.69 A/cm2 include two arcs, and two overlapping arcs are observed at 1 A/cm2. ADIS plots, with the impedance measured at 0.07 A/cm2 subtracted, are shown in the lower graph in the figure. Based on the ADIS plots it can be concluded that the impedance is independent of the current density at frequencies above 100 Hz, whereas two processes observed at approximately 0.4 and 10 Hz are current density dependent, the one increasing and the other decreasing in size with increasing current density.

Acknowledgement

The work is part of the research project e-STORE funded by the Innovation Fund Denmark.

Reference

S. H. Jensen, A. Hauch, P. V. Hendriksen, M. Mogensen, N. Bonanos, T. Jacobsen. (2007). A Method to Separate Process Contributions in Impedance Spectra by Variation of Test Conditions. Journal of The Electrochemical Society, 154 (12), B1325-B1330.

Figure

Nyquist plots (upper graph) and ADIS plots (lower graph) of EIS measured on a PEMEC operating at 0.07, 0.35, 0.69 and 1 A/cm2. The ADIS plots represent the difference between the differentiated real part of the impedance at each current density and the differentiated real part of the impedance collected at 0.07 A/cm2.

Figure 1
(Invited Plenary) Improving the Catalytic Properties of Non-Precious Metal Catalysts - Milestones in the Development of Me-N-C Catalysts
Authors: Kramm Ulrike Ingrid
Published: February 2020

Me-N-C catalysts are today’s most active non-precious metal catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). The application of these catalysts dates back to 1964 when Jasinski was the first demonstrating ORR activity of different phthalocyanines in alkaline electrolyte. The most important steps in improvement of ORR activity and stability were made by the heat-treatment of MeN4-macrocycles in 1976 and the pyrolysis of independent metal, nitrogen and carbon sources in 1989 as shown by Jahnke et al. respectively Gupta et al..

However, especially during the last decade important progress in the development and fundamental understanding of these catalysts was gained. Based on these findings the ORR activity was boosted significantly. This motivated researchers worldwide to contribute to the development of Me-N-C catalysts and to the controversy of the origin of ORR activity.

In this contribution the most important milestones in the development of Me-N-C catalysts will be summarized. Based on this rational criteria can be defined for the further optimization of these catalysts with respect to a final implementation in the car.
Enduring Anion-Exchange Membrane Fuel Cells
Authors: Holdcroft Steven , Britton Benjamin , Wright Andrew G. , Weissbach Thomas
Published: February 2020

Alkaline anion exchange membrane fuel cells have become a topic of substantial interest in recent years, opening up a new electrochemical environment for hydrogen fuel cells. Facile kinetics for the oxygen reduction reaction open the promise of non-PGM or even non-metal AEMFCs, and radical stability. The most challenging aspect for the field, as defined by the 2016 DOE AMFC III Workshop, is membrane and ionomer stability in alkaline conditions at elevated operating temperatures. Few papers report endurance data, and best practices for in situ fuel cell conditioning and electrochemical characterization are still being developed by the community.

Here, we report that HMT-PMBI exhibits membrane and ionomer stability in situ as AEMFCs in relevant conditions for device operation. These fuel cells demonstrate re-equilibration from extensive carbonation and complete re-conditioning in a shut-down / start-up cycle. We further report operation in typically challenging conditions, e.g. increased temperature and reduced humidity. Finally, we report on our attempts to define best-practices for electrochemical characterization.
Investigating Catalyst-Electrolyte Interface By Microelectrode, Infrared Reflection Adsorption Spectroscopy and Neutron Reflectometry
Authors: Dumont Joseph H , Hjelm Rex , Watkins Erik , Chung Hoon T , Martinez Ulises , Atanassov Plamen , Kim Yu Seung
Published: February 2020

Understanding of the catalyst-ionomer interfacial behavior is critically important for fuel cell research. In fact, alkaline membrane fuel cells (AMFCs) have shown limited performance compared to proton exchange membrane fuel cells due to relatively poor hydrogen oxidation reaction (HOR) kinetics [1]. Previous work has shown that cationic adsorption at the surface of the catalyst was closely related to the HOR activity [2, 3]. Here, we present the results of a study of the benzyltrimethyl ammonium electrolyte-Pt interface in hydrogen oxidation reaction (HOR). More specifically, we will discuss the adsorption of the cationic group that may inhibit the HOR activity of Pt electrocatalysts. Microelectrode, Infrared Reflection Adsorption Spectroscopy (IRRAS) and Neutron Reflectometry are complementary tools to investigate the catalyst-ionomer interface.

Acknowledgement

US department of Energy Fuel Cell Technologies Program (Program Manager: Nancy Garland) supports this research through Fuel Cell Incubator Project. We also wish to acknowledge Oak Ridge National Laboratory Spallation Neutron Source, the NIST Center for Neutron Research and the Los Alamos Neutron Science Center.

References

[1] W.C. Sheng, H.A. Gasteiger, Y. Shao-Horn, “Hydrogen Oxidation and Evolution Reaction Kinetics on Platinum: Acid vs Alkaline Electrolytes,” J. Electrochem. Soc., 157, B1529 (2010).

[2] H. T. Chung, U. Martinez, J. Chlistunoff, Y. S. Kim, Y. K. Choe, and I. Matanovic, “Impact of Organic Cation Adsorption on the Hydrogen Oxidation Reaction of Pt in Alkaline Fuel Cells”, 2015, ECS Meeting Abstracts, 1510-1510

[3] Sung-Dae Yim, Hoon T. Chung, Jerzy Chlistunoff, Dae-Sik Kim, Cy Fujimoto, Tae-Hyun Yang, Yu Seung Kim, “A Microelectrode Study of Interfacial Reactions at the Platinum-Alkaline Polymer Interface,” J. Electrochem. Soc., 162, F499 (2015).
Electrochemical Degradation of Nafion Ionomer to Functionalize Graphene as a Support for Core-Shell Palladium-Ruthenium Alloy @ Platinum Electrocatalysts
Authors: Kuo Chih-Chia , Chang Yu-Chen , Chou Chao-Lin , Chou Shih-Cheng , Wu Pu-Wei
Published: February 2020

A simple but effective electrochemical route to functionalize graphene is demonstrated. Cyclic voltammetric sweeps are performed in 0.5 M H2SO4 aqueous solution on electrodes containing carbon cloth, graphene, and Nafion ionomer. With supply of ambient oxygen, the formation of hydroxyl radicals from the oxygen reduction reaction during CV cycles initiates the decomposition of Nafion ionomer that engenders oxygenated functional groups on the graphene surface. Raman analysis suggests a minor change for the graphene structure. Exploring various amounts of Nafion ionomer, we determine the optimized conditions for graphene functionalization. Contact angle is used to evaluate the effect of Nafion ionomer decomposition. X-ray photoelectron spectroscopy is employed to study relevant functional groups. Afterwards, nanoparticles of Pd9Ru are synthesized and impregnated on those functionalized graphene (FGN) via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples suggest successful formation of alloy without presence of individual Pd and Ru nanoparticles. Images from transmission electron microscope confirm the average size of 3-4 nm. Subsequently, the Pd9Ru/FGN undergoes Cu under potential deposition, followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd9Ru surface (Pd9Ru@Pt). Intensive experimental work is ongoing to investigate the electrochemical active surface area (ECSA) and electrocatalytic activities of Pd9Ru@Pt/FGN.
Impact on Diffusion Parameters Computation in Gas Diffusion Layers, Considering the Land/Channel Region, Using the Lattice Boltzmann Method
Authors: Espinoza Mayken , Sundén Bengt , Andersson Martin
Published: February 2020

A deep understanding of the behavior of microstructural parameters in proton exchange fuel cells (PEFCs) will help to reduce the material cost and to predict the performance of the device at cell scale. Changes in morphological configuration, i.e., fiber diameter and fiber orientation, of the gas diffusion layers (GDLs) result in variations of fluid behavior throughout the layer, and therefore; the microstructural parameters are affected. The aim of this study is to analyze, for three selected fiber diameters and different percentages presence of inclined fibers, the behavior of the different microstructural parameters of the GDLs.

This study is carried out over digitally created two-dimensional GDL models in which the fluid behavior is obtained by means of the Lattice Boltzmann method (LBM). Once the fluid behavior is determined, the microstructural parameters, i.e., the porosity, gas-phase tortuosity, obstruction factor, through-plane permeability, and inertial coefficient, are computed. Several relationships are found to predict the behavior of such parameters as function of the fiber diameter, presence of inclined rods or porosity. The results presented in this work are compared and validated by previous theoretical and experimental studies found in the literature.
Structural Characterization and Transport Modeling of Pt and Pt Alloy Polymer Electrolyte Fuel Cell Cathode Catalyst Layers
Authors: Cetinbas Firat , Ahluwalia Rajesh , Kariuki Nancy , More Karren L. , Cullen David A. , Sneed Brian , Winarski Robert P. , Ilavsky Jan , De Andrade Vincent , Myers Deborah J
Published: February 2020

In recent years, numerous Pt-based nanoparticle catalysts with very high oxygen reduction reaction activity have been developed, most of these based on transition metal alloys of Pt with or without post-synthesis de-alloying. As intrinsic electrocatalytic activities have been improved, the performance limitation of the cathode catalyst layers has shifted from activity to facile transport of reactants to catalytic sites. Electrode structure has thus become increasingly important in defining electrode performance. Effective transport of reactants through the thickness of the electrode (~10 µm) is highly dependent on the agglomerate structure and spatial distribution of the conducting phases and the pores. Ultra-small angle scattering and TEM analyses have shown that the agglomerate structure of electrodes based on representative high activity Pt alloy catalysts is different than that of Pt catalyst-based electrodes. In this presentation, we will compare the structure of Pt alloy-based electrodes and Pt electrodes, characterized by a variety of techniques, including ultra-small-angle X-ray scattering, TEM, and X-ray tomography. The information obtained from these techniques has been used as input to an electrode structural model. The model has been probed to analyze the transport processes of protons, electrons, oxygen, and water. The results from alloy and Pt-based electrodes fabricated from inks with different ionomer to carbon ratio, solvent, and ionomer equivalent weight have been examined to establish the empirical relationship between the microstructure and ink composition and the ultimate performance of the electrode layer.
1,2,3-Triazole-Functionalized Polysulfone Synthesis and Application in Proton Exchange Membranes for Low and High Temperature PEMFC
Authors: Sood Rakhi , Donnadio Anna , Giancola Stefano , Kreisz Aurélien , Jones Deborah J. , Rozière Jacques , Cavaliere Sara
Published: February 2020

The 1,2,3-triazole functionality demonstrates high chemical stability towards severe hydrolytic, oxidizing, and reducing conditions, even at elevated temperatures. Furthermore together with aromatic character and ability to form hydrogen bonds, it is reported to possess anti-oxidant properties1. All these features make polymers functionalized with 1,2,3-triazole of interest in proton exchange membranes as reinforcement or matrix for application in low and high temperature fuel cells.

We will describe a fast and high-yielding synthesis of 1,2,3-triazole functionalized polysulfone through microwave-assisted copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry. Polymers with various degrees of substitution of the side-chain functionality of 1,4-substituted 1,2,3-triazole with alkyl and aryl pendant structures were prepared and characterized to assess the completeness of the reaction. The thermal and thermo-chemical properties of the modified polymers were also characterized.

In one approach, cast membranes of 1,2,3-triazole functionalized polysulfone were doped with phosphoric acid for application in HT-PEMFC and their properties compared with conventional polybenzimidazole based systems. These novel membranes presented promising performance with high proton conductivity in anhydrous conditions and satisfactorily high elastic modulus2.

In another strategy with targeted low temperature PEMFC applications, nanocomposite membranes were prepared based on functionalized polysulfone and a perfluorosulfonic acid ionomer. As already evidenced for PBI-PFSA composites3, the specific interaction between the basic triazole functionalized polymer and the acidic ionomer lead to electrolytes with improved mechanical properties and without significant loss in proton conductivity.

1. J. Totobenazara and A. J. Burke, Tetrahedron Lett., 56, 2853–2859 (2015).

2. R. Sood, A. Donnadio, S. Giancola, A. Kreisz, D.J. Jones, S. Cavaliere, ACS Appl. Mater. Interf., in press.
Sulfonated and Partially Fluorinated Poly(aryl) Multiblock-Co-Ionomers for Fuel Cells
Authors: Bender Johannes , Kerres Jochen A.
Published: February 2020

In this paper, proton exchange membranes are presented on the basis of multiblock co-ionomers. The multiblock-co-ionomers are prepared from hydrophobic, partially fluorinated polymer [1] and hydrophilic, sulfonated ionomer blocks [2]. The synthesis of the individual polymer blocks is done by nucleophilic aromatic step-growth polycondensation. The multiblock-co-ionomer membranes are cast and dried according to standard procedure. The interest in multiblock-co-ionomer membranes for use in PEMFCs is that they form microphase- or nanophase-separated regions [3]. The areas with hydrophobic character ensure the stability of the membrane and the areas with hydrophilic character of the proton conduction. In case of longer hydrophilic blocks it is necessary to blend the multiblock-co-ionomers with basic polybenzimidazoles like PBI-OO or F6-PBI for mechanical stability.

In this contribution the first results in terms of characterization by means of NMR spectroscopy, molecular weight distribution, thermal stability and proton conductivity will be presented.

Literature:

1: Kerres. J. A.; Xing, D.; Schöneberger, F. J.Polym. Sci.
PART B: Polym. Phys.
2006, 44, 2311-2326

2: Kerres. J. A.; Schöneberger, F. J.Polym. Sci.
PART A: Polym. Chem.
2007, 45, 5237-5255

3: Kerres, J. A. Polymer Reviews
2015, 55, 273-306
Hydrogen Oxidation Reaction-Selective Electrocatalysis Via Fine Tuning of Platinum Ensemble Sites Using Dodecanethiol to Enhance the Durability of Automotive Fuel Cells
Authors: Park Gi-Woong , Yun Su-Won , Kim Yong-tae
Published: February 2020

We suggest a simple, inexpensive approach for enhancing the durability of automotive proton exchange membrane fuel cells by selective promotion of the hydrogen oxidation reaction (HOR) and suppression of the oxygen reduction reaction (ORR) at the anode in startup/shutdown events. Dodecanethiol forms a self-assembled monolayer (SAM) on the surface of Pt particles, thus decreasing the number of Pt ensemble sites. Interestingly, by controlling the dodecanethiol concentration during SAM formation, we can precisely tune the number of ensemble sites to an optimum such that it is sufficient for the HOR but insufficient for the ORR. Thus, a Pt surface with an SAM of dodecanethiol clearly shows HOR-selective electrocatalysis. We demonstrate clear HOR selectivity in unit cell tests with the actual membrane electrode assembly as well as in an electrochemical three-electrode setup with a thin film rotating disk electrode configuration.
Relating the Influence of Surface Characteristics of Carbon Electrocatalyst Support to the Performance and Durability of a PEMFC through Calorimetric, Adsorption, Spectroscopic and Electrochemical Measurements
Authors: Jimenez Morales Ignacio , Dupont Marc , Cavaliere Sara , Jones Deborah J. , Rozière Jacques , Zajac Jerzy , Larsen Mikkel Juul , Odgaard Madeleine , Mornaghini Flavio , Rodlert Marlene
Published: February 2020

The role played by the surface properties of carbon blacks used as electrocatalyst supports in fuel cell electrodes is crucial in determining the performance and durability characteristics of the final membrane electrode assembly. These key surface properties include the polar character arising from the presence of heteroatoms, and the proportion of the surface area that corresponds to graphitic carbon sites.

We have used flow calorimetry to characterise the surface properties of a family of carbon blacks having the same BET surface area (400±10 m2/g), but different pore size characteristics and different properties in terms of polar and graphitic surface sites. The preferential heat of adsorption of n-dotriacontane and n-butanol for basal plane sites and polar sites respectively has been determined for the carbon sites immersed in n-heptane1. The overall hydrophobic character of the carbon surface was evaluated by measuring the heat of adsorption of n-butanol from its aqueous solution2.

Platinum nanoparticles prepared by a microwave-assisted polyol method2 were deposited on each of the carbons, and the electrochemical surface area, the mass and specific activity of the Pt/C samples were determined. Membrane-electrode assemblies were prepared using the electrocatalysts at the cathode and they were tested in fuel cell over a range of temperatures and relative humidities, when the observed performance could be related to the relative hydrophobic/hydrophilic properties of the carbons. Further, the stability of the carbons to electrochemical corrosion was assessed by submitting them to high voltage (1.4 V/RHE) and determining the corrosion current and the corresponding mass loss, and the results related to the graphitic character of the carbons determined from flow microcalorimetry and Raman spectroscopy.

This understanding will be beneficial in the tuned design of PEMFC electrocatalyst supports for the targeted operation conditions. This work demonstrates the importance of calorimetric methods in characterising carbons for electrochemical applications.

References

1. J. Zajac, A. J. Groszek, Carbon 35 (1997) 1053-1060.

2. L. Kaluža et al., Electrocatalysis, (2016) http://dx.doi.org/10.1007/s12678-016-0312-3.
Nanofibrous Electrode Design By CNT-Winded Pt/TiO2 for Superior PEMFC Performance and Durability at High Temperature
Authors: Ji Yunseong , Cho Yongil , Jeon Yukwon , Hwang Ho Jeong , Lee Jin Goo , Park Myeonggeun , Lee Gicheon , Jang Jeongseok , Jeon Oksung , Kwon Oh Chan , Hwang Jusoon , Shul Yong Gun
Published: February 2020

Fuel cell is one of the most promising electrochemical energy conversion devices that has many advantages such as high efficiency, high power density, CO2 free, noise free, rapid start up, etc. Especially, polymer electrolyte membrane fuel cell (PEMFC) has been shown a lot of attention due to its high power density and relatively good portability. Generally, Pt supported on carbon black is used as an electrocatalyst in PEMFC. However, carbon corrosion is one of the main problem for electrode structure collapse and catalyst activity loss, which can be further accelerated at high temperature. Therefore, we need to find an alternative catalyst support material that is electrochemically stable and interacts strongly with the catalyst active sites.

Recently, metal oxide supports have been reported as promising materials due to their excellent mechanical resistance and inherently higher stability. Among many candidates, titanium dioxide (TiO2) support has an extraordinary stability under severe acidic atmosphere, which provides the possibility to directly use as a support material. However, the low electrical conductivity, catalytic activity and surface area of TiO2hinder the direct apply to the PEMFC electrode.

In order to solve these problems, we prepared TiO2 nanofibers by electrospinning method and platinum nanoparticles are deposited by microwave-assisted polyol method to synthesize an effective electrode catalyst. Then, CNT was winded around the catalyst surface to boost up the electrical conductivity. Furthermore, we found a modified Pt electronic structure that takes advantage of the strong synergetic interactions of TiO2 nanofibers, Pt nanoparticles and winded-CNT. This structure influences on a decrease of the d-band vacancy of Pt due to electron transfer from the support, resulting in an improved oxygen reduction reaction. Therefore, the cathode with the CNT modified Pt/TiO2 nanofiber composite shows higher catalytic activity due to the elimination of the drawback associated with conductivity and enhanced electronic active structure. As from various PEMFC tests, our CNT-Pt/TiO2 catalyst shows superior performance and durability, which is definitely distinguishable at high temperature condition of 120 oC and RH 40% compare to the commercial Pt/C.
Development of Hydroxide-Stable Anion-Conducting Functional Groups
Authors: Weissbach Thomas , Wright Andrew G. , Holdcroft Steven
Published: February 2020

Immobilized benzimidazolium cations as functional groups in anion exchange polymers can be used in alkaline anion exchange membrane fuel cells (AAEM-FCs), electrolyzers, or water purification systems, but are prone to hydroxide attack. Steric protection by proximal methyl groups has been shown to drastically increase hydroxide stability (A. Wright, S. Holdcroft ACS Macro Lett. 2014, 3, 444-447.). To further improve stability, model compounds, representing the ion exchange sites of AAEMs, were investigated for their hydroxide stability. By means of density functional theory (DFT), we studied degradation mechanisms, such as de-methylating SN2 reaction of methylated benzimidazolium cations with hydroxide ions and the attack of hydroxide on the C2 position of the benzimidazolium. Some of these results have also been compared to experimental stability tests of model compounds and polymers (A. G. Wright, T. Weissbach, S. Holdcroft Angew. Chem. Int. Ed.
2016, 55, 4818-4821.). The findings of this study enable the design of new materials for AAEM-FCs.
Decoupling the Influences of Molecular- and Mesoscales on Macroscopic Transport Properties in Perfluorosulfonic-Acid Membranes
Authors: Crothers Andrew Robert , Shi Shouwen , Radke Clayton J. , Weber Adam Z
Published: February 2020

Performance of polymer-electrolyte-fuel-cells (PEFCs) links strongly to thermodynamic and mass-transport properties of the polymer membrane. The quintessential PEFC-membrane material is perfluorosulfonic-acid (PFSA) polymer, which phase separates into nanoscale hydrophilic water-filled domains through which ions and water transport and into hydrophobic polymer-matrix domains that provide structural integrity and durability. Although considerable progress has been made to reduce reactant mass-transport limitations in PFSA membranes, mass-transport is still a critical area of concern. Aqueous electrolyte transport across a phase-separated membrane is inherently a multiscale problem with aqueous-dissolved species moving through nanoscale domains that are connected to form a transport network at the intermediate mesoscale. To guide the optimization of PEFC material design and operation, we decouple the impact of micro and macro length-scale on mass transport in PEFC membranes.

Specifically, molecular-scale interactions between aqueous-electrolyte and polymer in hydrophilic domains of PFSA membranes are modeled with mean-field local-density theory aligned with an experimentally consistent 3D domain geometry. Our molecular-scale description of membrane conductivity accounts for solvation, electrostatics, solvent dielectric saturation, finite size, and confinement effects. The microscale framework is validated against atomistic simulations and, subsequently, up-scaled to predict macroscale conductivity and solvent absorption by accounting for the interconnectedness of the hydrophilic domains. Excellent agreement is found with experimental data, as shown in Figure 1. Our proposed multiscale model for membrane conductivity and solvent sorption provides a new tool to explore potential avenues for improving PFSA membrane performance.

Acknowledgements

This work was funded by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231 and by the National Science Foundation Graduate Research Fellowship under Grant No. DGE 1106400

Figure 1.3M PFSA membrane conductivity of proton-form membranes as a function of water content as determined from the model (open) and experiments (filled, with lines to guide the eyes) for equivalent weights of 1100 (circles), 1000 (squares), and 825 g/mol (SO3-) (diamonds)

Figure 1
Metal Oxide Nanocrystals Supported on Carbon Nanotubes As Bifunctional Electrocatalysts in Reversible Alkaline Membrane Fuel Cells
Authors: Zhao Shuai , Rasimick Brian , Mustain William E , Xu Hui
Published: February 2020

Hybrid structure of Co3O4 nanocrystals supported on carbon nanotubes (CNTs) was previously synthesized in our lab, and it exhibits excellent bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) activities in alkaline media. More importantly, the hybrid nanomaterials showed great durability in a broad cycling potential range, from 0.0 V to 1.9 V (vs. RHE), which is a harsh environment that no previous hybrid structure reported has demonstrated stability in.

In this study, we further explored other types of structure using similar synthesizing procedure, but different metal precursors (forming single, binary or ternary oxide solid solution with cobalt acetate, nickel acetate, manganese acetate, iron acetate or copper acetate) and solvents to pursue better performance. Other parameters such as CNT size and post-treatment conditions were also altered to optimize the synthesis procedure.

The CNT-based hybrid electro-catalysts were made into membrane electrode assemblies (MEAs) to be tested in reversible alkaline fuel cells. The MEA fabrication was optimized in aspects of: catalyst ink preparation (by tuning the ionomer type, ionomer/catalyst ratio, and sonication length), membrane selection (alkaline membrane types, pre- and post- activation), catalyst-coated membrane fabrication (painting, spraying, hot pressing condition) and cell assembly. The MEAs were then tested in fuel cell mode and electrolyzer mode intermittently. MEA structural characterizations were carried out before and after these tests to study catalyst degradation mechanisms.

This work may provide perspectives for bifunctional catalyst synthesis and MEA design for reversible alkaline fuel cells.

Acknowledgement:The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-EE0006960.
Platinum Based Catalysts for Direct Alcolhol Oxidation and Oxygen Reduction Reaction
Authors: Man Tran Van
Published: February 2020

In this study, we report about the activity of different catalysts based on nanoplatinum and/or platinum alloys and nanocarbons for alcolhol oxidation.

Firstly, we introduce about the synthesis of nanocatalysts by reduction in aqueous solution using NaBH4 and Ethylene Glycol as reductant. Then we present the synthesis of thin films of Platinum and bimetallic platinum-ruthenium on carbon paper and fluorine-doped tin oxide coated glass (FTO) by electrostatic spray deposition (ESD). The alcolhol electro-oxidation in acidic and alkaline media were investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Oxygen reduction reaction was investigeted using a rotating disk electrode and the three-electrode cell operating MetrOhm AutoLab-302N. Compared to Pt, the bimetallic catalysts displayed an enhanced activity toward alcolhol electro-oxidation reaction and some for oxygen reduction reaction. The beneficially effect of combination Ru with Pt was also found to be influenced by the nature of metallic precursors and substrates used in the ESD technique.