bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Polypyrrole Encapsulated Tin Oxide Nano Powder By Spontaneous Co Precipitation and Evaluating for Lithium Ion Battery Anode Material
Authors: Ravikumar Raman , Gopukumar Sukumaran
Published: February 2020

The tin oxide has been prepared by spontaneous co precipitation method. Pyrrole has been polymerized and encapsulated on to the tin oxide nano particle using FeCl3 as a polymerizing agent. The prepared material has been well characterized to understand the structural and morphological nature. XRD study confirms the nature of crystal is tetragonal and the having space group P42/mnm, the SEM images shows the flaky formation of polypyrrole consisting tin oxide. TEM images also supports for the formation of uniform tin oxide and encapsulation of polypyrrole. SEAD pattern of the material reveals the uniform distribution of the tin oxide particle. The cloudy ring SAED pattern endorses for the polypyrrole matrix in the composite. The present study is an attempt to overcome the present-day volume expansion problem induced by the lithiation and de-lithiation in to the SnO2 particle. During this alloying reaction the particle undergoes large volume change. The polypyrrole is believe to be act as a back bone, which encapsulating tin particle and attached to the similar structure to form a sheet of the composite matrix. Since the polypyrrole is well known for its conductivity and the lithium transfer would be made ease. These said properties of the composite material is suitable for the superior capacity and its retention.

Figure 1
Binder Free Graphene- Based Electrodes with Excellent Pseudocapacitive Performance
Authors: Chabi Sakineh , Xia Yongde , Zhu Yanqiu
Published: February 2020

Owing to the high impact of the electrode’s architecture on the energy storage and power performance, it is very important to create optimum structures that provide efficient short paths for ion and charge transportation. Given excellent advantages of graphene, e.g. very high surface area, and excellent mechanical properties, this material is an ideal candidate to serve as an electrode matrix to stabilise electroactive materials for the charge-discharge process [1].  

In this study, three dimensional (3D) binder free graphene composites have been synthesised by a two-step process, a chemical vapour deposition of the graphene followed by a chemical or electrochemical deposition of the redox counterpart. Pure graphene (GN), Polyaniline-graphene (PANI-GN), Polypyrrole-graphene (PPY-GN) and some other electrodes will be described in this work, and their electrochemical performance  will be studied by using  combined cyclic voltammetry, impedance spectroscopy and galvanostatic charge discharge techniques. Effects of the electrode dimensionality (3D vs 2D) and the binder on the performance will be investigated and explained.

Figure 1 (a) is a SEM image of 3D graphene foam. The open porosity feature of the foam facilitates effectively the ion intercalation and extraction. Figures 1 (b) and 1 (c) are the cyclic voltammetry and Nyquist curve of the 3D PANI-GN. In contrast to the pure graphene and PANI, the composite electrode showed a much better electron conductivity and higher performance.

The performance data have also revealed that using the porous 3D graphene foam as the electrode matrix and eliminating the insulating binder from the electrode structures result in an improved conductivity of the electrode, with excellent cycle life. The improved electrochemical performance efficiency is due to the dual energy storage mechanism and the synergetic effect of the graphene foam and redox counterpart.

Reference:

1.            Chabi, S., et al., Ideal Three‐Dimensional Electrode Structures for Electrochemical Energy Storage. Advanced Materials, 2014. 26(15): p. 2440-2445.

Figure caption

Figure 1: SEM image of graphene foam (a) cyclic voltammetry of 3D PANI-GN (b) and Nyquist curve of 3D PANI-GN in 0.5 M H2SO4.

Figure 1
Impedance Spectroscopy of Industrial Batteries
Authors: Stoynov Zdravko , Vladikova Daria , Schiavetti Massimo , Fastelli Irene
Published: February 2020

The successful application of the Impedance Spectroscopy for measurement and quality control of batteries should obey a number of specific requirements, correspondent to the nature of the batteries as objects under investigation. Batteries are nonlinear and non-stationary large statistical systems with distributed parameters in macro- and micro-scale. Processes of charge and mass-transfer take place in their electrodes, changing the chemistry and the habitus of the active electrode materials. 

Starting with the very first successful measurement of a small Lead-acid battery in 1976 [1], we developed a set of complementary techniques providing for reliable measurements of battery impedances, data handling and analysis. The techniques for inductive errors evaluation and correction, for the 4-Dimentional data treatment [2] of the evolving battery State of Charge will be discussed in details. Special attention will be given to the interpretation of the battery impedance as a property of a fuzzy system with un-known parameters distribution. The Differential Impedance Analysis which solves this problem and the related Spectral Transforms are powerful tools for batteries evaluation and quality control [3].

These techniques will be illustrated with practical examples of impedance measurements of large industrial Lead-acid and Li-ion batteries and stacks fabricated by different technologies and for different purposes.

 Some related side phenomena as: (i) presence and destruction of the passive layer; (ii) increased inductance of stacks as well as impedance observation of local in-homogeneities in Li-ion batteries will be also discussed.

 References

 1. M. Keddam, Z. Stoynov, H. Takenouti, J. Appl. Electrochem. 7 (1977) 539.

2. Z. Stoynov in: C. Julien, Z. Stoynov (Eds.), Materials for Lithium- ion Batteries, Kluver Academic Publishers, 3/85 (2000) 359.

3. Z. Stoynov and D. Vladikova, in Encyclopedia of Electrochemical Power Sources, edited by U. Garche ( Elsevier, 2009) pp. 632-642.
Aqueous Sodium-Ion Battery As Post Lithium-Ion Battery
Authors: Okada Shigeto , Kano Yusuke , Nakamoto Kosuke
Published: February 2020

Three kinds of secondary batteries, nickel metal hydride, Li-ion and Na/S battery were commercialized in Japan for the first time. Among them, Li-ion battery became the most popular power sources for PDA, because of the highest energy density. However, Li-ion battery is difficult to use for large-scale batteries, because its organic electrolytes are flammable, expensive and less conductive.

     Recently, aqueous electrolyte has been recognized as an attractive alternative and much attention has been paid to its development, because it has 3 big advantages about the conductivity, nonflammability and cost. In addition, water is an ideal solvent that dissolves a lot of various salts. Here, the most important thing is the selection of electrode active materials to avoid decomposition of the aqueous electrolyte. An aqueous Li-ion battery with LiMn2O4 cathode and VO2 anode was first reported by J. R. Dahn's group [1]. Since them, several combinations of cathodes and anodes have been reported as aqueous Li-ion battery. Theoretically, higher cell voltage more than 1.2 V cannot be obtained in the aqueous battery. So, it is unnecessary to dare to use Li in the aqueous batteries. Nevertheless, there is few report about aqueous Na-ion battery, in comparison with aqueous Li-ion battery. As one of the few exceptions, aqueous sodium-ion hybrid device with Na0.44MnO2cathode and active carbon anode was first proposed by Carnegie Mellon University, 4 years ago [2].

     In this presentation, we introduce the aqueous Na-ion battery with pyrophosphate Na2FeP2O7 cathode and NASICON-type NaTi2(PO4)3 anodes. Because these polyanionic electrodes have flat voltage plateaus at 3.0 V and 2.1 V vs. Na/Na+, respectively. These redox voltages are almost located within the potential window of the aqueous electrolyte. In addition, Fe and Ti are the first and the second cheapest redox couple in transition metals, respectively.

References

[1] W. Li, J. R. Dahn and D. S. Wainwright, Science, 264 (1994) 1115.

[2] A. D. Tevar and J. F. Whitacre, J. Electrochem. Soc., 157 (2010) A870.
Development of Novel High Energy Density Sodium Layered Oxide Cathode Materials
Authors: Gruar Robert , Adamson Paul , Smith Katherine , Treacher Joshua , Ledwoch Daniela , Kendrick Emma
Published: February 2020

The large-scale utilisation of renewable energy technologies depends on solving the intermittency of energy production with large scale energy-storage solutions. The Lithium-ion battery has been widely considered as the technology of choice to meet the future energy challenge. However, increasing demand for Li based energy storage technologies is likely to tax current Li production. There is growing research and commercial interest in other metal ion battery technologies that could be developed to meet the needs of large scale energy storage applications. As such, the room temperature Na-ion secondary battery has been the subject of increasing research and development due to its feasibility to compete with the already well-established Li-ion secondary battery.1 Although, there are many technical barriers to overcome before Na-ion technology becomes competitive with current metal ion batteries. However, recent research into Na-ion systems has shown that some of the known Na-ion battery materials have advantages over the current Li-ion counterparts.2

 In this publication, we present detailed characterisation of novel sodium ion cathode materials based on a layered oxide framework as strong candidates for Na-ion battery cathode materials. We will present a review of layered oxides (Na Nix TMyO2, TM = Ti, V, Cr, Mn, Fe, Co, Ni, and a mixture of 2 or 3 elements). Single TM layered oxide systems are well characterised not only for their electrochemical performance but also for their structural transitions during electrochemical cycling.1 Binary TM systems are often favoured as modifications through doping seem to address issues of low reversible capacity, capacity retention, operating voltage, and structural stability when compared to the single TM analogues.2 As a consequence, some materials already have reached a specific energy density of 578 mW h g−1 comparable to that of LiFePO4.3 Furthermore, some binary and ternary TM systems have shown exceptional stability and rate capability.4

Herein, we present development work of Na Nix Mny TM1TM2 O2 quaternary and higher substituted sodium layered oxides.5 We demonstrate that further substitution within the layered oxide structure is beneficial to improving reversible capacity, capacity retention and operating voltage of these materials. These higher order substitutions leading to materials which show comparable electrochemical properties to simple Li ion technologies. We have begun development of Full cell technology based on some of the best performing layered oxides.

 

N. Yabuuchi, et al. Chem. Rev., 2014, 114 (23), pp 11636–11682

L. Yuechuan, et al. Chem. Mater. 2014, 26, 5288−5296

X. Li et al.  Electrochemistry Communications 49 (2014) 51–54

H. Yoshida, N. Yabuuchi and  S. Komaba Electrochem. Commun., 34 (2013), pp. 60–6

J. Barker, et al. Doped Nickelate Compounds WO 2014/009710A1
Evidence for a Mixed-Phase Discharge Product and Superoxide-Mediated Discharge Pathway in a Mg/O2 Battery
Authors: Vardar Gulin , Sleightholme Alice , Siegel Donald J , Monroe Charles W
Published: February 2020

Metal/O2 batteries have the potential to achieve extremely high energy densities, and metal/O2 batteries based on magnesium are predicted to have one of the highest.1 Shiga et al. have demonstrated rechargeable, non-aqueous Mg/O2 cells that operate above room temperature.2
,
3 The need for elevated temperatures can be negated by using a Mg2+ electrolyte that can deposit and dissolve Mg at room temperature. We have produced Mg/O2 test cells using a modified-Grignard-reagent electrolyte, which has oxidative stability higher than 4V vs. Mg/Mg2+ and is viable at room temperature.4

We will discuss our progress in exploring discharge and recharge characteristics of non-aqueous Mg/O2 cells. Although Mg/O2 batteries have been demostrated using non-aqueous electrolytes in the past, the nature of the discharge product is not well understood. Figure 1 shows the discharge product on a porous-carbon positive electrode after first discharge. We have elucidated the Mg/O2 discharge-product composition using several characterization techniques, including scanning electron microscopy, energy dispersive spectroscopy, Auger electron spectroscopy, X-ray diffraction and Raman spectroscopy. The discharge product predominantly comprises MgO. In addition to MgO, there is evidence of a substantial minority of MgO2, as well as trace Cl. The energy efficiency for the first cycle is 42%, lower than other metal/O2 chemistries,5
,
6 but comparable to prior elevated-temperature Mg/O2 cells.2

The open-circuit potential (OCP) prior to first discharge of the non-aqueous Mg/O2 cell is 2.0V, which is lower than would be expected for the direct electrochemical formation of MgO or MgO2 (2.95V and 2.91V vs. Mg/Mg2+, respectively). This observation is consistent with discharge-product formation via a superoxide-ion intermediate, which forms from molecular O2 at 2.03 V vs. Mg/Mg2+. Superoxide then drives an O2-releasing precipitation of MgO2, which subsequently disproportionates to O2 and MgO – chemical reactions that do not affect the cell voltage, and rationalize the observed discharge-product composition. 

(1)        Zu, C.-X.; Li, H. Energy Environ. Sci.
2011, 4, 2614.

(2)        Shiga, T.; Hase, Y.; Kato, Y.; Inoue, M.; Takechi, K. Chem. Commun. (Camb)
2013, 49, 9152.

(3)        Shiga, T.; Hase, Y.; Yagi, Y.; Takahashi, N.; Takechi, K. J. Phys. Chem. Lett.
2014, 5, 1648.

(4)        Nelson, E. G.; Brody, S. I.; Kampf, J. F.; Bartlett, B. M. J. Mater. Chem. A
2014.

(5)        Hartmann, P.; Bender, C. L.; Vračar, M.; Dürr, A. K.; Garsuch, A.; Janek, J.; Adelhelm, P. Nat. Mater.
2013, 12, 228.

(6)        Ren, X.; Wu, Y. J. Am. Chem.  Soc.
2013, 135, 2923.

Figure 1
Interface Study of All-Solid-State Lithium Batteries with Garnet-like Structure Llzo Electrolyte
Authors: Lee Jae Myung , Lee In Sung , Nam Sang Cheol , Kim Do Hyeong
Published: February 2020

All-Solid-State Lithium battery, which is consist of solid electrolyte, is expected the most promising candidate for next generation energy storage devices for its high safety, high energy density and long cycle life 1-3]. Because all these advantages were attributed to the electrolyte materials, most of the studies are focused on the electrolyte materials themselves.

Among many other lithium ionic conductors, the Garnet-like structure LLZO (Li7La3Zr2O12) is the most promising candidate for its high ionic conductivity (~0.1mS/cm), non-reactivity with air, and high chemical stability both with lithium metal and oxide cathode materials. There are many reports about modification of LLZO with doping elements and structural changes of LLZO, however, there are less reports of manufacturing process of All-Solid-State lithium batteries with LLZO or interfacial properties between cathode and electrolyte.

In this study All-solid-state lithium batteries with two different types of LLZO electrolyte/cathode composite electrodes were manufactured. The first type was based on sputtering process and the second one was based on co-firing process. (1) type 1 : Electrolyte green sheets were casted by dry casting, then they were sintered in oxygen environment. Each electrode was polished by sand papers to get a flat surface, and it was installed in vacuum chamber for sputtering of LiCoO2 layer. The thickness of sputtered LiCoO2 cathode film was 1um. (2) type 2: the cathode and electrolyte composite green sheets were casted by dry casting method. Those composite green sheets were sintered simultaneously (co-firing) in oxygen environment. The Lithium metal anode layer was prepared on the surfaces of the electrolyte sides in those composite electrodes by thermal deposition method and a gold film was deposited by sputtering process on the surfaces of the cathode for current collection. The Electrochemical properties of composite electrodes were evaluated by charge-discharge cycle test and electrochemical impedance analysis method. The interfaces in composite electrodes between cathode and electrolyte were investigated by spectroscopic methods.

Referecnes

[1] Ramaswamy Murugan,et al. Angew. Chem. Int. Ed. 2007, 46, 7778 –7781.

[2] Ezhiyl Rangasamy, et al. Solid State Ionics 206 (2012) 28–32.

[3] Kai Chen, et al. Electrochimica Acta 80 (2012) 133– 139.
Modeling Electrochemical Reactions - Methods, Phenomena and Problems from Metals to Oxides to Organics
Authors: Auer Alexander A
Published: February 2020

Catalytic reactions involing oxygen are omnipresent in modern science. May it be in cellular respiration, in corrosion processes

or in energy conversion and storage, the reduction and evolution of this species plays a central role. In Biology, for example

iron or manganese containing enzymes efficiently cleave of form the oxygen-oxygen bond. In fuel cells, platinum aids in converting

the energy stored in hydrogen and oxygen. In electrolyzers, iridium oxide might be the catalyst of choice for oxygen evolution. 

If one now considers approaches for the simulation of the electronic structure of systems like metals, oxides and enzymes, one

finds that very different approaches are applied, even different communities and schools exist - Terms like solid state physics, semiconductor

physics, quantum chemistry or bioinorganic chemistry come to mind. Is this merely a reflection of the historical process in which these

disciplines evolved, or is there an expalanation why catalytic reactions on metals are treated with a very different toolbox from the methods common 

in biocatalysis ?

Im my presentation I will give an overview of the phenomena in oxygen reduction and evolution and discuss differences and similarities

of electrocatalytic reactions for metals, metal oxides and molecules. A central scheme will be the electronic structure focusing on the

availability to supply charge and spin to the active site of a catalyst. This includes discussing the question when the energies of intermediates

are sufficient to understand a catalytic reaction or if transition states need to be included. Is it sufficient to have an estimate for the density of states

in order to understand heterogenous reactions or are more details required to identify the major influences for catalysis ?

This overview, which is meant to inspire different fields to join their effords,

will be illustrated by examples from my own work on platinum nanoparticles and extended carbon structures,

by examples from our department on biocatalysis as well as examples from the literature.
Sulfonic Acid-Functionalized Hybrid Proton Exchange Membranes Synthesized By Sol-Gel for Direct Methanol Fuel Cells
Authors: Mosa Jadra , Durán Alicia , Aparicio Mario
Published: February 2020

Organic/inorganic hybrid membranes based on (3-glycidoxypropyl) trimethoxysilane (GPTMS) and 3-mercaptopropyl trimethoxysilkane (MPTMS) have been prepared by sol-gel method and organic polymerisation, as candidate materials for proton exchange membranes in direct alcohol fuel cell (DMFC) applications. The –SH groups of MPTMS are oxidized to sulfonic acid groups, which are attributed to enhance the proton conductivity of hybrid membranes. FTIR, Raman and XPS were used to characterize and confirm the hybrid structure and oxidation reaction progress. Membranes characterization includes ion exchange capacity, water uptake, methanol permeability and proton conductivity to confirm their applicability in fuel cells. All the membranes were homogeneous thermally and chemically strong. In particular, our hybrid membranes demonstrated proton conductivities as high as 0.03 S/cm, at high temperature, while exhibiting high methanol permeability as compared to Nafion®. These results show that this kind of hybrid membranes possess high proton conductivity and a high barrier to methanol permeation due to the proton conducting path through the silica pseudo-PEO network in which sulfonic acid groups work as proton donor. Collectively, our results indicate that crosslinked MPTMS-GPTMS oxidized hybrid membranes offer great potential for use as PEMs in DMFC applications.
Finite Thickness Effects on Nafion Properties in the PEMFC Catalyst Layer, Probed By in Situ Neutron Reflectometry
Authors: DeCaluwe Steven C , Dura Joseph A.
Published: February 2020

A major technical challenge impeding the optimization of polymer electrolyte membrane fuel cells (PEMFCs) is a lack of understanding regarding Nafion properties inside the fuel cell catalyst layer (CL).  Inside the CL, thin Nafion layers (typically on the order of 2 – 80 nm thick) cover solid electrode particles and agglomerates.  In this thickness range, dimensional confinement and interfacial effects at solid, liquid, and vapor phases alter the properties of the films.  While recent studies have explored water content and transport properties in this thickness range to demonstrate reduced water mobility for films below roughly 60 nm in thickness, the effects of thickness and substrate variation on water uptake and Nafion structure in this range are still debated.   Thus far, an unambiguous documentation of Nafion composition and structure for thicknesses typical of the PEMFC CL has not been presented.  We present here the use of neutron reflectivity (NR) as an in situ probe of structure and composition for Nafion films with thicknesses of 5 – 200 nm.  NR measurements provide simultaneous thickness and composition information for thin-films under controlled conditions, via an SLD depth profile with sub-Ångström resolution for structural elements thicker than roughly 1.5 nm.  Neutrons transmit easily through sample chamber walls and have an inherent sensitivity to hydrogen isotopes, with a large SLD variation between H and D isotopes, making NR ideal for in situ measurements of thin-film Nafion hydration.

Through the application of multiple NR measurements, elemental conservation, and Bayesian analysis, results presented will document varying water sorption and interfacial structures in thin-film Nafion for varying thickness, substrates, and humidity levels.  Results provide an unambiguous confirmation of the reduced water sorption with reducing thickness below 60 nm, a detailed analysis of the sheet-like lamellar phase segregation on SiO2 substrates, as well as an illustration of how substrate modification can affect Nafion properties. Figure 1 shows the variation in water sorption with varying film thickness.  As previously observed, for layers that approximate the phase-segregation of bulk Nafion films (“bulk-like”) water uptake decreases steadily for film thicknesses below 60 nm.  However, within multi-lamellar polymer structures found at hydrophillic substrate interfaces, the water content reaches a minimum for films roughly 20 nm thick, and increases for films thinner than 15 nm.  Furthermore, the average water content within the multi-lamellar structures is slightly higher than in the bulk-like outer layers.  Simple numerical simulation results will be presented to discuss the implications of Nafion structural and composition variations in the CL for PEMFC performance.

Figure 1
PEM Fuel Cell Electrodes Prepared By Photocatalytically Deposited Pt on TiO2 and Successive Electrospinning
Authors: Narayan Manoj Krishna Kayarkatte , Delikaya Öznur , Roth Christina
Published: February 2020

For successful commercialization of low temperature proton exchange membrane (PEM) fuel cells, the system should have a long life and a high performance. Further, to make them cost effective a decrease in Pt loading is also deemed necessary.

Pt supported on titania nanoparticles have shown to possess high stability. Unlike standard carbon, TiO2 itself doesn’t corrode in fuel cell operation conditions. Also, TiO2 is shown to form stronger bond with Pt owing to ‘strong metal support interaction’ (SMSI) [1], increasing the stability of the system itself. Due to the oxygen spillover effect, titania also acts as a co-catalyst, enhancing the oxygen reduction reaction [2]. Here, Pt/TiO2 is prepared by reducing a Pt precursor photocatalytically under UV illumination and directly on the support [3].

Recently in another development, electrospinning was found as an efficient way to prepare porous electrodes with very low Pt loading [4]. Electrospinning facilitates the preparation of a variety of fiber networks and architectures thus enabling to achieve porous structures which are required to enhance the sluggish oxygen reduction reaction and decrease the platinum loading in a PEM fuel cell. The versatility of electrospun materials not only depends on the precursor, but also on modifying the solution and process parameters, giving a considerable control over the morphology.  

In this work, these two things are integrated together. First Nafion containing a small amount of PAA is mixed to form the electrospinning solutions with addition of Pt precursor along with titania in different amounts to obtain various loadings. In the presence of a strong source of UV light the Pt precursor is reduced to Pt and deposits itself on the TiO2. Fig. 1 shows the scanning electron micrograph of the 20 wt.% Pt/TiO2 catalyst held on a fibrous PAA/Nafion structure. The catalyst layer is prepared by electrospinning directly onto the GDL. The obtained catalyst layer is hot pressed on Nafion membrane to fabricate membrane electrode assembly, which will be later studied for H2/O2 fuel cell system. 

References:

[1]       Tauster SJ. Acc Chem Res., 20,389–94 (1987).

[2]       Diebold U. Surf Sci Rep., 48,53–229 (2003).

[3]       Ma J, Habrioux A, Alonso-Vante N. J Solid State Electrochem., 17,1913–21(2013).

[4]       Cavaliere S, Subianto S, Savych I, Jones DJ, Rozière J. Energy Environ Sci., 4,4761(2011).

Fig. 1 Scanning electron micrograph of electrospun PAA/Nafion fibers containing 20 wt.% Pt/TiO2

Figure 1
The Study of Anhydrous Binary and Ternary PVDF-HFP/Oxalic Acid/DMA Blended Polymer Electrolytes Systems for Fuel Cell Applications
Authors: Singh Marisa , Missan Harinder Pal Singh
Published: February 2020

A new series of anhydrous binary and ternary acid-base systems composed of Oxalic acid (OA), Dimethylacetamide (DMA) and Poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) has been developed. Ionic conductivity in the range of 10-2 S/cm was observed for binary acid-base compositions at temperatures above 100oC. The acid and base were added to the polymer in various compositions to improve the properties of polymer electrolyte such as proton conductivity and thermal stability. The ternary system with the highest proton conductivity was in the range of 10-3 S/cm at 150oC. IEC values were observed to compliment the proton conductivity values. SEM studies showed DMA plays an important role in improving the morphology of the electrolyte. Thermal stability studies were carried out on these materials and it was found that they had high thermal stabilities up to 350oC.
Characterization of Carbon Fiber Electrode for Vanadium-Based Redox Flow Batteries
Authors: Narita Ayumi , Kaneko Yuji , Sato Yukari , Negishi Akira , Nozaki Ken , Kato Tohru
Published: February 2020

Electrochemical properties of vanadium-based redox flow batteries (RFB) depend on many factors, such as redox chemical species, electromotive force, concentration of active materials, viscosity of electrolyte solution, electrode materials, electrode characteristics, and so on. One of the most important factors that regulate the RFB performance is the properties of electrodes.

  In the case of actual vanadium-based RFB, carbon felt/fiber electrodes were used. Electrochemical performance of such carbon felt/fiber electrodes was treated in average. To evaluate RFB properties quantitatively, we adopted carbon single fiber electrode.

　Carbon single fiber electrodes were prepared from carbon electrodes for vanadium RFB to examine the relationship between the carbon electrode and battery performance. Carbon single fiber electrodes were evaluated electrochemically. Statistical analysis was applied for about 10 carbon single fiber electrodes. Electrochemical responses of carbon fiber electrodes were compared with the previous results [1].

References:

[1] H. Kaneko, K. Nozaki, Y. Wada, T. Aoki, A. Negishi, and M. Kamimoto, Electrochim. Acta, 36, 1191 (1991).
Experimental Investigation of the Influence of Pressure on the Performance of Polymer Electrolyte Water Electrolysis Cells
Authors: Suermann Michel , Schmidt Thomas J. , Büchi Felix N
Published: February 2020

Fluctuating electric energy production from renewable sources is increasing. While this is desired from an environmental point of view because production does not match consumption, storage is required to avoid curtailment [1]. Dynamically operable polymer electrolyte water electrolysis (PEEC) may be used to convert excess electric energy from fluctuating sources into chemical energy, i.e. hydrogen and oxygen [2]. For storage, transportation or methanation of hydrogen and optionally oxygen, pressure levels up to 300 bar, for mobility up to 800 bar are needed.

Conventional, mechanical compression of hydrogen to the above mentioned pressure levels is inefficient, noisy and many compression stages are required which cause high investment costs and intensive maintenance. In contrast, electrochemical compression in high pressure (HP) PEEC promises to be more efficient, silent and low maintenance. On the one hand theoretically higher pressure leads to higher thermodynamic voltages, while on the other hand it may decreases the transport losses due to smaller gaseous bubbles, especially at high current densities [3].

Experimental results of HP-PEEC up to several hundred bar are discussed, investigating the influence of HP on transport losses at high current densities. The evolution of the different overvoltages (kinetic, ohmic, mass transport), determined using high frequency resistance measurements and tafel extrapolation, is discussed as a function of gas pressure. In detail the influence of different porous titanium sinter current collector media on mass transport losses is discussed as function of temperature, pressure and current density. It is shown that there seems to be an optimum average pore diameter at about 10 µm (Fig. 1).

Literature:

[1] C. J. Barnhart, et al., Energy Environ. Sci., 6 2804-2810 (2013).

[2] F. Barbir, Solar Energy, 78(5) 661-669 (2005).

[3] S. A. Grigoriev, et al., International Journal of Hydrogen Energy, 34(14) 5986-5991 (2009)

Figure 1
Recent Advancements in Redox-Flow Cells and Promising Opportunities
Authors: Perry Mike L.
Published: February 2020

Redox-Flow Cells (RFCs) possesses several key advantages that make this technology potentially well suited for large scale energy-storage applications.  This is especially true of applications that require high energy-to-power requirements (i.e., multiple-hour discharge times at rated power), since the energy capacity can be increased by simply adding reactant solution without necessarily requiring (or negatively impacting) the power-delivery components.  Despite this inherent scaling-factor advantage relative to conventional battery systems, the initial capital cost of flow batteries has been the major barrier to commercialization of RFC-based products.  Capital-cost targets for grid-scale energy storage are challenging; battery systems for major grid-scale applications must cost less ($/kWh) than those currently used for most portable or transportation applications.  One attractive path to cost reduction is the development of RFCs with substantially higher power densities than conventional cells.  United Technologies Research Center (UTRC) has recently developed and demonstrated high performance RFCs in stacks operating in complete Prototype RFB Systems.  A summary of these results has been presented previously.  Therefore, a major focus of this talk will be on new materials and concepts that can potentially enable additional RFC cost reductions.  This includes both advanced cell materials (e.g., electrodes, separators/membranes, bipolar plates), as well as advanced reactant solutions.  Key system-performance indices provide the basis for the formulation of key property requirements for these proposed advancements.  A brief review of the state-of-the-art of each these major materials will be included, as well as some proposed advanced technologies.  The major goal of this presentation is to help researchers focus on potential opportunities that have the greatest likelihood of yielding substantial improvements RFC technology that can have significant commercial impact.

 

Acknowledgements

The author would like to thank his multiple colleagues at UTRC who have been an essential part of UTRC’s advanced flow-battery team.
Building a Better Redox Flow Battery - Innovative Diagnostics to Visualise Reactant Transport
Authors: Rubio-Garcia Javier , Kucernak Anthony R. J.
Published: February 2020

While the optimization of PEMFCs and RFBs require addressing multiple issues, both systems share an operation mechanism based on pumping a fluid (a gas or a liquid) containing chemically reactive species across the face of an electrode. As a consequence of this characteristic, a significant source of inefficiency is linked to mass transport limitations including high pressure drop or inhomogeneous reactant flow distribution across the electrode. Previously, strategies including infrared mapping, (1) magnetic resonance imaging (2) or neutron radiography (3) were employed in an attempt to investigate fluid transport phenomena (predominantly for fuel cells). However, although those studies rendered valuable results, the measuring procedures can be considered as expensive and require delicate equipment.

In this contribution, a simple and low cost methodology to study the mass transport processes in RFBs is presented. This approach relies on the instantaneous electrochemiluminescence of Luminol. By simply recording the emitted light with a low cost camera,(4) concentration profiles at the surface of the electrode were obtained presenting high temporal and spatial resolutions. In addition, modifications on the electrolyte formulation and flow rate permitted identifying turbulent flow areas located at the turn of the flow field as well as leading to the design of improved components.

References:

(1) Wang et al., Journal of Power Sources, 157, 181–187 (2006).

(2) Tsushima et al., Magnetic Resonance Imaging, 23, 255-258 (2005).

(3) Trabold et al., International Journal of Heat and Mass Transfer, 49, 4712–4720 (2006).

(4) Lopes et al., Journal of Power Sources, 274, 382–392 (2015).
Regenerative Fuel Cells for Energy Storage Application: Performance Limitation Studies
Authors: Yufit Vladimir , Hewa Dewage Harini , Brandon Nigel P.
Published: February 2020

Redox flow batteries are a potentially versatile and attractive solution to store and deliver energy over the kW/kWh to MW/MWh range. A variety of redox flow chemistries exist, with all-vanadium battery being the most mature and developed.  Nonetheless, all-vanadium systems suffer from a relatively low power density, specific energy and high cost, associated with the use of vanadium based electrolytes. These issues can be circumvented by replacing the vanadium anolyte or catholyte with a cheaper alternative. Particularly, novel regenerative fuel cells have been developed that utilise a combination of a liquid and a gaseous redox reactions; either hydrogen oxidation reaction on the anode side or oxygen reduction reaction on the cathode side.  Previous work by the authors has demonstrated a regenerative fuel cell based on hydrogen/vanadium redox reactions whichachieved a specific power of 200 mW/cm2. Further optimisation of this system has increased the power density to more than 400 mW/cm2. This paper will present a study of the performance limiting factors in the Regenerative Hydrogen Vanadium Fuel Cell, showing how this information can be generally implemented in other energy storage systems utilising hydrogen and metal redox couples.
Catalytic Activities of Perovskite Oxide Electrodes for Oxygen Reduction in Alakline Solutions
Authors: Miyazaki Kohei , Miyahara Yuuto , Fukutsuka Tomokazu , Abe Takeshi
Published: February 2020

Introduction

There has been increasing interest in fuel cells using alkaline electrolytes. In the research of alkaline fuel cells, much attention has been paid to oxide electrocatalysts since their costs are much lower than those of noble metal catalysts. As the results of many researchers, it is found that perovskite oxide is one of the promising candidates for electrocatalysts for oxygen reduction in alkaline solutions. Since most perovskite oxides have inadequate electron conductivities, it is necessary to use additives such as carbon black for providing electron paths for oxides in the electrodes. While the using of additives offers better catalytic performance of oxides, the additives make it difficult to observe the catalytic activities of oxides. Therefore, we have investigated the catalytic activities of perovskite oxides using thin-film electrodes prepared. Through electrochemical measurements, we found that carbon black had catalytic activities for the initial 2e oxygen reduction, and perovskite oxides were active for the following decomposition reaction of peroxide. In this study, we report the catalytic behaviors of thin-film electrodes of perovskite oxides.

Experimental

Thin-film electrodes of perovskite oxides were prepared by the pulsed laser deposition (PLD) method. Pellets prepared with oxide powders of La0.8Sr0.2MnO3, La0.8Sr0.2CoO3, La0.5Ca0.5MnO3, and La0.5Ca0.5CoO3 were used as PLD targets. Resultant perovskite thin-films were characterized by X-ray diffraction (XRD) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). A three-electrode cell was used in electrochemical measurements, which consisted of perovskite thin-film, Ag/AgCl, and Pt wire as working, reference, and counter electrodes.

Results and discussion

XRD patterns of resultant perovskite thin films were in good agreement with previous data of powder diffraction. Therefore, we successfully prepared thin films of polycrystal perovskites. The results of ICP-AES showed PLD method copied the target composition of oxides. Linear sweep voltammograms showed small current densities for oxygen reduction on perovskite thin-film electrodes. Electronic conductivities of perovskite thin films were evaluated by cyclic voltammetry of [Fe(CN)6]3-/[Fe(CN)6]4-, and we confirmed the prepared electrodes had adequate conductivities for electrochemical measurements. As a result, we concluded that perovskite oxides needed an assisting catalyst such as carbonaceous materials to exhibit the catalytic activities of oxygen reduction.
Modelling and Validation of Water Hydration of PEM Fuel Cell Membrane in Dynamic Operations
Authors: Liso Vincenzo , Nielsen Mads Pagh
Published: February 2020

Fuel cells convert chemical energy of hydrogen and oxygen directly in to electricity. High efficiency and zero emission have made them a prime candidate for powering the next generation of electric vehicles. PEM fuel cells require good hydration in order to deliver high performance and ensure long life operation. Water is essential for membrane proton conductivity which increases by nearly six orders of magnitude from dry to fully hydrated. Adequate water management in PEM fuel cell is crucial in order to avoid an imbalance between water production and water removal from the fuel cell.

In the present study, a novel mathematical zero-dimensional model has been formulated for the water mass balance and hydration of a polymer electrolyte membrane. This model incorporates all the essential fundamental physical and electrochemical processes occurring in the membrane electrolyte and considers the water adsorption/desorption phenomena in the membrane. The effect of diffusivity model, surface roughness and water content driving force is considered. The model is validated against experimental data.

In the results it is shown that the fuel cell water balance calculated by this model display better fit with experimental data-points compared with model where only water transport equilibrium were considered. We conclude that this discrepancy is due a different rate of water transport when membrane absorption/ desorption is considered in the model.

Many studies have erroneously considered fuel cell membrane in equilibrium condition disrigarding non-ficknian behavior of the cell membrane. For this reason the model presented in this study becomes useful when studying PEM fuel cell system in dynamic conditions.
Vacuum Assisted Graphene Oxide Membranes for Polymer Electrolyte Membrane Fuel Cells
Authors: Holmes Stuart Martin , Maniam Kranthi Kumar
Published: February 2020

Undisputedly hydrogen is the preferred and prominent fuel for polymer electrolyte membrane fuel cells (PEMFCs) because of its high electro reactivity for the anodic reaction, the lack of onsite green-house gas emissions (pure water is the only product) and higher cell efficiency. The presence of various oxygenated functional groups can facilitate the proton transportation through reformation of hydrogen bonds and makes graphene oxide (GO) itself as a good candidate as a proton exchange membrane in low temperature fuel cells. Besides ionic conductivity, GO can act as a physical barrier separating the fuels such as hydrogen and oxidant and prevents their cross-overs. In the recent times, significant attention has been shifted towards employing pristine/Virgin GO membranes as such in low temperature polymer electrolyte fuel cells. A number of preparation methods have been proposed to synthesise free-standing GO films in the recent past. However, the influence of method on the membrane properties and applications in fuel cells needs to be addressed and requires further exploration.In this work, graphene oxide membranes of different thickness will be prepared using two different methods: vacuum evaporation and hydrosol evaporation. The influence of the method of preparation, thickness, will be studied in relation to the membrane properties including proton conductivity, ion exchange capacity, and water uptake, swelling behavior, thermal stability and fuel cell performance. A comparative study made with the conventional membrane electrode assembly (Pt/C-Nafion-Pt/C) will be discussed in detail.
Start-up Effects in Alkaline Fuel Cell Stacks
Authors: Akhtar Naveed
Published: February 2020

Any fuel cell operation relies on successful start. In particular, successful and rapid startup of proton exchange membrane fuel cell (PEMFC) from cold start is of great importance for their commercialization. Unlike PEMFCs, liquid alkaline fuel cells (AFCs) are less prone to freezing problems due to the use of aqueous potassium hydroxide solution as electrolyte. The aqueous potassium hydroxide solution has low freezing temperature which prevents the blocking of pores at sub-freezing temperatures to a certain extent. However, the successful start-up in liquid alkaline fuel cells is subjected to other issues which are not common in solid membrane type fuel cells. In liquid electrolyte AFCs, the only barrier between fuel and oxidant is the liquid electrolyte. If during startup the electrolyte is not fully filled within the electrolyte chamber, the reactant gases can enter into the said chamber and creates gas pockets. This phenomenon is highly non-desirable as combustible gas mixture can be trapped and the useful voltage from the cell declines. Few experiments were designed to understand this startup effect and to prevent the failure. The results show that filling-up all the electrolyte chambers prior to reactant gases entry prevents this phenomenon. Furthermore, a relatively high pressure electrolyte chamber filling at startup evacuates the static air from the chamber.
From Fundamental Electrocatalytic Studies to Half-Cell Investigations of Electrode Performance
Authors: Polymeros George , Jovanovic Primoz , Kulyk Nadiia , Hodnik Nejc , Zeradjanin Aleksandar R. , Mayrhofer Karl J.J.
Published: February 2020

The major environmental issues linked to fossil fuel utilization, as well as their depletion with time, demand sustainable alternatives for energy conversion and storage. Fuel Cells and Electrolyzers are potential candidates for providing solutions into this direction. Major scientific efforts have been invested during the past decades for improving the catalyst performance, which is defined in an equally important way by its activity and stability. While the catalytic behavior is often studied on a fundamental level at low current densities in a potential region where the mass transport induced error is negligible, the operating conditions in applications consist typically of high current densities with significant mass transport issues. Furthermore the electrochemical interface where the reaction takes place is a confined liquid-metal interface in fundamental investigations, which does not truly represent the so called three phase boundary (tpb) situation at the electrode of a real reactor. In order to bridge fundamental research on electrocatalytic behaviour with the actual applied challenges, we have utilized an alternative experimental tool, namely the Floating Cell. This cell enables the investigation of the electrocatalytic behavior in a broader potential range by overcoming the mass transport issues of the reactant by creating a tpb. In this work we try to demonstrate a step by step approach in the direction of clarifying the particularly complicated regime in the three phase boundary, since for every part of this interface there are numerous parameters, which can have a considerable impact on the catalytic performance. As a result we will discuss the utilization of catalysts in the electrode layer, as well as the potential of this approach for degradation studies and the quick optimization of electrode structures for different reactions in general.