bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of SO2 Poisoning on the Electrochemical Activity of LSCF and LSM Electrodes
Authors: Wang ChengCheng , Jiang San Ping
Published: February 2020

Solid oxide fuel cells (SOFCs) offer great promise for the efficient and cost-effective conversion of chemical energy of fuels to electricity. However, sulfur in the air stream is one of the major contaminants affecting the performance stability of cathodes of SOFCs such as La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and La0.8Sr0.2MnO3 (LSM) perovskite oxide. In this report, the effects of operating temperatures, current densities, and SO2 concentrations on the electrochemical performance of LSCF and LSM cathodes are investigated. Sulfur poisoning of LSCF is more pronounced at lower temperatures, i.e., 700 oC. According to SIMS result, sulfur deposition occurs inside the LSCF electrodes and is most pronounced on the surface of LSCF at 700 oC, forming primarily SrSO4, while sulfur deposition occurs mainly near the electrode/electrolyte interface for LSM electrodes. Similar electrode resistance change of porous LSCF electrodes after being poisoned under open circuit condition and cathodic current passage at 700 oC indicates that sulfur poisoning effect of LSCF has no direct relationship with polarization current. The concentration of SO2 has a significant effect on the performance degradation of LSCF and LSM electrodes. Sulfur poisoning is not reversible. The reaction mechanism between sulfur and LSCF and LSM electrodes is discussed.
Acid-Base Membranes Based on Poly(1-vinylimidazole) for Fuel Cell Applications
Authors: Stewart Kerrilee Ayel , Missan Harinder Pal Singh
Published: February 2020

Novel acid-base electrolyte membranes have been developed using the acid-base blending of a basic polymer poly(1-vinylimidazole) (PVIm) and an acidic polymer poly(ethylene-co-acrylic acid) (PEAA). High non-aqueous ionic conductivities of the order of 10-2 – 10-3 S/cm were observed for acid-base blend electrolytes over the temperature range of 30-120 oC and are found to be stable over the temperature range measured. The highest ionic conductivity was observed for 2-8 composition and was postulated to be due to better interaction between the acid and base sites along with better morphology. The blend electrolytes developed are found to be stable up to temperatures in excess of 450oC, even reaching 500 oC for 5-5 compositions. Nano-composite acid-base blend membranes using the 2-8 composition were then developed with the subsequent addition of nano-tubular titania into the electrolyte matrix. The ionic conductivity has been found to be effected by the addition of nano-tubular phase and is higher than that obtained for the parent electrolyte. This increase in conductivity is attributed to the better morphology of the electrolytes with the addition of nano-tubular titania into the matrix as inferred from SEM studies. Nanocomposite membranes were also found to be more thermally stable than the parent membranes. The addition of acid-functionalized nanotubular titania was found to further increase the ionic conductivity of the acid- base blend membranes whilst maintaining good thermal stability.
The Rate Limiting Step (RLS) for the Oxygen Reduction Reaction at the Cathode of Polymer Electrolyte Membrane Fuel Cell
Authors: Reda Mahmoud R.
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) can be operated by hydrogen and pure oxygen (not air) by in-situ photo-catalytic splitting of water (gasoline of the future). Recently, several auto makers have introduced H2-fed fuel cell vehicles on the road. However, some concerns, i.e., catalyst and membrane’s cost and durability, catalyst activity, membrane proton conductivity, and water management, still exist. In order to make the fuel cell vehicle affordable and durable, further work needs to be done to improve each of the above mentioned aspects [1]. In a recent review by Ramaswamy and Mukerjee [2] have shown that the mechanism proposed by Damjanovic et al. describes the rate RLS. The purpose of this publication is to show that the rate limiting step for the ORR at the cathode of PEMFC is the rate of dissolution of gases oxygen in the aqueous media. It is well known that the Henry constant for oxygen in aqueous solutions is very low at range of temperature between 60 to 80 ̊ C (figure 1). The second purpose is to derive an equation that shows the strong relationship between the mass transfer coefficient and oxygen solubility. Strong supports for such a mechanism are:

1-In 2010 Erlebacher and co-workers [3] discovered a new ionic liquid that has strong affinity to absorb oxygen and were used to improve the rate of ORR.  2- The enhancement of the rate of ORR after humidification of the cathodic region (humid air contains dissolved oxygen) while humidification of the anodic region (can humidify the membrane and increase its conductivity) has no effect on the rate of ORR [4-6]

1-Perry M.L. and Fuller T.F., Journal of the Electrochemical Society 149, S59 (2002)

2-Ramaswamy N., and Mukerjee S. Fundamental Advances in Physical Chemistry Article ID 491604, (2012).

3-Snyder et al. Nature Materials 9, 904, (2010).

4-Ciureanu M. J. Applied Electrochemistry 34,705–714 (2004).

5-Xu H., Song Y., Kunz H.R., and Fenton J.M. , 205th meeting of the Electrochemical Society, San Antonio, Texas, (2004).

6-Zhang J., Tang Y., Song C., et al.  Electrochimica Acta 53, 5315–5321 (2008).

7- Jeon D.H., Kim K.N., Baek S.M.,Nam J.H. In. J.of Hydrogen Energy, 36,19, 12499-12511 (2011).

Figure 1
Plasma-Coating of Ti and Ta on Graphite Composite As Corrosion-Improved Bipolar Plate in PEM Electrolysis
Authors: Sievers Gustav Wilhelm , Dempwolf Christoph , Hickmann Thorsten , Brüser Volker
Published: February 2020

In Proton Exchange Membrane (PEM) Electrolysis bipolar plates have to be more corrosion resistant than bipolar plates in PEM Fuel Cells. Several materials have been evaluated as cost-efficient material in PEM Electrolyzers. Since the electrochemical conditions in PEM Electrolyzers are quite harsh, cost-efficient materials like stainless steel or graphite composites are not stable. Coating the material with corrosion resistant material by magnetron sputtering is one possibility to enhance the stability. Gago et al.[1] have been coating stainless steel for example with Ti by vacuum plasma spraying. However, Ti is only useable if the oxidation potential is not too high, otherwise it will form an insulating TiO2 layer. Tantal has good corrosion protective characteristics and is not forming an insulating layer.[2]

We developed a plasma process to deposit protective coatings on graphite composite bipolar plates. Therefore we used unbalanced magnetron sputtering of Ti and Ta. A new magnetron sputtering process was applied to keep the temperature of the graphite composites constant. Furthermore a combined plasma-process was used to enhance the stability of the deposited layer by activating the graphite composite. The Ti and Ta coatings were tested in a heated (T = 353 K) electrochemical cell amperometric at 2 V vs. RHE and by cyclic voltammetry in oxygen saturated 0.5 M H2SO4. We figured out the layer quality with the 4-Point Probe before and after each experiment. Furthermore we evaluated the film characteristics by microscope (SEM, light microscope), XRD and XPS.

We could demonstrate that the coating is protecting the graphite composite as bipolar plate material in harsh electrochemical environment which was choosen close to real conditions in PEM Electrolyzers. Thereby it should be possible to lower the cost of bipolar plates in PEM electrolyzers substantial.

[1]      A. Gago, A. Ansar, N. Wagner, J. Arnold, K.A. Friedrich, Titanium coatings thermal spraying bipolar plates PEM electrolyzer, in: 64th Annu. Meet. Int. Soc. Electrochem., 2013.

[2]      O.E. Kongstein, N. Guillet, A. Ødegård, Rapport technique DEHT-DR-10/051, 2010.
Kinetics of the Bromine Reaction at Carbon-Polymer Composite Electrodes in the Presence of Complexing Agents
Authors: Berlouis Leonard , Bryans Declan , Spicer Mark , Reglinski John
Published: February 2020

The zinc-bromine hybrid redox flow battery (RFB) is one of the few battery systems that have seen implementation for the medium to large scale energy storage.  One of the issues identified with this flow battery is that of bromine crossover from the positive electrode to the zinc electrode, leading to loss of current efficiency.  One of the ways in which this problem can be overcome is through the use of organic-based complexing agents which tie up the bromine as a thin surface layer and an immiscible liquid phase which is pumped from the electrode surface into an external reservoir.  In this paper, we examine in detail the kinetics and chemistry of formation of these complexed bromine ion pairs and establish the concentrations of the various complexing agents required to achieve full complexation of the electrogenerated bromine species.  The initial phases of the study used small chain (2,3 and 4-carbon) symmetrical tetraalkylammonium bromide salts to investigate the bromide oxidation and the stages of film formation on a variety of carbon-composite electrodes commonly employed in RFB systems.  These data were then compared to the classical responses obtained on Pt and glassy carbon electrodes.  What is clearly evident from the study is that the electrochemical reversibly of the Br-/Br2
reaction is attenuated on the carbon-composite surfaces in the presence of the complexing agents and leads to a second oxidation process at more positive potentials (Figure 1).   The nature of this second oxidation and of the surface species formed is investigated using in-situ Raman spectroscopy and its electrochemical characteristics examined using electrochemical impedance spectroscopy and potentiodynamic polarisation techniques.  Substantial changes in the electrochemical responses are recorded when film formation occurs and this event also led to a large increase in the measured impedance, requiring the use of an additional low frequency time constant element in the Randles equivalent circuit employed to fit the impedance spectrum acquired.  The magnitudes and trends observed in the impedance parameters at the different concentration and complexing species employed will be discussed in the presentation.  Since in an operational Zn-Br2 RFB system during charge, the oxidation reaction will be occurring on composite carbon surface covered with the Brx
- complex, how this film impacts on the kinetics of the charge and discharge reaction will impact on the voltage efficiency.  The understanding of the behaviour of these simpler complexing agents will thus enable the electrochemistry of more complex species, e.g. 1-methyl-1-ethylpyrrolidinium bromide, to be better understood and so lead to improvements in the efficiency of the process occurring at the positive electrode of the zinc-bromine hybrid RFB.

Figure 1
Oxygen Reduction Catalysis on Model Pt Electrodes
Authors: Bandarenka Aliaksandr S
Published: February 2020

The use of model electrodes, particularly single crystals, represents a unique opportunity to better understand the performance of real-world (nanostructured) materials: identify active sites, elucidate factors responsible for selectivity and stability of the catalytic centers.

This approach is of growing importance for the electrocatalysis of the oxygen reduction reaction (ORR), which is nowadays one of the key reactions for both fundamental science and various technological applications. The latter include promising automotive applications or larger scale industrial processes, where it is involved in modern schemes of electrolytic production of chlorine (so-called oxygen depolarized cathode technology). From the point of view of fundamental science, the ORR has become an important model process which is critical for better understanding of reactions at electrified solid / liquid interfaces.

The common way of improving the activity of Pt towards ORR and many other reactions is a modification of the electronic properties of the surface through alloying it with other (mostly transition) metals. One can distinguish approaches which are based on “bulk”, “sub-surface” and “surface” alloying. Additionally, introduction of specific (often quasi-periodic) defects can also result in a drastic increase in the ORR activity. In the presentation, examples will be given of how the above-mentioned approaches can be used to design active surfaces; and how the model electrodes can help in better understanding of the performance of electrocatalytic systems.
Mechanistic Insights of CO2 Reduction to Methanol: DFT Study
Authors: Kumari Neetu , Haider M Ali , Sinha Nishant , Basu Suddhasatwa
Published: February 2020

Theoretical calculations were performed, using density functional theory (DFT), to estimate the energetics of the elementary steps involved in the conversion of CO2 to methanol on the CeO2 (110) surface. Due to high oxygen storage capacity and mixed ionic electronic conductive nature, ceria based materials have been suggested to enhance the electrocatalytic activities in solid oxide electrolysis cell. However, no study so far has highlighted the role of extended ceria surface alone in carrying out the CO2 reduction reaction. The energetics of suggested mechanisms, via formate (HCOO) and carboxyl (COOH) intermediates, for CO2 hydrogenation to methanol were studied on stoichiometric and reduced ceria surface. Calculations were performed to determine the most favorable adsorption orientation and corresponding binding energy of reaction intermediates. The adsorbed formate intermediate species on the stoichiometric ceria surface, were observed to be stable with higher binding energy (-223 kJ/mole) as compared to the carboxyl (Ebinding = -37 kJ/mole), and is likely to be a spectator. In order to produce methanol via formate mediated routes, HCOO requires to be subsequently hydrogenated to H2COOH which ultimately needs to dissociate into H2CO and OH. The dissociative elementary step of this route is significantly endothermic (DErxn=64 kJ/mol). On the other hand, the mechanistic routes involving carboxyl (COOH) shows all the way exothermic steps on the CeO2 (110) surface, except only to the dissociation of COOH into CO and OH, to produce methanol. The dissociation step is thermoneutral (DErxn~5 kJ/mol) on stoichiometric ceria and slightly endothermic (DErxn=24 kJ/mol) on reduced ceria. Activation barrier for the dissociation step (COOH → CO+OH) is estimated to be 127 kJ/mole, which is significantly higher as compared to the other expected rate limiting, CO2 hydrogenation (CO2+H→COOH) step (Ea=37 kJ/mole). We will extend this work to analyze the activation barriers on reduced ceria surface which will ultimately give an inference of the effect of oxygen vacancy on the reduction of CO2 to hydrocarbons.
Introducing Dichromate (Cr2O7
2-), an Oxidant with 100x the Current Density of O2 at 1/70th Its Solubility, and Other High-Power Oxidants for Redox Flow Batteries and Fuel Cells
Authors: Finkelstein David A. , Kirtland Joseph D. , Da Mota Nicolas , Stroock Abraham D. , Abruña Héctor D.
Published: February 2020

While electrochemical fuels sample the range of the elements, from BH4
– to NH3 and Li to Zn, exploration of oxidants usually starts and ends with O2, a low-power oxidant with solubility <1 mM.  In the studies presented, oxidants with solubilities up to 7,000 mM are characterized and demonstrated to produce current densities 100 times greater than O2 at just 100 mM.  Alternative oxidants used in redox flow batteries (VO2
+, Ce4+) and fuel cells (H2O2, MnO4
–) are compared against the unorthodox oxidants ClO–, S2O8
2–, IO3
–, CrO4
2–, and Cr2O7
2–.  It is shown that Cr2O7
2– produces among the highest current densities of all oxidants studied, at a diverse array of catalyst materials, and does so without the familiar drawbacks of precipitation and bubble-producing decomposition of MnO4
– and H2O2, respectively.  Cr2O7
2–'s high n (number of e– transferred per molecule), D (diffusion coefficient) and C
max (maximum concentration) offer a route to achieving order-of-magnitude increases in the current and power densities of redox flow batteries currently using VO2
+ or Ce4+, which have low values for all three parameters.
Improved Performance of the Membrane-Electrode Assemblies with Titanium Metallic Foams in Fuel Cells
Authors: Choi Hyelim , Kim Minjeong , Kim Ok-Hee , Cho Yong-Hun , Sung Yung-Eun , Choe Heeman
Published: February 2020

Fuel cells are attracting significant attention as a promising futuristic technology for energy conversion. Their energy densities are orders of magnitude greater than those of conventional batteries, capacitors, and are even comparable to the power and energy densities of internal combustion engines. Because the key component of the fuel cell performance is the structure of electrode in the membrane electrode assemblies (MEAs), the optimization and modification of the electrode structure has been the main research subject for the performance and the durability improvement of polymer electrolyte membrane fuel cells (PEMFCs). This study uses a new design approach for the MEA: use of titanium foam as gas diffusion layer (GDL). In other words, freeze-cast titanium foams are applied to the MEAs in place of the GDL, resulting in a significant improvement of the MEA in the single cell performance test. This is because of its unique three-dimensional strut structure promoting highly efficient catalytic reactions. We believe that this paper suggests implications in the commercialization of PEMFCs, because the Ti foam fabricated in this study provides an excellent electrochemical performance, and longer-term reliability and chemical stability, which can reduce the loss of Pt catalyst and hence, the cost of PEMFCs.
Synthesis and Characterisation of Pd-Ni-Sn Electrocatalyst for Use in Direct Ethanol Fuel Cells
Authors: Jongsomjit Sompoch , Prapainainar Paweena , Sombatmankhong Korakot
Published: February 2020

One critical challenge to commercialise direct ethanol fuel cells (DEFCs) is catalyst poisoning

associated with the strongly adsorbed CO intermediate on catalyst’s surface at low temperature. The present work

therefore aimed to develop a highly electrochemically active catalyst which is durable to the presence of CO

contaminant. Different Pd-Ni-Sn compositions impregnated on carbon black were synthesised by sodium borohydride

reduction method which can be classified as mono-, binary- and ternary-catalyst systems at which 20%w Pd/C was

utilised as a base catalyst. The addition of 5-20%w Ni and/or 5-20%w Sn metals was found to increase catalytic

activity and catalyst stability for ethanol oxidation reaction (EOR). Several diagnostic techniques were employed to

assess their suitability for use in DEFCs including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS),

transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive spectrometry (SEM-EDX)

and electrochemical techniques. The XRD and XPS spectra verified that the existence of Pd, Ni and Sn in the asprepared

catalysts was in the oxidation state of Pd0 and Pd2+, Ni2+ (in form of Ni(OH)2) and Sn4+ (in form of SnO2),

respectively, which were known to promote the EOR and CO oxidation. The average particle size was in the range of

5.46-10.56 nm for all samples. By using SEM-EDX, it was found that the actual ratios of metal loadings were relatively

similar to the desired compositions and their surface morphology was uniformly distributed. Moreover, electrocatalytic

activity towards EOR was evaluated using cyclic voltammetry in 1M ethanol (in 1M KOH). Among various catalytic

compositions, 20%w Pd/C containing 10%w Ni and 10%w Sn exhibited excellent catalytic activity and CO tolerance as

the maximum current density of 146 mA cm-2 for EOR and the highest electrochemical surface area were obtained

while lowering the CO-stripping peak potential to -0.525 V (vs Ag/AgCl).
Progress in Studying Mediator Supercapacitor
Authors: Zhou Xiangyang , Cai Jinshu , Wang Yuchen , Zhang Chen , Qiao Xiaoyao , Mansour Azzam
Published: February 2020

When mediators (redox molecules) are mixed into an ion conducting polymers, the material will have a high ionic conductivity and electronic conductivity potentially providing a high storage capacity and charge/discharge rate. On the basis of our previous work of developing I2/NaI and K3Fe(CN)6/K4Fe(CN)6based supercapacitors, we studied the ionic conductivity, electronic conductivity, and capacity of the electrode materials as a function of concentration of mediators and temperature. A modified percolation model was proposed and used to describe the observations. In another line, we fabricated prototypes using commercially available materials.

The ionic and electronic conductivities were evaluated using a series of AC/DC measurements. The results indicate that for the electronic conductivity, there is a critical mediator concentration at which the conductivity steps up two orders of magnitude. For the ionic conductivity, the increase with mediator concentration is smooth. When the temperature decreases from 20°C to -20°C, the ionic conductivity decreases ~8 folds but is still greater than 10-3 S/cm. This demonstrates that the presence of mediators in the material helps maintain a high ionic conductivity at -20°C. Cyclic voltammetry and charge/discharge test results are correlating and consistent with the conductivity measurement results. A percolation model was created with consideration of motion of the mediators at a given temperature. The simulation results agree well with the experimental data. The theoretical analysis indicates that charge exchange between mediator molecules promotes ionic conductivity via causing instant imbalance of the local charge distributions. Finally, supercapacitor prototypes were fabricated using the electrode materials with PVDF/LTFS and a mediator. The specific energy was 25 Wh/kg at 0.2 kW/kg or 10 Wh/kg at 25 kW/kg after cycling 2000 times.
Investigation of Discrete Wavelet Transform-Based Denoising Technique in Noise-Riding Eovs of the Polymer Electrolyte Membrane Fuel Cell
Authors: Kim Minkyu , Tak Yongsug , Kim Jonghoon
Published: February 2020

With more increased interest in renewable energy for reducing air pollution and accomplishing low or zero emission, the polymer electrolyte membrane fuel cell (PEMFC) has been recognized as the most attractive and promising candidate with the merits of low-operating temperature, fast start-up ability, and high efficiency, etc. Specifically, for an efficient operation of the PEMFC, it is absolutely required to obtain the fuel cell management system (FCMS). Among several factors in the FCMS, the state-of-health (SOH) diagnostic methodology is more critically considered for reliability and durability of the PEMFC. For this purpose, an experimental output voltage signal (EOVS) that adequately depicts a single cell and fuel cell stack behavior is used as fundamental information. Then, the most significant task for achieving an improved SOH diagnosis is to gain an elaborate EOVS. Unfortunately, because of the use of unexpected and instantaneous sensing of noise-riding EOVS in the FCMS, it is unavoidable that non-corrected EOVS surely results in erroneous SOH. Consequently, it is strictly required to implement an innovative research that can find a solution to aforementioned problem. Thus, this research newly gives insight to the design and implementation of the discrete wavelet transform (DWT)-based noise reduction in the noise-riding EOVS, namely denoising technique. At the DWT in this research, the noise-riding EOVS can be assumed as an original signal with non-stationary and transient phenomena according to the multi-resolution analysis (MRA) with a function of both time and frequency localization. The detailed procedure for denoising the noise-riding EOVS is as follows. First, through the MRA, it is possible to decompose the noise-riding EOVS into two sub-bands of low- and high-frequency components, An
and Dn
. Second, to adjust the detailed coefficient in high-frequency component, two denoising methods of hard- and soft-thresholding with VisuShrink-based threshold value are implemented so as to clearly separate the signal from the noise. Finally, the inverse DWT is used to reconstruct the de-noised EOVS using an adjusted detailed coefficient. Experimental results definitely showed the robustness of this proposed approach. Consequently, it can be sufficiently expected to have an optimal solution for noise reduction of the EOVS and to lead an improved FCMS. For reference, an experimental apparatus was basically designed for obtaining the noise-riding EOVS from the PEMFC by the ‘Materials and Electro-Chemistry Laboratory in Inha University’.

Figure 1
2-Dimensional Supercapacitor Wires to Overcome Intrinsic Low Energy Density
Authors: Park Jongseok , Nam Inho , Park Soomin , Bae Seongjun , Yoo Young Geun , Yi Jongheop
Published: February 2020

Although a large number of reports on 2D flexible and stretchable energy storage devices have emerged within the past decade, 1D structure systems such as wires for higher flexibility, bio-compatibility and wearability have been desired for broader application of electronics. As a result of these requirements, wire-shaped devices among the cutting edge technologies in energy storage field are taking center stage for application to postmodern electronics and various fields such as fashion and culture. In view of mechanics, plane structures in 2D essentially have a unidirectional folding characteristics. On the other hand, wires with 1D structure have an omnidirectional serpentine structure in the other axes. In contrast to 2D planar formats, it is much easier for wire types to be integrated into more sophisticated structures such as woven textiles that can be used in our daily life.

 Although wire systems have a large structural potential, some fundamental obstacles hinder the use of wire-type energy storage. Electrochemical performances of wires are still underneath those of 2D plane cells. Many researchers have made efforts to overcome these barriers of wire-type energy storage devices. Most of them suggests ways to shape electrodes into cylindrical wires and a choice of material to maximize the performance as high as possible. In this study, however, we did not stick to using superb materials or constructing a cylinder, but theoretically analysed the origin of undefeatable charge-storage property of 2D plane over 1D wire. Based on this analysis we verified that a difference between wire-type and conventional planar supercapacitors induced the fundamental limits of wire-type supercapacitors. This limit is termed “energy lag effect.” With these derived information, we have first proposed the simultaneous incorporation of favorable electrochemical performance of 2D system and high flexibility of 1D system into solely one device. To exclude the identified limits, we designed a supercapacitor thread in unique structure that completely differs from conventional wire-type energy storage systems. The supercapacitor thread was designed as a dual plane-helix structure and proved not to show energy lag effects, experimentally or analytically.
Solid Polymer Electrolytes: Material Design As Gel or Membranes for Battery Applications
Authors: Srour Hassan , Monnereau Cyrille , Bucher Christophe
Published: February 2020

The development of polymer electrolytes has drawn the attention of many researchers in the last three decades as they find applications not only in lithium batteries but also, in other electrochemical devices such as super capacitors and electrochromic devices, etc. These polymer electrolytes have several advantages over their liquid counter parts. they are expected to replace flammable and leakage-prone organic solvent-based as electrolytes in future energy storage devices. In addition, these electrolytes have no internal shorting and non-combustible reaction products at the electrode surface existing in the liquid electrolytes [1-2].

In this communication, we will present a novel methodology, and straightforward conceptual approach for convenient preparation of gel-type polymers and membrane electrolytes [3] ( figure 1). We will demonstrate their morphologies and mechanical properties by rheological measurements of the gel under different strains and by XPs. Finally, we will illustrate the potential of the resulting gels as quasi-solid materials for energy storage applications through the study of different parameters such as: electrochemical stability, lithium diffusion and ionic conductivity properties,cycling test.

[1] Mecerreyes, D., Prog. Polym. Sci
36(12), 1629-1648 (2011).

[2] Yuan, J.; Mecerreyes, D.; Antonietti, M., Prog. Polym. Sci
38(7), 1009-1036 (2013).

[3] Srour, H.; Ratel, O.; Leocmach, M.; Adams, E. A.; Denis-Quanquin, S.; Appukuttan, V.; Taberlet, N.; Manneville, S.; Majesté, J.-C.; Carrot, C.; Andraud, C.; Monnereau, C., Macromol. Rapid Commun. 36 (1), 55-59 (2015)

Figure 1
Enhanced Conversion and Storage of Solar Energy Using an All-Vanadium Continuous Photoelectrochemical Flow Reactor
Authors: Wei Zi , Shen Yi , Liu Dong , Liu Fuqiang
Published: February 2020

With a demonstrated high Faradaic efficiency of 95%, an all-vanadium (all-V) photoelectrochemical storage cell (PESC) has been deemed as a promising candidate for efficiently capturing and storing solar energy.(1, 2) In this work, we further enhanced photocurrent of the existing all-V PESC by 5X by utilizing forced convective transport of the reactants throughout the cell in a continuous flow reactor, such that diffusive transport is only required over a short length scale relative to the cell dimension. It has been found that the maximum solar storage performance of the all-V PESC device tends to be limited by ionic and reactant transport, since we already employed vanadium redox species with fast electrochemical kinetics. Zero-resistance ammetry (ZRA) and electrochemical impedance spectroscopy (EIS) were employed to study the photoelectrochemical response of this system during conversion and storage of solar energy under both illumination and dark. It was discovered that introduction of flow during photoelectrochemical conversion greatly enhanced the photocurrent by 5 times comparing to the static condition (Fig. 1). Furthermore, EIS results indicated that both charge transfer resistance and interfacial capacitance were greatly reduced with convective flow of vanadium redox. On the other hand, variation of flow rate, if above a certain threshold, didn’t have a noticeable impact on the photocurrent under the range we explored. To better understand the photoelectrochemical behavior of the system, a CFD-based numerical simulation was carried out to understand the influence of flow rate on the photocharging process as well as the reaction limiting factors during solar energy storage. 

Reference:

1.      D. Liu, W. Zi, S. D. Sajjad, C. Hsu, Y. Shen, M. Wei and F. Liu, ACS Catalysis, 5, 2632 (2015).

2.      Z. Wei, D. Liu, C. Hsu and F. Liu, Electrochemistry Communications (2014).

Figure 1
Electrospun Carbon Nanofibers Decorated with Mn3O4 for Vanadium Redox Flow Battery
Authors: Di Blasi Alessandra , Busacca Concetta , Di Blasi Orazio , Briguglio Nicola , Antonucci Vincenzo
Published: February 2020

A flexible electrospun carbon nanofiber (CNF)-based electrode decorated with Mn3O4 is prepared starting from a solution containing polyacrilonitrile (PAN) mixed with manganese acetate (Mn(OAc)2). A thermal treatment at 270°C in air and a subsequent at 900°C in inert gas allow to obtain a flexible electrospun carbon nanofibers decorated with spinel manganese oxide (denoted as Mn3O4/CNF) characterized by suitable performance for vanadium redox flow battery (VRFB) application. Pristine electrospun carbon nanofibers CNF were prepared by using a similar method to compare the electrochemical data with respect to the decorated CNF. A homogeneous distribution of the metal oxides on the carbon nanofibers is showed by scanning electron microscopy (SEM) analysis. Cyclic voltammetry (CV) curves show a higher electrocatalytic activity toward the [VO]2+/[VO2]+ as well as the V2+/V3+ redox reactions with respect to the pristine electrospun CNF electrode, both in terms of peak to peak separation, DE[VO]
2+
/[VO
2
]
+ = 0,15 V vs. 0,28 V, and Ipa/Ipc[VO]
2+
/[VO
2
]
+ ratio, 1,48 vs 1,58, respectively. The improved performance is attributed to the hydrophilicity enhancement due to the oxygen groups availability that favour the surface mechanism process on the carbon nanofibers decorated with metal oxide nanoparticles.
Electrolyte-Electrode Interactions and Interphases
Authors: Russell Selena M. , Cresce Arthur v. , Xu Kang
Published: February 2020

As lithium-ion batteries evolve toward higher cell voltage and capacity, developing detailed knowledge of the electrolyte-electrode interface is critically important. While there is general agreement on solid electrolyte interphase (SEI) formation on graphitic anodes, clear evidence of passivation at the cathode interface remains elusive. This presentation discusses our efforts in investigating the interphases in Li ion batteries, on both cathodes and anodes. Primarily using in-situ electrochemical atomic force microscopy (EC-AFM) and confocal Raman spectroscopy, our studies focus on the live-formation of electrolyte-cathode interphases.
Batteries Under the Microscope: 3D and 4D Image-Based Characterization
Authors: Gelb Jeff , Finegan Donal , Brett Daniel J.L , Shearing Paul R.
Published: February 2020

In recent years, there has been a rapid growth in the development and application of Li-ion batteries in many aspects of daily life. From portable electronic devices to electric vehicles, global reliance on portable energy storage solutions is projected to continue growing throughout the next decade. To facilitate adoption of the Li-ion battery technologies, much of the current research is focused on improving electrode chemistries and developing novel cells, capable of lasting for longer time periods to reduce the need for frequent recharging. In spite of these developments, however, there exists little in the literature to show exactly how battery materials respond to charge cycling and why batteries ultimately fail.

Within the context of the present study, multi-length scale X-ray microscopy (XRM) was used to image a commercial 18650 Li-ion battery from the 20 µm length scale to the 0.1 µm length scale in 3D, to identify the relevant information observable at each resolution level. Correlative light- and scanning-electron microscopies were employed to provide additional information about the structure of the electrodes and to provide resolution down to the nanometer scale. The results revealed a complex, multi-scale structure to the battery electrodes, ranging from bulk defects (at the largest length scale) to porosity & tortuosity (at the hundred nanometer length scale) and sub-particle defects (on the 100 to sub-100 nm length scale).

One of the key advantages offered by X-ray imaging is the non-destructive nature of the 3D image-based characterization. With this in mind, the second part of the present study focused on utilizing this feature to perform a 3D imaging study before and after aging the battery, in a “4D” experimental design. Another sample from the same manufacturer was used for this study and imaged with 2 µm resolution in order to capture the finer cracks forming as a function of operation. The battery was imaged in its pristine state, charge cycled 100 times, and then the same specimen was imaged again using the same imaging conditions. From the 3D volumetric results, several cracks were observed to form on the outer side of the roll, following the capacity fade observed in the testing apparatus. This result has suggested the significance of microstructure-based degradation and pointed toward the importance of using image-based characterizations in Li-ion battery operational and lifetime studies.

In this presentation, we will present the study outlined here, both in terms of the 3D and the 4D investigations of the commercial 18650 Li-ion battery cells. The experimental design will be discussed in detail, including the imaging apparatus and the correlative imaging setup. Furthermore, the 3D imaging results will be shown alongside a discussion of the relevant geometric parameters at each length scale, and the results of the 4D investigation will be presented showing the defect formation as a functio
A New and Fast Depth Profile Analysis for Li Ion Battery Electrode - Elemental Composition of Conductive and Non Conductive Coatings Including Li, O, H, C
Authors: Savadkouei Kayvon , Hunault Philippe , Chapon Patrick , Gaiaschi Sofia
Published: February 2020

Rf GD-OES (Radio Frequency Glow Discharge - Optical Emission Spectroscopy) is a technique which can provide a Depth Profile Elemental Composition of coatings and thin films. In the case of the Li ion Battery Electrodes, it is possible to get the variation of all the elements in the organic coating and underneath layers until the substrate. Almost all the elements can be analyzed at the ppm level including Li, O, H, C, Cl, F, N...

Conductive and non-conductive materials can be analyzed. Due to the very fast sputtering rate, only few minutes would be necessary to analyzed Electrodes. This technique is complementary to SIMS, XPS... but much more affordable. Special sample holder for samples which are Air Sensitive (containing Li) have also been designed to avoid any contact with air. After a brief explanation of the theory, the presentation will focus on Li Ion Battery Electrode applications, but other applications linked to the Energy Storage (as corrosion, defect,...) will also be presented.
SnO2/NiO/Carbon Composite Nanofibers Produced By Forcespinning of Poly Acrylonitrile /SnO2 Precursor As Anodes for Lithium Ion Batteries
Authors: Alcoutlabi Mataz , Agubra Victor , Zuniga Luis , Flores David
Published: February 2020

The development of alternative anode materials out of flexible nanofibers has seen a growing interest. In this paper, binary carbon nanofiber electrodes of SnO2/NiO and Tin nanoparticles are produced using a scalable technique, Forcespinning (FS) and subsequent thermal treatment (calcination). The Sn/C nanofibers were porous and flexible, while the SnO2-NiO nanofibers had “hairy-like” particles and pores on the fiber strands. The nanofiber preparation process involved FS the Sn/PAN and SnO2/NiO/PAN precursors into nanofibers and subsequently stabilizing in air at 280oC and calcination at 800oC under an inert atmosphere. The flexible composite nanofibers were directly used as working electrode in lithium-ion batteries without a current collector, conducting additives, or binder. The electrochemical performance of the SnO2/NiO/C and Sn/C electrodes showed a comparable cycle performance of about 675 mAhg-1 after 100 cycles. However, the SnO2/NiO/C electrode exhibited a better rate performance than Sn/C anode and was able to recover its capacity after charging with a higher current density. The synthesis and processing methods used to produce these nanofibers clearly was a factor for the high rate capability and excellent cyclic performance of these binary composite electrodes, largely on the account of the unique structure and properties of the composite nanofibers.
Nb4N5/Nb2O5/r-GO Composites As Anode Materials for High Power Lithium Ion Batteries
Authors: Yan Yan , Lai Chun-Han , Dunn Bruce , Tolbert Sarah H
Published: February 2020

Lithium-ion batteries have been extensively investigated for a range of portable electronic devices, but a major downside to current technology is the slow charging speeds. A potential solution is to utilize pseudocapacitve materials, in which the diffusion length for lithium ions is short. For example, Nb2O5 is a promising anode material with almost no kinetics limitations for solid-state Li+ diffusion due to the facile two-dimensional Li+ transport pathways within the structure. However, it is also a large bandgap semiconductor, with a low bulk electrical conducitivity of ~3.4 x 10-5 S cm-1at 300 K. The low electronic conductivity hinders its high-rate performance, especially for thick electrodes with high mass loadings.

Numerous composite structures have been explored to improve the sluggish mobility of electrons in Nb2O5, such as blending with carbon nanotube, graphene composites, and carbon coating. Here we report an Nb4N5/Nb2O5/reduced graphene oxide (rGO) composite structure with improved kinetics prepared via partial nitridation of Nb2O5. Nb4N5 shows excellent metallic conductivity of 2000 S cm-1, which facilitates the interparticle electron conduction pathway in combination with the conductive graphene scaffold. Very high capacity retention at high charging/discharging speed is achieved in these materials, though the high power density comes at some cost of the capacity because the nitride is electrochemically inactive. One important advantage of the niobium oxide/nitride system, compared to pure Nb2O5/carbon composites is improved interface between the electrochemically active material and the conductive coating, since Nb2O5 can transform to Nb4N5 with almost no structural change. The composite also has a high volumetric capacity, since carbon additive is not needed in slurry electrodes. We believe metal oxide/metal nitride composites could provide a new design for high power electrode materials.
Catalyst-Selective Direct Liquid Fuel Cells without the Need for an Ion-Exchange Membrane to Separate the Anode Fuel and the Cathode Oxidant
Authors: Yu Xingwen , Pascual Emilio J. , Wauson Joshua C. , Manthiram Arumugam
Published: February 2020

Among the several types of direct liquid fuel cells (DLFCs) under development with various liquid fuels, the direct methanol fuel cell (DMFC) is in the forefront. However, this technology is currently in a difficult situation. The challenges of the relatively well-developed DMFCs with the proton-exchange membrane (PEM) include (1) the high-cost of Nafion membrane, (2) the sluggish kinetics of electrode reactions (rely on the high-loading Pt-based catalysts), and (3) the crossover of the methanol fuel through the PEM.1
,
2 According to the above issues, two approaches have recently been proposed and attempted, which can individually overcome the challenges of (1) – (3). Operation of the DMFCs under alkaline condition is able to enhance the kinetics of the electrode reactions.3 Operation of the DMFCs under a laminar-flow principle can avoid the use of the expensive PEMs and without the fuel crossover concerns. However, each of these two approaches brings new unexpected problems. Operation of the DMFCs under alkaline conditions needs an OH--exchange membrane which is currently not quite available. The laminar-flow membraneless DMFCs can only be built to a miniature scale, which limits their practical applications.4

Herein we present a membraneless alkaline DLFC approach developed under a catalyst-selective philosophy. By employing a non-platinum, highly selective cathode catalyst (MnNiCoO4/N-MWCNT, MnNiCoO4 nano-particles on a nitrogen-doped multi-wall carbon nanotube)5 with favorable activity for the oxygen reduction reaction (ORR) but without any activity for the fuel oxidation reaction (FOR), membraneless-operation of the DLFCs is turned into reality without any concerns about the fuel crossover from the anode to the cathode.

The first example of this presentation is an alkaline membraneless DMFC system with methanol as the anode fuel. The second example is an alkaline direct formate fuel cell (DFFC) with aqueous potassium formate solution as fuel. In comparison to the CH3OH-favorite catalyst PtRt/C and the HCOOK-favorite catalyst Pd/C, the MnNiCoO4/N-MWCNT does not show activities for oxidation of either CH3OH or HCOOK. The fuel cell performances of the membraneless DMFC (PtRu/C ǁ CH3OH/KOH ǁ MnNiCoO4/N-MWCNT) and the membraneless DFFC (Pd/C ǁ HCOOK/KOH ǁ MnNiCoO4/N-MWCNT) are superior to those of the traditional membrane-based DMFCs.

References

 

1.    X. W. Yu and S. Y. Ye, J Power Sources, 2007, 172, 133-144.

2.    T. R. Ralph and M. P. Hogarth, Platin Met Rev, 2002, 46, 117-135.

3.    J. R. Varcoe and R. C. T. Slade, Fuel Cells, 2005, 5, 187-200.

4.    S. A. M. Shaegh, N. T. Nguyen and S. H. Chan, Int J Hydrogen Energ, 2011, 36, 5675-5694.

5.    X. W. Yu and A. Manthiram, Catal Sci Technol, 2015, 5, 2072-2075.
(Invited) Synthesis and Photophysical Properties of Porphyrin-Fullerene Linked Dyads with a Oligo-p-Xylene Bridge
Authors: Imahori Hiroshi
Published: February 2020

Photoinduced electron transfer (ET) is one of the most fundamental processes in physics, chemistry, and biology. In the reaction center of natural photosynthesis, photoinduced ET generates a long-lived charge separation (CS) state with ~100% efficiency, leading to light-to-chemical energy conversion. In contrast, photoinduced CS at the interfaces of organic photovoltaic cells and dye-sensitized solar cells generates electron-hole pair, eventually achieving light-to-electricity conversion. However, the interfaces of semiconductor/dye and donor/acceptor (D/A) in artificial photosynthesis and organic photovoltaic cells often suffer from the partial or even large loss of the CS state at the early stage, which has still been controversial and not unveiled owing to inevitable inhomogeneous spatial distribution of D-A components.

In this context D-A linked systems have generated remarkable interest for the last few decades. The D-A covalent linkage can eliminate complex factors arising from diffusion in solutions and assess the photoinduced ET properties precisely with the help of homogenous spatial distribution of the D-A components.  So far these systems have provided fundamental information on photoinduced ET. Impact of various ET parameters, i.e., driving force, electronic coupling, reorganization energy, and temperature, on ET rate has been evaluated by using elaborated D-A linked molecules. In particular, a well-defined D-A linked molecule with a rigid bridge has allowed us to shed light on photoinduced ET more accurately. Here we show unprecedented dependence of the final CS efficiency on D-A interaction (i.e., electronic coupling) that can be changed systematically in the D-A linked models with a one-dimensional (1D) nonconjugated bridge. We have thoroughly examined the photoinduced ET properties by using femtosecond to microsecond time-resolved transient absorption (TRTA) and electron paramagnetic resonance (TREPR) spectroscopies.

 References

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[2] H. Imahori and Y. Sakata, Eur. J. Org. Chem. (Microreview), 1999, 2445-2457.

[3] H. Imahori, Y. Mori, and Y. Matano, J. Photochem. Photobiol., C: Photochem. Rev., 4, 51-83 (2003).

[4] H. Imahori, Org. Biomol. Chem. (Perspective), 2, 1425-1433 (2004).

[5] H. Imahori, J. Phys. Chem. B (Feature Article), 108, 6130-6143 (2004).

[6] H. Imahori and S. Fukuzumi, Adv. Funct. Mater. (Feature Article), 14, 525-536 (2004).

[7] H. Imahori, Bull. Chem. Soc. Jpn. (Award Accounts), 80, 621-636 (2007).

[8] T. Umeyama and H. Imahori, J. Phys. Chem. C (Feature Article), 117, 3195-3209 (2013).