bluuebunny/crossref_metadata_2025 huggingface dataset:
Biomimetic Nanocomposite Electrodes for Enhanced Electron Transfer in Microbial Fuel Cells
Authors: Yuede Nicole Elizabeth , Khan Hafsa J , Vukaj Frank N , Keleher Jason J.
Published: February 2020

Microbial fuel cells (MFCs) have gained attention as a source of renewable energy because of their ability to directly convert chemical potential into electrical potential. While the fundamental mechanisms of MFCs have been explored, there are still gaps in understanding the correlation of biofilm formation to voltage and current response using polymeric electrode materials. This work investigated the relationship between microbial-surface adhesion and the kinetics of electron transfer. Utilizing the biofilm-surface interfacial properties studied via atomic force microscopy (AFM), nanocomposite materials were synthesized to increase the electrical output in the MFC. Additionally, open circuit potential (OCP) of the anode compartment was measured to determine an optimal system of electron generation which was then implemented in a dual chambered MFC reactor. The cellulose based-electrodes impacted Escherichia coli (E. coli) adsorption while increasing conductivity when compared to standard carbon cloth materials. Initial results have indicated that electrodes functionalized with an additional fuel source increased the rate of adsorption, impacting the overall electron generation. Future work aims to synthesize a regenerative composite electrode material for increased voltage response and MFC efficiency.
(Invited) Growth of Fullerene Fragments Using the Diels-Alder Cycloaddition Reaction
Authors: Méndez Francisco , Alonso Julio A. , Mojica Martha
Published: February 2020

Density Functional Theory has been used to model the Diels-Alder reactions of the fullerene fragments triindenetriphenilene and pentacyclopentacorannulene with ethylene and 1,3-butadiene. The purpose is to prove the feasibility of using Diels-Alder cycloaddition reactions to grow fullerene fragments step by step, and to dimerize fullerene fragments, as a way to obtain C60. The dienophile character of the fullerene fragments is dominant, and the reaction of butadiene with pentacyclopentacorannulene is favored.
Influence of the Supporting Electrolyte on the Structure-Transport Properties of PFSA Membranes for Redox Flow Batteries
Authors: Kushner Douglas I. , Kusoglu Ahmet , Weber Adam Z.
Published: February 2020

Redox flow batteries (RFBs) are poised at becoming one of the most promising technologies that are being explored for grid-scale energy storage from discontinuous power sources such as wind and solar.[1] This has resulted in a need for continued development and understanding of new redox couples and their supporting electrolyte counterparts, as well as improving membranes for RFB operation while reducing cost. Membranes employed in RFB technology are largely comprised of the perfluorosulfonic acid (PFSA) family (e.g. Nafion, Aquivion, and 3M PFSA) which exhibit different material properties depending on the surrounding environment, such as transport properties.[2] The structure-property relationships of PFSAs are well-known and studied,[3] providing the initial framework for our understanding; however, much of this work has been performed in either vapor or liquid water. Thus, it is of interest to elucidate how the structure and transport properties of PFSAs change in various electrolytes used in RFBs.

In this work, we discuss our progress in linking the electrolyte concentration-dependent nanostructure to the transport of ions in PFSA membranes. Sulfuric acid and hydrochloric acid represent the majority of supporting electrolytes used in RFB applications and are therefore the primary focus of this study. The polymer’s nanostructure in electrolytes is analyzed using small angle X-ray scattering (SAXS) in-situ, in order to understand the influence of the type and concentration of the supporting electrolytes on the characteristic morphological features of the membrane. Then, nanostructural information is linked to the ion transport through the membrane, via conductivity. Linking the conductivity and polymer morphology provides a better understanding of the structure-transport relationships of PFSAs in electrolytes, and their implications for membrane performance in a RFB cell.

Perry, M.L. and A.Z. Weber, Advanced Redox-Flow Batteries: A Perspective. Journal of the Electrochemical Society, 2016. 163(1): p. A5064-A5067.

Tang, Z., et al., Composition and Conductivity of Membranes Equilibrated with Solutions of Sulfuric Acid and Vanadyl Sulfate. Journal of the Electrochemical Society, 2013. 160(9): p. F1040-F1047.

Kusoglu, A. and A.Z. Weber, New Insights into Perfluorinated Sulfonic-Acid Ionomers. Chem Rev, 2017. 117(3): p. 987-1104.
Long-Term Atmospheric Corrosion of Hot-Dip Galvanized Steel and Zn-Al Coated Steel
Authors: Thierry Dominique , Persson Dan
Published: February 2020

Hot dip galvanized steel and zinc alloyed coated steel such as ZnAl are widely used in the building industry. However, despite large efforts made to study the corrosion products formed on zinc under atmospheric weathering conditions (see for instance reference 1 and 2), very few data exist on HDG and zinc alloyed coated steel [5].

This work is a part of a larger research program were steel with different zinc coatings are exposed on a worldwide basis on well characterized exposure sites in Europe, Asia and North America, see Table 1.

Corrosion rates of hot dip galvanized steel and zinc aluminum coated steel (e.g. Zn5%Al and Zn 55% Al) were determined after 1, 2, 4 and 6 years of exposure under different climatic conditions.

The formation and development of corrosion products was followed by detailed analysis of samples exposed 0.5, 1, 2, 4 and 6 years using XRD, FTIR-spectroscopy and SEM-EDS. The data are discussed in view of current knowledge in the atmospheric corrosion of zinc, HDG and Zn-Al coated steel materials [1-6]

Table 1. Test sites in the exposure program

Code

Name

Country

Distance to Sea(m)

A

Brest
France
<5

B

Bohus-Malmön (I)
Sweden
<5

C

Bohus-Malmön (II)
Sweden
300

D

Ijmuiden
Netherlands
2600

E

Cadiz
Spain
750

F

Jiangjin
China
̴900 km

G

Ostrawa
Czech Republic
̴500 km

H

Dubai
UAE
2000

I

Daytona Beach
USA
100

J

Quindao
China
10

K

Wanning
China
100

L

Bangkok
Thailand
35 km

M

Sattahip
Thailand
10

N

Singapore
SIngapore
10

References

1-I. Odnevall, C. Leygraf, Corros. Sci. 34 (1993) 1213–1229.

2- I. Odnevall, C. Leygraf, Corros. Sci. 36 (1994) 1551–1567.

3- N. Le Bozec, D. Thierry, M. Rohwerder, Dan Persson, G. Luckeneder and L. Luxem, Effect of CO2 on the atmospheric corrosion of ZnMgAl coated steel, Corrosion Science, 74, pp 379-386, 2013

4- E. Diller, B. Lescop, S. Rioual, G Nguyen, D. Thierry and B. Rouvello, Initial formation of corrosion products on pure zinc and MgZn2 examined by XPS: Corrosion Science 79, pp 83-88, 2014.

5- D. Persson, N. Le Bozec, T. Prosek, D. Thierry, G. Luckenader , Corrosion Science Vol 90, pp 276-283, 2015.

6- D. Persson, D. Thierry, N. Le Bozec: Corrosion products formation on Zn55Al upon exposure in marine atmosphere, Corrosion Science, 720, 2011.
Effect of Molybdenum on Pit Initiation at Manganese Sulfide Inclusions in Stainless Steel
Authors: Nishimoto Masashi , Muto Izumi , Sugawara Yu , Hara Nobuyoshi
Published: February 2020

Stainless steels sometimes suffer from pitting corrosion in chloride environments. The pit initiation sites for commercial stainless steels have been attributed to sulfide inclusions such as MnS. It is well known that addition of Mo enhances the pitting corrosion resistance of stainless steels, and the role of Mo has been studied extensively. However, it is still debated how Mo inhibits pitting corrosion of stainless steels. In this study, a microelectrochemical technique was applied to clarify the role of Mo addition in the inhibition of pit initiation at MnS inclusions in stainless steels.

Two re-sulfurized stainless steels were prepared by vacuum induction melting (50 kg ingot): one was Mo-free (18Cr-10Ni-0.8Mn-0.03S), and the other was Mo-added (18Cr-10Ni-2.3Mo-0.8Mn-0.03S). The ingots were hot-rolled. In these steels, S was added to form MnS inclusions. To reduce the delta-ferrite phase in the steels, they were heat-treated at 1273 K for 96 h, followed by hot-rolling at 1473 K from 20 mm down to about 12 mm in thickness. Additional heat-treatment was conducted at 1273 K for 96 h and at 1323 K at 0.5 h, and the steels were finally water-quenched. After heat-treatment, the steels were cut into specimens with dimensions of 15 mm × 25 mm × 5 mm. The specimens were abraded with a series of SiC papers up to 1500 grit and then were polished by a diamond paste down to 1 µm. Potentiodynamic polarization curves were measured in naturally aerated 0.1 M NaCl (pH 5.5) at 298 K. The electrode area was ca. 100 µm × 100 µm. All the potentials reported in this study refer to the Ag/AgCl (3.33 M KCl) electrode (0.206 V vs. standard hydrogen electrode at 298 K). The potential scan rate was 3.8 × 10–4 V/s (23 mV/min).

To analyze the effect of Mo on the pit initiation at the MnS inclusion, the anodic polarization curves were measured in 0.1 M NaCl. Figure 1a shows the polarization curves of a small area with the MnS inclusions in Mo-free and Mo-added specimens. Figures 1b and 1c show the SEM images of the inclusions in Mo-free and Mo-added specimens after polarization. The experiments were started at –0.2 V. The gradual increases in the current densities of both specimens above ca. 0.1 V are due to the anodic dissolution of the MnS inclusions. The large increase in the current density of the Mo-free specimen at 0.4 V was attributed to the stable pit initiation at the inclusion. As shown in Fig. 1b, a pit was initiated at the MnS/steel matrix boundary. On the other hand, the current density of the Mo-added specimen decreased to the level of the passive state of stainless steel above ca. 0.45 V. In Fig. 1c, no pit was observed in the Mo-added specimen even though the bare steel surface was exposed by the dissolution of the MnS inclusion. Mo species were estimated to be released from the exposed bare steel surface. This suggests that Mo species inhibited pit initiation at the MnS/steel boundary.

Figure 1
In Situ Transmission Electron Microscopy to Uncover Electrochemical Reactions
Authors: Shahbazian-Yassar Reza
Published: February 2020

This talk gives an overview of the PI’s research program on the opportunities and challenges of in situ transmission electron microscopy (TEM) to study novel two dimensional materials and metal oxides for Li-ion and Na-ion battery applications. Various anode materials including SnO2, ZnSb, MnO2 , phosphorene were subjected to lithiation process and the transport of Li ions was visualized within their atomic structure. For SnO2 nanowires, it was observed that the Li ion transport results in local strain development preferably along (200) or (020) plans and [001] crystallographic directions. Extremely fast ionic transport was also observed along [100] directions of phosphorene and in ZnSb crystalline materials indicating that atomic structure engineering of electrode materials can provide an efficient path for the movement of larger ions such as sodium ions overcoming their sluggish kinetics. In one-dimensional materials the structural engineering of tunnels and the tunnel stabilizers can be very effective in allowing the ions to be transported at fast rates. Overall a summary will be given on new science obtained from the in situ TEM studies and how this new information can help to further grow the opportunities in materials designed for electrochemistry.
Battery Durability and Reliability Under Electric Utility Grid Operations:Representative Usage Aging
Authors: Baure George , Devie Arnaud , Dubarry Matthieu
Published: February 2020

Battery Energy Storage Systems (BESSs) can facilitate renewable energy sources integration onto the grid. For this application, these systems are expected to last for a decade or more, but the actual battery degradation under different real-world conditions is still largely unknown. In this work, three years of lithium titanate BESS usage in Hawai'i were analyzed. In addition, the representative usage was subjected on individual cells under controlled laboratory conditions to study the degradation mechanisms and enable life prognosis.

The BESS was found to be operational 90% of the time and it stored a cumulative 1.5 GWh of energy, which represented more than 5000 equivalent full cycles on the cells. From this BESS usage data, an initial estimate of BESS degradation was provided and a representative duty cycle was developed. The analysis of the maintenance cycles indicated that these 5000 equivalent cycles induced an estimated 5-10% degradation of the single cells. The battery duty cycle was characterized based on 5 parameters: pulses duration, pulses intensity (current), state of charge (SOC) swing range, SOC event ramp rate, and temperature. The average usage consisted of several 9-second C/2 charge and discharge pulses organized to generate 5% SOC swings with a 0.75% SOC/min ramp rate at 35°C. However, extreme values such as currents up to 4C, swings of 100% SOC, and temperatures above 50°C were also recorded.

Laboratory testing and analysis, in conjunction with a more thorough SOH estimation protocol, resulted in a detailed description of degradation that improved the predictions of the remaining useful battery life. Based on the BESS representative usage profile, cycle-aging and calendar-aging experiments were designed to test the degradation of the associated Li-ion cells in a controlled fashion. It was proven that the cell temperature history had the strongest impact on battery degradation followed by the C-rate and the state of charge. Interestingly, the impact of SOC, both on the cycle-aging and the calendar-aging experiments, was revealed to be counterintuitive. During cycle aging, small SOC swings were more detrimental than larger ones. During calendar aging, batteries lost capacity faster at low SOC than at high SOC. The associated degradation mechanisms and their path dependency were analyzed using incremental capacity analysis.
(Invited) Chemomechanical Behavior of Composite Electrodes in Li-Ion Batteries: Experiments and Modeling
Authors: Zhao Kejie
Published: February 2020

The chemomechanical behavior of composite electrodes is largely different from that of single particles or mono-phase materials. The stress field, state of charge, and mechanical failure are strongly affected by the local details of the microstructure. On the experimental side, we study the structural disintegration of NMC cathode materials of a hierarchical structure by tracking the microstructural evolution of different marked regimes. Decohesion of primary particles constitutes the major mechanical degradation which results in the loss of connectivity of the conductive network and impedance increase. We employ operando nanoindentation to measure the evolution of elastic modulus, hardness, and interfacial strength of NMC cathodes at different states of charge and different cycles. We further use home-developed computational program to investigate the chemomechanical behavior of NMC composites in reconstructed 3D models. An ample space of design is open for the optimization of the capacity and mechanical performance of electrodes by tuning the size, shape, and pattern of active particles, as well as the properties of the inactive matrix.
Dendrite Formation in Silicon and Li-Metal Anodes in Lithium-Ion Batteries
Authors: Selis Luis , Seminario Jorge
Published: February 2020

Silicon and lithium metal anode are promised anodes for the lithium-ion batteries because of their large theoretical capacity. Unfortunately, dendrite growing have extremely restricted practical application for years. The slow drift velocity of the Li-ions of approximately 1 mm/hour, makes the growth of a dendrite to take hours, nevertheless, when the Li-ion arrives to the anode, the important reactions only take approximately 1 ps. This large difference in time-scales allows us to perform a molecular dynamics simulation with a faster lithiation, so we can have important results in reasonable computational times. We performed simulations of a pre-lithiated silicon anode (Li15Si4) in a nanosized square, representing a crack of the solid electrolyte interphase, thus the electrolyte is in direct contact with the anode. We found that selected charge distributions in the anode surface helps the dendrite grow. The charge distribution in the anode surface that most favors the lithium dendrites formation are neither the strongest nor weakest charges instead the intermediate charges. We analyze the force with which the dendrites grow and the pressure that a solid electrolyte interface (SEI) would must resist to avoid cracks, and after we perform a simulation with a Li metal anode covered of a SEI of LiF already cracked, we found that have a part of the anode is cover by the SEI meanwhile other part of the anode have direct contact with the electrolyte solution favor the lithium dendrite formation and we analyze the effect of change the way to charge the battery(current constant and voltage constant) after we analyze why charge the battery in a high temperature slows down the lithium dendrite formation and the effect of charge the battery with a different C-rate, this C-rates used in this work are in the magnitude of 1010, in both anodes the electrolyte is composed of 1M LiPF6 salt solvated in ethylene carbonate (EC).
All Electrochemical Process for Synthesis of Si Coating on TiO2 Nanotubes As Durable Negative Electrode Material for Li-Ion Batteries
Authors: Nemaga Abirdu Woreka , Mallet Jeremy , Guery Claude , Molinari Michael , Morcrette Mathieu
Published: February 2020

Although silicon is a promising negative electrode material for Li-ion batteries, its practical application has been hindered by the huge volume expansion resulting poor cyclic stability. It has been demonstrated that ultra-thin (< 50 nm) amorphous Si shown an excellent cyclic stability. However, the energy density delivered from the ultra-thin film is not sufficient for high energy application and increasing the thickness leads to the fracture of the film. Therefore, it is a key to design a conductive substrate with high surface area to enhance adhesion and Si active mass before reaching the fracture thickness. In this work, amorphous silicon (a-Si) film electrodeposited on self-organized TiO2 nanotubes is investigated as durable negative electrode material for Li-ion batteries. The nanostructured composite electrodes were fabricated by a two-step cost effective electrochemical process. Firstly, TiO2 nanotube arrays were synthesized by anodizing of Ti foil. Subsequently, thanks to room temperature ionic liquid, conformal Si film was electrochemically coated on the TiO2 nanotubes for the fabrication of nanostructured a-Si/TiO2 nanotube composite negative electrodes. Compared to other strategies where Si is used as a form of thin films, the TiO2 nanotube arrays provide several advantages such as a strong mechanical support to buffer Si volume expansion, a high surface area to increase Si active mass, and the direct contact of the nanotubes with the Ti current collector facilitates 1D electron transport and avoids the need of adding inactive binders or conductive additives. The influence of the Si loading as well as the crystallinity of the TiO2 nanotubes have been studied in terms of capacity and cyclic stability of the composite electrode. For an optimized Si loading, it is shown that the amorphous state for the TiO2 nanotubes enables to get stable lithiation and delithiation with a total areal charge capacity of about 0.32 mA h cm-2 with improved capacity retention of about 84% after 50 cycles. The specific capacity contribution of Si in the composite is estimated to be about 900 mAh/g after 50th cycle. However, the Si deposited on crystalline TiO2 nanotubes showed poor cyclic stability independently from the Si loading.

Fig. 1 SEM images of TiO2 nanotubes formed by anodizing Ti foil (left) and after Si coating of the nanotubes via electrodeposition from room temperature ionic liquids (right).

Figure 1
(Invited) Dimensional Crossover for New Functionalities in MOFs
Authors: Kitagawa Hiroshi
Published: February 2020

Here, we demonstrate a bottom-up approach for the fabrication of well-defined dimensional-crossover nano-architectures with high tunability using metals and organic molecules as building blocks or linkers. We succeeded in rationally constructing assemblies; (1) ladders and tubes which are located in dimensional-crossover region between 1D and 2D, (2) surface metal–organic frameworks (SurMOFs) which are located in dimensional-crossover region between 2D and 3D, and (3) nanoparticles coated with MOFs or polymers which are located in dimensional-crossover region between 0D and 3D.
An ORR Identical Location STEM Investigation of the Stability of Pt3-Ni Octahedra Supported in Hollow Graphitic Spheres
Authors: Paciok Paul , Knossalla Johannes , Göhl Daniel , Ledendecker Marc , Jalalpoor Daniel , Pizzutilo Enrico , Heggen Marc , Schüth Ferdi , Mayrhofer Karl , Dunin-Borkowski Rafal E.
Published: February 2020

The activity of a catalyst towards the oxygen reduction reaction (ORR) is determined by its surface composition and structure. Although careful synthesis strategies have managed to improve the ORR activity of Pt by a factor of 40 in recent years, the long-term stability of supported catalysts still poses a challenge.[1] One approach that can be used to supress degradation phenomena, such as particle migration and agglomeration, is incorporation of the active metal species in the pores of a conducting, porous graphitic matrix, in order to hinder the motion of the alloy particles. [2-4]

Here, we describe the synthesis, characterization and stability of octahedral Pt3NiMo nanoparticle catalysts supported in hollow graphitic spheres. By combining electrochemically active surface area (ECSA) measurements, identical location scanning transmission electron microscopy (STEM) and measurements performed using an in situ electrocatalytic scanning flow cell coupled to an inductively coupled plasma mass spectrometer (SFC-ICP-MS), we demonstrate the stabilizing effect of the hollow graphitic spheres on the PtNi octahedra. After 10800 cycles, the octahedra are found to have retained their shape, with only a small loss of ECSA.

In summary, we demonstrate the successful incorporation of shaped bimetallic nanoparticles into a porous support. This design strategy can be used for other catalytic reactions and opens new ways for achieving space confinement of faceted Pt alloy particles.

References:

[1] P. Strasser, Science
2015, 349, pp 379-380.

[2] C. Galeano, J. C. Meier, V. Peinecke, H. Bongard, I. Katsounaros, A. A. Topalov, A. Lu, K. J. J. Mayrhofer, F. Schüth, J. Am. Chem. Soc.
2012, 134, pp 20457– 20465.

[3] S. Mezzavilla, C. Baldizzone, A.-C. Swertz, N. Hodnik, E. Pizzutilo, G. Polymeros, G. P. Keeley, J. Knossalla, M. Heggen, K. J. J. Mayrhofer, F. Schüth, ACS Catal., 2016, 6 (12), pp 8058–8068.

[4] E. Pizzutilo, J. Knossalla, S. Geiger, J. P. Grote, G. Polymeros, C. Baldizzone, S. Mezzavilla, M. Ledendecker, A. Mingers, S. Cherevko, F. Schuth, K. J. J. Mayrhofer, Adv. Energy. Mater.
2017, 7(20).
(Invited) Platinum Single-Atom Catalysts for Electrochemical Reactions
Authors: Lee Hyunjoo
Published: February 2020

As a catalyst, single-atom platinum may provide an ideal structure for platinum minimization. The single-atom catalyst of platinum supported on titanium nitride nanoparticles were successfully prepared with an aid of chlorine ligands. Unlike platinum nanoparticles, the single-atom active sites predominantly produced hydrogen peroxide in the electrochemical oxygen reduction with the highest mass activity reported so far. The electrocatalytic oxidation of small organic molecules, such as formic acid and methanol, also exhibited unique selectivity on the single-atom platinum catalyst. A lack of platinum ensemble sites changed the reaction pathway for oxygen reduction reaction toward two electrons pathway and formic acid oxidation toward direct dehydrogenation, and also induced no activity for methanol oxidation. The single-atom platinum showed high mass activity and unique selectivity for the electrochemical reactions. Additionally, the role of the support may have a significant impact on the catalytic properties similar to that of the ligand molecules in homogeneous catalysts. The support effect was demonstrated by preparing the single-atom platinum catalyst on two different supports, titanium carbide and titanium nitride. The formation of single-atom Pt was confirmed by STEM, EXAFS, and in-situ IR spectroscopy. Pt1/TiC showed higher activity, selectivity, and stability for electrochemical H2O2 production than Pt1/TiN. Density functional theory calculation presented that oxygen species have strong affinity into Pt1/TiN possibly acting as surface poisoning species, and Pt1/TiC preserves oxygen-oxygen bond more with higher selectivity towards H2O2 production. The support in single-atom catalysts actively participates in the surface reaction, not just acting as anchoring sites for single-atoms. The Pt single-atom electrocatalyst was also prepared on Sb-doped SnO2 (Pt1/ATO), and it was used to fabricate direct formic acid fuel cell.
Synthesis and Characterization of Nitrogen-Doped Ordered Mesoporous Hollow Carbon Spheres for the ORR
Authors: Maricruz Salazar-Oropeza , Escobar-Morales Beatriz , Reguera Edilso , José Escorcia-García , Rodriguez-Varela F.J. , Alonso-Lemus Ivonne Liliana
Published: February 2020

This work presents the synthesis by a hydrothermal procedure of metal-free nitrogen-doped Ordered Mesoporous Hollow Carbon Spheres (N-OMHCS) starting from a SiO2 template. N-OMHCS powders have been functionalized with methanol using the intermittent microwave heating technique to produce the N-OMHCS-f sample. Then, N-OMHCS and N-OMHCS-f have been evaluated as cathode electrocatalysts for the Oxygen Reduction Reaction (ORR) in 0.5 mol L-1 KOH, with the rotating ring-disk electrode technique (RRDE). The morphology of N-OMHCS and N-OMHCS-f is that of hollow porous spherical particles of carbon of 280 nm in diameter. The chemical composition analysis shows that N-OMHCS-f is composed of basically C and O. The electrochemical results indicate that N-OMHCS-f are active for the ORR, with an onset potential of 0.81 and 0.82 V/RHE and a limiting current of -3.6 and -2.3 mA cm-2, respectively. On the other hand, both electrocatalysts produce about the same amount of H2O2 (between 14 and 26 %). Meanwhile, the number of electrons transferred at the electrocatalysts is between 3.6 and 3.8, which is close to a 4e- transfer mechanism. The catalytic activity of N-OMHCS and N-OMHCS-f can be attributed to their high specific surface area and porous structure, which provides a triple phase region promoting the adsorption-desorption of O2.
Imidazolium-Based Grafted Anion Exchange Membranes: Interplay between the Morphology and Anion Transport Behavior
Authors: Zhao Yue , Yoshimura Kimio , Hiroki Akihiro , Kishiyama Yoshihiro , Shishitani Hideyuki , Yamaguchi Susumu , Tanaka Hirohisa , Maekawa Yasunari
Published: February 2020

Anion-exchange membranes (AEMs) have been regarded as an alternative to proton-exchange membranes (PEMs) in energy conversion devices, due to the advantage of saving expensive platinum catalysts. However, neither the molecular design nor the property understanding is sufficient for developing AEMs capable of practical fuel cell applications. It is crucial to thoroughly study the current AEMs in terms of microphase structures and conducting properties. Recently, we developed a new graft type of AEMs by radiation-induced grafting method, where imidazolium and styrene monomers were grafted into poly(ethylene-co-tetrafluoroethylene) (ETFE) base films under a dose of 80 kGy from the 60Co γ-ray source (QST, Takasaki), followed by alkylation and ion exchange reactions. These AEMs exhibit well-balanced properties of high ion conductivity (> 100 mS/cm at 80oC) and good stability, which are believed to be controlled by the microphase structure of the membrane. In this report, we investigate the memrbane structure and reveal the relationship between structure and properties, using small-angle neutron scattering (SANS) method.

Fig. 1 shows typical SANS intensity profiles, I(q), of pristine ETFE films (profile 1), grafted-ETFE membranes (profile 2), dry AEM (profile 3) and AEM equilibrated in D2O (profile 4) as a function of scattering vector q. The different morphologies which can be deduced from the SANS profiles are also shown in the figure. The experiments confirm the semi-crystalline feature of AEM conserved from the original ETFE base film, which is the key factor for the high membrane mechanical stability, and show the dependence of the structure on hydration. Contrast variation experiments performed on AEM equilibrated in water mixtures of H2O and D2O, further show that graft polymers and water consist the hydrophilic ion channels [1]. Since graft polymers distribute randomly in AEM, well-connected hydrophilic ion channels are feasibly formed, which is the key factor for the high membrane conductivity.

Above all, the interplay between the morphology and properties can be characterized as follows: 1) semi-crystalline base film offers good mechanical properties; 2) graft polymers and water form ion channels to promote the conductivity.

Figure 1
Metal Organic Frameworks Based Catalysts for ORR: The Effect of the Transition Metal on the Catalytic Activity
Authors: Elbaz Lior , Gonen Shmuel , Lori Oran
Published: February 2020

Fuel cells are promising alternative energy conversion devices. Their high energy density and efficiency in addition to the consumption of environmentally-friendly fuels such as hydrogen, drew a lot of attention in recent years. However, there are still some challenges to overcome. The most common cathode catalyst used to expedite the oxygen reduction reaction is platinum, which is relatively scarce and expensive. Many attempts to replace the platinum with precious group metal-free (PGM-free) catalysts were made, most of them are metal-nitrogen complexes in which iron and cobalt exhibit the best activity. One of the most prominent PGM-free catalyst family now-days are metal organic frameworks (MOFs).

Owing to their unique chemistry and physical properties, metal-organic Frameworks (MOFs) are an interesting class of materials which can be utilized for a wide array of applications. MOFs have been proposed to be used as catalysts for fuel cells, but their low intrinsic electronic conductivity hampered their utilization as-is. In this work, we present the synthesis and application of MOF-based PGM-free catalysts for oxygen reduction based on a unique metal-organic framework-carbon composite material. Benzene tricarboxylic acid-based MOFs were synthesized inside activated carbon (AC) with four different, first row transition metals: Mn, Fe, Co, and Cu. The MOFs@AC were analyzed electrochemically to measure their catalytic activity. Further physical and chemical characterizations were performed to measure the materials properties. The MOFs@AC are found to be conductive and active catalysts for oxygen reduction reaction in alkaline environment. Surprisingly, the Mn-based MOF@AC exhibits the best performance with onset potential of 0.9 V vs. RHE and almost four-electron mechanism, as opposed to most other known PGM-free catalysts, which show that Fe and Co as the most active metal. In this talk, we will share our most recent findings from studying these unique materials.
Durable Oxygen Evolution Catalysts for Alkaline Membrane Water Electrolysis
Authors: Xu Hui , Zhao Shuai , Wu Gang
Published: February 2020

The utilization of renewable energy has substantially driven more attention into electrolysis technologies. An electrolyzer can utilize “off peak” electricity from solar or wind farms to produce hydrogen or other fuels. These chemicals can then be operated in a fuel cell mode to generate electricity when needed or used for other industrial applications. However, current hydrogen production from electrolysis comprises only a small fraction of the global hydrogen market due to the high costs that results from expensive materials even if “free” electricity from renewable energy can be acquired.

Alkaline membrane water electrolysis enables to use non-precious metals (or oxides) as the catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). This is very meaningful as the commercial OER catalyst IrOx for proton exchange membrane (PEM) electrolysis is very expensive; more importantly, the global storage and production of iridium is very scarce, tremendously limiting the mass production and deployment of PEM electrolyzers. However, there have rarely reported active and durable OER and HER catalysts for alkaline membrane water electrolysis, particularly in a membrane and electrode assembly (MEA) level; most previous studies on the OER and HER catalysts were focused on the rotating disk electrodes (RDEs).

We have investigated a series of OER catalysts including Co3O4 supported on carbon nanotubes (Co3O4/CNTs), binary transitional metal oxides (nickel cobalt oxide, NiCo2O4), and nanocarbon composites (FeCoNiMn-derived N-doped graphene tube, NC-FeCoNiMn4). These catalysts have first demonstrated remarkable durability in the RDE tests, subject to extensive voltage cycling from 0.0 V to 1.9 V. These catalysts have been integrated with other components including alkaline membrane and ionomer to test their MEA performance. It was discovered that both membrane and ionomers have a significant impact on the MEA performance and durability. The alkaline membrane and ionomer can quickly degrade upon high-voltage operations, leading to rapid MEA performance decay. However, the decayed performance can be restored after the introduction of diluted hydroxide solution (e.g, 0.1 M KOH) to the electrolyzer cell.

Therefore, this work can provide insightful guidance on the MEA design for alkaline membrane water electrolysis. Most importantly, the interaction between the catalyst and the ionomer will be investigated.

Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-EE0006960.
Electron Injection on Metal/n-Doped Semiconducting Polymer
Authors: Sakiyama Shin , Mizutani Naoki
Published: February 2020

Efficient n-type doping was not established since the dopants dose not dissolve in same organic solutions of polymer semiconductors. Evaporative Spray Deposition using Ultra-dilute Solution (ESDUS) method enabled it recently. We have already reported efficient n-type doping of poly(2-methoxy-5-(2’-methyl-hexyloxy)-p- phenylenevinylene) (MEH-PPV: LUMO: 3.1 eV, HOMO: 5.2 eV). The high doping efficiency as much as 15% was realized. In organic devices composed of non-doped organic semiconductors, electron injection barrier is basically equal to the gap between LUMO of the organic semiconductor and work function of the el ectrode. It is still open question how the barrier is formed in the n-doped polymer/electrode. The metal/semiconductor junction of n-doped polymer has not been studied yet. In this research, we have fabricated electron only devices (EOD) of an n-doped polymer semiconductor using electrodes of Al and Ca. The electron injection from Al or Ca was examined.MEH-PPV (Mw = 40,000-70,000 Aldrich) and Cesium carbonate were used as a host polymer and an n-type dopant, respectively. The asymmetric EOD using Al for bottom and top electrodes and and a top Ca electrode having a lower work function (3.0 eV) were fabricated. The current-voltage (J-V) characteristics were measured in vacuum without breaking vacuum after the top electrode deposition. J-V characteristics of asymmetric EOD (Fig. 1), Al(50nm)/MEH-PPV:Cs2CO3 (110nm)/Ca(50nm) are fabricated. The current density was drastically increased as the doping concentration increased. The asymmetric EODs, current density in the forward bias was about 1 order of magnitude larger than that in reverse bias at low doping concentration at 0, 0.2, 2.0 wt%.However, the current density was almost overlapped in forward and reverse bias at the doping concentration of 10wt%. The disappearance of the rectification property suggests that the quantum tunneling takes place due to the very thin depletion layer at Al/MEH-PPV junction at the high doping concentration. In order to evaluate depletion layer width on Al/MEH-PPV junction, C-F measurement was carried out. As a result of the calculation, the depletion layer width of the 0.2 wt% doped device was 16.3 nm, the 2.0 wt% doped device was 9.3 nm, and the 10.0 wt% doped device was 3.3 nm. These results suggest that the depletion layer narrows as the doping concentration increases and the rectification property disappears in the 10 wt% doped device by quantum tunneling. The depletion layer width when quantum tunneling was observed in the p-type organic device, Au/ZnPc:0.3%F4-TCNQ/Au, was 5.2nm. Compared with this depletion layer width of 5.2 nm at metal/p-type organic semiconductor junction, it can be said that the value of 3.3 nm calculated this time is sufficiently narrow to observe quantum tunneling.
Theoretical Modeling of the Electrochemical Lithiation Processes of Lithium-Sulfur Battery Cathodes Based on Sulfur/Graphene-Nanosheets Composites
Authors: Perez-Beltran Saul , Balbuena Perla B
Published: February 2020

The theoretical energy density of 2.5 kWh/kg of sulfur, plus its low-cost availability and environmentally friendliness, makes of lithium-sulfur (Li-S) batteries one of the most promising alternatives to fulfill the need of energy storage devices for high energy-demanding applications such as electric vehicles and smart grids. However, the successful commercialization of Li-S batteries is still challenged by the low utilization of sulfur, linked to its poor electronic/ionic conductivity and its continuous irreversible dissolution into the electrolyte in the form of long-chain lithium-polysulfides. So far, the mixing of sulfur with carbon has led to its better physical confinement and chemical sequestration in the cathode. However, the details of the sulfur-carbon interaction and its effects on the electrochemical lithiation processes during battery cycling are still largely unknown.

Here we aimed at characterizing the structure of sulfur/graphene-nanosheets composites (SC composite) and understand its effects on the electrochemical lithiation processes during battery cycling. Reactive molecular dynamics (ReaxFF) calculations provided information on the cathode microstructure and the bulk reduction products upon lithiation. Ab initio molecular dynamics simulations (AIMD) along with density functional theory (DFT) optimizations, yield details of the effects of different electrolyte compositions on the SC composite capabilities for retention of sulfur and the polysulfide formation paths.

We elucidated that a stronger sulfur-carbon interaction not only contributes to a better electronic conductivity but also leads to an alternative sulfur reduction path without the formation of long-chain polysulfides, which might help to explain the improved cycling stability observed in sulfurized polyacrylonitrile composites reported in the literature. In addition, we observed that different electrolyte compositions might be beneficial too by allowing an easier recovery of S-C bonds upon charging. We believe the results from this work can contribute to improving the synthesis methodologies of sulfur-carbon composites leading to a more rapid commercialization of lithium-sulfur batteries.
An Organic Electrolyte Additive for the Suppression of Li Dendrite in Li Metal Based Batteries
Authors: Kim Hee-Sang , Didwal Pravin N. , Park Chan-Jin
Published: February 2020

Li metal has been known as an ideal anode material for high performance batteries due to its high theoretical specific capacity and lowest working potential. However, Li metal is thermodynamically unstable in polar aprotic electrolytes: it reacts with the electrolytes to form a solid electrolyte interface (SEI) layer. This layer, when a stable SEI layer is formed, it can prevent the direct contact between Li metal and liquid electrolyte and further decomposition of the electrolyte. Nevertheless, the non-uniform chemical composition of the SEI layer can induce an uneven current distribution on the Li surface, which causes Li dendrite growth and resulting electric short circuit. Thus far, approaches focused on making the stable and uniform SEI layer to prevent Li dendrite formation from modulating the electrolyte component and preventing the use of electrolyte additives.

In the present work, we suggest the use of an electrolyte additive for forming a uniform and stable SEI layer on Li surface for suppressing the growth of Li dendrite. The base electrolyte of 1 M LiTFSI in TEGDME was used for tests. The Li symmetric cell containing the electrolyte additive was galvanostatically cycled over 500 cycles for each charge and discharge time of 2 h at a current density 1 mA cm-2, which was >50 times longer than that of the Li symmetric cell without additive in electrolyte. This electrolyte additive helps to make a stable and uniform SEI layer, leading to effectively suppressing the growth of Li dendrite. Further, the electrolyte additive can be used in the Li metal based batteries such as a Li-O2 battery. The Li-O2 cell containing the additive was cycled for longer than 200 cycles at a current density of 0.1 mA cm-2 under the limited capacity mode of 1000 mAh g-1, which was >4 times longer than that of the Li-O2 cell without the additive in electrolyte. This electrolyte additive remarkably improved the electrochemical performance, especially cyclability of Li-O2 batteries.

Figure 1
Singlet Oxygen in Non-Aqueous Battery Chemistries
Authors: Mourad Eléonore , Mahne Nika , Schafzahl Lukas , Petit Yann K , Schafzahl Bettina , Renfrew Sara E , Kramer Denis , Fontaine Olivier , Wilkening Martin , Slugovc Christian , McCloskey Bryan D. , Borisov Sergey M. , Freunberger Stefan A
Published: February 2020

The redox chemistry of O2 moieties has come into the focus of much of the forefront battery research such as metal-O2 batteries and Li-rich layered oxides (1, 2). O2 evolution is in either case a critical yet not fully understood phenomenon (1, 3). For example, operation of the rechargeable metal-O2 batteries depends crucially on the reversible formation/decomposition of metal (su)peroxides at the cathode on discharge/charge. The greatest challenge facing progress arises from severe parasitic reactions that decompose the electrolyte as well as the porous electrode. These processes have serious consequences. So far these parasitic reactions have been ascribed to the reactivity of superoxide and peroxide. Yet, their reactivity cannot consistently explain the observed irreversible processes. Unsurprisingly, strategies to mitigate the irreversibilities proved only partially successful. Therefore, only better knowledge of parasitic reactions may allow them to be inhibited.

Here we discuss our recent insights into irreversible parasitic reactions caused by the highly reactive singlet oxygen (1O2) during cycling of non-aqueous batteries that have so far been overlooked. They account for the majority of the parasitic products on discharge and nearly all on charge in Li-O2 and Na-O2 cells (4-6). Moreover, singlet oxygen forms upon oxidizing Li2CO3 above 3.8 V vs Li/Li+ (7). Li2CO3 is a universal passivating agent in Li-ion battery cathodes and decisive in interfacial reactivity. It is also a common side product in Li-O2 cathodes, as well as the targeted discharge product in Li-O2/CO2 batteries. We will further discuss work on open question with respect to 1O2 non-aqueous battery chemistries such as catalysts, electrolytes, mediators, quenchers and other additives as well as the formation mechanism and the implications for metal-O2 cells and intercalation chemistries. Awareness of the highly reactive singlet oxygen gives a rationale for future research towards achieving highly reversible cell operation in a broad range of cell chemistries.

References

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2012, 11, 19.

(2) McCalla, E. et al.. Science
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(3) Luo, K; et al. JACS
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(4) Mahne, N., et al. Nature Energy
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(5) L. Schafzahl, et al, Angew. Chem. Int. Ed., 2017, 56, 15728.

(6) N. Mahne, O. Fontaine, M. Thotiyl, M. Wilkening & S. A. Freunberger, Chem. Sci., 2017, 8, 6716.

(7) N. Mahne, S.E. Renfrew, B.D. McCloskey & S.A. Freunberger, Angew. Chem. Int. Ed., doi: 10.1002/anie.201802277.
Structural Transformations Leading to the Oxygen Evolution Active Phase for Fe Containing Layered Double Hydroxides
Authors: Dionigi Fabio , Zeng Zhenhua , Sinev Ilya , Merzdorf Thomas , Sarodnik Hannes , Drnec Jakub , Greeley Jeffrey , Roldan Beatriz , Strasser Peter
Published: February 2020

NiFe based (oxy)hydroxides have been identified among the most active catalysts for the oxygen evolution reaction (OER) in alkaline electrolytes.1 Their crystal structure is known as layered double hydroxide (LDH) and is composed of layers of edge sharing metal oxygen octahedra that are intercalated with water molecules and charge balancing anions (Figure 1, insert).2 The incorporation of Fe3+ ions in Ni(OH)2 layers is considered to be responsible for the formation of this structure and its activity enhancement.3 Similarly, incorporation of Fe3+ into Co(OH)2 leads to CoFe LDH. This catalyst has also superior OER activity respect to Fe-free Co(OH)2.4 Despite their structure is well characterized, there are evidences that the OER active structure of LDH catalysts during OER is different than the one of the as prepared materials.3 In particular, oxidative deprotonation and the electrocatalytic reaction might lead to reversible structural differences that are only observable with in operando or in situ methods. More investigations are necessary, since the identification of the OER active structure of a catalyst is important for designing more active and stable catalysts. Theoretical predictions based on density functional theory (DFT) can guide this process, however so far different atomic models have been used in DFT calculations due the lack of clear structural information concerning the crystalline phase of Fe containing LDH under OER active conditions.

In this presentation we will discuss the results of an in operando X-ray absorption spectroscopy and diffraction study on crystalline NiFe and CoFe LDH nanostructured catalysts. We identified the structure of the catalytically silent and active catalyst state and observed that for both catalysts the interlayer distance contracts under operating conditions to a similar value (figure 1). Our results show structural modifications under operating conditions which correlate with the electrochemical activity in alkaline electrolyte. Thus they provide new insights into the structure of the active catalysts state which will help to understand the processes under catalytic conditions.

Figure 1. Shift of the (003) diffraction peak associated to the interlayer distance for NiFe LDH catalysts between the resting state (black) and OER active state (red) (unpublished). 3D structural model of the as prepared NiFe LDH with intercalated water and carbonate ions shown in the insert.

Figure 1