bluuebunny/crossref_metadata_2025 huggingface dataset:
Li Vs. Na Batteries - Investigation of the SEI and Conversion Mechanisms of Nanostructured Fe2O3 Composites Electrodes Via Soft X-Ray Photoelectron Spectroscopy
Authors: Philippe Bertrand , Valvo Mario , Lindgren Fredrik , Rensmo Hakan , Edström Kristina
Published: February 2020

The properties of the SEI layers formed on composite nanostructured iron oxide electrodes upon cycling in Li- and Na-half cells[1] containing analogous electrolytes (i.e. LiClO4, NaClO4) have been investigated by an advanced non-destructive analysis based on Soft X-ray Photoelectron Spectroscopy (PES). Using synchrotron radiation, this approach has enabled probing the corresponding SEI layers at different depths by varying the photon energy hν, in the range of 100-1200 eV. [2,3] This methodology has granted access to a careful study of both the intimate structure and the compositions of these passivating films formed upon initial lithiation/sodiation of the electrode.[4] In this respect, understanding the SEI features without causing any interference or damage during the PES measurement processes has proved crucial to obtain a deeper insight into the specific mechanisms that lead to the formation of such films. The latter have a crucial technological relevance, since they directly affect the electrochemical performances of the active materials undergoing a particular electrochemical reaction, e.g. in a Li or Na cell. The results of this study will be presented highlighting the differences and the similarities that exist between these two electrochemical systems. In particular, it will be shown that such step-by-step analysis conducted on various electrodes left in a defined state of charge upon reduction (i.e. Li+ or Na+ uptake) and oxidation (i.e. Li+ or Na+ release) has revealed interesting differences for the structure of their respective SEI layers, as well as different covering properties in both cases. Finally, the mechanisms of nanostructured iron oxide upon reaction with Li+ and Na+ ions will be discussed. Additional information will be provided on the conversion reaction occurring at low potentials vs. Li+/Li and Na+/Na when the thickness of the grown SEI layer was not critical and has allowed probing the underlying active material, its oxidation state and surrounding chemical environment.

References

M. Valvo, F. Lindgren, U. Lafont, F. Björefors, K. Edström, J. Power Sources 245 (2014) 967.

B. Philippe, R. Dedryvère, J. Allouche, F. Lindgren, M. Gorgoi, H. Rensmo, D. Gonbeau, K. Edström, Chem. Mater. 24 (2012) 1107.

S. Malmgren, K. Ciosek, M. Hahlin, T. Gustafsson, M. Gorgoi, H. Rensmo, K. Edström, Electroch. Acta 97 (2013) 23.

B. Philippe, M. Valvo, F. Lindgren, H. Rensmo, K. Edström, Chem. Mater., 26 (2014) 5028
Free-Standing LiNi0.5Mn1.5O4/Carbon Nanofiber Network Film As Light-Weight and High-Power Cathode for Lithium Ion Batteries
Authors: Fang Xin , Ge Mingyuan , Rong Jiepeng , Shen Chenfei , Liu Yihang , Zhang Anyi , Zhou Chongwu
Published: February 2020

Light-weight and high-power LiNi0.5Mn1.5O4 / carbon nanofiber (CNF) network electrodes are developed as high voltage cathode for lithium ion batteries. The LiNi0.5Mn1.5O4 / CNF network electrodes are free-standing and can be used as cathode without using any binder, carbon black or metal current collector, and hence the total weight of the electrode is highly reduced while keeping the same areal loading of active materials. Compared with conventional electrodes, the LiNi0.5Mn1.5O4 / CNF network electrodes can yield up to 55% reduction in total weight and 2.2 times enhancement in the weight percentage of active material in the whole electrode. Moreover, the LiNi0.5Mn1.5O4 / carbon nanofiber (CNF) network electrodes showed excellent current rate capability in the large current test up to 20C (1C = 140 mAh/g), when the conventional electrodes showed almost no capacity at the same condition. Further analysis of polarization resistance confirmed the favorable conductivity from CNF network comparing with conventional electrode structure. By reducing weight, increasing working voltage and improving large current rate capability simultaneously, the LiNi0.5Mn1.5O4 / CNF electrode structure can highly enhance the energy/power density of lithium ion batteries, and thus holds great potential to be used with ultra-thin, ultra-light electronic devices as well as electric vehicles and hybrid electric vehicles.
In-Situ Observation of Lithium Whisker Growth during Li Electrochemical Deposition
Authors: So Kangpyo , Su Cong , Kushima Akihiro , Li Ju
Published: February 2020

In spite of extensive research that has been done for several decades to utilize the lithium (Li) metal anode, Li metallic anode is still suffering from dendritic structure growth and low columbic efficiency. We address this problem with a new viewpoint for the mechanism of the Li dendritic structure growth and origin of low columbic efficiency. Our in-situ optical/TEM observation reveals that the growth of the dendritic structure starts from the root instead of the tip. The oxidation of Li metal was observed in the middle of the structure. This observation has a discrepancy with conventional dendrite growth mechanism. The elemental mapping suggests the partial dissolution of Li in the interface between the Li metal and copper (Cu) current collector. This observation further suggests that the Li dendritic structure growth from its root was originated from Li-Cu alloying process. We expect that the mechanism of Li root growth during electrodeposition will contribute to a new paradigm on Li metal anode application such as Li-ion, Li-S and Li-air batteries for the next generation of energy storage.
Electrochemical Stiffness Measurements of Graphite Anodes for Li-Ion Batterie
Authors: Tavassol Hadi , Jones Elizabeth M. C. , Sottos Nancy R. , Gewirth Andrew A.
Published: February 2020

We report on measurement of the electrochemical stiffness of the graphite anodes during Li exchange in Li-ion batteries. Graphite is the most common anode material used in commercial Li-ion batteries. During lithiation and delithiation of the graphite anodes, Li-graphite intercalation compounds with varying Li content (Li
x
C6, 0 ≤
x ≤ 1), and graphene layer spacing are formed.  Hence, Li intercalation and de-intercalation causes considerable mechanical changes in the whole electrode.

We use curvature bending measurements to monitor stress changes in a thin graphite electrode constrained on an inert, rigid substrate. In a separate experiment, we employ digital image correlation to track strain changes in a free-standing, unconstrained graphite electrode. Combining in-situstress and strain analyses enables us to extract the potential-dependent stiffness of the graphite anodes during lithiation-delithiation cycles.

As expected, graphite anodes develop compressive stress during lithiation (ca. 10 MPa). The compressive stress is removed during delithiation. Strain response also corresponds with the Li deposition and removal, as graphite anodes expand during lithiation (ca. 1.5 % linear strain) and contract over delithiation. The electrode exhibits an initially stiff response at high potentials and low lithium contents, and then gradually softens during early formation of dilute stage I of the Li-graphite intercalation compound.  As the potential is lowered and lithium content increases, several oscillations in the stiffness are observed, which correspond with the phase transitions during different stages of graphite lithiation.  The evolution of stress, strain and stiffness data provides quantitative information on the coupled electro-chemo-mechanical response of the battery electrodes and insight on material strategies to increase battery reliability.
Interfacial Study of the Role of SiO2 on Si Anodes Using Electrochemical Quartz Crystal Microbalance
Authors: Hubaud Aude A. , Schroeder David J. , Yang Zhenzhen , Dogan Fulya , Vaughey John T.
Published: February 2020

One of the challenges associated with silicon as an anode material for Li-ion batteries is the

formation of an unstable solid-electrolyte interphase which, forms continuously while consuming

lithium and other components; and consequently contributes to irreversible capacity. To elucidate

some of the details of the formation and subsequent dissolution of species that form during lithiation of

silicon anodes we have produced thin film silicon electrodes with and without an oxide layer and

analyzed these during lithiation and delithiation using an electrochemical quartz microbalance with in-

situ dissipation (EQCM-D). Measurements were conducted both in EC:EMC and EC:DEC:FEC based

electrolytes. Mass loss during lithiation was observed in both solvents systems when an oxide layer

was present on the electrode and this was found to be associated with Li2O dissolution using solution

and solid state NMR.
Semi-Empirical Study on Lithium Diffusion into Electrode Materials for Lithium Batteries
Authors: Kwon So-Yeon , Shin Heon-Cheol
Published: February 2020

The decrease in power density of lithium batteries at low temperature is one of main obstacles for their widespread use in transportation systems. In spite of many works on low temperature performance, the key factors affecting the temperature-dependent power degradation still remain unclarified in many battery systems. Successful analysis of power performance is dependent critically on how to estimate accurately the resistances of the electrode reactions such as interfacial charge transfer and solid state lithium diffusion.

In particular, lithium diffusion is hard to be analyzed when the electrode materials undergo a phase transition during charge-discharge process. As a matter of fact, many researchers have still analyzed lithium transport phenomena by using typical relations derived on the assumption of atom diffusion into single phase. For instance, they carried out typical potentiostatic intermittent titration technique, cyclic/linear sweep voltammetry, or electrochemical impedance spectroscopy and then estimated the solid state diffusion coefficient from Cottrell, Randle-Sevcik, or Warburg equation, respectively. However, it is quite unlikely that such a method might give a reliable value of diffusion coefficient because the phase transition significantly influences the electrochemical response. Although a few works investigated lithium transport by considering the coexistence of two phases, the analysis of lithium transport kinetics through biphasic materials is still a great challenge.

In this work, a viable way to analyze lithium transport phenomena through the materials experiencing phase transition is suggested. The method includes the experimental determination of the charge amount transferred during the phase transition and the subsequent numerical estimation of apparent lithium diffusion coefficient for the same amount of charge in a hypothetic single phase.

The apparent diffusion coefficients of transition metal oxides undergoing phase transformation during charge-discharge process were determined at different temperatures to obtain the activation energy for lithium diffusion. The estimated values of diffusivity and activation energy are compared with those in the literatures and their validity is critically discussed. Furthermore, from the comparison with the activation energies for interfacial reactions estimated from the electrochemical impedance spectroscopy, main factors affecting power performance, esp. low temperature power decline of transition metal oxides are suggested.
Electrochemical Approach for the Synthesis of Carbon-Metal Fluoride Nanocomposites for Lithium Batteries
Authors: Munnangi Anji Reddy , Fichtner Maximilian
Published: February 2020

Metal fluorides are assuming importance as electrode materials for rechargeable lithium batteries as they possess high gravimetric and volumetric energy densities and are thermally stable. However, metal fluorides are insulators, exhibits sluggish kinetics and undergo large volume changes during electrochemical discharge and charge. Mechanochemical synthesis of carbon metal fluoride nanocomposites (CMFNCs) was suggested to address these problems [1]. Recently we reported a facile chemical approach for the synthesis of C-FeF2 nanocomposites by reductive intercalation method using CFx as a precursor [2]. The C-FeF2 nanocomposites obtained by this method showed high reversible lithium storage due to the incorporation of nanocrystalline FeF2 in electronically well-connected graphitic domains.

Here we propose and demonstrate a rather general approach for the synthesis of CMFNCs at room temperature using CFx as precursor. CFx is known as a cathode material for lithium primary batteries. During discharge process lithium reacts with CFx and form C+LiF. In other words this is an electrochemical method for the synthesis of C-LiF nanocomposites. Fundamentally, it is possible to extend this approach for the synthesis of other C-MFx nanocomposites if the reaction of metal with CFx is thermodynamically feasible provided with suitable metal ion transporting electrolyte. Figure 1 show the discharge curve obtained with CFx cathode and Fe metal foil as anode and Fe2+ transporting liquid electrolyte. During the discharge process the Fe2+ is released into the electrolyte at anode and the CFx is reduced at cathode to form C-FeF2. The discharged electrode was analyzed by XRD and formation of FeF2 is confirmed. The as synthesized C-FeF2 nanocomposites showed excellent reversible lithium storage properties. Further, we have succeeded in the synthesis of various C-MFx nanocomposites by the proposed electrochemical approach. 

References:

F. Badway, N. Pereira, F. Cosandey, G. G. Amatucci, J. Electrochem. Soc. 2003, 150, A1209.

M. Anji Reddy, B. Breitung, V.S.K. Chakravadhanula, C. Wall, M. Engel, C. Kübel, A. K. Powell, H. Hahn and M. Fichtner, Adv. Energy Mater.
2013, 3(3), 308.

Figure 1
Pore Collapse and Regrowth in Lithiated Si Anodes Determined By in-Operando Neutron Reflectometry
Authors: Dura Joseph A. , DeCaluwe Steven C , Dhar Bal-Mukund , Huang Liwei , Yang Kaikun , Owejan Jon , Zhao Yiping , Talin A. Alec , Wang Howard
Published: February 2020

Structure and composition changes of an 11 nm thick amorphous silicon (a-Si) thin film anode, capped with a 4 nm thick alumina film are measured, in operando, by neutron reflectometry (NR) and electrochemical impedance spectroscopy in a lithium half-cell.  NR data are analyzed to quantify the a-Si thickness and composition at various states of charge over six cycles. The a-Si anode expands and contracts upon lithiation and delithiation, respectively, while maintaining its integrity and low interfacial roughness (£1.6 nm) throughout the cycling.  The apparently non-linear expansion of the a-Si layer volume versus lithium content agrees with findings from previous thin-film a-Si anode studies.  However, a proposed pore collapse and regrowth (PCRG) mechanism explains apparently minimal volume expansion of the film as a whole for low Li content in terms of linear expansion of the solid domains within the initially porous amorphous Si. In the PCRG model, the porosity is first consumed by the expansion of solid domains upon lithiation, after which the film as a whole expands linearly with Li content with a proportionality factor found to be 8.48 cm3/mol-Li, which is similar to that of crystalline Si.  Porosity is reversibly reestablished at 5-28% upon delithiation. Data also show that the alumina protective layer on the a-Si film functions as an effective artificial solid electrolyte interphase (SEI), which maintains its structural integrity, low interfacial roughness, and a relatively small transport resistance. No additional spontaneously-formed SEI is observed in this study.
Electrochemical Impedance Spectroscopy Study of Failure of Commercial LiFePO4 Cells Under Overcharge Conditions
Authors: Liu Yadong , Li Zhe-Fei , Liu Qi , Xie Jian
Published: February 2020

One of the major problems remaining to be solved for the lithium-ion batteries (LIB) is the safety issue, especially, the failure of LIB cells under extreme conditions (overcharge, over-discharge, high temperature, low temperature, etc.). A Li-ion cell experiences overcharge/over-discharge when it is practically used in a battery pack for electric vehicles (EVs) hybrid electric vehicles (HEVs) because the capacity variation of different cells in the pack and difficulty to control the state of charge (SOC) of each single LIB cell/module in a battery pack exactly the same1,2.

Electrochemical impedance spectroscopy (EIS) was employed to investigate the failure phenomena of commercial 18650 Li-ion batteries at different states of charge (SOCs) under overcharge conditions. The change of voltage profile, discharge capacity, charge acceptance, temperature, and impedance were characterized and analyzed during overcharge cycles. During overcharge cycling, the charge acceptance, charging efficiency, cell temperature, and cycle life change dramatically with cycle numbers. The EIS results at different cycle numbers were characterized and analyzed (Fig. 1). Further study of the EIS for LiFePO4 cells at different SOCs (0, 50, and 100%) revealed that these de-convoluted parameters show similar patterns of changing with cycle numbers; and some of them, the Ohmic resistance, resistance of SEI, charge transfer resistance and Warburg coefficient, are associated with failure and can be used as indicators of incoming failures.  EIS results from both the two-electrode system and the three-electrode system were compared, demonstrating that the direct application of EIS to the practical 18650 LiFePO4 cells can lead to results as reliable as those obtained from the three-electrode system. The three-electrode result showed that impedance of the cathode is much higher than the anode, and both the impedance of anode and cathode increase significantly when the cell is failed caused by overcharge, which indicates that both the SEI on the anode surface and CEI on the surface of the cathode are changed a lot during overcharge process (Fig. 2). In short, the EIS can be an effective tool to monitor the state of health (SOH) of the battery or pack and issue an early warning signal before the failure happens.

Reference

1. P. G. Balakrishnan, R. Ramesh and T. Prem Kumar, Journal of Power Sources, 155, 401 (2006).

2. J. Chen, C. Buhrmester and J. R. Dahn, Electrochemical and Solid-State Letters, 8, A59 (2005).

Figure 1
Dual-Function Air Cathode for Metal-Air Batteries: Integrating Oxygen Reduction Catalysis with Pulse-Power Capability
Authors: Rolison Debra R. , Long Jeffrey W. , Chervin Christopher N. , Kucko Nathan W. , Nelson Eric S.
Published: February 2020

The air cathode in a metal–air battery is the lung of the energy-storage device—with power output limited by the transport of gas-phase molecular oxygen into the structure of the cathode, transport of dissolved molecular oxygen across the electrolyte-wetted electrode surface, and the rate at which that surface catalyzes electroreduction of O2. Too much electrolyte within the electrode structure confers pneumonia and an inability to sustain even moderate loads. Zinc–air at 400 W h kg–1 is an established battery technology with an energy density three times that of Li-ion, but its broader applicability is hampered by low specific power and limited rechargeability. We have solved the inability to recharge zinc without dendrite formation [1,2], but low specific power lies with performance limitations at the air cathode. We have solved this problem by departing from customary air-cathode fabrication approaches. We adopt a “multifunctional nanoarchitecture” design in which the solid and void components in a macroscale electrode structure are controlled and modified on the nanoscale to provide balanced pathways for electronic and ionic conductivity, facile permeation/transport of electrolyte and gas-phase O2 through a 3D interconnected void volume, and optimal electrocatalytic turnover for O2 reduction. We achieve this desirable blend of functionality by fabricating carbon-fiber paper filled with a pyrolytic carbon nanofoam. The nanofoam papers are produced in x–y scalable forms with variable electrode thickness (50–300 μm), tunable pore sizes (10–1000 nm), high specific surface areas (>400 m2 g–1), and a highly conductive carbon framework (>15 S cm–1) [3]. This electrode design not only improves performance for typical air-cathode operation via efficient O2 reduction catalysis at 10 nm–thick birnessite manganese dioxide (MnOx) “painted” onto the walls of the carbon nanofoam but also imparts new function: air-independent pulse power as derived from the pseudocapacitance of the MnOx coating. Manganese (III) sites in the post-pulsed oxide spontaneously recharge to Mn(IV) in the presence of oxygen—making the oxide ready and available for subsequent pulse-power discharge. The application of our “dual function” air cathode to alkaline Zn–air cells imparts pulse-power capability (>1 F cm–2for >10 s) otherwise absent in a battery that already provides the advantages of high energy density, low cost, and safety of operation.

This work was funded by the Office of Naval Research.

[1]   D.R. Rolison, J.W. Long, J.F. Parker, U.S. Patent Application #20140147757.

[2]   J.F. Parker, C.N. Chervin, E.S. Nelson, J.W. Long, D.R. Rolison, Energy Environ. Sci.
7(2014) 1117–1124.

[3]   J.C. Lytle, J.M. Wallace, M.B. Sassin, A.J. Barrow, J.W. Long, J.L. Dysart, D.R. Rolison, Energy Environ. Sci.
4 (2011) 1913.
Mass Transfer Overpotentials in Dispersed Pt/C and De-Alloyed PtNi/C Polymer Electrolyte Fuel Cell Cathodes
Authors: Wang Xiaohua , Peng Jui-Kun , Ahluwalia Rajesh , Myers Deborah J , Yang Zhiwei
Published: February 2020

While oxygen reduction reaction (ORR) mass activities, measured at high voltages, that exceed the DOE 2020 targets (>0.44 A/mg PGM @ 900 mV) have been demonstrated for carbon-supported Pt alloys and core-shell nanoparticle catalysts [1], the full performance of promising catalysts such as these have yet to be achieved in MEAs when operating at high current densities (> 1 A/cm2in air) [2]. To reach a high power output per gram PGM (8 kW/g, DOE 2017 Target), requires high utilization of the electrocatalytic sites as well as low oxygen transport resistance in the cathode catalyst layers. To determine the electrode properties limiting the performance of the de-alloyed PtNi/C based cathode, a standard Pt/C catalyst was annealed to grow the mean particle size to one that is comparable to that of d-PtNi/C catalysts (approximately 5.5 nm). Catalyst-coated membranes with cathodes comprised of a standard Pt/C, annealed Pt/C, and d-PtNi/C at loadings of 0.1 mg Pt/cm² with various ionomer to carbon ratios were fabricated, tested, and characterized under a variety of test conditions [3]. Modeling of these polarization curves to determine the sources of the observed voltage losses (i.e., purely resistive, kinetic, or mass transport) showed that mass transport losses are higher with d-PtNi/C and annealed Pt/C-based cathodes than standard non-annealed Pt/C, while the kinetic losses are lower for d-PtNi/C and standard non-annealed Pt/C as compared to the annealed Pt/C due to higher area-specific activity and higher enhanced surface area, respectively.

Acknowledgements

This work is part of a collaborative project with Johnson Matthey Fuel Cells, United Technologies Research Center, the University of Texas-Austin, and Indiana University-Purdue University of Indianapolis.  The authors wish to thank the U.S. Department of Energy’s Fuel Cell Technologies Office for support.  Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, under contract DE-AC-02-06CH11357.

References

Han, B.; Carlton, C.E.; Kongkanand, A.; Kukreja, R.S.; Theobald, B.R.; Gan, L.; O'Malley, R.; Strasser, P.; Wagner, F.T.; Shao-Horn, Y.; Energy Environ. Sci., DOI: 10.1039/c4ee02144d.

Debe, M.K.; Steinbach, A.J.; Hendricks, S.M.; Kurkowski, M.J.; Vernstrom, G.D.; Atanasoski, R.T.; Hester, A.E.; Haug, A.T.; Lewinski, K.A.; Deppe, S.K.; “Advanced Cathode Catalysts and Supports for PEM Fuel Cells”, DOE Hydrogen Program Annual Report 2012;

Myers, D.; Kariuki, N.; Ahluwalia R.; Wang X.; Peng J.-K.; “Rationally Designed Catalyst Layers for PEMFC Performance Optimization”, DOE Hydrogen Program Annual Report 2014;
Manufacturing Cost Analysis for Grid Storage: Lithium-Polysulfide Flow Battery
Authors: Ha Seungbum , Gallagher Kevin G.
Published: February 2020

Energy storage systems are increasingly seen as a critical component of the electricity grid to support extensive deployment of intermittent renewable energy such as solar and wind systems. The flow batteries with low cost and high energy density are promising for reaching these challenging energy storage target owing to their power and energy separation characteristics. Lithium-polysulfide (Li-PS) flow batteries are of particular interest due to their high theoretical energy density, and relatively inexpensive raw materials for grid storage applications. Unfortunately, present state-of-the-art technologies are too expensive for broad deployment. One possible pathway to reduced system costs is increasing manufacturing volume and engineering advancements. System cost reductions in manufacturing costs and associated overheads are identified as the single largest cost-savings opportunity for today's battery-based storage options. The simpler assembly process for a flow battery is projected to be a key distinguishing factor compared to enclosed cells. In addition, increasing production volume and market competition will lead to lower material costs. Here in, we examine in detail the manufacturing cost and additional mark-up of Li-PS flow battery by using techno-economic model, and it is compared to enclosed system(Li-ion) and aqueous flow battery(Vanadium redox flow battery). Here we show the consequences on system price breakdown to assess the cost benefits of simple assembly process and mass manufacturing, Figure 1.

Figure 1
Development of High Capacity Catholyte Material for Non-Aqueous Redox Flow Batteries
Authors: Huang Jinhua , Su Liang , Ferrandon Magali , Brushett Fikile , Burrell Anthony K. , Zhang Lu
Published: February 2020

Non-aqueous redox flow batteries (NRFBs) have attracted increasing attention due to their significant potential to integrate the renewable energy sources (e.g., solar and wind) into electrical grid. Unlike the traditional rechargeable batteries which store energy within solid electrodes, the active materials of NRFBs are stored in a flowable phase in two external tanks and pumped to a power-generating electroreactor. This configuration offers remarkable flexibility in terms of energy, power and even safety control. Material development of redox active molecules, especially redox active organic molecules (ROMs) is crucial to enable the extensive deployment of this energy storage technology. A family of dimethoxybenzene based molecules has drawn significant attention due to their excellent electrochemical behavior as NRFB catholytes. In this presentation, our recent efforts toward the high capacity catholyte material deriving from our previous research on 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxybenzene) will be discussed. The developing story of those new ROMs as well as their electrochemical reversibility, solubility, conductivity, and galvanostatic cycling will be covered.
Organic Sodium Based Flow Batteries Utilizing Transition Metal and Metal Free Complexes
Authors: Shamie Jack S , Shaw Leon , Liu Caihong , Sprenkle Vincent
Published: February 2020

The utilization of redox flow batteries (RFBs) for large scale energy storage has acquired much interest due to the large cycle life and flexibility in system via the decoupling of energy and power. Although RFBs show increasing promise, they suffer from low energy density due to the utilization of aqueous electrolytes which are limited in voltage due to hydrogen and oxygen evolution. A new hybrid sodium based flow battery has been developed which utilizes a molten sodium alloy anode separated from the flowing catholyte by a solid beta”-alumina membrane. An organic catholyte consisting of either transition metal complexes which can be cycled through several oxidation states or metal free organic complexes has been investigated in conjunction with the molten anode. Spectrographic techniques such as UV-Vis and IR absorption will be used to analyze the transitions at different states of charge and at various cycles to determine both the change in valence of the active species as well as the shift of chemical bonds which may affect the reversibility of the systems.
Electrochemical Modification of Carbon Surfaces with Functional Polymers
Authors: Devadoss Anando , Xue Cuihua , Tsai Han-Kuan
Published: February 2020

Surface modification of carbon materials with biological molecules under ambient condition is desirable for construction of biosensor and bioelectronic devices. Some of the desirable factors for surface modification are (i) robust attachment of biomolecules for stable biosensor response, (ii) high surface coverage of biomolecules for good signal/noise ratio and wide dynamic range, and (iii) rapid modification under ambient condition for facile and scalable manufacturing.

A new method to electrochemically modify carbon electrodes using a benzothiadiazole-based conjugated polymer will be discussed. The method provides rapid modification of carbon materials with biomolecules, robustly attached to the surface through the polymer. The usefulness of the method will be demonstrated by construction of an electrochemical cholesterol biosensor. The biosensor exhibits amperometric detection of cholesterol in buffer and serum samples in presence of a soluble mediator. Details regarding the preparation of biomolecule-coupled polymer, surface modification and sensor performance will be discussed.
The Mechanism of Electrochemical Oxygen Reduction: A Combined DFT and in-Situ ATR-IR Study on Model Semiconductor Surfaces Ge(100) and ZnO
Authors: Biedermann P. Ulrich , Nayak Simantini , Erbe Andreas
Published: February 2020

The electrochemical oxygen reduction reaction (ORR) is a fundamental reaction with relevance in many fields including fuel cells and corrosion.  The reaction mechanism is controversially debated and strongly dependent on the electrocatalytic surface, electrolyte, pH and applied potential.  Many studies have focused on high-performance noble metal catalysts, however, semiconducting oxides often form at the metal/electrolyte interface.  Therefore we have studied the ORR mechanism at model semiconductor electrodes, using a combination of in-situ attenuated total reflection infrared (ATR-IR) spectroscopy and DFT modeling.  We have identified several reaction intermediates on the n-type Ge(100) surface [1,2] and on zinc oxide by their characteristic vibrational modes. 

The reaction mechanism in terms of elemental steps of electron transfer and proton transfer and hence including charged intermediates is studied with DFT. The model is based on small clusters representing the surface interacting with the solvated ORR intermediates.  Solvent effects were treated by a combination of explicit water molecules and a self-consistent reaction field approach.  The influence of pH and electrode potential on the energetic course of the ORR reaction is analysed.  We identify the catalytically active surface site and propose a detailed catalytic cycle in terms of electron transfer, proton transfer and bond breaking/forming as elemental steps.  The calculated IR-frequencies agree well with our experimental results. 

[1]    S. Nayak, P.U. Biedermann, M. Stratmann, A. Erbe, Pys. Chem. Chem. Phys. 15, 5771 (2013)

[2]    S. Nayak, P.U. Biedermann, M. Stratmann, A. Erbe, Electrochimica Acta 106, 472 (2013)
Using Vapor-Grown RuxPty and RuxPdy Nanoparticles to Investigate the Hydrogen Oxidation Reaction Mechanisms in Alkaline Electrolyte
Authors: St. John Samuel , Atkinson Robert W. , Unocic Raymond R , Papandrew Alexander B. , Zawodzinski Thomas A.
Published: February 2020

We have developed a method for the synthesis of metallic and alloy nanoparticles dispersed on carbon supports that is based on a chemical vapor deposition process. This technique is applied here to investigate the mechanism of the hydrogen oxidation reaction (HOR) in alkaline media for which competing theoretical frameworks have been proposed in the literature. Such frameworks either hypothesize that molecular hydrogen dissociative adsorption (Tafel step) is rate limiting or that electron transfer (Volmer/Heyrovsky step) is rate limiting.

Our objective was to elucidate the HOR reaction mechanism using Tafel slope data collected in alkaline media while using small changes in alloy composition to look for trends in the changes of M-H binding energy as a descriptor for activity changes. Such data will be used to inform future in situ investigations of adsorbate coverage and binding energy using x-ray spectroscopy.

Pt, Pd, Ru, as well as alloys of RuxPty and RuxPdy nanotubes were synthesized from metal-organic precursors onto Vulcan carbon support. Standard electrochemistry was conducted in conventional three-electrode cell hardware with a working electrode deposited onto glassy carbon with a Pt wire counter electrode and a double-junction Ag/AgCl reference electrode. Electrochemical data were collected at 2500 rpm under 1 atm H2 in 0.1M KOH at 1 mV/s to minimize the contribution from capacitive currents. HOR activity was measured using staircase voltammetry, averaging the sampled current over the last 20% of the dwell time. Data were fit according to the standard Tafel analysis approach to determine Tafel slope along with fits by specific electrochemical models particular to a Tafel or Volmer rate-determining step.

HAADF-STEM images of the nanoparticles and XRD data suggest alloyed nanoparticles with some intraparticle atomic clustering. Electrochemical charging currents were consistent with similar surface and bulk compositions. The activity results revealed that the rate-determining step depends upon the choice of alloy materials and that both mechanisms present themselves accordingly. Additionally, the Pt-rich alloys with Ru exhibited HOR activity several times higher than pure Pt and comparable to the mass-transport limited current. These results suggest not only that a low-cost, alkaline anode catalyst is possible, but also that it is tantalizingly close to reality.
Layer-By-Layer Assembled Enzyme Cascade for Catalyzing Oxidation of Sucrose for Biofuel Cells
Authors: Zhang Yuanyuan , Arugula Mary , Williams Shannon , Simonian Aleksandr
Published: February 2020

Feasibility of layer-by-layer (LbL) assembly via electrostatic interaction in development of multi-enzyme based biosensors was successfully demonstrated in our previous research. In this study, application of LbL technique was extended for the first time in assembly of multi-enzyme, invertase (INV) and NAD+-dependent glucose dehydrogenase (GDH) for cascade catalytic oxidation of sucrose for biofuel cell application. The system was constructed through LbL assembly of electrostatically interacted INV and GDH armored multi-walled carbon nanotubes (MWCNT-INV and MWCNT-AChE) with a set of cushioning bilayers consisting of MWCNT-polyethyleneimine (PEI) and MWCNT-DNA on screen printed electrode (SPE). The LbL architecture shows great advantages for sequential enzymatic reaction that it favors the efficient penetration of substrate and products in a cascade system. The utilization of MWCNT facilitates the direct electron transfer from sucrose oxidation and enhances the current generated. The current density of 104.08±0.85 μA/cm2 using Amperometry was currently achieved with 50 mM sucrose and 1 mM NAD+ on SPE with a surface area of 0.2 cm2 in PB buffer 6.0 at room temperature. The current density of LbL assembled electrode can be further improved by optimization of buffer pH, concentration of NAD+ as well as sucrose concentration. Therefore, the results indicated that the versatile LbL assembly is a simple and efficient way to co-immobilize CNT-multi-enzyme for cascade system, showing great potential in enzymatic biofuel cell development.
Fabrication of Thermally Stable Ultra-High Density Particle-in-Cavity Nanostructure with Tunable Size and Density
Authors: Xu Cheng , Wong Justin C. , Zhao Yang , Li Luping , Ziegler Kirk J
Published: February 2020

This work reports a simple and effective method to fabricate large scale particle-in-cavity (PIC) nanostructure with tunable size from 10-100 nm. By using pre-patterned anodized alumina template (AAO) as a mask for reactive ion etching, the hexagonally ordered nanoporous structure can be transferred onto various substrates including glass, ITO-coated glass, and silicon. With the protection of an organic polystyrene layer, the AAO template can be easily transferred with great consistency and minimal contamination. This method also provides versatility in fabricating multiple unique nanostructures depending on the choice of gas used for RIE. Additionally, the nanoparticles can be deposited into nano-cavities using a variety of techniques such as e-beam evaporation, sputtering with annealing or spincoating of pre-made nanoparticle suspension. Furthermore, Au PIC nanostructure has demonstrated excellent thermal stability compared to Au nanoparticles deposited on flat surface. This method provides great potential not only for the investigation of nanopatterning and nanoparticle assembly but also for enhanced surface Raman scattering and many nanowire based devices including sensors, electronics and photovoltaics.
Investigation of Mass Transport in Mesoporous Semiconducting Thin Film Electrodes
Authors: Meunier Carl , Roberts Ethan , Remsen Edward E. , Haverhals Luke M.
Published: February 2020

Development of novel thin film electrodes may enable new commercial products ranging from in vivo biosensors to solar cells.  A critical consideration that assists the engineering of working devices is mass transport of electro-active species and solvent/electrolytes within porous thin film electrodes.  Our presentation will focus on the fabrication and characterization of transport within thin film electrodes fabricated from titanium dioxide nanospheres, nanorods and nanotubes via sol-gel methods.  We will present initial characterization data for films deposited on indium tin oxide coated glass slides by doctor blade techniques.  Results include bright field and phase microscopy characterizations that probe the pore structure, surface morphology, and that yield physical dimensions of the films. Electron microscopy data will be presented that characterize particle dimensions and morphological differences resulting from multiple processing procedures.  Powder x-ray diffraction data will be presented that investigate the crystal structure of the semiconducting films.  Finally, mass transport properties as investigated by cyclic voltammetric techniques will be presented.  Results will be correlated with fabrication techniques and associated material types and morphologies.
Study of the Kinetics of Redox Active Polymers in Non-Aqueous Media Under High Mass-Transfer Conditions Using Scanning Electrochemical Microscopy
Authors: Lichtenstein Timothy , Rodríguez-López Joaquín
Published: February 2020

We present on the use of Scanning Electrochemical Microscopy (SECM) to quantify the reaction kinetics of redox active polymers with molecular weights between 21 and 318 kDa that have been shown as promising mediators for non-aqueous redox flow cell batteries. [1] The promise of these mediators is that they are highly soluble in cost effective organic solvents, e.g. up to 2.7 M in acetonitrile, have tunable size, and reversible electrochemical behavior. However, it is not well understood how the kinetics of electron transfer, and its mechanisms, might change on these polymers with increasing size and concentration. Experiments have also shown that these polymers produce electroactive films on Pt and C electrodes, therefore elucidating the charge transfer properties of these films is important in evaluating their electrochemical performance under flow conditions. SECM can be used by combing the information obtained from approach curves in the feedback mode with the steady state voltammetry at ultramicroelectrodes of known size to determine the electron transfer rate and other kinetic information. [2] Imaging of polymer films in the feedback mode can also complement with useful information about the heterogeneity of charge transfer and charge transport on working electrodes. Fundamental knowledge of the kinetics of redox active polymers allows for better prediction of the effects of size and functionalization for analogous systems.

[1] Gavvalapalli, N.; Hui, J.; Cheng, K.; Lichtenstein, T.; Shen, M.; Moore, J.S.; Rodríguez-López, J. J. Am. Chem. Soc. 2014, 136, 16309-16316

[2] Mirkin, M. V.; Bard, A. J. J. Anal. Chem.
1992, 64, 2293–2302.
Charge-Transfer and Photocatalytic Hydrogen Production By Hydrogenase Photobiohybrids
Authors: King Paul W , Brown Katherine A , Mulder David W , Ratzloff Michael W , Lubner Cara
Published: February 2020

Hydrogenases are metalloenzymes that catalyze H2 activation at of ≥104 s-1 using base metals (Fe, Ni, S) and a polypeptide framework. Understanding the structural properties of hydrogenases, including the cataltyic site cofactors, has provided inspiration for designing highly functional synthetic catalysts. We have been invetigating hydrogenase structure-function and use as electrocatalysts on nanostructured electrodes, and photocatalysts in solution-phase assemblies with nanomaterials. In both cases, the hydrogenase provides the catalytic power for converting photo(electro)chemical energy into H2. The chemistry of (nano)materials can be used control their physical and molecular properties over a wide-range of energy and size scales for integrating with the catalytic and sturctural propeties of hydrogenases. As a result, the biohybrid complexes are being investigated as models to determine how material compositions, charge-transfer interfaces and bulk properties affect the mechanisms that support photocatalysis. A summary of our recent progress in this area of research will be presented.
Controlled Layer-By-Layer Polymer/DNA Coating of Carbon Nanotubes for Gene Delivery Applications
Authors: Majedi Fatemeh Sadat , Keshvari Hamid , Hasani-Sadrabadi Mohammad Mahdi , Renaud Philippe , Tayebi Lobat
Published: February 2020

Considering the growing attention toward gene delivery, different vectors have been developed; viral and non-viral. Although viral vectors have shown higher DNA transfection efficacies, but features such as their complicated preparation procedure, the risk of being immunogenic, and their limited capacity for gene transfer, has led scientists to think about non-viral carriers. Using nanoparticles as genetic carriers introduced a new era in this field. Due to their ease of functionalization, less toxicity, and higher capacity, nanoparticles are now considered as suitable carriers for gene delivery. Moreover, one-dimensional nanomaterials have proved to have better cell internalization. As an interesting method to form or manipulate polymeric nanoparticles, we have recently developed microfluidic devices for having adjustable and uniform particles at nanoscale. Applying variable central and lateral flows, the resulted particles can be tuned as our desires.  In the present work, we have used short length carbon nanotubes (CNTs) as our carrier due to its needle like structure that makes it suitable for cell internalization. Then it is coated it in a layer-by-layer procedure, through sequentional microfluidic platform, with Chitosan (decorate CNT with positive charges), plasmid DNA, and again Chitosan (protect DNA and provide positive charges). The first chitosan layer balances the charge for better DNA interaction, performed in the first micromixer, and the final chitosan coat, which is done in the third micromixer, tunes the charge for better cell internalization. The results confirm the ability of our microfluidic systems to finely tune the coating thickness (in each step), DNA loading content, and the overall charge of these vectors which can affect the protein expression of target cells.
(Invited) Anti-Ambipolar, Gate-Tunable p-n Heterojunctions
Authors: Hersam Mark C.
Published: February 2020

The recent emergence of two-dimensional (2D) materials has enabled the realization of atomically thin heterostructure devices [1].  Of particular interest are heterojunctions based on p-type and n-type semiconductors since these devices possess non-linear, gate-tunable transport characteristics. Here, we demonstrate a gate-tunable p-n heterojunction diode using thin films of semiconducting single-walled carbon nanotubes (s-SWCNTs) and single-layer molybdenum disulfide (SL-MoS2) as p-type and n-type semiconductors, respectively [2]. The vertical stacking of these two direct band gap semiconductors forms a heterojunction with electrical characteristics that can be tuned with an applied gate bias over a wide range of charge transport behavior ranging from insulating to rectifying with forward-to-reverse bias current ratios exceeding 104. The transfer characteristic of this p-n heterojunction shows a unique 'anti-ambipolar' behavior with two off-states at either extreme of the gate voltage range and a current maximum in the middle. The continuous transition from positive to negative transconductance in an anti-ambipolar characteristic enables operation of analog communication circuits with a reduced number of circuit components compared to unipolar transistors. Anti-ambipolarity can be widely generalized to heterojunctions of other materials such as s-SWCNTs and n-type amorphous indium gallium zinc oxide (a-IGZO), ultimately leading to all solution processed p-n heterojunctions at the wafer scale [3].

[1] D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, "Emerging device applications for semiconducting two-dimensional transition metal dichalcogenides," ACS Nano, 8, 1102 (2014).

[2] D. Jariwala, V. K. Sangwan, C.-C. Wu, P. L. Prabhumirashi, M. L. Geier, T. J. Marks, L. J. Lauhon, and M. C. Hersam, "Gate-tunable carbon nanotube-MoS2 heterojunction p-n diode," Proc. Nat. Acad. Sci. USA, 110, 18076 (2013).

[3] D. Jariwala, V. K. Sangwan, J.-W. T. Seo, W. Xu, J. Smith, C. H. Kim, L. J. Lauhon, T. J. Marks, and M. C. Hersam, "Large-area, low-voltage, anti-ambipolar heterojunctions from solution-processed semiconductors," submitted, 2014.
Covalent Functionalization of Graphene
Authors: Hirsch Andreas
Published: February 2020

We will report on new covalent functionalization concepts for graphene. For this purpose we reductively activate graphene to generate metal graphenides. These intermediates can be quenched by electrophiles such as diazonium compounds, alkyl iodides, iodonium salts, protons and bromine. For the representative structural characterization of the reaction products we have developed statistical Raman spectroscopy and Raman microscopy together we TGA/MS/GC. This allows us to determine not only the precise degree of functionalization but also allows for the investigation of the spatially resolved product homogeneity. In some case the degree of functionalization is so high that yellow fluorescent graphene derivatives were obtained.