bluuebunny/crossref_metadata_2025 huggingface dataset:
Charge Transfer Kinetics in LiFePO4 Porous Electrodes: Butler-Volmer Equation Vs Marcus Theory
Authors: Bai Peng , Bazant Martin Z.
Published: February 2020

The local rates of charge transfer in carbon-coated LiFePO4 porous electrodes are extracted from chronoamperometry experiments by a simple statistical theory,1 which yield curved Tafel plots that cannot be explained by the standard Butler-Volmer (BV) model for lithium intercalation. The microscopic Marcus-Hush-Chidsey (MHC) model,2 however, accurately captures the deviation from the Tafel slope (α=0.5) at overpotentials larger than 150mV. The fitted reorganization energy is in excellent agreement with the Born solvation energy for electron transfer between the carbon coating and the Fe2+/Fe3+ redox site estimated from first principles dielectric properties, which implies that the kinetics are limited by electron transfer at the solid (carbon) – solid (LixFePO4) interface, rather than by lithium ion transfer at the liquid (electrolyte) – solid interface, as previously assumed. This discovery suggests the need for a paradigm shift in mathematical modeling of electrochemical systems, replacing the BV equation with quantum mechanical theories of electron transfer3 and incorporating statistical effects of non-equilibrium thermodynamics.4 The proposed method of chronoamperometry and Tafel analysis generalizes Chidsey’s method for homogeneous monolayers and allows fundamental rate constants to be determined for phase-transforming particles and porous electrodes.

References

1. Bai, P., Tian, G.Y. Statistical kinetics of phase-transforming nanoparticles in LiFePO4 porous electrodes. Electrochim. Acta
89, 644-651 (2013).

2. Chidsey, C.E.D. Free-Energy and Temperature-Dependence of Electron-Transfer at the Metal-Electrolyte Interface. Science
251, 919-922 (1991).

3. Marcus, R.A. Electron-Transfer Reactions in Chemistry - Theory and Experiment. Reviews of Modern Physics
65, 599-610 (1993).

4. Bazant, M.Z. Theory of Chemical Kinetics and Charge Transfer based on Nonequilibrium Thermodynamics. Acc. Chem. Res.
46, 1144-1160 (2013).

Figure

Tafel plot of the reaction rates extracted from chronoamperometry experiments, which deviate from the Butler-Volmer (BV) model, but can be captured by the Marcus-Hush Chidsey (MHC) model. Overpotentials are scaled to the thermal voltage kBT/e≈25.7mV.
Modular Electrolyte Additives: Decoupling Uniform Deposition and Stability
Authors: Cheng Gang , Kaye Steven S. , Li Bin
Published: February 2020

The stability and cycle life of lithium-ion batteries are limited by unfavorable reaction between the electrodes and electrolyte. To reduce this problem, electrolyte additives are used to passivate the cathode and/or anode with a protective coating. To function effectively, such additives must both deposit uniformly on the electrode surface and form an electrochemically inert coating. These dual constraints severly limit the set of viable additives.

Wildcat Discovery Technologies has developed a new, modular additive concept in which additives are bound to a molecular core that enables uniform deposition on the electrode surface. Attachment of conventional additives to the core molecules provides improved SEI stability, increasing coulombic efficiency, cycle life, and thermal stability. Furthermore, by decoupling the requirements for uniform coating and chemical stability, new classes of additives can be used. In this talk, I will discuss the development of these modular additives as well as their performance with a both commercial and future cell chemistries.
Fluoroethylene Carbonate As an Promising Additive for γ-Butyrolactone based Electrolytes
Authors: Kasnatscheew Johannes , Wagner Ralf , Winter Martin
Published: February 2020

Compared to the actual state of the art electrolyte (SOTA) for lithium ion batteries (LIBs), a novel electrolyte with better safety and lower costs and at the same time equal electrochemical performance was developed and investigated in this work. This electrolyte consists of a mixture of γ-Butyrolactone (GBL) as a solvent with fluoroethylene carbonate (FEC) as solid electrolyte interphase (SEI) additive and lithium tetrafluro borate (LiBF4) as electrolyte salt. Raman spectroscopy measurements indicated that the salt is completely dissociated by the solvent GBL which is the reason for the enhanced ionic conductivity compared to the SOTA electrolyte. The oxidation stability of this mixture is sufficient for the use in actual LIBs. Cyclic voltammetry with a T44 graphite electrode revealed the positive influence of the SEI additive FEC. The addition of FEC (1 % by wt.) enabled fully reversible de-/ intercalation of lithium ions into graphite. Furthermore, 1 M LiBF4 in GBL + FEC (1 % by wt.) improved the coulombic efficiency of T44 graphite in the first cycle of constant current cycling experiments and in addition, no capacity fading was observed after 50 cycles. On NCM electrodes a stable cycling was observed as well, obtaining similar performance compared to the SOTA electrolyte, even at an increased cut-off potential of 4.6 V vs. Li/Li+.
Zinc-Cobalt Alloy Deposited on the Titanium Surface As Electrocatalysts for Borohydride Oxidation
Authors: Tamasauskaite-Tamasiunaite Loreta , Lichusina Svetlana , Balciunaite Aldona , Zabielaite Ausrine , Simkunaite Dijana , Vaiciuniene Jurate , Selskis Algirdas , Norkus Eugenijus
Published: February 2020

The present work is focused on the investigation of the electrochemical oxidation of borohydride in alkaline solution on low-cost ZnCo alloy deposited on the titanium surface (denoted as ZnCo/Ti). The ZnCo alloy coatings with the thickness of ~5 µm were deposited on the titanium surface (1 x1 cm) via electrodeposition from the electrolyte described in Ref. [1]. Prior to ZnCo alloy deposition, the titanium plates were degreased with acetone and then pretreated in diluted H2SO4 (1:1 vol) at 90 oC for 10 s. Cobalt coatings with the thickness of ~3 µm were deposited from the same electrolyte [1] with only difference that zinc ions were excluded from the plating bath.

The morphology, structure and composition of the prepared catalysts were examined by FESEM, EDS and ICP-OES. Activity of the fabricated catalysts was investigated towards the oxidation of borohydride by means of cyclic voltammetry and chronoamperometry.

It was found that the ZnCo alloy coating, electrodeposited on the titanium surface, consists of ~81.3 at. % of Zn and ~16.1 at. % of Co.

It has been determined that the Co/Ti and ZnCo/Ti catalysts catalyzes oxidation of H2 generated by catalytic hydrolysis of BH4
– and direct BH4
– ions oxidation. Notably, the H2 oxidation current densities measured on both catalysts are similar and reach up to 60 mA cm–2, whereas, the borohydride oxidation current densities are ~3-6 times higher on the ZnCo/Ti catalysts than those obtained on the Co/Ti catalyst. The chronoamperometry and chronopotentiometry studies also confirmed a high electrocatalytic activity of the ZnCo/Ti catalyst for the direct electro-oxidation of BH4
– ions as compared to that of Co/Ti electrode.

The ZnCo/Ti catalysts are promising low-cost anode material for direct borohydride fuel cells.

References

[1] E. Juzeliûnas, S. Lichušina. Patent of the Republic of Lithuania No. 5481 26.03.2008.
Analysis of Polarization and Impedance Under Phosphine Induced Anode Degradation in a Planer SOFC
Authors: Sezer Hayri , Celik Ismail Bektas , Yang Tao , Pakalapati Suryanarayana Raju
Published: February 2020

An in house three dimensional computational model for planar solid oxide fuel cells, DREAM SOFC, is used to predict the phosphine induced performance degradation in large planar cells. The empirical model parameters are calibrated for one dimensional button cell code by using available experimental data for button cell. These parameters are used in DREAM SOFC to perform degradation simulations for planar cells. These calculations are based on a cell level model which includes anode, electrolyte, cathode, and interconnect components of the cell. The V-I curves obtained at different points on the degradation curve shows that while PH3 coverage increases the voltage losses increase, slowly at first and sharply after some time. The impedance curves predicted for a typical button cell shows impedance response of anode supported the cell while anode is exposed to phosphine. Anode and cathode losses are significantly visible from the impedance calculations. These impedance calculations show that the increase in the activation losses in the anode is the major loss for the cell degradation and they increase sharply during faster degradation regime. This study focus on a similar study on a relatively large planar cell.
Modeling of Transport Mechanisms in SOFCs with Microstructure Reconstruction of Porous Electrodes
Authors: Yang Tao , Celik Ismail Bektas , Pakalapati Suryanarayana Raju , Gerdes Kirk
Published: February 2020

In this study, different mass and charge transport mechanisms for SOFCs are analyzed. Various reaction mechanisms are used on both anode and cathode with properties obtained from microstructure reconstruction of porous materials. Micro scale dynamics modeling of oxygen reduction on LSM/YSZ composite cathodes and detailed reaction mechanisms on anodes are incorporated in our simulation. To be more realistic, the microstructures of porous electrodes are reconstructed based on experimental observations, and the corresponding properties, e.g. specific interface area and porosity, are included in our simulation. With the validation of our full cell model by comparing with the results of other simulations and experiments, we predict the performances of SOFCs, e.g. concentrations, polarization, electrochemical impedance etc. Moreover, a parametric study is performed with the full cell model using different distributions of porosity. The resulting amplitude and frequency of impedance changing with the different porosity distributions are analyzed. The results obtained further better understanding of the processes that occur in SOFCs.
Density Functional Theory Studies of Formic Acid Oxidation on Pd (111), (100) and (110) Facet
Authors: Huang Shanqisong , Hu Chenyao
Published: February 2020

In the last fifty years, great interest and investment have been devoted to direct formic acid fuel cells (DFAFC) for its high-energy conversion efficiency, low operating temperature, low pollutant emission, ease of handling and processing of the liquid fuels, and integrated well with the existing energy infrastructure[1-3]. The electro-oxidation of formic acid in DFAFC is currently being investigated by many research groups.

Pd is the one of the most promising anode catalysts used in DFAFC due to its higher formic acid oxidation activity and excellent CO tolerance[4]. However, the study of structure sensitivity of formic acid oxidation on Pd (111), (100) and (110) facet is rare. So weather the dsorption behaviors and oxidation mechanisms of formic acid on different Pd facets are the same.

In the present study, we calculated the adsorption and decompostion of formic acid on the Pd (111), (100) and (110) Facet. The results show that Pd (100) is the best facet for the dissociation of formic acid, which means the (100) facet exhibit the highest activity toward the formic acid electrooxidation.

Reference

[1] Chen, X. et al., J. Am. Chem. Soc., 133(11), 3693 (2011).

[2] Maiyalagan, T. et al., J. Power Sources, 211, 147 (2012)

[3] Mazumder, V. et al., Nano Lett., 12(2), 1102 (2012)

[4] Yang, J. et al., J. of Mater. Chem., 21(10), 3384 (2011)
Local Proton Conductance in the Proton Exchange Membranes: A Density Functional Study
Authors: Singh Raman Kumar , Tsuneda Takao , Miyatake Kenji , Watanabe Masahiro
Published: February 2020

The performance of the proton exchange membrane fuel cells (PEMFCs) is closely related to the performance of the proton exchange membranes and many researchers have focused on the development of new proton-conducting polymer membranes as an alternative to Nafion (DuPont) membranes. Recently, the multiblock sulfonated poly (arylene ether sulfone)s (SPE) containing highly sulfonated hydrophilic component seem to be very promising candidates and have shown many advantages over Nafion. However, their proton conductivities are still lower than Nafion at low relative humidity conditions.1 To make clear why perfluorinated polymer membrane Nafion is superior to other membranes in the proton conductivity at low humidity, we firstly compared their hydrated structures. It was found that minimum three water molecules are needed to detach a proton from the sulfonic acid group in both membranes and the SPE membrane has two types of the sulfonic acid groups: active “separated” and inactive “paired” groups for proton conductance. To explore the possibility of the proton conductance in the vehicle mechanism at low humidity, we examined the relay model (Fig. 1) of protonated water clusters between the sulfonic acid groups in Nafion and found that it needs 33 kcal mol-1, which is common in usual reactions. This seems to indicate that relay model may contribute to the high proton conductivity of Nafion at low humidity.2

[1] K. Miyatake, B. Bae and M. Watanabe, Polym. Chem., 2011, 2, 1919.

[2] R. K. Singh, T. Tsuneda, K. Miyatake and M. Watanabe 2013 (Submitted)
INVITED TALK - In Situ Electronic Structure Measurements and Correlations to Reactivity on Hetero-Structures for Solid Oxide Fuel Cells
Authors: Yildiz Bilge , Chen Yan , Ma Wen , Kim Jae Jin , Tuller Harry L.
Published: February 2020

Strontium-doped lanthanum cobaltite is one of the most promising cathode candidates for intermediate temperature solid oxide fuel cells. Recently, the hetero-interfaces between the perovskite (La,Sr)CoO3 (LSC113) and the Ruddlesden-Popper (La,Sr)2CoO4 (LSC214) phases have shown highly enhanced oxygen exchange kinetics. This observation offers the potential for a new class of cathode structure design, either via multilayering or by forming vertical heteroepitaxial nanocomposites, with high densities of these special interfaces. In this work, nanoscale multilayers and vertically aligned nanocomposites of LSC113/
214 have been prepared by pulsed laser deposition. Their surface chemistry was characterized by Auger Electron Spectroscopy with high spatial resolution, and their surface electronic structure was probed by scanning tunneling microscopy at elevated temperatures and in oxygen gas. The intimate contact of LSC214 to the LSC113 phase, rendered the charge transfer on the LSC214 surface to be more facile, contributing to enhanced oxygen reduction reactivity near the LSC113/
214 interfacial regions intersecting the surface. The enhancement of the ORR kinetics is also confirmed by EIS measurement at relatively low temperatures below 400 oC. The surface chemistry at higher temperatures ages by time and hides the improvements that arise from the coupling of these two phases through their interface. These observations lead to a novel means for SOFC cathode fabrication with enhanced performance and provide guidelines for identifying other promising cathode candidates.
Effect of Sintering Atmosphere and Particle Size on the Ionic Conductivity of Gadolinia-Doped Ceria
Authors: Batista Rafael Morgado , Muccillo Eliana Navarro Santos
Published: February 2020

Gadolinia-doped ceria has been intensively investigated over the last decades as a promising electrolyte and electrode material for intermediate-temperature solid oxide fuel cells [1]. The sintering behavior of this solid electrolyte in reducing atmosphere is different from that in air, because of the reduction of Ce4+ to Ce3+[2]. In this case, changes in the microstructure and in the related properties are expected to occur, due to variation in the oxygen-vacancy concentration.

In this work, the effects of the sintering atmosphere and the particle size of powders on densification and ionic conductivity of Ce0.9Gd0.1O2-δ were systematically investigated.

Ce0.9Gd0.1O2-δ commercial powders (>99.5%, Fuel Cell Materials) with specific surface area ranging from 7.4 to 210 m2.g-1were used as starting materials. Cylindrical pellets were prepared by uniaxial and isopressing following by sintering at 1250°C for 2 h under different atmospheres.

The average initial particle size of the powders was evaluated by nitrogen adsorption (Quantachrome, NOVA 1200) using the BET method. Characterization of the sintered materials was carried out by density measurements, thermodilatometry (Anter-1161, Unitherm), electronic Raman spectroscopy (InVia Raman microscope, Renishaw), electron paramagnetic resonance (Bruker-EMS), field-emission scanning electron microscopy (FEI, Inspect F50) and impedance spectroscopy (HP4192A). The mean grain size was estimated by the linear intercept method.

The sintered pellets reached relatively high densities (93 to 97% of the theoretical value) independent on the sintering atmosphere. The particle size determined by nitrogen adsorption of the starting powders was: 112, 23 and 4 nm for powders, hereafter named S1, S2 and S3, respectively. The linear shrinkage curves show that good densification of gadolinia-doped ceria is attained depending on the initial size of the powder particles. However, for isothermal treatments the densification is homogenized and all sintered pellets reached high values after 1250°C for 2 h.

All investigated properties changed to some extent with the sintering atmosphere and the initial particle size of the starting powders. The grain conductivity, for example, of Ce0.9Gd0.1O2-δ pellets sintered in air and under inert atmospheres (argon and nitrogen) exhibit the same bulk conductivity not depending on the sintering atmosphere, in spite of the changes observed in the electron paramagnetic signal.

References

[1] H. Yahiro, Y. Eguchi, K. Eguchi, H. Arai, J. Appl. Electrochem. 18 (1988) 527.

[2] Z. He, H. Yuan, J. A. Glasscock, C. Chatzichristodoulou, J. W. Phair, A. Kaiser, S. Ramousse, Acta Mater. 58 (2010) 1866.
Zirconia Sensor Device for In Situ Monitoring of Metalpowder Oxidation for Energy Storage Applications
Authors: Milshtein Jarrod David , Basu Soumendra Nath , Gopalan Srikanth , Pal Uday Bhanu
Published: February 2020

A zirconia oxygen sensor was designed to monitor the gas-solid oxidation reaction characteristics of metal/metal-oxide powder beds for energy storage applications. Energy is stored in the metallic state and released during oxidation. This in-situ monitoring device allows for determination of the oxidation state of the metal oxides during reactions in real time, as well as calculation of the chemical reaction rate constants. The signal output of the sensor was analyzed for oxidation of and diffusion into the powder bed. The oxygen transport mechanisms occurring inside the sensor were described to further understand the signal outputs from the sensor. Two metal/metal-oxide systems were examined using this device to demonstrate its performance. The simple Ni/NiO system was chosen to demonstrate feasibility, and the complex W/WO3 system was chosen to demonstrate versatility of the sensor for actual energy storage applications.
Effect of Doping and Preparation Methods in Solid Electrolyte for Lithium Batteries
Authors: Beck Faith , Dontigny Martin , Zaghib Karim , Wang Donghai , Paranthaman Mariappan P , Goodenough John B. , Manivannan A.
Published: February 2020

Recently, solid electrolytes with reasonable room temperature lithium ionic conductivity are being examined for high energy density batteries with safe operation. Several solid state electrolytes based on sulfides and oxides have been investigated [1]. Among them, Garnet phase materials have shown significant improvement in conductivity [2]. Garnet has cubic and tetragonal phases of which the cubic is high temperature with a high ionic conductivity value of 10-4 S/cm [3]. Several doped compositions have also been reported in order to improve the cubic phase ionic conductivity [4]. LLTO Perovskite system has also been reported for high ionic conductivity value of 10-4 S/cm [5,6]. Currently, we have synthesized a Ti, Cr, Ta doped Li7La3Zr2O12and LLTO by a simple Pechini process to investigate their ionic conductivities.

A Pechini method was used to synthesize these compoundsusing nitrate salts, ethylene glycol and citric acid in a 38:36:26 ratio respectively in de-ionized water. The samples were dried in an oven overnight at 120°C and then heat-treated at different temperatures to achieve the desired phases. The optimized product was heat treated at 1000°C for six hours, pelletized and then sintered again at higher temperatures (1200°C) to perform the ionic conductivity measurements using impedance spectroscopy.

Samples were characterized by XRD for phase analysis and electrochemical impedance performance has been investigated under varying temperatures and voltages. The effect of doping on the phase transition in LLZO and LLTO will be presented. Figure 1 shows the impedance plot for the Ta doped garnet (Li7La3Zr1.5Ta.0.5O12) at room temperature. Ionic conductivity value of 1.27(x10-4) S/cm has been obtained.

Detailed impedance measurements on systematic doping of Ti, Cr, Ta etc. in LLZO and LLTO phases using various sample preparation conditions, various ohmic contacts for the pellets will be discussed.

Figure. 1 Impedance plot for Li7La3Zr1.5Ta0.5O12
at room temperature.

Acknowledgements

This work has been supported by the US Dept. of Energy/NETL, EERE program. FRB acknowledges Oak Ridge Institute for Science and Education (ORISE) fellowship.

References

[1] J.W. Fergus, Journal of Power Sources, 195 (2010) 4554-4569.

[2] E. Rangasamy, J. Wolfenstine, J. Sakamoto, Solid State Ionics 206 (2012) 28-32.

[3] I. Kokal, M. Somer, P.H.L. Notten, H.T. Hintzen, Solid State Ionics 185 (2011) 42-46.

[4] Y. Jin, P.J. McGinn, Journal of Power Sources 196 (2011) 8683-8687.

[5] B. Antoniassi, A. H. M Gonzalez, S. L. Fernades, C. F. O. Graeff, Materials Chemistry and Physics 2011, 127, 51.

[6] O. Bohnke, Q.N. Pham, A. Boulant, J. Emery, T. Salkus, M. Barre, Solid State Ionics 2011, 188, 144.
Effects of Electrolytes on the Photoelectric Properties of TiO2-Based Dye-Sensitized Solar Cells
Authors: Shang Mingwei , Liu Benjamin , Dong Zhenhua , Dong Zhenyu , Sun Qiong , Dong Lifeng
Published: February 2020

The unique photoelectric properties of TiO2, which make it a better choice of dye-sensitized solar cells with high efficiency, have attracted a lot of interest in recent years. Especially, single-crystal rutile TiO2 nanorod arrays have been extensively investigated. In this study, in order to improve the photoelectric properties of TiO2 and analyze the effects of different electrolytes on the performance of TiO2 based dye-sensitized solar cells, the solar cells were fabricated with iodine base electrolyte, sulfur based electrolyte and inorganic solid state electrolyte, CsSnI2.95F0.05, as electrolyte respectively, and Pt deposited on the conductive face of fluorine-doped tin oxide (FTO) glass as the counter-electrode. TiO2 nanorod arrays were treated with ethanol solution of cis-diisothiocyanato-bis-(2,2,-bipyridyl-4,4,-dicaboxylato)-ruthenium()bis(tetrabutyl-ammonium) (N719, DYESOL) for 18h before the cell assembly. Open-circuit voltage (V
OC), short-circuit current density (J
SC) and impedance of the solar cells with these three kinds of electrolytes were measured respectively, and then their conversion efficiencies were calculated. The TiO2 based solar cell fabricated with CsSnI2.95F0.05 showed the highest conversion efficiency of about 8.9%, which was much higher than those of the solar cells fabricated with the other two kinds of electrolytes.
Photocatalytic Hydrogen Production from Noble Metal Free Systems
Authors: Coutsolelos Athanassios Georgios , Charalambidis Georgios , Weinstein Julia A. , Guldi Dirk M. , Lazarides Theodore , Delor Milan , Sazanovich Igor , Georgakaki Irene , Peuntinger Katrin , Daphnomili Dimitra , Landrou Georgios , Kahnt Axel , Gryko Daniel , Sabatini Randy , McCamant David
Published: February 2020

Abstract

With the global energy demand constantly rising, the need for developing new abundant and environmentally benign sources of energy is ever increasing.1 Consequently, solar energy is expected to play an increasingly important role in the future. One of the major strategies for solar energy conversion that is currently under development is the light-driven splitting of water into its constituent elements. Inspired by nature’s extensive use of metalloporphyrins as solar energy harvesters and electron transfer agents, artificial porphyrins have found prominent use as photosensitizers in hydrogen producing schemes.2The photocatalytic production of hydrogen can be accomplished by systems containing a photosensitizer, an electron relay, a sacrificial electron donor and a catalyst. The great challenges that remain in the field include the development of systems, which employ earth-abundant materials, and the improvement of the systems activity and durability.

Here, we report two noble metal free bioinspired photocatalytic systems, which use porphyrins or a corrole as photosensitizers and the cobaloxime as a catalyst (Figure 1). In the first one a water soluble Zn porphyrin was used as the photosensitizer and [CoIII(dmgH)2(py)Cl)] as the catalyst (Figure 1 left part). This system is effective in photoinduced H2 production in MeCN/water 1:1 with TEOA as a sacrificial donor.3 In the second one the photosensitizer is directly coordinated to the cobaloxime catalyst (Figure 1 right part). From transient absorption studies we observed an electron transfer from the chromophore to the cobalt catalyst, whereas the photocatalytic H2 production was low.4

REFERENCES

T. S. Teets, D. G. Nocera, Chem. Commun. 2011, 47, 9268.

J. R. Darwent, P. Douglas, A. Harriman, G. Porter, M. C. Richoux, Coord. Chem. Rev. 1982, 44, 83.

T. Lazarides, M. Delor, I. V. Sazanovich, T. M. McCormick, I. Georgakaki, G. Charalambidis, J. A. Weinstein, A. G. Coutsolelos, Chem. Commun. accepted, DOI: 10.1039/C3CC45025B.

K. Peuntinger, T. Lazarides, D. Dafnomili, G. Charalambidis, G. Landrou, A. Kahnt, R. P. Sabatini, D. W. McCamant, D. T. Gryko, A. G. Coutsolelos, D. M. Guldi, J. Phys. Chem. C, 2013, 117, 1647.
Catalytic Particle Size Effects in the Catalytic CO2 Electroreduction on Cu
Authors: Knights Hemma , Reske Rulle , Behafarid Farzad , Roldan Beatriz , Strasser Peter
Published: February 2020

A combined experimental and computational study of catalytic particle size effects during CO2 electroreduction on size-controlled Cu nanoparticles is presented. Cu nanoparticle catalysts in the 2 – 15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to bulk Cu electrode. An increase in the catalytic activity as well as the H2 and CO selectivity was observed with decreasing Cu particle size, in particular for particles below around 2 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed with smaller particle size. A spherical Cu particle model was used to analyze the size dependence of the surface atomic coordination, which was correlated to experimental results.
Thermal Activiation of Sr3Fe2O7-δ Electrocatalysts for Water Oxidation at Neutral pH
Authors: Takashima Toshihiro , Ishikawa Koki , Irie Hiroshi
Published: February 2020

One of the great challenges in artificial photosynthesis is the development of efficient catalysts for oxidation of water to molecular oxygen. To date, the most extensively investigated catalysts for O2 evolution are nanostructured IrO2 and RuO2.1 They are robust and efficient water oxidation catalysts that exhibit high turnover frequencies under mild conditions. However, the high cost and scarcity of noble metals severely limit the widespread use of these catalysts for solar fuel production. Thus, considerable effort has been devoted for development of efficient catalysts based on more abundant materials. Recently, we demonstrated that stabilization of the Mn3+ species relative to charge disproportionation (2Mn3+ → Mn2+ + Mn4+) is an effective strategy to lower the overpotential under neutral pH.2,3 In this study, we examined O2 evolution activity of Sr3Fe2O7-δ
at various temperature conditions, as Sr3Fe2O7-δ
is known to show the charge disproportionation (2Fe4+ → Fe3+ + Fe5+) below 70 oC.4

A Sr3Fe2O7-δ
film electrode was prepared by a spray drying method. Sr3Fe2O7-δ
polycrystalline was synthesized by solid state reaction of SrCO3 and Fe2O3 and then suspended in ethanol. The suspension was deposited on a fluorine-doped tin oxide (FTO) electrode held on a 170 oC hotplate. The concentration of dissolved oxygen was monitored simultaneously with current density versus potential measurements using a needle-type oxygen microsensor.

Figure 1 shows polarization curves of a Sr3Fe2O7-
δ electrode at 30 oC and 70 oC. Upon sweeping the electrode potential at 30 oC, an increase in both anodic current and dissolved O2 concentration was observed at an onset potential of approximately 1.1 V. This result indicates that the observed anodic current was attributed to water oxidation. It should be noted that when the solution temperature was raised to 70 oC, the onset potentials for O2 production showed a negative shift from 1.1 V to 0.9 V. In this presentation, we will discuss the origin of the observed difference in O2 evolution activity at between 30 oC and 70 oC as well as temperature dependent efficiency of charge disproportionation of Fe4+.

References

1. Y. Zhao, E. A. Hernandez-Pagan, N. M. Vargas-Barbosa, J. L. Dysart, and T. E. Mallouk, J. Phys. Chem. Lett., 2, 402 (2011).

2. T. Takashima, K. Hashimoto, and R. Nakamura, J. Am. Chem. Soc., 134, 18153 (2012).

3. T. Takashima, K. Hashimoto, and R. Nakamura, J. Am. Chem. Soc., 134, 1519 (2012).

4. K. Kuzushita, S. Morimoto, S. Nasu, and S. Nakamura, J. Phys. Soc. Jpn., 69, 2767 (2000).
Improved Solar Energy Extraction Using a Combined Photo-Electrochemical / Thermal System for Domestic Applications
Authors: Ronaszegi Krisztian , Fraga Eric S. , Brett Dan J. L.
Published: February 2020

Hydrogen generation is a significant area of energy research, with the aim to deliver low-cost, renewable energy sources which are environmentally friendly. One possible method is solar water splitting via photo-electrochemical reaction. Photo-electrochemical (PEC) hydrogen generation is a promising technology and alternative to photovoltaic (PV)-electrolyser combined systems. Although the PEC technology is promising, the efficiency of this technology is limited by thermodynamics and technical issues. Recent research has focused on aspects of materials development to improve efficiency. With multiple band-gap electrodes, the thermodynamic efficiency, and so the overall generated hydrogen quantity, can be increased. In the case of applications where there is a heating requirement beyond the need to generate hydrogen, there are further options for extracting energy from the solar resource by utilizing the longer wavelength radiation.

Just as it is possible to have a PV/T hybrid system, the PEC unit may also be used in a PEC/T hybrid mode, thus delivering both heat and power as a CHP system. Despite the promise of PEC technology, there is little research on it in terms of modelling and system simulation. According to the knowledge of the authors there is no published research on such hybrid systems.

In this work, a model of a hybrid PEC/T system has been implemented. Simulations with this model were carried out to compare PEC technology and its developments in terms of energy gain in a home environment where both heat and electricity demands are used. When there is heat demand, a buffer tank is implemented for heat storage.

Case studies were considered, consisting of a typical three-person household in the UK to investigate the present and the near-future capability of energy supplying and reduction of CO2 emission according to the UK building energy regulation.

Results show that single band-gap photo-electrode materials are not able to cover completely the energy demands for the household if demand includes space and hot water heating. However, with multiple band-gap electrodes and with extra solar heat (or combined PEC-thermal) utilization the system efficiency can be significantly increased.
Catalyst Durability in Low Temperature Polymer Electrolyte Fuel Cells
Authors: Stevenson Matthew , van Schalkwyk Francois , Levecque Pieter , Pattrick Gary , Conrad Olaf
Published: February 2020

Durability in the context of commercial applications can be defined as the number of times that a counter is increased by 1 before a measure of performance reaches a threshold beyond which it is considered a fail. For catalysts in fuel cells the counter is often conveniently chosen to be either hours of operation or number of cycles and the performance threshold is typically some percentage of a beginning-of-life performance metric, such as specific activity or metal surface area. Degradation is the process of performance decline and this tutorial will highlight some of the current research trends in the study of degradation mechanisms and the strategies to mitigate the effect of degradation-inducing processes.

Most catalysts are multi-component systems comprising an electrically conducting support material, typically carbon black, and a catalytic material, typically platinum. Both are subject to degradation under most operating conditions, sometimes independently, but more often influenced by each other. The second half of the tutorial will present some of the recent advances in the increase of durability by varying the catalyst components.
The Impact of Sulphate Anions on the Catalyst Durability for PEMFC
Authors: Stamatin Serban Nicolae , Nørgaard Casper Frydendal , Andersen Shuang Ma , Skou Eivind Morten
Published: February 2020

Platinum based nanoparticles supported on high surface area carbons still remain the most used reference for the activity and durability of fuel cell catalysts. Usually, a catalyst thin film supported on a rotating disk electrode in a liquid electrolyte is connected in a three electrode electrochemical cell setup. This has been proven to be the best technique to predict the activity and durability of a catalyst in real fuel cell [1]. It has been proven that there are differences in activity between perchloric acid and sulphuric acid [2]. Recently, it has been shown that the sulphate anions are poisoning the catalyst surface which can give rise to different degradation mechanisms then from the studies in perchloric acid [3].

Taking into consideration that different research groups are characterising catalysts in either sulphuric acid or perchloric acid and there is proof of the difference in activity, this work is focused on emphasizing the difference between durability studies in perchloric and sulphuric acid as revealed by Fig. 1. In order to determine the impact of anions on the overall degradation a series of experiments conducted in perchloric acid, sulphuric acid and half MEA have been conducted. As a measure of the durability, Pt dissolution has been monitored by AAS of the electrolyte.

Fig. 1 ESA loss vs number of cycles in 0.5 M perchloric acid (red line) and sulphuric acid (black line). The degradation took place in a two compartment - three electrode electrochemical cell and the electrode was cycled between 0.05-1.3 VRHE at 0.2 V s-1.

Acknowledgement

This work has been supported by the Danish PEMFC Catalysts for Boosted Activity and Enhanced Durability (Energinet. dk project no. 2011-1-10669).

References

[1] H. A. Gasteiger, D. R. Baker, R. N. C. Hydrogen Fuel Cells: Fundamentals and Applications; Wiley: Copenhagen, 2010

[2] Meier, J. C.; Galeano, C.; Katsounaros, I.; Topalov, A. A.; Kostka, A.; Schu, F.; Mayrhofer, K. J. J. ACS Catalysis 2012, 2, 832–843.

[3] K. Kodama, A. Shinohara, N. Hasegawa, K. Shinozaki, R. Jinnouchi, T. Suzuki, T. Hatanaka, Y. Morimoto ECS Transactions, 58 (1) 363-368 (2013)
Electrochemical Intramolecular Aminooxygenation of Unactivated Alkenes
Authors: Xu Hai-Chao , Xu Fan
Published: February 2020

Intramolecular aminooxygenation of unactivated alkenes is achieved electrochemically. Cyclization of the anodic oxidation-generated nitrogen-centered radicals onto alkenes followed by trapping of the resulting carbon-centered radicals with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical afford aminooxygenated products in high yield and diastereoselectivity.
Synthesis of 1,4-Bis(diaryl)-1,3-Butadiynes Bearing Two Amino Moieties by Electrochemical Reaction Site Switching and Their Solvatochromic Fluorescence
Authors: Mitsudo Koichi , Kamimoto Natsuyo , Nakamura Nariaki , Suga Seiji
Published: February 2020

Recently, π-conjugated compounds have been on focus because they are known to be as key building blocks for pharmaceuticals and potent candidates for electrochemical and optical materials. While the optical and electrochemical properties of π-conjugated compounds highly depends on the structure, it has not been easy to predict these properties. It is the reason why facile and diversity-oriented methodologies to construct π-conjugated structure have been strongly required. From such a point of view, we have investigated electrochemically assisted coupling reactions for constructing π-conjugated compounds, and recently reported sequential coupling reactions which include Pd/Cu-catalyzed electro-oxidative homo-coupling of p-bromophenylacetylene to give 1,4-bis(p-bromophenyl)-1,3-diyne and subsequent Suzuki–Miyaura coupling with arylboronic acids leading to 1,4-bis(diaryl)-1,3-butadiynes.1 Two reaction sites of p-boromophenylacetylene, terminal alkyne and Br group, could be discriminated in a virtually complete manner by on/off application of electricity, and we called the strategy as “Electrochemical Reaction Site Switching (e-RSS)”. Several arylboronic acids could be applied to the reactions, and the reactions proceeded selectively to give 1,4-bis(diaryl)-1,3-butadiynes in good to excellent yields.

During the course of the investigation, we unexpectedly found that 1,4-bis(diaryl)-1,3-butadiyne bearing two dimethylamino groups at p-position exhibited solvatochromic fluorescence. To the best of our knowledge, while there have been many reports on the amines which exhibit solvatochromic fluorescence, there have been few reports on the solvatochromic fluorescence of diamines which have small dipole moment. Most of the amines exhibiting solvatochromic fluorescence so far have a strong acceptor moiety. This unexpected result prompted us to get deeper insight into this unusual phenomenon; however the poor solubility of diaminodiynes prevented us from further investigation. We therefore designed novel 1,4-bis(diaryl)-1,3-butadiynes bearing two dialkylamino or diphenylamino groups at p-position of the terminal benzene rings. The butadiynes could be easily synthesized by e-RSS with the corresponding p-aminoarylboronic acids. As expected, thus obtained diynes could be solved into several solvents and they exhibited solvatochromic fluorescence. We will discuss the detail of the synthesis of 1,4-bis(diaryl)-1,3-butadiynes bearing two dialkylamino or diphenylamino groups at p-position, and their unique optical properties.

(1) Mitsudo, K.; Kamimoto, N.; Murakami, H.; Mandai, H.; Wakamiya, A.; Murata, Y.; Suga, S. Org Biomol Chem
2012, 10, 9562-9569.
Structure and Electrochemistry of Cation Substituted "Layered-Layered Composite" Cathode Materials for Li-Ion Batteries
Authors: Lee Eungje , Long Brandon R. , Croy Jason R , Balasubramanian Mahalingam , Key Baris , Maroni Victor A. , Thackeray Michael M. , Johnson Christopher S.
Published: February 2020

Recently, Li- and Mn-rich ‘layered-layered’ composite materials have drawn much attention as possible high-energy cathode materials for next generation electric vehicles. However, continuous voltage fade (VF) during cycling has been observed with virtually all Ni-Mn-Co based compositions and understanding and arresting the VF is urgently required for its commercial application. The voltage fade is thought to be related to the instability of the composite ‘layered-layered’ structure. Such structural relaxation could be induced by oxygen loss during initial high voltage charging process and/or cation migration during cycling.

Cation substitution may be a way to retard VF of Li-rich layered cathode materials if the substituent can alter the path of structural degradation during the first charge in the parent phase. Our hypotheses for substitution study contain three criteria: (1) strong bonding with oxygen is required, (2) the oxidation state of the dopant can go higher than +4 and is stable (mitigate oxygen loss), and (3) it should form reversible dumbbell configuration with Litet during deep charge in order to maintain structural stability. Each substitution tried can fit into one of these classifications. This presentation will show the results from such substitutions and will describe the chemistry of these materials.
Synthesis and Understanding of Layered Li-Rich Nickel Manganese Oxides for High Voltage Lithium Ion Batteries
Authors: Boulineau Adrien , Simonin Loic , Colin Jean François , Peralta David , Feydi Pierre , Fabre Frederic , Chapuis-Rey Marlene , Daniel Lise , Martinet Sebastien , Patoux Sebastien
Published: February 2020

In the search for high capacity cathode materials for Li-ion batteries, layered oxides with the general formula Li(LiXMnYMZ)O2 (M=Ni, Mn, Mg, ...) either described as xLi2MnO3 · yLiMO2 are receiving much attention. These oxides are characterised by the presence of lithium in the transition metal layers, and high Mn content, leading to high capacities up to 250mAh.g-1. However, upon cycling, they present complex structural changes that are still misunderstood.

In this context, our group worked jointly on synthesis development and understanding of the structure evolution occurring into the lithium rich layered cathode material Li1.2Mn0.61Ni0.18Mg0.01O2.

The first step was to study one material synthesized using a solid state route. 1st cycle characterization was investigated by XANES, in situ XRD and SQUID magnetic measurements. We showed that the main first-charge plateau is a twophase process where a new phase is created. This extra phase apparition was confirmed by Electron Energy Loss Spectroscopy (EELS) spectra interpretation. Therefore, Squid magnetic measurements allow a 1st cycle mechanism proposition.

Evolutions after cycling test (50 cycles) have also been investigated using advanced microscopy tools (High Resolution STEM EELS spectrum imaging). The stability of the spinel defect structure is pointed out to explain the material ageing and the electrochemical performances decrease on cycling.

Others synthesis routes were developed, especially solvothermal way enabling a better primary particles size, composition and morphology control. Higher performances and cycling behaviour have been obtained and further understanding studies are under progress to match with experimental observations.
Synergy Between Metal Oxide Nanofibers and Carbon Substrates for Rechargeable Lithium-Oxygen Batteries
Authors: Yin Jun , Kim Jangwoo , Patel Bharat , Chakrapanb Srinivasan , Lee Sangho , Joo Yong Lak
Published: February 2020

Rechargeable lithium-oxygen batteries have attracted increasing interests presently, according to high energy density rivaling that of current batteries. However, one of demanding challenges has been the low practical capacity that called for improvement of the substrates and electrocatalysts in the air cathode. In this report, we have demonstrated the use of several types of metal oxide nanofibers (e.g., ZnO, Co3O4, etc) as the cathode materials in single-cell measurements, which were synthesized by water-based electrospinning, tuned by various precursor loadings and diverse thermal treatments. The characterizations of metal oxide nanofibers are carried out by an array of techniques, including SEM, XPS, XRD and Raman spectrum. In addition to charging – discharging evaluation, the correlation between the battery performance, such as capacity and cyclability, and the change of surface properties, such as surface area, pore distribution and defect state are also presented. In particular, our results reveal that when metal oxide nanofibers are incorporated into various carbon substrates (e.g. carbon black and CNT.), the resulting metal oxide/carbon hybrid catalysts exhibit great synergy, leading to the higher capacity close to 10,000 mAh/g, and better stable performance over tens of cycles.
Non-Paste Based Composite Cathode Electrode for Lithium Air Battery
Authors: Kosivi Joyce , Gomez Jamie , Nelson Ruben , Kalu Egwu Eric , Weatherspoon Mark H
Published: February 2020

Lithium air batteries have remarkable high theoretical energy density of about 12 kW·h/kg (43.2 MJ/kg) excluding the oxygen mass. However there are many short comings from its efficiency including limitations due to the use of binders. Non-paste based cathode electrode fabricated without the use of binders is explored for application in a Li-air cell. Electroless-electrolytic nickel-molybdenum oxide deposited on a porous carbon substrate was evaluated as the oxygen reducing cathode elctrocatalyst in a Li-air cell. Results will be presented on the cycling data obtained using an electrolyte containing 1 M LiPF6 and DMSO. Cell performance shows good stability for the reduced oxygen species (superoxide) O2
– ion.
Design and Fabrication of 3D Battery Electrodes
Authors: Dunn Bruce , Cirigliano Nicholas , Kim Chang-Jin , Smith Leland , Hur Janet
Published: February 2020

New generations of microscale devices that serve such application areas as sensing/actuation, communication and health monitoring will require power sources whose footprint areas are on the order of square millimeters. Three-dimensional (3D) battery architectures offer a novel approach capable of powering such devices by using the third dimension, height, to increase the amount of electrode material within a given footprint area. Moreover, by using 3D electrode designs which minimize the ionic path length between electrodes, there is the prospect of achieving high energy and power density within the small footprint area. In this paper, we report on the fabrication and properties of battery electrodes comprised of arrays of vertically-aligned carbon rods. Testing these arrays as negative electrodes for lithium ion secondary batteries shows that the electrodes exhibit good reversibility for lithium and achieve areal capacities greater than 5 mAh cm-2 at a current density of 0.1 mA cm-2, although there is capacity fade with cycling. The fabrication process demonstrated here offers the opportunity to tune rod dimensions and aspect ratios, the key design features which determine energy and power densities for 3D battery architectures.