bluuebunny/crossref_metadata_2025 huggingface dataset:
Dark Current Suppression of Germanium Photodiode Using Metal-Interlayer-Semiconductor-Metal Structure with TiO2 interlayer
Authors: Zang Hwan-Jun , Yu Hyun-Yong
Published: February 2020

Germanium (Ge) photodetectors (PDs) are promising optoelectronics device for advanced Si photonics and optical interconnection due to excellent absorption property, near-infrared wavelengths, and process compatibility with Si-based complementary metal-oxide-semiconductor (CMOS). Ge metal-semiconductor-metal (MSM) PDs have many advantages over Ge PIN PDs in terms of low capacitance, high bandwidth, and process simplicity. However, Ge MSM PDs have large dark current because of a low hole barrier height induced by severe Fermi-level pinning between the metal and Ge, which results in poor sensitivity and large power consumption of PDs.

In this work, the dark current of Ge MSM PD was tremendously reduced by introducing asymmetric metal-interlayer-semiconductor-metal (MISM) structure [Fig. 1]. As shown in Fig 2, a thin TiO2 layer was selected as the interlayer to reduce hole dark current by enhancing the hole Schottky barrier and the proposed structure can collect the photo current efficiently due to almost zero conduction band offset between TiO2 and Ge.

Low p-type Ge wafer was used to minimize bulk defect current. To form MISM structure, TiO2 interlayer was deposited by atomic layer deposition (ALD) system at process temperature of 250 °C. To increase responsivity, finger-type PD was used with 10 um finger spacing and 10 um finger width. Metal-semiconductor (MS) contact region is defined by e-beam lithography and etched by 6:1 buffered HF, then metal-interlayer-semiconductor (MIS) contact region is defined by e-beam lithography. Cu contact was formed by e-beam evaporation and lift off process.

As a result, MISM structure exhibits tremendous dark current reduction by approximately 4,000 times at a bias voltage of 1 V. The dark current reduces as the TiO2 thickness increases as shown in Fig. 3. In case of 1 nm-thick TiO2 interlayer the dark current is hardly reduced compared to symmetric MSM structure because most of holes can flow through 1 nm-thick TiO2 interlayer by tunneling. The hole dark current from the metal side diminishes as TiO2 thickness increases because hole tunneling probability decreases. The dark current with 3 nm-thick and 5 nm-thick TiO2 is reduced by 64 times and 3,970 times at 1 V, respectively, from symmetric MSM structure. As shown in Fig. 4, photo I-V measurement was carried out on asymmetric Ge MISM PD with 5 nm-thick TiO2 interlayer with collimated infrared laser (λ=1.55 um). Measured photo current value was 0.2 mA and it was saturated at 0.6 V, and the sensitivity of the PD was 24.52 at 1 V. 

In summary, we tremendously suppress dark current by approximately 4,000 times at 1 V using MISM structure. TiO2 interlayer of asymmetric MISM structure efficiently decrease hole dark current, and this structure can be promising structure for dark-current suppression in Ge MSM PD.

Figure 1
Metal Oxide Nanofiber Calcination Studied By Environmental TEM
Authors: Zhang Wenjing , Simonsen Søren Bredmose
Published: February 2020

Environmental transmission electron microscopy (ETEM) has proven to be a powerful method for studying nano-scaled changes in catalyst materials during exposure to reactive gasses and elevated temperatures [1-3]. In this work, we use ETEM to observe the structural dynamics of electrospun nanofibers during calcination, i.e. while elevating the temperature in the presence of O2. The ETEM movies show nanofiber shrinkage due to polymer oxidation followed by formation, coarsening and sintering of oxide nano-crystals in the fiber. The results show that a nanofiber can be directly transformed to a nanotube or to a nano-pearl string by controlling the calcination temperature.

Electrospinning is a powerful, efficient and cost-effective method to produce one-dimensional (1D) materials [4]. Combined with sol-gel chemistry and calcination, electrospinning has been used to produce a variety of 1D metal oxide nanomaterials that bring remarkable performance enhancement in many energy devices. (e.g. lithium ion batteries, solid oxide fuel cells). The perovskite lanthanum strontium cobalt oxide (LSC), which has been intensively studied for electrochemical devices, is synthesized in this work.

A Titan 80-300 (FEI) transmission electron microscope (TEM) equipped with at differential pumping system allowing for exposure to the specimen of a few mbar of a reactive gas was used. TEM images were recorded while exposing the fibres to 2 mbar of O2 and ramping the temperature from room temperature to 900 °C by 5 °C/min. Thermal analysis was performed at the same oxygen partial pressure balanced in N2 and same ramping rate to link structural dynamics with polymer oxidation and decomposition of the precursers.

[1] S.B. Simonsen, I. Chorkendorff, S. Dahl, M. Skoglundh, S. Helveg, “Coarsening of Pd nanoparticles in an oxidizing atmosphere studied by in situ TEM”, Surf. Sci. Available online, doi:10.1016/j.susc.2015.11.003

[2] S.B. Simonsen, K. Agersted, K.V. Hansen, T. Jacobsen, J.B. Wagner, T.W. Hansen, L.T. Kuhn, “Environmental TEM study of the dynamic nanoscaled morphology of NiO/YSZ during reduction”, Appl. Catal. A:gen 489 (2015) 147

[3] S.B. Simonsen, S. Dahl, E. Johnson, S. Helveg, “Direct Observations of Catalytic Soot Oxidation on a Nano-Scale using Environmental Transmission Electron Microscopy”, SAE Int. J. Mater. Manuf. 1 (2009) 199

[4] W. Zhang, P.N. Pintauro. “High Performance Nanofiber Fuel Cell Electrodes”. ChemSusChem, 4 (2011) 1753

Figure 1
(Invited) Overview on the Application of Solid State Electrolytes in Li-Ion Batteries and Beyond
Authors: Xiao Jie
Published: February 2020

In recent years, much effort has been pursued in developing solid state electrolytes for Li-ion batteries and beyond. While advances have been made in this field, challenges still exist. A few excellent review papers have been published discussing the mechanism and synthesis of solid state electrolytes with some examples of reducing the interfacial resistances between particles, which provide useful information to understand solid state chemistry underlying the electrolytes. Different from previous overview, this talk will categorize different solid state electrolytes according to their applications including Li-ion batteries, Li-air, Li-S batteries and Li metal protection. Both fundamental science and practical applications will be discussed and the energy density will be projected to compare with state-of-art Li-ion batteries.
First-Principles Investigation of the Surface Reactivity and Electronic Property of Dopant-Promoted SrTiO3 Catalysts for SOFC Anode Application
Authors: Ham Hyung Chul , Kim Hee Su , Yoon Sung-Pil , Han Jonghee , Nam Suk Woo
Published: February 2020

The strontium titanium oxide (SrTiO3) has received much attention as an alternative anode material for solid oxide fuel cell (SOFC) owing to its high phase stability and sulfur/carbon resistance in typical SOFC anode operating conditions. However, SrTiO3 has exhibited the low electronic/ionic conductivity and poor electro-catalytic activity toward fuel oxidation, leading to the high overpotential of SOFC.  Therefore, it is very imperative to develop highly conductive and active SrTiO3 – based anode catalysts. In this work, we will present some recent density functional theory (DFT)+U calculation results we have on the role of dopants in enhancing the electronic/ionic conductivity and catalytic reactivity of SrTiO3–based catalysts: that is, (1) the origin of improved electronic/ionic conductivity in yttrium(Y)-doped SrTiO3 (2) mechanism of H2 oxidation on the surface of yttrium(Y)-doped SrTiO3 (3) Role of dopant(M) in enhancing H2 oxidation in Sr1-xYxTi1-yMyO3 . This work hints the importance of knowing how to properly tailor the surface reactivity of oxide-based anode materials for achieving wanted electro-catalytic activity for SOFC application.
Subtraction Impedance Spectra in Solid Oxide Fuel Cells Operating on Alternative Fuel Reformate Streams Poisoned By Inorganic Impurities
Authors: Das Debanjan , Lvov Serguei N.
Published: February 2020

Poisoning effects on anode by three inorganic impurities on the performance of a solid oxide fuel cell were tested, analyzed and compared by applying electrochemical impedance spectroscopy (EIS) and equivalent circuit modeling (ECM). A series impedance subtraction method was applied on the tested cells to account for only the degradation occurring in the cell anode due to impurities. This approach provided an alternative way to understand changes occurring in one particular electrode in the cell and identify the effect caused by the corresponding change in fuel conditions, provided other conditions remained same. Due to the fact that the respective SOFC electrodes and electrolyte were connected in series in an electrochemical circuit, cell performance change can be attributed to the anode in this approach. Degradation of the cell performance caused by inorganic impurities was characterized by measuring EIS spectra at a constant current density of 0.3 A cm-2 for a diesel fuel reformate blend. The concentrations of impurities were selected in accordance with the levels expected after commercial biogas or diesel fuel cleaning processes. Critical electrochemical processes and degradation mechanisms which affect cell performance were identified and quantified. The impurities tested were sulfur, chlorine and siloxane at various ppb/ppm levels over a time period of 200-300 h. Sulfur and siloxane caused the most prominent degradation and the associated best fit electrochemical cell parameters, Gerischer and Warburg elements, were applied respectively for better understanding of the degradation processes. Degradation due to chlorine mainly occurred at the high frequency region of the spectrum which dominated the charge transfer processes in the cell. We have demonstrated that such an approach can help in generating finger-print spectra for a cell poisoned by a specific impurity or a combination of various impurities under different operating conditions.
Electrolyte Effects in Manganese Oxides in Context of Water Splitting: In Situ SERS and Corrosion Studies
Authors: Ranjan Chinmoy , Pavlovic Zoran Miroslav , Gao Qiang , Schloegl Robert
Published: February 2020

Non noble metal "earth abundant" electrocatalysts will significantly reduce the costs and make it possible to use electrochemical water splitting (electrolysis) on a very large scale. Non noble metal catalysts can be an effective replacement even if their electrochemical activities are a fraction of their noble metal counterparts. If these catalysts can be developed to an extent where their operational lifetime would become comparable to their noble metal counterparts, a large part of the problem would be solved. MnO2 is earth abundant and well known for catalyzing oxygen evolution. A form of MnOx cluster is known to catalyze water oxidation in photosynthesis.

            In order to understand the limitations of this catalyst under the operational conditions, it is important to study this material in situ. Electrodeposited of MnOx on the surface of Au was studied using in situ Surface Enhanced Raman Spectroscopy (SERS) is used for tracking the structural changes of hydrous MnOx. Significant amount of potential and electrolyte dependent material dynamics were revealed in the MnOx system. Besides in-situ study of catalyst structure, ex situ analysis of corrosion using flow cells combined with atomic emission spectroscopy was carried out alongside explicit detection of oxygen. Various kinds of electrolytes were used to evaluate the effects of cations, anions and solution pH on molecular structure and performance of MnOx catalysts. Charge to radius ratio of alkali metal ions affected the reactivity of the oxides and was seen to influence reaction under both potentiostatic and potentiodynamic conditions with Li+ and (K+, Cs+) containing electrolytes showing the lowest and highest activities respectively. Strong effects on catalyst structure and performance were also seen when various anions such as perchlorate or borate were inluded in the electroytes being investigated.

References:

Qiang Gao, Chinmoy Ranjan,* Zoran Pavlovic, Raoul Blume, and Robert Schlögl. ACS Catalysis 2015, pp 7265-7275

Figure 1
A New Series of Anolyte Molecules for Non-Aqueous Redox Flow Batteries
Authors: Duan Wentao , Huang Jinhua , Brushett Fikile R. , Wang Wei , Moore Jeffery S. , Liu Jun , Wei Xiaoliang , Zhang Lu
Published: February 2020

Nonaqueous redox flow batteries (NRFB) have emerged as a promising next-generation grid-scale energy storage solution because of their wide voltage window and hence potential higher energy densities.1-4 The development of redox active materials is essential to enable extensive deployments of such technology. Catholyte (high potential) molecules have been extensively investigated and reported,5,6 while in contrast there is still a dearth of anolyte (low potential) counterparts.

In this presentation, we report the design of a new anolyte molecule series. The materials, for both pristine and modified forms, are composed of aromatic heterocyles. These molecules exhibit low electrochemical potentials and high solubilities in organic solvents. Coupling with catholyte molecules, high cell voltages around 2.4 V could be achieved, as shown from cyclic voltammetry (CV) results of the pristine form in Fig. 1a. Flow cell performances are evaluated at a concentration of 0.5 M. As shown in Fig. 1b, excellent efficiencies are observed at a current density of 10 mA/cm2, with columbic efficiency (CE) ~ 93%, voltage efficiency (VE) ~ 77%, and energy efficiency ~ 72%. Influences of solvents and supporting electrolytes are also covered.

References:

1. W. Wang, Q. Luo, B. Li, X. Wei, L. Li, Z. G. Yang, Adv. Funct. Mater.
2013, 23, 970

2. K. Gong, Q. Fang, S. Gu, S. Li, Y. Yan, Energ. Environ. Sci.
2015, DOI: 10.1039/C5EE02341F.

3. G. L. Soloveichik, Chem. Rev.
2015, DOI: 10.1021/cr500720t.

4. X. Wei, W. Xu, J. Huang, L. Zhang, E. Walter, C. Lawrence, M. Vijayakumar, W. A. Henderson, T. Liu, L. Cosimbescu, B. Li, V. Sprenkle, W. Wang, Angew. Chem. Int. Ed.
2015, 54, 8684.

5. J. Huang, L. Cheng, R. S. Assary, P. Wang, Z. Xue, A. K. Burrell, L. A. Curtiss, L. Zhang, Adv. Energy Mater. 2015, 5, 1401782.

6. J. Huang, L. Su, J. A. Kowalski, J. L. Barton, M. Ferrandon, A. K. Burrell, F. R. Brushett, L. Zhang, J. Mater. Chem. A
2015, 3, 14971-14976.

Figure 1
Alkaline Organic Redox Flow Battery
Authors: Lin Kaixiang , Chen Qing , Marshak Michael P. , Gerhardt Michael R. , Eisenach Louise A. , Gordon Roy G. , Aziz Michael J.
Published: February 2020

We report a high performance aqueous redox flow battery employing inexpensive, stable and non-toxic organic materials in alkaline electrolyte. An anthraquinone in the negative electrolyte paired with ferro/ferricyanide in the positive electrolyte results in an open circuit voltage of 1.2 V, a peak galvanic power density exceeding 0.7 W/cm2, and a membrane crossover rate three orders of magnitude lower than with inorganic redox couples [1]. Additionally, a redox-active non-quinone organic negative electrolyte, prepared from a single-step coupling reaction of inexpensive bulk commodity chemicals, exhibits an open-circuit voltage exceeding 1.15 V against ferro/ferricyanide. This molecule has a room temperature solubility of 4 M electrons, yielding a charge density of organic negative electrolyte of 108 Ah/L.

[1] K. Lin, Q. Chen, M.R. Gerhardt, L. Tong, S.B. Kim, L. Eisenach, A.W. Valle, D. Hardee, R.G. Gordon, M.J. Aziz and M.P. Marshak, "Alkaline Quinone Flow Battery", Science
349, 1529 (2015)
Aqueous Redox Flow Batteries Based on a Nitroxyl Radical Compound
Authors: Orita Akihiro , Verde Michael , Sakai Masanori , Meng Ying Shirley
Published: February 2020

We report on novel aqueous redox flow batteries (RFBs) based on 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL) as an active material.  TEMPOL is a stable and highly water-soluble nitroxyl radical compound.  Electrochemical and UV-VIS measurements highlight that the pH value of electrolyte has a significant impact on the redox reversibility of TEMPOL.  The half-wave potential of TEMPOL was determined to be 0.61 V vs. Ag/AgCl (0.83 V SHE.). Furthermore, its peak separation of 73 mV at a sweep rate of 10 mV s-1 is close to the theoretical value (59 mV) expected for a reversible one-electron reaction.  We demonstrate that the diffusion coefficient of TEMPOL in neutral aqueous solution is comparable to the vanadium ions used in practical RFBs.  TEMPOL also exhibits a quasi-reversible redox reaction, defined by a distinct kinetic rate constant, in near-neutral aqueous solutions.

  We show that RFBs incorporating TEMPOL catholyte and Zn-based anolyte have an average discharge voltage of 1.46 V and an energy efficiency of 80.4% during the initial cycle, when subject to a constant current of 10 mA cm-2.  We also introduce a green aqueous RFB using TEMPOL catholyte and anthraquinone-2,7-disulfonic acid disodium salt (AQ27Na2) as anolyte.  This green RFB contains no toxic or flammable compounds, and exhibits an open-circuit voltage of 1.22 V and an average discharge voltage of 0.74 V.  The TEMPOL/Zn and TEMPOL/AQ27Na2 RFBs both show stable and long-term cycling at 10% SOC. Our approach offers a promising direction to develop inexpensive, environmentally-friendly, and safe RFBs.
Molecular Transport through Ion-Selective Membranes in Quinone-Based Redox Flow Batterie
Authors: Chen Qing , Eisenach Louise A. , Valle Alvaro W. , Gerhardt Michael R. , Wong Andrew A. , Beh Eugene S. , Aziz Michael J.
Published: February 2020

The use of organic molecules such as quinone/hydroquinone in a redox flow battery (RFB) is a promising path toward inexpensive grid-scale electricity storage [1,2]. Because of their relatively large size, the molecules also provide the opportunity to mitigate capacity loss associated with active material crossover that is encountered in RFBs that utilize vanadium ions or bromine. Here we first discuss the effect of crossover on cell performance metrics, including current efficiency, energy efficiency, and capacity retention. We quantitatively compare the impacts from crossover and other loss mechanisms, such as leakage and molecule decomposition in a quinone-bromide RFB [3]. By using UV-Vis spectroscopy in a concentration-driven crossover cell, the crossover rates of different quinone molecules through ion-selective membranes are measured. The rate of crossover is shown to depend on the molecular structure and net charge of the migrating species. The results provide valuable insights with regard to molecule and membrane selection enabling molecular crossover through ion-selective membranes to be effectively minimized.

References:

1. B. Huskinson, M. P. Marshak, C. Suh, S. Er, M. R. Gerhardt, C. J. Galvin, X. Chen, A. Aspuru-Guzik, R. G. Gordon, and M. J. Aziz, Nature, 505, 195–8 (2014).

2. K. Lin, Q. Chen, M. R. Gerhardt, L. Tong, S. B. Kim, L. Eisenach, A. W. Valle, D. Hardee, R. G. Gordon, M. J. Aziz, and M. P. Marshak, Science, 349, 2013–2016 (2015).

3. Q. Chen, L. Eisenach, and M. J. Aziz, J. Electrochem. Soc., 163, A5057–A5063 (2016).
(Invited) Enhanced Electrochemical and Catalytic Properties at Strained Exsolution Particles
Authors: Irvine John , Neagu Dragos
Published: February 2020

Metal particles supported on oxide surfaces promote many of the reactions and processes that underpin the global chemical industry and are key to many emergent clean energy technologies. At present, particles are generally prepared by deposition or assembly methods which, although versatile, usually offer limited control over several key particle characteristics, including size, coverage, and especially metal-surface linkage. In a new approach, metal particles are grown directly from the oxide support though in situ redox exsolution. We demonstrate that by understanding and manipulating the surface chemistry of an oxide support with adequately designed bulk (non)stoichiometry, one can control the size, distribution and surface coverage of produced particles. We also reveal that exsolved particles are generally strained being epitaxially socketed in the parent perovskite which appears to be the underlying origin of their remarkable stability, including unique resistance of Ni particles to agglomeration and to hydrocarbon coking, whilst retaining catalytic activity and enhanced electrochemical activity..
Dynamic Chemical Expansion of Thin Film Non-Stoichiometric Oxides at Extreme Temperatures
Authors: Swallow Jessica G. , Kim Jae Jin , Maloney John M. , Chen Di , Smith James F. , Bishop Sean R. , Tuller Harry L. , Van Vliet Krystyn J.
Published: February 2020

Thin film non-stoichiometric oxides are of interest as electrodes and electrolytes in electrochemical energy conversion devices including solid oxide fuel cells and electrolyzers because of their potential to lower device operating temperatures and as model systems to aid in investigating rate limiting kinetics. Many of these non-stoichiometric oxides undergo chemical expansion, or composition-dependent volume change, upon ‘breathing’ of oxygen that can result from variations in temperature, oxygen partial pressure, and electrical bias. However, thin film responses are not always accurately predicted based on bulk models or experiments. Understanding the time-resolved operando chemical expansion of non-stoichiometric oxide thin films is essential for modeling and predicting the development of stress and strain in actual devices during temperature excursions or gas interruption. In this work, we report a novel method for measuring chemical expansion of thin films of non-stoichiometric oxides at temperatures up to 650°C and demonstrate its application to the model fluorite-structured system (Pr, Ce)O2-δ (PCO). In this technique, we vary the oxygen activity of the material of interest by applying an oscillating electrical bias across a supporting yttria stabilized zirconia (YSZ) electrolyte, and use a high-temperature, depth-sensing instrumented indenter to detect the amplitude and phase lag of the material’s expansion response, allowing us to characterize nm-scale chemical expansion in PCO films with sub-second-scale resolution.  We relate the observed frequency and temperature-dependent response to fundamental processes governing expansion kinetics and compare our results with available defect models for PCO. This ‘electrochemomechanical spectroscopy’ provides an accessible means of characterizing how factors such as film thickness, composition, or microstructure, influence the operando chemomechanical deformation of non-stoichiometric oxide-based devices on short time scales.
(Invited) LLZO Ceramic Electrolytes: A Path Forward to Solid-State Batteries?
Authors: Doeff Marca , Cheng Lei
Published: February 2020

The appeal of solid-state batteries is clear; there are no flammable liquid components to leak or catch fire, and the possibility of using lithium anodes suggests that higher energy density than currently obtainable with Li-ion configurations should be possible. The emergence of garnet-structured electrolytes based on Li7La3Zr2O12 (LLZO) are particularly attractive for such devices because of their high conductivities and apparent stability against lithium. Still, there are many challenges associated with LLZO, including difficulties in densifying the materials and high interfacial resistances at the lithium electrodes. Work in our group has been directed towards overcoming these obstacles. Classical ceramics processing techniques have been used to produce samples up to 94% dense, as thin as 200 microns, with excellent control over grain size and grain boundary chemistry.  Synchrotron techniques such as soft x-ray absorption spectroscopy (XAS) and x-ray photoemission spectroscopy (XPS) reveal that the main culprit leading to high interfacial resistance at lithium electrodes is lithium carbonate, either present as a by-product of synthesis or produced upon exposure to air.  Polishing in inert atmosphere removes this impurity and lowers the interfacial impedance, but is not practical commercially. Through grain boundary engineering, it is possible to substantially reduce the sensitivity of samples to air exposure, greatly reducing the tendency towards formation of lithium carbonate and resulting in much lower interfacial impedances at lithium electrodes.
(Invited) Mechanical Stabilty of Solid Electrolyte Interfaces in Solid-State Batteries
Authors: Sakamoto Jeff
Published: February 2020

Solid-state electrolytes and solid-state batteries have recently garnered significant interest to enable unprecedented performance and safety.  While in theory, the performance of solid-state batteries is appealing, in practice numerous manufacturing and cell design challenges are expected owing to the brittle nature of ceramic-based solid electrolytes.  To address these challenges, the mechanical properties of solid electrolytes must be characterized.  The purpose of this work is to characterize the salient properties of promising oxide and sulfide solid electrolytes to facilitate their transition into the manufacturing and testing of solid-state battery prototypes.  Mechanical properties such as the elastic and shear moduli, Poisson’s ratio, fracture toughness, and hardness are presented and their implications discussed.  Additionally, a novel approach to conduct in situ, non-invasive, non-destructive mechanical characterization during and after cycling solid-state prototype cells will be presented.
Lithium Chemical Potential Change in Lithium Ion Battery Cathodes Under Mechanical Strain
Authors: Amezawa Koji , Funayama Keita , Kimura Yuta , Mahunnop Fakkao , Nakamura Takashi , Kuwata Naoaki , Kawamura Junichi , Kawada Tatsuya
Published: February 2020

In solid-state ionic devices, such as all-solid-state lithium ion batteries (LIBs) and solid oxide fuel cells (SOFCs), mechanical strain might be induced at the electrode/electrolyte hetrointerfaces during the cell fabrication process and the operation because of differences in the crystal structures and the chemical/thermal expansion coefficients. Such mechanical strain at the heterointerfaces might affect thermodynamic and kinetic properties of the electrodes and the electrolyte, resulting in deterioration or improvement of the devices’ performance.

In this work, we investigated the influence of mechanical strain on lithium chemical potential in cathode materials for LIBs. Dense thin film electrodes, such as LiCoO2 and LiFePO4, were fabricated on a solid-state lithium ion conductor, such as Li0.29La0.57TiO3 (LLT) and Li7La3Zr2O12 (LLZ). The change in the lithium chemical potential in the electrode was evaluated by measuring electromotive force (EMF) between the electrode under compressively- or tensely-strained condition and one under stress-free condition.

A clear EMF was generated when a mechanical strain was applied to the electrode. Typically, a positive and negative EMF was observed for a compressive and tensile stress, respectively. When the mechanical strain was released, EMF returned to zero. EMF seemed to increase proportionally with increasing the amount of mechanical strain. Such an EMF accompanied with the mechanical strain was discussed from thermodynamic points of view and, as results, could be related to the lithium partial molar volume of the electrode material.

References

[1] K. Funayama, T. Nakamura, N. Kuwata, J. Kawamura, T. Kawada, K. Amezawa, Electrochemistry, 83(10), 894-897 (2015).

[2] K. Funayama, T. Nakamura, N. Kuwata, J. Kawamura, T. Kawada, K. Amezawa, Solid State Ionics, in press.
Water Distribution Oscillations in a PEMFC Under Low Cathode Humidification: Neutron Imaging and Transient Two-Phase Modeling
Authors: Sanchez Daniel G , Boillat Pierre , Biesdorf Johannes , Forner-Cuenca Antoni , Cochet Magali , García-Salaberri Pablo A. , Vera Marcos , Friedrich K. Andreas
Published: February 2020

Water management is one of the most relevant issues for the successful operation of Polymer Electrolyte Membrane Fuel Cells (PEMFCs). An excessive humidification of the inlet gas streams produces an accumulation of liquid water in the porous electrodes, which hinders the transport of reactants towards the active catalyst sites, thereby decreasing cell performance (an effect known as flooding). On the other hand, an insufficient level of humidification lowers the ionic conductivity of the membrane, also leading to a performance reduction. The complex water management further challenges the transient operation of PEMFCs, so that fast changes of the humidification conditions should be avoided as far as possible.

 Previous work has shown the existence of periodic oscillations between high- and low-current density levels in cells operated with dry cathode and fully humidified anode streams1, 2. This oscillatory behavior is associated to the periodic wetting (ignition) and drying of the membrane. The ignition process is caused by the transient accumulation of liquid water at the anode inlet, which is then transported downstream the channel. This leads to a rehydration of dried, deactivated areas of the cell, thereby decreasing the membrane (high frequency) resistance. The ignition process is then followed by a progressive drying of the membrane, so that the ignition/drying (high-/low-current density) cycle repeats itself again and again.

 In this work, the spatio-temporal distributions of liquid water during both ignition and drying processes have been visualized using in-plane high-resolution neutron imaging3. Two MEAs with different membranes (Nafion® 111 and Nafion® 117) were investigated to assess their impact on the transient distribution of water throughout the cell. In addition, the experimental data have been compared with the predictions of a transient two-phase macroscopic model. The combined experimental and numerical investigation conducted in this work-in-progress will provide insight on the complex water transport phenomena that take place in operating PEMFCs.

 References

1. D. G. Sanchez, D. G. Diaz, R. Hiesgen, I. Wehl, and K. A. Friedrich, J. Electroanal. 635 Chem., 649, 219 (2010).

2. D. G. Sanchez, A. Ortiz, and K. a. Friedrich, J. Electrochem. Soc., 160, F636 (2013).

3. P. Boillat, G. Frei, E. H. Lehmann, G. G. Scherer, and A.Wokaun, Electrochem. Solid St., 13, B25 (2010).
3-D Inkjet Printed Electrode Microstructures for Solid Oxide Electrolysers and Fuel Cells
Authors: Kleiminger Lisa , Farandos Nick , Kelsall Geoff H.
Published: February 2020

Increasing contributions of renewable energy sources to electrical power grids necessitates the development of advanced energy storage technologies. Reversible high temperature solid oxide electrochemical reactors are one possible solution, whereby surplus electrical energy can be converted into chemical energy in electrolyser mode and re-converted into electrical energy in fuel cell mode as power demand peaks.

Increasing the densities of triple phase boundaries (electrode | electrolyte | reactant gases in pores) at which the electrochemical reactions occur, increases energy conversion efficiencies of solid oxide fuel cells (SOFCs) and electrolysers (SOEs). Electrode structures based on infiltrated-scaffolds have enhanced triple phase boundary densities and better pore size control than those from conventional fabrication methods such as powder mixing. However, fabricating scaffolds reproducibly and predictably at micrometre scales is challenging. Hence, we used a  3D inkjet printer (Ceradrop X-Series) with three multi-nozzle print heads, to produce scaffolds with achievable feature size resolutions of ca. 30 μm in the horizontal plane and 1 μm in the vertical direction (Figure 1A).

For printing SOFCs and SOEs, we developed a printable yttria-stabilised zirconia (YSZ) colloidal dispersion (‘ink’) with sub-micrometre precursor particles. This ink was used to print gas-tight YSZ electrolytes ca. 8 mm thick onto ‘green’ NiO-YSZ substrates, on top of which we printed arrays of micro-pillars with ca. 100-120 μm diameter. The printed cells were heat treated at 600 °C to combust organic additives stabilising particles against aggregation, followed by sintering at 1500 °C. The micro-array was then infiltrated with a 1 molar aqueous nitrate precursor solution of La0.8Sr0.2MnO3-
δ(LSM). Following multiple infiltrations and decomposition of nitrates at 500 °C, the entire cells were calcined at 1100 °C to form the LSM positive electrode (Figure 1B).

Electrochemical performances of these cells with tailored microstructures will be presented for electrolyser and fuel cell modes, for various operating temperatures and gas mixtures (e.g. CO2, H2O, CO, H2).

Figure 1
(Invited) In Operando Studies of Chlorine Induced Anode Degradation in SOFCs Operating with Methane and Biogas
Authors: Walker Robert A , Reeping Kyle W. , Bohn Jessica , Owrutsky Jeffrey C , Qadri Syed Noorullah , Kirtley John D. , Steinhurst Daniel A
Published: February 2020

Vibrational Raman spectroscopy, IR emission spectroscopy and near IR thermal imaging coupled with voltammetry and impedance measurements was used to explore the effects of chlorine on electrolyte supported solid oxide fuel cell (SOFC) performance and durability.  Ni-YSZ SOFC anodes were exposed to 110 ppm dry CH3Cl at 650°C and 700˚C for up to four hours while intermittently exposing the cell to either methane (CH4) or a biogas surrogate (methane/carbon dioxide; 50:50 by mole fraction) for ten minute intervals. In these experiments Raman spectroscopy was used to monitor carbon accumulation kinetics. Electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurements performed with cells at 650˚C operating with CH4 (and exposed to CH­3Cl) showed marked degradation.  Degradation with biogas was even more aggressive.  In both instances, degradation was irreversible as removal of the chlorine source did not result in complete recovery of performance.  These findings stand in contrast to previously reported results of SOFCs operating with H2 in the presence of a chlorine contaminant.  Curiously, at 700˚C degradation slows significantly with cell performance diminishing slightly before reaching an asymptotic limit.  These results suggest that the presence of carbon facilitates formation of volatile nickel chloride species resulting in substantive damage to anode microstructure.
(Invited) Ce(Mn,Fe)O2/La(Sr)Fe(Mn)O3 Nano Size Film As a Dense Anode for Low Temperature Solid Oxide Fuel Cells
Authors: Ishihara Tatsumi , Yoshikai Masaru , Ju Young Wan , Ida Shintaro
Published: February 2020

Solid oxide fuel cells (SOFCs) have been attracting much interest as alternative and efficient energy conversion system for next generation.    Ni–yttria stabilized zirconia (YSZ) cermets anode film was prepared with laser ablation method. However, large volumetric changes of cermets film and Ni agglomeration cause micro-crack and delaminating thin film in reducing atmosphere. Therefore, investigations for thin film anode have been hardly progressed up to now. We studied dense La(Sr)Fe(Mn)O3-δ (La0.6Sr0.4Fe0.9Mn0.1O3-δ, LSFM) thin ceramic film as an dense anode concept for expanding reaction site from three phase boundary (anode–electrolyte–gas) to two phase one (anode–gas phase) by PLD process. In our previous work, metallic substrate was studied as the porous anode in IT-SOFC. The Ni–Fe substrate exhibited excellent tolerance against thermal-/redox- cycling. Furthermore, the cell using Ni–Fe anodic metal substrate exhibited fairly high power density at intermediate temperature. However, the power density of metal-supported cell was slightly lower than that of cermets-supported cell in our previous study because of limited number of three phase boundary. In order to achieve high power density and stability of intermediate temperature solid oxide fuel cells (IT-SOFC),  Ce(Mn,Fe)O2(CMF)-La(Sr)Fe(Mn)O3-δ (LSFM) dense nano-film anode is introduced between Ni–Fe metallic substrate and LaGaO3 base oxide electrolyte. Although it is believed that three phase boundary (TPB) is essentially required for anode active site, the cell using CMF-LSFM mixed conducting thin film anode exhibits reasonable power density comparing with that of the cell with a simple porous Ni–Fe anode, however, slightly decreased comparing with that of LSFM single layer. The maximum power density of the cell having CMF-LSFM film is approximately 2.0 W/cm2 at 973 K. On the other hand, application of double columnar composite of CMF/LSFM shows much smaller anodic overpotential and higher power density at intermediate temperature. Therefore, this study reported the dense film of CMF and LSFM with few 100 nm thickness can be used as dense anode.
Protonic Ceramic Fuel Cell Stacks
Authors: Ding Hanping , Duan Chuancheng , Tong Jianhua , Le Long , Ricote Sandrine , O'Hayre Ryan , Sullivan Neal P
Published: February 2020

In this report, we present our work on development of fuel cell stacks based on proton-conducting ceramic materials. Such protonic-ceramics have demonstrated great promise for addressing the technological challenges now facing the solid-oxide fuel cell community.  Protonic ceramic fuel cells (PCFCs) based on BaCe0.7Zr0.1Y0.1Yb0.1O3-δ have demonstrated high power density at low operating temperatures, achieving 450 mW / cm2 at 500 ºC under hydrogen fuel [1, 2]. PCFCs may also be more amenable to internal reforming of hydrocarbon fuels (CH4 + H2O => 3 H2 + CO). Proton conduction removes H2from the anode stream, thereby shifting the internal-reforming equilibrium chemistry towards the products, promoting higher methane conversion.  While these materials show great promise, no multi-cell PCFC stacks have been fabricated to date.

In this presentation, we review our progress in extending previous single “button-cell” experiments to small fuel-cell stacks. The stack design is shown in Figure 1; PCFC membrane-electrode assemblies (MEAs) are bonded within a ceramic frame, and the frame is packaged within ferritic-steel interconnects. Fabrication of MEAs involves solid-state reactive sintering (SSRS), where the protonic-ceramic fuel cell material is formed from simple parent oxides during co-sintering of the anode-electrolyte assembly.  This single-step fabrication greatly reduces MEA-manufacturing costs and improves yields.

Multi-cell stack prototypes have been demonstrated. A three-cell stack based on BaCe0.2Zr0.6Y0.2O3-δ electrolyte shows open-circuit voltage that approaches the theoretical Nernst potential (Figure 1), and demonstrates excellent stability over 500 hours of continuous operation. The stack also yields reasonable power density, reaching 250 mW/cm2at 650 ºC. Moving forward, higher performance is expected as we improve fabrication and packaging methods.

Citations:

[1] C. Duan, J. Tong, M. Shang, S. Nikodemski, M. Sanders, S. Ricote, A. Almansoori, R.P, O’Hayre, “Readily processed protonic ceramic fuel cells with high performance at low temperatures,” Science
349: 6254 (2015) 1321-1326.

[2] J. Kim, S. Sengodan, G. Kwon, D. Ding, J. Shin, M. Liu, G. Kim, “Triple-conducting layered perovskites as cathode materials for proton-conducting solid oxide fuel cells,” ChemSusChem
7(2014) 2811–2815.

Figure 1
Characterization and Performance of Proton Conducting Solid Oxide Fuel Cells Manufactured Using Reactive Spray Deposition Technology
Authors: Myles Timothy D. , Ouimet Ryan , Kwak Dongwook , Maric Radenka
Published: February 2020

Proton conducting solid oxide fuel cells (p-SOFC) have received attention recently as an alternative to traditional high temperature SOFCs [1]. This new class of p-SOFCs offer the potential to significantly reduce the cost of production due to the opportunity to lower the operating temperature from upwards of 800 °C down to as low as 500 °C. This shift is made possible by a modified class of ion conducting materials such as yttrium doped barium zirconate (BYZ) which has comparable ionic conductivity to yttria-stabilized zirconia at lower temperatures [2]. With a decrease in the operating temperature, it becomes possible to make use of inexpensive materials for cell construction such as stainless steels vs. expensive super alloys. This cost savings is a major driver towards practical commercialization of p-SOFCs. This work seeks to employ a novel flame based technique, Reactive Spray Deposition Technology (RSDT) [3], in manufacturing of a complete p-SOFC on a metal support. This technique involves dissolving organometallic precursor compounds (typically ethlyhexanoate ligands) into combustible solvents. The mixture is sprayed from an atomizing nozzle in an open atmosphere and ignited. The resulting heat of combustion due to the solvent is used to decompose the dissolved compounds and produce thin films via gas to particle conversion. The use of the flame eliminates the need for separate, costly sintering steps generally needed in traditional manufacturing processes. Secondary nozzles can be utilized to introduce different support and binder materials resulting in a single-step manufacturing process for the anode, electrolyte, and cathode of the p-SOFC. The current work focuses on the production and initial characterization of a p-SOFC using a Ni-BYZ anode, BYZ electrolyte, and lanthanum strontium cobalt ferrite (LSCF) cathode on a porous metal support. The deposited materials are characterized using SEM, STEM, and XRD techniques. Initial button cell performance is also reported.

References:

[1] F. Lefebvre-Joud and G. Gauthier, and J. Mougin, J. Appl. Electrochem., 39 (2009) 535-543.

[2] Y. Yoshihiro, R. Hernandez-Sanchez, and S. M. Haile, Chem. Mater., 21 (2009) 2755-2762.

[3] R. Maric, J. Roller, and R. Neagu, J. Therm. Spray Techn., 20 (2011) 696-718.
(Invited) Enhanced Electrochemical Activites in Perovskite Oxides through Strain Control of the Oxygen Stoichiometry
Authors: Lee Ho Nyung
Published: February 2020

Functional ionic defects, such as oxygen vacancies, in perovskite oxides facilitate catalysis critical for energy storage and conversion devices. However, the deliberate control of oxygen stoichiometry in perovskite-based oxides is challenging due to difficulties in activating these functional oxygen defects at the reduced temperatures required for the low temperature operation of energy storage and generation devices, such as batteries and fuel cells. Here, we use strontium cobaltite (SrCoOx) “oxygen sponge” to show that epitaxial strain is a powerful tool towards controlling the oxygen vacancy concentration even in highly oxidizing environments, including conditions during the oxygen evolution reaction (OER) that otherwise fully oxidize unstrained SrCoOx. Our computational approach found that the thermodynamic barrier towards oxygen activation could be lowered by applying a small biaxial tensile strain (~30% with 2% strain). The corresponding change was also experimentally observed, yielding an increasingly oxygen deficient state. The additional oxygen vacancies created by strain artificially enhance the cobaltites’s catalytic activity towards the OER by over an order of magnitude. Our findings demonstrate that strain, rather than simply relying on ambient conditions, can act as the key tuning parameter of oxygen stoichiometry in the next generation of catalytic oxides, functionalizing vacancies for realizing low temperature energy applications.

* This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division (synthesis, theory, and optical and physical property characterization) and by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy (electrochemical characterization).
(Invited) Electrospun Particle/Polymer Fiber Mats As Fuel Cell and Battery Electrodes
Authors: Pintauro Peter N.
Published: February 2020

Electrospinning is gaining popularity as a convenient and robust technique for fabricating non-woven mats of sub-micron diameter polymer fibers. Although not as well studied, the technique can also be used to prepare particle/polymer fiber networks with high intra- and inter-fiber porosity.  Such fibrous networks can be used as porous electrodes in fuel cells and batteries, where high interfacial electrode area, i.e., the accessibility of electrode material within a 3-D anode or cathode architecture, is of prime importance. In this talk, a review of recent experimental work on nanofiber mat architectures for hydrogen/air fuel cell cathodes and lithium battery anodes and cathodes will be presented, where the particle loading in the fibers is very high. The fuel cell work is focused on fibers containing carbon supported Pt or Pt-alloy powders with various perfluorosulfonic acid polymer based catalyst binders. The fuel cell power output using such a cathode is very high for ultra-low Pt loadings.  Additionally, carbon corrosion of nanofiber cathodes, as determined from voltage cycling experiments, can be minimized by proper adjustment of the hydrophilic/hydrophobic properties of the catalyst binder. For Li battery applications, nanofiber anodes have been prepared and evaluated, where the fibers are composed of either TiO2 and carbon powders with poly(acrylic acid) binder or carbon powder and poly(vinylidene fluoride) (PVDF). Here, the volumetric capacity of a fiber anode at charge/discharge rates of 1C-3C are considerably higher than those measured with a conventional slurry anode. Electrospinning can also be used to prepare ultra-thick anodes with high areal capacities, e.g., 2.5 and 1.3 mAh/cm2 at charge/discharge rates of 1C and 2C, respectively. Similarly, Li battery nanofiber cathodes with LiCoO2 and carbon powders in a PVDF binder have been fabricated and evaluated at various areal capacities and C-rates.   Experimental details for both fuel cell and battery electrodes will be presented in this talk, including the procedures for electrospinning fibers, the methods for characterizing the fiber mats, and the properties and performance of the particle/polymer mats in a given application.
Effective Nickel and Ruthenium Modified Palladium Anode Catalysts for Ethylene Glycol Oxidation in Alkaline Medium
Authors: Da Silva Rodrigo Garcia , De Andrade Adalgisa Rodrigues , Servat Karine , Morais Claudia , Napporn Teko W. , Kokoh Kouakou Boniface
Published: February 2020

As one of the attractive fuels in the direct alcohol fuel cell applications, the ethylene glycol electrooxidation was investigated in alkaline medium on Pd-based bimetallic catalysts (PdM/C, where M = Ni, Ru). These electrode materials were synthesized by polyol method, using ethylene glycol as both solvent and reducing agent. The resulted anode catalysts displayed effectiveness toward the oxidation of ethylene glycol. The latter molecule was also scrutinized as potential fuel which can be converted by cogeneration into energy (5.2 kWh kg-1) and particularly to added value product. Ex situanalytical measurements with liquid chromatography/Mass spectrometry provided evidences on the identification of glycolate as the main reaction product on the PdM/C anode materials (Figure 1).

The identification of some adsorbed intermediates and the final reaction products, was also supported by combining electrochemical (cyclic voltammetry, chronoamperometry) and in situreflectance infrared spectroscopy experiments. The PdNi/C catalyst showed the highest intrinsic catalytic activity for the ethylene glycol oxidation. From FTIR experiments our findings gave evidences that the initial molecule skeleton was conserved and carbon monoxide was observed in a low amount.

Acknowledgements

R. Garcia Da Silva gratefully acknowledges FAPESP (2012/07464-0; 2013/25632-0) and CNPq for his fellowship.

Reference

L.M. da Palma, T.S. Almeida, V.L. Oliveira, G. Tremiliosi-Filho, E.R. Gonzalez, A.R. de Andrade, K. Servat, C. Morais, T.W. Napporn, K.B. Kokoh, RSC Adv., 4, 64476 (2014).

Figure 1. Glycolate1isolated and identified by LC-MS as the main compound issued from the ethylene glycol oxidation at the Pd-M/C (M = Ni and Ru) catalysts in alkaline medium.

Figure 1