bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrocatalysts for Direct Alcohol Oxidation Fuel Cells Prepared Using Ion Beam Assisted Deposition Technique
Authors: Poplavsky Vasily
Published: February 2020

Active layers of the electrocatalysts for oxidation of methanol and ethanol were prepared by ion beam assisted deposition (IBAD) of platinum and activating rare earths metals (Ce, Yb) onto carbon (AVCarb® Carbon Fiber Paper Р50 and Toray Carbon Fiber Paper TGP-H-060 Т) supports. The deposition method is characterized by the use of deposited-metal ions as assisting ions. Metal deposition and mixing between the precipitable layer and surface of the substrate by accelerated ions of the same metal were carried out on the experimental unit from a neutral vapor fraction and the vacuum-arc discharge plasma of a pulsed electric arc ion source, respectively. Ion accelerating voltage is 10 kV; vacuum – 10–
2 Pa.

Investigation of the composition and microstructure of layers was carried out by RBS, SEM, EPMA and XRF methods. It has been established that the obtained catalytic layers contain atoms of the deposited metals and substrate material, as well as impurity oxygen atoms; their thickness reaches ~30–100 nm. Content of platinum atoms in the layers is ~2×1016 cm–2, concentration of deposited metals atoms in the maximum of distribution equals about a few at.%.

According to investigations with use of cyclic voltammetry the electrocatalysts with prepared layers exhibited high catalytic activity in the reactions of electrochemical oxidation of methanol and ethanol, which form the basis for the principle of operation of low temperature fuel cells (DMFC and DEFC) (Figure 1).

Figure 1. Cyclic voltammograms in the ethanol comprising solution of electrocatalyst prepared using ion beam deposition of ytterbium and platinum onto Toray Carbon Fiber Paper TGP-H-060 Т

In comparison with the traditional multistage chemical methods of preparation of the deposited catalysts, the proposed IBAD method appears to be promising and often more preferable. It allows of the introduction of micro amounts of a doping impurity in the near-surface of a substrate under non equilibrium conditions and of the formation of cohesive catalytic layers at ultra-low platinum consumption.

Figure 1
Enhanced Water Activation By High Oxophilicity of LaMnO3 Supports for Ag-Based Electrocatalysts in Alkaline Media
Authors: Lee A-Yeong , Park Shin-Ae , Kim Yong-tae
Published: February 2020

Recently, Alkaline fuel cells (AFCs) have regained attention because, compared to the acid environment, an alkaline media provides a less corrosive environment to the catalysts and electrodes. One of the main advantages of AFCs is the possibility to replace Pt-based electrocatalysts with non-Pt electrocatalysts.[1] In recent studies, catalytic activity was improved by the influence of interaction between metal and metal oxide. Also researcher have studied to find the ORR mechanisms.[2,3] In this study, the influence of interaction between Ag and perovskite oxide, also electrocatalytic performances in alkaline medium were investigated.
A PEFC Parametric Study: CO Tolerance As a Function of Operating Conditions
Authors: Williams Stefan , Rockward Tommy , Mukundan Rangachary
Published: February 2020

Abstract:

One of the current barriers listed in the Safety Codes and Standards section of the Fuel Cell Technologies Office Multiyear Research, Development, and Demonstration Plan is: ‘insufficient technical data to revise standards’ [1]. More specifically, SAE J2719 and ISO-14687-2 are two recently developed standards for gaseous hydrogen fuel specifications whose revisions are being planned [2,3]. Both standards are applicable for fuel cell vehicles and each governs contaminants and their maximum allowable concentration in H2. Of the contaminants listed in these fuel specifications, we focus our efforts on carbon monoxide (CO), whose allowable level is 200 parts per billion (ppb). In our Polymer Electrolyte Fuel Cell (PEFC) parametric study, we utilized 25cm2 Membrane Electrode Assemblies (MEAs) with 2015 DOE target loadings for platinum (0.15mg Pt/cm2). While it is virtually impossible to test the impact of CO using all of the possible testing conditions, we have systematically formed a set of experiments (Table 1) that encompasses a broad spectrum of Fuel Cell (FC) operating parameters. For each experiment, we fixed the cell temperature at 80oC and operated the FC at 1 A/cm2 with H2 and air stoichiometric flows equivalent to 83% and 50% utilization, respectively. The table reflects the parameters we vowed such as: relative humidity (32, 50, and 100% RH), back pressure (ambient, 150kPa, and 275kPa) and CO concentration (0.2, 0.5, 1.0ppm). The CO dosage remained constant throughout the experiments conducted in this study. In this presentation we will provide data to modelers for enhancing their predictive capabilities in order to help the FC community deduce the CO impact at other operating condition.

References:

http://energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_safety_codes.pdf

SAE J2719: Hydrogen Fuel Quality for Fuel Cell Vehicles, www.sae.org

ISO 14687-2, Hydrogen Fuel – Product Specification, Part 2: PEM fuel cell applications for road vehicles, http://www.iso.org/iso/catalogue_detail.htm?csnumber=55083

 

Acknowledgements:

The authors gratefully acknowledge the financial support of the DOE Fuel Cell Technologies Office and the support of Technology Development Manager, Charles (Will) James, Jr

Figure 1
Liquid Cooled PEMFC Bipolar Plates Development for Stationary Applications
Authors: Patularu Laurentiu G , Schitea Dorin , Varlam Mihai , Carcadea Elena , Stefanescu Ioan
Published: February 2020

High power density along with low gravimetric and volumetric characteristics for Proton Exchange Membrane Fuel Cell stacks are desired in order to be successfully implemented in the stationary applications market.

Liquid cooling is currently the most widely used cooling strategy used in PEMFC stacks construction, especially for those who incorporate a large active area and high number of cells, since the heat transfer coefficients with liquid flow are much higher than airflow for the same pumping power.

This paper presents the manufacturing steps for an in house production of graphite type PEMFC bipolar plates with internal liquid cooling circuit and investigation results for a short stack construction based on 92cm2 active area.
Probing the Electrochemical Characteristics of Carbon-Supported Platinum Catalysts
Authors: Rockward Tommy , Spears Andre , Dumont Joseph H , Sansiñena José-María , Chlistunoff Jerzy
Published: February 2020

Platinum (Pt) is the state-of-the-art catalyst for both anodic and cathodic reactions that occur in polymer electrolyte fuel cells (PEFCs). However, the cost of platinum has severely hindered the commercialization and distribution of PEFCs. One of the challenges for the next generation of fuel cells is to significantly reduce the Pt content of both electrodes while maintaining excellent activity and high durability. By anchoring platinum to carbon substrates, the amount of platinum can be substantially reduced without compromising its activity. While this approach may address the cost concerns; it may also induce durability issues depending on the operating conditions. In this work, we have investigated the effects of aging on different carbon supported, low Pt loading catalysts, using accelerated stress tests (AST). These tests consist of series of voltammetric cycles conducted in solution to accelerate the rate of degradation of the carbon support. Structural, chemical, and morphological information will be presented via X-ray techniques (XRD and XRF) along with electron microscopy (SEM,TEM). Electrochemically active surface area (EASA) will be measured via H2 adsorption and desorption along with CO stripping techniques. The electrochemical activity of the catalysts versus the number of cycles will be shown using RRDE as well as some complementary fuel cell data. Preliminary results show a decrease the EASA with time; however, the rate and extent of decay varied depending on the type of carbon support.
Promotion Effect of Adding Cr/Al/Fe to Cu/ZnO on the Stability of Hydrogen Produciton Catalyst for Dimethyl Ether Steam Reforming
Authors: Xie Jing , Ding Kaijie , Li Ranjia , Yu Changchun , Ban Shuai , Zhou Hongjun
Published: February 2020

Steam reforming (SR) of dimethyl ether (DME) is one of the promising ways to produce hydrogen for fuel cells (FCs) [1]. DME is harmless with a high H/C ratio, handling DME is easy because it is liquefied under ca. 6 atm and conventional facilities providing LPG can be used due to the similarity of DME to LPG.Coppper based materials were considered as good catalyst for DME SR [2]. However the durability of copper based catalysts is not good because of the copper sintering as reaction running. There are two ways to improve the durability of copper based catalysts, one is to enhance the dispersion of copper or to improve the thermal stability of copper by forming a spinel oxide or alloy [3].

γ-Al2O3 was used as support. The Cu/ZnO/γ-Al2O3, Cu/ZnO/Cr2O3/γ-Al2O3 and Cu/ZnO/Fe2O3/γ-Al2O3 catalysts were prepared by impregnation method. The nitrates were impregnated into support for 6 h, then dried at 323 K for 12 h, calcined at 823 K for 4h. The DME SR was carried out with a fixed bed flow reactor under atmospheric pressure using 1 g of catalyst at 773 K. After the catalyst was reduced by 12 v% H2/Ar at 503 K for 3 h, the mixed gas of DME and N2 (20 v%) were fed into the reactor with GHSV=500 ml/(g·h), the water was pumped into the reactor though a 473 K heater. The H/C ratio was 3. The catalysts were characterized by means of XRD, TPR, SEM, and BET.

Steam reforming of DME was carried out at 773 K over Cu/ZnO/γ-Al2O3, Cu/ZnO/Cr2O3/γ-Al2O3 and Cu/ZnO/Fe2O3/γ-Al2O3 catalysts. The conversion of DME and the hydrogen yield reached 100% and 87% respectively for Cu/ZnO/γ-Al2O3 at the initial stage. The durability of this catalyst exhibted degradation. After running for 97 h, the hydrogen yield decreased to less than 60%. The reason for this degradation was supposed to be the sintering of copper, therefore, a metal oxide with better thermal stability was added into the catalyst to prevent the sintering of copper. The time-on-stream results indicate that the addtion of Cr2O3 or Fe2O3 can improve the durability of the catalyst for DME SR significantly. After running for 100 h, the hydrogen yield was kept at 84% and 85%, respectively. Figure 1 is the time-on-stream result of DME conversion over Cu/ZnO/ Cr2O3. Figure 1 is the time-on-stream result of DME conversion over Cu/ZnO/ Fe2O3. The mechanism of the improvement of the durability of catalysts were further investigated by XRD, SEM, BET and TPR.

Figure 1
A Study on Performance By Oxygen Concentration According to Driving Environmental of Fuel Cell Vehicle
Authors: Goo Youngmo , Kim Myong-Hwan , Yoo Seung Eul
Published: February 2020

Partial pressure of oxygen is a significant factor for determining performance of fuel cell. As is well known, the oxygen concentration in air is generally 21%, but it is about 20% at urban area which has numerous vehicles and is reduced by 18% at underground parking lot with stuffy ventilation facilities. Also, the oxygen concentration in air is 21% at a high altitude, but efficiency of fuel cell vehicle can be decreased by low oxygen partial pressure.

In this study, change of fuel cell performance was analyzed by applying empirical equation about I-V curves using experimental results according to oxygen concentration.

The performance of fuel cell in oxygen concentration of 18%~23% and altitude of 0~4km was prospected by a deducted empirical equation. In case of stoichiometric ratio(SR) 2.0, performance of fuel cell in oxygen concentration of 18% was decreased over 10% in comparison with concentration of 21%, the results was revealed as reduction in performance of 22%. Also, the performance of fuel cell at 4km altitude appeared decrease of 25% owing to low partial pressure.
Observation and Analysis of Nafion Solution By Frozen TEM Technology
Authors: Yoshida Toshihiko , Sugimori Hidekazu , Miyazawa Atsuo , Matsumoto Hidetoshi , Konosu Yuichi , Sasabe Takashi , Uemura Suguru , Kameya Yuki , Terao Takeshi , Iriguchi Norio , Shinohara Kazuhiko , Hirai Shuichiro
Published: February 2020

Nafion has been well known as the standard perfluorosulfonated material in the field of Polymer Electrolyte Membrane Fuel Cell and has been irreplaceable materials as a membrane and an ionomer of catalyst layer. Many researchers have investigated the proton conduction, water-uptake, mechanical property and nano-structure1,2).As for nano-structure researches, small angle X-ray scattering and small angle neutron scattering revealed the morphology characterization of Nafion solution3). X-ray irradiates many molecules in Nafion solution.The characterization was attributed to average information.TEM is very useful apparatus to observe nano-structure of materials. It is applicable to samples which withstand a vacuum condition.Nafion solution is not able to be observed by TEM because of high vapor pressure of solution. Freeze method is an idea to measure Nafion solution. In case of freeze method using liquid nitrogen, vaporized nitrogen severely damaged the sample. In case of another freeze liquid ethane method Figure1, liquid ethane was cooled by liquid nitrogen to avoid vaporization of ethane.Figure 2 shows TEM photograph of Nafion solution. Objects of rod structure were observed, some rods seemed to be linked each other and dark points also observed.

Rod structure with radius 1.2 to 3.6 nm and length 16nm was predicted when entangle molecular weight 54904), EW=1000 and Nafion molecular weight between 0.1million and 1million were applied.Rod structure of TEM photograph is interpreted as the prediction.Dark points of TEM Photograph might be nano-crystals of PTFE part of Nafion.SAXS measurement of Nafion solution also showed nanocrystal with interval of 18nm. This interval value fairly fits to distances between dark points.

This presentation is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

References

1)Kenneth A. Mauritz and Robert B. Moore, “State of Understanding of Nafion”, Chem. Rev. 2004, 104, 4535-4585

2)Adam Z. Weber and John Newman,” Modeling Transport in Polymer-Electrolyte Fuel Cells”, Chem. Rev. 2004, 104, 4679-4726

3)Makoto Yamaguchi, Takuro Matsunaga, Kazuki Amemiya, Akihiro Ohira, Naoki Hasegawa, Kazuhiko Shinohara, Masaki Ando and Toshihiko Yoshida, “Dispersion of Rod-like Particles of Nafion in Salt-Free Water/1-Propanol and Water/Ethanol Solutions”, J. Phys. Chem. B 2014, 118, 14922-14928

4)Souheng Wu; “Characterization of Polymer Molecular Weight Distribution by Transient Viscoelasticity: Polytetrafluoroethylenes”, Polymer Engineering & Science, 1988 - Wiley Online Library

Figure 1
Probing the Active Site Structures of Iron-Based ORR Catalysts
Authors: Hu Yang , Li Qingfeng , Jensen Jens Oluf , Zhong Lijie , Cleemann Lars Nilausen
Published: February 2020

Highly active and durable electrocatalysts for the oxygen reduction reaction (ORR) are undoubtedly essential for the commercialization of polymer exchange membrane fuel cells. Recently, two types of iron-based catalysts have been extensively studied and reported to be active and stable towards ORR in acidic electrolyte. One is the well-recognized FeNx/C catalyst, and the other is the catalyst with structures of graphitic layer encapsulated metal particles. Generally, catalysts synthesized by pyrolysis of different iron- and nitrogen-containing precursors always contain both structures, making it impossible to distinguish the role of each structure during the ORR. Using a high temperature autoclave approach, we synthesized two model catalysts with almost exclusively one desired structure in each catalyst. Based on detailed characterizations in terms of catalyst structure and composition as well as electrochemical tests, the active site structures of these two catalysts and their correlation with the ORR performance are explored.

Figure 1. Schematic illustration of the two possible active sites.

Figure 1
Hydrogen Sulfide Tolerance in High Temperature Pemfcs
Authors: Vassiliev Anton , Cleemann Lars Nilausen , Li Qingfeng , Jensen Jens Oluf
Published: February 2020

The effect of hydrogen sulphide (H2S) poisoning on the anode of H3PO4-polybenzimidazole based fuel cells has been investigated. High temperature PEM fuel cells (HT-PEMFC) offer a number of advantages that allow for a simple electricity generating system. Of the main importance is the ability to operate on reformate hydrogen without extensive purification [1]. Most of the research is concentrated on CO poisoning mitigation, but as the feedstock often contains sulphur contamination or sulphur-containing odorant additives, the poisoning effect of sulphur on Pt electrodes at elevated temperatures should not be overlooked. Little literature is available on the topic [2, 3]. Present work shows the effect of anode H2S poisoning on 25 cm² HT-PEMFCs operated at 160 °C, evaluated by polarisation curves and electrochemical impedance spectroscopy (EIS).

Cells exposed to 0.2 – 50 ppm H2S in the fuel supply show no significant signs of voltage degradation when operated at 160 °C and 200 mA/cm². The main effect is seen at higher current densities with 10 – 50 ppm levels of contamination, where concentration overpotentials cause the voltage to drop off. The effect is partly reversible, as the voltage at high current densities recovers upon switch back to pure hydrogen operation. This is contrary to the low temperature PEM fuel cells, where the voltage degradation with only trace amounts of H2S is rapid even at low currents and irreversible [4, 5].

Prolonged exposure to 1 – 50 ppm H2S in the fuel supply show a time-dependant nature of the sulphur poisoning with the major voltage degradation occurring within the first 24 hours. Again, the effect is only visible at intermediate and high currents and is partly reversible when the fuel is changed to pure hydrogen after several days of operation with H2S contaminated fuel.

EIS measurements at 200 mA/cm² showed no change in the series resistance. Occurrence of a semicircle at low frequencies, growing throughout the prolonged exposure measurements could indicate increased levels of adsorption of sulphur on the Pt sites of the electrode, thus explaining the concentration overpotentials recorded at high current densities.

[1]        Q. Li et al., Progress in Polymer Science, 2009, 34 (5), p. 449-477.

[2]        T.J. Schmidt and J. Baurmeister, ECS Transactions, 2006, 3 (1), p. 861-869.

[3]        G. Qian and B.C. Benicewicz, Ecs Transactions, 2011, 41 (1), p. 1441-1448.

[4]        V.A. Sethuraman and J.W. Weidner, Electrochimica Acta, 2010, 55 (20), p. 5683-5694.

[5]        I. Urdampilleta et al., ECS Transactions, 2007, 11 (1), p. 831-842.
Degradation of SOFCs By Phosphorus Impuriteis: Impedance Spectroscopy and Microstructural Analysis
Authors: Kikuchi Yuhdai , Sunada Kyouhei , Matsuda Junko , Taniguchi Shunsuke , Shiratori Yusuke , Sasaki Kazunari
Published: February 2020

Introduction

SOFC is considered as a promising power generation system due to high electric efficiency and fuel flexibility. But, coal gas, for example, contains various impurities. In this study, phosphorus poisoning effect to Ni-ScSZ cermet anodes is analyzed by measuring Electrochemical Impedance Spectroscopy (EIS). Spectroscopy data are analyzed by the distribution of relaxation times (DRT) method1to investigate details of electrode resistance. Furthermore, microstructural analysis was made by electron microscopy.

Experimental

Electrolyte-supported cells with ScSZ (10 mol% Sc2O3
- 1 mol% CeO2-89 mol% ZrO2) plate (20 mmφ×0.2 mmt) were used in this study. Mixture of 56 wt% NiO and 44 wt% ScSZ was used for the anode and was sintered at 1300 oC for 3 h. Mixture of (La0.8Sr0.2)0.98MnO3 (LSM) and ScSZ with a weight ratio of 1:1 was used for the cathode. Electrode area was 8×8 mm2 and Pt mesh was used as the current collector. Figure 1 describes the experimental setup. P2O5 container is locating at the fuel upstream to mix phosphorus impurity which is evaporated as PH3. PH3 concentration was specified as 2ppm by a TG-DTA measurement. The fuel consisted of 67% H2 and 33% H2O. Cell temperature was 800oC. Table 1 shows EIS condition. EIS data analyzed by DRT enable identification of electrode processes. FESEM-EDX was applied to investigate changes in the anode microstructure and composition by the cell performance tests.

Results and discussion

Figure 2 shows EIS spectra measured after 1h, 50h, and 100h. Figure 3 shows the DRT result of the Fig. 1 data. DRT peak becomes gradually visible due to the increase in impedance. DRT peak around 10-1~10-2 sec may originate from the diffusion of H2 gas2. Figure 3 shows SEM-WDX mapping of nickel and phosphorus. Ni particle is condensed and Ni-P compounds are formed on the anode surface. Therefore, cell performance degradation by inhibiting gas diffusion and forming Ni-P compound in the phosphorus poisoning of Ni-based anodes.

References

(1) A. Leonide et al., Journal of The Electrochemical Society, 155(1), B36-B41 (2008).

(2) T.H. Wan et al., Electrochimica Acta, 184, 483-499 (2015).

Figure 1
Effect of PEALD YSZ on Bi-Layered Electrolyte with Nanoscale Structure
Authors: Yu Wonjong , Cha Suk Won , Cho Gu Young , Hong Soonwook , Lee Yeageun , An Jihwan
Published: February 2020

Low temperature solid oxide fuel cell (LT-SOFC) has been considered as a one of the solution for alleviating a few drawbacks of conventional solid oxide fuel cells such as limited material selection, high performance degradation, and sealing problem. To lower the operating temperature of SOFC, reducing thickness of the electrolyte down to nanometer scale has been suggested as an effective way for lowering ohmic resistance mainly caused by ionic transport.

Atomic layer deposition (ALD) is a superior method for providing conformal and high aspect ratio thin film due to its sequential process. Recently, plasma enhanced ALD (PEALD) shows advanced properties for lowering C contamination and improving the crystallinity of the thin film. We believe that PEALD with these characteristics could be used to fabricate ultrathin and high quality ionic conducting electrolyte. In this study, PEALD is utilized for fabricating yttria-stabilized zirconia (YSZ) on nanoporous substrate and, furthermore, electrochemical performance of PEALD YSZ is comparatively characterized with sputtered YSZ.

The effect of PEALD YSZ electrolyte on bi-layered YSZ/YDC electrolyte was electrochemically characterized. Nanoporous anodic aluminum oxides (AAOs) were used as substrates for the fabrication of YSZ/YDC bi-layered electrolyte SOFCs. A cell with PEALD YSZ electrolyte showed higher open circuit voltage (OCV) of ~1002 mV and peak power density of ~182 mW/cm2 at 450 oC comparing with a cell with sputtered YSZ electrolyte. This OCV value of PEALD YSZ signifies high quality of electrolyte for gas tightness and electron blockage. The surface grain structures of YDC electrolyte sputtered on different underlying layers were comparatively analyzed by employing field emission scanning electron microscope (FESEM). The analysis indicated larger grain boundary of YDC electrolyte on PEALD YSZ resulting in higher performance of thin film SOFCs.

Figure1. Electrochemical impedance spectroscopy (EIS) analysis for PEALD and sputter YSZ cells measured at 0.6V

Figure 1
3D Reconstruction and Thermal Stress Analysis of Re-Oxidized Ni-YSZ Anode Functional Layer of Solid Oxide Fuel Cells
Authors: Kim Jun Woo , Bae Kiho , Choi Hyung Jong , Kim Namkeun , Stenfelt Stefan , Shim Joon Hyung
Published: February 2020

Nickel (Ni) has been widely used in the anode of solid oxide fuel cells (SOFCs) because of its high electrocatalytic activity towards oxidation of H2, good electronic conductivity, and formation of pores when initial nickel oxide (NiO) is reduced to Ni. When SOFCs operate at high temperature (> 800 °C), Ni can be re-oxidized to NiO when there is an interruption of fuel supply, air inflow due to deterioration of seals, or excessive supply of H2O in fuels. Volume expansion of Ni can occur significantly during this re-oxidization, and it can induce severe stress which may cause cracks and changes in anode’s microstructure. In this study, re-oxidized Ni-YSZ anode functional layer (AFL) was 3D reconstructed by using image data obtained from focused ion beam-scanning electron microscopy (FIB-SEM), which is powerful technique to separate the elements and visualize the 3D structure. Then, microstructural properties such as volume fraction, phase boundary density, and connectivity were analyzed using image processing tool. 3D mesh model for finite element analysis (FEA) was generated and thermal stress was analyzed at various temperature. In thermal FEA, we calculated and found some NiO-YSZ interfaces exhibited large thermal stress with magnitude larger than 317 MPa, which is the ultimate tensile stress of Ni phase. This is because the lack of porosity in NiO-YSZ AFL inhibits the release of thermal stresses generated at high temperature. Thus, this high thermal stress could cause critical failure on the cell structure because re-oxidized Ni-YSZ anode still contains Ni phase (< 10 vol %). The details of the 3D reconstruction, image processing, and FEA results will be presented in the conference.
Current Constriction at Electrode/Electrolyte Interfaces in Solid Oxide Cell Electrochemical Devices Calculated Via 3D Reconstructions
Authors: Nielsen Jimmi , Jørgensen Peter Stanley , Graves Christopher
Published: February 2020

Electrochemical devices such as batteries, fuel cells, electrolysers, electrochemical reactors and electrochemical sensors are important technologies for the present and the future society. For further improvement or maturing of the various technologies it is important to understand, characterize and minimize the different losses within the devices.

Historically the first generation of solid oxide fuel cell (SOFC) was electrolyte supported. In order to be able to reduce the electrolyte thickness and thus improve performance, the second generation anode supported solid oxide fuel cell (AS-SOFC) was developed. Today’s state-of-the-Art AS-SOFC has an electrolyte thickness of approximately 10 μm. Efforts are currently being made to reduce the electrolyte thickness further to achieve even higher performance [1-2]. However, as will be evident from the present study this may have its limitations, as a further reduction in the electrolyte thickness may lead to an increase in resistance due to the onset of lateral currents within the electrolyte layer.

The magnitude of the current constriction resistance of the individual electrode/electrolyte assemblies and the optimum electrolyte thickness depend on the structural characteristics of the electrodes. Attempts at quantifying the current constriction resistance have previously been made and models have been developed which assumes a uniformly distributed array of either squares or circles [3-4]. However, this is often not a good assumption as the electrode/electrolyte interfaces are much more complex. First of all, the electrode and electrolyte interface is not planar nor is the electrode and electrolyte transition infinitely sharp. Secondly, the contact points are neither squares nor circles, which are distributed as an array. The aim of the present study is therefore to use 3D tomography electrode/electrolyte interfacial reconstructions in numerical Finite-Element-Method (FEM) calculations to get more accurate estimations of the current constriction resistance and the effect of varying the electrolyte thickness.

[1] F. Han et al., Journal of Power Sources, 218, 157–162 (2012).

[2] C. Ding and T. Hashida, Energy Environ. Sci., 3, 1729–1731 (2010).

[3] T. Kenjo and T. Nakagawa, J. Electrochem. Soc., 143, L92–L94 (1996).

[4] J. Fleig, J. Maier, in: Proc. 5th Int. Symp. Solid Oxide Fuel Cells, U. Stimming, S. C. Singhal, H. Tagawa, W. Lehnert, Editors, p. 1374, The electrochemical Society, Pennengton NJ (1997).
Oxygen-Excess-Type Ionic Conducting Thin Film for Fuel Cell Application
Authors: Mineshige Atsushi , Kobayashi Mio , Saito Atsushi , Yoshioka Hideki , Mori Ryohei , Yazawa Tetsuo
Published: February 2020

Oxygen-excess-type lanthanum silicate (LSO) is a promising electrolyte material for intermediate-temperature SOFCs because of its high ion conductivity and low activation energy for conduction. In this study, the anode-supported solid electrolyte cell based on Mg-doped LSO, La9.8(Si5.7Mg0.3)O26.4(MDLS), was developed, and its electrical properties and fuel cell performances were evaluated.

The MDLS film was applied on top of the Ni-MDLS substrate by spin coating using nano-sized MDLS printable paste. The half cell obtained was then coated with (La0.6Sr0.4)(Co1-y
Fe
y
)O3-δ
cathode material.

The open circuit voltage of the cell was about 1.1 V, indicating that MDLS is a pure ionic conductor, and good gas-tight electrolyte was obtained. The ohmic and polarization resistances of the cell at 873 K were 3.2 and 3.1 Ω cm2, respectively. Both were able to be reduced with optimizing preparation conditions of MDLS, and inserting an interlayer between cathode and MDLS. As a result, the cell performance was largely improved, and the cell showed the power density of 855 and 97 mW cm-2 at 1073 and 873 K, respectively. It is expected that high performance intermediate-temperature SOFCs will be constructed using LSO-based electrolyte.
3D Printing Microstructured Li-Garnet Electrolytes for Solid-State Lithium Batteries
Authors: McOwen Dennis W. , Hitz Gregory , Wen Yang , Gong Yunhui , Hamann Tanner , Hu Liangbing , Wachsman Eric D
Published: February 2020

Recent advancements in solid electrolytes have brought all solid-state lithium batteries much closer to a commercial reality. Lithium garnet materials such as Li7La3Zr2O12, or LLZ, are ceramic lithium conductors that have several uniquely advantageous properties: they are completely non-flammable, low cost to produce, and stable to lithium metal, which has an energy density more than 10x higher than standard graphite electrodes (3860 mAh/g). The main areas challenging the development of all-solid-state Li-ion batteries, however, have been relatively low ionic conductivity compared organic liquid electrolytes (~1 mS/cm compared to 10 mS/cm) and high interfacial impedance due, in part, to poor solid-solid contact at the electrolyte/electrode interface. However, by controlling the thickness of the electrolyte separating the two electrodes down to the order of tens of microns, the contribution of the conductivity to the overall resistance of the bulk electrolyte can become negligible. To address the interfacial impedance requires tailoring the architecture of the electrolyte surface to maximize accessible interfacial area and reduce the resistance for Li+ cation transfer at that interface.

Using an advanced 3D printer, different approaches were taken to optimize fabrication of both thin, low resistance solid electrolyte films and films with sophisticated surface microstructures. The creation of various geometries (e.g., grid patterns, multilayer structures, etc.) and their impact on pore structure and interfacial area was investigated in depth and will be discussed. Furthermore, electrodes were infiltrated into each of the pore structures and analyzed using SEM to determine which geometry facilitated the most extensive and intimate electrode-electrolyte contact. As a demonstration of the potential impact of microstructured solid electrolytes, electrochemical testing results of the 3D printed ordered structures was compared with the random-porosity structures of the same material created by tapecasting. The ordered microstructures consistently delivered better performance due to improved electrode-electrolyte contact. This work sheds light on the importance of the solid electrolyte surface, and how tuning its structure can help to overcome the challenges of solid-state batteries.
The Effect of Heating Rate on Li Losses from Al Stabilized Li7La3Zr2O12
Authors: Dermenci Kamil Burak , Turan Servet
Published: February 2020

Li-ion batteries are considered as the most promising candidate for energy storage systems of EV’s. However, if the range of vehicle is increased, widely used flammable and explosive electrolytes will decompose. To enhance safety for EV applications, nowadays, solid electrolytes come forward. Among them, Al stabilized cubic Li7La3Zr2O12 (LLZO) shows superior electrochemical properties in terms of conductivity and stability window. During synthesis excess amount of Li must be supplied because of the volatile behavior of Li at high temperatures. The amount of excess Li is strongly dependent on heating rate during heat treatment. So, the optimization of heating rate is necessary to prevent excess Li losses.

In this study, Al stabilized LLZO will be synthesized by solid state reaction method with a heating rate of 1, 2, 5 and 10 °C/min. Their thermal behavior will be evaluated with Thermal Analysis with a heating rate of up to 10 °C/min. Their crystal structures and impurity phases will be determined by X-Ray Diffraction Techniques. Scanning Electron Microscopy will be used in order to present microstructure of synthesized pellets. Their electronic conductivities will be assessed with Potentiostatic polarization method by applying 10 V.
In-Situ AFM Observation of Highly Oriented Pyrolytic Graphite in PC-Based Electrolyte Solution Containing Magnesium Ion
Authors: Kokumai Ryohei , Song Hee-Youb , Fukutsuka Tomokazu , Miyazaki Kohei , Abe Takeshi
Published: February 2020

Introduction

Graphite is used as a negative active material in lithium-ion batteries. The surface film, called solid electrolyte interphase (SEI) formed in ethylene carbonate (EC)-based electrolyte solution, plays an important role in reversible lithium-ion intercalation and de-intercalation reaction. When propylene carbonate (PC) is used as organic solvent, electrolyte decomposition and exfoliation of graphite layers occurred. We reported that lithium-ion intercalation and de-intercalation in PC-based electrolytes was succeeded using high concentrated lithium salt electrolytes or containing multivalent cations[1-3]. However, the SEI formation mechanism in PC-based electrolyte solution containing multivalent cation was not clarified. In this study, we investigate the surface morphology changes of highly oriented pyrolytic graphite (HOPG) electrode in PC-based electrolytes containing Mg2+ by in-situ Atomic Force Microscopy (AFM) to clarify the SEI formation mechanism.

Experimental

A three-electrode cell was used for electrochemical measurements. A HOPG was used as a working electrode and lithium foils were used as a counter electrode and a reference electrode. Electrolytes were prepared from lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2, LiTFSA), magnesium bis(trifluoromethanesulfonyl)imide (Mg(N(SO2CF3)2)2, Mg(TFSA)2), and PC. The molar ratio of two cation was fixed to be Mg2+/Li = 1.2. AFM observation was conducted during the CV measurements. All potentials were referred to Li/Li+.

Results

Figure 1 shows the cyclic voltammograms and in-situ AFM image at 1st cycle of HOPG. Large reduction peak at around 0.7 V appeared in the first cycle but disappeared in the second cycle. This result indicated that irreversible electrolyte decomposition, which was related to SEI formation, occurred at the initial cycle. In the AFM image obtained between 0.508 V and 1.204 V, precipitates appeared on the HOPG surface at 0.66 V. In EC-based electrolyte solution, hill-like structures and blister structures by the co-intercalation and decompostion of solvated-lithium ion were observed around 0.9 V. However, these structures were not observed in this system. Therefore, it is proposed that the addition of Mg2+ suppressed the co-intercalation of solvated lithium ion and SEI was formed by the surface reaction.

Reference

[1] S.-K. Jeong et al., J. Power Sources, 175 (2008) 540.

[2] S. Takeuchi et al., Electrochim. Acta, 56 (2011) 10450.

[3] S. Takeuchi et al., submitted.

Acknowledgment

This work was partially supported by CREST, JST and JSPS KAKENHI Grant Number 16H04216.

Figure 1
Phase Segregated Bimetallic Alloys As Electrocatalysts for Electrochemical Carbon Dioxide Reduction
Authors: Higgins Drew Christopher , Hahn Christopher , Hatsukade Toru , Jaramillo Thomas F
Published: February 2020

Operating in tandem with renewable electricity supplies (i.e., wind or solar), electrochemical synthesis of chemical and fuel products from carbon dioxide (CO2) represents a sustainable method to fuel the energy needs of society. The primary shortcoming of this technology is the lack of catalysts that are both sufficiently active and selective. The ability to produce further reduced (> 2 electron) fuels and chemicals, such as hydrocarbons, alcohols and carbonyls, is most attractive from an economic standpoint. Catalyst surface structure engineering or alloying are both effective strategies to favour selectivity towards these targeted compounds.

More specifically, our group’s catalyst material discovery efforts on bimetallic alloys have been capable of controlling selectivity of various CO2 reduction products, owing to the effects that alloying has on the adsorption energies of key reaction intermediates. A notable drawback of many bimetallic systems however is that their low alloy formation energies cause them to segregate under the reactive conditions encountered during CO2reduction [1]. This results in an enriched surface layer of the less reactive element, and a consequential loss of the benefits achieved through alloying.

In this work we turn to a new class of bimetallic CO2 reduction catalysts, consisting of elements that are immiscible on the bulk scale. These phase segregated systems (Figure 1A) are employed in an attempt to tailor catalyst selectivity towards further reduced products. Thin films of these catalysts are prepared and tested in our custom designed electrochemical cell (Figure 1B) that allows excellent detection capabilities towards liquid based products such as alcohol and carbonyl compounds [2]. We show that by employing phase segregated systems with varying compositions and constituent elements we are able to tune the selectivity of bimetallic CO2reduction electrocatalysts.

[1] H. Hansen, C. Shi, A. Lausche, A. Peterson, J. Norskov, Phys. Chem. Chem. Phys., 2016, 18, 9194.

[2] K. Kuhl, E. Cave, D. Abram, T. Jaramillo, J. Amer. Chem. Soc., 2012, 5, 7050.

Figure 1
Electrochemical Methane Reforming Using SrZr0.5Ce0.4Y0.1O3-d proton-Conductor Cell
Authors: Maeda Shota , Kurashina Daisuke , Leonard Kwati , Lee Young-Sung , Matsumoto Hiroshige
Published: February 2020

Hydrogen will be an important energy carrier and its demand will increase significantly in the coming years. Technologies to separate hydrogen from various hydrogen production processes will thus be required. Currently steam reforming of natural gas is the most common method to produce hydrogen. The process is generally carried out at high temperature and the produced hydrogen is usually mixed with other gases. The recovery of hydrogen at high temperature without the need for cooling will significantly enhance the efficiency and performance of the system. The way to use a solid oxide cell as a membrane reactor for hydrogen production can work for this purpose. The use of high temperature proton conducting membranes to pump out the hydrogen will be a useful approach to recover highly pure hydrogen.

 In the present study, dense SrZr0.5Ce0.4Y0.1O3-δ (SZCY541) perovskite membrane was combined with NiO-SZCY541 electrode to produced hydrogen via steam reforming of methane. SZCY541 was prepared by conventional solid state reaction using SrCO3, CeO2, ZrO2, Y2O3 as precursors. The precursors were appropriately weighed, mixed and calcined at 1350 oC for 10 h in air, then ball-milled and the obtained powder pressed into pellets, and sintered at 1700 oC for 10 h in air. The hydrogen pumping was performed at 600 – 800 oC in moist CH4 and 1% H2atmosphere. The atmosphere of each electrode was measured by gas chromatography. Material resistance, electrode voltage were evaluated using a current interrupt method.

When the gas composition was measured as a function of the current, it was seen that hydrogen at the anode decreased while that at the cathode gradually increased. The rates are consistent with the theoretical calculated efficiency using Faraday’s law. Only hydrogen could be separated without the permeation of the other gases at the cathode. The anode overvoltage was observed to deteriorate due to the addition of methane. In this conclusion, high temperature proton conducting membranes can be used to pump hydrogen for the separation of pure hydrogen from the reforming of methane. It was also possible to confirm the effects of overvoltage application.

Figure 1
A Novel Two-Step Water-Splitting Electrochemical Cycle for Hydrogen Production
Authors: Choi Bokkyu , Panthi Dhruba , Nakoji Masateru , Tsutsumi Kaduo , Tsutsumi Atsushi
Published: February 2020

We propose a novel electrochemical water-splitting cycle consisting of two-step electrochemical reactions for oxygen and hydrogen production by introducing an intermediate electrode. Two-step water electrolysis offers the following advantages: (i) higher-purity hydrogen can be obtained because hydrogen and oxygen gases are generated in different steps and (ii) high energy conversion efficiency for hydrogen production can be achieved by reducing the ohmic overpotential between the electrodes through the use of a thinner separator than a conventional one. Furthermore, a pulsed current can be supplied to the electrolysis cell, which leads to a low concentration overpotential by increasing the reacting species concentration in a diffusion layer. In the present study, manganese dioxide (MnO2) was selected as the intermediate electrode because its oxidation-reduction potential is located between the potentials of the hydrogen and oxygen evolution reactions.
(Invited) Thermodynamic Theory of Durability of Soecs and SOFCs: The Role of Electrode Polarization
Authors: Virkar Anil V.
Published: February 2020

It is well-known that SOECs exhibit greater propensity for degradation than SOFCs. In a similar fashion, it is also known that batteries are more to degradation during charging than during discharging. SOFCs (power generation) and batteries can also degrade during discharge. This is related to cell imbalance. The greater the variability in the individual cell resistances in a stack or battery pack, the greater is the tendency for degradation. Onsager transport equations play a crucial role in degradation. A fundamental consideration is whether an electrochemical device is operating in galvanic mode or electrolytic mode. A battery during charging or SOEC generating hydrogen operates in electrolytic mode. A single battery cell during discharge or a single SOFC in power generation operates in galvanic mode. However, degradation in an SOFC stack or a battery pack during discharge initiates in an unbalanced cell, which actually operates in electrolytic mode. In any electrochemical device, transport coefficients must include not only transport through the electrolyte membrane but also transport across electrode/electrolyte interfaces and the corresponding polarization resistances. The main objective of this presentation is to quantitatively demonstrate the role of electrode polarizations in affecting durability. In addition, the resistance to electron transport across electrode/electrolyte interfaces will also be discussed. Some experimental results on degradation of cells with different characteristics will be presented.
Correlating the Onset of Coking with Electrode Surface Chemistry during CO2 Electrolysis with Near Ambient Pressure X-Ray Photoelectron Spectroscopy
Authors: Bishop Sean R. , Wang Jiayue , Tsvetkov Nikolai , Lu Qiyang , Gallet Jean-Jacques , Bournel Fabrice , Crumlin Ethan J , Lu Qiang , Yildiz Bilge
Published: February 2020

Recycling carbon dioxide into carbon monoxide as a feedstock for industry and transportation has become of great interest as a means to reduce the impact of humanity on the environment. Due to the high thermodynamic efficiency inherent in electrochemical reduction of CO2 at high temperatures (~800 oC), solid oxide electrolysis is an attractive method for CO production. Furthermore, in steam and CO2 co-electrolysis (SOE), the hydrogen and CO products constitute syngas, of significant importance to industry. Additionally, SOE of CO2 is actively being explored by the National Aeronautics and Space Administration (NASA) to generate O2 for rocket propellant and life support for future missions to Mars. Mitigating degradation of SOE cell performance over time remains a key challenge of the technology. For example, carbon accumulation (coking) on the cathode electrode during reduction of CO2, particularly problematic in dry conditions, leads to mechanical and electrochemical degradation of the cell. Other degradation modes, well known in the solid oxide fuel cell community, such as large electrode volume changes during redox (i.e., chemical expansion) with subsequent mechanical failure are also of concern. As a result, electrodes have been developed to counter these degradation modes in electrolysis and fuel cell operation. The majority of studies have largely been guided by empirical evidence indicating coke tolerant electrodes. In this presentation, we describe an investigation into the relationship between gas/solid interface compositional and operational factors that lead to the onset of coking. We take advantage of surface sensitive spectroscopy performed in situ in controlled gas atmosphere and temperature, known as near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS).

NAP-XPS was used to evaluate conditions leading to coking using CO/CO2 mixtures at approx. 200 mTorr total pressure at 450 oC. Electrical bias was applied to ceria based films, deposited using pulsed laser deposition on “buried” Pt electrodes, supported on ionic conducting substrates of yttria stabilized zirconia to in situ drive the CO2 reduction reaction. Two different Gd doped ceria based films were studied, one with Zr doping (suggested to exhibit greater coke tolerance) and one without. The surface spectroscopy analysis yields information about the relationship between onset of coking, surface defect concentration (e.g., oxygen vacancies), surface composition (e.g., relative cation and impurity), and area specific resistance. In this presentation, we will discuss the relationship between these factors, as well as the role of gas composition (CO/CO2).
Experimental Investigation of Operating Parameters in Power Generation By Lab-Scale Reverse Electro-Dialysis (RED)
Authors: Choi Insoo , Han Jun Young , Yoo Sung Jong , Henkensmeier Dirk , Kim Jin Young , Lee So Young , Han Jonghee , Nam Suk Woo , Jang Jong Hyun , Kim Hyoung-Juhn
Published: February 2020

The reverse electro-dialysis (RED) is a renewable technology to produce electricity by mixing of differently concentrated water. In this study, the authors fabricated lab-scale RED, and attempted to evaluate the RED performance upon different operating parameters. Firstly, the effect of salinity ratio on the performance was examined by varying the concentration of low-salinity water. The performance was optimized by open circuit voltage (OCV) and cell resistance with salinity ratio. Individual resistances were analyzed by impedance spectroscopy, and their impacts on power output were addressed. Secondly, the effect of flow rate of salinity solutions was studied, and it was found to affect the concentration polarization in RED. Lastly, the effect of the flow rate of electrode rinse solution was investigated, which increased the ionic shortcut current and decreased boundary layer resistance. Consequently, estimations on the trends in power output by changing operating parameters were made to determine effective operation of RED.