bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Throughput Electrochemistry of Li-Mn-Co-Ni-O Positive Electrodes
Authors: McCalla Eric
Published: February 2020

In the search for high-energy Li-ion positive electrodes, the layered lithium NMC oxides have been studied extensively. Despite wide interest in this system, until recently, the phase diagram remained poorly understood resulting in many conflicting reports in the literature. Combinatorial synthesis, coupled with X-ray diffraction, was used to determine the phase diagrams under various synthesis conditions [1-2]. The unexpected complexity seen in this system included multiple 3-phase regions that transform during cooling along with boundaries to single phase regions which shift during cooling. Despite the deepended understanding of the structural phase diagram, there now remains a very limited exploration of how the electrochemical properties evolve across these complex phase spaces. Herein, we adapt a high-throughput electrochemical testing system wherein 64 samples are cycled simultaneously in order to measure the cycling of the mg-scale powder combinatorial samples. The methodology involves using a solution-dispensing robot is used to make the samples by co-precipitation synthesis followed by high temperature annealing. The samples are subsequently mounted in the combinatorial electrochemical cell and cycled simultaneously. Given that the combinatorial samples here are powders, made using synthesis methods comparable to those used commercially, the results scale-up very well. Beyond the proof-of-concept of the novel high-throughput measurements, results on hundreds of samples in the Li-Mn-Ni-Co-O system of extreme interest as next-generation positive electrodes will be presented. Consequences for further studies in this popular composition space will be discussed.

References:

[1] McCalla, E., Rowe, A. W., Shunmugasundaram, R., & Dahn, J. R. (2013). Structural study of the Li–Mn–Ni oxide Pseudoternary system of interest for positive electrodes of Li-ion batteries. Chemistry of Materials, 25(6), 989-999.

[2] Brown, C. R., McCalla, E., Watson, C., & Dahn, J. R. (2015). Combinatorial study of the Li–Ni–Mn–Co oxide pseudoquaternary system for use in Li–Ion battery materials research. ACS combinatorial science, 17(6), 381-391.
Coupled Mechanical and Electrochemical Analyses of Reconstructed LiFePO4 By FIB/SEM in Lithium-Ion Battery
Authors: Kim Sangwook , Huang Hsiao-Ying Shadow
Published: February 2020

For an energy storage application such as electrical vehicles (EVs), lithium-ion batteries must overcome limited lifetime and performance degradation under specific conditions. Particularly, lithium-ion batteries show significant capacity loss at higher discharging rates (C-rates). In this work, we develop computational models incorporating coupled electrochemical-mechanical-thermal factors in order to reveal the relationship between the experimentally observed capacity loss and predicted mechanical stresses during electrochemical (dis)charging. Specifically, a multiphysics finite element model consisting of electrochemistry, heat generation, mass transport, and solid mechanics is developed to investigate thermal- and diffusion-induced stresses with the reconstructed porous microstructures of commercial LiFePO4 batteries. It has been suggested that porous microstructures in electrodes could mitigate the electrolyte reactivity for an improved battery life and safety. Therefore, the reconstructed porous microstructures from Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) images are adopted. The integrated experimental measurements and computational simulations show that: (1) lithium-ion cells electrochemically tested at 3.6C have 30% capacity loss versus cells tested at 1.2C; a corresponding stress increase of 150% is observed from the multiphysic simulations, (2) the thermal models verified by in operando temperature measurement via the fiber Bragg grating (FBG) sensor demonstrate that increasing temperature results in larger thermal stresses during (dis)charging. However, increases in thermal stress due to higher temperature played a lesser role at higher C-rates, (3) lithium ion concentration distribution is location dependent, that is, at any time and at any given C-rates, the outer layer of the particle exhibits a higher concentration than that inside the particle, and (4) higher diffusion-induced stresses are observed at the connecting areas between particles, suggesting that the higher stresses may result from higher concentration variations in the connecting area. This study presents results that include evolutions of lithium ion concentration and mechanical stresses and could help to provide insight into the decreasing electrochemical performance of lithium-ion batteries at higher C-rates.
Reactivity of Layered Oxide Surfaces with CO2 and Moisture
Authors: Sicklinger Johannes , Beyer Hans , Hartmann Louis , Sedlmeier Christian , Pritzl Daniel , Riewald Felix , Gasteiger Hubert A.
Published: February 2020

Layered Oxides such as NCM111 are state-of-the-art cathode active materials (CAMs) for commercial applications as well as promising candidates for even higher energy density batteries by raising the nickel content up to 80% (NCM811) and beyond.1 However, recent studies2–4 have demonstrated the high reactivity of Ni-rich CAMs with CO2 and moisture, which is highly problematic for industrial electrode manufacturing processes. In addition, the electrochemical performance of NCM811 is drastically deteriorated by CO2 and moisture induced surface contamination.5

We present an in-depth surface analysis by X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NCM based cathode materials before and after exposure to CO2-containing atmospheres with high relative humidity. In addition, we study the extent of surface contamination by performing thermogravimetric analysis coupled with mass spectrometry (TGA-MS). The impact on cell performance is revealed by gassing analysis via on-line electrochemical mass spectrometry (OEMS) and full-cell cycling tests. The impact of the Ni content on the surface contamination of NCM type CAMs as well as the role of the Brunauer-Emmet-Teller (BET) surface area will be elucidated. A possible strategy to mitigate the reactivity of CAM surfaces with CO2 and H2O might be the chemical modification of active material surfaces using analogous approaches to those proposed in the literature.6–8 The effectiveness of such surface treatments to prevent surface contamination will be evaluated.

Acknowledgements:

This work is financially supported by the BASF SE Battery Research Network.

References

G. E. Blomgren, J. Electrochem. Soc., 164, A5019–A5025 (2017).

I. A. Shkrob, J. A. Gilbert, P. J. Phillips, R. Klie, R. T. Haasch, J. Bareño and D. P. Abraham, J. Electrochem. Soc., 164, A1489–A1498 (2017)

S. E. Renfrew and B. D. McCloskey, J. Am. Chem. Soc., 139, 17853-17860 (2017).

N. V. Faenza, L. Bruce, Z. W. Lebens-Higgins, I. Plitz, N. Pereira, L. F. J. Piper and G. G. Amatucci, J. Electrochem. Soc., 164, A3727–A3741 (2017).

R. Jung, R. Morasch, P. Karayaylali, K. Phillips, F. Maglia, C. Stinner, Y. Shao-Horn and H. A. Gasteiger, J. Electrochem. Soc., 165, A132–A141 (2018).

J. Choi, J. Kim, K.-T. Lee, J. Lim, J. Lee and Y. S. Yun, Adv. Mater. Interfaces, 3, 4–9 (2016).

E. M. Erickson, H. Sclar, F. Schipper, J. Liu, R. Tian, C. Ghanty, L. Burstein, N. Leifer, J. Grinblat, M. Talianker, J. S. Shin, J. K. Lampert, B. Markovsky, A. I. Frenkel and D. Aurbach, Adv. Energy Mater., 7, 1700708 1-10 (2017).

Y. Su, S. Cui, Z. Zhuo, W. Yang, X. Wang and F. Pan, ACS Appl. Mater. Interfaces, 7, 25105–25112 (2015).
High Energy Density Lithium Secondary Battery with S Cathode and Si Anode Based on Carbon Nanotube Sponge
Authors: Hori Keisuke , Noda Suguru
Published: February 2020

The lithium secondary batteries with higher energy density is strongly required for electric vehicle application. The sulfur cathode and silicon anode show high theoretical capacity (1675 mAh gsulfur
-1 and 3580 mAh gsilicon
-1). Nevertheless, both active materials change their volume during charge-discharge cycles, which leads to pulverization of electrodes. Therefore, it is difficult to load large amount of active material in the electrode. Limited values of active material results in low capacity in total system of batteries due to the large mass of metal current collector (Al and Cu). To solve the problem, self-supporting, sponge-like paper of carbon nanotubes (CNTs) can be a candidate for non-metal based 3D current collector, which can reduce the mass of current collector. It also accommodates large amount of active material due to high porosity. Previously, we have developed S-CNT cathode and Si-CNT anode [1] and demonstrated high capacity for their individual half cells [1]. In this work, we combined them to achieve higher energy density full cell without any metal current collector.

Submillimeter-long few-wall CNTs produced by fluidized-bed chemical vapor deposition method [2] were used for the 3D current collector. 30-μm-thick CNT paper was fabricated via dispersion and filtration of the CNTs, and the S-CNT cathode was fabricated by sublimation of sulfur into the CNT paper. The Si-CNT anode was fabricated by co-dispersion and co-filtration of Si nanoparticles (50, 100, and 150 nm in diameter) and the CNTs followed by carbon coating by chemical vapor deposition. Lithium was pre-doped to the Si-CNT anode either by contacting it with Li foil in electrolyte or by electrochemically using Li foil as counter electrode. The full cell of the S-CNT cathode (58 mass% S) and the LixSiy-CNT anode (70 mass% Si) showed a high initial discharge capacity and energy density of over 320 mAh/g and 540 Wh/kg based on the total mass of the cathode and anode.

[1] T. Kowase, et al, J. Power Sources, 363, 450 (2017).

[2] Z. Chen, et al., Carbon, 80, 339, (2014)
In-Situ AFM Imaging of Solid Electrolyte Interphase on Silicon Negative Electrodes with an Artificial Surface Layer
Authors: Haruta Masakazu , Kijima Yuki , Ogura Nanako , Konaga Hiroto , Doi Takayuki , Inaba Minoru
Published: February 2020

Silicon is regarded as the most promising negative electrode material for next-generation lithium-ion batteries because of the high theoretical capacity. We have developed a Si powder with a flake shape (Si LeafPower®, Si-LP, OIKE & Co., Ltd.) that is 100 nm thick with a 3-5 μm lateral dimension.[1-3] The Si-LP electrode demonstrates a superior cycle performances because the unique flake structure resists pulverization during charge and discharge cycling. For further improvement of cycle performances, inhibition of reductive decomposition of electrolytes on the Si negative electrode is necessary. We tried to suppress the electrolyte decomposition by an artificial surface coating on Si thin films and investigated formation of solid electrolyte interphase (SEI) by in-situ atomic force microscopy (AFM) coupled with a potential sweep.

An amorphous Si thin film with the thickness of 100 nm was deposited by RF magnetron sputtering on a mirror polished Cu substrate. After that, LiF layer was sequentially deposited on the Si film electrode by the RF sputtering. AFM observations coupled with cyclic voltammetry were performed in a liquid immersion sample stage equipped with electrochemical connectors. The Si thin film as a working electrode and Li wires as a counter and a reference electrodes were immersed in the electrolyte of 1 M LiTFSI/EC+DEC (1:1 by vol.). AFM scan was conducted with a conventional contact mode at a room temperature in an Ar-filled glovebox. The potential was managed with a potentiostat/galvanostat and the sweep rate was 0.5 mV s-1.

In the first cycle of the cyclic voltammetry for the Si film electrode without LiF, a small cathodic current began to flow ~2 V, and a current peak arose around 0.9 V. This current peak disappeared in the second cycle, which indicated an irreversible reductive decomposition reaction of the electrolyte and formation of SEI on the Si electrode. In the AFM image coupled with the potential sweep, surface deposits emerged from ~0.9 V corresponding to the potential of the electrolyte decomposition. On the other hand, a reductive current peak and surface deposits caused by the electrolyte decomposition were not observed in the Si film electrode with LiF coating. Furthermore, the Coulombic efficiencies of the Si film electrodes improved by the LiF-coating. These results indicated that the LiF layer on the Si electrode prevented the electrolyte decomposition, and thus LiF is a very important component for SEI layer.

Acknowledgments: This work was supported by ALCA-SPRING (JST, Japan) and KAKENHI (JSPS, Japan) Grant Number 16H04649.

References: [1] M. Saito et al., J. Power Sources, 196, 6637 (2011); [2] M. Haruta et al., Electrochimica Acta, 224, 186 (2017).; [3] M. Haruta et al., Electrochimica Acta, 267, 94 (2018).
Electrical Conductivity of Prussian Blue Analogues (Cu, Ni, K Cu, K Ni)
Authors: Kumari Manisha , Redel Engelbert
Published: February 2020

Prussian Blue, Fe+3₄[Fe+2₆]₃·xH₂O is a typical hexacyanometalate network, in which cyanide ligand coordinates octahedrally with the metal ion. Interstitial cations and metal vacancies balance the local charge in PB structure. This octahedrally coordinated cyanide ligand with metal ion imparts high electrical conductivity to PB. Other than high electrical conductivity, hexacyanometalate offers interesting redox property. That makes PB suitable material for microelectronics applications such as Resistive Random Access Memories (RRAM).

PB shows change in colour during redox transitions when transitions metal cations are associated with it. The change in colour is due to charge transfer between transitions metal cations and hexacyanometalate group. This charge transfer tunes the electrical conductivity of PB compounds. Here we tune the electrical conductivity of PB by adding transition metal cations (Cu, Ni, K Cu, K Ni) into it.

Conduction mechanism will be explained based on ab initio and density of states calculations. From these calculation results, we also explain the contribution of each metal on hopping and band transport, which is the responsible conduction mechanism for varying electrical conductivity in PB analogues.
The Thermal Properties of Pristine and Loaded HKUST-1 Thin Films Under Different Environmental Conditions
Authors: DeCoster Mallory E , Redel Engelbert , Baumgart Helmut , Hopkins Patrick E
Published: February 2020

Metal Organic Frameworks (MOFs) may prove as useful materials for the improvement of the efficiency of thermoelectrics. An improved Figure of Merit could be realized by taking advantage of the intrinsically low thermal conductivity of their porous organic makeup and improving the electrical conductivity by infiltrating the pores with selective host molecules. This study experimentally examines the thermal properties of HKUST-1 Metal Organic Framework (MOF) thin films using Time Domain Thermoreflectance (TDTR). The time scale associated with TDTR allows for a valid representation of thermal transport within the solid network of the porous composite. The MOF thicknesses vary from 200-350 nm and are constructed from Cu++ dimers and benzene-tricarboxylate (BTC) units which form a crystalline, 3-D porous structure with a pore diameter of 1.2 nm. The available pores allow the loading or storage of guest molecules, such as tertracyanoquin odimethane (TCNQ). We find evidence of no size effects on the thermal conductivity of the thin MOF films with thicknesses ranging from 200 – 350 nm. Additionally, the introduction of TCNQ host molecules within the infiltrated MOF does not significantly alter the thermal conductivity compared to the pristine samples. Exposure to ambient atmosphere causes an increase in the thermal conductivity of both the pristine and infiltrated MOFs, indicating that water adsorption may be occurring and altering the thermal properties of these materials. Activation of the pristine MOF recovers the thermal conductivity of the ideal state (before exposure to an ambient air environment) showing further application of these materials as a thermal switch.
Thermoelectric Characterization of Copper Hexacyanoferrate
Authors: Hosseini Pouya , Wittstock Gunther , Kumari Manisha , Redel Engelbert , Lin Pengtao , Zhang Kai , Baumgart Helmut
Published: February 2020

Copper Hexacyanoferrate K2Cu[Fe(CN)6] nH2O forms a typical non-porous coordination network, in which cyanide ligand bridge Cu and Fe ions with octahedral coordination environment. Interstitial cations, e.g. K+ and metal vacancies balances the local charge in metals. This octahedrally coordinated cyanide ligand with metal ions of mixed valence determine the redox properties as well as the high electrical conductivity of these films. The electrical conductivity can be tunes by adding different transition metal cations (e.g. Cu, Ni) within the coordination network.

Crystalline films of K2CuFe(CN)6
were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM), X-ray photoelectron spectroscopy to confirm crystallinity, elemental composition and valence states. While the structural properties are understood, little is known about the thermoelectric application potential of these Prussian Blue Analogues. This presentation will report our findings and discuss our electrical characterization measurements utilizing Hall effect measurements to elucidate electrical properties such as carrier concentration, resistivity, mobility, Hall coefficient and an assessment for possible future applications. In addition, a complete thermoelectric characterization is being performed by employing a Lab-on-a-Chip test method, which enables deposition of metal-organic framework compounds through a mask for simultaneous measurements of the Seebeck coefficient and the thermal conductivity.
(Invited) MOF Thin Film Based Chemiresistor Gas Sensors
Authors: Xu Gang
Published: February 2020

Metal oxide (MOX) semiconducting materials, such as ZnO, SnO2, In2O3 and WO3, are the main active materials for chemresistor gas sensor due to their low cost, portability, real-time operability and ease of use. MOX based gas sensor has been developed for many industrial and domestic applications on detecting volatile organic compounds (VOCs). However, several ways such as cross-sensitivity adjustment, electronic noses and gas pre-separation by other instrument have been developed to optimize its performances, but MOX gas sensor still need to overcome the poor selectivity and high working temperature for broader commercial applications.

Metal organic frameworks (MOFs) feature regular pores, ultra-large surface areas, tuneable framework structures and open-metal sites. These features make MOFs an ideal candidate to overcome the above mentioned long-term bottlenecks of chemiresistor gas sensor . Here, we demonstrate this possiblity by two strategies of material design to optimize the performances of gas sensor:1) high quality semi-conductive MOF thin film was prepared to act as sensing active layer directly; 2) MOX@MOF core-sheath structured nanowire array was design and prepared to act the sensing active layer. The chemiresistor gas sensors based on above materials have not only exhibited improved sensitivity, but also reduced the working temperature.[1,2] Given that MOF material has greatly variable and designable structure and properties, new material designed with MOFs is promising to simplify the structure and decrease the cost of gas sensor for its application on wearable devices, intelligent automobile, smart electrical home appliances and other precise detection fields in future.

Refences:

1. Ming-Shui Yao, Xiao-Jing Lv, Zhi-Hua Fu, Wen-Hua Li, Wei-Hua Deng, Guo-Dong Wu, and Gang Xu* Angew. Chem. Int. Ed.
2017, 56, 16510.

2. Ming-Shui Yao, Wen-Xiang Tang, Guan-E Wang, Bhaskar Nath, and Gang Xu* Adv. Mater. 2016, 28, 5229.

Figure 1
Metal-Organic Frameworks Based Materials for Electrocatalyst
Authors: Li Guangqin
Published: February 2020

How to design and synthesize of efficient and earth-abundant catalysts for a wide variety of electrochemical energy storage and conversion reactions is a great challenge. Guided by the advantage of component manipulation, morphology control, and structure engineering, advanced MOF-based materials have exhibited remarkable activity, selectivity, and stability for various energy-conversion processes, manifesting great potential for replacing precious-metal-based catalysts in next-generation energy devices. We have studied MOF based materials (Pd@HKUST-1) for hydrogen storage1. Recently, we have synthesized a porous carbon nanomaterial loaded with cobalt nanoparticles (Co@NC-x/y) derived from pyrolysis of a Co/Zn bimetallic zeolitic imidazolite framework, which exhibits incredibly high activity as bifunctional oxygen catalysts2. For instance, the optimal catalyst of Co@NC-3/1 has the superb ORR activity with onset potential of ~1.15 V and half-wave potential of ~0.93 V. Moreover, its OER activity is better than commercial IrO2 and it also presents a long-term stability for 2000 circles and a Tafel slope of 85 mV dec-1.

References

[1] Li G., Kobayashi H., Taylor J. M., Ikeda R., Kubota Y., Kato K., Takata M., Yamamoto T., Toh S., Matsumura S., Kitagawa H. *, Nature Mater., 13, 802 (2014).

[2] Li Y., Jia B., Fan Y., Zhu K., Li G. *, Su C.-Y. *, Adv. Energy Mater., 201702048 (2017).
Development of PEFC Membrane Electrode Assemblies for Iron-Doped Metal Organic Framework Catalysts
Authors: Uddin Md. Aman , Langhorst Lisa , Guo Yuqi , Zhang Hanguang , Chen Mengjie , Cullen David A. , More Karren L. , Xu Hui , Wu Gang , Litster Shawn
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) have been identified as one of the most promising technologies for future electric vehicles by using clean H2 with much improved energy conversion efficiency, long range, and rapid refueling. However, due to the large amount of platinum group metal (PGM) catalyst used in their electrodes, their prohibitively high cost hinders broad commercialization of PEFCs for transportation. Therefore, there is a critical need to develop low cost, high-performance PGM-free cathode catalysts that have the potential to dramatically transform the economics of PEFC commercialization by reducing catalyst costs by one to two orders of magnitude. However, before PGM-free cathodes become viable, several technical challenges associated with PGM-free cathodes must be addressed, including insufficient activity and stability of the catalysts, and serious water flooding and large transport losses in the electrodes.

Overcoming those barriers and ultimately meeting the challenging automotive PEFC performance targets requires comprehensive research and development effort on new PGM-free cathodes. In this work, we use a newly developed approach to synthesize PGM-free catalysts for Fe-doped metal-organic framework (MOF) precursors that yield atomically-dispersed FeN4-type active sites. These catalysts exhibit high activity and improved stability at typical fuel cell operating voltages. This presentation will focus on the development of membrane electrode assemblies with cathodes prepared from this catalyst. Specific areas that will be covered are water management in thick PGM-free cathodes, ionomer integration, and cathode fabrication. The implementation of these new materials and electrode designs is supported by a suite of advanced experimental and simulation tools that identify performance and durability bottlenecks, devise solutions, and establish rational material design and future synthesis targets.

This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office (FCTO) under Award Number DE-EE0008076. The authors gratefully acknowledge research support from the Electrocatalysis Consortium (ElectroCat), established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under Contract Number DE-EE0008076.
Adsorption Behavior of PGM-Free Catalysts By Near-Ambient Pressure X-Ray Photoelectron Spectroscopy
Authors: Dzara Michael , Artyushkova Kateryna , Shulda Sarah M , Ngo Chilan , Crumlin Ethan J , Gennett Thomas , Pylypenko Svitlana
Published: February 2020

Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are an important component in the portfolio of renewable energy technologies that are important for our society. While being green technology, PEMFCs rely on precious metals to catalyze the oxygen reduction reaction (ORR) on the cathode side. Several approaches have been explored in order to reduce the amount of precious metals, including core-shell structures, extended thin films, and various alloys with non-precious metals. Potential solutions also include PGM-free catalysts made with earth abundant, inexpensive elements. One promising area of PGM-free catalyst development is the integration of nitrogen and iron into high surface area carbon nanostructures.1,2 These materials have significantly improved in activities over the past decade, yet their heterogeneous nature motivates further study into the nature of the active sites, with the goal of improving activity, active site density, and stability.

Multi-technique, multi-scale characterization of these materials, under ex situ and in situ conditions, provides opportunity to better understand surfaces of the materials under relevant conditions and to optimize various interfaces in these systems for optimum performance. In this work near-ambient pressure x-ray photoelectron spectroscopy (nAP-XPS) is used to investigate adsorption and desorption behavior of a diverse set of catalysts and supports, which contain nitrogen and iron sites of interest. Challenges associated with analysis of nAP-XPS data from adsorption and desorption studies include: i) presence of different types of potential sites and the multitude of binding energy shifts that could be happening upon adsorption on these various sites, ii) subtle changes in the spectra associated with adsorption/desorption due to low number of potential sites for adsorption, and iii) sampling depth limitations of the technique.3 To overcome these challenges, we explore less conventional approaches to analysis of the XPS N 1s and O 1s spectra, and complemented XPS with other in situ techniques such as diffuse reflectance infrared fourier transform spectroscopy (DRIFTS).

Figure 1. XPS N1s difference spectra comparing adsorption and desorption processes on a PGM-free FeNC material.

Jaouen, F., Proietti, E., Lefèvre, M., Chenitz, R., Dodelet, J.P., Wu, G., Chung, H.T., Johnston, C.M., and Zelenay, P., Energy Environ. Sci.
4, 114 (2011).

Wood, K. N., O’Hayre, R., and Pylypenko, S. Energy Environ. Sci.
7, 1212 (2014).

Matanovic, I., Artyushkova, K.; Strand, M. B., Dzara, M. J., Pylypenko, S., Atanassov, P., Core Level Shifts of Hydrogenated Pyridinic and Pyrrolic Nitrogen in the Nitrogen-Containing Graphene-Based Electrocatalysts: In-Plane vs Edge Defects. J. Phys. Chem. C
120, 51 (2016)

Figure 1
(Invited) Medium Temperature Fuel Cells: Stack and Material Advances
Authors: De Castro Emory Sayre , Pavlicek Ryan , Sharma Manav , Kanellopoulos Thomas , Zelenay Piotr , Yin Xi
Published: February 2020

Fuel cells that operate between approximately 150 oC and 250 oC accrue certain advantages, most notably facilitated operation with low grade / low cost hydrogen sourced from carbon feedstocks, direct oxidation of high energy density fuels such as dimethyl ether, robust cathode performance in the presence of air contaminants, absence of balance of plant components for stack water management, high quality heat, and readily sourced materials of construction. Fuel cells running at these intermediate temperatures with phosphoric acid as the electrolyte currently hold the record for a commercial lifetime warrantee (1). Yet, lower temperature polymer electrolyte fuel cells (PEFC) operating at under 100 oC and comprised of a conductive membrane, electrodes, and gas diffusion layers offer the potential for low cost assembly at high volumes, especially if these components are made with roll-to-roll processes. The better of these two technologies would be a hybrid high temperature Membrane Electrode Assembly (MEA) based on phosphoric acid electrolyte.

Advent Technologies identified and developed a pyridine polymer based TPS® system using phosphoric acid imbibed into the membrane matrix. Advent’s TPS membranes operate over a wide temperature range from ~120 °C to greater than 200 °C. In 2014, Advent became the licensee of BASF’s PBI MEA (P1100W) and gas diffusion electrode technology. Advent develops, manufactures, and markets both PBI and TPS MEAs. Thus, these two platforms fulfill the promise of the operating features of the phosphoric acid electrolyte with the manufacturing ease of MEAs.

This presentation will present an overview and survey of advances pertaining to medium temperature fuel cells. The survey will include examples of membrane developments including next generation PBI as well as TPS MEAs operating at over 200 °C with direct fuels. We will present several commercial successes utilizing the features of medium temperature fuel cells. Lastly, we will show the results of Advent’s efforts in leveraging our HT MEAs in medium temperature stack technology in the 100W to 3kW range.

1. http://www.doosanfuelcell.com/en/main.do
Impact of Gas Diffusion Layer Mechanics on PEM Fuel Cell Performance
Authors: Irmscher Philipp , Qiu Diankai , Janßen Holger , Lehnert Werner , Stolten Detlef
Published: February 2020

In a stack assembly cells are clamped together and therefore mechanical interactions are induced into the stack. The mechanical behaviour has a strong influence on the performance. For example the gas diffusion layer (GDL) is a porous layer which will lose its porosity if the pressure level is too high, whereas the contact area between GDL and flow field needs high pressure for a low contact resistance [1].

In this study experiments are performed to investigate the mechanical behavior of different GDL materials in a Polymer Electrolyte Membrane (PEM) Fuel Cell. The relationship between pressure on the active area and the performance of a single cell is determined. For this purpose, a test cell from Baltic Fuel Cells GmbH, Germany, is used, which allows to change the pressure level during fuel cell operation and to record performance curves. Thus, the optimum operating point of the cell can be determined. To distinguish which mechanical effects have an influence, ohmic resistance [2] and permeability measurements depending on the mechanical load on the GDLs were performed. To analyze the mechanical structure scanning electron microscope (SEM) pictures were taken from the different GDLs.

The test results regarding the optimum pressure level show that the performance decreases strongly at pressures below 0.6 N/mm². This is explained by the increasing contact resistance between the individual components. At higher pressure levels the expected performance optimum is achieved for some GDL materials. The SEM pictures reveal that the fibres took mechanical damages starting from dents up to GDL areas with a high amount of broken fibres. But some materials show a different behaviour from that. For example a pressure level above 1 N/mm² results in a constant performance plateau, an increase of the pressure up to 3 N/mm² does not increase or decrease the performance anymore. The contact resistance is no longer noticeably reduced at these pressures, while even at the maximum pressure of 3 N/mm², enough gas passes through the porous GDL to the membrane, so the porosity is still sufficient.

These results show that the mechanical behavior influences the characteristics of the GDL and the performance of the fuel cell. A minimum pressure of 1 N/mm² on the entire active area should be ensured for the used GDL types for an optimum performance of a PEM fuel cell, whereas the maximum clamping pressure depends strongly on the type of GDL which is used.

D. Qiu, P. Yi, L. Peng, X. Lai; Assembly design of proton exchange membrane fuel cell stack with stamped metallic bipolar plates; International Journal of hydrogen energy 40 (2015) 11559-11568

D. Qiu, H. Janßen, L. Peng, P. Irmscher, X. Lai, W. Lehnert; Electrical resistance and microstructure of typical gas diffusion layers for the proton exchange membrane fuel cell under compression; (2018) submitted
(Invited) Further Excursions into the Probing of Internal and Interfacial Structure of Ionomer Thin Films
Authors: Karan Kunal
Published: February 2020

The critical importance of catalyst layer ionomer in numerous transport phenomena (proton conduction, oxygen and water transport) and also in catalyst utilization at multiple length scales is well acknowledged [1]. Thickness-dependent properties such as proton conductivity, water uptake, swelling and water diffusivity have now confirmed that ionomer thin films possess properties significantly different than those of the bulk ionomer materials [2]. Previous work from our group, both independent and collaborative, confirmed suppression of proton conductivity in thin films [3], wettability changes with film thickness and thermal annealing [4], influence of substrate on internal structure [5] and water uptake [6], similarity of T2-relaxations in proton NMR of thin and thick films [7] and recent discovery of temperature-dependent vibrational mode of Nafion ionomer [8].

Tremendous progress made on the topic of ionomer thin films over the past decade has been summarily presented in a recent review [2]. However, many aspects of ionomer thin film structure and properties still remain unknown. For example, despite the confirmation of strong thickness-dependence of ionomer properties for film below 50 nm thickness, one question continues to elude us: what is the critical thickness below which ionic domains cannot be sustained? In a quest to answer this question, we have employed high-resolution electron microscopy to deduce the presence/absence of ionic domains in 4-30nm thin films. There is indication of a critical thickness below which domains are evidently not present.

Recent neutron reflectometry measurements from our group have focussed on the quantification of interfacial water (Pt/ionomer interface) and water in the bulk phase of the ionomer thin films on platinum substrate. The results acquired to date indicate that both interfacial and bulk water are dependent on the ionomer molecular structure. Complementing these measurements with GISAXS, ellipsometry, QCM and impedance spectroscopy – a clearer picture of the ionomer structure-property is emerging.

The talk will share these new results and discuss the implications of the findings on fuel cell behaviour.

Reference:

Karan, Current Opin. Electrochem. 5 (1), (2017) 27-35.

Kusoglu, A.Z. Weber Chem Rev, 117 (3) (2017), 987-1104

K. Paul, R. McCreery, K. Karan, J Electrochem Soc, 161 (14) (2014), F1395-F1402

K. Paul, H.K.K. Shim, J.B. Giorgi, K. Karan, J Polym Sci Part B: Polym Phys, 54 (13) (2016), 1267-1277

Kusoglu, D. Kushner, D.K. Paul, K. Karan, M.A. Hickner, A.Z. Weber, Adv Funct Mater, 24 (2014), 4763-4774

K. Shim, D.K. Paul, K. Karan, Macromolecules, 48 (22) (2015), 8394-8397

NE De Almeida, DK Paul, K Karan, GR Goward, J Phys Chem C 119 (3), (2015) 1280-1285

VO Kollath, K Karan, Physical Chemistry Chemical Physics 18 (37), (2016) 26144-26150
A Kinetic Modeling Approach to Estimate the Lifetime of Polymer Electrolyte Fuel Cell Membranes Under Accelerated Stress Test Conditions
Authors: Khattra Narinder Singh , El Hannach Mohamed , Wong Ka Hung , Kjeang Erik , Lauritzen Michael Victor
Published: February 2020

Failure of membranes used in polymer electrolyte fuel cells is attributed to the in-situ chemical degradation of the membrane that is further exacerbated by the mechanical stresses generated due to hygro-thermal cycling during fuel cell operation. The chemical radical attack on the polymer chains within the membrane leads to gradual loss of the material and randomly distributed stress concentration sites are created. These sites are then subjected to repeated swelling and shrinkage of the membrane, eventually leading to the appearance of micro-cracks and/or pin-holes in the membrane. To simulate the lifetime of a fuel cell membrane in such an environment, it is therefore important to consider both these effects that occur simultaneously in the membrane. A stochastic modeling approach is presented in this work that takes into consideration the rates of chemical and mechanical degradation of the membrane incorporated into a two-dimensional membrane lattice network. While the rate of chemical degradation is based on the solution of reaction kinetics occurring in a fuel cell membrane, the mechanical degradation rate is evaluated using a stress-biased, thermally activated process. Depending upon any given chemical and mechanical load, and using appropriate physical properties of the membrane, the model can predict, within reasonable error, the time to crack initiation in the membrane based on a probabilistic non-homogeneous Poisson-type process. The membrane lifetime predictions are validated against test data acquired for membranes subjected to accelerated stress tests.
Polymer Electrolyte Fuel Cell Degradation through Foreign Cation Contamination, Proton Depletion and Carbon Corrosion
Authors: Banas Charles Joseph , Arman Md. Tanvir Alam , Uddin Md Aman , Park Jaehyung , Bonville Leonard J. , Pasaogullari Ugur
Published: February 2020

Foreign cation contamination causes accelerated degradation in polymer electrolyte fuel cells (PEFCs). Because foreign cations have a higher affinity to the sulfonic acid side chains, they replace protons in perfluorosulfonic acid (PFSA) membranes, reducing ionic conductivity and lowering water content, leading to reduced oxygen reduction reaction kinetics.1-2

While foreign cations are known to cause several degradation mechanisms in PEFCs, no study has examined the influence of cationic contamination on carbon corrosion. In this work, we report on the results from 400 hour fuel cell tests were performed on commercial, as-received and Ca2+ contaminated catalyst coated membranes (CCMs) to evaluate the effects of long term exposure of foreign cations on fuel cell performance and degradation. Following testing, significant thinning of the cathode catalyst layer was observed across the entire active area in the contaminated cell, while only localized thinning was observed in the as-received baseline CCM.

Analysis of the elemental maps and line intensity profiles of platinum (Pt) obtained from energy dispersive X-ray spectrum (EDX) shows minimal change in total platinum content across the thickness of the catalyst layer, and hence loss of carbon is suspected to be the cause of the thinning. A numerical model2 is employed to show the foreign cation redistribution during testing, which shows proton depletion in the cathode catalyst layer when the CCM is contaminated with foreign cations (shown in Figure 1). We hypothesize that this lack of protons leads to accelerated carbon corrosion in the cathode to supply protons to oxygen reduction where foreign cations block transport of protons. A carbon corrosion scheme is presented which shows that under the operating potentials of the cell, carbon oxidation can occur, leading to the observed thinning.

References

1) T. Okada et al., J. Phys. Chem. B, 103, 3315-3322 (1999).

2) M.A. Uddin and U. Pasaogullari, J. Electrochem. Soc.
161(10), F1081-F1088 (2014).

Figure 1
Phosphonated Ionomers for Ion-Pair Coordinated High Temperature Pemfcs
Authors: Lee Albert S , Park Eun Joo , Atanasov Vladimir Milanov , Kerres Jochen , Jia Hongfei , Kim Yu Seung
Published: February 2020

High temperature proton exchange membrane fuel cells (HT-PEMFCs) offer significant advantages over PEMFCs operating below 100 °C including the lack of need for humidifiers and smaller radiator sizes due to simplified thermal management, potentially providing a solution to vastly reduce the cost of fuel cells and their application to automobiles.1 Polymer electrolytes based on phosphoric acid-doped polybenzimidazole have given decent fuel cell performance, but suffer from stability issues stemming from the leaching of the liquid phosphoric acid carrier electrolyte at either lower temperatures or when exposed to water.2 While our previous development of ion-pair coordinated electrolyte systems improved the versatility of fuel cell operation temperature,3 this study investigates the optimization of HT-PEMFC performance through various electrodes formulation with a phosphonated ionomer based on a pentafluorostyrene,4 mitigating the need for electrode post-doping procedures. In this presentation, we report the benefits of using phosphonated ionomers for ion-pair coordinated membrane fuel cells under anhydrous conditions.

References

Chandan, M. Hattenburger, A. El-kharouf, S. Du, A. Dhir, V. Self, B.G. Pollet, A. Ingram, W. Buljaski, J. Power Sources, 2013, 231, 264-278.

Li, J.O. Jensen, R.F. Savinell, N.J. Bjerrum, Prog. Polym. Sci., 2009, 34, 449-477.

-S. Lee, J.S. Spendelow, Y.K. Choe, C. Fujimoto, Y. S. Kim, Nature Energy, 2016, 1, 16120-16124.

Atanasov, A. Oleynikov, J. Xia, S. Lyonnard, J. Kerres, J. Power Sources, 2017, 343, 364-372.
Shape-Controlled Pt Nanoparticles for the Electro-Reduction of Oxygen
Authors: Safo Isaac Adjei , Oezaslan Mehtap
Published: February 2020

Undoubtedly, shape-controlled Pt nanoparticles are of great interest in today´s fuel cell research, because they build a unique bridge between UHV-prepared single crystals and industry-related catalysts. Since most of the fundamental studies for the oxygen reduction reaction have been performed by using single crystals, the knowledge transfer to real nanoparticle catalyst system is heavily limited.[1-3] However, surfactants and capping agents are required to control the growth, orientation and size of the seeds to form nano-scaled single crystals with high mono-dispersity. Therefore, simple strategies to clean the superficial surfaces of the single nanocrystals without any structural and electro-catalytic losses are needed.

In this work, we investigated shape-controlled Pt nanoparticles like nanocubes for the ORR by using various synthetic routes. We revealed that the electronic structure of these shape-controlled Pt nanoparticles is modified in dependence on the kind of surfactant or capping agent used in the preparation. To understand the interaction between surfactant and metallic surface, which strongly affect the number of catalytically active centers and thus the catalytic ORR activity, we used a combination of different techniques like high resolution (scanning) transmission electron microscopy (HR-(S)TEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR). In addition, we provide cleaning procedures to successfully remove the surfactant without any particle shape loss. For instance, a combination of solvent washing and electrochemical cleaning increase the electrochemically surface area of the Pt nanocubes by a factor of 10 – 15. This immeasurably boosts the catalytic properties of the Pt nanocubes for the ORR. Nevertheless, after successful cleaning process the structural stability and electrochemical durability of the “naked” Pt single-nanocrystals were investigated by applying accelerated degradation protocols. A structural transformation of the single nano-crystals to near-spherical nanoparticles was identified to be dependent on the electrochemical potential and the number of scans. Our goal is to better understand the interplay between surfactant-metal interaction and electrochemical reaction process for the development of highly active nano-crystal surfaces and to fill the knowledge gap between single crystal surfaces and nano-scaled polycrystalline materials for the ORR.

Reference

[1] M. Oezaslan, F. Hasché, P. Strasser, The Journal of Physical Chemistry Letters, 4 (2013) 3273-3291.

[2] D. Li, C. Wang, D.S. Strmcnik, D.V. Tripkovic, X. Sun, Y. Kang, M. Chi, J.D. Snyder, D. van der Vliet, Y. Tsai, V.R. Stamenkovic, S. Sun, N.M. Markovic, Energy & Environmental Science, 7 (2014) 4061-4069.

[3] I. A. Safo, M. Oezaslan, Electrochemical acta, 241 (2017) 544 - 552
Electrochemical Stability Studies of Nanostructured Carbon Based Pt-Cu Electrocatalysts for the Oxygen Reduction Reaction
Authors: Valenzuela-Muñiz Ana Maria , Pech-Pech Ildefonso Esteban , Verde Gómez Ysmael
Published: February 2020

One of the main objectives for the large-scale commercialization of proton exchange membrane fuel cells (PEMFC) is the reduction of the active metals loading at the electrodes, since the most utilized is the platinum (Pt) a very expensive material. As a feasible alternative, alloys and core-shell nanostructures are being studied in order to achieve this goal. However, the stability of these types of structures is still a drawback. On the other hand, carbonaceous materials are historically used as support of the metallic particles; the intrinsic characteristics of carbon have allowed creating better electrocatalysts. In this research work, an extensive study of the electrochemical stability of Pt-Cu/Carbon system was performed. Pt-Cu nanostructures were supported over different carbonaceous materials, and the performance towards the oxygen reduction reaction (ORR) in acid medium was evaluated. The nanoparticles were obtained by chemical reduction method using sodium borohydride as reducing agent and hexadecyltrimethylammonium bromide as surfactant at room temperature and without applying inert atmosphere. Cooper nanoparticles were enriched with Pt on their surfaces and supported on two different supports; Vulcan XC-72 Carbon and Carbon Nanotubes, keeping the metal loading below 10 wt.%. The Pt-Cu nanoparticles show spherical morphology and average size of around 10 nm as determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Structural characterization by X-ray diffraction (XRD) and electrochemical analysis obtained by linear and cyclic sweep voltammetry reveal that the structure of the Pt-Cu nanoparticles as well as their electrochemical stability to catalyze the ORR are dependent on both, the nature of the nanoparticle structure as well as the support. The obtained results could have a significant impact on the design of new nanostructured cathodic electrocatalysts for clean energy conversion in a PEMFC, and will be presented at the conference.