bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the Design of High-Energy-Density Graphite Negative Electrodes on the Electrochemical Performance
Authors: Malifarge Simon , Franco Alejandro A. , Delobel Bruno , Delacourt Charles
Published: February 2020

Energy density of current Li-ion cells still need improvement for wide-spreading sales of electric vehicles. One can increase energy density of cells based on state-of-the-art active materials, such as graphite, by using thicker and/or lower-porosity electrodes, which contain a higher active-material loading. A downside of this approach is that in addition to enhancing the cell energy density, these thick/dense porous electrodes suffer lower cell power capability because of higher electrolyte transport limitations across the electrode. Large concentration and potential gradients develop across the electrode, leading to significant polarization increase and the possible occurrence of side reactions, such as Li plating. Active particle shape may also contribute to electrolyte transport limitations; Anisotropic particles may stack in a preferred direction that likely impede ionic transport. When studying high-energy-density porous electrodes, it is then essential to correlate the electrochemical performance with design parameters. Physics-based models, such as the Newman porous electrode model [1], prove effective to attempt such a correlation.

In this work, industry-grade graphite porous electrodes with different thicknesses and porosities are studied by a variety of electrochemical techniques such as rate-capability tests, pulse tests and electrochemical impedance spectroscopy. Electrode tortuosities are estimated with a model analysis of impedance diagrams of symmetric graphite/graphite cells. Tortuosity values lie well above what is predicted by the Bruggeman relation possibly because the graphite particles have a platelet-like shape that promotes a stacking perpendicular to ionic pathways. Cycling and rate performance as well as electrochemical impedance of several high-loading-electrode designs are compared.

[1] T.F. Fuller, M. Doyle, J. Newman, Simulation and Optimization of the Dual Lithium Ion Insertion Cell, J. Electrochem. Soc. 141 (1994).

Figure 1
Coupling of Pore-Phase and Solid-Phase Networks for Simulating Heat and Mass Transport in Porous Transport Layers
Authors: Konduru Vinaykumar , Allen Jeffrey S
Published: February 2020

Reactant, water, and heat transport through Porous Transport Layers (PTL), also known as Gas Diffusion Layers (GDL), can be simulated using a variety of computational architectures and transport models. A common approach is to create detailed reconstruction of geometry from tomographic data and use a Lattice-Boltzmann model for computing transport within the material. Another common approach is to simulate the material using a network of transport resistance elements and then use continuum, phenomenological, or Lattice Boltzmann models for computing transport through the network.

For either approach the computational domain should be representative of the morphology and structure of the PTL being simulated. Geometric reconstructions of tomographic data naturally capture the morphology and structure, but at great computational expense when simulating heat and mass transport. A computationally efficient method is to create an abstraction of the PTL in a simple, regularized domain known as a pore-network model (PNM). This latter approach resolves the issue of computational expense, but lacks a clear relationship to the original structure and morphology of the PTL that is generally stochastic.

The stochastic morphology of a PTL can be characterized using a probability distribution of void volume size, known as a pore size distribution, which is invariant with respect to sample size. Pore size distribution data can be obtained using porosimetry or tomography and is almost universally based on spherical pore volumes.

This presentation discusses a methodology for transforming a spherical pore size distribution data into a pore-network model domain. This methodology maintains the appropriate stochastic distribution, physical size and bulk porosity of the original PTL. The resulting PNM domain is unique to the original PTL sample; meaning that the pore-network is material or manufacturer specific. Thus, simulation of reactant and water transport is also material or manufacturer specific.

The methodology developed transforms a spherical-pore size distribution into a regularly-spaced network of pore cylinders; referred to as the pore-phase network. In order to simulate thermal transport in a PTL using the PNM architecture, the solid portion of the original material must also be transformed into a complimentary solid-phase network. The solid-phase network should also preserve the original stochastic morphology and bulk porosity of the PTL. In this methodology, the two networks (pore-phase and solid-phase) are generated independent of one another, connected only through the distribution of unit cell porosities. In this manner thermal transport through the solid-phase network can be validated independently of liquid water transport through the pore-phase network and vice-versa. When combined, the dual PNM networks capture the coupled thermal and mass transport through the PTL.
Numerical Predicting of Liquid Water Transport inside Gas Diffusion Layer for PEMFC Using Lattice Boltzmann Method
Authors: Satjaritanun Pongsarun , Shimpalee Sirivatch , Weidner John W. , Hirano Shinichi , Lu Zijie , Shum Andrew , Zenyuk Iryna V. , Ogawa Shohei , Litster Shawn
Published: February 2020

The purpose of this work is to use a numerical simulation applying the Lattice Boltzmann Method (LBM) [1-2] technique to understand the two-phase transport of liquid water and air inside the gas diffusion layers (GDLs) used in polymer electrolyte membrane fuel cells (PEMFC). The liquid water breakthrough dynamics described by the capillary pressure across the GDLs with and without a microporous layer (MPL) are the major focus in this work. The model geometries of GDLs and MPLs used in this study were obtained by three dimensional reconstructed micro-structure from both Nano and Micro X-ray computed tomography (CT). The overall predictions of water breakthrough pressure agree with the data observed in the experiment. They also reveal that the breakthrough pressure and liquid water evolution inside the GDL samples are different when the wetting properties of GDL and/or MPL are changed. Figure 1 gives an example of model geometries for the simulation. It consists of both GDL and MPL those were taken from Nano X-ray CT. This also includes a crack that was observed from the image. Figure 2 shows an example of the predictions of water evolution inside the GDL and MPL. When the liquid water was pushed from MPL to GDL, liquid water spread all over the MPL before it moves toward the GDL. This is because the pressure required to push the liquid water thru the MPL structure or the crack in MPL is higher than the pressure used for liquid water spreads on the top of MPL [3].

References:

U. Frisch, B. Hasslacher, Y. Pomeau, Physical review letters 56 (14) (1986) 1505-1508.

G. R. McNamara, G. Zanetti, Physical Review Letters 61 (1988) 2332-2335.

P. Satjaritanun et al., J. Electrochem. Soc., submittied (2017).

Figure 1
Transport Resistances in Fuel-Cell Catalyst Layers
Authors: Chowdhury Anamika , Radke Clayton J. , Weber Adam Z.
Published: February 2020

Catalyst layers (CLs) in polymer-electrolyte fuel cells have garnered the attention of researchers due to their association with high local mass-transport resistance at low catalyst loadings [1, 2]. Nevertheless, the genesis and nature of CL resistance(s) is still under debate. CLs are only a few micrometers thick with complex geometry and heterogeneous phases making in-situ examination of CL transport processes extremely difficult.

In this study, we probe the nature of CL resistances experimentally and theoretically. Using a hydrogen-pump limiting-current modality, we deconvolute the various gas-transport-related resistances without the impact of those associated with the oxygen-reduction reaction (e.g., water production) [3]. An analytical model to quantify the experimental measurements is developed to analyze the data and to elucidate limiting regimes. Our new results are in agreement with literature limiting-current measurements.

Similar to previously reported studies [4], the model demonstrates that the transport of the reactant to the surface through the ionomer film tends to be the dominant resistance in CLs with a linear dependence on the inverse of Pt loading (i.e., roughness factor) [5]. Further, we study the dependence of this resistance on operational parameters including pressure, RH, temperature, gas molecular mass, and ionomer type. The garnered information exposes the controlling resistances, especially in comparison to ex-situ ionomer thin-film properties. Our efforts can be utilized to understand and develop mitigation strategies for local CL resistances.

Acknowledgements

We would like to thank helpful discussions and data provided by KC Neyerlin at NREL. This work was funded under the Fuel Cell Performance and Durability Consortium (FC PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231.

References:

A. Weber and A. Kusoglu, Journal of Material Chemistry A, 2,17207–17211 (2014).

A. Kongkanand and M. F. Mathias, The Journal of Physical Chemistry Letters, 7, 1127 (2016).

F. Spingler, A. Phillips, T. Schuler, M. Tucker and A. Weber, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.036

N. Nonoyama, S. Okazaki, A. Weber, Y. Ikogi and T. Yoshida, Journal of The Electrochemical Society, 158 (5), B416 (2011).

T. Greszler, D. Caulk and P. Sinha, Journal of The Electrochemical Society, 159, F831 (2012).
Measurement of Mechanical Behavior of Pristine Fuel Cell Electrodes Using Water Surface
Authors: Kim Sanwi , Kim Jae-Han , Oh Jong-Gil , Jang Kyung-Lim , Jeong Byeong-Heon , Hong Bo Ki , Kim Taek-Soo
Published: February 2020

Mechanical robustness of polymer electrolyte fuel cell (PEFC) electrodes is essential to keep the performance and to improve the durability. To increase the mechanical robustness, mechanical behavior of PEFC electrodes should be investigated because the mechanical failures such as cracks, tears and punctures are critical to lifetime decrease. However, there are no attempts to investigate the mechanical behavior of a pristine electrode without any substrates because it has been a significant challenge due to its porous and brittle nature. Therefore, we present a novel method that can be used to investigate the mechanical behavior of free-standing PEFC electrodes on the water surface. The water surface enables measurement of the mechanical properties of electrodes due to its high surface tension and low viscosity. To separate the pristine electrode from the decal transfer film without damage, we adopted an innovative ice-assisted separation method. The tensile tests on water surface were conducted to understand of the effect of the ionomer content and Pt loading. Young’s modulus, elongation at break and tensile stress at break increased with increasing ionomer content in all Pt loading conditions. Also, the scaling law relationship of E~ρ1.6 between Young’s modulus and density was suggested. Our method can be used to design mechanically robust electrode for PEFC or evaluate the degradation degree of electrodes.
Investigation of PEMFC Performance and Property of the Gas Diffusion Layers Utilizing the Numerical Model
Authors: Hirano Shinichi , Shimpalee Sirivatch , Lu Zijie , Satjaritanun Pongsarun , Weidner John W.
Published: February 2020

The overpotential at the cathode is significantly large in the proton exchange membrane fuel cells; therefore, the oxygen concentration in the oxygen reduction reaction (ORR) area is vital. Condensed water in the flow field and the gas diffusion layer (GDL) reduces oxygen transport to the ORR area. The enhancement of the mass transport of liquid water and oxygen is critical to improve fuel cell performance particularly at the high current density operations. It is required to reduce the total active area in the fuel cell stack and also it is leading to the significant cost reduction. Experimental investigation of oxygen transport has been limited by an inability to resolve water saturation-dependent properties. The two-phase thermos-fluid dynamics model of GDL was developed with Lattice Boltzmann Method (LBM) and it was integrated with computational fluid dynamics (CFD) based proton exchange membrane fuel cell (PEMFC) model to simulate the fuel cell performance with given design parameters and operational conditions [1, 2]. This work, utilizing the developed model, investigates the correlations between fuel cell performance and GDL structures and material properties. Some empirical studies were pursued and structure and property of the micro porous layer (MPL) in the GDL is correlated to the fuel cell performance particularly high current densities [3-5]. The model simulates the fuel cell performance with various porosity and permeability of MPL in the cathode GDL to investigate those correlations. Also the two-phase model can show the presence of residual liquid water in the cathode GDL which effects on the fuel cell performance. It can distinguish the residual liquid water in the GLD underneath of the flow field channel ribs and under the channels. Figure 1 gives an concept of integrated CFD based PEMFC model with micro-scale GDL model with LBM. Figure 2 shows residual liquid water in the cathode GDL with various operating conditions. In this fuel cell design, residual liquid water is correlated with cathode conditions, relative humidity, rather than the current density. It shows the potential capability of a model-based investigation of mass-transport to find solution of design and operational conditions in the PEMFC.

 

References:

1. S. Shimpalee, et. al., ECS Trans., 6493): 693-654 (2014)

2. S. Shimpalee, et. al., Multi-scale Modeling of Transports inside PEMFC By Combining Multiphase, Abstract 2387, 230th ECS Meeting, Honolulu, HI, Oct. 2, 2016.

3. Y. Aoyama, et. al., ECS Trans., 69 (I7): 743-752 (2015)

4. J. Eller, et. al., ECS Trans., 50(2): 477-486 (2013)

5. J. Eller, et. al., ECS Trans 69(17): 523-531 (2015)

Figure 1
A 1D+1D Model of Direct Ethanol Fuel Cells Based on an Optimized Kinetic Mechanism for Ethanol Electro-Oxidation Involving Free and Adsorbed Intermediate Species
Authors: Sánchez-Monreal Juan , García-Salaberri Pablo A. , Vera Marcos
Published: February 2020

Ethanol electro-oxidation is known to proceed through a series of elementary reactions that involve free and adsorbed species, like acetyl, hydroxyl, and carbon monoxide, and lead to a mixture of oxidation products such as acetaldehyde, acetic acid, carbon dioxide and methane. The major electro-oxidation products of ethanol on Pt electrodes are acetaldehyde and acetic acid, instead of carbon dioxide, making incomplete oxidation of ethanol one of the main challenges for the development of Direct Ethanol Fuel Cells (DEFCs). As recently shown by the authors [1], acetaldehyde plays an important role because it is not a truly final product of the reaction, but a free intermediate species that can be oxidized to acetic acid or, even further, to carbon dioxide. The kinetic model presented in [1] showed its capability to be adapted, via genetic algorithm optimization, to different binary Pt-based catalyst compositions, reproducing the anode overpotential and product selectivity in a wide range of operation conditions. Moreover, the consideration of several intermediate species enabled improved modeling of the crossover flux and the resulting mixed potentials induced at the cathode side.

In this work, we present a 1D + 1D model for liquid-feed DEFCs. One-dimensional convective transport along the channel is coupled to a one-dimensional model that accounts for species transport through the MEA, as well as electrochemical kinetics, including the mixed potential due to ethanol/acetaldehyde crossover. The complex kinetics of the multi-step ethanol oxidation reaction is described with the model proposed in [1]. A simple along-the-channel convective model is used to describe the downstream variation of the concentrations of the different species. This provides, in particular, the variation of the local current density. The results show that the current density distribution is highly dominated by the decrease of the ethanol concentration down the anode channel, together with the change of the production/consumption rate of free species. The variation of the ethanol and acetaldehyde concentration impacts the anode reaction rates and the ethanol/acetaldehyde crossover flux, which affects the cathode reaction rates.

References

[1] J. Sánchez-Monreal, P. A. García-Salaberri, M. Vera, Mathematical Modeling of Direct Ethanol Fuel Cells Using a Multi-Step Chemical Kinetic Mechanism, ECS Trans. 72 (2016) 1-16.
Synthesis of a Polymer Electrolyte Based on Silicotungstic Acid, Performance, and Mechanical Durability in a Proton Exchange Membrane Fuel Cell
Authors: Motz Andrew R , Kuo Mei-Chen , Herring Andrew M
Published: February 2020

While perfluorinated sulfonic acids (PFSA)s have many desirable qualities for use as a membrane separator in a polymer electrolyte membrane fuel cell (PEMFC), they suffer from decomposition via radical attack and excessive swelling. These two properties reduce the chemical and mechanical durability, respectively, of PFSA materials in the operating environment of a fuel cell. Through using heteropoly acids (HPA)s as an ion-conducting, crosslinking moiety, these short comings of PFSA membranes can be overcome. HPAs are known to be highly conductive [1] and are able to react with radicals. Our approach is to use a commercially available fluoroelastomer and functionalizes using HPA crosslinks. First, FC-2178 (polyvinylidene-co-hexafluoropropylene) is functionalized with phosphonic acid containing sidechains. Next, lacunary silicotungstic acid is covalently bonded to acidic sicechains. This material is stable in aqueous environments, unlike blends of HPA and PFSA. The results of in-situ evaluation of these membranes show impressive durability in accelerated stress test (AST). The loss of open circuit voltage (OCV) in the chemical degradation test is much less than traditional films, resulting in >0.8V OCV after 500 hrs. Also, the minimal swelling of this material leads to greater durability in humidity cycling ASTs with negligible H2 crossover after 20,000 dry wet cycles. Overall, this material shows great promise in outperforming PFSAs in chemical and mechanical ASTs.

References:

[1] Nakamura, O.; Kodama, T.; Ogino, I.; Miyake, Y., High-Conductivity Solid Proton Conductors - Dodecamolybdophosphoric Acid and Dodecatungstophosphoric Acid Crystals. Chemistry Letters 1979, 17-18.
Multiscale Computational Framework for Discovery of Active, Durable and Non-Precious Electrocatalysts for Fuel Cell Systems
Authors: Han Byungchan , Kwon Choa , Hwang Jeemin
Published: February 2020

Innovative design of high functional materials in renewable energy systems plays a key role in powering transportation vehicles and portable electronics. This presentation introduces frontiers of research works by the first principles-based computational framework concerted on the purpose. As the example, nanoscale electro-catalysts in proton exchange membrane fuel cells (PEMFCs), Li-air batteries and solar cells for fuel generation are shown. It is clearly suggested that the method provide new design concept beyond conventional wisdom through the identification of fundamental descriptors and process mechanisms on and atomic level essentially leading to high efficiency of a whole system. The framework is potentially developed into a computational platform for the materials genome approach, which can substantially reduce the time period necessary from discovery to commercialization into markets of new materials.
Understanding the Effect of the Anion of the Ionic Liquid on the Activity of the Oxygen Reduction Reaction on Pt/C
Authors: Huang Kan , Song Tangqiumei , Morales-Collazo Oscar , Jia Hongfei , Brennecke Joan F
Published: February 2020

The efficiency of the oxygen reduction reaction (ORR) is determined by many factors, among which the adsorption of non-reactive species on the Pt surface and oxygen concentration near the Pt interface are considered the most important. Extensive research has focused on developing novel Pt based catalysts with sophisticated structures designed to weaken the adsorption of oxygenated species and enhance ORR activity. Recently, ionic liquid (IL) with high oxygen concentration have been proposed as another countermeasure to accelerate the reaction rate. (1, 2)

The choice of anion of the IL, in particular, can have a significant effect on the oxygen solubility. To investigate how oxygen solubility in the IL improves the ORR activity and durability, a series of ILs with various anions designed to enhance oxygen solubility were synthesized and characterized. Surprisingly, the electrochemical studies showed that the ORR activity was not sensitive to the oxygen solubility in the ILs, but showed significant dependence on the oxides free Pt sites (1- θ
OHad). (Fig.1)

The degree of IL coverage on the Pt was quantitatively estimated using (bi)sulfate ion as an indicator. It was found that the ORR activity was promoted when there was partial IL coverage, while full IL coverage resulted in degradation of the performance. Durability studies showed that in the presence of the IL Pt dissolution can be mitigated. A balance between activity and stability can be achieved with an optimized IL coverage.

1. J. Snyder, T. Fujita, M. W. Chen and J. Erlebacher, Nat Mater, 9, 904 (2010).

2. J. Snyder, K. Livi and J. Erlebacher, Advanced Functional Materials, 23, 5494 (2013).

Figure 1
Enhanced Ru Utilization with High Stability of (RuxCoy)Se2/C Electrocatalyst toward Oxygen Reduction Reaction
Authors: Zheng Jiwu , Gong Qing , Gong Shuiping , Yang Weifeng , Cheng Xuan , Zhang Ying , Li Hengyi
Published: February 2020

The CoSe2 nanoparticles were first prepared through microwave synthesis, and followed by chemical reduction of Ru on the CoSe2 surface. The transformation of orthorhombic to cubic CoSe2 phase took place upon the subsequent heat treatment at 400 ℃, which led to the formation of (RuxCoy)Se2/C nanoparticles. A small amount of Ru introduced into the CoSe2 significantly enhanced the activity of (RuxCoy)Se2/C toward oxygen reduction reaction, and high Ru utilization was achieved. The half-wave and open-circuit potentials were 0.68 V and 0.88V (vs. RHE), respectively, with the electron transfer number of 4.0 in 0.1 mol/L HClO4. The mass activity of the (RuxCoy)Se2/C catalyst reached 0.09 mA/mg Ru at 0.75 V, which is comparable to that of the commercial Pt/C catalyst (0.10 mA/mg Pt). Only 15 mV decrease in half-wave potential was observed after 1000 cycles in 0.1 mol/L HClO4, showing good stability.
Carbon Nanotube- and Nanoporous Carbon-Based Pt and Non-Pt Fuel Cell Catalysts with High Performance and Durability
Authors: Yang Jun , Tao Jie , Fujigaya Tsuyohiko , Nakashima Naotoshi
Published: February 2020

Development of Pt-based and non-Pt-based electrocatalyst for fuel cells and batteries with high performance, durablity, and scalability is a strong social demand for the next-generation eco-friendly energy society[1].

In this meeting, we summarize our recent studies on i) development of a carbon nanotube (CNT)-based almost “immortal” fuel cell catalyst prepared by a double-polymer wrapping method [2], ii) pristine carbon nanotube/iron phthalocyanine hybrids with a well-defined nanostructure that show excellent efficiency and durability for oxygen reduction reaction[3], iii) decorating unoxidized-carbon nanotubes with homogeneous Ni-Co spinel nanocrystals that show superior performance for oxygen evolution/reduction reactions[4], and iv) a highly-durable CO-torelant poly(vinylphosphoric acid)-coated electrocatalysy supported on a nanoporous carbon[5].

References

[1] T. Fujigaya, N. Nakashima, Adv. Mater., 2013, 25, 1666-1681.

[2] M. R. Berber, I. H. Hafez, T. Fujigaya, N. Nakashima, Sci. Rep.,
2015, 5, art no. 16711.

[3] J. Yang, F. Toshimitsu, T. Fujigaya, N. Nakashima, J. Mater. Chem. A, 2017, 5, 1184-1191

[4] J. Yang, T. Fujigaya, N. Nakashima, Sci. Rep., 2017, 7, art.no.45384.

[5] Z. Yang, I. Moriguchi, N. Nakashima, ACS Appl. Mater. Interfaces, 2016,
8, 9030–9036.
X-Ray Absorption Study of Sputtered Pt-CeO2 Catalyst Used in PEM-FC
Authors: Fiala Roman , Drnec Jakub , Vaclavu Michal , Matolin Vladimir
Published: February 2020

The proton exchange membrane fuel cell (PEMFC) is supposed to be an environmentally friendly near-future power source for mobile devices. The crucial problem in the fuel cell technology field is the finding of a stable, efficient and economical catalyst for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) at working conditions of PEMFC. The Pt catalyst, which is widely used due to fact that this catalyst is only really functional enough, is an expensive material. Moreover, unfortunately all of the less expensive Platinum bimetallic alloys as ORR catalysts enhancing the activity rapidly degrade in acidic environment and ORR condition [1].

We have already shown that Pt-CeO2sputtered catalyst exhibits high specific power (thousand-times higher power per mg of platinum and only few times lower power density in comparison with Pt reference catalyst) so such material could be an appropriate for PEMFC anode (HOR) [2,3,4].

Presented work is aimed for understanding the role of Pt and Ce chemical states and Pt-Ce interactions in HOR and ORR catalytic activity investigated in-situ using X-ray Absorption Near Edge Structure (XANES). Additionally, the performance and endurance of this catalyst obtained through direct testing in fuel cell test station are presented. Then, morphology determined by scanning electron microscopy and photoelectron spectroscopy results is shown.

[1] G.-F. Wei et al., Energy Environ. Sci.,4(2011) 1268

[2] R. Fiala et al., J. Nanosci. Nanotechnol.,11 (2011) 5062–5067

[3] V. Matolin et al., Langmuir, 26 (2010) 12824–12831

[4] V. Matolin et al., Int. J. Nanotechnol., 9 (2012) 680–694

Figure 1
Synthesis of N-Doped Graphene By Sonochemical Liquid Exfoliation and Its Electrochemical Performance for ORR in Alkaline Media
Authors: Figueroa-Torres Mayra Z , Alonso-Lemus Ivonne Liliana , Escobar-Morales Beatriz , Rodriguez-Varela F.J. , Fernández-Fuentes Antonio
Published: February 2020

The graphene is a promising material for many potential application. However, industrial scale manufacturing has been limited because most of these methods are not readily scalable. The development of strategies that make viable large-scale production of graphene is a great challenge. A promising approach is the production of stable graphene dispersions from the exfoliation of graphite in water and organic solvents. The exfoliation of graphite by ultrasonication is a very versatile technique that has already demonstrated its effectiveness in dispersing graphene in solvents with different physical and chemical properties. In this contribution, we reported a fast and simple synthesis of graphene sheets from graphite flakes through ultrasound assisted method. Pure dimethylformamide (DMF) was used as organic solvent. Ultrasound time was evaluated in a range of 30 to 120 minutes. The quality of exfoliation and the morphology were determined by Scanning Electron Microscopy (SEM), Raman Spectroscopy (RS) and X-Ray diffraction (XRD). Additionally, graphene was functionalized by solvothermal treatment in order to obtain nitrogen doped graphene. Metal-free electrocatalyst were also obtained. The total nitrogen and carbon were determined using a CHNS analyzer. The functional groups determinates by FTIR found in graphene are carboxyl and amine groups. Preliminary results obtained by Raman spectroscopy indicates that nanocarbon materials has a molecular structure composed by a mixture of graphene and exfoliated graphite. The electrochemical performance of the material for the oxygen reduction reaction (ORR) was tested by rotation disk electrode technique (RDE). It was observed that stable graphene suspensions could be prepared using DMF. Results demonstrate that ultrasonication time is a key parameter to control the yield and size of graphene, when sonication time was higher than 60 minutes the production of graphene decreased. Electrochemical evaluation revealed that these materials are electroactive for ORR in alkaline media. Therefore, the sonochemical synthesis is an attractive massively scalable and simple method for preparation of graphene to energy applications.
Titanium Oxide Nanosheets for Proton-Exchange Membrane Oxygen Evolution Electrocatalysts
Authors: Archer Randall , Godinez-Salomon Fernando , Rhodes Christopher
Published: February 2020

Electrocatalysts used for the oxygen evolution reaction (OER) within the acidic environment of proton-exchange membrane (PEM) electrolyzers typically use precious metal oxides, IrOx and RuOx, which are extremely expensive and have a very limited supply. Approaches that can significantly reduce or eliminate the precious metal content of acidic OER catalysts and that provide high activity and stability are of significant interest. Toward this end, we have investigated using titanium dioxide nanosheets for acidic OER electrocatalysts. Expressing TiO2 within a nanosheet morphology allows expression of specific facets that may allow increasing the activity. Further, the OER activity may be enhanced through substitution of different transition metals within the structure to tune the surface electronic structure as well as increase the electronic conductivity. The TiO2 and substituted TiO2 nanosheets were prepared using solution-phase synthesis routes. The structure of the nanosheets was determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The OER activity and stability substituted TiO2 nanosheets were determined using a rotating disk electrode configuration and will be presented. The ability to create precious metal-free OER catalysts that provide high activity and stability provides the potential for significant reduction of the cost of PEM electrolyzers used for important applications including automotive hydrogen fueling stations and on-demand hydrogen production for industrial applications.
(Invited) Technological Aspects of Interfaces between Ionic, Mixed Conducting and Other Components in Solid Oxide Fuel Cells
Authors: Minh Nguyen , Lee Yoon Ho
Published: February 2020

Interfaces between various components (ionic conducting, electronic conducting, mixed conducting, and electrically insulating) in a SOFC stack – their behavior and characteristics at operating temperatures of about 500o to 1000oC - play the key role in determining stack performance, reliability and durability/life. Interfaces in SOFC stacks include different types of material (metals, ceramics, and glasses) and require different properties (electrochemical, electrical, chemical, and mechanical): electrode-electrolyte (ceramic-ceramic interface; fast electrochemical reactions and minimal poisoning by contaminants required), electrode-interconnect (ceramic-metal interface; good electrical contacts and minimal contact losses/changes required), and sealant-interconnect/electrolyte (glass-metal/ceramic interfaces; adequate and reliable sealing/mechanical properties required). This paper provides an overview of characteristics and behavior of interfaces in SOFC stacks from the viewpoint of the requirements to enable practical applications and discusses certain technological aspects of cathode-interconnect interfaces, cathode-electrolyte interfaces in reverse operation, sealing interfaces, and interfaces in thin-film SOFCs operating at reduced temperatures.
(Invited) Role of Ion-Conducting Membranes in Synthesis and Use of Sustainable Fuels
Authors: Soloveichik Grigorii L.
Published: February 2020

Replacement of conventional catalytic technologies for synthesis of sustainable, carbon-neutral fuels with direct electrochemical synthesis has a potential for big energy savings due to reduction of number of process steps and pressure/temperature. In addition, electrochemical technologies are easily scaled down to allow for low capital, modular plants that match the scale of renewable energy production. The use of these fuels in electrochemical devices opens a path to cost-effective long-term energy storage and distributed energy generation. Development of low cost, ion-selective membranes with low area specific resistance is, along with electrocatalyst development, critical for the success of such technologies. Not less important is development of membrane manufacturing methods at a practical scale.

This presentation will review prospective technologies using ion-selective membranes for synthesis of carbon-neutral fuels for chemical energy storage and their use for generation of electricity (using fuel cells) and hydrogen. Advantages of electrochemical synthesis of ammonia from nitrogen and hydrogen or water compared to the conventional Haber-Bosch process will be discussed. Other processes include direct electrochemical synthesis of alcohols from CO2. The requirements to ion-selective membranes for these processes and fuel cells will be presented.

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical energy storage and transformation for grid scale and automotive applications. The Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program funds the development of transformational technologies to reduce the barriers to widespread adoption of intermittent renewable energy sources by enabling the conversion of energy from these sources, water and air to energy-dense zero-carbon liquid fuels and their use for electricity or hydrogen generation. REFUEL projects targeting various ion conducting membranes as well as related projects supported by ARPA-E through OPEN program will be highlighted.
(Invited) Review of Progress in Solid Oxide Fuel Cell at FuelCell Energy
Authors: Ghezel-Ayagh Hossein , Borglum Brian P
Published: February 2020

Significant progress has been made towards the development of Solid Oxide Fuel Cell (SOFC) at FuelCell Energy Inc. (FCE). The genesis of the advances in the technology is rooted in scale-up of the Company’s anode-support technology made by the TSC (Tape Casting-Screen Printing-Sintering) Process. The anode supported thin electrolyte planar cell platform was adopted for its higher power density at reduced operating temperature (600-800°C). Traditional materials, such as Ni/YSZ anodes, YSZ electrolytes and perovskite cathodes have been utilized in a basic cell structure. Research and development has been successful in developing better electrochemical functional areas at both cathode/electrolyte and anode/electrolyte interfaces. This was achieved through materials advancement, microstructure optimization, and manufacturing process integration. Cell materials development advancements have been made in performance, endurance, cell size (area) scale-up and cost reduction. These advancements led to an enhanced cell performance by reducing cell ASR (Area Specific Resistance) while reducing cell cost through cell design changes and materials reduction. Scaled-up cell size of up to 1000 cm2 have been made and tested with the current baseline cell size of 550 cm2 as the standard unit size for building SOFC stacks. The baseline stack design has been successfully scaled-up from 120-cell 550 cm2 cell area (16 kW nominal) stack. Using standardized manifolds and gas-electrical interconnects, these stacks have been successfully integrated into stack towers and arrays.

FCE recently designed, built, and tested a 50 kW fully automated SOFC system under a Co-operative Agreement with Department of Energy. In a follow-on DOE supported project, currently, FCE is engaged in design and construction of larger 200kW units that utilize baseline factory-built stack blocks representative of the future MW-scale power plants.
Improved Electrocatalytic Activity and Durability of NiMn2O4-CNTs as Reversible Oxygen Reaction Electrocatalysts in Zinc-air Batteries
Authors: Li Xuemei , Li Haoran , Nie Qi , Zhang Lei , Qiao Jinli
Published: February 2020

Faced with the increasingly serious energy crisis, fuel cells, as a clean and efficient power source, have become the most promising energy conversion devices and attracted significant attention during the last decades. Oxygen reduction reaction (ORR) at the cathode of fuel cells plays a decisive role in determination of the performance, and electrocatalysts with high-performance ORR are essential for practical applications. However, some big technical challenges are still encountered due to their inherently sluggish of cathodic ORR, which usually requires a significant number of noble metal catalyst [1, 2]. To overcome these bottlenecks, great attention has been paid to pursue non-precious metal or metal-free carbonaceous materials. Mesoporous carbon materials have been used for ORR due to their preeminent textural characteristics, high surface area, mechanical stability and mesoporous structure. However, the properties of mesoporous carbon materials base on not only the sizes and loction of the pore, but the heteroatoms doped into the carbon framework. It is believed that the quantity of N-doped and S-doped in carbon will be vastly different, if it was annealed at various reaction temperatures [3]. Herein, we use N and S co-doped mesoporous carbon which is prepared by polyquaternium-7 as a starting material to investigate the reaction with N2 at various temperatures.

Nitrogen and sulfur co-doped mesoporous carbons were prepared by homogeneously mixing polyquaternium-7 and ferrous sulphate and silica. After drying overnight, the resulting solid was ground to a fine powder and then calcined at 600, 700, 800, 900 and 1000 for 1 hour in a nitrogen atmosphere. The silica was washed off in excess sodium hydroxide and dried. The excess metal Fe was removed in sulfuric acid at 85 ℃. Finally, the resulting catalytic graphite was pyrolyzed at 600 to 1000 ℃ for 1 hour again. Results of electrochemical characterizations for ORR were studied by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) employing rotating disk electrode (RDE) technique. It is found that the temperature of the heat treatment is a significant parameter in synthesizing the high performance ORR catalysts.

References

[1] M.J. Wu, J.L. Qiao, K.X. Li, X.J. Zhou, Y.Y. Liu and J.J. Zhang, Green Chem. Vol., 18,2699 (2016)

[2] M. Arenz, K.J. Mayrhofer, V. Stamenkovic, B.B. Blizanac, T.Tomoyuki, P.N. Ross and N.M. Markovic, J. Am. Chem. Soc. Vol., 127,6819 (2005)

[3] S.B.Yang, L.J. Zhi, K. Tang, X.L. Feng, J. Maier, K. Müllen, Adv. Funct. Mater. 22, 3634 (2012).
Optimizing the Thickness of Esb-GDC Bilayer Electrolytes for Efficient Low Temperature Operating SOFCs
Authors: Ren Yaoyu , Abdul Jabbar Mohammed Hussain , Huang Yi-Lin , Robinson Ian , Stanley Patrick , Pesaran Alireza , Wachsman Eric D.
Published: February 2020

Bilayer electrolytes with high oxide ion conductive materials such as Er2O3-stabilized Bi2O3 (ESB) and Gd-doped CeO2-
δ (GDC) were developed to lower the operating temperature of solid oxide fuel cells (SOFCs) without compromising their efficiency[1]. In a bilayer electrolyte design, optimizing the thickness of ESB to GDC (r
ESB/GDC) and the total electrolyte thickness (h) can help to maximize the SOFC performance. However, such optimization of electrolyte thicknesses requires elaborate understanding on the voltage drop across SOFC components. In this work, efforts are made to study the voltage drop across various layers of SOFCs on a Ni-GDC based anode-supported cell. The anode-supports were deposited with ESB-GDC bilayer electrolytes with varying r
ESB/GDC and h. In particular, the voltage drop across ESB (V
ESB), GDC+anode (V
GDC+anode) and the whole cell (V
total) were determined at open circuit voltage and under load conditions. These measurements were performed by positioning the voltage probes between ESB/GDC and ESB/cathode. The behavior of V
ESB, V
GDC+anode, and V
total with a varying r
ESB/GDC and h were monitored and analyzed. Specific losses that could potentially limit the overall SOFC performance with reference to electrolyte thicknesses are addressed.

[1] E.D. Wachsman, K.T. Lee, Science, 334 (2011) 935-939.
(Invited) Cathodes for High Rate, Long Cycle Life Lithium Sulfur Batteries
Authors: Wixom Michael , Wu Qingliu , Zhang Pu , Aurora Peter
Published: February 2020

Practical applications of lithium sulfur batteries remain limited by utilizing a limited fraction of the available sulfur and by fast capacity fading. The root causes are poor electronic conductivity of the cathode combined with high solubility of intermediate polysulfide products formed during cycling. Novel cathode materials based on conductive nanoporous ceramic host address these limitations. The promising electrochemical performance is achieved through high chemical affinity to both non-polar sulfur and polar polysulfide species. The features of Navitas’ ceramic cathode design to enhance LSB performance and life include: (1) nanoporous structure will better accommodate sulfur volume changes during cycling; (2) mechanical strength and conductivity will enable high utilization of sulfur; and (3) high affinity to both sulfur and polysulfides will minimize sulfur dissolution.

Structural and electrochemical properties will be presented. The host material possesses a surface area of 101 m2/g and porosity of 50% as designed. Melt-diffusion of sulfur has been used to impregnate sulfur into the porous ceramic host. Thermal gravimetric analysis (TGA) confirmed that controllable amount of sulfur (50% - 70%) sulfur could be impregnated into the porous host. The ceramic cathode exhibits promising electrochemical performance in lithium sulfur cells. The initial charge capacity of >900 mAh/g was higher than baseline cathodes based on mesoporous carbon. The ceramic cathode also shows improved rate capability, retaining 80% capacity at 1C and 73% capacity at 2C. Navitas’ ceramic cathode retains 82% capacity after 100 cycles. Based on the initial results, electrode design and projected performance of large format cells will be discussed.
Temperature Evolution As a Novel Indicator for State of Health Estimation of Lithium-Ion Cells
Authors: Wu Yao , Jossen Andreas
Published: February 2020

Performance degradation of lithium-ion cells is inevitable during their application. Hence, state of health (SoH) estimation is crucial for battery management, especially in electric vehicles (EV), where the demands on the cell performance are more stringent. Conventional SoH estimation is often based on the cell capacity or impedance. Nevertheless, online capacity and impedance measurements are rarely achievable owing to the diverse and dynamic operation conditions. An alternative indicator should replace capacity and impedance to make SoH estimation more manageable.

In our work, an aging test matrix, including calendar and cycle life aging, is carried out on a commercial lithium-ion pouch cell. The stress factors are temperature (25 °C, 40 °C, 55 °C) and discharge rate (1C, 3C, 5C). Performance tests are conducted every two weeks to measure the actual capacity of the tested cells in a climate chamber at 25 °C. The performance test consists of two continuous constant current (CC) and then constant voltage (CV) charge/discharge cycles with 1C (5 A). The cut-off voltages are 2.7 V and 4.2 V with a cut-off current of C/20 (0.25 A). During the performance tests, a temperature sensor is attached to the surface center of each cell to monitor the surface temperature evolution.

During the analysis of the surface temperature evolution from the performance tests, a strong cooling effect is detected in the 1C CC charge process after about 0.4 h charging. The dT/dt curve of a new cell is shown in Fig. 1, along with its temperature evolution curve, to identify the position of the maximum cooling effect, i.e. the dT/dt minimum. Then, t0 is defined as the period from the charge beginning to the dT/dt minimum during 1C CC charging. In Fig. 2, a linear correlation between t0 and the cell actual capacity is noted with a coefficient of determination (R2) of 0.93. This correlation is analyzed for the aforementioned cells aged under both calendar and cycle life conditions. Furthermore, various stress factors have little influence on the linear correlation behavior of the cells. Accordingly, t0 could be employed as a new indicator for SoH estimation of lithium-ion cells.

Figure 1
LiPO2F2 As an Additive in Li[Ni0.5Mn0.3Co0.2]O2/Graphite Pouch Cells
Authors: Ma Lin , Liu Qianqian , Dahn Jeff R
Published: February 2020

Lithium ion cells with longer lifetime, higher energy density and better rate capability are of interest for electric vehicle (EV) makers. The use of electrolyte additives is one of the most effective ways of improving cell performance1–3. In this work, LiPO2F2 was used as an electrolyte additive to promote the performance of Li[Ni0.5Co0.2Mn0.3]O2
(NMC532)/graphite pouch cells. LiPO2F2 was graciously provided by Guangzhou Tinci New Materials Technology Co. and Shenzhen Capchem Technology Co.

Experiments were performed using a high temperature (60°C) storage system, the ultra high precision charger (UHPC) at Dalhousie University, electrochemical impedance spectroscopy (EIS), in-situ gas evolution measurements and long term cycling tests (40°C and 20°C). LiPO2F2
containing cells demonstrated excellent capacity retention at both 40°C and 20°C, better impedance control, gas reduction and good rate capability at room temperature. The results of advanced characterization methods such as XPS and NMR to elucidate the impact of LiPO2F2 on the solid electrolyte interface layers will be reported, if available.

Figures 1a - 1c) show that LiPO2F2-containing NMC532/graphite pouch cells have better capacity retention, lower polarization growth and higher energy efficiency during long term cycling between 3.0 and 4.3 V at 40°C. Figures 1d - 1f) show that LiPO2F2-containing NMC532/graphite pouch cells have less voltage drop, less gas production and better impedance control during storage testing at high temperature (60°C). The results here suggest that LiPO2F2 is a very promising electrolyte additive for improving cell performance from many perspectives. The synergetic effect between LiPO2F2 and other useful electrolyte additives needs to be explored carefully.

References:

1. M. Nie, J. Xia, L. Ma, and J. R. Dahn, J. Electrochem. Soc., 162, A2066–A2074 (2015).

2. D. Aurbach, K. Gamolsky, B. Markovsky, Y. Gofer, M. Schmidt, and U. Heider, Electrochimica Acta, 47, 1423–1439 (2002).

3. K. Xu, Chem. Rev., 114, 11503–11618 (2014).

Figure 1(a-c) Normalized discharge capacity (a), the difference between average charge voltage and average discharge voltage (b) and energy efficiency versus cycle number for NMC532/graphite pouch cells with or without LiPO2F2 in 1.2M LiPF6 EC/EMC (3/7) during constant-voltage-constant-current (CCCV) cycling between 3.0 and 4.3 V at 40°C with a current corresponding to C/3 (cut-off current is C/20). Figures 1d – 1f show voltage versus time (d), gas production (e) and impedance change (f) during storage testing (500 hours) at 4.4 V for NMC532/graphite pouch cells with or without LiPO2F2 in 1.2M LiPF6 EC/DMC (3/7) at 60°C. In Figure 1f, the solid lines represent the results before storage and the dashed lines represent the results after storage.

Figure 1