bluuebunny/crossref_metadata_2025 huggingface dataset:
Pairing Asymmetric Gas Diffusion Media for High-Power Fuel Cell Operation
Authors: Atkinson Robert W. , Garsany Yannick , Bethune Keith , St-Pierre Jean , Gould Benjamin D. , Swider-Lyons Karen
Published: February 2020

Proton exchange membrane fuel cell (PEMFC) power production is highly influenced by the properties of the gas diffusion media (GDM). The GDM typically comprise a mesoporous carbon layer (MPL) on top of a porous carbon-fiber gas diffusion layer (GDL) which are both wetted with polytetrafluoroethylene (PTFE) to modify their water retention. In a PEMFC, the GDM are compressed to either side of the catalyst coated membrane. The GDM are active in the fuel cell transport processes including electron and heat conduction, water removal, and distributing reactant gases to the catalyst layers, which affects the electrochemistry in the catalyst layers. These transport phenomena rely on both the properties of the GDM solid phase and its voids, making optimization of GDM material properties challenging. The majority of reports in the PEMFC literature addressing GDM focus solely on the cathode, since water is produced at this electrode and its ineffective removal can block active sites and occlude O2 diffusion. Most research reports use symmetrical anode and cathode GDM. To date, there has been less discussion on the role of the anode GDM or how anode and cathode GDM properties can be selected in concert to increase fuel cell power output, despite that a significant amount of water in a fuel cell is rejected to the anode.

We consider that anode and cathode GDM properties, such as air permeability, must be chosen in unison to improve cell water management. In our previous work, we used X-ray computed tomography to observe that dry-laid, non-woven, Freudenberg GDM maintain large void volume while permitting high compressive stress, ultimately resulting in lower contact and ohmic resistances and better mass transport compared to another distinct class of GDM (wet-laid, SGL).1

In this work, we make a range of PEMFCs using a suite of Freudenberg GDM to study the influence of anode and cathode GDM air permeability and how these properties may be paired to improve cell hydration and increase fuel cell power production in a broad range of operating conditions. Fuel cells are characterized with cyclic voltammetry, electrochemical impedance spectroscopy (EIS), gravimetric analysis, and limiting current measurements to quantify the sources of mass transport resistance. Gradients of GDM material properties from anode to cathode improve cell hydration and facilitate water removal to reduce mass transport resistances and enable higher power operation.

1. “The Role of Compressive Stress on Gas Diffusion Media Morphology and Fuel Cell Performance,” R. W. Atkinson III, Y. Garsany, B. D. Gould, K. E. Swider-Lyons, I. V Zenyuk, ACS Applied Energy Materials, 2017, 1 (1), 191–201.
Limiting Current Measurements of Oxygen Transport Resistance in Platinum Group Metal-Free Fuel Cell Cathodes
Authors: Langhorst Lisa , Uddin Aman , Zhang Hanguang , Wu Gang , Litster Shawn
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) currently have a significant commercialization cost due to the price of the platinum or platinum-alloy catalysts they use on the cathode. Platinum group-metal (PGM) free catalysts have the potential to reduce this cost, but have lower volumetric activity, requiring the use of thicker catalyst layers. The increased catalyst layer thickness results in an increase in through-plane oxygen-transport resistance. In addition to that resistance, there are additional non-resistance due to diffusion through water filled pores and across ionomer films. Here, we elucidated the relative magnitude of the various oxygen-transport resistances from limiting current density measurements. To extract the various resistances, we measured the limiting current density for three PGM-free fuel cells with varied catalyst loading, testing each with varied total pressure and carrier gas (Helox, dry air, and 5% O2). Measuring limiting current density at various pressure separates pressure-dependent resistances from pressure-independent resistances. Pressure-dependent resistances include intermolecular gas diffusion while pressure-independent resistances include both Knudsen diffusion and diffusion through thin ionomer films that cover the catalyst. For increased loading and reduced local fluxes at the active site, local microstructure and ionomer thin-film diffusion resistances are less significant. Also, because of the lower volumetric activity and local oxygen flux, those resistances are generally lower within PGM-free cathodes. Varying the carrier gas influences the bulk gas diffusion. From this, and comparison to literature, the component of oxygen-transport-resistance due to the catalyst layer was determined apart from the channel and gas diffusion media of the cathode. Such information can be used to advance the morphology and materials of PGM-free cathodes for enhanced O2 transport and fuel cell power density.

DOE ACKNOWLEDGEMENT

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 the Electrocatalysis Consortium (ElectroCat), established as part of the Energy Materials Network under theU.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under Contract Number DE-EE0008076.
Towards a High-Performance DMFC Membrane Electrode Assembly Using Iron-Doped Metal Organic Framework Catalysts on the Cathode
Authors: Abdelrahman Mohamed Elfadil , Velez Daniel , Zhang Hanguang , Wu Gang , Li Xianglin , Litster Shawn
Published: February 2020

Direct methanol fuel cells (DMFC) have several advantages for a broad spectrum of energy density demanding applications, ranging from portable devices to stationary backup power. DMFCs deliver power at high efficiencies compared to internal combustion technologies and use high energy density methanol as the fuel. However, DMFCs face several challenges, including methanol crossover at the cathode and slow methanol oxidation reaction (MOR) kinetics at anode that impede its performance. Hence, high loadings of a platinum group metal (PGM) catalyst are normally needed on both the anode and cathode, leading to high raw material catalyst costs. In this work, a PGM-free iron catalyst derived from metal organic framework precursors (Fe-MOF) is used on the cathode side to catalyze the oxygen reduction reaction (ORR). The PGM-free cathode has shown a high tolerance to methanol crossover relative to standard PGM catalysts and high performance relative to previously reported DMFC PGM-free cathode performances in the field. A wide range of operating conditions were tested, and we evaluated the maximum power density using pure oxygen and air with varying methanol concentration. We conducted our tests with a custom, integrated H2 reference electrode that separately provided the anode and cathode overpotentials. This is necessary for cell and electrode optimization since DMFC anode overpotentials are large relative to that of H2 PEMFCs and cannot be used as a quasi-reference electrode. Furthermore, we performed long term durability tests to evaluate PGM-free catalyst stability in the DMFC environment.

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-EE0008440.
Impact of Shut-Down Procedures on Performance Recovery of Proton Exchange Membrane Fuel Cells
Authors: Barbir Frano , Pivac Ivan
Published: February 2020

It has been noticed that after intentional or unintentional interruption of fuel cell operation or durability testing, such as due to equipment maintenance, normal start-up/shutdown procedure, system failure, overnight rest, continuous electrochemical in situ testing, etc., its performance often improves. This indicates that some of the performance loss is recoverable. The goal of this study is to investigate the impact of shutdown procedure and duration of the shutdown period on PEM fuel cell rejuvenation. An already conditioned standard 50 cm2 (single) fuel cell was exposed to an accelerated stress test (AST) protocol consisting of voltage cycling, designed to target electrocatalyst degradation, but with the intentional recovery periods (so-called soak time steps) every 2500 voltage cycles. Before and after every intentional soak time, a series of diagnostic methods (namely polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry, linear sweep voltammetry) were performed. Different shutdown procedures, as well as different duration of the soak time period were tested and their impact on performance recovery evaluated. Figure 1 shows degradation as calculated electrochemical surface area loss during AST and recovery after each shutdown period. The results suggest that cause of the reversible degradation could be accumulated water within the cell and/or presence of oxygen within the catalyst layer leading to formation of Pt oxides on the catalyst surface. The prolonged soak time step reduces recovery effect, while rapid reduction of the cell temperature with ice proved to be counterproductive for performance recovery. Shutdown procedure without shortly-connected resistor has shown no effect on recovery. Shutdown procedure without nitrogen purge proved to be the most effective for performance recovery.

Figure 1
Investigation of Concentration Overvoltage Increase in Low Pt-Loading PEFC
Authors: Takei Shota , Uda Keisuke , Nagayama Mayumi , Sasaki Kazunari , Hayashi Akari
Published: February 2020

Introduction

Although fuel cell vehicles (FCVs) have already been commercialized, the cost reduction of PEFCs is required for full-scale distribution of FCVs, and so it is essential to reduce the amount of Pt, which is an expensive precious metal used as an electrode catalyst. So far, our research group has been working on preparation and performance evaluation of membrane electrode assembles (MEAs) with different cathode Pt-loading in order to determine the minimum requirement of Pt1. Then, we have found that concentration overvoltage increases in the very low Pt-loading region, lower than 0.20 mgPt/cm2. This is considered that resulting low carbon content (thin cathode layer) has led to increase in the water volume fraction in the catalyst layer under the same current density, even though the gas transfer distance is rather shorten. Therefore, in this study, we are aiming to investigate the mechanism of increase in concentration overvoltage in detail in order to reduce concentration overvoltage.

Experimental

The 1 cm2 MEAs were fabricated by a spray printing method2 using the Pt/C catalyst and Nafion® electrolyte. Here, the amount of anode Pt/C was fixed to 0.30 mgPt/cm2 (0.35 mgC/cm2), and the amount of cathode Pt/C was varied from 0.05 to 0.60 mgPt/cm2 (0.06-0.70 mgC/cm2). For the Pt/C catalyst, on the purpose of examining the influence of hydrophilic/ hydrophobic characters of carbon, TEC10E50E (46.5%Pt/KB) and TEC10E50EA (46.6%Pt/Graphitized KB (GKB)) were used. Then, current-voltage (I-V) characteristics and ECSA of MEAs were evaluated. Furthermore, impedance was also measured, and ohmic, activation, and concentration overvoltages were separately analyzed.

Results and discussion

For successful drain of water from the cathode layer in order to reduce concentration overvoltage, two approaches, such as changing evaluation conditions of MEAs and controlling the surface character of carbon supports in MEAs.

First, the humidity condition of MEA evaluation was changed from RH100% to 57%, and I-V performance was evaluated. As a result, no change in concentration overvoltage was observed on changing relative humidity. This is probably because the generated water is rather effective on concentration overvoltage than relative humidity of MEA evaluating condition.

Next, MEAs prepared using Pt/KB and Pt/GKB for the cathode and I-V performance was evaluated. As a result, as shown in Fig. 1, reduction of concentration overvoltage was confirmed by using Pt/GKB with 0.23 mgC/cm2, where increase in concentration overvoltage was already seen in case of Pt/KB. This is most likely because successful water drain derived by the hydrophobic character of GKB in comparison to KB. In other words, this result has suggested that controlling the hydrophobic character of carbon supports can reduce the concentration overvoltage even for low Pt-loading MEAs. Detailed discussion will be reported through further changing the amount of carbon.

Figure 1
Droplet Dynamics and Removal from Polymer Electrolyte Fuel Cell Channels Using Acoustic Pressure Waves
Authors: Stolberg Preston R. , Coverdill Alexander , Mortazavi Mehdi , Benner Jingru , Chauhan Vedang , Santamaria Anthony D.
Published: February 2020

Liquid water management in polymer-electrolyte-membrane (PEM) fuel cell reactant channels is critical to system performance, stability, and lifespan. A balance between cathode catalyst layer water generation and removal must be maintained to ensure proper membrane hydration while preventing flooding. Liquid water transport through the gas-diffusion-layer (GDL) results in droplet formation in reactant channels that may be removed via flow gas drag forces. This work investigates the effect that acoustic wave transmission in reactant flow gases has on liquid water droplets growing on the GDL surface. While recent and past work has shown this method may be useful toward preventing liquid buildup in reactant channels, fundamental analysis of the droplet behavior is lacking [1-3]. In this study experiments were performed using a transparent ex-situ flow channel of 3.5 (h) x 3.7 (w) mm cross section as shown in Figure 1a. Water droplet formation was controlled using a digital syringe pump injected through a port on the backside of the GDL. Air and Hydrogen were used to simulate both cathode and anode flow conditions. A speaker was connected in series with the feed gas and flow channel whereby acoustic signals were generated and passed through the reactant channel. Transducers measured pressure upstream and downstream of the droplet while a high speed camera captured images of the droplets motion from the side (Figure 1b). Early results show that pressure waves effect droplets pinning behavior on the GDL surface. Previous work has shown that a maximum contact angle hysteresis exists for droplet removal from GDLs. While gas flow causes droplet contact angle hysteresis, this work shows that oscillations caused by the acoustic waves may shift the droplet over the max hysteresis tipping point enabling removal.

References:

M. Schafer, J.S. Allen, Improved water removal from fuel cell flow channels via natural frequency excitation of free surfaces, ECS Transactions 41 (1), 1887-1896, 2011

Allen, Jeffrey S., "Water removal from gas flow channels of fuel cells" (2013), Patent#: 8524410, https://digitalcommons.mtu.edu/patents/120

Mortazavi, A.D. Santamaria, J.Z. Benner, V. Chauhan, Enhanced Water Removal from PEM Fuel Cells Using Acoustic Pressure Waves, Journal of The Electrochemical Society, 166 (7), F3143-F3153, 2019

Figure 1
Contamination of Pt Catalyst with Carbon Monoxide during Hydrogen Evolution
Authors: Yilmaz Abdurrahman , Pasaogullari Ugur
Published: February 2020

Absorption of carbon monoxide (CO) on the platinum catalyst hampers the hydrogen oxidation and evolution reactions by affecting the reaction kinetics and reducing the electrochemical active surface area [1, 2]. In this paper, we use electrochemical impedance spectroscopy (EIS) to investigate the electrode poisoning on the hydrogen evolution reaction (HER) with the presence of CO. Single cell proton exchange membrane fuel cell (PEMFC) hardware with a low loading catalyst coated membrane (CCM) is operated in electrochemical hydrogen pump (EHP) mode. EIS data is collected every 5 minutes during poisoning with pure H2 or CO-H2 mixture on the anode and cathode. The Nyquist plot shows only one semicircle due to reaction kinetics, and this semicircle diameter increases significantly with time.

EIS measurements are performed in galvanostatic and potentiostatic modes. Both methods show that cathode poisoning has significant influence on hydrogen evolution, however, electrochemical surface area is significantly reduced at constant potential compared to constant current. At constant current operation, cell potential tends to increase accelerating the removal of CO. The highest impact on reaction kinetics is observed while both anode and cathode electrodes are poisoned at the same time. Anode electrode poisoning is more effective than cathode electrode poisoning on the rate of oxidation and evolution reactions at constant current. However, both electrodes have similar impacts at constant potential. Moreover, over potential of the anode electrode increases significantly during the CO poisoning at constant current operation compared to over potential of cathode electrode.

References

G.A. Camara, E.A. Ticianelli, S. Mukerjee, S.J. Lee and J. McBreen, 149(6), A748 (2002).

N.R. Elezovic, Lj. Gajic-Krstajic, V. Radmilovic, Lj. Vracar and N.V. Krstajic, Electrochim. Acta, 54, 1375 (2009).

Figure 1
Chemical and Mechanical Reinforcement of PFSA Membranes with Functional Nanofibers
Authors: Akrout Alia , Duquet Fanny , Taillaides Melanie , Cavaliere Sara , Rozière Jacques , Jones Deborah J.
Published: February 2020

Fibre webs of polybenzimidazole modified with radical scavenger nanomaterials have been prepared and embedded in perfluorosulfonic acid ionomers.
(Invited) The Glass Transition of Perfluorosulfonic Acid Membranes in Consideration of Thermal Processing-Property Relationships
Authors: Moore Robert B , Orsino Christina Marie , Novy Melissa H , Duchesne Denis , Dahlke Gregg , Chen Lisa
Published: February 2020

Perfluorosulfonic acid ionomers (PFSAs) are the benchmark materials used as proton-exchange membranes (PEMs) in fuel cells. Conventional PFSA membranes have a chemical structure consisting of a PTFE backbone with randomly distributed perfluoroether side chains that terminate with a sulfonic acid group. These polar -SO3H groups, distributed within a matrix of non-polar PTFE segments, tend to aggregate forming a complex nanostructured network of hydrophilic domains. Further percolation of these domains (generally observed with increasing water content) provides pathways for efficient transport of protons (or other ions) and water in a variety of membrane-based electrochemical energy conversion and storage applications. To enhance or optimize the transport properties of a given PFSA, a variety of solvent casting and post-processing thermal treatments have been developed to facilitate molecular mobility during morphological development. In this presentation, we will focus on molecular-level considerations of the glass transition, T
g, of PFSAs with respect to thermal drying and annealing protocols used in conventional PFSA membrane processing. Using dynamic mechanical analysis (DMA), we have previously assigned the true T
g of H+-form Nafion® to be associated with a weak β-relaxation observed near -20 °C. Recently, we have found that the β-relaxations in other PFSAs (e.g., 3M PFSA and Solvay’s Aquivion®) can also be assigned to the glass transitions of these polymers. Nevertheless, the β-relaxations of all these PFSAs are weak in comparison to the dominant α-relaxation, associated with a transition from a physically crosslinked, H-bonded network to a dynamic network that allows for significant reorganization of the polar functionalities during thermal processing.
Broadband Dielectric Spectroscopy Study of the Ion Dynamics in Blends of Polymerized and Molecular Ionic Liquids
Authors: Kinsey Thomas , Glynn Kaitlin , Sangoro Joshua R
Published: February 2020

The primary focus in describing the decoupling of ion dynamics from the structural relaxation and dynamic glass transition (Tg) in polymerized ionic liquids (PILs) has been the effect of polymer molecular weight and chemistry of the ionic repeat unit. A particular aspect that has not been studied in attempt to understand the physicochemical properties of these fascinating materials is the concentration dependence of PILs with their low molecular weight or monomeric derivatives. Here we present studies of mixtures containing the low molecular weight monomer and the corresponding polymer of [(methacryloyloxy)ethyl]dimethylammonium (DMAEMA+), the quaternized ammonium cation of dimethylaminoethyl methacrylate, with the bis[(trifluoromethyl)sulfonyl]imide (NTf2) counter anion. The temperature dependent ion dynamics were measured using broadband dielectric spectroscopy. Our results show that there is an exponential relationship between the dc conductivity and concentration which decreases with temperature. At ~80mol% PIL this this inverse relationship between log σ0 and concentration “saturates” then reverses approaching 100% PIL. Only a single calorimetric glass transition temperature was observed for each of the concentrations measured. The Tg is concentration independent from 0-75% (~-60°C) then rapidly increases to that of the polymer (~55°C). The S-N-S bending modes, as observed in the Raman spectrum of the blends, blueshifts with increasing concentration, but exhibits a slight redshift from 85-100% polymer. This suggests the anion becomes more coordinated to the cation with increasing polymer concentration, but then reverses approaching pure polymer. In concert with results from a recent simulation study, we suggest that the ion hopping mechanism changes drastically from dilute to concentrated PIL/IL blends at a characteristic concentration (~85% for DMAEMA+ NTf2), but then this mechanism reverses as the ion dynamics and structural relaxation become decoupled in the pure polymer. A continuation of these concentration dependent studies of PIL and low molecular weight ionic liquid blends is a promising direction toward fully understanding the dynamics in these systems for rational design of PILs.

Figure 1
Ionomer Aggregation in Dispersions: Revealing the Role of Solvent By a Fully Atomistic MD Study
Authors: Tarokh Atefeh , Karan Kunal , Ponnurangam Sathish
Published: February 2020

Ionomer dispersions are a key ingredient for fabrication of fuel cell catalyst layers. The structural characteristics of ionomer (e.g. Nafion) in dispersions and thereby in the colloidal catalyst ink (comprising Pt/C catalyst and ionomer in a solvent/media) has been speculated to play an influential role in the structure, property and performance of CLs made thereof [1-5]. How or why the chains of the sulphonic acid containing perfluorinated ionomers interact with each other in organic solvents or water or water-alcohol mixtures to form aggregates is not understood. The shape and size of aggregates are still under debate [6]. Furthermore, the commonly deployed x-ray, neutron and light scattering techniques for characterization of ionomer dispersion are limited in their capabilities to shed light on the internal structure of the aggregates, i.e. chain entanglement and coiling, solvent induced swelling, as well as the clustering or dissociation of sulphonic acid. Our all-atom Molecular Dynamics (MD) study aims to reveal the role of solvents on the aforementioned aggregation behavior and aggregate characteristics. Nafion ionomer in common lab solvents such as toluene, IPA, ethanol, glycerol, formic acid, formamide and water was simulated. The results reveal that depending on the solvent ionomers aggregate either due to ionic interactions between protonated sulphonate ion pairs (Figure 1a) or due to hydrophobic effects (Figure 1b). Interesting structure is observed for mixture of alcohol and water (Figure 1c), consistent with the structure proposed by Los Alamos researchers (Welch et al)[6].

The presentation will discuss the results in further details including aggregate shape/size, chain conformation, ionic cluster shape/size, and acid deprotonation for various solvents. A new aggregation phase diagram will be introduced.

References:

[1] Uchida et al, 1995, J Electrochem Soc, 142, 463 ; [2] Malek et al, 2007, J. Phys. Chem. C, 111, 13627; [3] Ghelichi et al, 2016, J Macromolecules, 49,1479; [4] Mashio et al, 2016, Electrochim Acta, 202,14; [5] Mabuchi et al, 2017, J Electrochem Soc,80, 577; [6] C.Welch et al, 2012, American Chemical Society, 1,1403.

Figure 1
Nano-Rod Typed PtFes Ternary Catalyst for Oxygen Reduction Reaction in PEMFCs
Authors: You Daejong , You Eunyoung , Lee Sungchul
Published: February 2020

Nano-rod typed electrocatalyst of platinum–iron-sulfur (R-PtFeS) nanoparticles on carbon support were synthesized via a modified polyol process in teflon-sealed reactor. Overlapping the two-dimensional mapping of each element from a scanning transmission electron microscope (STEM) in a single particle of PtFeS confirm rod typed morphology, which consist of the Sulfur stabilized iron–scare and platinum-rich content near the particle surface with average size around 3.5nm and X-ray diffraction patterns of the R-PtFeS catalyst suggest successful formation of alloy without presence of individual Pt, Fe, and S nanoparticles. The electrochemical surface areas (ECSAs) and ORR activities of R-PtFeS catalysts were measured using a rotating disk electrode technique with cyclic voltammetry and the linear sweep method. The R-PtFeS catalysts showed the higher activity for ORR than that of Pt and spherical typed PtFe catalysts without sulfur (S-PtFe), which might be attributed to more favorable compressive strain between the FeS alloy in the core region and the Pt atom in the shell region. More importantly, the durability of the R-PtFeS catalyst is higher than that of Pt catalyst after 3000 potential sweeps, which was ascribed to the covalent bonds of sulfur for Fe. Furthermore, The PEMFCs single cell performance employing R-PtFeS catalyst exhibits an enhanced cell performance compared to a single cell using the Pt catalysts, demonstrating the importance of electronic and geometric control of Pt alloy nanoparticles that can improve the catalytic activity and stability. This synergistic combination of the anchoring effect of sulfur for the iron and morphology control for the Pt could provide the direction of development of Pt catalyst toward the oxygen reduction reaction.
Elucidating the Structural Composition of a Fe-N-C Catalyst By Nuclear and Electron Resonance Techniques
Authors: Wagner Stephan , Auerbach Hendrik , Tait Claudia , Martinaiou Ioanna , Shyam Kumar Chethala Neelakandhan , Kübel Christian , Sergeev Ilya , Wille Hans-Christian , Behrends Jan , Wolny Juliusz , Schünemann Volker , Kramm Ulrike Ingrid
Published: February 2020

Today, state of the catalysts in proton exchange fuel cells are platinum-based. Cost estimates show that basically the catalyst is one of the most expensive components in the FC stack. While platinum is very active for the hydrogen oxidation reaction, large quantities (approx. 80 % of the overall Pt content) are required on the cathode for the oxygen reduction reaction (ORR).

Thus, alternative catalysts are required. Fe-N-C catalysts achieve very promising ORR activities in PEFC applications. The most active ones are prepared from zinc immidazole frameworks in combination with an iron source (and nitrogen precursor), that are then pyrolysed at temperatures of 900 °C or even higher. This makes it very likely that inorganic spectator species are formed.

In order to get some more fundamental insight, in this work we focused on the characterization of a Fe-N-C model catalyst. The material was prepared from iron porphyrin supported on carbon with low iron loading at 600 °C followed by acid leaching. For this condition, previous results indicate that still the overall amount of FeN4 centers remain intact, but transforms to slightly different local environments.

Herein, we will show by the use of nuclear inelastic scattering (also known as Nuclear Resonance Vibrational Spectroscopy), low temperature Mössbauer spectroscopy and Electron Paramagentic Resonance spectroscopy that the above given conclusion was wrong: even for these mild preparation conditions large amounts of spectator species are found, that overlay in room temperature Mössbauer spectroscopy with the so-called D1 doublet, previously assigned as ORR active site by us and others.

Nevertheless, still the catalyst contains about 50 % FeN4 centers, thereof a partial fraction that is coordinated by oxygen molecules.

These results underline the importance of in-depth analysis of Fe-N-C catalysts as the amount of spectator species should be decreased in best case to zero, in order to avoid side reactions.
Fuel and Water Management in Direct Methanol Fuel Cells
Authors: Blankenau Isaac , Marten Lauren , Li Xianglin
Published: February 2020

This study has designed and setup experiments to measure the performance of MEAs made from Johnson Matthey’s gas diffusion electrodes (anode: 3 mg/cm2 Pt and 1.5 mg/cm2 Ru; cathode: 1.25 mg/cm2 Pt). The polarization curves of MEAs with fuel and water management layers, which are porous materials with different wettability and mass transfer resistance, have been experimental measured with dilute methanol solutions (3M or less). In addition, the water crossover, and methanol crossover, as well fuel efficiency, energy efficiency have been estimated from changes of weight and concentration of methanol solutions before and after constant current discharge experiments.

Results show that adding a fuel management layer between the methanol channel and the MEA can significantly reduce the water and methanol crossover rate and increase the fuel and energy efficiency. The net water flux across the electrolyte membrane could be less than the water flux caused by electro-osmotic drag flux. In other words, the water flux by diffusion and convection could be from cathode to anode when a fuel management layer is applied. However, the fuel management layer also reduces the water flux from the channel to the MEA and increases the ohmic resistance of the electrolyte membrane. A water management layer between the MEA and cathode channel is recommended to reduce the water loss through the cathode, reduce the water and methanol and water crossover rate, and increase the fuel efficiency. This water management layer does not deteriorate the water flooding since the operating current of methanol fuel cells (<0.5 A/cm2) are typically much lower than that of proton exchange membrane. The limiting current with or without the water management layer keeps almost the same. In addition, if a fuel management layer is applied to reduce the methanol crossover, a thinner electrolyte membrane is recommended because it requires less water to be hydrated and it has relatively low ohmic resistance.
(Invited) Solid State Electrolyte for Li-Metal Based High Capacity Battery Application
Authors: Wu James J.
Published: February 2020

NASA future missions demand safe, high specific energy (>400 Wh/kg) batteries. Current state-of-the-art (SOA) lithium-ion batteries (LIBs) can only provide ~150-200 Wh/kg in energy capacity, which is unable to meet NASA’s future energy goals, and also pose safety issues due to the use of liquid flammable electrolyte. There are intense on-going development activities to increase battery energy density. The use of Li metal as an anode material has emerged as one highly attractive option for achieving high-energy, next generation batteries. This is because Li has many advantages. It is the lightest metal, but also has the highest theoretical capacity. It also has the lowest potential, which boosts whole cell voltage, and Li metal is 100% active material and requires no binder. Thus, Li metal is an ideal anode material for high energy battery chemistries. Lithium metal based advanced battery chemistries are envisioned to be mission enhancing and, in many cases, mission enabling for future space and aeronautic applications.However, the reliable use of this exceptionally high capacity anode in a commercial rechargeable battery has not been achieved due to safety and reliability concerns resulting from thermal runaway and short-circuit issues due to dendritic growth on the Li metal anode from lithium plating during charge-discharge cycles.

A solid state electrolyte, such as garnet/ceramic or solid polymer nanocomposite electrolyte, is a promising approach to make Li metal safely cycling. The solid state electrolyte is non-flammable and eliminates leakage and fire hazard by replacing the liquid flammable electrolyte. However, the low-ionic conductivity and high interfacial impedance are the key issues to be overcome. In this presentation, the research activities on solid state electrolyte development funded by the NASA Advanced Energy Storage System program and by the NASA Center Innovative Fund will be presented, and the progress and results will be also discussed.
(Invited) Electrocatalysis and Photoelectrochemistry Based on Modified Titanium Dioxide Nanomaterials
Authors: Chen Aicheng , Dondapati Jesse , Van Der Zalm Joshua , Chen Shuai , Prins Scott
Published: February 2020

With an ever-increasing population, the importance of industrial processes to ensuring enough food and energy are produced to meet increasing demand cannot be understated. Unfortunately, these processes often produce byproducts that become waste and cause ecological damage. A large concern arises when these waste products enter the water system, resulting in serious consequences for the environment. Various methods have been explored towards the removal of these pollutants. Catalysis plays a key role in chemical production, energy conversion and storage, air purification, water treatment, food processing, and the life sciences. In this presentation, we report on the preparation and modification of TiO2 nanostructured materials as advanced electrocatalysts and photocatalysts for environmental applications and water disinfection.

TiO2 nanopores and nanotubes were directly grown on a titanium substrate using anodization processes. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction were employed to characterize the formed TiO2 nanostructures. The electrocatalytic and photocatalytic activities of the nanoporous and nanotubular TiO2 were investigated by the degradation of phenolic pollutants and lignin, a byproduct of the pulp and paper industry, as the model pollutants. The formed TiO2 nanostructures were further treated using electrochemical methods in enhance their catalytic activities. The effectiveness of electrochemical and photoelectrochemical degradation of phenolic species and lignin was determined by UV-Visible spectroscopy and total organic carbon analyzer. The effect of the growth time, the morphology, and the electrochemical treatment on the performance of the formed nanoporous and nanotubular TiO2 is discussed. In addition, the increasing lack of drinking water around the globe is of great concern. The synergistic effect of the integration of photocatalysis and electrocatalysis on bacterial disinfection is highlighted.
(Invited) In Situ/Operando X-Ray Characterization of Electronic Structure in Energy Materials Systems
Authors: Lee Jonathan R. I. , Ogitsu Tadashi , Wood Brandon C. , Bagge-Hansen Michael , van Buuren Tony
Published: February 2020

Characterizing the evolution in electronic structure of energy materials systems, e.g., (photo)electrochemical, electrocatalytic, etc., during operation is essential for fully understanding their behavior; the structure-property relationships derived from operando studies of functioning energy systems is critical for informing the tailored design of materials with enhanced performance as part of a feedback loop. Synchrotron-based soft x-ray spectroscopies, including both x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES), are ideally suited to the in situ/operando study of energy material structure. As element specific probes of the unoccupied and occupied electronic density of states, XAS and XES can yield insight into the bonding and composition/structure of materials across multiple length scales; moreover, these techniques are equally applicable to ordered and amorphous systems, and have the sensitivity to address structural changes in low concentration additives/dopants and bulk materials alike. Significantly, the advantages of XAS/XES are only fully realized via the close coupling of in situ experimental methods and advanced ab initio modeling, especially for highly complex, multi-component systems, to identify and interpret key spectroscopic signatures. We demonstrate the benefits of a combined experiment/simulation approach via the investigation of nanostructured carbon aerogel (CA) electrodes operating in prototypical electric double-layer capacitors. Simulations are leveraged to interpret spectral changes consistent with complex, reversible, and highly influential structural transformations: profound bias- and time-dependent evolution of the electronic structure under applied bias connotes both mesoscale (distortion of the porous networks) and nanoscale (specific adsorption) phenomena central to device performance. Although XAS/XES have the potential for impact across multiple EMN consortia, further discussion will focus on ongoing work centered around our combined experiment/simulation node within HydroGEN.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
(Invited) HPC4Materials Program: A National Laboratory - Industry Partnership in High Performance Computational Simulations
Authors: Miles Robin
Published: February 2020

The HPC4Materials program is a new Office of Fossil Energy-sponsored program with participation from the EERE Vehicle Technology Office and the Fuel Cell Technology Office with the aims of introducing industry to High Performance Computing (HPC) for advanced science and engineering simulations, transferring advanced simulation techniques developed at the National Laboratories to industry and developing new materials to promote the energy objectives of the sponsoring offices. Nine partner national laboratories have been working with a variety of large and small companies in a variety of industries. Examples include investigation of corrosion mechanisms in high-temperature, harsh environments and use of machine learning techniques to understand conditions in which fatigue failure might occur in power plant components. Many companies are interested in advanced simulation to reduce costs associated with product/or and process testing. Projects will be highlighted as demonstrations of how HPC can be used to reduce the risk of advanced development.
(Invited) HydroGEN Supernode: Linking Low Temperature Electrolysis/Hybrid Materials Properties to Electrode Performance
Authors: Alia Shaun M , Bender Guido , Ulsh Michael , Mauger Scott A , Pivovar Bryan S. , Dinh Huyen N , Weber Adam Z. , Danilovic Nemanja , Kusoglu Ahmet , Colon-Mercado Hector
Published: February 2020

The HydroGEN Energy Materials Network (EMN) supernode in low temperature electrolysis combines capabilities from the National Renewable Energy Laboratory (NREL), Lawrence Berkeley National Laboratory (LBNL), and Savannah River National Laboratory (SRNL) to perform relevant and ground-breaking research outside of EMN-funded projects. The low temperature electrolysis supernode focuses on: evaluating and bridging the gap between rotating disk electrode half-cell activity and membrane electrode assembly single-cell performance; and understanding how electrode composition and processing parameters affects device performance.

Ex-situ testing has been used to screen a variety of catalysts and correlate oxygen evolution activity to in-situ performance. Gaps between half- and single-cells were attributed to differences in configuration and standardized test parameters. While non-kinetic loss in membrane electrode assemblies are primarily due to resistance (ohmic), significantly larger transport losses are found in rotating disk electrodes due to electrode orientation and agitation. Differences in kinetics between these methods is primarily due to temperature. Increasing half-cell temperature and using flow cells can be used to bridge the gap between ex- and in-situ performance. Various oxygen evolution catalyst types, including different surfaces (metal/oxide), supports, surface areas, and components, were evaluated to address test differences across these material sets.

Additionally, electrode composition and processing parameters were evaluated for their affect in electrolysis performance. Although catalyst layer uniformity may not significantly affect device performance at high loading, coating methodology is critical at low loading. Various spray coating parameters, including ink composition (ionomer content, water/alcohol ratio), drying temperature, and deposition rate were evaluated and found to alter the resulting performance in membrane electrode assemblies. Ionomer content was further correlated to half-cell tests, where low content may adversely impact ink stability (catalyst layer uniformity) and the catalyst layer interface, while high content may lower performance through contaminant effects. Parameters from spray coating tests were applied to slot die and gravure coating methods to transfer this understanding to larger-scale processes. Efforts to tune coating parameters utilize rheology studies and ex-situ characterization to assess catalyst-ionomer-solvent interactions and ionomer thin films. Multiscale modelling was used to evaluate membrane electrode assembly performance and separate kinetic, transport, and ohmic losses. Composition and processing parameters were additionally applied to hybrid cycles.
Effect of Polymer Capping Layers on Initial Fracture Mechanism of Silicon Anodes
Authors: Coyle Jaclyn , Ban Chunmei , Burrell Anthony
Published: February 2020

Using silicon nanomaterials is a widely accepted strategy for mitigating the extreme volume expansion associated with the lithiation of silicon and the accompanying capacity fade. However, the high surface area of silicon nanomaterials provides more opportunity for electrolyte decomposition which leads to high irreversible capacity loss and low Coulombic efficiency. Silicon microparticles area available in large scale at a low cost and offer an alternative with lower surface area that have been shown to have high initial Coulombic efficiency. However, to make silicon microparticles viable, the drastic volume change and high stress of these larger particles must be mitigated. In order to develop a more thorough understanding of the initial lithiation mechanics of the silicon crystalline microparticles, this work studies the initial lithiation mechanism through model crystalline electrodes. We have discovered that the thickness of the crystalline silicon wafer itself affected the initial crack formation mechanism. The next step for this study was to modify the mechanical properties of the top surface layer of the crystalline silicon substrates by adding a polymer capping layer and observe how these polymer layers affect the electrochemically induced fractures in crystalline silicon anodes through TEM, SEM and ellipsometry analysis. Polymer films of typical binder materials such as PVDF, PAA and CMC as well as novel modified PAA polymer binders were deposited on crystalline silicon substrates and lithiated to the same extent as an uncoated silicon anode to directly compare crack formation under the same level of silicon lithiation. The results of this work provide important analysis targeted at the initial crack formation of silicon and how polymer capping layers affect the lithiation depth and cracking formation of crystalline silicon. These findings may be applied to create a viable capping layer to reduce cracking in larger, more economical, silicon particles.

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(Invited) Advanced Nanostructure Design and Novel Electrolyte Development for Si Anodes Towards Practical Applications
Authors: Li Xiaolin , Jia Haiping , Zhang Ji-Guang
Published: February 2020

Si has been regarded as the most promising anode material for next generation high energy Li-ion batteries. Among the tremendous effort made towards the practical application of Si anodes, the design of advanced nanostructures and the development of novel electrolyte systems are crucial in accommodating the Si volume change and enabling a stable solid electrolyte interphase. Recently, our group has made significant progress in these two aspects. In this talk, we will discuss the use of mesoporous Si sponges and hierarchical structured Si/CNT/C microspheres as high performance Si anode materials and the development of localized high concentration electrolyte for commercial nano-Si and graphite composite anodes. The discussion will be focused on high loading electrodes of ~3 mAh/cm2 and full cells towards practical applications.
Intrinsic Properties of Silicon-Electrolyte Interphase (SiEI) Studied through Individual Inorganic Components
Authors: Han Sang-Don , Wood Kevin N , Stetson Caleb , Norman Andrew G , Brumbach Michael , Coyle Jaclyn , Xu Yun , Harvey Steve , Teeter Glenn , Zakutayev Andriy , Burrell Anthony
Published: February 2020

The stabilization of a silicon-electrolyte interphase (SiEI) is a great challenge which limits the ability to approach theoretical capacity limits (about 3,600 mAh g-1, almost 10 times higher than that of graphite) in silicon (Si) anodes for next-generation lithium-ion batteries (LiBs). The SiEI is a less studied topic relative to the research devoted to battery components, in part, because of its complexity, reactivity and continuous evolution.1 However, the SiEI plays a key role in prevention of further electrolyte reduction and desolvation of Li+ions, which is directly related to electrochemical performance, lifetime and safety of batteries. For example, the unstable SiEI leads to irreversible capacity losses, poor cycling stability and a limited cycle life.2-4

In this study selected known SiEI components (i.e., SiO2, Li2Si2O5, Li2SiO3, Li3SiOx, Li2O and LiF) were prepared as amorphous thin films. The chemical composition, homogeneity, morphology and local electronic structure across the surface and the bulk were characterized using X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscope (AFM), and scanning-spreading resistance microscopy (SSRM). In addition, the physical, electrochemical and mechanical properties of individual constituents were characterized using electrochemical impedance spectroscopy (EIS), operandoXPS with an electron gun, and AFM (force distance curve) and scanning probe microscopy (SPM)-based nanoindentation.

This study delineates the components which are critical for stabilizing the SiEI. These findings enable rational design of new electrolyte additives and functional binders for the development of next generation LiBs.

References

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2. B. Philippe, R. Dedryvere, M. Gorgoi, H. Rensmo, D. Gonbeau, and K. Edstrom, Chem. Mater.2013, 25, 394.'

3. T. Jaumann, J. Balach, M. Klose, S. Oswald, U. Langklotz, A. Michaelis, J. Eckerta, and L. Giebelera, Phys. Chem. Chem. Phys.2015, 17, 24956.

4. B. T. Young, D. R. Heskett, C. C. Nguyen, M. Y. Nie, J. C. Woicik, and B. L. Lucht, ACS Appl. Mater. Interface2015, 7, 20004.