bluuebunny/crossref_metadata_2025 huggingface dataset:
Batteries Beyond Li-Ion: Is Na-Ion a Viable Option?
Authors: Palacin M Rosa
Published: February 2020

When we consider metal anode batteries, the density and redox potential of the metal itself are the keys to theoretical performance, with the largest figures of merit corresponding to lithium.  Moving from Li to Li-ion battery technology ensures viability from a safety point of view, to the expense of a large penalty in energy density.  In this case, lithium is only present as lithium ions which are the positive charge carriers in the system.  When considering possible alternative M-ion technologies, the theoretical performance depends on the electrochemical capacities and operating potentials of the negative and positive electrodes. Such figures are not in any way related to the capacity values of metal anodes except for the fact that the lowest negative electrode potential limit is set by the standard redox potential of the metal itself.  Thus, there is no reason why the Na-ion battery technology could not reach figures of merit comparable to those of the ubiquitous Li-ion, provided suitable electrode materials and electrolytes can be developed. 

Although it had fallen into oblivion for ca. 20 years, the Na-ion battery concept is not new and trends identified during the early days of intercalation and knowledge borrowed from the Li-ion battery field should foster its progress, on condition that due attention is also paid to intrinsic differences between lithium and sodium.

The talk will review recent research carried out at ICMAB-CSIC dealing mainly with the optimization of electrolyte formulation and the study of negative electrode materials, including hard carbon prepared from sugar pyrolysis and diverse titanium containing phases, such as Na2Ti3O7.  The assembly of full Na-ion laboratory cells using Na3V2(PO4)2F3 cathode, hard C anode and EC:PC:DMC based electrolyte will also be discussed.  These exhibit an operation voltage of 3.65 V, very low polarization and excellent capacity retention and power performance, which are comparable to state-of-the art lithium-ion technology based on similar electrode chemistry.

Finally, the possible development of alternative M-ion technologies will also be discussed.
Intercalation As a Two-Step Process: Modeling of Adsorption at Electrochemical Interfaces in Batteries
Authors: Lück Jessica , Latz Arnulf
Published: February 2020

Batteries based on a electrochemical lithium intercalation reaction are widely used and have many applications from costumer electronics to electromobility. Thus, insertion materials have attracted attention from practical aspects as well as fundamental interest in the exchange reaction occurring between the bulk electrode and the interface between electrode and electrolyte. Even though many reports have been published regarding bulk properties of electrolytes and insertion electrodes, like structural changes or diffusion and transport of ions in the electrode or the electrolyte, little is known about the processes at the electrolyte/electrode interface, like adsorption and desolvation on electrode surfaces. For deriving predictive models of batteries it is crucial to obtain a comprehensive understanding of the reaction mechanism taking place at the electrochemical interface.

Bruce et al. [1] proposed a 2-step-model for electrointercalation. Figure 1 shows this so called adatom model, where the fully solvated Li-ion in bulk electrolyte partially loses its solvation shell before getting adsorbed on the surface. Then it diffuses to a site, at which it can intercalate into the electrode. After this the adion loses the remaining solvent and gets incorporated in the lattice of the electrode. This proposed mechanism of a two-step-electrointercalation (desolvation/adsorption(=adion formation) and insertion) is confirmed for different insertion materials [2-4].

Considering some conversion materials like for lithium-sulfur-batteries, where Li-ions have to enter carbon spheres before reacting with sulfur, it's equally reasonable to assume first an adsorption step.

To include electrosorption, that is adsorption with partial desolvation, as an important step for intercalation and conversion reactions in batteries at the interface of a concentrated electrolyte and some active material, we derive equations for surface charges from thermodynamic and electrostatic considerations.

These derived equations are used as an intermediate step to couple the transport in the electrolyte and the solid phase with desolvation within a thermodynamic consistent reaction-transport model for Li-ion batteries [5]. Our developed model produces a reasonable coverage on the surface of the electrode while maintaining the transport properties of the cell.

[1] P.G. Bruce, et al., J. Electroanal. Chem., 322 (1992), pp 93-105.

[2] S. Kobayashi, et al., J. Phys. Chem. B, 109 (2005), pp 13322-13326.

[3] M. Nakayama, et al., J. Phys. Chem. C, 118 (2014), pp 27245-27251.

[4] M. Nakayama, et al., J. Phys. Chem. B, 107 (2003), pp 10603-10607.

[5] A. Latz, et al., Journal of Power Sources, 196 (2001), pp 3296-3302.

Figure 1.

Schematic diagram of the lithium intercalation reaction at the electrolyte – electrode interface

Figure 1
Characterization of Ionomer Thin Film Distributions in PEM Fuel Cell Catalyst Layers Using Advanced Analytical Microscopy
Authors: More Karren L. , Cullen David A.
Published: February 2020

Polymer electrolyte membrane (PEM) fuel cell performance degradation, particularly associated with the cathode catalyst layer, can be directly attributed to the stability and durability of individual material constituents comprising the membrane electrode assemblies (MEAs), including the electrocatalyst, catalyst support, and ionomer films.  The structural and chemical changes of these MEA constituents are quantified via advanced electron microscopy methods to elucidate the materials-specific degradation mechanisms contributing to performance loss, with the ultimate goal being microstructural and compositional improvements that will enhance MEA durability.  Research efforts at Oak Ridge National Laboratory are focused on the high-resolution microstructural and microchemical characterization of as-fabricated fuel cell materials (e.g., the individual materials constituents and the same materials incorporated in fresh MEAs), MEAs subjected to accelerated stress tests (ASTs) designed to degrade specific MEA components, and field-aged MEAs.  These studies are used to establish critical processing-microstructure-performance correlations and to elucidate the materials factors contributing to MEA degradation, performance loss, and failure.  Recently, high-resolution analytical microscopy methods have been used to directly image/map the distribution and chemistry of the ionomer layers within catalyst electrodes, both on a mm-level for assessing “bulk” ionomer dispersions and at the nm-level to understand the continuity and uniformity of thin ionomer films.  This presentation will focus on understanding ionomer distributions as a function of initial ionomer chemistry (e.g., solvents used), electrocatalyst content and dispersion, and type of carbon support used. Additionally, the stability of the ionomer films in cathode catalyst layers after ASTs designed for catalyst degradation and carbon corrosion will be evaluated.

________________________________________________________________________

Research sponsored by (1) the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy and (2) Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility.
Degradation Study of the Cells Operated Under Low or High Humidity Conditions at Cathode and/or Anode
Authors: Friedrich K. Andreas , Sanchez Daniel G , Ruiu Tiziana , Biswas Indro , Helmly Stefan , Schulze Mathias , Sanchez-Monreal Juan
Published: February 2020

Water management represents one of the main challenges for the design and operation of polymer electrolyte membrane fuel cells (PEMFC), the amount of water in the cell affects the performances and degradation processes. Commonly, the main goal is try to reduce the humidification in order to simplifying the humidification system and enhancing the performance stability of the cell. However, insufficient water content can lead to increased degradation and performance loss. These negative effects depend strongly on water distribution [1] in the cell and can therefore be highly non-uniform [2]. The relation between low humidification and degradation is complex and not yet fully understood. To bring more insight into this, the differences in the local conditions of the cell must be taken into account when examining performance and degradation. Thus, in this work, particular attention is paid to the local analysis of performance and degradation of cells operated under low or high humidity conditions at cathode and/or anode.

In order to study locally the degradation influence of inlet gas humidification on cell performance all the experiments were performaned with the DLR- PCB segmented cell current density measurements, other global effect were analyzed using in-situ diagnostic tools, such as cyclic voltammetry. The changes observed locally in the current densities distributions were investigated locally by post-mortem ex-situ investigations by XPS and SEM/EDX to determine changes in the chemical composition of the different layers during the experiment.

 [1] D. G. Sanchez and P. L. Garcia-Ybarra, Int. J. Hydrogen Energy, 37, 7279 (2012).

[2] D. G. Sanchez, D. G. Diaz, R. Hiesgen, I. Wehl and K. A. Friedrich, J. Electroanal. Chem., 649, 219 (2010).
Palladium Decorated Polymer Functionalized Graphene for Enhanced Electrocatalytic Oxygen Reduction Reaction in Alkaline Fuel Cells
Authors: Park Dong Chul , Ahmed Mohammad Shamsuddin , Jeon Seungwon
Published: February 2020

Newly synthesized Poly(3,4-ethylenedioxythiophene) functionalized graphene with palladium nanoparticles (denoted as Pd/PEDOT/rGO) has been introduced in electrochemical oxygen reduction reaction (ORR) for alkaline fuel cells (FCs). The structural features of catalyst are characterized by several instrumental techniques. The transmission electron microscopy (TEM) images suggest a well dispersed PdNPs onto PEDOT/rGO film. The ORR activity of Pd/PEDOT/rGO has been investigated via cyclic voltammetry and hydrodynamic voltammetry techniques in 0.1 M KOH aqueous solution. Comparative CV analysis suggests a general approach of intermolecular charge-transfer in between graphene sheet and PdNPs via PEDOT which leads to the better PdNPs dispersion and subsequently superior ORR kinetics. The Pd/PEDOT/rGO has superior electrocatalytic activity towards ORR than that of state-of-the-art Pt/C in respect to the half-wave potential and current density. Moreover, The mass activity of the Pd/PEDOT/rGO was measured as ~2 and ~9 times higher than that of Pt/C and Pd/rGO. The Koutecky–Levich and Tafel analysis suggest that the proposed main path in the ORR mechanism has direct four-electron transfer process with faster transfer kinetic rate on the Pd/PEDOT/rGO.
Catalytic Activity Evaluation of Palladium Decorated Damaged Carbon Nanotube for Direct Ethanol Fuel Cells in Anode
Authors: Joo Yuri , Ahmed Mohammad Shamsuddin , Jeon Seungwon
Published: February 2020

The sp2 p-conjugative structure, that allows the carbon nanotube (CNT) interact with various compounds and metal nanoparticles (NPs) through p–p interaction. The damage of p-conjugative sidewall of CNT can hamper the overall anodic activity. The CNT, as base material, has been prepared through a conventional acid treatment method up to 15h; the higher degree of sidewall damage has been observed in last 5 hours during treatment period. The short and long term acid treated CNTs have been subsequently fabricated with palladium NPs (denoted as CNT/Pd and CNT–Pd, respectively) and employed as ethanol oxidation reaction (EOR) catalysts for direct ethanol fuel cells (DEFCs). The structural features of catalyst are characterized by several instrumental techniques. The Barrett–Joyner–Halenda pore volume of CNTs have been increased upon increasing acid treatment time from 0.326 cm³ g−1 (1h CNT), 0.381 cm³ g−1 (5h CNT), 0.488 cm³ g−1 (10h CNT) to 0.598 cm³ g−1 (15h CNT). The kinetic parameters including poisoning tolerance have also been hampered by the surface damage. The CNT/Pd and CNT–Pd are express higher electrocatalytic activity and poisoning tolerance than that of Pd/C while Pd mass loading remains in the same amount.
The Catalytic Behaviour of Pt Clusters on Au and Pd/Au As a Function of Their Surface Coverage and Density
Authors: Al Amri Zakiya , Vasiljevic Natasa
Published: February 2020

Pt bimetallic structures such as Pt core-shell layers, alloys and clusters on different substrates have been a focus of intense research because they generally exhibit properties different from bulk Pt. The often improved catalytic activity of these structures makes them highly attractive for fuel cells applications[1].

Our understanding and decoupling of the effects responsible for the enhanced catalytic behaviour, such as bi-functional, electronic and ensemble effects, is incomplete. Numerous studies have been conducted so far with the aim of correlating surface activity with the structure and distribution of Pt on or in the catalyst surface [2-5]. It has been shown  that the catalytic activity of Pt nanoparticles decorated with ruthenium clusters (Ru/Pt catalyst) is twice that of the commercial 50 : 50 Ru/Pt alloy catalyst [2]. An enhancement of CO tolerance has been also found on supported Pt/Ru catalyst obtained by spontaneous deposition for a considerably lower Pt loading than in commercial catalyst[3]. The modified Au surface with Pt nanosize clusters [6] coverage as low as 15-25% of the substrate area, exhibit very high activity and incredible selectivity toward dehydrogenation of formic acid (HCOOH).

Our interest in this work are 2-dimensional model systems of Pt clusters electrodeposited on Au and Pd/Au. We used different electrochemical protocols to control Pt clusters’ size,  i.e. in terms of diameter, height and distribution: i) spontaneous adsorption of [PtCl4]2- complex and its potential controlled reduction e.g. the method often called ‘spontaneous deposition’ (SD) [2, 7] and ii) modified surface limited redox replacement (SLRR) method based on the galvanic replacement or partial underpotentially deposited metal layers. For each method successive application of optimized electrodeposition protocols yielded increased Pt surface coverage ranging from 0.25 to 1 area fraction. The surface coverage of Pt/Au and Pt/Pd/Au as well as the active area were determined electrochemically using H-UPD and CO-adsorption. The Pt clusters structure such the diameter, height and distribution were examined by scanning tunnelling microscopy (STM). The catalytic behaviour of Pt- nanostructures is analysed during HCOOH electro-oxidation and it is illustrated in the figure bellow.

References

1.            M. Debe, Nature, 2012. 486: 43.

2.            W. Chrzanowski; H. Kim and A. Wieckowski, Catal. lett., 1998. 50:  69.

3.            S. Brankovic; J. McBreen and R. Adzic, J. Electroanal. Chem., 2001. 503:  99.

4.            S. Bae; D. Gokcen; P. Liu; P. Mohammadi and S. Brankovic, Electrocatal., 2012. 3:  203.

5.            B. Du and Y. Tong, Phys. chem. lett., 2005. 109(38):  17775.

6.            M. Obradović; A. Tripković and S. Gojković, Electrochim. Acta, 2009. 55:  204.

7.            Chrzanowski and Wieckowski, Langmuir, 1997. 13:  5974.

Figure 1
Evaluation of Activity of Platinum-Ruthenium-Cobalt/Graphene Catalysts Towards Methanol Oxidation
Authors: Semasko Miroslav , Tamasauskaite-Tamasiunaite Loreta , Kepeniene Virginija , Balciunaite Aldona , Vaiciuniene Jurate , Drabavicius Audrius , Norkus Eugenijus
Published: February 2020

A simple approach – microwave synthesis was used to prepare platinum-ruthenium-cobalt/graphene catalysts (denoted as Pt-Ru-Co/GR). A series of Pt-Ru-Co/GR with the different molar ratios were prepared by microwave-assisted heating of the reaction mixture consisting of H2PtCl6, RuCl3, CoCl2 and ethylene glycol. The Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) were employed to characterize the synthesized Pt-Ru-Co/GR catalysts. The electrocatalytic activity of the synthesized catalysts towards the oxidation of methanol and CO was investigated by means of cyclic voltammetry and chrono-techniques. The electrochemically active surface areas of the prepared catalysts were determined from the cyclic voltammograms of the Pt-Ru-Co/GR catalysts recorded in a deaerated 0.5 M H2SO4 solution at a sweep rate of 50 mV s–1 by calculating the charge associated with hydrogen adsorption (220 µC cm-2).

It was found that the Pt-Ru-Co/GR catalysts with the Pt:Ru:Co molar ratios equal to 1:2:2, 1:1.7:5.6 and 3.5:1:23 were prepared. The EDX analysis confirm the presence of Pt, Ru and Co nanoparticles in the investigated PtCoRu/GR catalysts.

It has been determined that the Pt-Ru-Co/GR catalyst with the Pt:Ru:Co molar ratio equal to 3.5:1:23 has a higher electrocatalytic activity towards the oxidation of methanol in acidic medium as compared with that of other synthesized catalysts.
Mixed Reactant Low Temperature Fuel Cells: The Swiss-Roll Cell Design and Selective Electrocatalysts
Authors: Gyenge Elod L.
Published: February 2020

Eliminating the proton exchange membrane (PEM) together with the platinum-based anode and cathode catalysts and replacing the bulky bipolar plates with lighter and flexible alternatives, would significantly improve the economic outlook of low temperature fuel cells operated with liquid fuels. To address the afore-mentioned issues of PEM fuel cells, at the University of British Columbia we have developed a novel mixed reactant fuel cell design referred to as the Swiss-roll cell, fed with a two-phase mixture of liquid fuel and air (or oxygen) [1-5]. Here, a research progress review is presented related to both selective electrocatalysis and Swiss-roll cell engineering applied to two alkaline fuel cell systems: sodium borohydride – oxygen and sodium borohydride – nitrous oxide, respectively. On the anode, the borohydride electro-oxidation reaction is a complex, up to eight electron transfer process, with possibly competing hydrogen evolution generated by either faradaic (i.e., electrocatalytic) or non-faradaic (i.e., thermocatalytic) pathways.  Experimental results correlated with density functional theory modelling predictions are discussed focused on the borohdyride electro-oxidation mechanism on catalysts such as: Pt, Au and Os. On the cathode side, in case of the oxygen reduction reaction (ORR) in alkaline media the comparative performance of gas diffusion electrodes with electrocatalysts such as MnO2, Ag and Fe-aminoantypyrine (Fe-AAPyr) is presented. For nitrous oxide reduction, the electrode kinetics on Pd and Pt electrocatalysts are compared. It is shown that the selective electrocatalyst discovery combined with cell electrochemical engineering innovations enables significant improvements in the power output, reaching 250 mW/cm2 for the membrane-free Swiss-roll mixed-reactant direct borohdyride fuel cell operated at 50 0C and near atmospheric pressure using non-platinum anode and cathode catalysts.  

References:

A. Aziznia, C. Oloman and E.L. Gyenge, 
J.Power Sources

, 212, 154-160 (2012).

A. Aziznia, C. Oloman and E.L. Gyenge, 
ChemSusChem
, 6, 847-855 (2013).

A. Serov, A. Aziznia, P. H. Benhangi, K. Artyushkova, P. Atanassov and E. Gyenge, 
J. Mat. Chem. A,

 1, 14384-14391, (2013).

A. Aziznia, C. Oloman and E.L. Gyenge,
J.Power Sources
, 265, 201-213 (2014).

C. W. Oloman, British Patent GB 2474202, 2012.

Figure 1
Analytical Model for the Interdigitated Flow Field
Authors: Milshtein Jarrod David , Darling Robert M. , Bazant Martin Z. , Brushett Fikile R.
Published: February 2020

Flow fields in low-temperature fuel cells and redox flow batteries play the important role of facilitating reactant transport to porous electrode surfaces, where power-converting electrochemical reactions occur1. Of the four major flow field design categories (flow-through, parallel, serpentine, and interdigitated flow fields (IDFF)), the IDFF has demonstrated high current densities with only a moderate pressure drop. Although many studies have noted the performance enhancements offered by the IDFF, development has been limited to application-specific numerical or empirical studies2–4; no bottom-up design rules exist. This lack of design principles stems from an inability to analytically model species flux and flow profile through the complicated IDFF geometry. As such, this study offers the first analytical solution of the velocity and reactant distributions through a two-dimensional (2-D) IDFF. 

The flux of a species through the IDFF channel can be described by the Nernst-Planck equation in porous media, which is a conformally invariant mathematical function5. Thus, it is possible to achieve an analytical expression for reactant flux and / or streamlines through the IDFF via the method of conformal mapping
5. Through this strategy, the combined migration-diffusion-advection problem can first be solved in a straight channel, and then the straight-channel solution is mapped (Figure 1) to the more complicated IDFF geometry by exploiting the Schwarz-Christoffel transformation5. The original numerical 2-D model by Kazim et al. is solved in this work, analytically2; Figure 2 shows a representative velocity magnitude profile for an IDFF electrode cross section. Due to unwieldy equations which arise from the analytical construction, dimensionless numbers are developed to provide an intuitive understanding of transport relationships in the IDFF, and limiting cases of electrode thickness are considered. Ultimately a convenient framework for IDFF design rules is developed by analytically solving the transport equations, allowing for greater insight to system design.

Acknowledgements

We would like to acknowledge the financial support of the Joint Center for Energy Storage Research and the United States National Science Foundation Graduate Research Fellowship program.

References

1. X. Li and I. Sabir, Int. J. Hydrog. Energy, 30, 359–371 (2005).

2. A. Kazim, H. T. Liu, and P. Forges, J. Appl. Electrochem., 29, 1409–1416 (1999).

3. Y. Wang, S. Basu, and C.-Y. Wang, J. Power Sources, 179, 603–617 (2008).

4. R. M. Darling and M. L. Perry, J. Electrochem. Soc., 161, A1381–A1387 (2014).

5. M. Z. Bazant, Proc. R. Soc. Math. Phys. Eng. Sci., 460, 1433–1452 (2004).

Figures

Figure 1
Theoretical Study of Hydrogen Production from High Pressure PEM Electrolyzer Stack
Authors: Authayanun Suthida , Arpornwichanop Amornchai
Published: February 2020

Proton exchange membrane (PEM) electrolyzer is a promising technology and likely to be an important hydrogen generator. The ability to produce high purity-hydrogen and deliver it at a relatively high pressure is an important advantage of the PEM electrolyzer technology. The high pressure operation at the cathode cause hydrogen crossover from the cathode to anode and thus deteriorate of performance. In this work, PEM electrolyzer system to produce high pressure hydrogen with consideration of energy usage and hydrogen permeation is theoretically investigated. The electrochemical and hydrogen crossover model are coded by Matlab. The effect of pressure, temperature, current density and membrane thickness on designed stack performance is presented. The explosion limit of hydrogen-oxygen mixture is also taken into consideration to figure out optimal operating operation and parameter.
Effect of Composition, Particle Size and Structural Ordering on Stability of PtCu Electrocatalysts for Oxygen Reduction Reaction
Authors: Hodnik Nejc , Mayrhofer Karl J.J.
Published: February 2020

The polymer exchange membranes fuel cells cathode electrocatalyst activity and durability are still a major challenge hindering the commercialization of these devices, despite the use of noble materials like platinum alloys. Dealloying, that is removal of less noble metals, has become one promising strategy for producing Pt-based catalysts in all design categories (skeletal surface, nanoporous, core–shell nanoparticle configuration) (1).  Generally, dealloying can be triggered either chemically by acid leaching, or electrochemically by potential hold or cycling above critical potential (2-4). In this presentation I will discuss on the impact of Pt-alloy composition (5), size (6), structural ordering (4), and also the dealloying conditions on the formation of different morphologies, as well as the resulting ORR performance. By utilizing advanced characterization techniques (electrochemical scanning flow cell coupled with ICP-MS, identical location TEM and SEM – see Figure 1 and electrochemical in-situ TEM) together with conventional thin film rotating disc electrode I will provide new insights in to dealloying phenomena of PtCu alloy. 

Figure 1: SEM sequential images of a dealloying and degradation of PtCu3 electrocatalyst: a) as-synthesized, b) after 500 cycles between 0 and 1.2 V with 0.5 V/s, c) after 5k cycles between 0.6 and 1.2 V z 1 V/s in d) after 50k cycles between 0.6 and 1.2 V z 1 V/s in 0.1 M HClO4; (scale bar is 20 nm)

Acknowledgements

Nejc Hodnik would like to acknowledge the FP7-PEOPLE-2013-IEF Marie Curie Intra-European Fellowship (project 625462 - ElWBinsTEM).

References:

1.            M. K. Debe, Nature, 486, 43 (2012).

2.            L. Gan, M. Heggen, R. O’Malley, B. Theobald and P. Strasser, Nano Letters, 13, 1131 (2013).

3.            D. Wang, Y. Yu, J. Zhu, S. Liu, D. A. Muller and H. D. Abruña, Nano Letters, 15, 1343 (2015).

4.            N. Hodnik, C. Jeyabharathi, J. C. Meier, A. Kostka, K. L. Phani, A. Recnik, M. Bele, S. Hocevar, M. Gaberscek and K. J. J. Mayrhofer, Physical Chemistry Chemical Physics, 16, 13610 (2014).

5.            A. K. Schuppert, A. A. Topalov, A. Savan, A. Ludwig and K. J. J. Mayrhofer, ChemElectroChem, 1, 358 (2014).

6.            N. Hodnik, M. Zorko, M. Bele, S. Hočevar and M. Gaberšček, The Journal of Physical Chemistry C, 116, 21326 (2012).

Figure 1
Mitigating Membrane Degradation: Investigation of Lifetime and Fluoride Emission Rate from Modified Short-Side-Chain and Long-Side-Chain PFSA Membrane Electrode Assemblies during High Temperature Open Circuit Voltage Hold
Authors: Zaton Marta , Donzel Nicolas , Dupont Marc , Jones Deborah Jacqueline , Rozière Jacques
Published: February 2020

The incorporation of radical traps in the membrane or electrode of a fuel cell MEA based on perfluorosulfonic acid (PFSA)type ionomers has emerged as an important development enabling much increased fuel cell lifetime. Effective radical scavengers include transition metal ions and their oxides, in particular of cerium. We have developed novel nanofibre-networks comprising inorganic and organic polymer radical trap materials for incorporation either within the membrane or at the membrane electrode interface of MEAs comprising long-side-chain (LSC) and short-side-chain (SSC) PFSA membranes. MEAs were submitted to open circuit voltage hold testing at 50% relative humidity and 90 °C and the voltage decay and fluoride and sulfur emission rates were monitored with time. MEAs were investigated post-mortem for evidence of Pt migration (SEM-EDX), cerium migration where relevant, and PFSA backbone modification (19F NMR, Raman and XPS spectroscopies). The results show that non-protected SSC PFSA MEAs have a significantly lower (factor >20) fluoride emission rate on OCV hold than non-protected LSC PFSA MEAs, and the interpretations of this finding will be discussed. Implementing a nanofibre PFSA network enriched with cerium oxide nanoparticles at the membrane electrode interface at the anode side further reduces the FER of SSC PFSA MEAs, such that fluoride emission rate of anode-protected Aquivion® E79-03S MEAs is 300 times lower than that of non-protected Nafion®-212. These results will be compared in this presentation with those obtained on embedding a polymer nanofibre radical scavenger within PFSA membranes such as to establish a ranking of the effectiveness of CeOx type and alternative polymer type radical scavengers in reducing fluoride loss and membrane thinning, and extending MEA lifetime.
A Graphene Oxide Membrane Fuel Cell for Room Temperature Operation
Authors: Bayer Thomas , Sasaki Kazunari , Lyth Stephen Matthew
Published: February 2020

Fuel cells for portable consumer electronics such as smartphones or optical head-mounted displays should be operated at relatively low temperatures for user comfort. However they are generally operated at over 80˚C. Recently our group reported the characterization of a graphene oxide membrane fuel cell (GOMFC) with a power density of 35 mW/cm2 measured at 30°C, showing the potential of graphene oxide to be used as a fuel cell electrolyte at low temperature.1

Graphene oxide (GO) is a sp2/sp3-hybridized carbon material with carboxyl, hydroxyl and epoxy oxygen functional groups on the surface and edges, which promote water uptake and make it insulating to electrons.2 This is in contrast to graphene, which is highly electronically conductive and therefore suitable as e.g. a catalyst support.3,4 GO is an excellent gas barrier and displays significant proton conduction,5,6making it suitable as a fuel cell electrolyte.

Free-standing flexible GO membranes were prepared from GO dispersion in water by vacuum-filtration. These were characterized as a fuel cell electrolyte (Figure 1). GO was found to have improved gas barrier properties compared to Nafion, as well as higher tensile strength and water uptake. Despite the relatively low proton conductivity (around 1% that of Nafion), graphene oxide membrane fuel cells (GOMFCs) displayed reasonable power densities up to 35 mW/cm2 at room temperature, approaching the performance of Nafion-based fuel cells at this temperature. By further reducing the thickness of the graphene oxide membrane and taking advantage of the high gas barrier properties an improved power density of up to 80 mW/cm2was achieved.

References:

1. T. Bayer, S. R. Bishop, M. Nishihara, K. Sasaki, and S. M. Lyth, J. Power Sources, 272, 239–247 (2014).

2. D. R. Dreyer, S. Park, C. W. Bielawski, and R. S. Ruoff, Chem. Soc. Rev., 39, 228–240 (2010).

3. L. Jianfeng, K. Sasaki, and S. M. Lyth, ECS Trans., 58, 1751–1762 (2013).

4. S. M. Lyth, L. Jianfeng, and K. Sasaki, ECS Trans., 58, 1529–1540 (2013).

5. R. R. Nair, H. A. Wu, P. N. Jayaram, I. V. Grigorieva, and A. K. Geim, Science, 335, 442–444 (2012).

6. K. Hatakeyama et al., Angew. Chemie, 53, 6997–7000 (2014).

Figure 1
Organic Active Species for Nonaqueous Redox Flow Batteries
Authors: Saraidaridis James Demetrios , Suttil James A. , Sevov Christo S , Sanford Melanie , Monroe Charles W
Published: February 2020

Despite decades of research on redox flow batteries (RFBs), their widespread implementation for grid electricity storage has not manifested. In the U.S., the grid penetration of intermittent renewable power is currently too low to necessitate widespread storage, and alternatives less expensive than RFBs are available to utilities pursuing efficiency improvements. RFB development should focus both on improved performance and cost reduction. Most RFBs depend on high concentrations of expensive, environmentally impactful transition-metal-based active species to achieve viable energy densities [1]. One notable exception is the aqueous anthraquinone chemistry, based on an organic active species [2].

Polycyclic aromatic hydrocarbons (pAHs) have highly conjugated molecular structures, which offer redox activity that could be promising for all-organic RFBs. Byproducts of coal extraction and petroleum refining, pAHs are abundant and offer an inexpensive alternative to transition-metal complexes. Since they tend to offer widely separated, stable redox states, pAHs necessitate the wide electrochemical stability windows provided by polar, aprotic, nonaqueous solvents. Researchers previously attempted using the pAH rubrene in nonaqueous RFBs, but were discouraged by its extremely low solubility in conventional nonaqueous solvents.[3] Others have functionalized pAHs to form water-soluble quinone structures at the expense of large RFB operating potentials.[2]

We will focus on 9,10-diphenylanthracene(DPA)[4], a promising pAH for symmetric, nonaqueous RFBs. Figure 1 demonstrates the redox activity of DPA in acetonitrile, exhibiting couples at -2.2 V and 0.9 V vs. Ag/Ag+. A symmetric RFB based on DPA could, in principle, achieve a cell potential above 3V. As with rubrene, however, DPA suffers from solubility concerns: concentrations necessary for persuasive cell demonstration are unattainable. We modified DPA by appending various organic functional groups, examining the effects on solubility and redox activity. We functionalized the phenyl groups of DPA with both electron-withdrawing and electron-donating groups: methyl, methoxy, methoxycarbonyl, and more complicated ethylene-glycol based functionalities were investigated. Various nonaqueous solvents and supporting electrolytes are considered to optimize solubility.

[1] S. Eckroad. EPRI Report 1014836. 2007.

[2] Q. Liu et al. Electrochem. Comm. 12(2010): 1634.

[3] M. Chakrabarti, et al.
Electrochimica Acta.
52(2007): 2189.

[4] K. Santhanam, A. Bard. JACS.
88(1966): 2669.

Figure 1: Cyclic voltammogram of 0.001 M DPA/0.05 M TEABF4 in acetonitrile, glassy carbon WE (1mm diameter), Pt CE, 500 mVs-1, Argon atmosphere with <1ppm O2,H2O

Figure 1
CFD Modeling to Investigate the Performance of PEM Fuel Cells Affected By Cathodic Pressure
Authors: Wang Jiatang , Yuan Jinliang , Sundén Bengt
Published: February 2020

The proton exchange membrane (PEM) fuel cell is a promising energy conversion device.  However, the cost and durability of a PEM fuel cell are major challenges needed to be overcome before it will be widely used. The simulation is crucial for the design and optimization of practical devices based on deep understanding of coupled transport phenomena inside the fuel cell. It is widely known that the slower reaction in the cathode is a limiting factor and the cathodic operating pressure has a strong influence on the cell performance. In this paper, an open-source code OpenFOAM is employed to simulate the transport phenomena and electrochemical reactions in PEM fuel cells. The basic governing equations for continuity, momentum, mass and energy transfer are solved with appropriate source terms using a computational fluid dynamics (CFD) method.  A steady state and three-dimensional (3D) model is applied for single flow channels and multi-functional layers, i.e., bipolar plates, gas diffusion layers (GDLs), catalyst layers (CLs) and electrolyte. The distributions of gas compositions, pressure, temperature, activation loss, cell voltage and current density are captured and presented. The O2 partial pressure on the reaction sites resulting from transport and inlet pressure suggests an influence on the cell performance. The influence of removal of the inert gas N2 and production of H2O vapor on the O2 partial pressure is considered based on the multi-species transport model. To verify the accuracy of the simulation approach, comparisons between the computed results and literature data have been conducted.
New Upscaled Equations for the Reliable and Efficient Catalyst Layer Modelling in PEM Fuel Cells
Authors: Schmuck Markus , Berg Peter
Published: February 2020

Recently, we derived a rigorous macroscopic model for a porous catalyst layer in a PEM fuel cell [1,2]. Starting from a microscopic description, it accounts for the oxygen reduction reaction in periodically distributed pores, filled with liquid water. We now present first computational investigations of the newly derived macroscopic transport equations, which rely on characteristic porous media (corrector) tensors, Darcy's law and an effective Butler-Volmer equation. This macroscopic formulation is inherently linked to the dynamics at the microscale and it can be computed in a fairly straightforward manner under the assumption of local thermodynamic equilibrium. Our computational results demonstrate that this upscaling provides a convenient and efficient computational framework for the numerical investigation of optimal catalyst layer designs.

[1] M. Schmuck and P. Berg, Homogenization of a catalyst layer model for periodically distributed pore geometries in PEM fuel cells, Appl. Math. Res. Express. 2013(1):57-78 (2013).

[2] M. Schmuck and P. Berg, Effective macroscopic equations for species transport and reactions in porous catalyst layers, J. Electrochem. Soc. 161(8): E3323-E3327 (2014).
An Electrochemical Impedance Spectroscopy Study and Two Phase Flow Analysis of the Anode of Polymer Electrolyte Membrane Water Electrolysers
Authors: Dedigama Ishanka , Brett Daniel J. , Mason Thomas J. , Millichamp Jason , Shearing Paul R. , Ayers Katherine E
Published: February 2020

The effect of water flow rate on the performance of a polymer electrolyte membrane water electrolyser (PEMWE) was studied using an unpressurised lab-scale (25 cm2) cell. The linear polarisation curves obtained showed a voltage increase at higher current densities that increased with water flow rate. Electrochemical impedance spectroscopy (EIS) showed that while lower water flow rates lead to higher cell temperatures and reduced membrane resistance, mass transport losses dominate at high current density. As the water flow is exclusively in the bubbly regime, increase in mass transport limitation is attributed to bubble formation dynamics and reduced gas void fraction at higher water flow rates.

Figure 1
IrxRu1-XO2 Electrocatalysts for PEM Water Electrolysis
Authors: Banti Angeliki , Papazisi Kalliopi-Maria , Balomenou Stella , Tsiplakides Dimitrios
Published: February 2020

A potential method for storing energy from renewable energy sources into hydrogen is water electrolysis [1]. Direct electrochemical splitting of water is a non-polluting way to produce pure hydrogen and oxygen. Proton Exchange Membrane Electrolysis Systems have attracted great interest as a hydrogen production method. The combination of water electrolysers and fuel cells in coupled with renewable sources could provide an ideal green and efficient mode for future energy utilization systems. PEM water electrolysers offer various advantages [2] but the major disadvantage is the relatively high anodic overpotential for the oxygen evolution reaction (OER). Oxygen evolution occurs on noble metal electrodes but metal oxides like IrO2, RuO2, etc. are generally more active for oxygen evolution than metal electrodes [3]. However, issues like electrocatalyst stability and reduction of the catalyst loading are of great and continuous research interest. In this work, unsupported IrxRu1-xO2electrocatalysts, synthesized by the modified Adams fusion method, were evaluated as potential electrodes for water splitting.

Complete physicochemical characterisation of the synthesised materials was performed regarding their structure, morphology, specific surface area as well as surface composition using X-ray Diffraction (XRD), BET analysis, High Resolution Transmission Electron Microscopy (HTTEM) and X-ray Photoelectron Spectroscopy (XPS). The electrochemical performance and stability of the prepared electrocatalysts, casted on glassy carbon (GC), were evaluated with repetitive cyclic voltammetry in a typical three-cell electrode configuration using 0.5 M H2SO4solution. Furthermore, the mixed oxides have been used as anodes in Nafion® based MEAs and evaluated in a PEM electrolysis cell.

The results have shown that the synthesis method leads to the formation of rutile structure oxides with high surface area (90-127 m2/g) and nano-level particle size (5-7 nm). The stability of the mixed oxides during potentiostatic cycling has been proven remarkable, while the best performing MEA with an anode of Ir0.4Ru0.6O2 reached a current density of 320 mA/cm2at 1.7 V.

The work is supported by the European Space Agency (ESA).

References:

F. Barbir, Solar Energy 78 (2005) 661-669.

A. Deschamps, C. Etievant, V. Fateev, S. Grigoriev, A. Kalinnikov, P. Millet, V. Porembsky and C. Puyenchet, WHEC 16, Lyon France (2006).

V. Baglio, A. Di Blasi, T. Denaro, V. Antonucci, A.S. Aricò, R. Ornelas, F. Matteucci, G. Alonso, L. Morales, G. Orozco and L.G. Arriaga, J. New Mat. Electr. Sys. 11 (2008) 105-108.
Electronic Structure of Pt and Pt-Co Nano-Particles with O2 and O2/H2o Adsorption Revealed By in Situ xafs and Hard X-Ray Photoelectron Spectroscopy
Authors: Cui Yi-Tao , Harada Yoshihisa , Hatanaka Tatsuya , Nakamura Naoki , Ando Masaki , Yoshida Toshihiko , Ikenaga Eiji , Ishii Kenji , Matsumura Daiju , Li Rui , Oshima Masaharu
Published: February 2020

In order to clarify the effect of water adsorption on fuel cell cathode catalysis surface, we have investigated electronic structure of Pt and Pt-Co nano-particles with O2 adsorption and O2/H2O co-adsorption by in situ XAFS and in situ hard X-ray photoelectron spectroscopy (HAXPES).

 First, the electronic structure change under dry and humidified oxygen conditions at room temperature was measured by in situ HAXPES equipped with an ambient cell. The valence band (mainly Pt 5d) and Pt 4f spectra were successfully obtained under up to 1 mbar for the first time. Both valence band and Pt 4f spectra show that O2/H2O co-adsorption hindered oxygen adsorption. Based on our first principles calculation of valence band density-of-states (DOS) we have found that DOS just below Fermi level strongly decreases upon oxygen adsorption, while valence band spectra remain almost unchanged upon H2O adsorption. These results suggest that H2O molecules may occupy the oxygen adsorption sites on Pt surface more easily than oxygen, resulting in hindering the successive oxygen adsorption.

 However, under the more realistic condition at atmospheric pressure (1 bar) quite different results that the formation of higher oxidation states of Pt in Pt Pt L
3-edge absorption spectra was enhanced by water adsorption were obtained by high resolution (FWHM of about 2.5 eV) in situ XAFS, taking advantage of life-time free measurements1). It is difficult to observe these changes by conventional XAFS spectra with poor energy resolution (FWHM of about 5.2 eV). At the atmospheric pressure more frequent attack by oxygen molecules onto water-adsorbed Pt surface may replace water molecules by oxygen, resulting in the formation of hydrated hydroxyl intermediates and higher oxidation states which hinder oxygen reduction reaction. The molecular dynamics simulation2) also confirms the oxygen replacement on water-adsorbed Pt surfaces. This enhanced oxygen adsorption is more clearly observed for Pt nano-particles, probably because Pt nano-particles with stronger Pt-O bonding than Pt-Co nano-particles may further stabilize Pt-O bonding by additional adsorbed water. On the other hand, oxygen molecules on Pt-Co nano-particles may be difficult to form hydrated hydroxyl intermediates with adsorbed water, leading to less water effect on oxygen adsorption on Pt-Co.

 These results would be much helpful to understand why Pt-Co nano particles show higher ORR activity than Pt nano particles.

References:

1)   K. Hamalainen et al., Phys. Rev. Lett. 67, 2850 (1991).

2)   R. Li, et al., New J. Chem.,
38, 683 (2014).
Ionic Transport in Non-Uniform 3D Solid-State Li Ion Batteries
Authors: Mckelvey Kim , Edwards Martin , Ruzmetov Dmitry , Kolmakov Andrei , Ware Nicholas , El Gabaly Farid , Talin A. Alec , Dunn Bruce , White Henry S
Published: February 2020

Demonstration of all-solid state 3-dimensional (3D) Li-ion batteries has been a long standing goal for numerous researchers in the battery community interested in developing high power and high areal energy density storage solutions for variety of applications. The basic idea is to use the 3D geometry to maximize the volume of active material per unit area, while keeping its thickness sufficiently small to allow for fast Li diffusion. However, the introduction of 3D battery designs can result in a non-uniform electrolyte thickness in which the distance between the anode and cathode differs across different locations within the battery. This, in turn, can affect the battery performance. We explore, using finite element simulation methods, how a non-uniform electrolyte thickness can affect the ionic mass transport across a solid-state Li ion battery, and ultimately the performance of these types of batteries. We base our simulations on a working 3D solid-state (LiPON) Li ion battery, showing there is a good agreement between experiment and simulation. We explain how the performance of this battery is affected by the non-uniform thickness of the electrolyte, which introduces a non-uniform current density across both the anode/electrolyte and cathode/electrolyte boundaries.
Mechanism of Enhanced Pt ORR Catalyst By Atomic Layer Deposition-Based Oxide Functionalization
Authors: Karimaghaloo Alireza , Peev Thomas , Macedo Andrade Angela , Lee Min Hwan
Published: February 2020

In a recent study, ultrathin oxide overcoat was proven to have significant impact on the ORR kinetics of nanoporous Pt catalyst on yttria-doped zirconia (YSZ).1 In the report, a few nm thick ultrathin yttria-stabilized zirconia (uYSZ) was coated on the porous Pt cathode by atomic layer deposition (ALD). The coating was found not only to preserve the overall Pt morphology but also to improve the electrode reaction. The uniform and conformal geometry of the as-deposited overcoat became percolated at the operational temperature (~500°C), which is conjectured beneficial to the catalytic activity due to enlarged Pt/YSZ interfaces.

In this presentation, we present our revised understanding of how the ultrathin oxide overcoat improved the ORR catalysis through a parametric study. Geometrically well-defined Pt/uYSZ electrode structures were prepared by accumulating Pt nanoparticles through a colloidal process. We controlled the Pt nanoparticle size, dominant surface facets, overall electrode thickness, YSZ overcoat thickness and stoichiometry of overcoat. Pt nanocrystals with different sizes and controlled surface facets were prepared through wet chemical and electrochemical processes. We then performed electrochemical analysis at various temperature (400 – 700 °C) and oxygen partial pressure (0.01 – 1 atm). A series of characterization indicated that the enhanced ORR activity is most likely originated from the enhanced ‘chemical’ processes such as dissociation and transport. However, in samples with thin Pt electrode layer, the enhancement is largely ascribed to increased triple phase boundary areas.

This project is funded by the NASA MUREP Institutional Research Opportunity (MIRO) Program (Grant No. NNX15AQ01A).

1 I. Chang, S. Ji, J. Park, M.H. Lee, and S.W. Cha, Adv. Energy Mater. 5, 1402251 (2015).