bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct Formic Acid Fuel Cell: Anode Flow Field Designed Two-Phase Removal of Carbon Dioxide
Authors: Cardenas Jonathon E , Rice Cynthia A. 
Published: February 2020

Direct Formic Acid Fuel Cells (DFAFC) are a potential substitute in portable power devices surpassing the capacity of conventional batteries in everyday items such as cell phones and laptops. The challenge of maintaining high liquid phase formic acid (FA, HCOOH) concentrations within the catalyst layer at high current densities is due to the gaseous by-product carbon dioxide formation (HCOOH→ CO2 +2H+ + 2e-). The two-phase FA/CO2 results in mass transport limitations.
Previous studies have shown enhanced current density performance when the anode flow field is designed to flow the FA in a singular serpentine pattern[1], and the gaseous CO2 is removed through a semi-permeable separator near site of formation[2]. Fig.1 shows the current serpentine anode flow field’s geometry in ANSYS Fluent. The CO2 forms along the diffusion media//anode catalyst layer and disperses through the semi-permeable layer, after traversing the flow channel. The initial flow field prototype with a semi-permeable separator has issues with liquid FA break through. Improved sealing surface designs were investigated to improve the DFAFC’s efficiency. Mass transport of CO2 in the current semi-permeable anode flow field design results in a “barrier” of higher velocity in between the layers, Fig. 1. In addition, an eddy current appears at the point of entrance into the chamber, potentially re-circulating the CO2 bubbles and hindering removal.
Further modifications of the anode flow field, based on the present Computational Fluid Dynamics (CFD) model, are underway to eliminate the barrier and remove the eddy. The objects of the CFD modeling is to realize needed flow distribution improvements on future anode flow field, resulting in a higher rate of CO2 mass transport through the semi-permeable layer. Experimental validation of prototypes will be performed on the resulting model driven design optimizations.
[1] Limjeerajarus, Nuttapol, and Patcharawat Charoen-Amornkitt. "Effect of Different Flow Field Designs and Number of Channels on Performance of a Small PEFC." International Journal of Hydrogen Energy, 2015, 40, 7144.
[2] S. Saeed, A. Pistono, J. Cisco, C. S. Burke, M. Mench, C. Rice, Fuel Cells, 2017, 17, 48.

Figure 1
Thin Pore-Filling Electrolyte Membranes with Low EW Perfluorosulfonic Acid Ionomer and Their PEFC Performances
Authors: Yamaguchi Takeo , Tomatsu Jin , Oshiba Yuhei 
Published: February 2020

For next generation polymer electrolyte fuel cells (PEFC), membrane-electrode assemblies (MEAs) should be operated at high temperature and low humidity conditions. At low humidity condition, the cell performance decreases drastically due to the high resistance of proton conduction. Low equivalent weight (EW), which corresponds to high ion-exchange capacity, perfluorosulfonic acid (PFSA) polymer can improve proton conductivity, especially at low humidity condition, although membrane swelling will make problems. If the membrane becomes thinner, water transport between cathode and anode can be accelerated, which prevents the membrane from drying. However, increase fuel crossover results in poor durability of MEAs. A thin membrane with reduced swelling can be fabricated using pore-filling technique, where an inert and mechanically strong porous substrate is employed to fill the polymer electrolyte inside the pores [1]. Here, we develop thin pore-filling membranes with low EW PFSA polymer and evaluate fuel cell performances using the prepared membranes (Fig.1). As the substrate, we employed porous and thin ultra-high molecular weight polyethylene films (6 μm thick and 66% porosity) which can show high mechanical strength below 100 oC. As the filling polymer electrolyte, low EW (EW500~900) PFSA polymers were employed.
The prepared pore-filling membrane having 7 μm thick showed very little area change ratio before and after water immersion. The prepared membrane exhibited higher proton conductivity than that of the commercial Nafion® 211 (EW1100 PFSA polymer, 25 μm thick) in wide range of temperature and relative humidities.
MEAs with the pore-filling membranes were fabricated with catalyst layer including EW500 PFSA polymer as ionomer. The hydrogen crossover currencies with the 7 μm thick pore-filling membrane showed almost the same value with the MEA with 25 μm thick Nafion® 211. The substrate effectively suppresses the membrane swelling and reduce the crossover. The MEA with the pore-filling membrane showed high I-V performances with low humidity conditions. When H2-O2 fuel cell operated with 30% relative humidity at 100 oC, power density reached 1,000 mW/cm2. These results are attributed to improved proton conductivity, water transport and low crossover with the thin pore-filling membrane using tough substrate and low EW PFSA.
[1] T. Yamaguchi et al., Adv. Materials, 15, 1198 (2003); N. Hara, T. Yamaguchi, et al., J. Phys. Chem. B, 113, 4656−4663 (2009)

Figure 1
Nanocellulose: Abundant Biopolymer Membranes for Next-Generation Low-Cost Fuel Cells
Authors: Bayer Thomas , Selyanchyn Roman , Nishihara Masamichi , Fujikawa Shigenori , Sasaki Kazunari , Lyth Stephen Matthew 
Published: February 2020

Nafion has been the industry standard membrane for polymer electrolyte membrane fuel cells (PEFCs) for decades due to its high conductivity, mechanical stability and durability. However, it has several drawbacks such as poor performance at high temperatures / low humidity, use of harmful fluorine in its production, and as its high price. Therefore research into new membrane materials is necessary. Basic requirements for next-generation fuel cell membranes are sufficiently high proton conductivity, high mechanical strength, good hydrogen gas barrier, and low cost.
Nanocellulose is a biopolymer produced in bulk from abundant cheap cellulosic materials such as wood or cotton. Depending on its source, nanocellulose fiber dimensions can range from a few to several tens of nanometers in diameter, and are several micrometers in length. Nanocellulose paper with high mechanical strength and thermal stability up to 150°C has been reported.1,2 Previously, we showed that the hydrogen barrier of nanocellulose membranes is approximately 1000 times higher than Nafion.3 In addition, reasonable proton conductivity at high temperature (~5 mS/cm at 120°C) was shown by impedance spectroscopy. Based on these results we fabricated the world’s first nanocellulose “paper fuel cells” and successfully operated them as hydrogen fuel cells. The performance was stable, with no degradation over 24 hours.
Here, in order to increase the proton conductivity, we perform chemical modification of nanocellulose fibers. This chemical treatment resulted in an increase in the number of acidic functional groups, as well as modifying the microstructure. A strong increase in the proton conductivity was observed, with an associated increase in fuel cell performance. In addition, nanocellulose was composited with more established ionomer materials and the resulting membranes were investigated for their fuel cell properties.

References

1. Henriksson, M. et al. Cellulose Nanopaper Structures of High Toughness. Biomacromolecules
9,1579–1585 (2008).
2. Nogi, M. et al. High thermal stability of optical transparency in cellulose nanofiber paper. Appl. Phys. Lett.
102,181911 (2013).
3. Bayer, T. et al. High Temperature Proton Conduction in Nanocellulose Membranes: Paper Fuel Cells. Chem. Mater.
28, 4805–4814 (2016).

Figure 1
Nano- and Mesoscale Ion and Water Transport in Perfluorosulfonic-Acid Membranes
Authors: Crothers Andrew Robert , Radke Clayton J. , Weber Adam Z. 
Published: February 2020

High performance of polymer-electrolyte fuel cells requires rapid cation conduction through perflurosulfonic-acid (PFSA) membranes. Consequently, understanding water and aqueous cation transport in aqueous nanoscale domains (nano length scale) and connectivity and tortuosity of the microscale domains (meso length scales) is critical to optimizing PFSA membrane design. Due to transport coupling, membrane ionic conduction depends not only on electrostatic potential gradients but also on water content gradients (i.e. electro-osmosis). In this work, we model coupled cation and water transport in PFSA membranes at the nano- and mesoscale and predict macroscopic properties.
We adopt a mean-field local-density theory for cation and water chemical potentials to predict transport in the nanoscale PFSA aqueous domains. Cation-polymer electrostatic interactions and solvation energy are included. Concentrated solution transport theory (Stefan-Maxwell formulation) models diffusion and specifically accounts for dielectric friction induced by the strong electrostatic fields of charged polymer groups. To model the mesoscale, a resistor network that includes Stefan-Maxwell coupling quantifies transport along the segments of the collection of aqueous domains in PFSA membranes. The nanoscale model parameterizes the properties of each segment of the resistor network.
With this methodology, we decouple the influences of nano- and mesoscale resistances on macroscopic water and cation transport and electro-osmosis. At the nanoscale there is coupling between water and cation transport from both diffusional drag and electrostatic-driven convection. Electrostatic and pressure forces on the membrane are countered by immobilization of the polymer matrix. The models show the nature of electro-osmosis depends on water content and the vapor and electrostatic potential boundary conditions of the membrane. This work provides a compelling approach to elucidate the multiscale resistances to water and cation transport in PFSA membranes.
Building Thin Film Model Materials to Study Active Sites of PGM-Free Electrocatalyst for ORR
Authors: Xu Yun , Dzara Michael , Pylypenko Svitlana , Neyerlin K.C. , Kocha Shyam S. , Zack Jason W. , Perkins John D. , Dinh Huyen N. , Zakutayev Andriy 
Published: February 2020

Replacement of noble metal catalysts for oxygen reduction reaction (ORR) with transition metals can have a profound impact on clean and economical energy production. Although non-precious metals have been extensively studied as ORR electrocatalysts, there has been a long debate about what active site is responsible for the ORR and what the catalytic mechanism is. The mystery of the chemical nature of the active sites hinders the development of efficient and stable ORR catalyst. The biggest obstacle to resolving the mechanism is the fact that the active sites are buried in the bulk, porous catalyst and the components in the real catalyst are complicated. Here, we propose a thin film model approach to study the active sites of FeN thin film, deposited on top of glassy carbon by magnetron sputtering. Rutherford backscattering, X-ray diffraction and Raman spectroscopy were carried out to characterize bulk films and to determine deposition conditions that result in Fe tetrahedrally coordinated with nitrogen. The significance of this study is that this is the first time active sites are intentionally exposed to the surface and can be directly characterized by x-ray photoelectron spectroscopy (XPS). Bonding between Fe-N in the bulk film and N-C at the interface between FeN and glassy carbon have been confirmed by XPS. Rotating disk electrode experiments have been carried out to measure the ORR activity of Fe-N, C-N, Fe-C the Fe-N-C exposed surfaces by looking at thin Fe-N, C-N, Fe-C, and Fe-N-C films. This study will also provide answers to the controversy about whether carbon, nitrogen or iron is essential in the ORR catalyst.
Atomically Dispersed (AD)Fe-N-C Oxygen Reduction Catalysts for Polymer Electrolyte Membrane Fuel Cells
Authors: Chung Hoon T , Cullen David A. , Sneed Brian , Meyer Harry M , Lin Ling , Yin Xi , More Karren L. , Zelenay Piotr 
Published: February 2020

Atomically dispersed (AD)Fe-N-C catalysts are the ultimate goal towards achieving Fe catalyst size reduction. Such catalysts are expected to have unique properties that can be exploited for the purpose of developing highly active and durable oxygen reduction reaction (ORR) catalysts. The biggest challenge during the fabrication of atomically dispersed catalysts is to prevent clustering of atoms on the support during synthesis. In this work we address this challenge by employing metal organic frameworks (MOFs) as the structural precursor for (AD)Fe-N-C catalysts. Specifically, we (i) synthesize Fe-containing MOFs (Fe-MOFs) followed by (ii) heat treatment of the Fe-MOFs to produce (AD)Fe-N-C catalysts. The heat treatment converts Fe-MOFs to N-doped carbons, with the Fe atoms contained in the MOF being uniformly distributed on the N-doped carbons without observable agglomeration. In the approach used, maintaining the initial morphology of MOFs after the heat treatment step is key to taking advantage of the MOF structural features. In a preliminary experiment, we synthesized an Fe-containing nano platelet-shaped MOF support and heat-treated it at 1000 °C in an oxygen-free atmosphere to obtain atomically dispersed Fe atoms anchored on N-doped carbon nano-plates, (AD)Fe-N-Cnano-plates. Figure 1a (high angle annular dark field scanning transmission electron microscopy (STEM) images)demonstrates that the initial plate-like shape of the MOF, which is typically 30-50 nm wide and up to hundreds of nm long, is successfully maintained during the heat treatment at 1000 °C. Microporosity within the nano-plates is generated during the heat treatment, assuring high accessibility to the Fe atoms within the catalyst. The nitrogen content in the nano-plates measured by X-ray photoelectron spectroscopy is ca. 5 at.%. X-ray diffraction (XRD) confirms the absence of crystalline particles in (AD)Fe-N-Cnano-plates,, e.g., Fe-rich particles in particular. As shown in Figure 1b, aberration-corrected (AC)-STEM clearly indicates that all of the Fe is atomically dispersed over the N-doped carbon nano-plates (individual white dots in the image). No Fe-rich clusters or particles are observed, corroborating successful synthesis of atomically dispersed Fe-N-Cnano-plates catalysts. Electrochemical and fuel cell performance data will be presented attesting to high ORR activity of the (AD)Fe-N-Cnano-plates catalysts.

Figure 1
Fuel Cell Testing of Intermetallic Oxygen Reduction Catalysts
Authors: Pan Yung-Tin , Kim Yu Seung , Li Junrui , Sun Shouheng , Spendelow Jacob S 
Published: February 2020

Platinum-based alloy catalysts for the oxygen reduction reaction (ORR) continue to be the industry standard for fuel cell applications, but improvements are needed to increase ORR activity and durability. Despite extensive study, the effects of structure and composition on real world performance and durability in fuel cells are poorly understood. Most research to date has examined random alloy structures, but preliminary results from intermetallic catalysts, especially intermetallic tetragonal structured catalysts, have indicated that superior performance and durability can be achieved through creation of ordered intermetallic structures. Results so far indicate that the degree of ordering is a critical parameter in determining intermetallic catalyst activity and durability, with fully-ordered face-centered tetragonal (fct) FePt catalysts exhibiting substantially improved activity and durability compared to partially ordered phases [1].
Most work on intermetallic nanocatalysts reported so far has been based on ex situ testing methods that use an idealized aqueous electrochemistry environment. While these ex situmethods are inexpensive and convenient, they do not reliably predict performance and durability in real fuel cells. Therefore, rigorous catalyst testing in fuel cells is needed to build understanding of the relationship between catalyst properties and fuel cell performance and durability.
In this work, fct-FePt intermetallic nanoparticle catalysts have been subjected to the DOE catalyst AST (30,000 trapezoidal cycles between 0.6 and 0.95 V with 0.5 s rise time) in operating fuel cells. Comparison of characterization results from before and after testing serves to illustrate the changes in structure and composition that occur during the AST. Initial results depicted in Fig. 1 indicate that fct-FePt can have performance comparable to a baseline commercial Pt/C, despite the use of much larger particles (8-9 nm for fct-FePt/C vs. 2-3 nm for Pt/C). Notably, the fct-FePt exhibits lower loss of performance following the 30,000 cycle AST. Ongoing work seeks to reduce the fct-FePt particle size while maintaining fully-ordered structures, which could lead to substantial improvements in performance and durability.
Fig. 1. Fuel cell polarization behavior of Pt/C and fct-FePt/C before and after the 30,000 cycle AST.
References

Q. Li et al., "New Approach to Fully Ordered fct-FePt Nanoparticles for Much Enhanced Electrocatalysis in Acid," Nano Lett. 2015, 15, 2468−2473.

Acknowledgements
This research is sponsored by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy.

Figure 1
Surface-Limited Platinum Electrodeposition on Highly Ordered Pyrolytic Graphite
Authors: Farina Filippo , Ercolano Giorgio , Alpuche-Aviles Mario A , Cavaliere Sara , Jones Deborah J. , Rozière Jacques 
Published: February 2020

Recently we reported an overpotential electrodeposition method to deposit contiguous Pt nanoplatelets/thin films directly onto the surface of self-standing electrospun carbon nanofiber mats, leading to Carbon Nanofibrous Electrodes (NFEs) [1]. We demonstrated the high electrocatalytic activity and improved stability over high-potential prolonged cycling compared to conventional Pt nanoparticles on carbon. In order to study more in detail the Pt growth and the morphology of the obtained Pt surfaces as a function of the experimental parameters, we investigated such surface-limited electrodeposition employing Highly Ordered Pyrolytic Graphite (HOPG) as a model surface.
We studied Pt deposition on HOPG by contact-mode AFM imaging. Pt interconnected particles and Pt networks can be grown directly onto the substrate at high overpotential as a function of the deposition time, with no significant variation in thickness and size of the connected particles. A progressive coverage of the substrate surface is clearly present, eventually leading to the formation of Pt thin islands below 2 nm in thickness. We also show by TEM analysis that Pt(111) facets are preferentially deposited and grown on the substrate.
We studied the deposition mechanism at high overpotential. We will show that the Pt deposition is not diffusion-limited and that it overlaps with other processes. We will discuss the effects of these other processes (H2 evolution on Pt and HOPG) on the Pt deposition. Additional indications can be derived from computer simulations (e.g. DigiElch®) that approximate the experimental conditions. The rate constants used for the simulations were obtained experimentally and their variation with HOPG surface preparation will also be presented.
In this work we will present our advances towards understanding the nature of this surface-limited electrodeposition. The morphological and structural characterization of these Pt features on HOPG will be presented and discussed, along with some early insights on their growth mechanism.

[1] G. Ercolano, F. Farina, S. Cavaliere, D.J. Jones, J. Rozière, J. Mater. Chem. A 5 (2017) 3974-3980.
Reduced-Graphene-Oxide with Traces of Iridium or Gold as Active Support for Pt Catalyst at Low Loading during Oxygen Electroreduction
Authors: Kulesza Pawel J , Dembinska Beata , Zoladek Sylwia , Rutkowska Iwona Agnieszka , Miecznikowski Krzysztof , Negro Enrico , Di Noto Vito 
Published: February 2020

Chemically-reduced graphene-oxide-supported gold nanoparticles and traces of iridium are considered here together with loadings of platinum as catalytic materials for reduction of oxygen in alkaline and acid media, respectively. Comparison is made to the analogous systems based on conventional Vulcan carbon carriers. Gold nanoparticles are prepared by the chemical reduction method, in which the NaBH4-prereduced Keggin-type phosphomolybdate heteropolyblue acts as the reducing agent for the precursor (HAuCl4). Polyoxmetallate (PMo12O40
3-) capping ligands stabilize gold nanoparticle deposits, facilitate their dispersion and attachment to carbon supports. Indeed, it is apparent from the independent diagnostic voltammetric experiments (in 0.5 mol dm-3 H2SO4) that heteropolymolybdates form readily stable adsorbates on nanostructures of both gold and carbon (reduced graphene oxide and Vulcan). It is reasonable to expect that the polyoxometallate-assisted nucleation of gold has occurred in the proximity of oxygenated defects existing on carbon substrates. Under conditions of electrochemical diagnostic experiments (performed in 0.1 mol dm-3 KOH) the phosphomolybdate adsorbates are removed from the interface as they undergo dissolution in alkaline medium; and the Au nanoparticles (Au loading, 30 µg cm-2) remain well-dispersed on the carbon as evident from transmission electron microscopy. High electrocatalytic activity of the reduced-graphene oxide-supported Au nanoparticles toward reduction of oxygen in alkaline medium is demonstrated using cyclic and rotating ring-disk electrode (RDE) voltammetric experiments. Among important issues are possible activating interactions between gold and the support, as well as presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide (as evident from Raman spectroscopy). When using the silica or titania functionalized reduced graphene oxide as carriers for Au (or Ir) and Pt nanoparticles, the resulting systems have exhibited typically higher (certainly not lower) O2-reduction currents (relative to those recorded at conventional Vulcan-supported Pt at the same loading) in acid medium (0.5 M H2SO4). The RDE data are consistent with even lower formation of hydrogen peroxide. Furthermore, the durability of this family of catalysts was outstanding. Finally, by doping the reduced graphene oxide supported Pt with traces of Ir (<1 µg cm-2), decreases amounts of produced H2O2 (<1%) at potentials 0.6 V (vs RHE) or lower.