bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Through-Plane Humidity Distribution inside an MEA by Thin Film Sensor
Authors: Minami Ryotaro , Hasegawa Noriyoshi , Araki Takuto
Published: February 2020

A Proton exchange membrane fuel cell (PEMFC) is attracting attention as a clean and new power source system. However, there are several problems for commercial uses. One of the problems is water management inside the PEMFC. Too much water inside the PEMFC disturbs mass transport and leads to lower power density, on the other hand, proton exchange membrane (PEM) and an ionomer in a catalyst layer (CL) need water to maintain proton conductivity. In addition, water vapor and liquid water flow coexist inside the PEMFC because the operating temperature is lower than 100 degrees. Therefore, understanding water transport inside the PEMFC is difficult and a key to improve the cell performance. Especially, it has recently been noticed that a micro porous layer (MPL), which is inserted between a CL and a gas diffusion layer (GDL), controls the water transport and improve cell performance, but the role of the MPL is not clarified yet.

For understanding water transport through the membrane electrode assembly (MEA), relative humidity (RH) is an important factor. So, we developed a thin film humidity sensor (TFHS), which is capacitive type, for measuring RH inside the MEA. In our previous study[1], width of TFHS was 0.35mm. However, wider sensor prevents the mass transport more. In this study, we developed thinner TFHS whose width was 0.1mm.Capacitive type TFHS was developed with MEMS technology. Fig. 1 shows an overview and schematic cross section of TFHS. The humidity sensor consisted of Parylene, Ni and Au. Parylene, that is polymer material, was applied as an insulating material and a sensing material to obtain a uniform and homogeneous film. In addition, hysteresis of it was very small and a uniform and homogeneous film was evaporated. Ni was deposited as an electrode and it was thin enough to obtain water vapor permeability to sensing material. Au was deposited as reinforcement so as not to break the sensor when inserted inside the PEMFC.

In situ measurements with TFHS was investigated with supplying RH20% and RH60% gas. Flow rate of gases was 200 and 500 NmL/min respectively, and the separator temperature was set to 60oC. In this experiment, TFHS was inserted at the CL/MPL interface under the rib. In situ measurements were conducted three times at the each condition, and reproducible results were obtained. The results implies that water is mainly transported as vapor phase near the MPL. In the RH60 condition, liquid water may start to accumulate under the rib from 1.0 A/cm2 because RH change is almost saturated near the RH100%.

Reference

[1]. J. Tsujikawa, R. Minami, and T. Araki, ECS transactions, 69, 471-476, (2015)

Figure 1
Experimental and Numerical Investigation of Humidity Effect on Performance of PEM Fuel Cells
Authors: Liso Vincenzo , Al Shakhshir Saher , Nielsen Mads Pagh
Published: February 2020

In this study, we conducted an experimental test to evaluate the performance of a PEM single cell at different humidity level of the reactants (i.e. hydrogen and air). The motivation was to use the test dataset to validate a simple numerical model which predict the I-V curve of the cell when the humidity is varied. We conducted the test using a 50cm2 single cell, five-layer membrane electrode assembly composed of a Nafion 211 membrane and carbon paper as GDL. Relative humidity (RH) was varied alternatively between 50 and 100 percent both at anode and cathode side. We found that the best cell performance was obtained when RH was fixed at 100% both at anode and cathode side. On the other hand, cell performance was particularly affected when relative humidity was reduced at the cathode side. This can be explained by the decrement of water diffusion from the cathode to anode and therefore a loss in electrical conductivity. The test also showed that humidity mainly affects Ohmic losses rather than activation or overpotential losses. Ohmic losses are mainly related to water hydration in polymer electrolyte membranes.

The cell performance model considers only relationships for electro-osmotic drag, membrane ionic conductivity and diffusion coefficient of water in the membrane. Hydraulic permeability was neglected as the pressure difference between anode and cathode side was minimal during the test. Temperature, mass flow rate, and pressure were also important to estimate the water and mass balance. We fitted the model parameters to the test results and find out that cell ohmic resistance was the main relationship to be modulated at different humidity levels. In fact, there is a close link between water uptake, cell resistance, and membrane conductivity and thickness.

The model simplicity was essential because the code was aimed to be implemented in a larger fuel cell system model. The model will come useful to develop a strategy for water management.
Analysis of Ionomer Distribution in Catalyst Layers by Two-Stage Ion-Beam Processing
Authors: Suzuki Takahiro , Koyama Takamasa , Tsushima Shohji
Published: February 2020

Mass transport properties of catalyst layers (CLs) for proton exchange membrane fuel cells (PEMFCs) strongly depends on its structure. The ionomer is a proton-carrier material in the CLs. On the other hand, the gas transfer is prevented by the ionomer coated on a catalyst. Ionomer distribution in the CLs, therefore, have gathered much attention. Some papers have suggested methods to analyze the ionomer distribution [1-4]. However, quantitative validation is not enough so far. In addition, these methods especially focused on a microscopic local ionomer distribution. From the point of view of mass transfer, overall through-plane ionomer distribution is important as well as the microscopic distribution. In this study, a novel visualization method of the overall through-plane ionomer distribution in the CLs by using a two-stage ion-beam processing is suggested.

The first stage of the two-stage ion-beam processing is the formation of flat and smooth cross-section by a broad ion beam. The second stage is the selective removal of the ionomer in the catalyst layer by a focused ion beam. Scanning ion microscopic (SIM) images were obtained after the first and second stage. Smoothing filter was applied on the obtained SIM images. The SIM image after the second stage was then conducted threshold by Otsu method and a carbon distribution map was obtained. A pores distribution map is obtained from a combined image of the SIM image after the first stage and the carbon distribution map. The threshold was determined by a p-tile method with ionomer to carbon ratio (I/C). Ionomer distribution was extracted from the carbon and pores distribution maps.

The ionomer distribution of the catalyst layer with I/C 2.0 was analyzed as shown in Figure 1. A catalyst coated membrane was fabricated by a doctor-blading and decal-transfer method [5]. Lower side in the figures is the interface with a polymer electrolyte membrane (PEM) and upper edge is the bottom in the fabrication process before decal-transferring. The through-plane ionomer distribution is not uniform. Thin ionomer layer was formed at the interface with the PEM. This can be because of deposition of ionomer during the drying process.

Acknowledgments

This work was supported by JSPS KAKENHI Grant Number 15H03932.

References

[1] K. More, R. Borup, K. Reeves, ECS Trans., 3 (2006) 717-733.

[2] L.Guétaz, M. Lopez-Haro, S. Escribano, A. Morin, G. Gebel, D. Cullen, K. More, R. Borup, ECS Trans., 69 (2015) 455-464.

[3] S. Komini Babu, H.T. Chung, P. Zelenay, S. Litster, ACS Applied Materials & Interfaces, 8 (2016) 32764-32777.

[4] D. Susac, V. Berejnov, A.P. Hitchcock, J. Stumper, ECS Trans., 41 (2011) 629-635.

[5] T. Suzuki, H. Tanaka, M. Hayase, S. Tsushima, S. Hirai, Int. J. Hydrogen Energy, 41 (2016) 20326-20335.

Figure 1
(Invited) Fuel Cells for Naval Applications
Authors: Anderson Michele L
Published: February 2020

The high efficiency and scalability of fuel cell systems make them attractive for a range of Naval applications that span sensors and unmanned systems to microgrids and ships. Anticipated benefits include significant endurance enhancements that extend range and on-station mission capability and reduced use of fossil fuels to increase energy independence and energy security. Prior Navy and other agency investments in fuel cell stack technology, reactant storage and processing systems, and balance of plant components has enabled the design, fabrication and integration of practical fuel cell systems. These systems have demonstrated superior performance to other technologies and the ability to fill capability gaps that other technologies are unable to address. This paper will discuss the status of fuel cell systems for Naval applications and the challenges and opportunities for Fleet and Marine Corps implementation.
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
Energy Balance of an Photovoltaic/Fuel Cell Integrated Energy System
Authors: Hsueh Kan-Lin , Ting Fu-Pin , Lee Chun-I , Chang Wen-Sheng
Published: February 2020

The global installed capacities of photovoltaic and wind power are growing rapidly. To maintain the quality of grid power and balance between power supply and demand, the integration among photovoltaic, batteries, and fuel cells is necessary. The characteristics of these electric power productions are different. To achieve the balance between power supply and demand, mutual compensation among these power generations, scheduling and power regulation becomes very important. In-situ power monitoring, energy management and power dispatching is vital to power quality and their stability. The power rating and capacity of renewable energy, fuel cells, and storage subsystems are also depending on the variation of load and weather. The photovoltaic and fuel cell, and storage system at a particular scenario are simulated.
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
Metal Organic Framework-Modified Graphene-Based Catalyst for Oxygen Reduction Reaction
Authors: Zhuang Shiqiang , Nunna Bharathbabu , Lee Eon Soo
Published: February 2020

Nitrogen-doped graphene (N-G) is one of promising non-platinum group metal (non-PGM) catalysts for the oxygen reduction reaction (ORR). In this research, we investigated new N-G catalysts which are modified by the metal-organic framework (MOF), to enhance the electrochemical performance of N-G catalysts. The new MOF-modified N-G (N-G/MOF) catalysts with microporous structures are successfully synthesized by high energy nano wet ball milling methods with N-G and ZIF-8. The physical and chemical properties of new synthesized N-G/MOF catalysts are characterized several characterization methods such as XPS, XAS, SEM-EDS, TEM, XRD, BET and RRDE. The result shows that new microporous structures in NG/MOF catalysts were formed at 350 RPM which are totally different from structures of N-G and ZIF-8, and BET surface area is increased from 25 to 1103 (m 2 /gram). However, at 650 RPM the new microporous structures are suppressed to have no significant effect on the N-G structure. The ongoing research activities are trying to understand the synthesis reaction mechanism and to study the control of the synthesis mechanism through chemical and electrochemical characterizations of N-G/MOF catalysts. This research shows that the ZIF-8 could be a promising additive to modify physical, chemical, and catalytic performances of N-G catalysts. The successful accomplishment of the new N-G/MOF catalysts will provide the substantial way to the cost-effective and fuel-efficient energy conversion system.
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
Effect of Accelerated Stress Testing on High Temperature Proton Exchange Membrane Fuel Cell
Authors: Bandlamudi Vamsikrishna , Bujlo Piotr , Sita Cordellia , Pasupathi Sivakumar
Published: February 2020

The durability of high temperature proton exchange membrane (HT-PEM) fuel cells is very important for its long term performance and commercialization. Commercialization demands progress, especially in the development of fuel cell catalyst materials and carbon supports. The role of platinum and carbon in the catalytic layer are crucial for the stable performance of a fuel cell. Potential cycling is used to evaluate the stability of platinum and carbon support material of catalyst layer. Fuel cells operated under cycling conditions have lower durability than those operated under steady state conditions. The aim of this work is to study degradation of phosphoric acid doped polybenzimidazole membrane based fuel cell under accelerated potential cycling conditions. Potential cycling degrades fuel cell performance. Understanding this degradation related issues associated with potential cycling is necessary to improve the durability of HT-PEM fuel cell. The fuel cell is cycled between open circuit voltage and 0.5V for 6 minutes per cycle (as represented in figure 1) until 5000 cycles. The performance of fuel cell is characterized using polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry and linear sweep voltammetry at beginning of life and after the accelerated degradation test to investigate the effect of change in potential step from open circuit voltage to operating voltage of 0.5V. Cathode exhaust is monitored for carbon dioxide using real time infra-red spectroscopy and the condensed water is analyzed for phosphoric acid. Material characterization methods are used to evaluate the degradation mechanisms responsible for the observed performance loss.

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.
Ionic Functionalization of Polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene via Friedel-Crafts Bromoalkylation and Its Application for Anion Exchange Membranes
Authors: Jeon Jong Yeob , Mohanty Angela D , Tian Ding , Bae Chulsung
Published: February 2020

A new post-functionalization method of polystyrene (PS) block of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) is presented. Due to good chemical stability of backbone in alkaline condition, elastic mechanical property, nanoscale phase separation morphology, and commercial availability, SEBS is a promising candidate for preparation of anion exchange membranes (AEMs). Chloromethylation, the most frequently used reaction for AEM synthesis, of the PS block in SEBS generally results in low levels of functionalization or gelation.1, 2 To overcome these limitations our group has reported functionalization of SEBS for AEM applications using transition metal-catalyzed C-H borylation and Suzuki coupling reactions.3

Herein, we report another method “bromoalkylation” of aromatic rings at SEBS via the acid-catalyzed Friedel-Crafts alkylation of a tertiary alcohol. Compared to our previous report, this new synthetic route is much simple and does not require noble transition metals, affording the synthetic process more economical and scalable. Bromoalkylated tertiary alcohol is converted to a tertiary carbocation, which readily reacts with p electrons of the aromatic rings at PS block under acidic condition. Quaternary ammonium (QA) functionality and tether length between polymer backbone and cationic head groups were conveniently tunable by changing the structure of brominated tertiaryalcohols. A maximum of 80 mol. % of PS block could be functionalized.

A series of SEBS-based AEMs were prepared with different QA concentrations and tether lengths. The properties of membrane samples were investigated by comparing ion-exchange capacity (IEC), water uptake, OH- conductivity and morphology. Among them, SEBS-C3-TMA-0.8 (tether length, n=3; 80% of PS functionalization) has the highest IEC (1.62 mequiv g-1), and OH- conductivity of 93 mS cm-1 at 80 °C in water. Moreover, the IEC and OH-conductivity of all membranes were preserved after immersing them in 1 M NaOH at 80°C for 500 h.

1. Q. H. Zeng, Q. L. Liu, I. Broadwell, A. M. Zhu, Y. Xiong and X. P. Tu, J. Membr. Sci. 2010, 349, 237-243.

2. L. Sun, J. Guo, J. Zhou, Q. Xu, D. Chu and R. Chen, J. Power Sources 2012, 202, 70-77.

3. A. D. Mohanty, C. Y. Ryu, Y. S. Kim and C. Bae, Macromolecules 2015, 48, 7085-7095.

Figure 1
(Invited) Structured Electrochemical Materials Fabricated from Directed Self-Assembly of Block Copolymers and Advanced Lithography
Authors: Zhang Le , Cao Chi , Yakimov Alexandrina , Arges Christopher George
Published: February 2020

In this first part of the talk, the process of directed self-assembly will be presented for controlling the microphase separated structure in block copolymer electrolytes (BCEs) with astonishing fidelity. Key results highlight that ionic conductivity of BCEs followed an exponential growth curve with respect to ionic domain connectivity. Conversely, small amounts of terminal defects of the ionic domains rendered no advantage in ionic conductivity for microphase separated systems over non-phase separated systems. Ionic domain alignment to electrode surfaces with a tortuosity of 1 yielded a 4 order of magnitude improvement in ionic conduction over anti-aligned ionic domains. The results suggest that ‘perfect’, long-range ordered structures are necessary for maximizing BCE ionic conductivity.

The second part of the talk presents our work on structured electrochemical interfaces for fuel cell and water electrolysis applications. The structured interfaces were prepared by conventional micropatterning and advanced block copolymer lithography. Patterned electrochemical interfaces provide greater interfacial area values that reduce charge-transfer resistances. However, increasing the interfacial area by patterning deeper into electrochemical materials (e.g., into the polymer electrolyte membrane) gave rise to large mass transfer related resistances that eventually offset gains from reduction in charge-transfer resistances. The talk will highlight appropriate design heuristics for fabricating patterned electrochemical interfaces that optimize fuel cell and electrolyzer thermodynamic performance.
(Invited) Kinetic Modeling of the Borohydride Oxidation Reaction (BOR) at Gold and Platinum Electrodes
Authors: Olu Pierre-Yves , Braesch Guillaume , Bonnefont Antoine , Savinova Elena R. , Chatenet Marian
Published: February 2020

Due to their high theoretical energy density, direct borohydride fuel cells (DBFCs) are a promising alternative to proton exchange membrane fuel cells for mobile applications. However, the energy conversion efficiency of DBFCs is impeded by the hydrogen generation and escape from the anode upon operation. The hydrogen escape characteristics during the BOR depend strongly on the type of metal chosen as anode electrocatalyst, on the architecture of the catalyst layer and on the concentration of NaBH4 [1-4]. This shows the importance for further understanding of the BOR mechanism with regards to the influence of the experimental conditions on the reaction.

In this presentation, the results of recent experimental studies about the BOR on gold and platinum electrodes will be presented and discussed with the help of microkinetic modeling. The proposed kinetic model is able to reproduce the main features of electrochemical (rotating (ring-)disk electrode, RRDE) and differential electrochemical mass-spectrometry (DEMS) measurements for various concentrations of NaBH4 (5, 50 and 500 mM), and is in agreement with the results of DFT calculations and FTIR measurements [5-8]. These experimental findings enable to compare and discuss the BOR mechanism between Pt and Au surfaces accounting for the differences in hydrogen generation/oxidation during the BOR but also for the poisoning of the electrodes with adsorbed BOR intermediates.

This work was supported by the French ANR (project ANR-16-CE05-0009).

References

(1) Jusys, Z.; Behm, R. J. Electrochem. Commun.
2015, 60, 9.

(2) Freitas, K. S.; Concha, B. M.; Ticianelli, E. A.; Chatenet, M. Catal. Today
2011, 170, 110.

(3) Olu, P.-Y.; Job, N.; Chatenet, M. J. Power Sources
2016, 327, 235.

(4) Olu, P. Y.; Bonnefont, A.; Rouhet, M.; Bozdech, S.; Job, N.; Chatenet, M.; Savinova, E.Electrochim. Acta
2015,
179, 637.

(5) G. Rostamikia, M.J. Janik, J. Electrochem. Soc., 2009, 156 B86.

(6) G. Rostamikia, M.J. Janik, Electrochim. Acta,
2010, 55, 1175.

(7) B. Molina Concha, M. Chatenet, F. Maillard, E.A. Ticianelli, F.H.B. Lima, R.B. de Lima,Phys. Chem. Chem. Phys.,
2010, 12, 11507.

(8) B. Molina Concha, M. Chatenet, E.A. Ticianelli, F.H.B. Lima, J. Phys. Chem. C,
2011, 115 12439.
Hierarchical Titanium Nitride Nanostructures As Catalyst Scaffold for PEMFC Technology
Authors: Perego Andrea , Giuffredi Giorgio , Casalegno Andrea , DiFonzo Fabio
Published: February 2020

To overcome the high cost of the catalyst in Direct Methanol Fuel Cell (DMFC) technology, research is moving towards the reduction in the Pt loading in the electrodes by increasing the electrochemical surface area. To date, the state of the art of catalyst supports is dominated by mesoporous carbon. It shows high conductivity but suffer from stability issues especially on long term operation. As shown in the literature, titanium nitride (TiN) has a metal-like conductivity with an outstanding chemical stability [1], and moreover, it is reported to be functional towards the oxidation of adsorbate CO on platinum active sites [2].

In this contribution, we report about TiN catalysts support with self-assembled, hierarchical mesoporous nanostructure, grown by Pulsed Laser Deposition. This approach controls the gas dynamics of the nanoclusters-inseminated supersonic jet to differentiate the resulting impaction deposition, affecting the growth of the film. Platinum is deposited by means of pulsed electrodeposition and it shows a peculiar lamellar structure, most likely due to the strong electric field on the nanostructures.

Electrochemical and physical characterization are performed, showing performances towards both methanol oxidation and oxygen reduction, and revealing information about the interaction between catalyst, scaffold and reactants.

We demonstrate that it is possible to obtain a catalyst support with large surface area whose morphology can be controlled at the nanoscale. Such as a support could be ideal for the highest platinum utilization, and for the metal loading reduction, since it has similar effects with respect to the metallic Ru in commercial DMFC catalysts with a much lower cost. Stability at high potential is also investigated, and so is the possibility to use the same material as a cathode exploiting the stability of the TiN.

These results show the potential of a PVD based technique that opens the doors of the nanoscale to the fabrication of high performing electrodes whose morphological and electrical properties are easily tuned. This approach holds promises for a consistent reduction in the metal loading in DMFC technology.

[1] M. Wittmer, B.Studer and H.Melchior, Journal of Applied Physics, 52, 5722 (1981)

[2] M. Roca-Ayats, G. Garcia, J.L. Galante, M.A. Peña and M.V. Martinez-Huerta, Journal of Physical Chemistry C 117, 20769-20777 (2013)

Figure 1
N，P-Dual Doped Porous Carbon with Trace Level Co Doping As Highly Efficient Electrocatalyst for Oxygen Reduction Reaction
Authors: Yan Dafeng , Wang Shuangyin
Published: February 2020

Fuel cells and metal-air batteries are considered as the alternative clean energy devices in the future. Oxygen reduction reaction (ORR) is the key process among them for poor reaction kinetics, which has significantly limited the commercialization of these devices. So it is very important and necessary to seek efficient and inexpensive catalysts for the ORR. Since Dai’s group first reported that N-doped carbon nanotube showed high ORR performance, many researchers have developed many kinds of carbon materials. It has been accepted that heteroatom doping can effectively improve the activity of carbon materials. And also our group has successfully proved that the edge carbon was much active than the basal plane. In this work, we used a very simple method to prepare a novel carbon material with N, P-dual doping and much holes exposed on the surface. In addition, trace level Co doping in the carbon material forming Co-N-C active species can also enhance the ORR performance. On one hand, the doping can adjust the electronic structure of the near carbon atoms, which would induce more active sites for ORR. And on the other hand, the hole formed on the surface of carbon nanosheets would expose much edge sites and can improve the intrinsic activity of carbon. For the heteroatom doping and more exposed edge sites, the prepared carbon materials showed highly excellent ORR performance, nearly to that of commercial Pt/C.

Figure 1