bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Performance Evaluation of a Hybrid Hydrogen-Vanadium Reversible Fuel Cell
Authors: Nguyen Trung Van , Dowd Regis Paul , Powers Devon , Wycisk Ryszard , Pintauro Peter N
Published: February 2020

The hybrid hydrogen-vanadium reversible fuel cell consists of a gaseous hydrogen fuel cell electrode and a liquid vanadium flow battery electrode. This hybrid fuel cell system offers a feasible solution for storing electrical energy from the grid or directly from renewable energy sources such as wind and solar. This system is attractive over the all-vanadium system due to the 50% reduction in the amount of vanadium solution required. Furthermore, by replacing the negative vanadium electrode with a hydrogen electrode the effect of self-discharge by the crossover of unwanted ions (vanadium II and III) from the negative electrode to the positive electrode is eliminated. Another benefit of this two-phase hybrid system is the ease of separation of the cross-over species. In this presentation, the effects of operating and design variables such as the vanadium electrolyte flow rate, type of carbon electrodes, and Nafion membranes and electrospun membranes made of perfluorosulfonic acid (PFSA)/ polyvinylidene fluoride (PVDF), which are developed to reduce the crossover rate of vanadium ions, with different thickness will be discussed.

Acknowledgement

The work presented was partially funded by the National Science Foundation under Grant No. EFRI-1038234.

Figure 1
Effects of Copper Corrosion in the Performance of Polymer Electrolyte Membrane Fuel Cells
Authors: Johnson N Allwyn Blessing , Das Sarit Kumar , Sen Ashis Kumar
Published: February 2020

Copper Plates are widely used as the current collectors in Polymer Electrolyte Membrane (PEM) Fuel cells. With exposure to the atmosphere, copper oxidizes and causes bright copper surfaces to tarnish. This corrosion results in decreasing the current produced. This paper aims to examine the effects of copper corrosion in the performance of PEM Fuel cell. The experiments were conducted on a single PEM Fuel cell with working area of 25cm2 without external cell heating. The feed velocities of hydrogen and oxygen were fixed at 0.5 and 0.75 L min-1, respectively. To bring out the effect of corrosion, a set of copper plates were kept open to atmosphere in the temperature range of 30 – 40oC for 2 months. Then the corroded copper plates were used as current collectors in the PEM Fuel Cell and the performance was monitored. It was observed that ohmic losses increased drastically and the maximum voltage drop was 0.4V.

Figure 1
Performance Improvement By Introduction of Macropore Structure in Membrane Electrolyte Assembly Using Mechanical Properties of Polymer Electrolyte Membrane
Authors: Ahn Chi-Yeong , Kim Sungjun , Hwang Wonchan , Cho Yong-Hun , Sung Yung-Eun
Published: February 2020

We have introduced macropores that help improve mass transfer of fuel cell electrode by using simple mechanical method. Polymers generally have elastic and inelastic regions when strain is applied. Nafion®, which is commonly used as a proton conductive membrane for polymer electrolyte membrane fuel cell (PEMFC), has a relatively large inelastic region compared to the elastic region. When an electrode is applied to Nafion® membrane and strain of inelastic region is applied, the macropores are formed due to the difference in elastic modulus between the membrane and the electrode. The electrochemical performance of MEAs with macropores at various strain ratios was evaluated. We have discussed the cause of performance improvement and durability was also confirmed. Furthermore, research into MEAs that contain shape-controlled macropores is being studied as a replacement for randomly formed macropores.
Self-Healing Composite Membrane for Proton Exchange Membrane Fuel Cell Applications
Authors: Wang Liang , Advani Suresh G. , Prasad Ajay K.
Published: February 2020

We have developed a self-healing membrane based on microcapsules prefilled with Nafion solution. The microcapsules are designed to rupture when they encounter defects formed in the membrane such as cracks and pinholes, and then release the prefilled Nafion solution to heal the defects in-situ. A procedure was developed to prepare microcapsules with a urea-formaldehyde shell prefilled with a Nafion/tributyl phosphate self-healing solution. The prepared microcapsules were characterized by SEM with focused ion beam (FIB) and optical microscopy. Proton conductivity, mechanical properties, swelling and water uptake of the composite membranes based on microcapsules were measured and compared with that of pure recast Nafion membranes. Fuel cell performance with 6 and 10 wt% microcapsules/Nafion membranes was compared with that of a pure recast Nafion membrane. Durability testing comprising 220 hours of OCV-hold with relative humidity cycling confirmed that the self-healing functionality could greatly extend the life span of the fuel cell membrane.
Improved Electrochemical and Mechanical Properties of Poly(vinyl pyrrolidone)/Nafion® Membrane for Fuel Cell Applications
Authors: Kabir MD Lutful , Kim Hee Jin , Lee Chul Jae , Choi Sang-June
Published: February 2020

A novel blend of membranes made of Nafion® and poly(vinyl pyrrolidone) (PVP) was prepared and characterized to investigate its applicability in proton exchange membrane fuel cells (PEMFCs). In addition to being effectively proton conductive, the membranes exhibited better mechanical strength, chemical stability and adequate water retention ability as well as ion exchange capacity comparable to that of cast Nafion® membrane. The data obtained from an electrochemical impedance spectroscopy (EIS) fitting of the fuel cells revealed the membrane electrode assemblies (MEAs) made of 0.5 wt. % PVP/ Nafion® had lower ohmic and charge transfer resistance compared to that of Nafion® membrane. The intermolecular interactions and morphology of these membranes were assessed using Fourier-transform infrared spectroscopy and field-emission scanning electron microscopy. The results of the performance curve indicate that the introduction of PVP as a modifier played a vital role in improving the membrane performance. Accordingly, this solution casted polymer electrolyte membrane with suitable PVP content offers a simple way to improve electrochemical, mechanical and chemical properties and thereby promises the prospect for use in low-temperature PEMFCs.

Figure 1
(Invited) Direct Membrane Deposition – A Fast and Simple Technique for Membrane Electrode Assembly Manufacturing
Authors: Klingele Matthias , Vierrath Severin , Breitwieser Matthias , Klose Carolin , Thiele Simon
Published: February 2020

The membrane is one of the very central polymer electrolyte membrane fuel cell components. At the same time it must conduct protons and inhibit transport of electrons and cross-over of reactant gases. Additionally, degradation effects have to be small to ensure a long lifetime. While traditionally consisting of pure Nafion, up to date membranes contain nanofiber reinforcements and radical scavenger packages to decrease degradation effects. Thus, seminal membranes are multi-layer, multi-component structures.

In the state of the art, membrane electrode assemblies (MEA) are manufactured as catalyst coated membranes (CCMs). To form a CCM, electrodes are deposited either by the decal method, or by another deposition method.

In this talk we present a novel approach for MEA manufacturing. In the so called ‘direct membrane deposition’ (DMD) approach, liquid ionomer is deposited on the catalyst layers of two gas diffusion electrodes which are successively dried and pressed together to form an MEA. Interestingly, this approach enabled power densities more than two times higher than traditional CCM based approaches which are commercially available [1]. Also this approach allows for a simple fabrication of thin multi-layer membranes and improves the water management [2]. DMD applied to low Pt loading electrodes revealed very high power densities per gram Pt of up to 88 kW/g Pt [3]. An analysis of the underlying reasons for the improved performance values revealed a small influence of membrane resistance but mainly an influence in mass transport and charge transfer phenomena [4,5].

In this talk we highlight our latest developments in the field of DMD based manufacturing and give an insight on degradation and durability aspects.

References:

[1] M. Klingele, M. Breitwieser, R. Zengerle, S. Thiele, J. Mater. Chem. A 3 (2015) 11239–11245.

[2] M. Breitwieser, R. Moroni, J. Schock, M. Schulz, B. Schillinger, F. Pfeiffer, R. Zengerle, S. Thiele, Int J Hydrogen Energ 41 (2016) 11412–11417.

[3] M. Breitwieser, M. Klingele, B. Britton, S. Holdcroft, R. Zengerle, S. Thiele, Electrochem. Commun. 60 (2015) 168–171.

[4] M. Klingele, B. Britton, M. Breitwieser, S. Vierrath, R. Zengerle, S. Holdcroft, S. Thiele, Electrochemistry Communications 70 (2016) 65–68.

[5] S. Vierrath, M. Breitwieser, M. Klingele, B. Britton, S. Holdcroft, R. Zengerle, S. Thiele, J. Power Sources 326 (2016) 170–175.170 - 175.
A Thermo-Poro-Viscoelastic Model for the Behavior of Polymeric Porous Separators
Authors: Behrou Reza
Published: February 2020

Porous separator membranes play an important role in the long-term performance of lithium battery cells. They provide a barrier between two electrodes and enable migration of lithium ions through the pores, where lithium ions migrate through the electrolyte via diffusion-migration and reach the electrode materials.  During the discharge process, the intercalation of Li ions into active materials in the electrode leads to swelling of active particles, expansion of the electrode, mechanical stresses, and compression of the separator membrane. Moreover, the extreme thermal condition lessens the performance of the separator by closing the pores through a melting process. To assess the performance of the separator under mechanical and thermal conditions, we present a thermo-poro-viscoelastic model for polymeric porous separators. We study the thermo-mechanical behavior of fully saturated porous separators through the thermo-poromechanics formulations. Two-phase mixture with solid and fluid phases is considered. Governing and balance equations are presented for the solid-fluid mixture, where the displacement of the solid skeleton, temperature and fluid pore pressure are considered as unknowns with a quasi-static loading condition. The stress-strain behavior of the polymeric separator membrane is described by a viscoelastic constitutive law in the form of convolution integral, where the thermal effects are considered through the thermal strain. The flow of the fluid through the porous medium is described by the Darcy’s law. The constitutive equation for the Darcy fluid velocity is described by the permeability of the fluid. To present more realistic physical phenomena, the hydraulic conductivity is described as a function of the porosity in the solid phase. Numerical simulations are performed to study the performance of the separator in a saturated porous medium.
Structure-Activity-Durability Relationships of (CM+PANI)-Me-C PGM-Free Catalysts
Authors: Martinez Ulises , Komini Babu Siddharth , Holby Edward F. , Artyushkova Kateryna , Lin Ling , Chung Hoon T , Purdy Geraldine M , Zelenay Piotr
Published: February 2020

The development of durable and highly active platinum group metal-free (PGM-free) electrocatalysts is key to overcoming the greatest barrier in the commercialization of fuel cell electric vehicles: the high cost and limited availability of PGM catalysts utilized in polymer electrolyte fuel cells. While the majority of research on PGM-free catalysts has focused on developing active and selective materials for the sluggish oxygen reduction reaction (ORR), minimal work has been devoted to the understanding of the physical and chemical structure of active PGM-free catalysts and its relationship with the long-term stability of these novel materials. This understanding is imperative for the further development of next-generation PGM-free catalysts with improved activity and durability that could ultimately replace PGM-based ORR catalysts in fuel cells.

PGM-free catalysts with high volumetric activity, four-electron selectivity (i.e., low hydrogen peroxide yield), and long-term stability in highly acidic and strongly oxidizing environment of the fuel cell cathode are desired as replacements for PGM-based ORR catalysts. For this presentation, state-of-the-art PGM-free ORR catalysts, developed by our group [1, 2], which are obtained via high-temperature treatment of dual nitrogen precursors, cyanamide (CM) and polyaniline (PANI), different transition metal precursors (Fe, Co, Mn), and with or without carbon support are used as model PGM-free catalyst systems. Depending on the transition metal used, catalysts with different physical and electrochemical characteristic properties are obtained. Specifically, Fe-based catalysts are generally known for their high activity and low peroxide yield generation. However, Co- and Mn-based catalysts generate highly graphitic structures which could improve catalyst long-term stability. In this work, structure-activity-durability relationships are developed based on comprehensive physical, chemical, and electrochemical characterization of highly active (CM+PANI)-Me-C catalysts (Me = Fe, Co, Mn), correlating properties such as carbon structure, elemental speciation, and CO2 generation.

Acknowledgement

Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged.

[1] Chung, H.T., Holby, E.F., Purdy, G.M., Babu, S.K., Litster, S., Cullen, D.A. More, K.L., Zelenay, P. (2015). “Combining Nitrogen Precursors in Synthesis of Non-Precious Metal ORR Catalysts with Improved Fuel Cell Performance.” ECS Meeting Abstracts, MA2015-02 (37), 1278.

[2] Martinez, U., Holby, E.F., Dumont, J.H., Chung, H.T., Zelenay, P. (2016) “Non-PGM ORR Catalysts Based on Transition Metals Alternative to Iron.” ECS Meeting Abstracts, MA2016-01, 1719.
(Invited) Porous Hollow PtNi/C Nanoparticles and Their Many Facets
Authors: Asset Tristan , Chattot Raphaël , Le Bacq Olivier , Pasturel Alain , Drnec Jakub , Bordet Pierre , Nelayah Jaysen , Dubau Laetitia , Maillard Frederic
Published: February 2020

Porous hollow PtM/C electrocatalysts (where M is a 3d transition metal element) have proven to enhance remarkably the oxygen reduction reaction (ORR) kinetics in proton exchange membrane fuel cells. However, their mechanism of formation, the nature of adequate alloying elements and carbon supports as well as the rationale for their interesting electrocatalytic properties remain open questions.

Herein, we describe the mechanism of formation and growth of porous hollow PtNi/C NPs using operando wide angle X-ray scattering, scanning transmission electron microscopy and X-ray energy dispersive spectroscopy 1. The results show that Ni-rich NPs covered by a NixByOz shell form first before acting as a sacrificial template for the deposition of Pt2+ ions via galvanic replacement (Figure 1). Finally, the solid Ni-rich core@Pt-rich shell NPs are transformed into alloy hollow PtNi/C NPs via the nanoscale Kirkendall effect (a vacancy mediated interdiffusion mechanism). Density Functional Theory (DFT) calculations were then used to gain insights on the impact of atomic vacancies on the surface structure and the reactivity of the porous hollow PtNi/C nanoparticles 2. The DFT and experimental results show that porous hollow PtM/C nanoparticles feature unique catalytic advantages (i) open percolated structure exposing two catalytic surfaces (inner and outer), and (ii) structural defects that distort the metal lattice and produce catalytic sites that are highly active for both electrooxidation (COadsmonolayer electrooxidation, methanol and ethanol electrooxidation) and electroreduction (ORR) reactions.

1. R. Chattot, T. Asset, J. Drnec, P. Bordet, J. Nelayah, L. Dubau, F. Maillard, Nano Lett. (2017). DOI: 10.1021/acs.nanolett.7b00119

2. O. Le Bacq, A. Pasturel, R. Chattot, B. Previdello, J. Nelayah, T. Asset, L. Dubau, F. Maillard, ChemCatChem. (2017). DOI: 10.1002/cctc.201601672

Figure 1.Conventional and scanning transmission electron microscopy images and elemental maps of the different intermediate nanostructures forming during the synthesis of hollow PtNi/C nanoparticles.

Figure 1
Structure-Stability Relationships for Fuel Cell Catalysts
Authors: Lopes Pietro Papa , Li Dongguo , Strmcnik Dusan , Paulikas Paul Arvydas , Tripkovic Dusan , Martins Pedro F. B. D. , Markovic Nenad M , Stamenkovic Vojislav
Published: February 2020

Our control over the catalytic activity for the Oxygen Reduction Reaction (ORR) is greater than our present understanding of the factors affecting the stability of catalyst surface atoms. Despite the significant progress in imaging the overall changes at the nanoscale that takes place during advanced degradation test (ADT) protocols, little is known about structure-stability relationships. Nonetheless, recent developments in combining in situ electrochemical methods to inductively coupled plasma with mass spectrometry (ICP-MS) allowed identification of element specific dissolution processes. Specifically, the development of a Stationary Probe Rotating Disk Electrode (SPRDE) system provided insights on Pt dissolution and how it is structure sensitive, highly dependent on electrolyte and double layer composition, as well as influenced by the nature of the electrocatalytic reaction. This serves as a baseline to understand the functional links between structure, activity and stability for a variety of Pt-Metal alloys, how their atomic scale morphology controls stability and activity, its implications for nanoparticle systems, and what strategies can be successfully employed to improve both activity and stability of these surfaces.
Rotating Disk Electrode Study of Carbon Supported Pt-Nanoparticles Synthesized Using Microwave-Assisted Method
Authors: Vaarmets Kersti , Valk Peeter , Nerut Jaak , Tallo Indrek , Aruväli Jaan , Sepp Silver , Lust Enn
Published: February 2020

Carbon supported platinum catalysts are widely used in PEMFC applications. The catalytic activity of the catalyst is strongly dependent on size and size distribution of the Pt nanoparticles deposited onto porous carbon support. In this study, the microwave-assisted synthesis method was used to study the effect of the Pt particle size and content (mass%) on the electrochemical activity of oxygen reduction reaction1,2.

The Pt nanoparticles were deposited onto the carbon support using the microwave-assisted method3–6. H2PtCl6×6H2O (99.9%, Alfa Aesar) was dissolved in ethylene glycol (Riedel-de Haën), the carbon powder (commercial Vulcan XC72) was added and pH was regulated using NaOH. The synthesis mixture was heated in a commercial microwave oven until boiling two times. The product was filtered and thereafter washed with MilliQ+ water. Varying the pH level of the reaction media affected the Pt nanoparticle size and Pt content in the catalysts.

The X-ray diffraction and low temperature nitrogen sorption methods were used to characterize the catalysts materials.

The materials were electrochemically characterised using the rotating disk electrode technique as described by S. Kocha et. al 7,8 in 0.1 M HClO4 solution. The highest electrochemical surface area 93.8±13.3 m2g−1 with mass activity of 436 mA mg−1 and specific activity of 449 µA cm−2 have been achieved.

The content of platinum in the catalyst was determined before and after the experiments using the electrochemical dissolution of platinum from the electrode in 6 M HCl solution. The average weight percentage of Pt in different catalyst materials was 17.3±4.1.

References

1. B. C. H. Steele and A. Heinzel, Nature, 414, 345–352 (2001) .

2. H. A. Gasteiger, S. S. Kocha, B. Sompalli, and F. T. Wagner, Appl. Catal. B Environ., 56, 9–35 (2005).

3. W. X. Chen, J. Y. Lee, and Z. Liu, Chem. Commun., 2588–2589 (2002).

4. X. Li, W.-X. Chen, J. Zhao, W. Xing, and Z.-D. Xu, Carbon, 43, 2168–2174 (2005).

5. Z. Liu, J. Y. Lee, W. Chen, M. Han, and L. M. Gan, Langmuir, 20, 181–187 (2004).

6. S. Horikoshi and N. Serpone, Eds., Microwaves in nanoparticle Synthesis: Fundamentals and Applications, WILEY-VCH Verlag GmbH & Co KGaA, (2013).

7. K. Shinozaki, J. W. Zack, R. M. Richards, B. S. Pivovar, and S. S. Kocha, J. Electrochem. Soc., 162, F1144–F1158 (2015).

8. K. Shinozaki, J. W. Zack, S. Pylypenko, B. S. Pivovar, and S. S. Kocha, J. Electrochem. Soc., 162, F1384–F1396 (2015).

Acknowledgements This work was supported by Estonian target research project IUT20-13, Personal Research Grant PUT55, Estonian Centre of Excellence Projects No. 2014-2020.4.01.15-0011 and 3.20101.11-0030.
Uniformity of Carbon Supported Pt Nanocatalysts Produced By Arc Plasma Deposition
Authors: Saito Toshifumi
Published: February 2020

We propose a new approach for the preparation of Pt/C catalysts by arc plasma deposition (APD), in which Pt nanoparticles are deposited on carbon in a vacuum; this method has been applied in a number of fields other than fuel cell catalysts. The solid cathode material is transformed into a completely ionized plasma that leaves the cathode with a velocity of 1-2 x 104 m/s(this number is the same for all cathode materials). This velocity corresponds to an ion kinetic energy of 20 eV (light ions such ascarbon) to 300eV (heavy ions such as platinum). Thus, the cathode material is eroded and forms anenergetic plasma jet.

When carbon powder is irradiated with a platinum-based plasma, the Pt+ ions collide with the carbon and become atoms, which then migrate and interact with other Pt atoms to form nanoparticles (NPs) with dimensions of 2 to 3 nm on the carbon surface. Figure 1 shows a scanning electron microscopy (SEM) image of Pt NPs on Ketjen black. Although the surface of the Ketjen black is extremely rough, the NPs are seen to be uniformly distributed. We compared the electrochemical properties of Pt/C catalysts prepared by APD with those of the commercially available catalyst TEC10E50E. Although the electrochemical surface area (ECSA) was almost the same, the specific activity for Pt/C(APD) was about 2 times higher than that for TEC10E50E, which led to an approximately 2 times higher mass activity. However, one remaining problem with Pt/C(APD) is that NPs are not deposited in some regions. Figure 2 shows an SEM image of Ketjen black containing regions where no Pt NPs are present. To address this issue, we made improvements to the stirring vessel, and optimized deposition parameters such as the plasma pulse interval and the powder surface conditions. We will describe the effects of these optimizations on the electrochemical properties of Pt/C(APD).

Figure 1
Tuning the Alloy Behavior and Particle Size of Ptm (M=Ni, Co) Nanoparticles By Using in Situ High-Temperature X-Ray Diffraction
Authors: Werheid Matthias , Weber Daniel Jochen , Weber Philipp , Oezaslan Mehtap
Published: February 2020

Alloying process has emerged as a promising strategy to tailor the chemical, physical and catalytic properties of metals. According to the phase diagram, the physical and chemical properties and behaviors of macroscopic alloys are well known. On the atomic and nano-scale, the formation mechanisms of nano-alloys are, yet, poorly understood since nanostructured alloys possess different segregation tendency and reaction enthalpies compared to those of bulk materials. In the last 20 years, bimetallic alloy nanoparticles have attracted great attention in different fields such as catalysis, seniors, medicine due to their unique optical, electronic, magnetic, morphological and catalytic properties. Partial substitution of Platinum by less noble metals like Nickel or Cobalt enables to decrease the material costs in combination with improved electrocatalytic activity for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFC).[1,2,3] However, the alloyed state and the homogeneity of bimetallic PtM (M=Ni, Co) nanoparticle electrocatalysts are crucial for the manufacturing. A simple and facile synthetic route to prepare Pt-based alloy nanoparticles is the wet impregnation approach followed by thermal annealing. The challenge is to control the alloy formation and particle growth of these bimetallic nanoparticles. Therefore, the implementation of in situ high-temperature X-ray diffraction (HT-XRD) is a powerful tool to simultaneously probe the changes in crystallographic phases and crystallite size of these nano-alloys during the thermal treatment.[4,5]

We analyzed the formation dynamics and particle growth of carbon supported PtM (M = Co, Ni) alloy nanoparticles by using in situ HT-XRD. We developed a tool box how annealing control parameters such as heating rate, temperature and time influence the crystallographic phase structure, composition and crystallite size of the bimetallic nanoparticles. Afterwards, the alloy nanoparticles are tested for the ORR to correlate their structure, composition and particle size with the resulting catalytic properties.

The HT-XRD studies on Pt-based alloy nanoparticles enable to improve the preparation of nano-alloys with desired composition, crystalline phase and particle size for PEMFC applications.

References:

[1] F. Hasché, M. Oezaslan, P. Strasser, Journal of The Electrochemical Society, 2012, 159, B25-B34.

[2] J. Zhang (Ed.), PEM Fuel Cell Electrocatalysts and Catalyst Layers: Fundamentals and Applications, Springer-Verlag, London, 2008.

[3] Oezaslan, M.; Strasser, P., Journal of Power Sources, 2011, 196, 5240-5249.

[4] F. Hasché, M. Oezaslan, P. Strasser, PhysChemPhys,
2012, 13, 828-834.

[5] M. Oezaslan, F. Hasché, P. Strasser, Chemistry of Materials, 2011, 23, 2159-2165.
3D Pt-Ni Nanosponges Wrapped with Graphene-Dots and Their Application to Effective Catalysts for Oxygen Reduction Reaction
Authors: Choi Ho-Suk , Tran Quoc-Chinh
Published: February 2020

In this study, we first report how to synthesize 3D PtNi nanosponges without using surfactants. A 3D PtNi nanosponge wrapped with graphene dots was synthesized at room temperature using formic acid as a reducing agent and N-doped carbon dot as a structure-directing reagent. 3D PtNi nanosponge was formed only in the presence of carbon dots in the reaction solution. During the reaction, the N-doped carbon dots were reduced and exfoliated to graphene dots, which encapsulated PtNi nanocrystals. The composition of the developed nanosponge can be easily controlled by adjusting the reaction temperature. The prepared material exhibited excellent catalytic activity and durability for oxygen reduction reaction as compared with commercially available Pt/C. This is due to the self-supporting structure of interconnected nanosponge and the role of the graphene shell wrapping around the PtNi nanosponge. The proposed strategy has the potential to synthesize other multi-metal nanocrystals with 3D nano sponge structures that are expected to provide high catalytic performance in other electrocatalyses such as hydrogen evolution reaction and oxygen evolution reaction.
Effects of Transition Metal Doping in Pt/M-TiO 2 (M= V, Cr, and Nb) on Oxygen Reduction Reaction Activity
Authors: Bae Min-Jeong , Kim Jun-Hyuk , Kim Yong-Tae
Published: February 2020

High cost and low durability are unresolved issues that impede the commercialization of proton exchange membrane fuel cells (PEMFCs). To overcome these limitations, Pt/TiO2 is reported as an alternative electrocatalyst for enhancing the oxygen reduction reaction (ORR) activity and/or durability of the system. However, the low electrical conductivity of TiO2 is a drawback that may be addressed by doping. To date, most reports related to Pt/doped-TiO2 focus on changes in the catalyst activity caused by the Pt-TiO2 interaction (metal-support interaction), instead of the effect of doping itself; doping is merely considered to enhance the electrical conductivity of TiO2. In this study, we discuss the variation in the electronic fine structure of Pt caused by the dopant, and its correlation with the ORR activity. More extensive contraction of the Pt lattice in Pt/M-TiO2 (M = V, Cr, and Nb) relative to Pt/TiO2 and Pt/C leads to outstanding ORR specific activity of Pt/M-TiO2. Notably, a fourfold increase of the specific activity is achieved with Pt/V-TiO2 relative to Pt/C. Furthermore, an accelerated durability test (ADT) of Pt/V-TiO2 demonstrates that this system is three times more durable than conventional Pt/C due to the metal-support interaction.
Electrochemical Characterization of MEAs with Different Pt-Loading for the Efficient Use of Pt
Authors: Uda Keisuke , Noda Zhiyun , Sasaki Kazunari , Hayashi Akari
Published: February 2020

Introduction The reduction of Pt-loading particularly in PEFC cathode layers is essential for cutting the cost of PEFCs and further spreading PEFC technology. Nowadays, several approaches of reducing Pt-loading have been reported, and then the importance of optimizing the microstructure of cathode layers including carbon supports has been confirmed.1-2 Therefore, the objective of our research is to develop low Pt-loading PEFCs with high efficiency by optimizing the mount of both Pt and carbon. As a first step, MEAs with varied Pt-loading in cathode layers were prepared with a standard catalyst, TEC10E50E, and a common spray-printing method. Then, the minimum amount of Pt, which is necessary for cathode layers, was evaluated though the detailed electrochemical characterization.

Experimental MEAs with varied Pt-loading in cathode layers, such as 0.05, 0.10, 0.15, 0.20, 0.30, and 0.40 mg/cm2, were prepared, while the amount of Pt in anode layers were kept to 0.30 mg/cm2. Then, their performances were evaluated by measuring the IV response, impedance, and Hupd electric charge. Also, the cross-sections of cathode layers were observed by FIB-SEM.

Results and discussion From IR-corrected IV curves, activation overvoltage was separately analyzed. Activation overvoltage was clearly proportional to Pt-loading in the region of 0.05 - 0.15 (0.20) mg Pt/cm2, but did not change much in 0.15 (0.20) - 0.40 mg Pt/cm2. Therefore, further with ECSA analyses, the minimum amount of Pt needed for the cathode layer was determined to 0.15 - 0.20 mg Pt/cm2 in this experimental condition. Interestingly, concentration overvoltage increased with decrease in the amount of Pt. In this case, since the amount of carbon decreased, the thickness of cathode layers resulted in decreasing. Possible reasons for this phenomenon can be explained in Figure 1. Although the shorter pathway for fuel diffusion is expected to reduce concentration overvoltage, the blockage of the pathway by water produced during the fuel cell reaction should also be considered. If the same amount of water is produced in catalyst layers with the different thickness, the path is more easily blocked in the thinner layer, leading to higher concentration overvoltage. Therefore, optimization of the cathode layer thickness is also an important factor to design better PEFCs. Accordingly, we will report the approach to develop highly efficient MEAs using the minimum amount of Pt and also reducing concentration overvoltage through controlling the amount of carbon.

References

(1) M. Lee, M. Uchida, D. A. Tryk, H. Uchida, M. Watanabe, Electrochim, Acta, 56 4783 (2011).

(2) K. Takahashi, K. Kakinuma, M. Uchida, J. Electrochem. Soc. 163.(10) F1182 (2016)

Figure 1
Development and Implementation of Catalysts and Membrane Electrode Assemblies Based on Extended Thin Film Electrocatalysts
Authors: Alia Shaun M , Neyerlin K.C. , Hurst Katherine , Zack Jason W. , Mauger Scott A , McNeary William W , Weimer Alan , Medlin Will , Shulda Sarah M , Ngo Chilan , Pylypenko Svitlana , Pivovar Bryan S
Published: February 2020

Fuel cells (and hydrogen generation from renewable electrons) represent tremendous promise in pushing society towards a more sustainable energy system. One key barrier for such a future energy system is the need for platinum group metals for catalysis and the quantities required for efficient performance. It has been a long standing goal to continually increase performance and durability of electrochemical devices, and one promising approach has been the development and implementation of extended thin film electrocatalysts.1

Our team has extensively investigated extended surface catalysts as a novel platform for increased performance and durability at lower cost.2,3,4This presentation will highlight the advances of our team in the synthesis and implementation of extended surface electrocatalysts with a focus on PtNi nanowires (NWs) produced by atomic layer deposition (ALD) and spontaneous galvanic displacement (SGD), see Figure 1. While these materials have shown great promise in ex-situ (rotating disc electrode) studies, performance in-situ (fuel cell tests) has not yet fully reflected the performance potential seen in these ex-situ tests. In large part we attribute this to challenges in electrode fabrication and integration. This presentation will present results that focus on the differences between in-situ and ex-situ properties, quantification of performance losses in fuel cell tests, and our efforts to further improve performance and durability of such systems.

Figure 1. Polarization curves for PtNiNW based catalysts for catalysts synthesized by spontaneous galvanic displacement (SGD) and atomic layer deposition (ALD).

1. Mark K. Debe∗, Alison K. Schmoeckel, George D. Vernstrom, Radoslav Atanasoski, Journal of Power Sources 161 (2006) 1002–1011.

2. Shaun Alia, Svitlana Pylypenko, Arrelaine Dameron, KC Neyerlin, Shyam Kocha, Bryan Pivovar, J. Electrochem. Soc. 2016 163(3): F296-F301.

3. Shaun M. Alia, Svitlana Pylypenko, K.C. Neyerlin, Shyam S. Kocha, and Bryan S. Pivovar, J. Electrochem. Soc. 2015 162(12): F1299-F1304.

4. Shaun M. Alia, Svitlana Pylypenko, K.C. Neyerlin, David A. Cullen, Shyam S. Kocha, Bryan S. Pivovar, ACS Catalysis, 4, 2680, 2014.

Figure 1
Development of Electrocatalysts for PEFC By Encapsulating Pt Particles into Carbon Mesopores
Authors: Hayashi Akari , Fu Bo , Huang Ting-Wei , Noda Zhiyun , Sasaki Kazunari
Published: February 2020

Electrocatalysts for PEFC are generally composed by Pt dispersed on carbon supports and have an important role to determine the performance of PEFC. Decrease in Pt active sites during the long-time use becomes a serious problem for practical use of PEFC. Pt particles have tendency to agglomerate, or dissolve and re-precipitate under the potential cycles, resulting in the growth of particles. In this study, suppressing such Pt particle growth has been focused on. So far, increasing the durability of electrocatalysts by encapsulating Pt into the nanochannnels of mesoporous carbon (MC) has been reported in our group.1 The basic idea comes from reducing Pt mobility on the curved carbon surface, which has also been supported by theoretical study.2 In this particular report, the effect of pore characteristics, such as pore diameter and pore volume, on PEFC performance are evaluated.

MCs were made from the self-organization formaldehyde/resorcinol and Pluronic F127,3 but the procedure was slightly modified for each kind of MCs. Then, electrocatalysts were synthesized from platinum(II) acetylacetonate as a precursor by depositing ca. 30 wt% Pt on MCs. These MC based materials were used for the cathode, and a standard Pt/Ketjen black catalyst (TEC10E50E, TKK Corp.) was used for the anode, in order to prepare membrane electrode assemblies (MEAs).

Current-voltage (IV) characteristics of MEAs were measured in this study. Then, ohmic loss, concentration loss, and overvoltage were further analyzed separately after ohmic resistance was found by impedance measurements. When three electrocatalyts, a standard Pt/MC, Pt/air-treated MC, and Pt/high pore volume-MC, are compared, the concentration overvoltage resulted in high with the order of a standard Pt/MC > Pt/high pore volume-MC > Pt/air-treated MC. Regarding to the activation overvoltage, it is reduced with the order of Pt/air-treated MC < a standard Pt/MC < Pt/high pore volume-MC. The correlation between the pore structure and the PEFC performance will be discussed.

References

[1] Y. Minamida et al., ECS Trans., 64(3), 137 (2014)

[2] A. Staykov et al., J. Phys. Chem. C, 118, 8907 (2014)

[3] A. Hayashi et al., Electrochim. Acta, 53(21), 6117 (2008)
Engineered Carbons Supports (ECSs) for Cathode Oxygen Reduction Reaction Electrocatalysts
Authors: Serov Alexey , Lubers Alia , McCool Geoff , McKinney Sam , Romero Henry , Zulevi Barr
Published: February 2020

In the development of PEMFC fuel cells main attention is mainly devoted to the "active" portion of the catalysts system, the precious metal nanoparticles. While this approach has led to great improvement in specific activity, existing catalysts are still not meeting the combination of performance and cost necessary for the commercialization of PEMFC.

A key limitation to catalysts today arises from reliance on carbon blacks (CBs) supports that is a matrix for the precious metal catalyst nanoparticles, but which corrode under certain operating conditions. Carbon support modifications that rely on "top-down" graphitization of CB's have so far improved resistance to carbon corrosion, but at the cost of reduced stabilization of precious metal dissolution.

Pajarito Powder developed a "bottom-up" approach where Engineered Carbon Supports (ECSs) are made from organic precursors that yield highly graphitic materials with controllable morphology and increased resistance to corrosion. This method which is based on technologies licensed from the University of New Mexico [1,2], Northeastern University, and Los Alamos National Laboratory allows manufacture of carbonaceous powders with controllable level of graphitization with reasonably high yields. The final chemical structure (doping with heteroatoms), morphology (pore size and modality) and surface area can be precisely controlled by selection of organic molecules and types of sacrificial supports.

Pt/C catalysts made using these Engineered Carbon Supports maintain performance under carbon corrosion test protocols and thus demonstrate their utility in achieving the performance/price balance needed for commercializing PEMFCs. The catalyst characteristics and performance, as well as economics of this approach will be presented and discussed. In addition, preliminary results in synthesis and performance testing of hybrid catalysts made using platinum group metal -free (PGM-free) oxygen reduction reaction (ORR) catalysts made using the VariPore™ platform with and without Pt nanoparticles added will be presented.

[1] S. Stariha, K. Artyushkova, M. J. Workman, A. Serov, S. McKinney, B. Halevi, P. Atanassov "PGM-free Fe-N-C catalysts for oxygen reduction reaction: Catalyst layer design" J. Power Sources 326 (2016) 43–49.

[2] A. Serov, M. J. Workman, K. Artyushkova, P. Atanassov, G. McCool, S. McKinney, H. Romero, B. Halevi, T. Stephenson "Highly stable precious metal-free cathode catalyst for fuel cell application", J. Power Sources 327 (2016) 557-564.

Figure 1
Pt Nanoparticles Supported on Reduced Graphene Oxide-Carbon Black Hybrids As Robust Electrocatalysts in Polymer Electrolyte Membrane Fuel Cells
Authors: Yarar Kaplan Begüm , Haghmoradi Navid , Biçer Emre , Alkan Gursel Selmiye
Published: February 2020

Graphene has been utilized as an alternative catalyst support for new generation polymer electrolyte membrane fuel cell (PEMFC) with many outstanding properties which are associated with its 2 dimensional (D) structure [1]. However, restacking of individual graphene layers and the aggregation of platinum (Pt) nanoparticles result in low Pt utilization and low catalytic activity [2,3]. To overcome this problem, herein Pt nanoparticles supported on reduced garphene oxide-carbon black hybrids (rGO-CB) were synthesized by one-pot microwave-assisted synthesis (Figure 1.a). In this one step approach, not only restacking of graphene sheets was avoided by using CB but also Pt nanoparticles impregnated on both graphene and CB. By means of homogenous mixing of GO and CB, 3D CB was placed between the 2D graphene sheets. Therefore, the resultant hybrid possessed higher Pt utilization. In this study, hybrid catalysts were synthesized in varying ratios of GO:CB and optimum GO:CB ratio was selected. Structure of resultant catalysts were confirmed by Raman Spectroscopy, X-ray Diffraction (XRD), X-Ray photoelectron spectroscopy (XPS) and Transmission Electron Microscopy (TEM) techniques. The average diameter of the Pt nanoparticles was about 2-3 nm from TEM micrographs (Figure 1.b). Electrocatalytic activity of prepared catalysts towards fuel cell reactions (HOR and ORR) were investigated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The hybrid electrocatalyst was exhibited a much higher HOR and ORR catalytic activities than a Pt/rGO and Pt/CB electrocatalyst by enhanced utilization of Pt. Moreover, gas diffusion electrodes and membrane electrode assemblies were fabricated by using synthesized electrocatalysts and tested in the PEMFC. Pt/rGO-CB hybrid delivered a superior PEMFC performance with a maximum power density of 1091 mW cm-2 in comparison to those of Pt/rGO and Pt/CB.

References:

1) A.K. Geim and K.S. Novoselov. Nat Mater, 6,183-91 (2007)

2) L.T. Soo, K.S. Loh, A.B. Abu Bakar Mohamad , W.R.W. Daud, and W.Y.Wong. Appl Catal A, 497, 198–210 (2015)

3) S.H. Cho, H.N. Yang, D.C. Lee, S.H. Park, and W.J. Kim. J Power Sources, 225, 200-6 (2013)

Figure 1
Functionalized TiO2 Supported Pt Nanocatalysts for Oxygen Reduction Reaction in PEMFCs
Authors: Hwang Bing Joe , Su Wei-Nien , Shieh Bing-Jen , Tsai Mon-Che
Published: February 2020

The activity and durability of the catalysts used for the oxygen reduction reaction (ORR) are crucial to the commercialization of polymer electrolyte membrane fuel cells (PEMFCs). Pt is still the most common catalytic material for the PEMFCs. Many factors, such as the catalyst’s composition, size, shape, support, and adsorbates, are related to the catalyst’s performance; such matters have been extensively studied over the past several decades in pursuit of high ORR activity, long term stability, and reduced Pt consumption. Titanium oxidebased materials compared to traditional carbon supports have been seen as promising supports for nanosized catalysts in electrochemical applications because of their low cost, nontoxicity, and high stability in acidic and oxidative environments1,2. In this presentation, dual doping of anatase TiO2, used as a Pt catalyst support, both augments resistance against the carbon corrosion that commonly occurs in oxygen reduction reaction (ORR) Pt/C catalysts and promotes the generation of oxygen vacancies that allow better electron transfer from the nanosupport to Pt, thereby facilitating the oxygen dissociation reaction. The effects of the oxygen vacancies within the doped TiO2 nanosupport on ORR activity and stability are investigated both experimentally and by density functional theory analysis. The mass activity of Pt supported doped anatase TiO2 is shown to be 9.1 times higher than that of a commercial standard Pt/C catalyst after hydrogen reduction3. The oxidesupported nanocatalysts also show improved stability against Pt sintering under during cycling, because of strong metal−support interactions (SMSI).

References

1. VTT Ho, BJ Hwang et al., “Nanostructure Ti0.7Mo0.3O2 Support Enhances Electron Transfer to Pt:

Used as High Performance Catalyst for Oxygen Reduction Reaction”, 2011, J. Amer. Chem. Soc., 133,

11716–11724.

2. CJ Pan, BJ Hwang et al., “Tuning/exploiting Strong MetalSupport Interaction (SMSI) in Heterogeneous Catalysis”, 2017, J. Taiwan Inst. Chem. Eng., DOI.org/10.1016/j.jtice.2017.02.012.

3. MC Tsai, BJ Hwang et al., “Interplay between Molybdenum Dopant and Oxygen Vacancies in a TiO2

Support Enhances the Oxygen Reduction Reaction”, 2016, ACS Catalysis, 6 (10), 6551–6559.
Pt-Ni/WC Alloy Nanorods Arrays as ORR Catalyst for PEM Fuel Cells
Authors: Begum Mahbuba , Yurukcu Mesut , Yurtsever Fatma , Ergul Busra , Kariuki Nancy , Myers Deborah J , Karabacak Tansel
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) among the other types of fuel cells technology are attractive power sources especially for electric vehicle applications. Even though there is ongoing progress and plausible prospects of PEMFCs, there are several challenges that need to be overcome to make them successfully and economically viable. One of the most important concerns in a PEMFC is the sluggish kinetics of the cathodic oxygen reduction reaction (ORR) that requires an expensive platinum (Pt) catalyst with high weight loadings (~0.3 mg/cm2) to meet the power requirements, which is mostly responsible for the high cost of PEMFCs. Therefore, reduction in the major cost of the system can be achieved by increasing the ORR kinetics of platinum-based catalyst and by more efficient utilization of the Pt component. In addition, carbon support used in conventional Pt/C catalyst present problems including oxidation of carbon, formation of peroxide species causing degradation of polymeric membrane, and separation from the ionomer over time leading to loss of catalyst effectiveness. For this purpose, we developed vertically aligned nanorod arrays of tungsten carbide (WC) as a support and coated them with platinum-nickel (Pt-Ni) alloy shell. A glancing angle deposition (GLAD) technique was used to fabricate the WC nanorod arrays and the shell comprised of different atomic ratios of Pt:Ni prepared by a small angel deposition (SAD) technique for conformal thin film coating. We utilized a multi-source sputter deposition unit that is capable of performing GLAD and SAD in the same chamber. In our design, WC nanorods offer advantages including higher electron conductivity, thermal and chemically stability, compared to the conventional carbon support. In addition, GLAD WC nanorods are coated with SAD Pt-Ni thin film in the same deposition unit without breaking the vacuum allowing to minimize surface oxidation resulting in decreased contact resistance between Pt-Ni and WC. Moreover, Pt-Ni alloy shell can achieve superior ORR activity due to expected electronic and geometric effects. Pt-Ni/WC nanorods were deposited on glassy carbon electrodes and as well as on silicon substrates for evaluation of their electrocatalytic ORR activity and physical properties. Cyclic voltammetry and rotating disk electrode experiments were performed in a 0.1 M HClO4 electrolyte at room temperature to characterize the ORR activity and activity stability of Pt-Ni/WC nanorods. Scanning electron microscopy and X-ray diffraction methods were utilized to study morphology and crystallographic properties, respectively.