bluuebunny/crossref_metadata_2025_split huggingface dataset:
Laboratory-Scale Method for Fabricating High Performance Catalyst-Coated Membranes and Membrane Electrode Assemblies
Authors: Garsany Yannick , Sassin Megan B. , Gould Benjamin D. , Swider-Lyons Karen 
Published: February 2020

Laboratory-made membrane electrode assemblies (MEAs) for proton exchange membrane fuel cells typically perform poorly compared to commercial ones. A key issue is the difficulty with making a high performance catalyst coated membranes (CCMs) at the laboratory scale by unautomated processes that often leads to irreproducible results due to lack of control of important parameters in the catalyst layer (CL). We have developed a method to fabricate reproducible CCMs with high activity using direct ultrasonic spray deposition of electrocatalysts onto a heated commercial perfluorosulfonic membrane. The CCMs are optimized by varying the number of catalyst layers sprayed, the height of spay nozzle from the membrane, and the pressure used for hot pressing on CLs after spraying. Nitrogen adsorption and scanning electron microscopy (SEM) are used to investigate the effects of ionomer/carbon ratio (I/C) on the surface area, pore structure and morphology of the CLs. How the CCMs are assembled into MEAs is another key issue in the fuel cell performance, particularly the compression, which governs the porosity of the CL and gas diffusion media and resistance. The resulting MEAs are analyzed by I-V polarization, cyclic voltammetry and electrochemical impedance spectroscopy. A comparative study is also made with CCMs prepared with low equivalent weight Nafion ionomer in the CLs. Operating the cell at 80°C and 50 % RH, a cell voltage of 0.6 V a current density of 971 ± 41mA cm-2 is achieved in Air/H2 at a stoichiometric ratio of 2/2 at ambient pressure and increased to 1432 ± 131 mA cm-2 at a back pressure of 150 KPa. These tools can be used to guide the laboratory development and understanding of new catalyst layer structures and catalyst compositions.
Monolithic Carbon Foam-Supported Pd-Ni Catalysts for Ethanol Electro-Oxidation in Alkaline Media
Authors: Li Yinshi 
Published: February 2020

Anion-exchange membrane direct ethanol fuel cells are attractive owing to the fact that: i) the alkaline media speeds up the electro-kinetics of both the ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR), ii) low-cost Pd catalyst presents better catalytic activity for the EOR than Pt in alkaline environment, and iii) the ethanol possesses the advantages of high-specific energy and producing from cellulosic biomass.
Carbon foam promises to be a better monolithic catalyst support due to its three-dimensional honeycomb-type open cell structure, resulting in the high porosity and the large specific surface area [1]. In this work, the carbon foam-supported PdNi nanocatalysts (PdNi/CF) were synthesized by the layer-reduction method using NaBH4 as a reductant [2], and characterized by different physicochemical methods. The experimental results indicated that the PdNi nanocatalysts were evenly dispersed on the surface of the skeleton of the carbon foam, facilitating the mass and charge transfer. The electrocatalytic activity of PdNi/CF was optimized by testing different Pd/Ni atomic ratios. It has been demonstrated that the electrocatalytic activity of PdNi/CF was higher than that of Pd/CF, suggesting promising application in alkaline direct ethanol fuel cells.

References

[1] Y.S. Li, J.H. Lv, Y.L. He, A Monolithic Carbon Foam-Supported Pd-Based Catalyst towards Ethanol Electro-Oxidation in Alkaline Media, J. Electrochem. Soc., 2016, 163 (5): F424-F427.
[2] Y.S. Li, Y.L. He, Layer Reduction Method for Fabricating Pd-coated Ni Foams as High-performance Ethanol Electrode for Anion-exchange Membrane Fuel Cells, Rsc Adv., 2014, 4 (32): 16879-16884.
Metallocomplex-Based Electrocatalysts for the Oxidation of Hydrazine Derivatives
Authors: Yamazaki Shin-ichi , Asazawa Koichiro , Tanaka Hirohisa , Ioroi Tsutomu 
Published: February 2020

Hydrazine hydrate, which has high energy density, is one of desirable fuels for direct fuel cells. However, toxicity and volatility of this compound might prevent the wide spread of direct hydrazine hydrate fuel cells. In this context, hydrazine derivatives such as N, N-diaminourea (DAU) and methyl carbazate would be a possible remedy for this problem. These hydrazine derivatives are solid, and evaporation of them would be suppressed. Unfortunately, conventional metal catalysts such as Ni, Pt, and Co hardly oxidize these hydrazine derivatives.
In this work, we report a metallocomplex-based electrocatalyst for the oxidation of hydrazine derivatives. These catalysts completely differ from conventional metal-based electrocatalysts in that single atoms form active sites, and hence new oxidation activity would be expected.
We examined metalloporphyrin-based electrocatalysts for the oxidation of DAU. These complexes can oxidize DAU to give considerable current, while conventional Pt catalysts cannot oxidize DAU. The catalytic activities depend on the kinds of central metals; Co-, Rh-, Fe-, Ru-porphyrins give high current. The catalytic activity increased with the change in the ligand from porphyrins to phthalocyanines. Especially, Fe phthalocyanine gave high catalytic activity for the oxidation of DAU; the current exceeded 150 mA/cm2 at 0.6 V vs. a reversible hydrogen electrode (RHE).
There are two possible pathways of the electro-oxidation of DAU by Fe-PC: (1) DAU is directly oxidized by the electrode (direct pathway) and (2) DAU undergoes hydrolysis to produce hydrazine, and the generated hydrazine is oxidized by the electrode (indirect pathway). HPLC analysis and the dependence of the activity on the concentrations of DAU and hydrazine revealed that the oxidation of DAU proceeds mainly via a direct oxidation pathway.
Finally, we made a membrane electrode assembly (MEA) using Fe-PC as an anode catalyst, and examined the performance of the MEA (cathode catalyst is Pt/C and anion-exchange membrane is A201 (Tokuyama)). The cell gave a considerable power; open circuit potential is close to 0.6 V, and the short-circuit current is 180 mA/cm2 at 80 °C. To the best of our knowledge, this is the first report of a polymer electrolyte fuel cell that uses Fe-PC as an anode catalyst, while the electro-oxidation activity of Fe-PC has been studied for several decades.
The authors are grateful to Tokuyama Corporation for donating an ionomer (AS-4) and A201 membrane.
GISAXS Analysis for Ionomer Thin Films
Authors: Dudenas Peter , Kusoglu Ahmet , Hexemer Alex , Weber Adam Z 
Published: February 2020

Perfluorinated sulfonic-acid (PFSA) polymers are a class of ion-conducting polymers (ionomers) heavily utilized in fuel cells and similar electrochemical technologies. The hydrophobic backbone gives excellent mechanical properties, while the side-chain terminated with a hydrophilic acid group bestows superior proton conductivity. The crystallinity of the backbone is believed to be inversely proportional to conductivity and proportional to the mechanical modulus in bulk membranes. Demonstrated previously, the transport and mechanical properties of PFSA ionomers deviate from bulk membranes as the ionomers are confined into thin-film geometries.[1]Under such confinement, conductivity and water uptake decrease, while the modulus increases. Studying this deviation from bulk behavior is crucial as ionomer is present as thin films in the catalyst layer of these electrochemical devices.
In this work, we correlate the relative crystallinity of PFSA thin-films, calculated from Grazing-incidence Wide-angle X-ray Scattering (GIWAXS), to their mechanical properties measured using a cantilever bending system.[2]Using a laser array, thin-film stress can be measured as a function of humidity from which mechanical properties are calculated. This system allows the study of thin films on hard impenetrable surfaces that induce confinement effects, and probe the effect of interfacial interactions on different substrates. Understanding crystallinity and mechanical properties as part of the structure-property relationship will allow optimization of ionomer performance within the catalyst layer.

Acknowledgement

This work was sponsored by the Army Research Office under MIPR0010754069. The work utilizes beamline 7.3.3 at the Advanced Light Source, which is funded by DOE Basic Energy Science under contract number DE-AC02-05CH11231.

References

1. Page, K.A., et al., Confinement-driven increase in ionomer thin-film modulus. Nano Lett, 2014. 14(5): p. 2299-304.
2. Page, K.A., et al., In Situ Method for Measuring the Mechanical Properties of Nafion Thin Films during Hydration Cycles. ACS Applied Materials & Interfaces, 2015. 7(32): p. 17874-17883.

Figure 1. The cantilever bending system utilizes a laser array to measure thin film stresses. The setup has been modified to also measure film swelling simultaneously. Stoney’s equation shows the relationship between the radius of curvature of the substrate and the force exerted by the film. Es is the Young’s modulus, hs is the thickness and vsis Poisson’s Ratio, all of the substrate

Figure 1
Fe/N Co-Doped Carbon Materials with Controllable Structure As Highly Efficient Electrocatalysts for Oxygen Reduction Reaction
Authors: Wang Haiyan , Shao Minhua , Chen Jiajie 
Published: February 2020

Recently, carbon materials functionalized with transition metals and nitrogen (labelled as Me-N-C, where Me = Fe, Co, etc.) have been reported as a competitive class of non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR).1,2 However, the intrinsic nature of the active site is poorly understood and still remained controversial.3,4 Various kinds of non-crystalline MeN
x
C
y
moieties5 or the crystalline metal-based nanoparticles encased in surrounding graphitic carbon layers6 have been proposed as the main active sites. Me-N-C composite pyrolyzed at high temperaturegenerally contained metal-based nanoparticles encapsulated in carbon layers that are hard to remove completely by acid leaching. As a result, the co-existence of metal-based nanoparticles and non-crystalline MeN
x
C
y
moieties on the carbon surface makes its further theoretical analysis and experimental characterizations very difficult.
Here we develop a novel template-free strategy (see Fig.1) to synthesize a series of iron and nitrogen co-doped carbon materials (Fe-N-C) with controllable structure for ORR. These catalysts with well-defined structures not only possess remarkable ORR activity but also provide unique models for probing active sites of Fe-N-C composites. The most active catalyst shows a half wave potential at 0.86 V, which is much higher than that of Pt/C with the same mass loading. The activities of various Fe-N-C catalysts synthesized by different methods will be compared and the correlation of the activity with the structure will be presented. Possible active sites will be discussed.
Fig. 1 Synthesis of ORR catalysts with four different kinds of typical morphologies and the corresponding LSV curves.

References

(1) Wu, G; More, K. L.; Johnston, C. M.; Zelenay, P. Science, 2011, 332, 443-447.
(2) Masa, J.; Xia,W.; Muhler, M.; Schuhmann,W. Angewandte Chemie International Edition, 2015, 54, 10102-10120.
(3) Hu,Y.; Jensen, J. O.; Zhang, W.; Cleemann, L. N.; Xing, W. N.; Bjerrum, J.; Li, Q. Angewandte Chemie

International

Edition,
2014, 53, 3675-3679.
(4) Zhu, Y.; Zhang, B.; Liu, X.; Wang, D. W.; Su, D. S. Angewandte Chemie

International Edition, 2014, 53, 10673-10677.
(5) Zitolo, A.; Goellner, V.; Armel, V.; Sougrati, M. T.; Mineva, T.; Stievano, L.; Fonda, E.; Jaouen, F. Nature Materials, 2015, 14, 937-942.
(6) Deng, D.; Yu, L.; Chen, X.; Wang, G.; Jin, L.; Pan, X.; Deng, J.; Sun, G.; Bao, X. Angewandte Chemie
International Edition, 2013, 52, 371-375.
Investigation of Microstructure, Porosimetry, Water Uptake and Proton Conductivity of Machine Prepared Catalyst Layers for Pemfcs
Authors: Cantillo Nelly M. , Neal Christopher A. , Goenaga Gabriel A. , More Karren L. , Zawodzinski Thomas A. 
Published: February 2020

In this study, a set of experimental techniques have been adopted to characterize the fundamental properties of machine prepared catalyst layers (CLs) formed by different Pt:C ratios, highly graphitized carbon and 3M ionomer (825EW). Single cell performance with these catalyst layers was evaluated in order to analyze the relationship with the structural properties.
Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) nitrogen adsorption were conducted in a series of CLs with Pt:C ratio variations at a fixed ionomer:carbon (IC) ratio to investigate the microstructure including materials dispersion and porosity. This analysis was performed on both the CL in a fresh (as-prepared) condition and after subjected to a standard PEMFC protocol.
TEM images along with Pt size distributions of the 50:50 Pt:C fresh and post-operation samples are shown in Fig. 1. A significant widening of the Pt size distribution and a possible tendency towards a multimodal distribution is observed after FC operation. This behavior can be explained by a combination of Pt particle coalescence and dissolution/re-precipitation processes within the solidionomer, as has been suggested in previous studies.1

In order to assess the ionomer behavior in the machine prepared CLs, proton conductivity measurements and estimation of the proton conduction tortuosity was performed as a function of relative humidity (RH) in the single cell. Water uptake isotherms of the as-prepared CLs have also been acquired under well controlled RH levels. In contrast to typical Nafion®-based fuel cells, the 3M fuel cell reached its optimum performance at 60%-70% RH and suffered dramatic mass transfer losses at saturated humidity levels. Therefore, the 3M fuel cells are able to function fully under drier conditions than the Nafion units. However, the high sensitivity to the cells’ water content requires efficient water management during operation, especially at higher current densities.

References

More, K.L., Borup, R., and Reeves K.S. ECS Transactions, 3 (1) 717-733 (2006)

Figure 1
Graphene Oxide-Based Non Precious Metal Catalysts for Oxygen Reduction Reaction with Improved Selectivity and Performance
Authors: Dumont Joseph H , Martinez Ulises , Purdy Geraldine M , Dattelbaum Andrew M , Zelenay Piotr , Atanassov Plamen , Mohite Aditya , Gupta Gautam 
Published: February 2020

Due to the high cost of Pt-based catalysts for the anode and the cathode of polymer electrolyte fuel cells (PEFCs), their commercialization and distribution have been limited. Non-precious metal catalysts (NPMCs) with high activity and low peroxide yields [1, 2] represent a viable option for replacing the Pt-based catalysts for oxygen reduction reaction in the PEFC cathode. Graphene and graphene oxide-based catalysts have shown promising properties, such as good chemical stability and excellent conductivity, and they can be modified in a controllable manner by inducing functionalities [3]. However, the ORR activity of nitrogen-doped graphitic systems is lower than that of conventional nitrogen-doped mesoporous carbons. This is primarily due to fewer active sites on the basal plane than graphene edges and, secondly, due the re-stacking of n-doped graphitic sheets that forms an impermeable film, which limits the diffusion of reactants to the active sites. These key challenges have precluded the use of N-doped graphene-oxide catalysts for practical applications. In this presentation, we will show how the treatment of graphene oxide with solvents chosen based on Hansen’s solubility parameters, followed by nitrogen doping, results in the formation of active ORR catalysts [4]. Furthermore, we will use electrochemical treatment to enhance the four-electron selectivity of catalysts in oxygen reduction. Structural, chemical, and morphological information by X-ray techniques (XRD and XPS) will be presented, along with electron microscopy (SEM, TEM). The ORR activity graphene of oxide-based catalysts in both alkaline and acidic media, determined using a rotating ring-disk electrode (RRDE), will be presented. The results of this study are expected to aide in the synthesis of well performing graphitic ORR electrocatalysts with tunable activity and could lead in the future to better understanding of the mechanism ORR active site formation.

Acknowledgement

Financial support from the Los Alamos National Laboratory, Laboratory-Directed Research and Development (LDRD) is gratefully acknowledged.

References

[1] Wu, G., More, K. L., Johnston, C. M., Zelenay, P., Science, 332, 443-447 (2011).
[2] Bashyam, R., Zelenay, P., Nature, 443, 63-66 (2006).
[3] Qu, L., Liu, Y., Baek, J.-B., Dai, L., ACS Nano, 4, 1321-1326 (2010)
[4] Martinez, U., Dumont, J. H., Holby, E. F., Artyushkova, K., Purdy, G. M., Singh, A., Mack, N. H., Atanassov, P., Cullen, D. A., More, K. L., Chhowalla, M., Zelenay, P., Dattelbaum, A. M., Mohite, A. D.,Gupta, G., Science Advances, 2, 3
Non-Precious ORR Catalyst for PEMFC Application Using Iron, Nitrogen and Sulfur Co-Doped Few Layer Graphene
Authors: Vinayan Bhaghavathi Parambath 
Published: February 2020

The sluggish kinetics of oxygen reduction reaction (ORR) at the cathode of proton exchange membrane fuel cells (PEMFC) demand a high loading of precious platinum (Pt) or Pt alloy electrocatalysts [1]. The extensive implementation of fuel cell technologies for stationary and vehicular applications, however, demands the replacement of high cost and less abundant Pt with low cost and natural abundant electrocatalysts. Recent studies show the use of various non-precious metals, metal alloys, metal oxides and nitrogen doped carbon as alternative catalysts for ORR [2, 3]. Even though, these non-precious metal catalysts experience severe dissolution and large agglomeration under vigorous PEMFC operational conditions and subsequent catalyst performance degradation. In this work, we developed a facile method for making non-precious ORR catalyst using nitrogen (3.7 at. %), sulfur (2.4 at. %) and iron (1.3 at. %) co-doped porous graphene (Fe-NSG). The ORR activity and durability of catalyst in acidic media was investigated by half (Fig. 1) and full cell electrochemical measurements. RDE measurements of the Fe-NSG catalyst confirm a four electron transfer ORR process with high current density. PEMFC full cell measurements of the catalyst give a maximum power density of 225 mW cm-2 at 80 °C with good stability [4]. The high ORR activity and good stability of Fe-NSG electrocatalyst can be ascribed due to, (a) the comparatively higher electronegativity of doped N and S atoms (N: 3.04, S: 2.58) with respect to carbon (C: 2.55), which induces more charged sites within the graphene lattice favorable for oxygen adsorption and reduction, (b) presence of the large amount of pyridinic nitrogen, which can coordinate with iron cations and increase the density of ORR active Fe-Nx centers, (c) an optimum amount of sulfur within the non-precious catalyst suppress the iron carbide formation, and increases the formation of Fe-N4 ORR active species, (d) the unique confined morphology of Fe nanoparticles within the graphene layers suppress the agglomeration/dissolution of metal particles and increase their interfacial contact and durability.

References

F. Jaouen, E. Proietti, M. Lefevre, R. Chenitz, J.-P. Dodelet, G. Wu, H. T. Chung, C. M.

Johnston and P. Zelenay, Energy & Environmental Science, 2011, 4, 114-130.

Z. Chen, D. Higgins, A. Yu, L. Zhang and J. Zhang, Energy & Environmental Science, 2011, 4, 3167-3192.

M. Lefèvre, E. Proietti, F. Jaouen and J.-P. Dodelet, Science, 2009, 324, 71-74.

B. P. Vinayan, T. Diemant, R. J. Behm and S. Ramaprabhu, RSC Advances, 2015, 5, 66494-66501.

Figure 1
Electro-Polymerized Metallocorroles As Electrocatalysts for Oxygen Reduction
Authors: Elbaz Lior , Levi Naomi , Mahammed Atif , Gross Zeev , Friedman Ariel 
Published: February 2020

The most active non-precious metal catalysts (NPMCs) for oxygen reduction (ORR) to date are the pyrolyzed catalysts, inspired from Heme-like complexes. These are usually composed of iron and/or cobalt coordinated by nitrogens, claimed to resemble the structure of porphyrins and phthalocynines, on the surface of a carbon support. Unfortunately, the exact structure of the catalytic sites remains a mystery and the solution for this conundrum seems be almost impossible. The advantages of using such catalysts are: (1) their high activity and (2) low price, which is derived from the cost of their precursors. The disadvantages are: (1) low durability compared to precious metal catalysts, and (2) their unknown structure, which limits their further improvement in order to obtain both the activity and durability benchmarks needed to become good alternatives for precious metals.
One of the most promising options to resolve these issues is to find non-pyrolyzed molecular non-precious metal catalysts for ORR that could be tuned to match the necessary requirements. Recently, Metallo-corroles, a relatively new family of molecular catalysts was reported to have very good potential as non-precious metal catalysts for ORR. Inspired from the extensive work on the electropolymerization of metalloporphyrins, and its merits, we electropolymerized of metallocorroles on carbon electrodes to (1) increase their site density in order to overcome their relatively low electrocatalytic turnover frequency (when compared to platinum) and (2) use the proximity of active sites to move from 2- to 4-electroreduction of oxygen. Metallocorroles substituted with anilines were studied and electropolymerized. They show a significant enhancement in the overpotential required for the execution of ORR and tendency for 4-electron reduction to water. The electropolymerization, its characterization and the effect on the electrocatalytic activity of the electropolymerized metallo-corroles vs. the monomers will be presented.