bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Local Electrode Potentials in an Operating PEMFC Exposed to Contaminants
Authors: Spendelow Jacob S , Castanheira Luis , Hinds Gareth , Rockward Tommy , Langlois David A. , Mukundan Rangachary , Borup Rod L.
Published: February 2020

The use of a three-electrode cell, in which the potential of a working electrode can be accurately measured vs. a reference electrode (RE), is a standard practice in liquid-phase electrochemical experiments. However, the geometric constraints of a working PEMFC make use of a RE challenging. Incorporation of a RE into an operating PEMFC typically requires experimental compromises that prevent precise and accurate measurements from being obtained, and do not allow accurate spatial resolution of potential variation along the electrodes. As a result, PEMFC experiments are often performed using the PEMFC anode, which remains within a few mV of 0 V vs RHE during typical operation, as a pseudo RE.

Recently, the National Physical Laboratory (NPL) developed an effective technique for accurate in situ monitoring of local electrode potentials in a PEMFC. By inserting REs from the back side of the MEA, the NPL configuration eliminates the edge effects, lack of anode vs. cathode specificity, Ohmic losses, and current density distribution disruptions that have compromised previous fuel cell RE experiments.

We report here on the use of this RE technique to monitor local electrode potentials in an operating PEMFC during exposure to CO gas (Figure 1). CO is a common impurity in H2 gas and is known to poison Pt-based anodes. Levels of CO present in H2 fuel are expected to be in the ppb range for cells operating on pure H2 and the ppm range or higher for cells operating on reformate. Use of an RE can reveal the distribution of CO losses, and can also enable losses on the anode to be distinguished from those on the cathode. The results of this work demonstrate a new diagnostic capability that enables improved understanding of local conditions during PEMFC operation during transient or steady state operation.

Figure 1. Cell voltage (orange) and anode potential (blue) of a MEA operating at 1 A/cm2 with anode exposed to 20 ppm CO. CO was removed from the anode feed at t = 47 min. Gore MEA, with anode/cathode loading of 0.4/0.1 mg/cm2, 80°C, 100% RH, 100 kPaabs.

Figure 1
Bipolar Membrane Design for Hybrid PEM/AEM Fuel Cells
Authors: Ahlfield John M. , Liu Lisha , Chu Deryn , Kohl Paul A
Published: February 2020

Bipolar membranes fuel cells utilizing both anion and cation conductive materials have several advantages compared to their purely acidic or alkaline counterparts. The potential advantages include improved water management through self-hydration and facile electrode kinetics. Material transport properties play an important role in determining viability of membrane and ionomer materials. In addition, the cation-anion junction itself is a critical element in determining device performance because it must be sufficiently conductive to ionic species and mechanically stable to withstand the internal pressure from water formation. A series of electrochemical devices using different bipolar membranes have been fabricated for use in direct methanol and hydrogen fuel cells. This study examines both single- and two-membrane systems containing cation-anion junctions. These fuel cells were characterized by performance metrics and electrochemical impedance spectroscopy to determine specific areas for improvement in the bipolar devices. Operation under varying humidity was studied in order to understand water management necessary for bipolar fuel cells. These results will be used in the future optimization of bipolar devices.

Financial support from US Office of the Deputy Assistant Secretary of the Army for Defense Exports and Cooperation (DASA-DE&C) is gratefully acknowledged.
CNTs Grown on Al2O3 Spheres As an Efficient Catalyst Support for High Performance MEA in PEM Fuel Cells
Authors: Lim Eun Ja , Chang Kwang Hyun , Cho Seonghun , Park Seok-Hee , PARK Gu-Gon , Yim Sung-Dae
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have been widely accepted as a clean energy device because of its capability of generating high energy density and only water as a product via direct converting of the chemical energy into the electrical energy. However, durability problems originating from the carbon corrosion and Pt agglomeration have been one of the major issues for practical applications. The high potentials formed in a cell during the fuel cell operations lead to serious carbon corrosion in catalyst layers, which causes the decrease of cell performance. To resolve the carbon corrosion, highly durable carbon materials such as carbon nanotubes (CNTs) have been intensively studied. Although the corrosion-resistant characteristics of CNTs were efficient to utilize as an electrocatalyst support for PEMFCs, the difficulty in processing the CNTs mainly due to poor dispersibility and easy bundle formation in a catalyst ink limited their practical applications. In this respect, vertically aligned carbon nanotubes (VACNTs) have been tried and showed promising results in a PEMFC MEA. However, VACNTs need complex process to make MEAs, remaining the issues of mass production.

In this work, we report CNTs grown on Al2O3 (Al2O3-CNT) as an efficient support material for PEMFC MEAs. The catalyst support was designed to utilize durable CNT properties while resolving the CNT bundling problems. The catalyst was characterized by transmission electron microscope (TEM), field emission scanning spectroscopy (FESEM), and X-ray photoelectron spectroscopy (XPS) in order to investigate structural and electronic properties. The kinetics of O2 reduction is examined with the rotating disk electrode (RDE) technique. A potential cycling test was applied to evaluate durability of the catalyst. The electrochemical surface area (ECSA) of Pt/Al2O3-CNT slightly decreased (17 %), while Pt/C loses nearly 46 % of its ECSA of its initial value over repeated cycling test under carbon corrosion potential range, representing more durable properties of CNTs. The single cell test was also performed with Pt/Al2O3-CNT and Pt/C after fabricating the catalysts to MEAs. The performance of the Pt/Al2O3-CNT was comparable to that of Pt/C and showed better performance at high current density regions. Furthermore, after the accelerated stress test (AST), the Pt/Al2O3-CNT also showed approximately 2 times higher stability than Pt/C in a single cell test.
Synthesis of Highly Crosslinked Polymer/Inorganic Membranes and Discussion of the Resulting High Proton Conductivity and Chemical Stability
Authors: Motz Andrew R , Horan James L , Kuo Mei-Chen , Herring Andrew M
Published: February 2020

Heteropoly acids (HPA)s are a large class of inorganic acids that are known to have extremely high proton conductivities.[1] It has been demonstrated that doping perfluorinated sulfonic acid and hydrocarbon-based membranes with HPA is able to improve protonic conductivity, particularly under reduced humidity and elevated temperatures, but this method suffers from a lack of stability to water.[2,3] Even when the cesium salt (water-insoluble) is used, it is likely that agglomeration will occur overtime, as the HPA is not truly immobilized. Silicotungstic acid (SiW12O40
-4) is of particular interest for use in a fuel cell because it has been shown to be stable under relevant conditions.[4]

In an effort to mitigate agglomeration and water instabilities that plague most HPA containing films, we have covalently attached silicotungstic to 3M FC-2145 (polyvinylidene-co-hexafluoropropylene), forming a highly crosslinked polymer/hybrid network. First, phenol phosphonic acid (PPA) side chains are attached to FC-2145, and then two PPA groups react with a single, mono-lucunary silicotungstic acid (SiW11O39
-8), thus forming covalent crosslinks. This synthesis produces materials that have loadings of HPA, stable to boiling, in excess of 60wt%. The resulting material has high proton conductivity (>200 mS/cm at 90°C/95%RH) under humidified conditions as well as relatively high proton conductivity (>30mS/cm at 110°C/50%RH) under lower humidity conditions. This talk will include discussion on synthesis, transport properties, and preliminary chemical stability.

References:

[1] Nakamura, O.; Kodama, T.; Ogino, I.; Miyake, Y., High-Conductivity Solid Proton Conductors - Dodecamolybdophosphoric Acid and Dodecatungstophosphoric Acid Crystals. Chemistry Letters 1979, 17-18.

[2] Meng, F.; Aieta, N. V.; Dec, S. F.; Horan, J. L.; Williamson, D.; Frey, M. H.; Pham, P.; Turner, J. A.; Yandrasits, M. A.; Hamrock, S. J.; Herring, A. M., Structural and transport effects of doping perfluorosulfonic acid polymers with the heteropoly acids, H3PW12O40 or H4SiW12O40. Electrochimica Acta 2007, 53, 1372-1378.

[3] Wang, Z.; Ni, H.; Zhao, C.; Li, X.; Fu, T.; Na, H., Investigation of sulfonated poly(ether ether ketone sulfone)/heteropolyacid composite membranes for high temperature fuel cell applications. Journal of Polymer Science Part B: Polymer Physics 2006, 44, 1967-1978.

[4] Sweikart, M. A.; Herring, A. M.; Turner, J. A.; Williamson, D. L.; McCloskey, B. D.; Boonrueng, S. R.; Sanchez, M., 12-Tungstophosphoric Acid Composites with Sulfonated or Unsulfonated Epoxies for High-Temperature PEMFCs. Journal of The Electrochemical Society 2005, 152, A98.
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.
Low Platinum Content Catalyst on the Non-Stoichiometric Tungsten Oxide Based Catalyst Support for the Increased CO Tolerance in PEMFC
Authors: Marceta Kaninski Milica P , Brkovic Snezana M , Perovic Ivana M , Lausevic Petar Z , Saponjic Djordje P , Pasti Igor A , Nikolic Vladimir M
Published: February 2020

Abstract

Cost and durability are two major factors that delay large-scale production and commercialization of PEMFC’s. One of the technologically ready application of the proton exchange membrane fuel cells (PEMFC) is in the combined heat and power systems (µCHP), which are used in the individual households or buildings. The performance of the µCHP systems greatly depends on the purity of the hydrogen stream, which is produced via methane reforming process. To overcome low CO tolerance of the commercially used Pt electrocatalyst and to lower the catalyst content we have prepared non-stoichiometric tungsten oxide as a Pt based catalyst support. We have prepared several catalysts designated as 10% Pt/WO3-C, 20% Pt/WO3-C, 40% Pt/WO3-C. The structure and morphology characteristics of the prepared catalysts were investigated using XRD, TEM and SEM/EDX techniques. Investigations concerning electroactivity of these catalysts towards the hydrogen oxidation reaction (HOR) were performed using cyclic voltammetry, linear sweep voltammetry, forming an ultra thin catalyst layer onto RDE. Mechanism and the kinetics of the prepared catalysts towards HOR were evaluated and if was found that increased mass activity of the 10% Pt/WO3-C could be attributed to the interactive naure of the WO3 catalyst support. Obtained results clearly show increased CO tolerance of Pt/WO3-C catalyst compared to commercial Pt/C, which was confirmed by lowering the stripping potential of the CO, adsorbed on the surface of the 10% Pt/WO3-C. catalyst is more facile than that on commercial 40% Pt/C. These catalysts were employed as anode catalyst in the MEA, and the performance of single cell PEMFC were compared to commercial catalyst.
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.
Synergetic Effects of Edge Formation and Sulfur Doping in Graphene-Based Catalyst for an Efficient Oxygen Reduction Reaction
Authors: Oh SeKwon , Kim Jong Hoon , Kim MinJoong , Park Jeong Young , Cho EunAe , Kwon HyukSang
Published: February 2020

As an effort to enhance oxygen reduction reaction (ORR) activity of transition metal –nitrogen–graphene (M-N-C) catalysts, we propose a facile and effective strategy through forming edge site and doping S in M-N-C by facile ball milling method. The ORR performance of edge activated S doped Fe-N-graphene (EA-SFeNG) was dramatically enhanced than that of Fe-N-graphene by doping S and forming edge site. Its onset potential and half wave potential were positively shifted from 0.91, 0.77 VRHE to 1.02, 0.848 VRHE respectively, which was comparable to commercial 20 wt.% Pt/C (Vonset: 1.05V, V1/2: 0.865V) and it also exhibit better stability than Pt/C in alkaline media. The reasons for the high ORR activity can be attributed to the increase in defect density and the formation of SOx from the XPS and Raman analysis. Furthermore, we also experimentally confirm the correlation between ORR activity and the promoting factors (doping S, forming edge site) through measurement of work function by kelvin probe force microscopy. The KPFM results showed that doping S and edge activation treatment in FeNG reduce its work function from 4.10 eV to 4.01 eV, which facilitated ORR kinetics of EA-SFeNG.
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.
Emergence of Oxygen Reduction Activity in Niobium-Doped Titanium Oxides As Non-Platinum Cathode for PEFCs
Authors: Ishihara Akimitsu , Arao Masazumi , Yogi Chihiro , Matsumoto Masashi , Imai Hideto , Wu Chumeng , Nagai Takaaki , Matsuzawa Koichi , Napporn Teko W. , Mitsushima Shigenori , Ota Ken-ichiro
Published: February 2020

Development of non-platinum electrocatalysts for oxygen reduction reaction (ORR) is required for wide commercialization of polymer electrolyte fuel cells. We focused on titanium oxide-based electrocatalysts, because of their high chemical stability and much less expensive than platinum. We found that Ti-Nb complex oxide mixed with magneli phase titanium oxide (Ti4O7) had high ORR onset potential and superior durability [1]. However, the ORR current was small because of their large particle size. In this study, we have tried to prepare titanium oxide-based nano particles using multi-walled carbon nano-tubes (CNTs) as support via hydrolysis method. We examined the effect of heat-treatment condition such as temperature and time on the ORR activity. We prepared Nb doped titanium oxide [mass ratio of TiO2:Nb2O5= 8:2] supported CNTs with total oxide mass ratio of 20wt%. These catalysts were heat treated at 600-900 oC for 0-60 min under 4%H2/Ar atmosphere. The catalyst without heat-treatment had poor ORR activity. The heat-treatment under reductive atmosphere enhanced the ORR activity of the catalysts. Figure 1 shows the dependence of the ORR current at 0.6 and 0.7 V of the catalysts prepared at several temperatures for 10 min under 4%H2/Ar in 0.1M H2SO4 at 30 oC. The catalyst prepared at 800 oC showed highest ORR activity. The SEM observation indicated that the sizes of the oxide-based particles were around 20 nm for all catalysts with and without heat treatment. Therefore, the surface area of the oxide-base particles was almost the same. The dependence of the ORR activity was not responsible for the change of the surface area. The XRD patterns revealed that the catalyst without heat treatment was composed of anatase phase of TiO2, and the peaks due to the rutile TiO2 apparently appeared at around 700-800oC. In particular, the peaks due to Rutile TiO2 shifted at lower angular, suggesting that the niobium doped into the TiO2 phase. Thus, the Nb doping into rutile TiO2 could affect the ORR activity. Figure 2 shows the Ti 2p XPS spectra of these catalysts. As shown in Fig.2, the peak at 457.8 eV corresponding to Ti3+ (Ti2O3) as well as the peak at 459.2 eV corresponding to Ti4+ (TiO2) were observed. The peak due to Ti3+ increased from 600 to 800 oC, and decreased at 900oC. This behavior was well corresponded to the ORR activity. Therefore, we concluded that Ti3+ could act as active sites for the ORR. According to the XRD patterns, the Nb doping into rutile TiO2 proceeded with increasing the temperature from 700 to 800oC. The niobium doping generated the Ti3+ via electro-neutral principle. The formation of the Ti3+ in TiO2 rutile phase was considered to be essential for emergence of the ORR. [1] A. Ishihara et al., J. Electrochem. Soc, 163(7), F603 (2016).

Figure 1
Determining Membrane Degradation in Polymer Electrolyte Fuel Cells by Effluent Water Analysis
Authors: Bodner Merit , Rami Mija , Marius Bernhard , Schenk Alexander , Hacker Viktor
Published: February 2020

The degradation of the polymer electrolyte is one of the dominant factors, which limits the lifetime of the polymer electrolyte fuel cells (PEFCs). Therefore, the understanding and mitigation of all contributing degradation phenomena is fundamental in order to establish the PEFC as competitive product.

Membrane degradation is often quantified by analysing the fluoride emission rate by determining the fluoride content in the effluent water. However, when oligomers (i.e. larger polymer fragments) are released, the ion conductivity of the ionomer declines without extensive fluoride release, as the carbon backbone fluorine bonds are still intact. Thus, it is necessary to conduct effluent water treatment in order to determine the total fluorine emission rate (tFER) instead of the fluoride emission rate (FER) only [1].

In the presented work, an accelerated stress test (AST) was conducted in a single cell with a segmented S++ current scan shunt device with a sensor plate on the cathode for spatial current and temperature measurements in 10x10 and 5x5 segments, respectively. A membrane electrode assembly was characterised in situ [2]. Throughout 100 hours of stress testing, the effluent water was collected and used to determine the FER, using a fluoride selective electrode (Figure 1) [3]. Furthermore, effluent water samples were treated with KOH following different protocols. The alkaline treatment decomposes residual ionomer fragments for the detection of the total fluorine emission rate. The tFER allows more profound assumptions regarding the extent of the membrane degradation and further, gives insight into the underlying degradation mechanism.

In preliminary results it is shown that by conducting alkaline effluent water treatment at a temperature of 500 °C the amount of detected fluoride was increased significantly (Figure 2). Thus it can be concluded that not all emitted fluorine is detectable without previous treatment, indicating that the electrolyte membrane decomposes into oligomeric fragments.

Acknowledgement

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n° 621216.

[1] Aarhaug TA, Svensson AM. Degradation Rates of PEM Fuel Cells Running at Open Circuit Voltage. ECS Trans., vol. 3, ECS; 2006, p. 775–80. doi:10.1149/1.2356197.

[2] Bodner M, Cermenek B, Rami M, Hacker V. The Effect of Platinum Electrocatalyst on Membrane Degradation in Polymer Electrolyte Fuel Cells. Membranes (Basel) 2015;5:888–902. doi:10.3390/membranes5040888.

[3] Bodner M, Hochenauer C, Hacker V. Effect of pinhole location on degradation in polymer electrolyte fuel cells. J Power Sources 2015;295:336–48. doi:10.1016/j.jpowsour.2015.07.021.

Figure 1
Detection of Superoxide Anion Radical in Anion Exchange Membrane Fuel Cells Using in-Situ Fluorescence Spectroscopy
Authors: Zhang Yunzhu , Ramani Vijay K
Published: February 2020

Anion exchange membrane (AEM) stability is a long-standing challenge that has limited the widespread development and adoption of AEM fuel cells. It is essential to understand the mechanism of AEM degradation during fuel cell operation. There are multiple modes of AEM degradation, broadly classified as chemical, mechanical and thermal degradation. Chemical degradation is among the most destructive modes, and can be further sub-divided into nucleophilic degradation (induced by the hydroxide ion), and oxidative degradation (induced by reactive oxygen species). While the former has been extensively studied, there is minimal work on oxidative AEM degradation.

The reactive oxygen chemical species produced during the operation of an AEM fuel cell have hitherto not been detected during operation. Given the high pH, it is postulated that superoxide anion radicals (O2
·-), as opposed to hydroxyl radicals, are primarily involved in the degradation progress. The objective of this study was to confirm the O2
·- formation during AEM fuel cell operation and to monitor in real-time the rate of O2
·- generation in an operating fuel cell using in-situ fluorescence spectroscopy.

1,3-diphenlisobenzofuran (DPBF) was chosen as the fluorescence probe, the sensitivity of which towards O2
·- was evaluated by performing ex-situ experiments in a semi-batch reactor. We demonstrate that the fluorescence intensity of this dye selectively decreased upon exposure O2
·-. DPBF was then incorporated into an AEM (membrane was solution cast after mixing the dye with the casting solution), which was assembled into a fuel cell. O2
·-
 generation in an operating AEM fuel cell was then monitored via in-situ fluorescence spectroscopy using a bifurcated optical probe, when the cell was operated in H2/O2 mode. To confirm the impact of O2
·-
  on AEM degradation, independent experiments (without dye) were performed under identical conditions, under both H2/O2 and N2/N2 modes, and the ionic conductivity and ion exchange capacity were monitored to estimate degradation extent. From our in-situ fluorescence studies, we were able to estimate the rate constants and activation energy for oxidative AEM degradation in an operating AEM fuel cell.
CO2/H2o High Temperature Co-Electrolysis Using LaFeO3-Based Oxide Cathode
Authors: Wu Kuan-Ting , Ishihara Tatsumi
Published: February 2020

An increasing awareness of severe environmental impact has been seriously concerned due to the increasing demand for energy, the diminishing resources of fossil fuels, and the tremendous effects on climate change. An important indication is from global warming effect, caused by effluent greenhouse gas emission (mainly CO2). Therefore, efficient management and utilisation of CO2 and energy (generation and storage) are required attention urgently. Co-electrolysis of steam and CO2in a solid state electrolysis cells (SOECs) is a promising strategy, which may provide an approach to not only effectively reduce climate impact, but also produce useful fuels (such as syngas and hydrocarbon source) through waste heat. Thus, this allows the conversion of electricity into a fuel, while giving new opportunities for efficient and effective use of energy.

Ni-based cermet materials are usually used as fuel electrodes for SOECs, while constant circulation of reducing gas (H2 or CO) is required in order to prevent the oxidation of the metallic phase, which can lead to an issue of long-term operation. In addition, the stability of the conventional cathodes applied in electrolyser is still required to be much improved. Hence, decrease in degradation rate is essential for the application of high-temperature electrolyser. Therefore, utilisation of oxides as fuel electrodes has been highly suggested instead of metallic based electrodes. Previous our study has reported a promising LaFeO3-based perovskite material as a fuel electrode for CO2 electrolysis, showing a good activity and cell performance for CO2 reduction without carbon formation.[
1
]

In this study, we further investigate co-electrolysis of CO2 and steam, using LSGM and LaFeO3-based materials for the electrolyte and cathode, respectively. Galvanostatic measurements and electrochemical impedance spectroscopy has been conducted to investigate the cell performance. A comparable current density of over ~0.61 A/cm2 has been achieved at ~1.6 V and 800°C. This study was focused on the formation of the syngas CO/H2 in operation. The content of the product gases was measured by gas chromatography installed with a thermal conductive detector. As Ni-based cermet is used as a cathode, a H2-enriched gas composition was formed particularly at < 800°C because of the dominant electrolysis of H2O and water-gas shift reaction (CO+H2O↔CO2+H2). However, in case of LaFeO3-based perovskite oxide cathode, a reasonable electrolysis current was achieved and the CO/H2 ratio in product was similar to the CO2/H2O in feeding composition. This suggests that LaFeO3-based oxide is active to CO2 electrolysis and presents low activity for water-gas shift reaction. Therefore, using LaFeO3-based oxide as a cathode of a co-electrolyser may be feasible for the control of CO/H2 ratio.

[1] T. Ishihara, K.-T. Wu, S. Wang, ECS Trans. 2015, 66, 197.