bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nickel/Carbide Based Catalysts for Oxygen Evolution Reaction in Alkaline Solution
Authors: Song DongHoon , Kim MinJoong , Cho EunAe 
Published: February 2020

Hydrogen, produced by electrolysis, is one of the most promising means to store electricity coming from renewables and to address its intermittency. Due to the increase of global electricity share from renewable energy sources, large-scale storage systems are required. Alkaline electrolysis can be a suitable solution for the large-scale energy storage system. However, high overpotential and slow kinetics, particularly of the oxygen evolution reaction (OER), still limit the efficiency of the system. To enhance the efficiency of alkaline electrolysis cells, catalysts with high electrocatalytic activity for OER should be developed.
Platinum-like behavior of tungsten carbide in surface catalysis was first discovered by Levy and Boudart in 1973[1]. In addition, tungsten carbide was reported to have a Pt-like electronic structure by Colton in 1975[2]. Since then, tungsten carbide has been studied widely and expected to replace noble metal catalysts which are used in many electrochemical reactions. In this study, we researched tungsten carbide as a support for nickel, and formation of bi-metallic surfaces for developing a high activity OER catalyst.
WC was synthesized by two-steps. First, WC-Co was synthesized by heat treatment. Carbon nitride (g-C3N4) and tungsten chloride were used as a carbon and tungsten precursor. Cobalt precursor was also used to help carburization of tungsten. After synthesizing WC-Co, the acidic leaching process was followed by using sulfuric acid (H2SO4) to eliminate cobalt. Through additional mixing with 3d metal precursors and heat treatment, Ni/WC and NiFe/WC were synthesized. Furthermore, Ni/C was also prepared using same precursors as a counter group. Figure 1 shows the SEM images of the synthesized WC and Ni/WC. Cyclic voltammetry was performed to evaluate OER activity in 1 M KOH in potential range from 1 to 1.8 V.
Figure 2 shows the OER catalytic activities of synthesized catalysts and Ir/C. Pure WC and Ni/C had 430 mV and 394 mV overpotential at 10 mA∙cm-2 respectively. In 3d Metal/WC cases, Ni/WC and NiFe/WC showed only 335 mV and 314 mV overpotential at 10 mA∙cm-2. Both catalysts had higher electrocatalytic activity for OER than Ir/C in alkaline media.

References

[1] R. B. Levy, M. Boudart, Science, New series, Vol. 181, No. 4099 (1973) 547-579
[2] Richard J. Colton, Jan-Tsyu j. Huang, J.Wayne Rabalais, Chemical Physics Letters, Vol. 34, No. 2 (1975) 337-339

Figure 1
Influence of GDL Properties on Liquid Water Distribution and Temperature at CL Surface
Authors: Araki Takuto , Kobayashi Koki , Minami Ryotaro , Hashimura Sota 
Published: February 2020

Proper water management in proton exchange membrane fuel cell (PEMFC) is critical to achieve a high power density and durability of construction materials. The gas transport is blocked by liquid water remained in GDL, and it causes performance decrement with increase of concentration overpotential. The location of water accumulation is influenced by the temperature distribution inside GDL. At the same time, the temperature distribution is affected by the liquid water distribution, because the liquid water inside GDL decrease the effective thermal resistance. Then, the objective of this study was set to clear the mutual interaction between the liquid water distributions and temperature fields. For this purpose, temperature at the CL surface was measured using thin film thermocouple fabricated by MEMS based technology, and liquid water inside the GDL was visualized by X-ray CT.
The experimental conditions were shown in the table. The GDL thermal property, especially the thickness, was changed intentionally to get symmetrical temperature distributions, and the influence of the GDL thermal property on the liquid water distributions and temperature have been examined.
The thickness of the sensor was only about 9µm and the width is about 100µm. The electromotive force of the MEMS based sensor was confirmed to be proportional to the temperature difference. The MEMS sensor was inserted at the boundary between MPL and CL. The temperature rise from OCV was plotted in the bottom left figure. The temperature increased quadratically except for the high current density region of condition 4.
The visualized liquid water distributions were shown in right hand side figures. The accumulated water was observed in cathode side GDLs in all conditions, however, the highest saturation of water was observed near the rib surface of condition 4. The accumulated water at the rib surface was supposed to reduce the contact thermal resistance and decrease the temperature at the CL surface.

Figure 1
(Invited) Structure-Property Relathionships of Proton Conducting Membranes Studied By Synchrotron Radiation
Authors: Portale Giuseppe 
Published: February 2020

The properties of ion conducting polymers (ionomers) used as proton conducting membranes are strongly dictated by their nanostructure. Due to the strong difference in polarity between the acidic sulfonic groups and the apolar main polymer chain, these materials exhibit strong phase separation. X-ray and neutron scattering are among the best experimental techniques to investigate the ionomer nanostructure. In particular, synchrotron based small and wide angle X-ray scattering (SAXS and WAXS) are particularly suited to perform in-situ investigation on ionomers.
In this contribution, I will show our most recent results obtained by using synchrotron SAXS and WAXS on the investigation of the structure-property relationships in different ionomers. The structural knowledge acquired on the benchmark Nafion membranes is compared to that of its short-side chain counterpart (Aquivion) and to other non-perfluorosulfonated ionomers like sulfonated poly(ether ether ketone)s and sulfonated polysulfones. The nano morphology of Nafion and Aquivion can be qualitatively and (almost) quantitatively explained by a locally flat morphology, describing the morphology as an alternated assembly of water/ions and polymeric 2D domains. The same morphological model can be applied successfully to other fluorine-free ionomers, suggesting that a local flat morphology could be common to many proton conducting ionomers.
In the second part of my talk, I will show some recent in-situ SAXS experiments on microstructural changes occurring in different ionomer membranes under controlled temperature and humidity conditions. The data suggest local re-distribution of water inside the membranes that can lead either to membrane swelling (low temperature and high humidity) or to local ionic structure collapse (high temperature and low humidity). These experiments mimic very closely what may happen in a real fuel cell and the understanding of the results is crucial to improve the membrane performances.
Impact of Equivalent Weight and Side-Chain on Structure/Functionality of PFSA Ionomers and Thin Films
Authors: Kusoglu Ahmet , Shi Shouwen , Dudenas Peter , Weber Adam Z 
Published: February 2020

Perfluorosulfonic-acid (PFSA) ionomers play key roles in polymer-electrolyte fuel-cell (PEFCs), primarily as a proton-exchange membrane (PEM), and also as an electrolyte film in porous catalyst structures binding the catalytic agglomerates.1 Despite their wide adoption in PEFCs, most studies on PFSAs have thus far focused on Nafion, and studies on other PFSAs, in particular with varying side-chain chemistries and equivalent weights (EWs), have been relatively scarce. Therefore, it is of interest to elucidate how such changes in chemistry and EW influence the PFSA behavior, not only as a bulk membrane (i.e., PEM), but also as a catalyst-ionomer film (i.e., thin-film). In particular, the latter phenomenon could have important implications on explaining the mass-transport limitations in catalyst layers, which have been recently shown to be strongly related to the transport resistances at the ionomer thin-film.1,2

In this talk, the impact of EW and side-chain chemistry on structure/property relationship of various PFSAs will be explored as bulk membranes (> 20 μm) and dispersion-cast thin films (< 100 nm). PFSAs owe their combination of good transport properties and mechanical stability to their phase-separated morphology of conductive hydrophilic ionic domains and the hydrophobic backbone, which are connected via side-chains. It will be shown how this PFSA morphology is controlled by the fraction of backbone (via EW) and the side-chain length (via chemistry), which together govern the interrelation between transport and stability. Moreover, our investigations demonstrate the existence of universal correlations between the water-uptake and conductivity (chemical energies), and backbone crystallinity (mechanical energies), with a key role of the side-chain length in altering this balance between the chemical-mechanical energies. We will report the results of a systematic investigation on hydration, conductivity, mechanical properties and crystallinity of various types and EWs of PFSA ionomers to develop universal structure/function relationships. Lastly, it will be explored how these EW and side-chain effects influence the structure and properties of PFSA thin films when confined to nanometer thicknesses, and control their deviation from bulk membrane behavior. Our results provide new insights into the understanding and optimizing the PFSA ionomers' functionalities in fuel-cells, both as bulk membranes and as thin-films.

References

1. A. Z. Weber and A. Kusoglu, Journal of Materials Chemistry A, 2, 17207 (2014).
2. A. Kongkanand and M. F. Mathias, The Journal of Physical Chemistry Letters, 1127 (2016).

Acknowledgement

This work was funded under the Fuel Cell Performance and Durability Consortium (FC-PAD), by the Fuel Cell Technologies Office (FCTO), of the office of the Energy Efficiency and Renewable Energy (EERE), of the U. S. Department of Energy under contract number DE-AC02-05CH11231 and Program Development Manager Dimitrios Papageorgopoulos.
Gram-Scale Synthesis of Nitrogen-Doped Carbon Foams As Template-Free, Metal-Free, Non-Precious Electrocatalysts for Oxygen Reduction and CO2 Conversion
Authors: Lyth Stephen Matthew , Liu Jianfeng , Mufundirwa Albert , Smid Bretislav , Ma Sichao , Kenis Paul J.A. , Sasaki Kazunari 
Published: February 2020

Carbon foams are ideal materials for electrochemical applications due to their large surface area, high electrical conductivity, and stability over a wide electrochemical potential window. However, many of these materials are expensive; use complex multi-step synthesis protocols; and require the use of nanostructured template materials which must be removed with strong acid or alkaline. It is often difficult to control the porosity (and thereby optimize mass diffusion); and it is difficult to dope effectively with heteroatoms. We synthesize carbon foams at low cost and gram-scale, with large micron-scale pores, very thin walls, and very large surface area (e.g. 2500 m2/g), by thermal decomposition of sodium ethoxide.[1,2]
Crucially, by synthesizing and subsequently decomposing nitrogen-containing metal alkoxides, nitrogen-doped carbon foams can be made.[3] The nitrogen content can be varied over a wide range (e.g. <0.5 to 15 at%) by simply changing e.g. the precursor ratios. In addition, the ratio of e.g. pyridinic to tertiary nitrogen bonding can be tailored by changing the pyrolysis temperature. These materials do not contain transition metal contamination (confirmed by ICP-AES), unlike carbon nanotubes or carbon black. Therefore they can be used to probe the fundamental oxygen reduction reaction (ORR) activity of nitrogen-doped carbon in acid – a relatively under-represented topic, plagued by contamination issues.[4,5] We observe surprisingly high mass activity and onset potential for the ORR, with high electron transfer number. This work shows that 4-electron ORR is possible even in the absence of transition metals, most likely associated with tertiary nitrogen sites.[6] In alkaline medium, these catalysts are comparable to Pt/C, and undergo negligible degradation even over 60,000 load potential cycles.[7]
Finally, these materials are investigated for their electrochemical CO2 conversion activity to carbon monoxide, formic acid, methane, and ethane.

References

[1] S. M. Lyth, H. Shao, J. Liu, K. Sasaki, Int. J. Hydrogen Energy, 2014, 39, 376
[2] J. Liu, D. Takeshi, K. Sasaki, S. M. Lyth, J. Electrochem. Soc. 2014, 161, F838
[3] S. M. Lyth, Y. Nabae, N. M. Islam, et al., eJournal of Surface Science and Technology, 2012, 10, 29-32.
[4] S. M. Lyth, Y. Nabae, N. M. Islam, S. Kuroki, M. Kakimoto, S. Miyata, J. Nanosci. Nanotechnol. 2012, 12, 4887
[5] S. M. Lyth, Y. Nabae, N. M. Islam, S. Kuroki, M. Kakimoto, S. Miyata, J. Electrochem. Soc. 2011, 158, B194
[6] J. Liu, D. Takeshi, D. Orejon, K. Sasaki, S. M. Lyth, J. Electrochem. Soc. 2014, 161, F544
[7] J. Liu, K. Sasaki, S. M. Lyth, ECS Trans. 2014, 64, 1161
Mechanistic Analysis of Electrocatalytic CO Oxidation By a Rh Porphyrin on a Carbon Support
Authors: Yamazaki Shin-ichi , Maeda Yasushi , Asahi Masafumi , Siroma Zyun , Ioroi Tsutomu 
Published: February 2020

Electrochemical CO oxidation (CO + H2O → CO2 + 2H+ + 2e–) is important to counteract CO poisoning of Pt-based anode catalysts, since the reaction can reduce CO concentration on an anode of PEFC. However, the CO oxidation at anode potentials hardly occurs on conventional Pt-Ru electrocatalysts.
From these backgrounds, we have developed Rh-porphyrin-based electrocatalysts for CO oxidation [1, 2]. In the catalysts, molecules of Rh porphyrin are dispersed on a carbon black support. These catalysts can oxidize CO at much lower overpotentials than the Pt-Ru electrocatalysts [1-3]. A membrane-electrode assembly (MEA) that uses a Rh porphyrin as an anode catalyst gave significant power (>40 mW/cm2) when CO was supplied as a fuel [4]. A combined catalyst of a Rh porphyrin and Pt-Ru catalyst functions as a CO-tolerant anode catalyst [5].
However, the reason why Rh porphyrins can catalyze CO electro-oxidation at low overpotentials remains unclear. Mechanistic analyses on carbon-supported Rh porphyrin are needed to clarify the reason. The analysis would also contribute to further improvement of this catalyst. In this work, we report a possible reaction mechanism of CO oxidation by the catalyst. First, we examined the reactivity of Rh porphyrins dissolved in solution. This analysis enables us to discuss the CO activation mechanism by Rh porphyrins without the effect of carbon black support. A Rh porphyrin was treated with CO gas in dichloromethane to generate CO adduct of the Rh porphyrin. We characterize this CO-adduct, a possible intermediate of CO oxidation, by IR, NMR, and X-ray crystallography. The results indicate that CO coordinated on Rh atom is feasible to nucleophilic attack by water. Actually, the CO-adduct reduces an soluble electron acceptor in the presence of water. A possible reaction mechanism is shown in Fig. 1. An electrode works as an electron acceptor in the electrocatalytic CO oxidation.
In actual electroctalysts using Rh porphyrins, molecules are adsorbed on a carbon black support. Configuration of molecules on a carbon support would be also important for the catalytic activity. Then, we examined possible effects of the configuration by observing molecules on a highly oriented pyrolytic graphite with an atomic force microscope. The results show that certain ligand structure facilitates the configuration desirable for the high catalytic activity.
These analyses would be an answer for the question; why does Rh porphyrin can oxidize CO at lower potentials than conventional Pt-based catalysts.
This work was supported by Grant-in-Aids for Scientific Research (B) (No. 15H03853).
References
[1] S. Yamazaki et al., Phys. Chem. Chem. Phys. (2010) 12,8968.
[2] S. Yamazaki et al., Electrochem. Solid-State Lett. (2011) 14,B23.
[3] J. F. van. Baar et al., Electrochim. Acta (1982) 27,57.
[4] S. Yamazaki et al., Angew. Chem. Int. Ed. (2006) 45,3120.
[5] S. Yamazaki et al., J. Phys. Chem. C (2010) 114, 21856.

Figure 1
(Invited) Multi-Element-Doped Ceria-Based Metal Oxides for Advanced Proton Conducting SOFCs
Authors: Thangadurai Venkataraman , Singh Kalpana 
Published: February 2020

The ability of solid oxide fuel cells (SOFC) to convert the chemical energy of various kinds of fuels into electricity at high efficiency, and with reduced environmental impacts makes them an attractive technology for current and future plans for clean power generation. State-of-the-art yttria-stabilised ZrO2 (YSZ) electrolyte shows high conductivity (10-2 S/cm) at about 1000 °C [1]. However, the high operating temperature leads to durability and cost issues and hinders its full market implementation. Operating temperature of SOFCs can be lowered by employing ceramic proton conducting electrolytes based on doped- BaCeO3 which exhibits high proton conductivity (10-2 S/cm) in the intermediate temperature (IT, 400-700 °C) range [2]. However, the poor chemical stability of doped-BaCeO3 under SOFC by-products CO2, and H2O limits its use as stable electrolyte [2].
Here we report, perovskite–type Ba0.5Sr0.5Ce1-x-y-z
Zr
x
Gd
y
Y
z
O3-δ as proton conductors for IT-SOFCs [3]. A-and B-site of BaCeO3 were doped by more electronegative elements to improve its chemical stability under H2O and CO2 at elevated temperature. In terms of chemical stability and conductivity, Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ seems to be the optimal composition with conductivity of 10-3 S/cm at 700 °C in 3% H2O/H2. Open circuit voltage of 1.15 V at 700 °C for H2-air cell suggests pure ionic (proton) conduction in Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ [3]. The effect of sintering temperature on bulk and grain boundary conductivity of these oxides was investigated using dielectric loss spectroscopy [4]. Moreover, the difference in the relaxation times in the current study suggests that short-range and long-range proton dynamics seems to be differing to previous studies on Y-doped BaZrO3 systems [5]. Additionally, layered perovskite-type Gd0.5Pr0.5BaCo2O5+δ were characterised as cathode for H-SOFCs [6]. Symmetrical cell measurements under air and wet air gave an area specific resistance of 2.4 Ω cm2 and 1.9 Ω cm2 for oxygen reduction reaction at 700 °C [6]. The effect of phase purity and synthesis methods on the electrochemical performance of Ni+Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3
-δ anode composites was investigated through symmetrical cell measurements in 3% H2O/H2.

References

1) J. W. Fergus, R. Hui, X. Li, D. P. Wilkinson, J. Zhang, Solid Oxide Fuel Cells: Materials Properties and Performance, CRC Press, New York (2009).
2) K. D. Kreuer, Annu. Rev. Mater. Res. 33 (2003) 333.
3) R. Kannan, K. Singh, S. Gill, T. Fürstenhaupt, V. Thangadurai, Sci. Reports. 3 (2013) 2138.
4) K. Singh, A. Baral, V. Thangadurai, J. Am. Ceram. Soc. 99 (2016) 866.
5) Y. Yamazaki, F. Blanc, Y. Okuyama, L. Buannic L, J. C. Lucio-Vega, C. P. Grey, S. M. Haile, Nat. Mater. 12 (2013) 647.
6) K. Singh, A. K. Baral, V. Thangadurai, Solid State Ionics (2016) DOI:10.1016/j.ssi.2015.12.010.
Developing Cost-Effective Dense Continuous SDC Barrier Layers for SOFCs
Authors: Hardy John S , Coyle Christopher A , Nguyen Hoang V. P. , Lu Zigui , Stevenson Jeffry W 
Published: February 2020

Solid oxide fuel cells (SOFCs) with lanthanum strontium cobalt ferrite (LSCF) cathodes often employ a samaria-doped or gadolinia-doped ceria (SDC or GDC, respectively) barrier layer between the cathode and the yttria-stabilized zirconia (YSZ) electrolyte to inhibit Sr from migrating to the YSZ surface where it reacts to form electrically-resistive strontium zirconate during cathode sintering. Because the SDC must be sintered at limited temperatures (generally ≤1200°C) to avoid forming a CeO2-ZrO2 solid solution that has significantly lower ionic conductivity, screen printed barrier layers are often porous after firing. Electrochemical tests of cells with dense, continuous pulsed laser deposited (PLD) SDC found that these cells exhibited significantly higher performance than those with the conventional screen-printed porous SDC layers. Thus, PNNL began investigating the fabrication of dense, continuous SDC barrier layers using cost-effective deposition by screen printing which is amenable to industrial production of SOFCs. Many approaches to improve the SDC density have been explored including the use of powder with reduced particle sizes, inks with increased solids loading, and doping with sintering aids. While some of these tests were successful in enhancing the density of the SDC, the stresses induced by constrained sintering on the surface of previously-fired YSZ caused cracks and discontinuities in the SDC barrier layer. These results together with steps that have been taken to address the constrained sintering issue will be presented.
Limitations of Grain Boundary Engineering - Ionic Versus Electronic Conductivity
Authors: Huber Tobias M. , Navickas Edvinas , Sasaki Kazunari , Yildiz Bilge , Tuller Harry L. , Fleig Juergen , Chen Yan 
Published: February 2020

Much attention has recently been focused on the oxygen reduction via Sr-doped lanthanum manganite grain boundaries (GBs) since oxygen transport, as well as surface exchange is approximately 1000x faster at the GBs than for the LSM bulk. With this in mind, there is a strong incentive to tailor properties of thin films by GB engineering. To date, the effect on the el. conductivity has not been studied for such engineered films. In this study, changing microstructure, as well as strain, were found to heavily influence el. charge transport. More specifically, for example, the el. conductivity decreased while ionic conductivity increased with decreasing grain size. For given current collector distance, one could optimize grain size to achieve optimum mixed conductivity. In addition 18O tracer exchange experiments were performed on the same thin films in a novel operando experimental design to study the influence of cathodic bias upon surface exchange and transport properties of both LSM grains and GBs.
LSM thin films were deposited by PLD and analyzed by ToF-SIMS, Van der Pauw and impedance spectroscopy. SIMS profiles showed a large increase in 18O concentration in the LSM films with an apparent uphill diffusion. Such experiments were prior performed on microelectrode which require specially designed exchange equipment and a high degree of user expertise. Therefore a novel experimental design was developed which can be performed in conventional set-ups to study the influence of polarization in-operando. This new experimental design facilitates the ability to investigate several voltage changes in every required voltage region under SOFC operation conditions within one and the same thin film sample. The apparent uphill diffusion could be simulated by a 3D finite element model with two parallel and interacting diffusion pathways.