bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two-Dimensional Nanoframes As Bifunctional Oxygen Electrodes for Unitized Regenerative Fuel Cells
Authors: Rhodes Christopher , Godinez-Salomon Fernando , Archer Randall , Ying Yuanfang 
Published: February 2020

Proton exchange membrane (PEM) fuel cells provide high efficiencies and clean power generation, however to enable wide scale adoption approaches are needed to reduce costs, improve durability, and provide on-demand hydrogen generation. Unitized regenerative fuel cells (URFCs) that combine power generation with fuel/oxidant generation within a single system can reduce costs and lower weight and volume compared with separate fuel cell and electrolyzer systems. Improved bifunctional oxygen electrodes (BOEs) that have lower overpotentials for oxygen reduction reaction (ORR) and oxygen evolution reactions (OER), higher stabilities for extended operating times, and lower costs are needed for URFCs. For extended durability, non-carbon-supported catalysts are required for BOEs since carbon oxidation occurs at high positive potentials leading to significant performance degradation.
Our group has demonstrated metallic two-dimensional (2D) nanoframes can be derived from controlled temperature/atmosphere treatments of metal hydroxide nanosheets. Metallic Ni-Pt 2D nanoframes exhibit a unique porous nanoarchitecture that allows the use of unsupported (carbon-free) electrodes that have shown significantly higher ORR activities and stabilities compared with Pt/C. Incorporation of Ir and/or Ru in an integrated 2D NiPtxMy (M=Ru, Ir) nanoframe was investigated to obtain bifunctional (ORR and OER) electrocatalyst nanoarchitectures. Electrochemical analysis of unsupported metallic 2D nanoframes using rotating disc electrode experiments shows that incorporating Ni within the structure significantly improves both ORR and OER activities. Further, we have investigated using transition metal oxide-supported catalysts to reduce the precious metal loading while maintaining high activity and stability. The ability to control the structure and properties of 2D nanoframes provides a route to develop bifunctional electrocatalysts with high activity, extended durability, and lower cost.
Controlled Synthesis of Ptm (M=transition metal) Alloy Nanostructures Via Organic Solvents As High-Performance Oxygen Reduction Reaction Electrocatalysts
Authors: Shen Shuiyun , Wei Guanghua , Guo Yangge , Li Fan , Zhang Junliang 
Published: February 2020

Controlled synthesis of PtM (M=transition metal) alloy nanostructures via organic solvents as high-performance oxygen reduction reaction electrocatalysts Shuiyun Shen, Guanghua Wei, Yangge Guo, Fan Li, Junliang Zhang*
Institute of Fuel Cells, MOE Key Laboratory of Power & Machinery Engineering, Shanghai Jiao Tong University, Shanghai 200240, China

Abstract: It is undoubted that to commercialize the polymer electrolyte membrane fuel cells (PEMFCs), there remains a great challenge to further improve the oxygen reduction reaction (ORR) activity on Pt. It has been proved that alloying Pt with transition metal (Fe, Co, Ni, and so on) will improve not only the activity but also the durability towards the ORR [1]. More importantly, it is also found that crystal plane-oriented PtM alloy nanoparticles or nanostructures show much higher ORR activity and durability [2]. In this work, we propose to synthesize PtM (M=transition metal) alloy electrocatalysts with controlled composition and structures via organic solvents. The as-obtained electrocatalysts will be investigated as the ORR electrocatalyst for PEMFCs.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (21373135, 21533005 and 21503134), and the Science Foundation of Ministry of Education of China (413064).

References

[1] Gasteiger, H. A.; Kocha, S. S.; Sompalli, B.; Wagner, F. T., Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs. Appl Catal B-Environ 2005, 56 (1-2), 9-35.
[2] Chen, C.; Kang, Y.; Huo, Z.; Zhu, Z.; Huang, W.; Xin, H. L.; Snyder, J. D.; Li, D.; Herron, J. A.; Mavrikakis, M.; Chi, M.; More, K. L.; Li, Y.; Markovic, N. M.; Somorjai, G. A.; Yang, P.; Stamenkovic, V. R. Science 2014, 343, 1339-1343.
Electrochemical Probing on Structural Changes of Surface Composition and Geometry of Ptni Nanoparticles with Pt-Enriched Surface
Authors: Jeon Tae-Yeol , Kim Sang-Kyung , Lee Hyun Hwi 
Published: February 2020

Alloying Pt with M (M = Fe, Co, Ni, Cu, etc) has been extensively studied for increasing the oxygen reduction rate owing to the decreased bond strength of hydroxyl to Pt. Formation of Pt-enriched surface on the Pt-M alloy core can enhance both activity and durability, which generates several unique features that make it the most promising candidate for active and durable ORR catalyst, such as lower d-band center and consequent weaker bond strength of oxygen-containing adsorbates, and increased dissolution potential of surface Pt.
Our recent study on PtNi bimetallic nanoparticles with Pt-enriched surface for oxygen reduction reaction (ORR) will be presented with introducing conceptual understanding of electronic modification induced by the formation of Pt skin on PtM alloy.1 In particular, it will be discussed that the electrochemical properties, which were obtained from CO and reduced CO2 adlayer oxidation measurements before and after potential cycling under ORR conditions, provide us important informations for estimating the surface electronic and geometric states of pure Pt, PtNi, and Pt-enriched PtNi.
1. Jeon, T.-Y., Kim, S. K., Pinna, N., Sharma, A., Park, J., Lee, S. Y., Lee, H. C., Kang, S.-W., Lee, H.-K., Lee, H. H. Chem. Mater.
2016, 28, 1879-1887.
Elucidating Structure-Activity Relationships for the Oxygen Reduction Reaction at Mn-Based Perovskites
Authors: Fermin David , Celorrio Veronica 
Published: February 2020

Transition metal oxides such as perovskites (ABO3) are becoming an important class of materials in the context of oxygen electrocatalysis for alkaline fuel cells and metal-air batteries.1,2 Although these materials have been extensively investigated in the field of solid oxide fuel cells, their properties as oxygen electrocatalysts at room temperature are far from being fully rationalised. Establishing structure-activity relationships based on the electronic structure of the B-site, widely recognised as the main active site, is one of the key challenge in this field. Such information is extremely important towards designing catalysts with optimal B-site orbital occupancy, coordination number and metal-oxygen bond length.
In a recent study, we have shown that LaMnO3 exhibits over two orders of magnitude higher activity towards the ORR than other lanthanide perovskites (e.g. Co, Fe, Cr and Ni).3 Our analysis show that the origin of this high activity is linked to changes in the redox state at the Mn sites at potentials close to the formal ORR potential, leading to an increase in electron population at the key active site.
In this contribution, we shall focus on the structure-activity relationship of a family of LaxCa1-xMnO3 nanoparticles, assessing their activity as a function of the Mn-valency. We will provide a detailed analysis of the bulk and surface structure employing X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). Studies employing rotating ring-disc electrodes of the nanoparticles supported on mesoporous carbon films show that their activity towards the ORR are among the highest reported for transition metal oxides.4 We finally establish that the mean ORR activity of surface Mn sites increases as the Mn valency decreases.5 These studies highlight the need for independent assessment of key aspects such as the extent of A-site surface segregation and average Mn valency in order to establish consistent structure-activity relationships.
References:
1- A. Grimaud et al. Nat. Mater. 2016, 15, 121
2- J. Suntivich et al. Nat. Chem. 2011, 3, 647
3- V. Celorrio et al. ChemElectroChem 2016, 3, 283
4- K.A. Stoerzinger, ACS Catalysis 2015, 5, 6021
5- V. Celorrio et al. Catal. Sci. & Technol. 2016, 6, 7231
Dynamic Reaction Phenomena during Electrochemical Reduction of CO to Hydrocarbons on Copper
Authors: Trimarco Daniel Bøndergaard , Scott Søren B. , Bodin Anders , Sørensen Jakob E. , Mazzanti Nicola , Bagger Alexander , Pedersen Thomas , Hansen Ole , Chorkendorff Ib , Rossmeisl Jan , Vesborg Peter C. K. , Stephens Ifan E. L. 
Published: February 2020

We have recently developed a unique vacuum inlet system, which couples a mass spectrometer to an electrochemical experiment like a conventional DEMS/OLEMS system – but with an unprecedented combination of quantitative and ultrasensitive product detection with sub-second time resolution. [1]
Using this one-of-a-kind tool, we experimentally map out the behavior of Cu-based CO reduction. In particular, we study transient overproduction of methane. We find that a very pronounced, overproduction of methane (compared to ethylene) is the result of an electrochemical pre-treatment of the catalyst with molecular oxygen dissolved in the electrolyte. Mechanistic implications are discussed.
[1] D. B. Trimarco et al., Rev. Sci. Instrum. 86, 075006 (2015)

Figure 1
Catalysts Facet Orientation and Surface Modifications for Improved Activity of Alcohol Oxidation
Authors: Li Meng , Adzic Radoslav R 
Published: February 2020

Many problems encountered in hydrogen-fuel-cell technology, particularly those of hydrogen storage and distribution, can be circumvented by replacing hydrogen with liquid fuels, such as methanol and ethanol. However, the electrocatalytic oxidation reactions of methanol and ethanol are slow and incomplete even on the best existing Pt-based catalysts, which greatly impeded the wide-spread application of direct alcohol fuel cell (DAFC).
Our group demonstrated that one class of surfaces can be very active for the oxidation of methanol and ethanol [1]. These electrocatalysts consist of one Pt monolayer (PtML) under tensile strain when placed on extended or nanoparticle surfaces. Their activity and selectivity can be controlled with Pt-support interaction. Our experimental and DFT studies demonstrated a correlation between the strain induced by PtML-support interaction and the catalytic activity. Significant enhancement in the activity associated with the tensile strain and decreased activity associated with the compressive strain.
Most recently, we deposited PtML on Au single crystals and shape-controlled nanocrystals enclosed with different crystallographic facets[1,2], and electrochemical behaviors (Figure 1a) suggested that the deposited PtML possessed facets matching to the underlying Au. Surface structure can determine catalytic properties and a large density of atomic steps on high-index facets is especially desirable for breaking chemical bonds such as C-C bond splitting in ethanol total oxidation. Such property of translating facet-specific features from substrates to the supported PtMLopens new opportunities to enhance catalytic performances.
Another approach to improve activity involves modifying PtML surfaces with different co-catalysts. For example, Ru modified PtML/Au showed significantly enhanced activity for methanol oxidation and FTIR studies demonstrated that no adsorbed CO was formed during the reaction. The incorporation of co-catalysts such as Rh, Ir and Sn with PtML shifted onset potential of ethanol oxidation to more negative values (Figure 1b) and promoted a complete oxidation of ethanol to CO2.
Details of electrochemical, structural and spectroscopic studies, discussion of reaction mechanisms and possibilities of these findings to resolve the major impediment hindering the development of practical DAFCs and to open new studies of C-C bond splitting in variety of important reactions will be presented in the meeting.

Acknowledgements

This work was financially supported by the US DOE, Office of Basic Energy Science, Material Science and Engineering Division, Division of Chemical Sciences, Geosciences and Biosciences Division (Contract No. DE-SC0012704).

References

[1] M. Li, P. Liu, R. R. Adzic, J. Phys. Chem. Lett.
2012, 3, 3480−3485.
[2] F. Lu, Y. Zhang, L. Zhang, Y. Zhang, J. X. Wang, R. R. Adzic, E. A. Stach, O. Gang, J. Am. Chem. Soc.
2011, 133, 18074–18077.

Figure 1
Specific Metal-Polyoxometallate Interactions in Electrocatalysis, Photoelectrochemistry and Efficient Charge Propagation
Authors: Kulesza Pawel J 
Published: February 2020

Of particular interest to the preparation of advanced catalytic materials is efficient utilization of carbon nanostructures and noble metal nanoparticles, their stabilization and intentional activation, as well as organization into two-dimensional arrays, ultra-thin films or three-dimensional networks (e.g. through sequential attraction) on electrode surfaces. They can form nanosized materials with well-defined composition, structure and thickness that exhibit electrocatalytic properties toward oxidation of methanol, ethanol or dimethyl ether. We explore here the ability of inorganic structures to stabilize and derivatize metal and carbon nanostructures. Here certain nanostructured inorganic oxides (e.g. WO3, MoO3, TiO2, ZrO2, V2O5, and CeO2) and polyoxometallates of molybdenum or tungsten influence supported metal centers in ways other than simple dispersion over electrode area. Evidence is presented that the support can modify activity (presumably electronic nature) of catalytic metal nanoparticles thus affecting their chemisorptive and catalytic properties. Metal oxide nanospecies can generate –OH groups at low potentials that induce oxidation of passivating CO adsorbates (e.g. on Pt); they can potentially break C-H or C-O bonds (e.g. by hydrogen tungsten oxide bronzes); and they can possibly weaken C-C bonds during ethanol oxidation (e.g. through changes of the electronic properties of Pt).
Our research interests also concern development of systems for reduction of carbon dioxide. For example, instead of conventional Pd nanoparticles, nanosized Pd immobilized within ultra-thin films of polyoxometallates and their salts have been considered. Reduction of carbon dioxide begins now at less negative potentials and is accompanied by significant enhancement of the CO2-reduction current densities. Among important issues are specific interactions between hydroxyl and metal-oxo centers and metallic palladium sites at the electrocatalytic interface.
When it comes to photoelectrochemical water splitting, we demonstrate here utility of gold nanoparticles (modified or stabilized with Keggin-type and ruthenium-containing polyoxometallates, PMo12O40
3-, as capping agents) to enhance photocurrents generated by mesoporous tungsten trioxide, WO3, photoanodes irradiated with visible light in aqueous solutions. To demonstrate generation of localized surface plasmons, we have performed measurements using scanning near-field optical microscope (SNOM). The mechanism for the interaction between the gold plasmons and the semiconductor is complex but sound.
SnP2O7 Based Membranes for Intermediate Temperature Electrochemical-Synthesis of Ammonia
Authors: Ramaiyan Kannan Pasupathikovil , Maurya Sandip , Kim Yu Seung , Garzon Fernando H , Mukundan Rangachary , Kreller Cortney R. 
Published: February 2020

Electrochemical synthesis of useful chemicals such as ammonia through renewable electricity will ease problems associated with renewable energy storage. However, the strong NºN bond (941 kJ mol-1) poses a severe challenge for mild condition synthesis of ammonia. Several attempts toward electrosynthesizing ammonia at low and high temperatures included a variety of electrode materials ranging from glassy carbon electrode to precious metals and different proton and oxide ion conducting electrolytes [1]. Rates on the order of 10-9 mols-1cm-2 have been reported for both low and high temperature systems. While the formation of ammonia from H2 and N2 is exothermic, at low temperatures the reaction kinetics is too low for industrial production. The current high temperature Haber-Bosch process is too energy intensive and is not economically viable for small scale remote applications.
We report the synthesis of ammonia in a simple fuel cell configuration using a Sn2P2O7 – nafion composite membrane and Pt electrodes in the low-intermediate temperature range of 200-300°C. The composite membrane showed conductivity values in the range of 10 – 20 mScm-1 at 200°C. Our membranes retained high conductivity values after continuous operation over 300 hours. We observed an ammonia synthesis rate of 1.8x10-9 mols-1cm-2 under a bias of -0.1 V with Pt based electrodes and H2 and N2 as reactant gases.
References

V. Kyriakou, I. Garagounis, e. Vasileiou, A. Vourros, and M. Stoukides, Catalysis Today, 2016 http://dx.doi.org/10.1016/j.cattod.2016.06.014.
Effect of Carbon Support and Synthesis Method on Pt NP Utilization and Activity
Authors: Ketabi Sanaz , El Sawy Ehab N , Birss Viola 
Published: February 2020

A key requirement for the large-scale commercialization of proton exchange membrane (PEM) fuel cells is to produce highly active, durable catalysts, while minimizing the use of precious noble metals, especially platinum (Pt). Higher utilization of Pt catalyst can be realized by understanding the effect of the carbon support microstructure on the distribution and formation of Pt nanoparticles (NPs) and by optimizing the synthesis method. In this work, Pt NPs were fabricated using a simple alcohol reduction method and then varying the carbon support pore structure and surface properties. The catalysts were then tested for their activity in 1 M C2H5OH + 0.5 M H2SO4 solutions.
For Pt NP preparation, either ethanol or butanol were used as the solvent and reductant. The ethanolic or butanolic solution containing H2PtCl6 was then added to the carbon support dispersed in the same solvent at room temperature, and the mixture was heated at the boiling point for 2 hrs. In the case of the ethanol solvent, an aqueous alkaline solution was added to ensure the completion of Pt reduction [1]. However, this step was not used during synthesis when using butanol, due to its higher reducing power. Three types of carbon supports were investigated, Vulcan carbon (VC), Ketjenblack (KB), and colloid-imprinted carbon powders (CICs). The structure and distribution of the Pt NPs were confirmed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM).
Figure 1 shows the cyclic voltammograms of JM Pt/VC and Pt/CIC85 (i.e., 85 nm pore size), prepared by both the ethanol and butanol synthesis methods, in 0.5 M H2SO4. Even though the theoretical specific surface areas were 70-80 m2/gPt (particle size of 3-3.5 nm), the electrochemical active surface area (ECSA) was found to depend on the synthesis method and the carbon support. The ethanol oxidation activity of catalysts per Pt area for the three carbon supports is shown in Figure 2. A strong dependence on the carbon microstructure was observed, with Pt/CIC and Pt/KB, showing a higher activity than Pt/VC, likely due to their higher content of mesopores in the catalyst layer [2]. The correlation between catalyst activity and the carbon microstructure for each synthesis method will be discussed in detail.
References:
1. J. Xie, Q. Zhang, L. Gu, S. Xu, P. Wang, J. Liu, Y. Ding, Y.F. Yao, C. Nan, M. Zhao, Y. You, Z. Zou, Nano Energy (2016) 21, 247–257.
2. T. Soboleva, X. Zhao, K. Malek, Z. Xie, T. Navessin, S. Holdcroft, ACS applied materials and interfaces (2010) 2, 2, 375–384.

Figure 1
Interpretation of Nyquist Plot for Characterization of Electrode and Electrolyte Material Properties for Electrical Double Layer Capacitors
Authors: Mei Bing-Ang , Pilon Laurent 
Published: February 2020

Electric double layer capacitors (EDLCs) store energy via ion adsorption in the electric double layer forming at the electrode/electrolyte interfaces. This charge storage mechanism is very fast and highly reversible resulting in large power density and long cycle life. Applications range from regenerative breaking for hybrid electric vehicles to the smart grid. Electrochemical impedance spectroscopy (EIS) has been used widely to determine the properties of the electrode and electrolyte materials for EDLCs. The impedance of an EDLC half-cell can be measured by applying a low-amplitude sinusoidal voltage to a steady-state potential and divide the imposed potential by the output sinusoidal current. Nyquist plots showing the imaginary part as a function of the real part of the impedance is informative to determine the properties including electrode and electrolyte resistance, charge transfer or polarization resistance at the electrode/electrolyte interface, and capacitance of the half-cell. However, the interpretation of Nyquist plots has been a “subject of controversy”, with no clear relations between the shape in high, intermediate, and low frequency regime of the plot and a particular property of the device.
This study aims to derive guidelines for characterization of EDLC electrode and electrolyte materials from EIS measurements. To do so, Nyquist plots from EIC measurements were numerically reproduced for EDLC half-cells with planar electrodes in aqueous TEABF4 electrolyte. The continuum model used was based on the modified Poisson-Nernst-Planck model and accounted for (i) the Stern layer at the electrode/electrolyte interface, (ii) finite ion size, and (iii) binary and symmetric electrolyte. The effect of the electrode and electrolyte resistance, charge transfer or polarization resistance at the electrode/electrolyte interface, and the capacitances were separated numerically. This was done by varying the bulk ion concentration, electrolyte length, ion diffusion coefficient in the electrolyte, and/or the magnitude of steady-state potential. Therefore, the behaviour in each frequency regime in Nyquist plots that corresponded to a particular property was clarified.
Visualizing and Control Ion Transport and Phase Transition Processes in Epitaxial Oxide Thin Films
Authors: Du Yingge 
Published: February 2020

Complex oxide materials with ordered vacant lattice sites enable facile, synchronous electron/ion intercalation reactions, and have been extensively investigated for energy conversion and storage applications. A topotactic phase transition (TPT), in which the final crystal lattice is closely related to that of the original material, may occur through the displacement and exchange of atoms as a result of charge and mass transfer. Even though the change in crystal structure is small, a TPT can significantly alter the electronic structure, lattice charge, and physical properties of a material.
In this talk, I will show that thin-film deposition by molecular beam epitaxy (MBE) allows ultrahigh purity materials of this kind to be synthesized, together with accurate control over their thickness, doping level, and strain state for predictable structural and property modifications. In combination with advanced transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), and theoretical modeling, we were able to characterize and simulate ion transport and phase transition processes at a comparable length scale to provide fundamental insight into these processes. In one example, we show that ordered oxygen vacancy planes in SrCrO3-δ under different strain states (compressive vs. tensile) displays drastically different phase stability and O2- ion transport properties, which is of considerable interest in solid oxide fuel cells where fast oxygen ion transport at lower operating temperature is highly desired. In another example, I will present how we tune the structure and electronic properties of WO3 epitaxial thin films, and use them as model cathode materials for in situ TEM studies. The atomic scale ion (Li+, Na+, and Ca2+) intercalation, accompanied with a monoclinic to cubic phase transition, together with subsequent conversion reactions are revealed by STEM, EELS, NBD, and theory.