bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal-Organic Frameworks and Carbon Nanotubes – Imparting Electrical Conductivity to MOF Composites
Authors: Schulze Hendrik A. , Brechtken Benedikt , Schaate Andreas , Haug Rolf J. , Behrens Peter
Published: February 2020

Metal-organic frameworks (MOFs) and carbon nanotubes (CNTs) have emerged as two of the most promising material classes in the last few years. Both material classes have been thoroughly investigated regarding their structures, production methods, as well as physical and chemical properties. However, despite the versatility of MOFs, nearly all members are electrically insulating. Hence, these materials have not been the first choice in the field of electronic devices. On the contrary, CNTs show high electrical and thermal conductivities, combined with low densities and high mechanical robustness. Up to now, only a few MOF–CNT-composites have been described with the focus on hydrogen storage, the use in supercapacitors or as humidity sensors.[1-3]

In this work, we describe MOF–CNT-composites that combine the electrical conductivity of CNTs with the high porosity of MOFs and, furthermore, coagulate the CNTs to minimize unfavourable health effects. We present the results of the crystallization of the MOFs on CNTs by using the stable Zr-based MOFs of the UiO-66 group[4] with different linker molecules to create different chemical properties and electronic effects. The MOF particles sizes and morphologies are controlled be using modulated syntheses.[5]

The composites can be provided in different forms. On the one hand, strongly intergrown composites of MOF particles that have crystallized around carbon nanotubes, application as electrode materials in batteries or in thermoelectric can be envisaged. On the other hand, thin films of the composites can be anchored on different substrates. Furthermore, we also can create nanoobjects consisting of individual CNT bearing MOF nanoparticles (Fig. 1).

References:

[1] S.J. Yang, J.Y. Choi, H.K. Chae, J.H. Cho, K.S. Nahm, C.R. Park, Chem. Mater.
2009, 21, 1893–1897.

[2] P. Wen, P. Gong, J. Sun, J. Wang, S. Yang, J. Mater. Chem. A
2015, 3, 13874–13883.

[3] K.N. Chappanda, O. Shekhah, O. Yassine, S.P. Patole, M. Eddaoudi, K.N. Salama, Sensors and Actuators B
2018, 257, 609–619.

[4] J.H. Cavka, S. Jakobsen, U. Olsbye, N. Guillou, C. Lamberti, S. Bordiga, K.P. Lillerud, J. Am.
Chem. Soc.
2008, 130, 13850–13851.

[5] A. Schaate, P. Roy, A. Godt, J. Lippke, F. Waltz, M. Wiebcke, P. Behrens, Chem. Eur. J.
2011, 17, 6643–6651.

Figure 1
Superconductive (Cu)TTF@TCNQ Nanosheets Detected By Peakforce Tunneling Atomic Force Microscopy
Authors: Chen Dong-Hui , Fu Zhihua , Redel Engelbert
Published: February 2020

Superconductive (Cu)TTF@TCNQ Nanosheets have been deposited in various thicknesses and characterized through peakforce tunneling AFM.

TTF (Tetrathiofulvalene) and TCNQ (tetracyanochinodimethan) are conjugated organic molecules. However, they formed a “metallic conductive interface”, by a charge transfer (CT) complex. Whereby TCNQ is an acceptor molecule and TTF is a donor molecule. [1] Such charge transfer (CT) complexes possess an increased charge carrier concentration within the TTF@TCNQ nanosheets producing hole and electron carriers, donors and anions with holes, or cations and acceptors with electrons. Therefore, superconductivity have been reported for this system. [
2,3
]

Cu:TTF and Cu:TCNQ nanosheets have been deposited by in different thicknesses by various methods, e.g. spin-coating, dip-coating or electrodeposition methods. The thicknesses have been performed in the range of 2 nm to 30 nm. Peakforce tunneling AFM measurements can be performed on this systems. This TUNA characterizes ultra-low currents (<1pA) through the thickness of nanosheets, and is of particular importance when electrical characterization of conductivity samples is needed at high lateral resolution. High-resolution current mappings of these nanosheets were enabled as well as the corresponding morphology images. Moreover, The I-V currents in the range from pA to nA of these nanosheets have been detected due to the high sensitivity and accuracy of the Peakforce TUNA mode. The resistances of the (Cu)TTF@TCNQ nanosheets can be calculated by using this currents and then the conductivities were also been obtained accordingly.

These superconductive nanosheets will help to construct novel porous superconductive SURMOF hybrid materials in the near future for various device applications.

R
eference

Tang, Q.; Zhou, Z.; Chen, Z. J. Phys.
Chem. C, 2011, 115, 18531–18537.

Kirtley J. R.; Mannhart, J. Nat.
Mater., 2008, 7, 520-521.

Alves, H.; Molinari, A. S.; Xie, H.; Morpurgo, A. F. Nat. Mater., 2008, 7, 574-580

Figure 1
Resistive Switching Phenomena of Metal-Organic Framework Nanosheets Detected By Peakforce Tunneling Atomic Force Microscopy
Authors: Xiu Jingwei , Fu Zhihua
Published: February 2020

Graphene[1], an atom-thin sheet of carbon discovered in 2004, has created a brand new era in two-dimensional (2D) materials owing to its immense potential in both basic and applied research. In recent years, numerous new 2D nanomaterials possessing atomically thin structures have been investigated.[2] Metal-organic Framework (MOF) nanosheets, as a new category of 2D materials, exhibit diverse structural and physicochemical properties as a result of the self-assembly of metal ions or clusters and polydentate bridging ligands.[3] Arising from their unique structural features combining MOF and 2D nano-structures, MOF nanosheets exhibit unprecedented physical, electronic, chemical, and optical properties and offer implementation in application field.

Resistive random-access memory is a predominant candidate for future non-volatile memories. It relies on the formation/annihilation of highly conductive paths, leading to the creation of two stable and reversible resistive states.[4] To achieve the desirable memory characteristics, new materials and a better understanding of the physics triggering the resistive switching (RS) in this system are required. MOF nanosheets with ultrathin nanostructures, high-density active sites and rapid ion/electron transport can offer best opportunities for fundamental and technological research in the RS applications. However, the progress in fundamental understanding has been hampered by the extremely small sizes (of the region) involved in the RS transition region presenting a severe challenge for its physical characterization using conventional metrology methods.

PeakForce tunneling (PFTUNA) atomic force microscopy[5] provides direct, precise force which makes it shows high spatial resolution and routine high current sensitivity. Therefore, the MOF nanosheets combined with PFTUNA technology can present the best tradeoff between existing process technology and RS performances. In this work, we intend to synthesize Ag-S nanosheets with distorted hexagonal topology (Figure 1a-b). By mean of PFTUNA technology of AFM, MOF nanosheet based memory device is constructed and characterized (Figure 1c). A conductive probe to apply a voltage to the top electrode of the single device thereby setting the memory device into its state ON, i.e., its low-resistive state (LRS), or OFF state, i.e., its high-resistive state (HRS) (Figure 1d).

Figure 1
Local Static and Dynamic Field Fluctuations Near the Cu-Ion in HKUST-1 from 63cu-NMR
Authors: Bernal Oscar O , O'Dea Greta , Mohammed Zeinab H. , Redel Engelbert , Baumgart Helmut
Published: February 2020

We report on the local field fluctuations, both of static and dynamic character, at the position of the Cu ions in the Cu(II)-based porous metal-organic framework (MOF) HKUST-1 Cu2(BTC)3 powder. We will compare measurements done in the HKUST-1 pristine form of the material and HKUST-1 infiltrated with tetracyano-quinodimethane (TCNQ). NMR Spectroscopy is a sensitive local probe which can sample both magnetic and charge degrees of freedom of spin bearing nuclei, whose behavior is strongly affected by the magnetic and/or electric activity of neighboring atoms and electrons. Therefore, the loading of TCNQ into the open porous framework of HKUST-1 MOF should have a significant influence in the 63Cu-NMR linewidth.

We present data from 63Cu-NMR linewidth, frequency-shift and spin-lattice relaxation experiments in pristine HKUST-1, which display unusual temperature dependence: the linewidth indicating on the one hand a potential interaction between the 63Cu nuclei and the unpaired electrons in the paramagnetic system of Cu(II), and on the other hand, the frequency-shift together with the spin-lattice relaxation time indicating the existence of a substantial density of electron states at the 63Cu sites, with concomitant changes due to temperature variations. We will discuss these data and those obtained from similar experiments in HKUST-1 when infiltrated with TCNQ.

Work supported by the National Science Foundation under a Partnership for Research and Education in Materials PREM, grant DMR-1523588.
(Invited) Device Fabrication – Positioning and Alignment of MOF Crystals
Authors: Falcaro Paolo
Published: February 2020

Metal organic frameworks (MOFs) are a class of ultra-porous materials with exceptionally high accessible surface area and structure modularity due to the framework made of inorganic nodes coordinated by organic bridging ligands.[
1
2
,
3
]

A number of increasing studies investigate Metal-Organic Frameworks (MOFs) for a variety of functional applications including sensing, microelectronics, energy production, drug delivery and microfluidics.[
4
] However, MOF-based device fabrication requires synthetic protocols for the controlled growth of the ultra-porous crystals and their integration in suitable platforms.[
4
] This presentation will summarize the recent progress on MOF crystal engineering aspects from positioning technologies to alignment strategies. [
5
,
6
,
7
,8, 9,10,11,12] A particular focus of the presentation will be the current role of ceramics for MOF device fabrication.

References

[1] Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M. Science
2013, 341 (6149), 1230444.

[2] Guillerm, V.; Kim, D.; Eubank, J. F.; Luebke, R.; Liu, X.; Adil, K.; Lah, M. S.; Eddaoudi, M. Chem. Soc. Rev.
2014, 43 (16), 6141.

[3] Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem. Int. Ed.
2004, 43 (18), 2334.

[4] Falcaro, P.; Ricco, R.; Doherty, C. M.; Liang, K.; Hill, A. J.; Styles, M. J. Chem. Soc. Rev.
2014, 43 (16), 5513.

[5] Doherty, C. M.; Buso, D.; Hill, A. J.; Furukawa, S.; Kitagawa, S.; Falcaro, P. Acc. Chem. Res.
2014, 47 (2), 396.

[6] Zanchetta, E.; Malfatti, L.; Ricco, R.; Styles, M. J.; Lisi, F.; Coghlan, C. J.; Doonan, C. J.; Hill, A. J.; Brusatin, G.; Falcaro, P. Chem. Mater.
2015, 27 (3), 690.

[7] Ricco, R.; Malfatti, L.; Takahashi, M.; Hill, A. J.; Falcaro, P. J. Mater. Chem. A
2013, 1 (42), 13033–13045.

[8] Liang, K.; Ricco, R.; Styles, M. J.; Bell, S.; Kirby, N.; Mudie, S; Haylock, D.; Hill, A. J.; Doonan, J.; Falcaro, P. Nat.Commun
2015, 6, 7240.

[9] Liang, K.; Ricco, R.; Doherty, C.M.; Styles, M. J.; Hill, A. J.; Takahashi, M.; Falcaro, P. Adv. Funct. Mater.
2014, 24 (14), 1969.

[10] Toyao, T.; Liang, K.; Okada, K.; Ricco, R.; Styles, M. J.; Tokudome, Y.; Horiuchi, Y.; Hill, A. J.; Takahashi, M.; Matsuoka, M.; Falcaro, P. Inorg Chem Front
2015, 2, 434.

[11] Liang, K.; Carbonell, C.; Styles, M.J.; Ricco, R.; Styles, M. J.; Jiwi, C.; Richardson, J.J.; Maspoch, D.; Caruso, F.; Falcaro, P. Advanced Materials
2015, 28 (36), 7910

[12] Falcaro, P.; Okada, K; Hara, T.; Ikigaki, K.; Tokudome, Y.; Thornton W. A.; Hill A. J.; Williams T.; Doonan, C.; Takahashi, M. Nature Materials
2017, 16(3), 342.

Figure 1
(Invited) Optoelectronic Processes in Covalent Organic Frameworks
Authors: Bein Thomas
Published: February 2020

New opportunities emerge by spatially integrating photoactive molecular building blocks into the crystalline lattice of covalent organic frameworks (COFs), thus creating models for organic bulk heterojunctions and porous electrodes for photoelectrochemical systems. In this presentation, we will address means of controlling the morphology and packing order of COFs in thin films (1) and with spatially locked-in building blocks.(2) Regarding the latter, the design of well-defined periodic docking sites enables us to achieve remarkably high crystallinity with several multidentate building blocks and a series of linear bridging units.

We will discuss different strategies aimed at creating electroactive networks capable of light-induced charge transfer. For example, we have developed a COF containing stacked thienothiophene-based building blocks acting as electron donors with a 3 nm open pore system, which showed light-induced charge transfer to an intercalated fullerene acceptor phase.(3) Contrasting this approach, we have designed a COF integrated heterojunction consisting of alternating columns of stacked donor and acceptor molecules, promoting the photo-induced generation of mobile charge carriers inside the COF network.(4) Moreover, additional synthetic efforts have led to several COFs integrating extended chromophores capable of efficient harvesting of visible light, for example (5). Extending newly developed thin film growth methodology to a solvent-stable oriented 2D COF photoabsorber structure, we have recently established the capability of COF films to serve in photoelectrochemical water splitting systems.(6) The great structural diversity and morphological precision that can be achieved with COFs make these materials excellent model systems for organic optoelectronic systems.

(1) D. D. Medina, J. M. Rotter, Y. H. Hu, M. Dogru, V. Werner, F. Auras, J. T. Markiewicz,

P. Knochel, T. Bein, J. Am. Chem. Soc.
2015, 137, 1016.

(2) L. Ascherl, T. Sick, J. T. Margraf, S. H. Lapidus, M. Calik, C. Hettstedt, K. Karaghiosoff, M. Döblinger, T. Clark, K. W. Chapman, F. Auras, T. Bein, Nature Chem. 2016, 8, 310.

(3) M. Dogru, M. Handloser, F. Auras, T. Kunz, D. Medina, A. Hartschuh, P. Knochel,

T. Bein, Angew. Chem. Int. Ed. 2013, 52, 2920.

(4) M. Calik, F. Auras, L. M. Salonen, K. Bader, I. Grill, M. Handloser, D. D. Medina,

M. Dogru, F. Lobermann, D. Trauner, A. Hartschuh, T. Bein, J. Am. Chem. Soc.
2014, 136, 17802.

(5) N. Keller, D. Bessinger, S. Reuter, M. Calik, L. Ascherl, F. C. Hanusch, F. Auras, T. Bein, J. Am. Chem. Soc.
2017, 139, 8194.

(6) T. Sick, A. G. Hufnagel, J. Kampmann, I. Kondofersky, M. Calik, J. M. Rotter, A. Evans, M. Döblinger, S. Herbert, K. Peters, D. Böhm, P. Knochel, D. D. Medina, D. Fattakhova-Rohlfing, T. Bein, J. Am. Chem. Soc.
2018, 140, 2085.
(Invited) Moving Electrons and Holes through Porous MOFs and MOF-Supported Catalysts
Authors: Goswami Subhadip , Kung Chung-Wei , Palmer Rebecca , Farha Omar K. , Hupp Joseph T.
Published: February 2020

Porous, thin-film, water stable metal-organic frameworks (MOFs) are potentially highly attractive as electrocatalysts as they can present reactant-accessible catalysts at high areal concentration on electrode surfaces. Indeed, such films, if constructed from molecular catalysts, can present the equivalent of several hundred monolayers or more of catalyst -- amounts that can translate into decreases of hundreds of millivolts in kinetic overpotential relative to overpotentials for otherwise equivalent solution-phase electrocatalysts present at millimolar concentrations. Similar conclusions can be reached for catalysts consisting of MOF-node-supported, metal-oxygen or metal-chalcogen clusters. Required for efficacious electrocatalysis, however, is reasonable electrical conductivity, where the basis for conductivity may be site-to-site redox hopping or may instead operationally resemble band-like electronic conductivity. For electrode-supported MOF films having thicknesses of around a micron, site-to-site charge hopping rates on the order of 105 sec-1 should be sufficient to sustain catalytic currents of tens of mA/cm2. Alternatively, MOF electronic conductivities on the order of 10-2 Siemens/cm (roughly seven and a half orders of magnitude less than the conductivity of copper) should be sufficient to sustain catalytic currents of tens of mA/cm2 with only marginal iR penalties. Thus, in comparison to many applications, the degree of conductivity required for MOF thin-film mediated electrocatalysis is modest.

This presentation will describe some approaches to rendering highly-porous MOF films sufficiently electrically conductive to support electrocatalysis. Included will be examples of highly anisotropic electrical conductivity, underscoring the role that MOF topology can play in defining both hopping-like and band-like conductivity. Also included may be examples of intentional chemical modulation of MOF conductivity. Based on these and other examples, some potentially transferrable principles for designing electrocatalysis-competent, conductive MOFs will be proffered.
Hexahydroxytriphenylene/NiII MOF Compounds for Oxygen Reduction Reaction Catalysis
Authors: Moreau Florian , Tissot Antoine , Grimaud Alexis , Tarascon Jean Marie , Serre Christian
Published: February 2020

Materials which show satisfying electrocatalytic activities for Hydrogen Evolution Reaction (HER) or Oxygen Reduction Reaction (ORR) for fuel cell energy storage are mainly based on Platinum which has a very limited abundancy. Although a few chalcogenides, such as MoS2 or MnO2 show promising catalytic activity, it is inherently limited by the accessible surface area of these materials. Over the last decade, hybrid porous materials (or Metal-Organic Frameworks) with intrinsic electronic conductivity have been reported.1 MOFs potential assets as electrocatalysts are mainly due to the combination of three factors: i) Their crystalline nature allows a fine control of the spatial layout of active sites over a long range order, and potentially the tuning of conductivity. ii) Their hybrid nature gives rise to a very versatile chemistry and thus permits the systematic investigation of how both organic and inorganic counterparts influence on the material properties. iii) Their porosity provides a high density of accessible active sites.

Among electrically conductive MOFs, 2D triphenylene-based frameworks are of particular interest owing to their large π-conjugated systems and the resulting large conductivities. 2-4 Indeed, a hexaimino-triphenylene/NiII MOF system (Ni-HITP) was recently reported to show great electrocatalytic activity towards ORR.5

Although a few tricatecholate MOFs based on 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and MII cations (Co, Ni, Cu) have been reported,4 none of these have been tested for ORR electrocatalysis. We thus decided to investigate this system and isolated a previously unreported phase: Ni-HHTP-S which consists solely of 2D layers stacked in a staggered manner with blocked porosity. Interestingly, when thermally treated, Ni-HHTP-S undergoes a phase transition towards Ni-HHTP-E with eclipsed layers and accessible porosity. Both materials show different and high electrocatalytic activities towards ORR. This system thus offers a great opportunity to investigate the modulation of conductivity and catalytic activity of a 2D MOF, not only by its primary structure, but also by the secondary arrangement of its layers.This communication will present the frameworks characterizations and discuss their electronic conductivities and ORR electrocatalytic activities.

[1] L. Sun et al., Angew.
Chem. Int. Ed.,
2016, 55, 3566-3579.

[2] D. Sheberla et al., J. Am. Chem. Soc., 2014, 136, 8859-8862.

[3] M. Campbell et al., Angew. Chem. Int. Ed.,
2015, 127, 4423-4426.

[4] M. Hmadeh et al., Chem. Mater., 2012, 24, 3511-3513.

[5] E. Miner et al, Nat. Commun., 2016, 7, 10942.
Sub-Zero Cell Reversal Tolerance in Polymer Electrolyte Membrane Fuel Cells
Authors: Bashyam Rajesh , Bellerive Julie , He Ping
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have gained considerable attention in recent years for application in electric vehicles, portable devices, and cogeneration systems. Large scale commercialization of PEMFCs mainly requires addressing the high cost issues associated with the fuel cell stack in addition to the challenges associated in building H2 infrastructure. Though, significant amount of research has been carried out in developing low Pt loaded Membrane Electrode Assemblies to meet the 2020 DOE performance targets for automotive applications, there are still challenges associated in meeting durability requirements due to catalyst layer and membrane degradation. It is well documented voltage cycling during start-up/shutdown process leads to Pt dissolution and loss of electrochemical surface area of Pt and thereby affecting the durability. Fuel cells stacks need to be robust against both specific and non-specific failure modes. Specific failure modes of MEA can be predicted by operating conditions/parameters, however non-specific failure mode such as cell reversal is difficult to predict. Though, system level mitigation can be employed to minimize the impact of cell reversal, there is a potential cost trade-off associated with this approach. Ballard1 was first to develop and report the impact of cell reversal tolerance above sub-zero conditions with and without cell reversal tolerance catalyst in the MEA.

Cell reversals2 can occur mainly during reactant starvation and especially during H2 starvation under freeze start-up operation. This presentation will focus on evaluating the impact of operating parameters on cell reversal under sub-zero conditions and will highlight the mechanism and potential ways to improve cell reversal tolerance under sub-zero conditions. Figure 1 shows the impact of current density on cell reversal tolerance under sub-zero conditions3. As it can be seen, significant reduction in sub-zero reversal tolerance noticed with current density. To the best of our knowledge, we evaluated for the first time, the cell reversal tolerance under sub-zero conditions.

References

S.D.Knights, D.P.Wilkinson, S.A. Cambell, J.L.Taylor, J.M. Gascoyne and T.R. Ralph, Solid polymer fuel cell with improved voltage reversal tolerance. US Patent 6936370.

C. Qin, J. Wang, D. Yang, B. Li and C. Zhang, Proton Exchange Membrane Fuel Cell Reversal:A Review, Catalysts, 6, 2016, 197.

R.Bashyam, J.Bellerive, P.He, Fuel cell system and method of operating fuel cell system, German Patent application DE102016207786A1

Acknowledgement

We thank Volkswagen AG and Audi for funding this work.

Figure 1
Total Cost of Ownership of Fuel Cell Electric Vehicles Using Expert Assessments
Authors: Whiston Michael M. , Azevedo Inês , Litster Shawn , Whitefoot Kate , Samaras Constantine , Whitacre Jay
Published: February 2020

We calculated the total cost of ownership (TCO) of fuel cell electric vehicles (FCEVs) in 2017, 2020, 2035, and 2050. Our TCO model incorporates proton exchange membrane fuel cell (PEMFC) cost and durability data that we obtained during our expert elicitation interviews [1]. Our assumptions, including hydrogen storage system and fuel costs, are consistent with those published by the U.S. Department of Energy [2, 3]. We characterized the uncertainty associated with FCEV life cycle costs, and we compared our FCEV projections to the DOE’s 2035 projections for internal combustion engine vehicles (ICEVs), battery electric vehicles (BEVs), hybrid-electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). In our sensitivity analyses, we studied the dependence of FCEV TCO on vehicle lifetime, hydrogen fuel cost, and hydrogen storage system cost. All monetary values are expressed in 2017 USD.

On median, we estimated the FCEV TCO to be $0.42/mile in 2017, $0.33/mile in 2020, $0.19/mile in 2035, and $0.18/mile in 2050 (Figure 1). Our 2017 and 2020 estimates ranged widely. Our 2017 estimates ranged from $0.40 to $0.75/mile and 2020 estimates ranged from $0.31 to $0.51/mile. By 2035, FCEVs could be competitive with ICEVs, BEVs, HEVs, and PHEVs, as long as the PEMFC stack lasts sufficiently long. If the FCEV’s lifetime falls below 11 yrs, FCEVs could become more expensive than competing vehicles. At about 11 yrs, the FCEV’s TCO exceeds that of the BEV. If stack durability remains a challenge, replacing the stack could be economical. Achieving a hydrogen fuel cost below $4/kg H2 and hydrogen system cost below $390/kg H2 could further improve FCEVs’ competitiveness.

References

[1] Whiston, M. M., Azevedo, I., Litster, S., Whitefoot, K. S., Samaras, C., and Whitacre, J. F. “Expert Assessments of the Cost and Expected Future Performance of Proton Exchange Membrane Fuel Cells for Vehicles.” Proceedings of the National Academy of Sciences of the United State of America. Manuscript submitted.

[2] Nguyen, T. and Ward, J. “Life-Cycle Cost of Mid-Size Light-Duty Vehicles.” Record No. 16009. U.S. DOE, Washington, D. C.

[3] U.S. DOE. “Multi-Year Research, Development, and Demonstration Plan.” U.S. DOE, Washington, D. C. Accessed April 3, 2018. Available at https://www.energy.gov/eere/fuelcells/downloads/fuel-cell-technologies-office-multi-year-research-development-and-22

Figure 1
Atomic-Level Insight into Advanced Electrocatalyst Architectures
Authors: Becknell Nigel , Wang Rongyue , Lv Haifeng , Lopes Pietro Papa , Markovic Nenad M , Stamenkovic Vojislav
Published: February 2020

Oxygen reduction catalyst activity and durability is critical to the success of polymer electrolyte fuel cells (PEFCs) as an energy conversion technology. Typically, rare and costly platinum-based materials are used as catalysts for the oxygen reduction reaction. Efficient utilization and preservation of the Pt catalyst surfaces must be achieved in order to reach the activity and stability required to manufacture cost-competitive products powered by PEFCs with long lifetimes. Our approach to meeting this goal employs atomic-level control of the positioning of active elements within the multimetallic catalyst. By understanding the segregation and migration of Pt within a bimetallic alloy, we are able to design advanced three-dimensional architectures such as the excavated, rhombic dodecahedral nanoframe. Careful control of catalyst synthesis and surface treatments yield surface composition profiles that balance high catalytic activity (~1.4 mA/cm2 and ~0.6 A/mgPt at 0.95 V vs RHE) with the durability of the surface. We use atomic-level characterization such as ex situ TEM and in situ electrochemical ICP-MS to gain critical insight into the surface transformation during electrochemical cycling. These detailed studies are being combined with a synthetic scale-up effort to translate lab-scale (milligram) catalysts such as excavated nanoframes to the gram scale. The scale-up effort is critical to evaluating excavated nanoframes and other advanced architectures in a membrane electrode assembly (MEA), which is more likely to reflect real performance in the fuel cell stack. Ultimately, synthetic control and characterization at the atomic-level in combination with gram-scale catalyst synthesis provides the powerful ability to iteratively design advanced catalyst architectures that are thoroughly tested in both rotating disk electrochemistry and MEAs. These capabilities will yield new insight into low loading, high current density performance loss of MEAs, an enormous roadblock to the next level of major fuel cell commercialization.
Polynorbornene-Based Anion Exchange Membranes for Alkaline Fuel Cells
Authors: Huang Garrett , Mandal Mrinmay , Kim Yunbum , Kohl Paul A
Published: February 2020

Fuel cells based on alkaline exchange membranes (AEM) have garnered increased interest because of their inherent advantages over traditional proton exchange membranes (PEM). High pH operating conditions allow for more facile reaction kinetics, reduced platinum-group metal catalyst, and reduced fuel crossover issues. Moreover, these materials can be made from inexpensive precursors which can further drive down the cost of the membrane electrode assemblies (MEA) for fuel cells.

In this study, a variety of block copolymer AEMs based on based on vinyl addition and ring-opening metathesis polymerization of norbornenes was synthesized and characterized. Correlations were found between the ionic conductivity and mechanical properties and the polymer structure, channel size and phase separation. The AEMs were also used to construct MEAs for alkaline fuel cells and their performance was analyzed using electrochemical impedance spectroscopy.

Financial support provided by the ARPA-E IONICS program for G.H. and M.M. is gratefully acknowledged.
Self-Driven Strain Tuning in Transition Metal Nanocrystals for the Oxygen Reduction Reaction
Authors: Wang Lei , Zeng Zhenhua , Gao Wenpei , Maxson Tristan , Raciti David , Giroux Michael , Pan Xiaoqing , Wang Chao , Greeley Jeffrey
Published: February 2020

The elucidation of governing principles of catalyst activity from fundamental research on well-defined model systems, combined with the advances in controlled synthesis of the transition metal nanocatalysts, have led to the rational design and development of advanced nanocatalysts. One principle is to tune surface strain and thereby modulate the surface electronic structure and catalytic reactivity. This approach has been employed to identify transition metal and (hydroxy)oxide catalysts for energy-relevant electrocatalytic reactions. For oxygen reduction reaction on platinum as an example, previous studies have indicated that a 1% compressive strain may improve the activity over 300%.

While strain tuning of catalysts is very promising for activity enhancement, two challenges continue to limit the performance of these materials. First, the effect of strain on high-surface-area nanoparticle catalysts is often convoluted with nanoparticle shape and by the presence of undercoordinated defects, while model catalysts, where high specific activities is achievable by strain tuning, have prohibitively small mass activities and are therefore of limited practical interest. Thus, there is an urgent need to develop strain tuning strategies for nanomaterials that preserve the structural simplicity and high specific activity of single crystals while simultaneously possessing high surface areas and mass activities. In addition, strain in catalyst overlayers is often imposed by heterosubstrates, which may lead to interfacial reconstructions and strain release.

In this talk, in combination DFT calculations, electrochemical tests and TEM characterization, we will present a strategy to resolve these problems through self-driven strain tuning in transition metal nanocrystals with the characteristics of low-index single-crystal surfaces. As we demonstrate for the oxygen reduction reaction in alkaline fuel cells, this relationship could be exploited to enhance reaction rates by orders of magnitude in comparison with nanoparticle catalysts, suggesting that this self-driven tuning mechanism in transition metal nanocrystals can be a powerful strategy for the design and development of advanced catalytic materials.
(Invited) Gold Nanoparticles Modified with Platinum and Palladium As Electrocatalysts for Ethanol Oxidation Reactions
Authors: Shao Minhua , Xing Zelong , Chen Huimei
Published: February 2020

Electrooxidation of ethanol on noble metals, such as Pt in acidic and Pd in alkaline solutions is of particular interest due to its potential application in low-temperature direct ethanol fuel cells (DEFCs). The slow, incomplete oxidation of ethanol as well as the high price of Pt and Pd has impeded the wide application of DEFCs. In response to these challenges, several resembling core-shell electrocatalysts using Au nanoparticles were synthesized and evaluated for ethanol oxidation reaction (EOR).

It was found that the Pd shell is not uniform consisting of tiny Pd clusters with a coverage of 0.5-0.6. The EOR activity of this kind of structure is much higher than Pd/C in an alkaline solution. The forward peak current density of was 5 times higher than that of Pd/C. Furthermore, the onset potential for EOR of the former was ~100 mV more negative. An interesting particle size dependent EOR activity was also observed. With increasing the Au particle size (2.9 to 5.8 and 6.5 nm), the EOR activity increases. The strain and ligand effects from the Au core, together with the bifunctional mechanism from the core and shell can explain the observed activity trend. Similar core-shell catalysts with a Pt shell were also synthesized and evaluated for EOR in acidic electrolytes. In a further study, the core-shell particles were modified with Ru and SnO2, which showed enhanced activities. In situ spectroscopic studies were conducted to reveal the reaction intermediates and products of various catalysts to give more insights into the reaction pathway and activity enhancement mechanisms.
A Novel IrOx-Based Composite Material with High Oxygen Evolution Reaction Performance in Acidic Media
Authors: Cheng Junfang , Yang Jun , Kitano Sho , Cui Xuedong , Yamauchi Miho , Nakashima Naotoshi
Published: February 2020

With excellent oxygen evolution reaction (OER) activity and stability in acidic media, IrOx-based materials are regarded as the most suitable catalysts to fulﬁl the technological requirements in acidic conditions. However, because of the high cost of Iridium, it is crucial to reduce the Ir consumption without compromising catalytic activity[1
-
3].

In this study, we synthesized a novel IrOx-based composite catalyst by low temperature processes, and the obtained catalyst showed an outstanding OER performance in acidic media. The detail synthesis method, micromorphology and performance of the catalyst will be presented at the meeting.

References

[1] N. Mamaca, E. Mayousse, S. Arrii-Clacens, et al., Applied Catalysis B: Environmental, 2012, 111-112, 376– 380.

[2] H. Nong, H. Oh, T. Reier, E. Willinger, M. Willinger, V. Petkov, D. Teschner, P. Strasser, Angew. Chem. Int. Ed. 2015, 54, 2975–2979.

[3] E. Oakton, D, Lebedev, M. Povia, D. Abbott, E. Fabbri, A. Fedorov, M. Nachtegaal, C. Copéret, T. Schmidt, ACS Catal. 2017, 7, 2346−2352.
(Invited) High Performance and Noble-Metal Free Electrocatalysts for Water Electrolysis
Authors: Chen Shuo
Published: February 2020

For large scale water electrolysis, low cost and stable electrocatalysts are essential. In this talk, I will present our recent work using earth abundant (Fe, Mo, Ni, etc. based) electrocatalysts for both hydrogen evolution and oxygen evolution reactions. The electrocatalysts are directly synthesized and anchored on commercially available metal foams, which serve as robust supports. The electrocatalysts are highly active and stable, especially under large current densities. For example, our bifunctional iron/dinickel phosphide on nickel foams drives efficiently both hydrogen and oxygen evolution reactions in alkaline electrolyte. The full cell can reach a current density of 10 mA cm-2 with 1.42 V in 1 M KOH. Moreover, it delivers 500 mA cm-2 at the lowest 1.72 V and maintains the performance for at least 40 h without decay. The excellent performance is attributed to large surface area, porous structures, high electrical conductivity, favorable electronic structure, and abundant active sites of the electrocatalysts. Our designs and materials are promising for large-scale water electrolysis.
Palladium Nanoparticles on Nickel for Direct Methanol Solid Oxide Fuel Cell Catalyst
Authors: Koo Junmo , Jang Dong Young , Choi Hyeon Rak , Kim Jun Woo , Shim Joon Hyung
Published: February 2020

Direct Methanol Solid Oxide Fuel Cell (DMSOFCs) has been drawn comparable attentions in fuel cell society for its fuel flexibility and high energy density of methanol compared to that of hydrogen. However, carbon coking and carbon monoxide poisoning occur due to usage of methanol as fuel, which hinder electrode kinetics and eventually cause performance degradation. Therefore, demand of high performance catalyst with excellent stability has been risen for the widespread usage of DMSOFC. To these days, bimetallic Pt-Ru is known as the best DMSOFC catalyst for its superior methanol oxidation capability. However, high scarcity of Pt and Ru hinders the widespread commercialization of DMSOFC for its expensive price. Recently, Ni has been considered as promising alternative for Pt-Ru. Price of Ni is far lower than that of Pt or Ru, and Ni has respectable methanol oxidation ability. During electrochemical oxidation of methanol, however, carbon tends to deposited on the surface of Ni, which leads performance and stability degradation of Ni catalyst.

In this study, we deposited the palladium nanoparticles on the surface of Ni in order to obtain bimetallic Pd/Ni catalyst for DMSOFC application. Pd nanoparticles were deposited by DC magnetron sputtering and atomic layer deposition. DMSOFC with Pd/Ni catalyst were analyzed by current-voltage measurement and electrochemical impedance spectroscopy at the temperature range of 300 - 450 ºC. Pd/Ni catalyst showed enhanced performance and stability compared to bare Ni catalyst. Detailed analysis of experiment will be discussed in the presentation.
A Structural and Spectroscopic Investigation of Rhombohedral Pyrochlores M2La3Sb3O14 (M = Mg or Ca) Doped with Eu3+
Authors: Piccinelli Fabio , Carrasco Irene , Ma Chong-Geng , Srivastava Alok M , Bettinelli Marco
Published: February 2020

Mg2La3Sb3O14 and Ca2La3Sb3O14 are rhombohedral pyrochlores. A detailed structural investigation shows that, as a consequence of the larger difference in the ionic radii of La3+ and Mg2+ with respect to La3+ and Ca2+, in the former compound there is an ordered distribution of the cations and a local inversion symmetry for La3+ sites. On the contrary, because of the cationic disorder observed in Ca2La3Sb3O14, breaking of the local inversion symmetry at La3+ is observed. This very peculiar structural behavior has a big impact on the Eu3+ luminescence spectroscopy of the doped materials Mg2La3Sb3O14:1% Eu3+ and Ca2La3Sb3O14:1% Eu3+. Moreover, first-principles calculations confirm the structural evidence, and elucidate the structure-spectroscopy relationships of these Eu3+-doped materials.
Surface Ligands As Atomic Valves for Growth of Nanocrystal Quantum Dots
Authors: Lee Doh C
Published: February 2020

Growth of monodisperse quantum dots (QDs) is a pressing requirement in the context of commercial application as well as academic study, as the size uniformity is directly related to color purity in display products which have been commercialized. In the growth, surface ligands serve not only as a protection layer for QD surface but also controller for reaction kinetics. I will present our recent findings pertaining to these issues on the basis of different material examples.

Our study on the colloidal synthesis of InP QDs in the presence of Zn precursors will be discussed, in which size uniformity is markedly enhanced as compared to the case of InP QDs synthesized without Zn precursors. In the presence of zinc carboxylate, intermediate species containing Zn-P bonding appears. The Zn-P intermediate complex with P(SiMe3)3 exhibits lower reactivity than In-P complex. The formation of stable Zn-P intermediate complex results in lower reactivity, hence monodisperse QDs. Insights from the experimental and theoretical studies advance the mechanistic understanding and controlling of nucleation and growth of InP QDs.

We investigated diffusion of active species monomers through ligand layers using CdSe nanorods (NRs) as a model system. Colloidal NRs are of special interest for optoelectronic applications because its shape anisotropy leads to unique optical and physical characteristics, expandable with morphological and structural deviation. I present a new answer for detailed growth mechanism of colloidal semiconductor NRs. For this, we developed dual-diameter nanorod (DDNR) structure via colloidal synthesis, where two sections along the long axis in each NR have different diameters at a few nanometer scale. The vivid segmentation is an ideal platform for monitoring the growth process of NRs, presenting important determinants in the reactivity of distinguishable NR facets. By controlling the discovered factors, single-diameter NRs with controllable core position also became available. I will put the findings in perspective by outlining the effect of diffusion of monomers and surface growth reactions.
On the Assumption-Free Determination of Single-Ion Gibbs Energies of Transfer
Authors: Radtke Valentin , Ermantraut Andreas , Krossing Ingo
Published: February 2020

Since about 100 years, the quest on the determination of Gibbs energies of transfer of single-ions exists. While some consider that the chemical potential of single-ions is physically senseless, other determined Gibbs solvation energies or Gibbs transfer energies of single-ions with the help of extra-thermodynamic assumptions (e.g. TATB-assumption, ferrocene-assumption and others), thereby introducing an error of the respective quantity of insufficiently assessable magnitude.[1]

We suggest a procedure for the thermodynamically rigorous, experimental determination of the Gibbs energy of transfer of single-ions Δtr
G°(i, S1--> S2). The method is based on potential difference measurements between two electrochemical half-cells with different solvents (solvation cells) connected by an ideal ionic liquid salt bridge (ILSB).[2] We point out the specific requirements for the IL with regard to the procedure, thus ensuring that those parts of liquid junction potentials (LJP) at both ends of the ILSB cancel which depend on the redox system used. The remaining parts of the LJPs can be determined by separate electromotive force measurements, the knowledge of the ionic transference numbers and Gibbs energies of transfer of the used salts is mandatory. No extra-thermodynamic assumptions are necessary for this procedure. The accuracy of the target quantity is an inherent part of the measurements and depends, amongst others, on the ideality of the IL used. We present results concerning the crucial steps a) and b) of the methodology exemplarily for Ag+ and Cl− with S1 being water and S2 being acetonitrile as an important intermediate goal to evaluate our concept for the assumption-free determination of single-ion Gibbs transfer energies Δtr
G°(i, S1--> S2).[3] The used IL, [N2225]+[NTf2]−, shows nearly ideal behavior, that is, nearly identical diffusion of anion and cation, in the pure IL, but also in water and acetonitrile solution. Electromotive force measurements of solvation cells between S1 and S2 demonstrate Nernstian behavior for Ag+ concentration cells and constant like cell potentials for solutions with five tested Ag+ counterions.

The Gibbs transfer energies can be utilized to collect data for the unified scales of acidity pHabs and reducity and peabs and for their two dimensional plot, the Protoeletric Potential Map (PPM), enabling the possibility to easily compare acidities and redox potentials between different media.[4]

Literature:

[1] P. Hünenberger, M. Reif, Single-Ion Solvation. Experimental and Theoretical Approaches to Elusive Thermodynamic Quantities, The Royal Society of Chemistry, Cambridge, 2011.

[2] V. Radtke, A. Ermantraut, D. Himmel, T. Koslowski, I. Leito, I. Krossing, Angew. Chem. Int. Ed. 2018, 57, 2344.

[3] A. Ermantraut, V. Radtke, N. Gebel, D. Himmel, T. Koslowski, I. Leito, I. Krossing, Angew. Chem. Int. Ed. 2018, 57, 2348.

[4] D. Himmel, V. Radtke, B. Butschke, I. Krossing, Angew. Chem. Int. Ed., 2018, doi:10.1002/anie.201709057.
Vanadium Electrorefining in NaCl–KCl–VCl2 Melts
Authors: Polovov Ilya B. , Chernyshov Mikhail V. , Volkovich Vladimir A. , Rebrin Oleg I. , Rylov Alexander N.
Published: February 2020

Molten salt mixtures can be effectively employed for electrowining and electrorefining of relatively chemically active rare refractory metals having negative reduction potential. One of such metals is vanadium. However quality of the metal produced (impurities content and size of crystals in the deposit) and current efficiency in a standard vanadium electrorefining process does not fully correspond to the requirements. The current work was carried out aiming to determine the optimal conditions of operating industrial vanadium electrolysis baths.

The experiments on vanadium electrorefining were carried out in a semi-industrial electrolyser made of stainless steel. Crude vanadium metal was loaded in an anodic basket made of molybdenum. The experiments were performed in dry purified argon atmosphere, and glassy-carbon or nickel crucibles were used to contain the melt.

Vanadium-containing melts were prepared by dry chlorination of vanadium metal with subsequent absorption of chlorination products by fused salt mixtures. To stabilize vanadium(II) ions, the molten electrolyte was kept in contact with vanadium for 12–18 hours. Mean oxidation state of vanadium in the melt determined oxidimetrically was always close to two and didn’t depend on vanadium concentration.

The method of mathematical planning of experiments was used to determine optimal conditions of electrolysis. Current efficiently was chosen as a response factor. Variable parameters and their intervals were chosen on the basis of the preliminary experiments and the results of kinetic studies. Current density, vanadium concentration and specific quantity of electricity were selected as variables. Temperature had no effect on the current efficiency and increasing temperature only resulted in rising vapor pressure of the melt. Therefore, temperature was not included into variable parameters. Anodic current density was kept essentially constant between 0.1 and 0.15 A/cm2. Such anodic current density allowed maintaining average oxidation state of vanadium ions close to two in the course of the experiments.

The 23 full factor experiment was performed and the regression equation was obtained using the experimental results. All variable parameters were significant and the equation obtained was adequate. The influence of the quadratic term was insignificant. The response function was then obtained in the form of a dependence of the cathodic current efficiency on current density, vanadium concentration and specific quantity of electricity passed.

The most suitable parameters of vanadium electrorefining were determined using this equation and the experiment under the optimal conditions was carried out, Figure. The total amount of impurities in the refined product was below 0.09 wt. % and the current efficiency equaled to 0.96 g/A∙h.

Figure. High-purity electrolytic vanadium

Figure 1
Electrodeposition of Refractory Metals from Ionic Liquids
Authors: Maurer Joshua A.
Published: February 2020

Electrodeopostion of refractory metals from ionic liquids, including tantalum and niobium, has received a great deal of attention due to the potential of these coatings for a wide range of industrial applications. While deposition has been achieved from metal halide salts in both ionic liquids and classic high-temperature molten salt mixtures, these depositions have often resulted in the inclusions of sub-halide species in the coatings. Additionally, for ionic liquids, these processes have typically made use of high cost solvents that are not scalable for industrial applications. To improve the deposition process, we have explored the electrochemical process of producing refractory metal coating from a range of deep eutectic solvents and low cost ionic liquids. In order to understand the fundamental reaction mechanisms that govern the metal reduction and deposition, critical parameters, such as solvent coordination, have been modeled and characterized in solution. Moreover, analytical methods have been used to characterize the reduction process.