bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Modification of Ni-Rich Bimetallic Ni1-x Mx (M= Bi, Pd and Au) Nanoparticles for Glycerol Electro-Oxidation in Alkaline Media
Authors: Houache Mohamed S.E. , Shubair Asma , Hughesa Kara , Safari Reza , Botton Gianluigi A. , Baranova Elena A.
Published: May 2020

Glycerol partial electro-oxidation to produce various chemicals has attracted a great amount of attention in the decade [1]. Glycerol is the main by-product of biodiesel production and could be converted into high value-added chemicals. The control of catalyst selectivity and activity could be achieved through formulation of novel, nano-structured electrocatalysts. Nickel (Ni) is an attractive material for glycerol electro-oxidation (GEOR) in alkaline media [2], due to its natural abundance, anti-poising and good stability in alkaline media. Designing inexpensive nano-structured 3D Ni electrodes could improve the catalytic activity of Ni, whereas its selectivity could be modified by adding second metal [1].

In the present work, GEOR was investigated on Ni-based mono and bi-metallic Ni x Au 1-x, Ni x Bi 1-x and Ni x Pd 1-x (x = 98, 95 and 90 at. %) nanoparticles in 1M KOH. Ni nanoparticles were synthesized by heatless chemical reduction in ethanol using sodium borohydride (NaBH4) as the reducing agent. Resulting Ni-based NPs were characterized using XRD, XPS, TEM, SEM, EDS mapping, HAADF imaging and EELS. Electrochemical measurements were carried out on Ni-based NPs using cyclic voltammetry (CV), chronoamperometry (CA) and linear sweep voltammetry (LSV) at room temperature. Results showed that Ni, NiAu and NiBi NPs are active for GEOR and that reaction proceeds through the formation of NiOOH active phase similar to bulk Ni electrodes [3]. Coupling CA with in-situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) for the simultaneous analysis of products in the bulk electrolyte solution and on the Ni surface demonstrated that the main reaction products on Ni surface are glyceraldehyde, carbonyl and carboxylate ions. Whereas HPLC analysis reveals that Au, Bi and Pd adatoms strongly influence the reaction products by suppressing the pathways with C–C bond cleavage, hindering the formation of formate and enhancing the production of C2 and C3 products at different applied potentials (1.3, 1.4 and 1.55 V) and temperatures (25 and 50 oC).

The correlation of electrocatalytic activity and selectivity with nanoparticle will be discussed in terms of mass activities and product distribution during GEOR.

References

[1] M. S. E. Houache, K. Hughes, E. Baranova, Sustainable Energy & Fuels, 3 (2019) 1892-1915.

[2] M. S. E. Houache, K. Hughes, A. Ahmed, R. Safari, H. Liu, G. A. Botton, E. A. Baranova, ACS Sustainable Chemistry & Engineering, 7 (2019) 14425-14434.

[3] M. S. E. Houache, E. Cosar, S. Ntais, E. A. Baranova, J. Power Sources, 375 (2018) 310-319.
Tuning the Composition of Silicon Oxide Overlayers to Control the Performance of Platinum Electrocatalysts
Authors: Beatty Marissa Elizabeth , Esposito Daniel V. , Gillette Eleanor , Haley Alexis
Published: May 2020

Membrane coated electrocatalyst (MCEC) architectures have been demonstrated to be an attractive approach for improving the activity, stability, and selectivity of electrocatalysts. However, little is known how overlayer structure impacts different electrocatalytic properties. By analyzing the impact that overlayer composition has on electrochemical behavior, the relationship between MCEC structure and performance can be better understood. For a silicon oxide (SiOx)|Pt MCEC, limiting the conversion of polydimethyl-siloxane (PDMS) to SiOx during synthesis can result in varied concentrations of carbon and silicon-oxygen coordination in the overlayer film, allowing these factors to be manipulated and studied directly. These changes in composition are shown to affect the hydrophobic character of the overlayers, as well as impact the performance of electrochemical reactions that require water as a reactant. Specifically, platinum electrodes with partially converted SiOxCy overlayers showed decreased permeability for both water and protons when studying hydrogen evolution. Partially converted samples also exhibit clear shifts in CO oxidation potential compared to unencapsulated Pt, however, these shifts do not directly improve activity for the methanol oxidation reaction. Instead, samples that had the lowest extent of conversion showed the highest degree of current enhancement for methanol oxidation, despite these samples demonstrating a higher CO oxidation potential than samples with longer curing times. These observations offer insights into how the composition and properties of MCEC overlayers can affect different factors in an electrochemical system and offer an additional level of design for the development of future electrocatalyst architectures.
Single Site Substituted 2D Molybdenum Carbide and Its Application in Electrocatalysis
Authors: Kuznetsov Denis A. , Chen Zixuan , Kumar Priyank V. , Abdala Paula M. , Fedorov Alexey , Muller Christoph R.
Published: May 2020

Two-dimensional carbides and nitrides (MXenes) represent an excellent platform for the fundamental catalysis studies due to their well-defined and tunable structure and theoretically predicted activity in numerous catalytic reactions. However, the scope of metals capable of forming stable MXenes is limited mostly to early transition metals, making the investigation of properties inherent to mid or late transition metal carbides/nitrides challenging. Here, we present the synthesis and structural characterization of the Mo2CTx:M phases (M = Co, Fe; Tx = O, OH, F surface terminations), where M substituents occupy molybdenum positions in the Mo2CTx lattice, providing isolated Co/Fe sites. Our experimental and DFT studies demonstrate that metal substitution renders Mo2CTx:M active catalysts for the hydrogen evolution reaction. Overall, our work expands the compositional space of the MXene family by introducing materials with isolated metal sites incorporated into the stable matrix of Mo2CTx. The synthetic approach discussed here illustrates that tailoring the properties of MXenes for a specific application can be achieved via targeted substitution of the host metal.
Selective Removal of Excess V2O5 Via Electrochemical Etching for Reproducible Photoelectrochemical Water Oxidation Performance of BiVO4 Photoanodes
Authors: Jung Gihun , Shin Byungha
Published: May 2020

Monoclinic bismuth vanadate (BiVO4) is a promising candidate for photoanodes of photoelectrochemical (PEC) water oxidation due to its ability of visible light absorption, suitable valance band edge position and chemical stability under neutral electrolyte conditions. Among various fabrication methods for BiVO4, two-step process consisting of electrodeposition of Bi-based film followed by drop casting of V containing precursor solution to form to BiVO4 has been shown to produce BiVO4 photoanodes with high photoelectrochemical water oxidation performance. However, a careful removal of excess V2O5 is necessary in this fabrication method. The most common method of removing excess V2O5 is chemical etching by NaOH solution. However, in often cases, unwanted dissolution of BiVO4 occurs along with the etching of V2O5, which results in poor reproducibility of the PEC performance. Here, we developed a simple yet very selective etching method for the removal of excess V2O5 without any damage to BiVO4, which is based on electrochemical etching. BiVO4 photoanodes prepared by our electrochemical etching resulted in very reproducible PEC performance. Physical and chemical analyses of BiVO4 films after different etching methods (chemical vs. electrochemical) revealed that the loss of surface vanadium is the source of the fluctuation in PEC water oxidation performance. Details of material characterizations and electrochemical analyses will be presented.
One-Pot Synthesis of Pt-Free 3D-Catalyst for PEMFC
Authors: Roiron Camille , Celle Caroline , Heitzmann Marie , Jacques Pierre-André , Simonato Jean-Pierre
Published: May 2020

Pt-free catalysts for Oxygen Reduction Reaction (ORR) are broadly studied for Proton Exchange Membrane Fuel Cells (PEMFC) in order to widely develop hydrogen as a fuel for individual transportation. To reduce the performance gap between noble and non-noble catalysts, kinetics and thermodynamics are to be considered. The kinetics of the reaction is influenced by both the turn over frequency of the catalytic site and the density of said sites in the materials. The diffusion of gaseous reactants and liquid water produced is equally important as it modifies the thermodynamic of the reaction. For a long time now, Fe-C-N materials have been identified as the most promising Pt-free electrocatalysts for ORR despite the limited knowledge on the actual structure of the involved sites. Several approaches are currently studied to produce materials with high active site density and high porosity. Different carbon structures are modified to include active sites. The most reported and promising routes are Metal Organic Frameworks, polymers on carbon nanoparticles and silica templated organic structures.

In this new approach, carbon cryogels are chosen for their tunability and high specific surface area. Porous Fe-C-N catalysts are synthesized in one step by a modified resorcinol-formaldehyde aerogel method. Gelation, drying and pyrolysis steps are carefully studied and optimized to obtain a high density of accessible catalytic sites. The porosity of the formed materials is measured with nitrogen adsorption. Values of the Brunauer Emmett Teller (BET) surface area up to 800 m2/g are obtained. The impact of different synthesis parameters on catalytic activity is studied. To assess the catalyst’s performances toward ORR, rotating ring Disk Electrode measurements as well as Fuel Cell polarization curves will be reported.
Effect of Electrolyte Contaminants and Surface Roughness on the Constant Phase Element
Authors: Maurya Rajan , Neergat Manoj
Published: May 2020

The origin of constant phase element (CPE) to explain electrode/electrolyte interface is subject of debate in the literature. CPE behavior is generally attributed to the presence of reactivity, surface inhomogeneity, various crystal planes and atomic scale defects in the crystal; all these may lead to dispersion of local capacitance at the electrode/electrolyte interface. Therefore, electrode/electrolyte interface of polycrystalline Pt (Pt-PC) and smooth glassy carbon disk electrode (GCE) are investigated in ultra-pure H2SO4 (0.5 M) electrolyte. The surface of GCE is roughened mechanically to test the effect of roughness. The effect of intentional and unintentional contaminants are investigated using halide (Cl˗, Br-, I-) ions. It is found that the CPE is affected by the concentration and nature of anion in the electrolyte. Unintentional impurities and cations do not affect the CPE behavior.

Figure 1
Structural Evolution of Atomically Dispersed Ni/Fe Isolated Single Atoms on N-Doped Graphene By Pyrolysis Strategy for Highly Efficient ORR/Oer
Authors: Khan Kishwar , Luo Zhengtang
Published: May 2020

Single-atom catalysts (SACs) maximizing the metal utilization, and highlight the exceptional performance in various catalysis fields, attracted tremendous attention in material science and engineering. However, conventional synthesis of SACs involves high energy consumption at high temperature, enormous metal trash, poor yields, greatly impeding their performance. The mechanism of anchoring between metal SACs and carbon substrates is also not appropriately named. Here, we engineered graphene with dual separated metals synthesized by new approach for the efficient and low-cost electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). We tuned the supportive coordination environments by defects engineering techniques to optimize the catalytic activity. The variation in local coordination showed a strong influence on the chemical reactivity and could be exploited to control the catalytic performance. The electrochemical measurements show that the dual metal-doped nanocarbons enable ORR and OER catalysis at low overpotentials. We verified our new approach experimentally by using aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The density functional theory (DFT) calculation demonstration also justifies its working mechanism in detail. Apart from the demonstration of a new metal-doped carbon catalyst, the information garnered from this study will expand on existing knowledge in the field of heterogenous single-atom catalysis, where explanations of our systems may help to elucidate behaviors in other catalytic models.
Co-Based PGM-Free Catalysts for Oxygen Reduction in Proton-Exchange Membrane Fuel Cells
Authors: He Yanghua , Shi Qiurong , Wu Gang
Published: May 2020

Fe-Based atomically dispersed single site catalysts are the state of the art platinum group metal (PGM)-free catalysts in proton exchange membrane fuel cells (PEMFC). However, due to the Fenton reactions potentially causing degradation of ionomers and membranes, Fe content in PGM-free catalysts must be minimized. Therefore, development low-Fe or Fe-free cathode catalysts are urgently needed for durable and inexpensive PEMFCs. Based on our previous effort to develop nitrogen‐coordinated single Co atom catalyst derived from Co‐doped metal‐organic frameworks (MOFs) [1,2], in this presentation, we will further discuss our recent effort to elucidate the formation mechanisms of CoNx sited driven by thermal treatment. Also we will introduce our new progress to prepare electronspun Co catalysts and binary CoFe catalysts for oxygen reduction in acidic electrolytes. Detailed synthesis procedure, extensive characterization, and RDE activity and fuel cell performance will be discussed.

References

(1) Wang, X. X.; Cullen, D. A.; Pan, Y.-T.; Hwang, S.; Wang, M.; Feng, Z.; Wang, J.; Engelhard, M. H.; Zhang, H.; He, Y.et al. Nitrogen-Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells. Advanced Materials 2018, 30 (11), 1706758.

(2) He, Y.; Hwang, S.; Cullen, D. A.; Uddin, M. A.; Langhorst, L.; Li, B.; Karakalos, S.; Kropf, A. J.; Wegener, E. C.; Sokolowski, J.et al. Highly active atomically dispersed CoN4 fuel cell cathode catalysts derived from surfactant-assisted MOFs: carbon-shell confinement strategy. Energy & Environmental Science 2019, 12 (1), 250.
Use of Aditive Manufacturing for Electrocatalyst Fabrication for Oxygen Reduction Reaction
Authors: Zamora-Suárez Andres , López-González Berenice , Perez Jose de Jesus , Herrera-Celis José Luis , Cuevas-Muñiz Francisco Mherande
Published: May 2020

3D printers can be versatile and can be used in the design of monolithic or complex geometry energy systems. However, the biggest challenge is the development of materials that can be used as electrode surfaces. In this work, the results of electrodeposition of platinum over a ABS 3d printed surface are presented. Commercial conductive ABS was used for this purpose. In addition, some mixtures were prepared by mixing the ABS with vulcan carbon, the conductivity was measured by Kelvin sensing, obtaining 0.25 S/cm at 25% vulcan carbon, in constrast with 1.54x10-3 S/cm for commercial ABS, however this material becomes fragile and difficult to extrude. Electrodeposition was performed from H2PtCl4 in acidic media. SEM studies shown a homogeneous distribution of the platinum particles (circa 1 micron) in all the surface of the commercial ABS. After 1 minute of electrodeposition, the electroactive area is 10 times lesser than the obtained in a glassy carbon electrode. The electric resistance it is the main cause of this, however, it is a first aproximation to get electrodeposit in a ABS conductive material, and the horizon is promising for energy applications.
A Microelectronic Sensor Device Powered By a Small Implantable Biofuel Cell
Authors: Bollella Paolo , Lee Inhee , Blaauw David , Katz Evgeny
Published: May 2020

Biocatalytic buckypaper electrodes modified with pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase and bilirubin oxidase for glucose oxidation and oxygen reduction, respectively, were prepared for their use in a biofuel cell [1]. A small (millimeter-scale; 2×3×2 mm3) enzyme-based biofuel cell was tested in a model glucose-containing aqueous solution, in human serum, and as an implanted device in a living gray garden slug (Deroceras reticulatum), producing electrical power in the range of 2–10 μW (depending on the glucose source) [2]. A microelectronic temperature-sensing device equipped with a rechargeable supercapacitor, internal data memory and wireless data downloading capability was specifically designed for activation by the biofuel cell. The power management circuit in the device allowed the optimized use of the power provided by the biofuel cell dependent on the sensor operation activity. The whole system (power-producing biofuel cell and power-consuming sensor) operated autonomously by extracting electrical energy from the available environmental source, as exemplified by extracting power from the glucose-containing hemolymph (blood substituting biofluid) in the slug to power the complete temperature sensor system and read out data wirelessly. Other sensor systems operating autonomously in remote locations based on the concept illustrated here are envisaged for monitoring different environmental conditions or can be specially designed for homeland security applications, particularly in detecting bioterrorism threats.

References

Gamella, M., Lee, I., Guz, N., Blaauw, D., Katz, E. (2018). International Journal of Unconventional Computing, 14(1), 27-41.

Bollella, P., Lee, I., Blaauw, D., Katz, E., ChemPhysChem (2019), in press. DOI:10.1002/cphc.201900700
Pyrenyl Carbon Nanotubes for Covalent Bilirubin Oxidase Biocathode Design: Should the Nanotubes be Carboxylated?
Authors: Krishnan Sadagopan
Published: May 2020

Understanding the characteristics of nanomaterials in the context of electrode designs for bio-electrocatalysis is an emerging research direction. Applications for fuel cells, batteries, and biosensors are directly benefited. The objective of this study is to understand the influence of unfunctionalized multiwalled carbon nanotubes (MWNT) in comparison to carboxylated nanotubes (MWNT–COOH) for pi-pi stacking with 1-pyrenebutyric acid (Py) and covalent immobilization of bilirubin oxidase (BOD) enzyme toward the resulting oxygen reduction currents. We designed pyrolytic graphite-edge electrodes modified with MWNT/Py, MWNT–COOH/Py, or only MWNT–COOH for carbodiimide activation and BOD immobilization. The relative increase in surface –COOH groups as we move from MWNT to MWNT/Py to MWNT–COOH/Py modification is voltammetrically estimated. Although the MWNT–COOH/Py displayed the highest relative amount of surface −COOH groups, the oxygen reduction current was the largest for the BOD-immobilized MWNT/Py electrode than others. Results indicate that unfunctionalized MWNT is the optimal choice for pi-pi stacking with pyrene linkers and covalent BOD immobilization as biocathode for direct electrocatalysis with high current densities. Favorable hydrophobic MWNT surface to interact more closely with the electron-receiving T1 Cu site of BOD, as opposed to the relatively polar and more defective MWNT–COOH material due to functionalization, is suggested to be one of the underlying factors for the observed electrocatalytic trend.
Microbial Biocathode Catalyzing Oxygen Reduction and Processing Nitrification
Authors: Barrière Frédéric , Flinois Thomas
Published: May 2020

Oxygen biocathodes with electroactive biofilms on graphite electrodes were developed consistently and reproducibly from wastewater inoculum under a high ammonium content selective pressure in a batch microbial fuel cell configuration using ferrocyanide at the anode. The microbial biocathodes process nitrification reactions and catalyse the reduction of molecular oxygen with an onset potential of 0.0 V vs. Ag /AgCl, and a current density at -0.28 V of j = -296 μA/cm2 at pH 7 and 20 °C under oxygen saturation (Cf. Figure).These biofilms also reduce hydrogen peroxide (not shown) at +0.25 V, the potential of an electroactive species in the biofilm (Cf. Figure). The nitrification reactions performed by the biofilm are found to be associated with the catalytic reduction of dioxygen. Nitrification reactions were studied by assaying the nitrogen species (ammonium, nitrite and nitrate) and the effect of adding hydroxylamine, an intermediate of the enzymatic oxidation of ammonium. Metagenomic studies via 16S rRNA gene sequencing of the biofilms onto the colonized electrodes were performed 4 week after inoculation. These studies show that the cathodic biofilms were significantly enriched with Cupriavidus, a proteobacteria genus, that is likely to be responsible for the catalytic properties of the microbial biocathode.

The Figure shows the reduction of molecular oxygen by a colonized electrode at pH 7 and 20 °C in a 0.1 M fresh phosphate buffer as recorded with slow scan rate cyclic voltammetry. Scan rate: 1 mV/s. Green: abiotic graphite electrode under oxygen saturation. Black: biocathode under argon saturation. Red: biocathode under air. Blue: biocathode under oxygen saturation. Note also the chemically reversible system found at +0.25 V and assigned to the biofilm. Catalytic hydrogen peroxide reduction (not shown) occurs at the potential of this system.

Figure 1
3D Printing of Living MFC Anode
Authors: Freyman Megan Carey , Kou Tianyi , Wang Shanwen , Li Yat
Published: May 2020

3D printing helps to provide further control on electrode design. By using 3D printing to tune the geometry, porosity and dimensions of the structure, mass transport to functional microbes or sites in the structure can be improved. By embedding living microbes directly into the ink we can create 3D printed structures to help harness the activity of microbes and use them in functional devices. Here we demonstrate the incorporation of the living bacteria Shewanella Oneidensis MR-1 (S. Oneidensis MR-1) directly into an ink used for creating 3D printed structures. By incorporating S. Oneidensis MR-1 into a sodium alginate-cellulose ink we showed that S. Oneidensis MR-1 survives the 3D printing process through the prominent degradation of methyl orange azo dye from the surrounding solution in the presence of the living 3D printed structure. The viability was further confirmed using confocal microscopy. By incorporating carbon black into this ink we further demonstrate the direct printing of a living microbial fuel cell (MFC) anode. Electrochemical measurements showed there was good charge transfer between the S. Oneidensis MR-1 and the electrode surface. To our knowledge, this is the first report on implementing 3D printed bacteria structure as a living electrode for an MFC system. The capability of printing living and functional 3D bacterial structure could open up new possibilities in design and fabrication of microbial devices as well as fundamental research on the interaction between different bacterial strains, electrode materials, and surrounding environments.
(Invited) Structural Characterization of Nanoporous Materials Via Gas Sorption
Authors: Cychosz Struckhoff Katie
Published: May 2020

Recently, much effort has been devoted to the development of nanoporous materials which exhibit hierarchical pore structure with the appropriate balance of micro- and mesopores, as well as advantageous pore connectivity. The network of interconnected micro- and mesopores facilitates efficient transfer of fluids to and from active sites within and through the material, leading to benefits in numerous applications. Detailed insights into the pore architecture (pore size distribution, pore volume, and pore interconnectivity) are important because they control transport phenomena, diffusional rates, and govern selectivity.

Gas sorption is well suited for this because it assesses a wide range of pore sizes, spanning the entire micro- and mesopore range. Additionally, an in-depth characterization of the pore network can also be obtained with a detailed understanding of the adsorption and phase behavior of fluids confined in such complex pore structures. Here, we discuss recommended experimental and state-of-the-art data reduction methods for a comprehensive study of the pore architecture of nanoporous materials which includes: choice of adsorptive, accurate BET area calculation, DFT for pore size and volume determination, hysteresis scanning, and interpretation of material phase transitions.

Recent examples of the structural characterization of novel carbons, mesoporous zeolites, and MOFs will be discussed.
(Invited) Designing Electrodes with Low Tortuosity Pores By Freeze Tape Casting
Authors: Doeff Marca M , Yi Eongyu
Published: May 2020

The tortuosity of pores in composite electrodes for conventional lithium-ion batteries (LIBs) or “beyond lithium-ion batteries” is an extremely important parameter for optimizing performance. The lower the tortuosity, the shorter the path lengths that ions have to travel, which should result in better rate capability and charge acceptance. By using a method known as freeze tape casting (FTC), we are able to design electrodes with nearly unidirectional pores approximately normal to the film thicknesses. In this technique, an aqueous or non-aqueous slurry containing materials of interest is tape cast over a bed set at a temperature below the freezing point of the solvent. As the solvent freezes, the ice crystals that form exclude the solid particles, which segregate into columns. A freeze-drying step removes the ice, leaving behind the porous structure. In the case of conventional composite battery electrodes meant for use in cells with liquid electrolytes, the active materials, binder, and conductive additives can be cast together, similar to what is done by conventional tape casting. For solid-state batteries, a ceramic ionically conducting scaffold is first formed by the FTC process and then sintered to strengthen the pore walls. The scaffold is then infiltrated with active material and other components to form the electrode. In both types of systems, the film thickness, porosity, pore size and shape, and column thickness can be adjusted over a wide range by varying experimental parameters such as temperature, loading, and solvent type. For this talk, we will present several examples from our recent work including solid-state batteries using Li7La3Zr2O12 (LLZO) electrolytes, LIB graphite anodes for fast-charge applications, and sulfur electrodes for lithium/sulfur batteries.
FIB/SEM Nanotomography of a CO2 Electrolyzer Cathode Catalyst Layer
Authors: McLaughlin David , Thiele Simon
Published: May 2020

Silver catalysts have demonstrated selective reduction of CO2 to CO. CO produced by this reaction could replace fossil fuel derived CO as a feedstock for fuels and value added chemicals. Furthermore, gas diffusion electrodes based on silver catalyst have additionally achieved high current density. Thus, the foundation for development of this promising defossilization strategy has been laid. In order to implement this strategy it is necessary to optimize catalyst layers to improve their durability and efficiency. At the same time, current density and selectivity need to be maintained. Detailed understanding of the electrodes is necessary to achieve these goals. In particular, the wetting parameters and the delicate balance of molecular and ionic transport needs to be investigated. We posit that in analogy to fuel cells, resolving the catalyst layers is essential.

Tomographic reconstructions have successfully resolved the catalyst layers of fuel cells and water electrolyzers down to the nanoscale. So far, CO2 reduction gas diffusion electrodes have been imaged using X-Ray microtomography. However, the applied X-ray tomography was insufficient in resolving the nano-porous structure of these catalyst layers. We have reconstructed a porous silver catalyst layer using focused ion beam scanning electron microscope (FIB/SEM) tomography. It is thus possible to resolve the pores down to the nanoscale. Using the geometric representation, obtained from the reconstruction, we calculated geometric structure and mass transport parameters. Finally, we modeled the effect of (partial) flooding of the catalyst layer. We present the tomography alongside results for the porosities, diffusivities and conductivities of the catalyst layer.
Overcoming the Selectivity-Permeability Trade-Off with Nanoporous Carbon Nanotube Membranes
Authors: Chen Chiatai , Li Yifan , Meshot Eric R. , Buchsbaum Steven F. , Herbert Myles , Zhu Rong , Kulikov Oleg , McDonald Ben , Bui Ngoc , Jue Melinda L. , Park Sei Jin , Valdez Carlos A. , Hok Saphon , Doona Christopher J. , Wu Kuang Jen , Swager Timothy M. , Fornasiero Francesco
Published: May 2020

From energy storage to separation applications, performances of nanoporous membranes are typically limited by an inherent trade-off between transport rate and selectivity. For example, conventional protective garments sacrifice breathability to prevent exposure to harmful agents, and this trade-off severely hinders the duration of their active use. The discovery of enhanced fluid flow in single-walled carbon nanotubes (SWCNT) has provided a path toward combining the diametric properties of high selectivity and permeability into a single SWCNT-based material, yet successful demonstration of this promise remains elusive.

Using as example the design of novel materials for protective clothing applications, herein we demonstrate a smart, nanoporous, SWCNT membrane that overcomes the limitation of conventional protective garments. Specifically, we show that the adoption of nanometer-wide SWCNTs for ultrafast moisture conduction [1] enables a simultaneous boost in size-sieving selectivity and water-vapor permeability by decreasing nanotube diameter, thereby overcoming the breathability/protection trade-off [2].Our membrane platform can rapidly and selectively transition from a highly breathable state in a safe environment to a protective state when exposed to a chemical threat. Dynamic response to chemical stimuli is achieved through the physical collapse of an ultrathin copolymer layer on the membrane surface, which efficiently gates transport through the SWCNT membrane pores [2].Multifunctional SWCNT membranes such these present exciting opportunities in many other areas including energy-efficient separations, energy storage, and smart delivery.

References

1. N. Bui, E. R. Meshot, S. Kim, J. Peña, P. W. Gibson, K. J. Wu, F. Fornasiero, Adv. Mater., 28 (2016) 5871.

2. Y. Li, C. Chen, E. R. Meshot, S. F. Buchsbaum, M. Herbert, R. Zhu, O. Kulikov, B McDonald, N. Bui, M. L. Jue, S. J. Park, C. Valdez, S. Hok, C. J. Doona, K. J. Wu, T. M. Swager, F. Fornasiero, submitted (2019)

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
An Extensive Study of the Electrical Conduction in HKUST-1 Single Crystals
Authors: Koh Sang-Gyu , Nakaune Yusuke , Hachida Momoka , Morita Takumi , Kinoshita Kentaro
Published: May 2020

Metal-Organic Frameworks (MOFs), which is three-dimensional (3-D) nanoporous materials composed of metal ions and organic ligands coordinated together, has recently attracted enormous attention as functional materials for electronic devices owing to their structural and functional flexibility in the design, as well as relatively high thermal stability [1, 2]. Although there are some reports so far that guest molecule doping drastically improves the electrical conduction of MOFs, e.g. the electrical conductivity of HKUST-1 (Cu3(btc)2) increases by infiltration of TCNQ, most of those experiments has been done using pellet or polycrystalline film samples [3, 4]. To extract an intrinsic electrical current conduction, avoiding the influences of grain boundaries and the residual stress introduced into the film due to the substrate mismatching, the use of single crystalline sample is essential.

In this work, we investigated the dominant conduction mechanism of TCNQ-infiltrated bulk HKUST-1 single crystals which include much less grain boundaries and residual stress, by measuring the electrical conductivity as functions of a bias voltage, temperature, and pressure.

Sub-mm sized HKUST-1 single crystals were fabricated and infiltrated with TCNQ using a saturated TCNQ/CH2Cl2 solution. The temperature dependence of DC current between 30 °C to 110 °C in the ambient shows that a current at 10 V decreases with increasing temperature down to undetectable value of less than 1 x 10-12 A, although the current value at 30 °C of around 1 x 10-6 A is similar to that of polycrystalline films [3]. We also confirmed that the temperature dependence of DC current for un-infiltrated HKUST-1 single crystals almost agrees with those of the TCNQ-infiltrated ones. Therefore, TCNQ infiltration is not effective in improving an electrical conductivity and the relatively high electrical conductivity at 30 °C is attributed to the presence of water absorbed by samples from the ambient, which was confirmed by thermogravimetric analysis. These results indicate that the current we measured was attributed to the ionic conduction probably due to the electrolysis of water inside the nanoporous structure not to the electronic conduction. Therefore, it is implied that the drastic improvement of the conductivity in the TCNQ-infiltrated HKUST-1 reported in ref. [3] is due to the use of film instead of bulk single crystal. It is suggested that the residual stress introduced into the HKUST-1 film by substrate mismatching plays a key role in the improved electronic conduction of the TCNQ-infiltrated HKUST-1 system. We will also discuss the effect of applying high pressure to the single crystals.

References

[1] G. Wu et al., J. Am. Chem. Soc. 2017, 139, 1360−1363.

[2] Y. Liu et al., Angew.Chem.Int.Ed.2016,55,8884–8888.

[3] A. A. Talin et al., Science, 2014, 343, 66-69.

[4] M. R.-Torrente et al., Phys.Chem.Chem.Phys., 2019, 21, 25678.
Morphology, Composition and Sensor Performance of Nanoporous Au(Pt)
Authors: Wong Timothy , Ebrahimy Amirhossein Foroozan , Langelier Brian , El-Zoka Ayman Amr , Newman Roger C.
Published: May 2020

Recent atom-probe tomography (APT) and ATEM studies of dealloyed layers in binary AgAu and ternary AgAuPt alloys showed the various ways in which more-noble elements enrich during dealloying, at the atomic scale (1). We have since extended this research in several directions – towards less expensive alloys, lean in more-noble elements, and towards the potential applications of such materials in gas sensing.

In this presentation, we will start with a review of published and unpublished data from the APT study, which was done using alloys with 23 at% (Au + Pt). New information will then be shown for alloys with less than 6 at.% (Au + Pt). The dealloyed layers are very Ag-rich, and very interesting conflicts arise between enrichment of the more-noble element(s) on the ligament surfaces and the ultimate supply of those elements.

For gas sensing applications, we take advantage of the effect of adsorption on ligament surfaces on electron scattering during conduction in the confined metal phase. Delicate impedance measurements at the milli-ohm level show that two kinds of environmental effect can be distinguished. Adsorption of water or other gases up to several molecular layers induce changes in the measured resistance of the metal phase, while thicker layers induce a double-layer charge separation leading to capacitive changes.
In Situ UV-Visible Optical Spectroscopy Study of Nanoporous Gold Formation By Electrolytic Dealloying
Authors: Chacko Joel , Corsi John S , Welborn Samuel S. , Detsi Eric
Published: May 2020

Thin films of nanoporous gold (NP-Au) have been extensively studied for localized surface plasmon resonance [1,2], showing a strong structure-property relationship between the morphology of the porous network and resonant frequencies. In this talk, I will show how we take advantage of this structure-property relationship and use UV-Visible optical spectroscopy to study the morphology evolution in NP-Au thin films in situ during selective electrolytic leaching of the sacrificial Ag from Au-Ag parent alloy. The evolution of plasmon resonance frequencies obtained from in situ UV-Vis spectra are directly linked to the morphology evolution (development of pores and changes in structure size) and the chemical composition (change in Ag content) in NP-Au, as confirmed by ex situ electron microscopy data.

[1] A. Pröschel, J. Chacko, R. Whitaker, M. A. U Chen, and E. Detsi: Journal of The Electrochemical Society 166, H146-H150 (2019).

[2] E. Detsi, M. Salverda, P.R. Onck and J.T.M. De Hosson:

Journal of Applied Physics 115, 044308 (2014)
Pore Size-Controllable Synthesis of Bimetallic or Multiple Metallic Nanostructures
Authors: Chen Shutang , Chen Gugang
Published: May 2020

Nanoporous materials have generated a great deal of interest in catalysis, sensor, electronics, phase separation, and environmental remediation. However, it is still a big challenge to control pore size and reduce the pore to the nanoscale level. Here, we report a one-step general synthesis method based on galvanic replacement for the fabrication of Cu-based bimetallic or multiple metallic porous nanostructures. The pore size-control can be realized through adjusting reaction parameters such as temperature, precursor concentration, and reaction intervals. Furthermore, these porous nanostructures demonstrate excellent catalytic and conductive performance. We envision that such simple synthesis strategy could be extended to the design of other inorganic nanoparticles for various applications.
Low-Tortuosity, Highly Conductive, Vertically Aligned, Ultra-Thick Composite Electrode Design for Batteries
Authors: Fu Kun
Published: May 2020

Ultra-think electrode is very important for high-energy batteries. It requires to increase the volume ratio of active material to inactive material and to improve the electrochemical reaction kinetics with low-tortuous ion and electron transfer pathways. In this talk, I will introduce a vertically aligned carbon fibers framework to structurally and electrically reinforce electrode structure to obtain high conductivity and low tortuosity. Compared with the traditional LFP electrodes composed of randomly dispersed LFP particles and carbon black particles, the CF-LFP electrodes show significant improvements in active material loading, structural stability and electrochemical performance due to the unique vertical arrangement of carbon fibers inside composite electrode. Because the vertical arrangement of carbon fibers provides a fast electron/ion transport channel, it promotes the redox reaction kinetics in the electrodes. CF-LFP electrodes significantly enhance the capacity and rate capability. The thickness of the electrode can be up to 1 mm with a loading of ~128 mg/cm2 and a specific capacity of 154 mAh/g.
Modeling of Li-Ion Batteries with Highly-Ordered Hierarchical Electrode Design
Authors: Goel Vishwas , Chen Kuan-Hung , Namkoong Min Ji , Yang Chenglin , Kazemiabnavi Saeed , Mortuza S. M. , Mazumder Jyoti , Sakamoto Jeff , Dasgupta Neil P. , Thornton Katsuyo
Published: May 2020

The advent of battery-powered electric vehicles has generated a need for batteries that are both energy and power dense. Traditionally, thick electrodes with heavy active material loading are used for enhancing the energy density of a battery. However, thick electrodes (with a loading of > 2.5 mAh/cm2) limits the ionic transport inside the electrode, thereby limiting the power density of the battery1. Decreasing the thickness of the electrodes, as well as increasing the porosity, can enhance the power density of a battery, but this increases the fraction of electrochemically inactive materials, such as current collectors, separator, and packing material, leading to reduced energy density. Therefore, the conventional electrode design is constrained by the tradeoff between the energy density and power density.

In this presentation, we examine the role of channels within a thick anode in reducing the ionic transport limitation2,3. We apply the porous electrode model4 to simulate the effect of the channels on the ionic concentration gradient and reaction rate, as well as the resultant rate capability of the cell. We will describe the parameterization of the model using three-electrode measurements. The model results show substantial improvement in the electrolyte salt concentration because of channels as compared to that in the conventional electrodes at high charge rates such as 4C and 6C.

References:

1. Gallagher, K. G. et al. Optimizing areal capacities through understanding the limitations of lithium-ion electrodes. J. Electrochem. Soc.
163, A138–A149 (2016).

2. Kim, Y., Drews, A., Chandrasekaran, R., Miller, T. & Sakamoto, J. Improving Li-ion battery charge rate acceptance through highly ordered hierarchical electrode design. Ionics.
24, 2935–2943 (2018).

3. Nemani, V. P., Harris, S. J. & Smith, K. C. Design of bi-tortuous, anisotropic graphite anodes for fast ion-transport in Li-ion batteries. J. Electrochem. Soc.
162, A1415–A1423 (2015).

4. Newman, J. & Tiedemann, W. Porous-Electrode Theory with Battery Applications. AIChe J.
21, 25–41 (1975).
Modeling the Interfacial Chemistry of Graphene-Based Composite Electrode Materials for Lithium Ion Battery
Authors: Sharma Vidushi , Ghatak Kamalika , Datta Dibakar
Published: May 2020

High volumetric expansions, large compressive stresses, and subsequent interfacial debonding are largely associated with high energy density materials such as Silicon (Si). Incorporation of additional materials such as Graphene provides Si anode a porous skeleton, allowing Si to expand/contract easily with low mechanical stresses and continuous electrical contact with added advantages of flexibility, good conductivity, lightweight, and high surface Li diffusivity. The interface between Si and Graphene has been extensively studied computationally, and effects of its attributes on battery performance have been determined via experimental investigation of Si-Graphene based composite electrodes. Graphene significantly lowers the stresses in expanding Si, thus increasing its cycle life. In this study, specific interfacial attributes, which directly or indirectly contribute towards the strain accommodation in expanding electrodes have been analyzed, with the aim to create a model that will help in understanding and predicting the performance of graphene provided-interface in Lithium ion batteries. For this purpose, First Principle calculations are carried out using VASP to examine the interfacial chemistry of Si-Graphene system. Produced results are then further compared with additional electrode models: Tin(Sn) and Selenium(Se). While Sn is another high energy density material, which holds promise as anode for ion batteries beyond LIB, Se is a cathode material with superior electrical conductivity and lithiation rates. Both materials undergo strenuous phase changes during battery performance. Changes in interface characteristics post phase change of electrode have also been emphasized. It was understood that interfacial cohesive energy is not merely dependent upon the atomic attributes and type of bonding with the Graphene surface as mostly highlighted, but also on unaccounted for lattice mismatch between the crystalline electrode and Graphene. With changing phases and deviation in lattice constants, interface adhesion changes even though bonding between electrode and Graphene remains unchanged.
Digital Deposition of Graphite Electrodes and 3D Microstructure Optimisation
Authors: Kendrick Emma , Gastol Dominika , Capener Matthew
Published: May 2020

Water-based high viscosity graphite inks for automated digital deposition of Li-ion battery electrodes have been studied. The flow behaviour and visco-elastic properties of the inks were optimised for a digitally controlled additive manufacturing deposition method and high energy electrodes. A rheology modifier was introduced as an immiscible secondary fluid to control the flow behaviour of these inks. Through optimisation of the formulation, graphite electrodes with high mass loadings were achieved. Depending upon the rheology, both patterned or homogeneously coated electrodes were successfully deposited. The influence of the ink formulation upon the microstructure and electrochemical performance of the prepared anodes is discussed. 3D microstructure was analysed by 2-D electrode cross sectioning and scanning electron microscopy (SEM). It was observed that with an increase of the rheology modifier the alignment of the graphite particles, as well as the distribution of the conductive additive was altered considerably. The dispersion of the conductive additive improved up to 1% additive with greater alignment of the graphite particles, however at 10% additive clumping of the graphite particles was observed. The electrochemical performance of the different electrode microstructures was investigated through electrochemical cycling and impedance spectroscopy. Figure 1 shows the cross-sectional microstructure of the electrodes with 0% and 10% rheology modifier.

Figure 1
(Invited) Towards Addressing Fundamental Manufacturing Questions for Polymer Electrolyte Fuel Cell Electrodes
Authors: Mauger Scott A , Khandavalli Sunil , Wang Min , Park Janghoon , Baez-Cotto Carlos , Pfeilsticker Jason , Van Cleve Timothy , Neyerlin K C , Ulsh Michael
Published: May 2020

As a result of the expansion of material handling, backup power, and now, automotive markets for low-temperature fuel cells, the need to understand and overcome challenges to high-volume electrode production has never been greater. OEMs and system integrators globally are addressing these challenges specific to their systems and materials. However, fundamental questions remain to be answered, to the benefit of the entire industry. The interactions between the supported catalyst, ionomer, and dispersing media in the electrode ink, the method of dispersion of the solid constituents of the ink, and the interaction of the ink with the substrate, strongly impact the morphology and ultimately performance of the electrode. The ink formulation must also be appropriate for the coating and drying processes, the physics and parameters of which also impact electrode morphology and performance. Research efforts to address these questions are complicated by multiple pathways to construct the membrane electrode assembly (MEA) – including decal-transfer, catalyst-coated membrane, and gas-diffusion electrode structures – as well as a great variety of coating processes that could be used. These different structures not only potentially affect the performance of the MEA – and differently under different operating conditions – but they affect cost. In this talk, manufacturing pathways and challenges for electrodes will be discussed, and an overview of activities at the National Renewable Energy Laboratory to address these fundamental questions will be given.