bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of Porous Nanotubes for Simultaneous Improvements of Material Usage Efficiency and Catalytic Performance of Iridium-Based Water Oxidation Reaction Catalysts
Authors: Nam Yungi , Shin Byungha
Published: May 2020

Iridium (Ir) is the most widely used material for oxygen evolution reaction (OER) catalyst due to its great catalytic performance. However, Iridium is a very expensive element because it is one of the rarest elements on earth. Therefore, it is necessary to minimize Iridium consumption whilst maintaining the highest possible catalytic performance. One of common strategies to achieve a high catalytic performance is enlarging surface area by forming nanostructures; however, such nanostructures often limit mass transport of both reactants (liquid electrolyte) and products (oxygen gas), nullifying the benefit gained from the large surface area. Here, we developed a porous nanotube catalyst structure which can maximize its performance with a very small amount of Iridium and allow facile mass transport via pores formed on the sidewall of the nanotubes. The synthesis involves the formation of vertically aligned ZnO nanowires that serve as a template. Electrodeposition of Ni follows to conformally coat the ZnO nanowires. Careful control of wet etching conditions results in the complete removal of ZnO and partial removal of Ni shells forming pores on the Ni nanotubes. Finally, Ir is electrodeposited on the porous Ni nanotubes. The porosity of the structure can be controlled to optimize the catalytic performance. It can also be used as a catalyst template for other elements that need high performance while using a small amount of the material. The details of the synthesis and the electrochemical measurements of OER using our nanostructured Ir-based catalysts will be presented.
Rational Design of Copper Alloy Catalysts for Electrochemical CO2 Reduction
Authors: Akhade Sneha A , Weitzner Stephen Eric , Qi Zhen , Biener Monika M. , Varley Joel Basile , Baker Sarah E , Duoss Eric B , Wood Brandon C. , Biener Juergen
Published: May 2020

Electrochemical conversion of CO2 is a potentially exciting route towards production of sustainable drop-in fuels and chemicals using renewable electricity. A key obstacle in the commercial scale-up and deployment of CO2 utilization and conversion is the lack of active and selective catalysts. Across all monometallic candidates, Cu exhibits distinctive ability to electrochemically reduce CO2 to several products including methane and ethylene, albeit its multifunctional nature makes selectivity control challenging [1]. Alloying offers a means to break scaling relationships and uniquely manipulate the reactivity and selectivity in ways that would be hard to achieve using monometallic compositions alone. Here, we employ a coupled quantum mechanics/molecular mechanics (QM/MM) scheme [2] to screen various copper alloys for their reactivity and selectivity towards key rate-limiting and selectivity-determining steps in CO2 conversion. The activity-selectivity screening is carried out under reducing conditions to thoroughly probe the influence of the electrolytic ions under the applied potential on the alloy stability and reactivity. The results of these studies show how alloying in conjunction with electrolyte tuning can non-intuitively alter the surface electronic and catalytic properties of the catalyst leading to changes in activity-selectivity towards CO2 conversion. This serves to provide a rationale for improved composition and environment driven design and screening, and allows the use of chemical computation using nuanced, dynamical models of the electrochemical double layer[i].

[1] Y. Hori, in Handbook of Fuel Cells: Fundamentals, Technology and Application (VHC Wiley, Chichester, 2003), Vol. 2, 720-733.

[2] J. Haruyama, T. Ikeshoji and M. Otani, Electrode potential from density functional theory calculations combined with implicit solvation theory. Physical Review Materials (2018), 2(9), p.095801.

[i] This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.
Buffer Pka Impacts the Mechanism of Hydrogen Evolution in Water Catalyzed By a Cobalt Porphyrin-Peptide
Authors: Alvarez-Hernandez Jose L. , Sopchak Andrew , Bren Kara
Published: May 2020

A detailed study of the impact of buffer pKa
(pKa
5.6 to 10.5) on electrochemical hydrogen evolution at constant pH catalyzed by CoMP11-Ac, a cobalt porphyrin peptide, is presented. The addition of buffer leads to a significant enhancement of the catalytic current of up to 20-fold relative to its value in absence of buffer. Two distinct catalytic regimes are identified based on the buffer pKa
. In the presence of buffers with pKa
≤ 7.4 a fast catalysis regime limited by diffussion of buffer is reached. The catalytic half-wave potential (Eh
) shifts anodically (from -1.42 to -1.26 V vs Ag/AgCl/KCl(1M)) as the buffer pKa
decreases from 7.4 to 5.6, proposed to result from fast Co(III)-H formation following the catalysis-initiating Co(II/I) reduction. With higher-pKa
buffers (pKa
> 7.7), an Eh
= -1.42 V reflecting the potential of the Co(II/I) couple is maintained independent of the buffer pKa
, consistent with a rate-limiting Co(III)-H formation under these conditions. We conclude that the buffer species pK
a, even at constant pH, can have a large effect on both catalytic current and potential, as well as the rate-determining step of the reaction. Thus, buffer is a factor to consider in optimizing reaction conditions for hydrogen-evolving catalysis and for other proton-requiring reactions in water. Finally, buffer acids are shown to be a probe for studying hydrogen evolution mechanism in water.
High-Throughput Screening of Hydrogen Peroxide (Electro)Catalysts Using Scanning Electrochemical Microscopy (SECM)
Authors: Zhao Yuanya , Kromer Matthew , Adams Jason , Flaherty David , Rodriguez-Lopez Joaquin
Published: May 2020

Hydrogen peroxide (H2O2) is a powerful, versatile and environmentally benign oxidant that has gained relevance in industrial settings. Direct synthesis of H2O2 from O2 and H2, which is a method with low pollution and on-site production at potentially low cost, has attracted great interest. To realize this synthetic process, catalysts of high efficiency need to be developed to facilitate the reaction. In this study, scanning electrochemical microscopy (SECM) methods were used to conduct high-throughput screening of bimetallic nanoparticle catalysts (consisting of Au, Pt, Ni, etc.) for H2O2 generation from direct synthesis. In order to achieve high-throughput analysis, samples with multiple catalysts were fabricated. We used photolithography to produce wells that confined catalyst spots of a library of materials. Gold nanoparticles (AuNPs) were dispensed into these wells with a microdispenser, leaving the same amount of AuNPs at each spot. Droplets of corresponding metal salt solutions were added into the wells and then annealed to form bimetallic catalyst spots. The morphology and composition of fabricated spot arrays were characterized with SEM, TEM and EDS.

SECM measurements were performed to study the catalytic reactivity of the catalyst spots for H2O2 direct synthesis. From an electrochemical point of view, the entire process of H2O2 direct synthesis from H2 and O2 can be split into two half reactions, oxygen reduction and hydrogen oxidation. The first half reaction, oxygen reduction reaction (ORR), is a two-electron process reducing O2 into H2O2. The second half reaction, hydrogen oxidation reaction (HOR), converts H2 to protons. Only when a catalyst exhibits outstanding catalytic reactivity towards both two reactions, does it catalyze H2O2 direct synthesis efficiently in a thermocatalytic system. The catalytic reactivity for the two half reactions was investigated separately in a high throughput manner by SECM as the technique acquired information from the entire spot array in one scan and revealed catalytic performance for each spot in the array. SECM images were obtained to visualize catalytic reactivity of the spot array.

Finite element analysis simulation was done in COMSOL Multiphysics to acquire theoretical values for SECM experiments. The ultimate goal of this study is to identify a catalyst of a specific composition with the best catalytic reactivity for overall H2O2 direct synthesis. Such catalyst can be used in industrial H2O2 production to improve production efficiency and to reduce cost.
Accessing Catalytically Active Ordered Intermetallics Compounds Via Electrochemically Driven Phase Transformations
Authors: Hall Shoji
Published: May 2020

The conversion of O2 to H2O is an important fuel cell reaction for the recovery of renewable electricity from chemical fuels. Alloys of Pt-group metals (PGMs) with transition metals have emerged as catalysts with enhanced activity and durability for the oxygen reduction reaction (ORR). To date, most studies focus exclusively on alloys that adopt a Face-centered cubic (FCC) or Face-centered tetragonal (FCT) crystal lattice. Under ORR operating conditions, these materials evolve from alloys to Pt core-alloy shell materials, in this case both the alloy core and Pt shell retains the CCP type crystal structure; indicating that materials can dynamically change during catalysis.

Here we present the synthesis of Pd-Bi based ordered intermetallics by partial dealloying of a Bi rich alloy. We found that under ORR operation conditions, ß-PdBi2 which adopts a tetragonal lattice, transforms to Pd3B orthorhombic crystal structure; this transformation is mediated by oxidative Bi corrosion under potential cycling, and reconstruction of the atoms in the bulk. To the best of our knowledge, this is the first report of a material that exhibits an electrochemically driven, non-congruent phase transition among materials with different crystal structures. The resulting phase-converted Pd3Bi is stable and exhibits high performance for ORR. Phase-converted Pd3Bi outperform Pt and Pd metal, reaching mass activities of 2.6 A/mgPd, which is nearly 10X higher than Pt/C (~0.3 A/mgPt) and Pd/C (~0.2 A/mg) at 0.9 V vs the Real Hydrogen Electrode (RHE). The mass activity of Pd3Bi decreases by ~38% after 10,000 cycles, indicating that it is stable. Activation energy (Ea) determined by temperature dependent electro-kinetic measurements indicates that the activity enhancement on phase-converted Pd3Bi originates from anion-poisoning resistant behavior. These results establish that PGMs-based ordered intermetallics with low-symmetry crystal structures can be highly active and durable electrocatalysts.
Bio-Inspired Heterogeneous Catalytic Cascades
Authors: Atanassov Plamen
Published: May 2020

Bio-electrochemistry research in our group has been focused on building suitable materials and design of interfaces to accommodate biocatalysts, both enzymatic and microbial for most advantageous utilization in sensing, energy harvesting and water treatment technologies. Over the years we have demonstrated several enabling materials design approaches to address critical challenges in bio-electrocatalysis: facilitating charge transfer through tethering immobilization, enzyme orientation, hierarchically structured nano-materials integrated into device design, immobilization by encapsulation in polymer and silica matrixes and development of hybrid microbial/enzymatic and microbial/platinum group metal-free bio-electrochemical devices.

A critical challenge in building complex bio-nano-devices is the ability to combine several catalytic reactions into a “cascade” with channeling as underlying principle for effective multi-step catalysis.1One particularly complex area of our research over the last yeas has been in development of materials solutions for catalytic cascades, which would integrate bio-catalysis with molecular and heterogeneous catalytic steps.2-4We are currently engaged in a large program directed towards bringing together functional catalysts from the most distinctly different types: enzymes, molecular catalyst and metallic nanoparticles into a singular functional interface for realization of cascade reactions catalyzed by all these different species/moieties. We will illustrate the approach by discussing the synthesis of a hybrid enzyme/metal nano-particle/atomically-dispersed nano-material functional catalyst cascade.

This bio-inspired catalytic cascade aims to demonstrate the possibility of assembling heterogeneous catalytic reactions in sequence while the catalysts of three dissimilar classes are all immobilized on a 2D nanomaterial (graphene). The paper aims to bring a vision of building bio-electrochemical devices, where enzymatic catalysis will be enhanced by the heterogeneous and molecular one, with all catalytic moieties co-present at a single “designer interface” based on graphene-like carbonaceous material. This material allows ease of integration by printing into a paper-based microfluidic analytical platform designed for a confocal Raman microscope with in situspectro-electrochemical detection.5,6

1. Wheeldon, I., et al., Nature Chemistry,8 (2016) 299–309

2. Abdellaoui,S., et al., Chemical Communications, 53(2017) 5368-5371

3. Xia, L., et al., ACS Energy Letters., 2 (2017) 1435-1438

4. Perry, A., et al., ChemElectroChem, 4 (2017) 2336-2344

5. Andersen, N., et al., ChemElectroChem, 6 (2019) 246-251

6. Andersen, N., et al., ChemElectroChem, 6 (2019) 2448–2455

Figure 1
(Invited) Solvent-Based Synthesis and Integration of Nanostructured Alloying Electrode Composites with Controlled Surface Chemistry and Morphology
Authors: Holmberg Vincent C.
Published: May 2020

Careful control over composition, morphology, and surface chemistry are critical in virtually every materials system, and it is vital that these attributes are preserved in any scalable production process. This talk will explore the important role that the above characteristics play in our group’s research on the supercritical-fluid-based synthesis and integration of nanostructured, high-capacity alloying electrode materials for electrochemical energy storage in Li- and Na-ion battery systems. Clearly, careful control over interfacial chemistry and surface reactions are critical for the design of robust electrochemical systems. These nanostructured composite materials have short internal diffusion pathways, possess robust mechanical characteristics, and can be processed in either liquid dispersion or solid/powder form. We show that careful control over active material surface chemistry helps to facilitate robust solid-electrolyte interphase layer formation, demonstrate that nanowire-based alloying electrodes can maintain capacity retention in the complete absence of fluorinated additives, fluorinated electrolytes, and fluorinated binders, and show that electrode processing plays a critical role in the formation of a robust composite architecture and overall device performance. In addition, the effects of structural anisotropy and surface oxidation on the sodiation of high-power-density, nanostructured antimony alloying electrodes will also be discussed.
(Invited) The Relationship of Morphology and Catalytic Activity: A Case Study of Iron Corrole Incorporated in High Surface Area Carbon Supports
Authors: Elbaz Lior , Levy Naomi
Published: May 2020

In the past several years we have been thoroughly studying the performance of molecular catalysts for oxygen reduction based on metallo-corrole. We studied the effect of the metal center, substituents in their meso and beta positions and ORR mechanism at a wide pH range. The most influential factor was found to be the metal center while the effect of electro-negative substituents seems to diminish once these molecular catalysts were incorporated in porous carbon supports. Moreover, the overall activity and reaction selectivity has increased dramatically after this incorporation, and was found to be dependent on the carbon support. Specifically, metallo-corroles have shown to have unique catalytic properties for oxygen reduction when adsorbed on a high surface area carbon: BP2000. The nature of the interaction between carbon surfaces and metallo-corroles was identified in this work. The results suggests that the catalytic activity lays not in a bond between the carbon surface and the corrole molecule, but rather in the arrangement of corrole molecules within the porous structure of the carbon surface. This hypothesis was studied here using Electron Paramagnetic Resonance (EPR), X-ray diffraction (XRD), UV-VIS spectroscopy, elemental analysis, N2 adsorption and several electrochemical methods. BP2000 carbon was compared to four other carbons with different properties (oxygen surface groups, surface area, porous structure and crystallinity). All of these show that the Fe-corrole that was incorporated in BP2000 tends to adsorb in pores of 20-25 nm in diameter, which allow synergistic effects to take place, and enhance the electrocatalysis of oxygen reduction reaction.
Magnetic Filling of Microporous Silicon: An Interlink of Optical and Magnetic Behavior
Authors: Granitzer Petra , Rumpf Klemens , Reissner Michael , Michor Herwig
Published: May 2020

In the frame of this work microporous silicon (mPSi) is filled with magnetic metals (Ni, Co) resulting in a composite system with specific magnetic properties. The results are compared with mesoporous silicon (PSi) loaded with Ni nanoparticles (NPs) of comparable size. The mPSi offers luminescence in the visible, whereat this behavior is due to the small structure size in the range of a few nanometers (2 – 5 nm) [1]. The morphology of mesoporous silicon shows straight pores with a diameter up to 50 nm.

The mPSi samples are fabricated by anodization of a moderately doped p-type silicon wafer in a 10 wt% hydrofluoric acid solution. The challenging metal filling of these pores is carried out under cathodic conditions by pulsed electrodeposition. As electrolytes aqueous NiSO4 and CoSO4 solutions are employed. The microporous silicon offers a branched morphology and thus also the deposited nanosized metal structures are interconnected. The structure size of the porous samples is estimated by photoluminescence measurements to 5 nm which also determines the size of the deposits. Mesoporous silicon is produced by anodization of a highly n-doped silicon wafer resulting in straight pores of about 50 nm in diameter [2]. The loading of these samples with Ni NPs is also performed by electrodeposition.

Magnetic filling of meso- and microporous silicon, respectively means a change in the morphology as well as in the structure size of the magnetic precipitations and both influence the magnetic behavior of the composite system drastically. In the case of mPSi also the luminescence is influenced in its intensity and wavelength by the magnetic filling. The magnetic properties are investigated with a Vibrating Sample Magnetometer (VSM) and a SQUID, respectively. A luminescence spectrometer is used to measure the intensity and the peak position of the photoluminescence spectrum. The structure is investigated by SEM and TEM.

Field dependent magnetization measurements show a distinct difference between Ni filled mPSi and PSi loaded with Ni NPs. Considering mPSi filled with Ni and Co a strong magnetic anisotropy between the two magnetization directions applying a magnetic field perpendicular and parallel to the surface, respectively is observed, whereas in the case of Co this behavior is even more pronounced. Figure 1 depicts the hysteresis of mPSi and mesoporous silicon filled with Ni. The coercivities do not vary in a broad range between Ni and Co samples but the saturation field differs drastically between the two materials. In contrast mesoporous silicon loaded with Ni NPs offers only a small magnetic anisotropy caused by weak magnetic interactions between the Ni deposits.

Since the microporous silicon offers photoluminescence the huge magnetic anisotropy is of interest for magneto-optical applications.

[1] Handbook of Porous Silicon, Ed. L. Canham, Springer Int. Publishing, 2018.

[2] P. Granitzer, K. Rumpf, Semiconductor Science and Technology 31, 4004, 2016.

Figure 1
Hard Magnetic Composite: FePt Nanoparticles Grown within Nanostructured Silicon
Authors: Rumpf Klemens , Granitzer Petra , Gonzalez-Rodriguez Roberto , Coffer Jeffery , Reissner Michael
Published: May 2020

In this work porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures which offer a hard magnetic behavior. The difference of the magnetic characteristics between the two systems is figured out.

The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution [1]. The morphology offers separated pores of about 60 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO [2]. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure are used. FePt nanoparticles (NPs) are chemically grown inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied (Pt:Fe 1:1, 1:3 and 1:6). For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.

Magnetic characterization of the samples is performed by VSM (Vibrating Sample Magnetometer), the structure is analyzed by SEM, TEM and EDX.

The magnetic response of the two different composite systems is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.

Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.

Hard magnetic materials within nanostructured silicon give rise for on-chip applications using 3 dimensional arrays of nanomagnets.

[1] K. Rumpf, P. Granitzer, H. Michor, NRL 11, 398 (2016).

[2] X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski, J.L. Coffer, Chem. Comm. 49, 5760 (2013).

Figure 1
Resolving the Discrepancy in Tortuosity Determination for Battery Porous Electrodes Via a Numerical Approach
Authors: Nguyen Tuan-Tu , Demortiere Arnaud , Fleutot Benoit , Delobel Bruno , Cooper Samuel J. , Delacourt Charles
Published: May 2020

The tortuosity factor of porous electrode microstructure is a crucial input parameter for numerical models of batteries as it strongly influences the electrode performance. As such, it is very important to have a method to determine this parameter accurately, based on a definition that reflects the design of the cell.

Various experimental methods have been developed for either directly measuring or indirectly inferring the tortuosity factor; however, numerical approaches, based on 3D image data, are now gaining interest in the battery community, due to the advances in nanoscale tomographic imaging methods. The standard definition of the tortuosity factor solves the Fick diffusion equation at steady-state, i.e., between two parallel constant-value boundaries. Although this approach has been widely used for porous materials, including both electronic insulators (e.g., a battery separator), and electronic conductors (e.g., battery porous electrodes), it may be the case that the definition needs to be adjusted depending on the scenario being observed.

In this study, we intend to give an insight into the appropriate way to determine the tortuosity factor of battery porous electrodes and the impact of various tortuosity determination methods is investigated. An additional module that relies on the symmetric cell method [1] [2] was implemented in the TauFactor software package [3] to compare with the already-implemented diffusion-based method [4]. This symmetric cell method refers to the measurement of the ionic current distribution inside the pores using AC impedance based on a symmetric cell setup. Figure 1 shows the workflow for tortuosity determination applied in this study. The integration of this module in TauFactor might be interesting for tortuosity determination at the microscale since it is the same method as at macroscopic scale observed in various experimental approaches.

Figure
1
. Illustration of the workflow for tortuosity determination applied in this work. The module recently implemented in TauFactor allows calculation based directly on tomographic data in symmetric cell configuration, and generates a simulated impedance spectrum. A macroscopic model such as TLM or Newman’s model is used to extract the tortuosity value of the electrode.

References:

[1] Landesfeind, J. et al.; J. Electrochem. Soc.
2016, 163 (7), A1373–A1387

[2] Malifarge, S. et al.; J. Electrochem. Soc.
2017, 164 (11), E3329–E3334

[3] Cooper, S. J. et al.; SoftwareX
2016, 5, 203–210

[4] Cooper, S. J. et al.; Electrochimica Acta 251 (2017) 681–689

[5] Pouraghajan, F. et al.; J. Electrochem. Soc.
2018, 165

Figure 1
Using Scanning Ion Conductance Microscopy to Measure Ion Conductivity and Permeability in Porous Materials
Authors: Payne Nicholas , Dawkins Jeremy , Schougaard Steen Brian , Mauzeroll Janine
Published: May 2020

Composite electrodes can significantly improve the performance of an electrochemical device by maximizing surface area and active material loading. Typically, additives such as carbon are used to improve conductivity and a polymer is used as a binder leading to a heterogeneous surface film with thickness on the order of tens of microns.

For such composite electrodes, good ionic conduction within the film is critical to capitalize on the increased loading of active material and surface area. Ionic conductivity within a film can be tricky to measure directly and homogenization models based on porosity are often used as a proxy. Scanning Ion Conductance Microscopy (SICM) has traditionally been a topography-mapping microscopy method. We will outline a new function and demonstrate SICM’s capacity for measuring ion conductivity within lithium-ion battery composite electrodes.
Thick Aqueous Processed Cathodes Enabled By Phosphoric Acid Addition
Authors: Kukay Alexander J , Sahore Ritu , Hawley William Blake , Li Jianlin , Wood David L.
Published: May 2020

Aqueous processed cathodes for lithium-ion batteries are favorable for both cost and environmental reasons; however, these electrodes still face significant problems with increasing areal capacities (i.e. thickness). Transition metal leaching from high nickel content active materials creates a very basic slurry, pH in excess of 12. This slurry composition subsequently corrodes the aluminum current collector, which leads to hydrogen gas generation. As a consequence, bubbling at the electrode interface causes substantial damage to the dried electrode. As the loading of these electrodes is increased, this mechanism becomes more severe and results in lack of adhesion and cohesion. In this work we investigate the introduction of varying amounts of phosphoric acid to combat the rise in pH and suppress the corrosion at the current collector surface. Phosphoric acid was added in increments of 0.5, 1, and 1.5 wt% and the subsequent effects on slurry rheology, particle size, adhesion, and electrochemical cycling were investigated. In this work we report a technique for obtaining thick (6-8 mAh/cm2) cathodes that exhibit reduced surface cracking and display improved rate performance as compared to control samples.
Vibrational Spectroscopy in the Study of Composite and Nanostructured Materials for Electrochemistry
Authors: Korzeniewski Carol , Liang Ying , Bukola Saheed , Creager Stephen E
Published: May 2020

Our research group has recently demonstrated the ability to probe within composite membranes formed by sandwiching single layer graphene (SLG) between two Nafion layers (Nafion 211, 25 µm thickness). These graphene-sandwich membranes have shown high selectivity for proton transport across electrochemical cells [1,2]. Using a microscope equipped with an oil-immersion objective, the graphene layer is readily detected in confocal Raman microscopy depth-profiles (z-direction profiles) of the composite membranes. Spectra are sensitive to defects and stress within the buried graphene layer. This presentation will discuss the use of confocal Raman microscopy for structural characterization and spatial profiling in the development of composite polymer electrolyte membranes that contain a graphene layer as a barrier to ion transport. In a second application area, infrared spectroscopy is being adapted to investigate properties of Nafion ionomer particles in dilute dispersions and during transformation to gel and solid phases through the use of time-resolved attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Since the properties of dispersing fluids can affect the mechanical strength of solution-cast Nafion thin films [3], it is of interest to gain insights into ionomer properties in the dispersion and during phase changes. A well-resolved peak associated with vibrational motions of the Nafion side chain -SO3
-end group is shown to be sensitive to gel-phase development. The persistence of hydration water in the vicinity of the -SO3
-group helps maintain a constant local refractive index that limits optical distortion in the band as the ionomer assembles into the phase-separated framework structure of the solid membrane. ATR FTIR measurements predict trends in evaporative water loss from the dispersion and entry into the gel-phase consistent with expectations of gravimetric measurements and earlier studies [3] of Nafion ionomer dispersion properties.

1. Bukola, S., et al. J. Am. Chem. Soc. 2018, 140, 1743.

2. Bukola, S., et al., ACS Appl. Nano Mater.
2019, 2, 964.

3. Kim, Y.S., et al., Macromolecules
2015, 48, 2161.
Structure-Performance Relationships for SOFC Electrodes
Authors: Shekhar Rustam Singh , Bertei Antonio , Monder Dayadeep S.
Published: May 2020

The performance of solid oxide fuel cells (SOFCs) depends critically on the microstructure of the composite cermet electrodes used in these devices. This presentation will discuss how microstructure models can be used to predict the reaction site density and effective transport properties. These properties include active three phase boundary length, effective conductivities of the electronic and ionic phases, effective diffusivities, etc. which are then used in a coupled physics model to predict SOFC performance. These multiscale models will be demonstrated using two architectures for SOFC electrodes: a) conventional composite powder based electrodes using a sintered mixture of ionic conductor and electronic conductor particles, and b) infiltrated electrodes where the ionic conductor particles are sintered and then the electronic conductor phase is deposited on this scaffold using solution infiltration.

We will demonstrate the impact of changing the electrode `recipe' on cell performance, focussing on experimentally measurable and controllable parameters such as particle sizes and phase volume fractions. The figure illustrates this point by showing in the upper plot how the active three phase boundary length for infiltrated electrodes changes with varying electronic phase volume fraction and is an order of magnitude higher than that for conventional electrodes at a much lower volume fraction. Active three phase boundary length and other effective properties derived from the microstructure models when plugged into the multiphysics models simulating fuel cell performance clearly demonstrate how and why infiltrated electrodes are capable of dramatically higher performance (see lower plot). The presentation will close with recommendations for high performance SOFC electrode design keeping particle size constraints imposed by the high operating temperatures in mind.

Figure 1
Straightforward Approach for Epitaxial Growth of CuO over ZnO Nanorods: Heterostructure Study and Photoelecterochemical Water Splitting Performance
Authors: Sherazi Syed Tauqir A. , Khan Yaqoob , Batool Humera
Published: May 2020

Optimization of the band gap in semiconductors through tailored heterojunctions has received immense research interests for advancement in photovoltaic and photoelectochemical hydrogen production. Heteroepitaxial superstructures are considered as crucial for charge carrier flow at the semiconductor interface. The present research attempt disclosed the method of facile fabrication of perfectly aligned ZnO nanorods, followed by their uniform decoration with CuO nanoparticles. In consequence, heterojuction was developed, which was studied through XPS and TEM. High resolution TEM images provides the evidence of coherent epitaxial growth due to overlapping lattices of both materials across the interface by highlighting the lattice mismatch of 7%. The 7 degree plane loss is expected due to less matching of lattice constants and misorientation of the planes at the interface. This assembly provided better collection of photo-generated charge carriers in extended light absorption range, resulting in better performance of photelectrochemical (PEC) water oxidation device.

Figure 1
(Invited) Interfacial Phenomena at Electrochemical Interfaces: Insights from First Principles Simulations
Authors: Balbuena Perla B.
Published: May 2020

Ion transfer and electron transfer phenomena taking place at electrochemical interfaces are in large proportion responsible for macroscopic performance of devices such as batteries, fuel cells, and electrolyzers. Significant recent advances in surface science characterization techniques (including in situ and in operando analyses) together with those in first-principles computational tools pave the way to elucidate details otherwise hidden in complex, non-equilibrium transport and reaction phenomena. Here we will discuss some examples of the applications of computational techniques such as density functional theory, ab initio molecular dynamics, and constrained molecular dynamics, and effects of applied potentials, to electrode/electrolyte interfaces in Li metal and Li-ion batteries. In our examples we will emphasize what are the new insights from theory, how theory can inform/suggest experiments and/or elucidate experimental outcomes. We will also discuss the challenges and expectations for the future.
Multi-Scale Modeling of Void Evolution at Li/SEI Interface during Delithiation
Authors: Yang Chi-Ta , Qi Yue
Published: May 2020

Lithium metal electrodes promise high energy density batteries due to its high specific capacity (3,860 mAhg–1) and lowest reduction potential, but Li dendrite growth still occurs in both liquid electrolyte and solid electrolytes. In liquid electrolytes, the Li metal surface is always covered by inorganic and organic layers which is called solid electrolyte interphase (SEI) due to the reduction of electrolytes. In solid electrolytes, the Li metal surface is either covered by solid electrolytes itself or by an interlayer formed by the decomposed solid electrolytes. Therefore, the atomistic level of Li stripping and plating processes occur at the Li/SEI interfaces. Maintaining a smooth Li surface during cycling will prevent non-uniform current distribution and suppress Li dendrite growth. The Li surface becomes non-smooth, as collections of Li vacancies (voids) are generated when the stripping process removes Li atoms from the Li/SEI interface faster than vacancies being filled. The accumulation of voids can lead to the interface delamination or pitting as well as to nonuniform current distributions at the interface of Li metal, promoting Li dendrite growth in the following plating process. Ideally, if Li atom diffusion toward the Li/SEI interface is comparable with the rate of Li removal, the surface voids will be digested (filled) by the Li from the bulk, thus a smooth Li surface will be achieved during Li stripping. Therefore, we developed a multi-scale modeling method combining density functional theory (DFT) and Kinetic Monte Carlo (KMC) techniques to study the evolution/formation of voids at different Li/SEI interfaces. The KMC method simulates the void's evolution by capturing the competition between voids generation due to Li removal with the processes to fill the voids, including Li atom diffusion in all directions and the mechanical deformation. DFT is used to determine the stable Li/SEI interfaces, adhesion, Li vacancy formation and diffusion near the Li/SEI interface, and more importantly, providing the Li diffusion barriers toward and away from the Li/SEI interface as the key inputs for the KMC simulation. Based on Li vacancy formation energy landscapes, when voids are generated at the interfaces, Li/LiF interface tends to trap Li vacancies at the interface, while Li/Li2O interface tends to repel the Li vacancies. KMC simulations show consistent results that the voids created at the Li/LiF interface do not migrate to the bulk portion of the Li metal, while the voids at the Li/Li2O interface are filled by diffusion of Li atoms from the bulk, in other words, the voids are digested by the bulk Li. Thus, by varying coating materials, the Li/coating interaction will lead to different morphology of voids evolution at the Li metal surface. This multi-scale modeling approach is anticipated to be applied to a wide range of SEI and SEE materials to maintain a smooth Li surface during the striping process, in order to prevent Li dendrite growth.
(Invited) Determining Dielectric, Electronic, Magnetic, and Structural Properties of Van Der Waals Materials from First Principles
Authors: Vandenberghe William , Laturia Akash , Kramer Aaron Austin , Tiwari Sabyasachi , Van de Put Maarten
Published: May 2020

Van der Waals materials have recently received great interest in the research community because of the ability to exfoliate and grow mono- or few-layer materials. Some important future possible applications are found in the field of nanoelectronics where extremely scaled transistors or magnetic memory devices are envisioned. However, there are more than 1,000 van der Waals materials known to date and an exhaustive experimental investigation is very expensive. This makes the accurate theoretical prediction of materials properties from first principles, enabling the identification of the most promising van der Waals materials possible, very valuable.

We show how the dielectric, electronic, magnetic, and structural properties of various van der Waals materials can be determined from first principles. We exhibit our robust methodology to extract the dielectric response of a monolayer/few-layer structure and calculate the low- and high-frequency dielectric constant of hexagonal boron-nitride and transition metal dichalcogenides (TMDs). We reveal a relatively small dependence of the dielectric constant on the number of layers. Surprisingly, we find a very large ionic contribution the dielectric response in TMDs in the tetragonal phase.[1] We also show how elemental tellurium is a promising material for extremely scaled nanowires and a possible successor for silicon. We predict that when fabricated with extremely small diameter, tellurium nanowires have a bandgap that exceeds 1 eV, while silicon’s bandgap increases excessively to above 4 eV.[2] We also show how the van der Waals bonds in tellurium naturally favor the formation of nanowires. Finally, we show how the Curie temperature can be computed in dilute doped TMDs from first principles, taking into account crystal anisotropy.

[1] A. Laturia, M. L. Van de Put, and W. G. Vandenberghe, "Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk," npj 2D Materials and Applications, vol. 2, no. 1, p. 6, 2018/03/08 2018.

[2] A. Kramer, M. L. Van de Put, C. L. Hinkle, and W. G. Vandenberghe, "Trigonal Tellurium Nanostructure Formation Energy and Band gap," in 2019 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD), 2019, pp. 1-4: IEEE.
First-Principles Study of the Polaron Formation Process in Energy Materials
Authors: Yuan Shuaishuai , Bevan Kirk H
Published: May 2020

Polaron formation severely limits the conduction properties of many metal oxides utilized in electrochemical energy storage and conversion applications. Thus, to improve the charge performance of such energy devices, it is essential to understand the fundamental stages of polaron formation. In this work, we utilize the HSE06 hybrid functional to study the initial stage of the polaron formation process in a series of metal oxides. By separating out electronic and lattice energy contribution to the formation of electron polarons, we find that polaron formation barrier heights are directly correlated with an electronic relaxation delay, which is determined by the hybridization of the conduction band minimum. Our results indicate that the formation of polarons may be mitigated by suitably engineering the electronic structure of the material, through a delayed electronic relaxation mechanism. Overall, these results point towards a systematic bottom-up approach for engineering the conductivity and overall electrochemical rate performance of metal oxide energy materials.
(Invited) Pt/Metal Oxide/Ti and Pt/Metal Oxide/Carbon Composite Films for Ethanol Oxidation
Authors: Pickup Peter G , Hang Hui
Published: May 2020

Metal oxides such as RuO2 and SnO2 can promote the oxidation of organic fuels at Pt nanoparticles in a number of ways. These include changing the d-band level of the Pt via electron transfer (electronic effect) and providing surface –OH functionality for the oxidation of adsorbed CO (bifunctional effect) [1]. Carbon black coated with a mixture of Ru and Sn oxides has been shown to increase the activity of Pt for ethanol oxidation without a significant loss of selectivity for its complete oxidation to CO2 [2].

Here we report on the use of various mixed metal oxide composites prepared by thermal decomposition of metal acetylacetonate complexes (M(acac)n). Oxide layers were deposited onto Ti foil and high surface area carbon electrodes, and drop coated with preformed Pt nanoparticles. Cyclic voltammetry in H2SO4(aq) and polarization experiments in a proton exchange membrane cell were used to study the co-catalytic effects of the oxide layers. The use of acetylacetonate precursors provides a versatile method for screening libraries of oxide supported catalysts, as well as the production and screening of electrodes for fuel cells.

Initially, decomposition of Ru(acac)3 and Sn(acac)2 and their mixtures on Ti foil electrodes was investigated. These experiments reproduced the effects previously observed with oxide layers deposited on glassy carbon from KRuO4 and SnCl4 [3]. Deposits formed from both complexes increased the activity for ethanol oxidation of Pt nanoparticles drop coated onto their surfaces, while use of mixtures produced a strong synergistic effect. Deposits formed by thermal decomposition of a variety of other acac complexes, including Ga(acac)3, Zr(acac)4, and In(acac)3, also increased the activity of Pt nanoparticles for ethanol oxidation.

Mixed Ru+Sn oxides were also produced by thermal decomposition of Ru(acac)3 and Sn(acac)2 on carbon black, in order to better characterize the oxide deposits and produce catalysts that could be used in fuel cells. X-ray diffraction and energy dispersive X-ray spectrometry confirmed the presence of a mixed oxide. Preformed Pt nanoparticles were adsorbed onto the oxide coated carbon, supported on carbon fiber paper, and the resulting electrodes were evaluated for ethanol oxidation in a proton exchange membrane cell at 80 °C.

Acknowledgments:
This work was supported by the Natural Sciences and Engineering Research Council of Canada and Memorial University.

[1] G.M. Alvarenga, H.M. Villullas, Current Opinion in Electrochemistry, 2017, 4, 39-44

[2] D.D. James, R.B. Moghaddam, B. Chen, P.G. Pickup, Journal of the Electrochemical Society, 2018, 165, F215-F219

[3] R. B. Moghaddam and P. G. Pickup, Electrochim. Acta, 2012, 65, 210– 215
(Invited) A Combined Femtosecond Laser Treatment and Anodization Approach to Control Fibroblast Cell Growth on Titanium Alloys
Authors: Hassel Achim Walter , Lone Shaukat Ali , Mardare Cezarina Cela , Muck Martina , Florian Camilo , Weth Agnes , Krüger Jörg , Steinwender Clemens , Baumgartner Werner , Bonse Jörn , Heitz Johannes
Published: May 2020

Intra cardiac pace makers are an emerging technology. In case of revisions however they should not be found completely overgrown by fibroblasts. Titanium alloys which are used for their housings can be engineered. For this purpose the titanium alloy is surface treated by femtosecond laser ablation. The microstructure image obtained by secondary electron microscopy reveals a combination of micrometer spikes or cones superimposed by nanoripples or periodic nanoplate-like structure (LIPSS). To make the surface hydrophilic anodization was performed resulting in further smoothness of microstructure and a final thickness of 35±4 nm is estimated for oxide produced after anodization at 10 V vs. standard hydrogen electrode. The obtained electrochemical active surface area (ECSA) is approximately 8-9 times larger as compared to flat mirror polished titanium surface. Combined chemical analysis by Pourbaix diagram and (XPS) analysis reveal that titanium and aluminium are passivating into TiO2 and Al2O3 but the dissolution of aluminium in the form of solvated ion is inevitable. Finally, after exposing the anodized + laser treated titanium alloy sample to murine fibroblast environment, it is found that murine fibroblast cell growth is significantly restricted due to unique surface texture of the laser treated and anodized titanium alloy sample.