bluuebunny/crossref_metadata_2025 huggingface dataset:
3D Architected Pyrolytic Carbon Electrodes with Multi-Scale Controlling Factors
Authors: Narita Kai , Citrin Michael A , Yang Heng , Xia Xiaoxing , Greer Julia R
Published: February 2020

Engineering electrode architecture in rechargeable batteries has the potential to control transport trajectories of ions and electrons, which can significantly affect battery performance especially at high current rates and at high mass loadings. Many efforts have been dedicated to develop novel methods of engineering electrode architecture that include extrusion-based additive manufacturing and using sacrificial templates. These methods are limited in terms of producing resilient structures that can withstand the mechanical loads imposed during operation of the cell and are not yet capable of producing geometries that enable independent control of form factors in multi-scale ranges from micron to centimeters scales.

We developed a facile fabrication method of 3D architected carbon anodes using direct light processing (DLP) 3D printing of UV-curable resin and subsequent pyrolysis in an inert atmosphere. The specific architecture of these electrodes is fully controllable over every length scale: from local geometry (micrometer-scale) to control tortuosity and mass loading, as well as global geometry (centimeter-scale), to intergrade into any device geometries. In addition, the architected pyrolytic carbon electrode is free-standing and binder-free, enabled by the monolithic structure and great electrical conductivity of carbon.

To demonstrate the architected carbon electrode as an anode in lithium ion batteries, we fabricated 1 mm-thick 3D periodically architected carbon electrodes with simple cubic-like geometry and characterized its electrochemical performance by constructing a half-cell against a lithium metal counter electrode. Battery cycling of these electrodes using a coin cell showed reversible capacity of ~230 mAh/g (or 7 mAh/cm2) at a 16 mA/g (or 0.6 mA/cm2) and its capacity retained over 85 % until 100 cycles. Uniaxial compression tests revealed its high structural integrity, enabling the architecture to be maintained even after 300 cycles under pressure in a coin cell.

We further studied a correlation between electrode architecture design and battery performance by varying transport path of Li-ion in electrolyte independently from tortuosity of porous structure and Li-ion transport path in the electrode. In addition, key considerations to optimize electrode architecture will be discussed based on the comparison between stochastic structure of conventional slurry and designed electrode architecture under the same electrode material.

This multi-scale tunable fabrication method may give a new path not only to electrode design in conventional planner cells but also to a 3D interdigitated full battery.
Achieving Scalable Production of Hybrid Electrolytes through Slot-Die Coating
Authors: Dixit Marm , Hatzell Kelsey B.
Published: February 2020

Lithium metal based all-solid-state batteries (ASSBs) can achieve high energy densities due to high theoretical capacity of lithium and low redox potential (3860 mAh/g, 3.04 V)1-2. Solid electrolyte materials are being sought to replace liquid electrolytes to enable the lithium metal chemistry. Solid electrolytes are mainly classified into two material categories (1) organic and (2) inorganic3. Organic materials are mechanically robust and easier to process but they possess poor ion transport properties. Inorganic materials possess high ionic conductivity but have poor manufacturability. Gravimetric calculations suggest that electrolytes with ≤ 60 μm thickness need to be manufactured to achieve competitive energy densities4. Additionally, the processing platform should ideally merge with existing battery manufacturing infrastructure to enable the transition to ASSBs. Hybrid electrolytes combine an inorganic conductor with a polymer electrolyte which improves the mechanical properties and inhibits dendrite growth in metal batteries (i.e. short circuiting). This work demonstrates the use of slot-die coaters to manufacture hybrid electrolytes with functional gradation. A custom-made bench-top slot-die coater is used to investigate the impact of ink composition. Initial results have shown that the system is sensitive to processing variability, with nano-scale interactions in the ink phase impacting the macroscopic ink properties and the coating structure5-6. This work focuses on demonstrating manufacturing capabilities for hybrid electrolytes with local control using slot-die coaters. Slot-die coaters are extensively used in industrial scale roll-to-roll manufacturing7 making the process technically viable. References: 1. Dixit MB, Regala M, Shen F, Xiao X, Hatzell KB. Tortuosity Effects in Garnet Type Li7La3Zr2O12 Solid Electrolytes. ACS Appl Mater Interfaces 2018;11:2022–30. 2. Shen F, Dixit M, Xiao X, Hatzell K. The Effect of Pore Connectivity on Li Dendrite Propagation Within LLZO Electrolytes Observed with Synchrotron X-ray Tomography. ACS Energy Lett 2018;3:1056–61. 3. Fan L, Wei S, Li S, Li Q, Lu Y. Recent Progress of the Solid-State Electrolytes for High-Energy Metal-Based Batteries. Adv Energy Mater 2018;1702657:1–31. 4. McCloskey BD. Attainable Gravimetric and Volumetric Energy Density of Li-S and Li Ion Battery Cells with Solid Separator-Protected Li Metal Anodes. J Phys Chem Lett 2015;6:4581–8. 5. Hatzell KB, Dixit MB, Berlinger SA, Weber AZ. Understanding Inks for Porous-Electrode Formation. J Mater Chem A 2017;5:20527–33. 6. Dixit M, Harkey B, Shen F, Hatzell KB. Catalyst layer ink interactions that affect coatability. J Electrochem Soc 2018;165:F1–8. doi:10.1149/2.0191805jes. 7. Department of Energy. Roll to Roll Processing Technology Assessment. 2015.
3D Printing of Solid-State Electrolytes for Li-Ion Batteries: Processing and Morphology Optimization
Authors: Wood Marissa , Gao Xiaosi , Wan Liwen , Bayu Aji Leonardus Bimo , Ye Jianchao
Published: February 2020

Solid-state batteries promise substantially higher energy densities and improved safety compared to traditional Li-ion batteries due to the replacement of flammable liquid electrolyte with solid-state materials. These advantages make them excellent candidates for next generation energy storage, but many processing and performance challenges must first be addressed. While several different types of solid-state electrolytes have been proposed, inorganic materials such as Li6.4La3Zr1.4Ta0.6O12 (LLZTO) have attracted much interest due to their high ionic conductivities and good mechanical and electrochemical properties. However, these materials are brittle and prone to large interfacial resistance, and many of the current fabrication techniques are difficult to scale up for manufacturing. 3D printing is an excellent tool to help solve some of these challenges, since it is scalable and capable of creating tailored architectures and compositions that can facilitate Li+ transport and reduce interfacial resistance. We report the development and optimization of ink formulations and processing conditions for 3D printed solid-state electrolytes. Since the electrolyte must be sintered after printing to densify the structure and achieve good ionic conductivity, initial particle size is an important consideration for both ink rheology and sintering success. We investigated the effect of milling solvent on particle size and lithium loss, both of which can affect the final ionic conductivity. In addition, while samples are traditionally mechanically pressed to aid densification during sintering, this technique cannot be used with printed architectures. Therefore, we explored other strategies to facilitate densification, including incorporating additional materials to act as sintering aids and optimizing ink composition and active material volume fraction. Samples were analyzed by SEM, XRD, and EIS to correlate processing and sintering conditions with electrochemical performance. Our results demonstrate significant progress toward 3D printing architected solid-state electrolytes with good ionic conductivity for high-energy-density solid-state batteries.
Analysis of the Formation, Evolution, and Alternatives of the Solid-Electrolyte Interface in Li-Metal Batteries
Authors: Seminario Jorge M. , Galvez-Aranda Diego Eduardo , Gamero T Milenka , Selis Luis , Ponce Victor H , Franco-Gallo Franz
Published: February 2020

Lithium−metal is a desired material for anodes of lithium−ion batteries because of its large theoretical specific capacity of 3,860 mAh/g, the highest known so far. Unfortunately, there are several problems that restrict the practical application of lithium−metal anodes, like the formation of dendrites among others. Li-metal batteries based on solid electrolyte materials are expected to be the next-generation battery with high energy density and enhanced cycle life, however, one of the key limitations is the poor knowledge about the solid electrolyte-electrode interfaces. In this work, first-principles calculations are performed to investigate the electrochemical stability of the interface between a lithium-metal anode and sulfide solid electrolytes. Ab initio molecular dynamics simulations reveal the formation of solid electrolyte interphase. Sulfide-based materials mixed with halogens are candidates for solid state electrolytes in advanced lithium batteries. They are expected to have high ionic conductivity and electrochemical stability against Li-metal. Analyzing the interface with Li-metal through ab initio molecular dynamics simulations, it is found that the sulfide is unstable, forming Li2S but it may passivate the surface of the anode. This decomposition of groups against Li-metal form Li-S bonds, despite the higher P-S bond energy. We include here a study of lithium dendrite formation on a Li−metal anode covered by a cracked solid electrolyte interface of LiF with a typical liquid electrolyte using classical molecular dynamics on a model nanobattery. We tested a few protocols of charge the nanobattery. We found that the mere presence of a crack in the SEI boosts and guides dendrite formation.
Ionic and Electronic Transport Properties of Lithium-Metal-Oxygen Systems
Authors: Amin Md Ruhul , Belharouak Ilias
Published: February 2020

Mixed conducting spinel (e. g. LixMn1.5Ni0.5O4 ) and layer structure materials (NCA, NMC) have been used as cathode for lithium ion batteries due to their high energy and power density. Ionic and electronic transport properties of these materials play an important role to help designing particle morphology and loading of active materials in order to get better electrochemical performances. Also these compounds can be ordered or disordered depending on the arrangement of Mn and Ni in the crystal structure. The charge-discharge behavior of ordered and disordered structures has been tested by several research groups. However still it is not clear which structural composition is suitable for a high performance battery. It is also not clearly understood if the rate performance of the material is limited by bulk transport properties or interfacial reactions. Here we report on the electronic and ionic conductivity and diffusivity of these materials which has been determined separately by using ion and electron blocking cell configurations as a function of lithium concentration on sintered dense pellets. For spinel, the disordered phase exhibits about fifteen time higher electronic conductivity than the ordered phase at room temperature in the lithiated state. The conductivities of the partially delithiated ordered phase measured at a given temperature increase monotonically with increasing delithiation at x = ~0.3 and beyond that the electronic conductivity is almost leveled up. In contrast, the electronic conductivity of disordered phase initially decreases with delithiation and comes down to the level of lithiated ordered phase. After that it exhibits almost the same electron conducting behavior as of ordered phase [1, 2]. The lithiated ordered and disordered phases exhibit the same order of magnitude of ionic conductivity and diffusivity. On the other hand electronic conductivity of layer structure materials gradually increase with increasing the state of charge whereas ionic diffusivity gradually decreases up to 50% state of charge and again increases on further charging [3, 4]. Chemical diffusion during electrochemical use is limited by lithium transport, but is fast enough over the entire state-of-charge range to allow charge/discharge of micron-scale particles at practical C-rates.

References

R. Amin and I. Belharouk, J. Power Sources, 348 (2017) 311–317.

R. Amin and I. Belharouk, J. Power Sources, 348 (2017) 318–325.

R. Amin,Y.-M. Chiang, J. Electrochem. Soc.
,
163 (8), (2016) A1512-A1517.

R. Amin, D. B Ravnsbæk, Y.-M. Chiang, J. Electrochem. Soc. 162 (7) (2015) A1163-A1169.
(Invited) Mixed Conducting Metal Oxides for Intermediate Temperature Solid Oxide Cells
Authors: Thangadurai Venkataraman
Published: February 2020

Startling new reports on climate change demands an acceleration on the progress of renewable energies in order to reduce carbon emissions. Among various energy sources that can be integrated into renewables, solid oxide cells (SOCs) top the list in terms of fuel flexibility. SOC is an electrochemical cell in which ceramic electrolyte is sandwiched between two porous electrodes. Lowering SOCs’ operating temperature (800 – 1000 °C) to intermediate temperature (IT) (500 – 700 °C) has been one of the key research areas to expand material selections and lower the cost. However, IT-SOC’s cathode, in particular, faces the issue of slower kinetics for oxygen reduction reaction (ORR). Several mixed ion-electron conducting (MIEC) cathode materials for ITs [1-3] have been tested to compensate the lower power output due to reduced temperatures, where challenges remain for solving stability and compatibility issues. Here, we report, the effect of doping Nd and Cu in A- and B-site of various Ba- and Sr-based perovskite-type MIECs, as potential cathodes for IT-SOCs [4-5]. Mechanism of ORR reactions through aforementioned MIECs will also be discussed.

References

F. Shin, W. Xu, M. Zanella, K. Dawson, S. N. Savvin, J. B. Claridge, M. J. Rosseinsky, Nat. Energy 2 (2017) 16214.

Kannan, K. Singh, S. Gill, T. Fürstenhaupt, V. Thangadurai, Sci. Rep. 3 (2013) 2138.

Duan, D. Hook, Y. Chen, J. Tong, R. O'Hayre, Energy Environ. Sci. 10 (2017) 17.

Oz, K. Singh, D. Gelman, V. Thangadurai, Y. Tsur, J. Phys. Chem. C 122 (2018) 15097.

Mulmi, V. Thangadurai, Chem. Commun. 55 (2019) 3713.
(Invited) High-Temperature Mixed Conducting Membranes and Reactors for Direct CO2 Capture and Conversion
Authors: Huang Kevin , Zhang Peng
Published: February 2020

Direct CO2 capture and conversion have been an active research area in recent years due to its importance in addressing the current global warming/climate change and future depletion of fossil fuels and creating a carbon neutral ecosystem. The benchmark technology for CO2 capture is the post-combustion amine absorption, which is energy intensive and cost prohibitive to large-scale commercial implementation. In comparison, the CO2 conversion technologies are still at their infancy with many technical challenges in efficiency and selectivity to be overcome, but primarily being explored in low-temperature solution-based and high-temperature solid-oxide-based electrochemical cells with solar or electrical energy as the input. Here we present a new type of high-temperature membrane reactors operated on mixed conducting chemistry for direct CO2 separation and instant conversion. In the presentation, we will first discuss the chemistries of three basic types of mixed ionic/electronic conductors designed for CO2 separation and conversion. We will then present materials and synthesis of the membranes, followed by testing the performance of membrane reactors with mock-up flue gas as the feeding gas and methane/ethane as the sweeping gases. The performances of oxidative conversions of methane and ethane are characterized by conversion rate of the reactants, selectivity and yield of the products and flux density of both reactant and product species. Finally, the fundamental separation and conversion mechanisms will be discussed in detail.
Quantifying Electrocatalytic Structure-Property Relationships with Surface Science, Electrochemistry, and Density Functional Theory
Authors: Kauffman Douglas R. , Deng Xingyi , Sorescu Dan
Published: February 2020

We have coupled electrochemistry, surface science, and density functional theory (DFT) calculations to quantify structure-property relationships in well-defined oxygen evolution reaction (OER) electrocatalysts. The OER is an essential component in electrochemical CO2 reduction, H2 evolution, and NH3 synthesis reactions. Mixtures of nickel, cobalt, and iron have shown remarkable alkaline OER activity, but atomic-level understanding of how OER activity evolves with the catalyst shape, size, composition, and support are still lacking in the literature. Our approach uses ultra-high vacuum techniques to grow well-defined transition metal electrocatalysts with precisely controlled morphology, composition, and loading. Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy determine the catalyst’s size, aspect ratio, thickness mass loading, and oxidation state. Electrochemical OER testing then correlates mass activity, turnover frequency, and specific current density with the catalyst structure and composition. Our results with ultrathin, two-layer thick (2L) Fe2O3 nanocatalysts showed a linear relationship between the population of edge-site Fe atoms and overall OER activity, and edge-site Fe atoms are approximately 150 times more OER active than Fe atoms on the catalyst surface. In fact, 2L-Fe2O3 nanocatalysts with a high density of Fe edge-site atoms demonstrated better OER performance than an Ir-oxide catalyst. Post-reaction STM and XPS analysis confirmed that particles retained their structure and identified hydroxylated Fe edge-site atoms along the catalyst perimeter as key OER active sites. Complementary DFT modeling confirmed these experimental observations by predicting more thermodynamically favorable OER at Fe edge-site atoms due to beneficial modification of intermediate binding. Extension of this work to Ni/Fe and Co/Fe systems is revealing additional insight into the structure-dependent activity of bimetallic OER electrocatalysts, and our approach provides atomic-level structure-property relationships that would be extremely difficult, if not impossible, to quantify with traditional approaches.
Strategies for Tuning Optoelectronic Properties of TiO2 Nanomaterials for Solar Photovoltaic Studies
Authors: Delekar Sagar D. , Panda Dillip
Published: February 2020

Third generation solar cells are mainly focusing on the use of nanomaterials as host components for solar-to-electrical conversions. Among the various nanomaterials, TiO2 is one of the most promising candidates used in solar devices due to their remarkable structural and opto-electrical properties. However, bare TiO2 nanomaterials have the various constraints in efficient solar energy conversions. In the present research endeavors, TiO2 nanomaterials have been modified with the different strategies such as dyad anchoring, dye-quantum dot sensitization, composites of carbon nanostructures with sensitizers, metal ion doping with sensitizers so as to tune its optoelectronic properties for efficient solar energy harvesting. In addition, the interconnectivity between the various components and their optoelectronic properties of modified TiO2 for solar energy conversions have been studied in detail.

In the dyad system, a supramolecular ruthenium(II)phthalocyanine··peryleneimide (RuPc···PI) has been anchored on the surfaces of TiO2 and thereafter these TiO2-dyad sensitized solar cells have assembled in a bottom-up fashion. Upon photo-irradiation at air-mass (AM) 1.5, the dyad-based solar devices convert solar light to electricity of 2.1%; which is higher than that of individual dyes. In next strategies, the synthesized CdS quantum dots (QDs) have connected electrostatically to the surfaces of TiO2 nanoparticles (NPs) and thereafter, this binary hybrid heterojunction is further self-assembled physically with N719 dye to form ternary TiO2 NPs-CdS QDs-N719 photoelectrodes. These co-sensitization devices reported the solar energy conversion efficiency (η) up to 2.35 %. In addition, anatase TiO2 NPs is anchored on the surface of functionalized carbon nanostructures (MWCNTs or RGO); which is further sensitized with Ru(II) dyes for solar devices having efficiency reached to 6.21%. In another modification, Cr(III) as well as Mo(VI) ions are inserted into TiO2 host lattice and then their composites with CNs are further sensitized for boosting the solar energy conversions and reached up to 7.69 % of efficiency.

Figure 1
(Invited) EMN Datahub Capability to Accelerate Discovery
Authors: Sivaraman Chitra , Munch Kristin , Macduff Matt , Lansing Carina , Gunter Dan
Published: February 2020

The Energy Materials Network (EMN) consortia has been set up to accelerate U.S. materials development and innovation by facilitating access to the national laboratories’ capabilities, tools, and expertise. Each consortium has created its own DataHUB portal for managing data generated by its experimental and simulation studies. These DataHUB portals provide core capabilities such as data storage, discovery and access control. In addition, based upon the needs of the specific consortium, each portal has been customized to provide domain-specific capabilities for data ingestion, curation, and analysis. In developing the DataHUB portals, the data teams across the consortia have coordinated their efforts and adopted common technologies and frameworks to minimize the duplication of efforts. This talk will provide an overview of the DataHUBs’ approach, successes, and challenges in collecting, managing and curating data for the EMNs.
Effects of Metal-Doping and Surface Modification on Hydrogen Production Activity of Metal Nanoclusters
Authors: Choi Woojun , Kwak Kyuju , Kim Minseok , Lee Dongil
Published: February 2020

Identification of an efficient hydrogen evolution reaction (HER) electrocatalyst is one of the challenging tasks in the development of alternative energies to replace fossil fuel. Although many efforts to develop active HER catalysts, it is still difficult to answer what are the main factors that influence on HER activities. Among many researches, two factors are commonly accepted;that is, thermoneutral binding step with H+ (∆GH = ~0 eV) on solid metal catalysts and proton shuttling effect of secondary coordinated ligand of molecular catalysts. Ligand protected Au nanoclusters that show both metallic and molecular-like properties exhibit distinctive electrochemical and HER features. The HER activities of Au nanoclusters could be improved by doping of foreign metal and surface modification. In this presentation, we report electronic structures and catalytic properties of Au25(SR)18 and bimetallic PtAu24(SR)18 nanoclusters (SR = thiolate). The modified catalytic activities were demonstrated by linear sweep voltammetry and controlled potential electrolysis. HER turnover frequency (TOF) of Au25(C6S)18, where C6S is hexanthiolate, dramatically increased from 8.8 s-1 to 33.4 s-1 at -0.6 V vs. RHE upon doping of Pt into Au25(C6S)18 to form PtAu24(C6S)18. The TOF of Pt-doped nanocluster was further increased by introducing proton-relaying sulfonate ligands, leading to TOF of 100 s-1 at -0.6 V.
Development of Integrated Scanning Electrochemical Cell Microspectroscopy for Characterization of Redox and Reactive Electrochemistry
Authors: Prabhakaran Venkateshkumar , Edgecomb Joseph , Johnson Grant
Published: February 2020

Understanding molecular-level transformations resulting from electrochemical reactions is important for designing efficient and reliable systems for energy conversion and storage. In this work, an integrated scanning electrochemical cell microspectroscopy (iSECCMS) platform is developed by combining a high spatial resolution electrochemical scanning probe technique with in situ ultraviolet visible (UV-VIS) absorption/fluorescence spectroscopy. The iSECCMS platform is used for spatially-resolved characterization of electrochemically-active redox systems and the results are compared to those obtained with conventional ex situ 3-electrode electrochemical measurements to establish the reliability of the technique. Using 6- carboxyfluorescein as a fluorescent probe, the iSECCMS platform is employed to measure the effect of detrimental generation of reactive oxygen species (ROS)/H2O2 on the active sites for the oxygen reduction reaction (ORR). Carbon-supported tantalum-doped titanium oxide catalysts, a cathode employed in low temperature polymer electrolyte fuel cells (PEFCs), are examined as a model system. We establish that the iSECCMS platform provides an opportunity for spatially-resolved mapping of both electrochemical activity and capture transient intermediate species (e.g. ROS) in functional electrochemical interface.
Physical Translation of Optical Excitation into Nanoscale Semiconductor Morphologies
Authors: Carim Azhar I , Batara Nicolas A. , Hamann Kathryn R , Meier Madeline Claire , Premkumar Anjali , Atwater Harry A , Lewis Nathan S
Published: February 2020

Electrodeposition of chalcogen alloy films under illumination can spontaneously generate nanopatterned films with significant periodic and multi-dimensional order. The feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern can be controlled by manipulating the input optical excitation. Isotropic morphologies consisting of ordered arrays of nanopores were generated using unpolarized illumination whereas linearly polarized light resulted in highly-anisotropic nanoridge/trough morphologies with the in-plane orientation of the patterns controlled by the direction of the light polarization. The pattern periodicity was encoded by the illumination spectral profile. A single periodicity in single spatial direction was only generated even with the use of broadband and multimodal spectral profiles and multiple polarization inputs and the periodicity was found to be sensitive to all investigated tuning of such profiles. Structures with nonequal periodicities in the two orthogonal in-plane directions could also be generated and both periodicities could be independently controlled. Overall structural complexity correlated could be scaled by increasing the complexity of the optical inputs. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that morphology development was directed by evolution of the growth interface to maximize anisotropic light collection.
Stabilization of the Ionic Liquid – Electrode Interface from Large Nonpolar Groups in Ionic Liquids and Ionic Liquid Mixtures
Authors: Klein Jeffrey Michael , Squire Henry John , Gurkan Burcu
Published: February 2020

Electrochemical capacitors, also called electrical double layer capacitors (EDLCs), can store energy in the interface between an electrode and an electrolyte. The interface where charge is stored influences more than simply EDLCs due to its presence at any charged surface. Conventional electrolytes, organic and aqueous based, form a well described electrode – electrolyte interface. However, conventional electrolytes are often limited in their application due to restrictions in thermal and electrochemical stability. Ionic liquids (ILs) are an emerging class of electrolytes with improved thermal and electrochemical stability compared to conventional electrolytes, however, the interface is poorly understood. Current understanding of the conventional systems cannot be completely transferred to ILs because they are not sufficiently described as point charges, and because ILs contain no solvent. Completing our understanding of the complex IL-electrode interface will greatly influence the efforts at designing task specific ILs for electrochemical devices. Here it is demonstrated that quaternary ammonium cations with large nonpolar substituent groups directly impact the anion density near the electrode at positive potentials. This work also addresses whether or not the unique IL-electrode interface is formed from a process which expels void space from the local environment, or by replacing “non-participating” neutral ion pairs with “participating” free ions.

Potential driven structuring of four neat ILs and two IL mixtures has been examined on a glassy carbon electrode. Potential dependent capacitance (differential capacitance), measured by electrochemical impedance spectroscopy, was used to examine the formed IL - glassy carbon interface. Differential capacitance curves were paired with physical measurements of viscosity, density, and conductivity as represented in a Walden plot. The Walden plot was used to estimate the extent to which the ions of the IL were dissociated. There appeared to be no trend between the extent of dissociation and the differential capacitance behavior. The absence of a trend between dissociation and differential capacitance suggests that the interface is not described by a simple model depending solely on the number of free ions in the interface. Instead, the interface depends more heavily on the intermolecular interactions between the constituent ions such as ion – ion repulsions and steric repulsions. It is shown in the differential capacitance curves that the ILs containing large non polar substituent groups have a more stable interface associated with the accumulation of anions. Stabilization of the interface holds even for mixtures of ILs where the minor component contains the large nonpolar group. Results from this work offer ways to selectively tune the ion density in the IL-electrode interface at specific electrode potentials.
Co3O4 Nanocube -3DrGO Hybrid Structure: Efficient Non-Noble-Metal Electrocatalyst with High-Performance for Oxygen Evolution Reaction
Authors: Purkait Taniya , Pandey Prashant , Kamboj Navpreet , Dey Ramendra Sundar
Published: February 2020

Oxygen Evolution reaction (OER) by water splitting is one of the emerging technologies for the ongoing research in the field of sustainable, clean yet highly efficient energy generation. Electrocatalysis for OER is a key step forward towards achieving this goal and enormous efforts has been devoted recently on the development of high-performance electrocatalysts that are cost-effective, abundant as well as environmentally benign. Transition metal based non-noble electrocatalysts anchored on high-surface area, conductive carbonaceous support serves the dual purpose of being highly catalytically active as well as having excellent stability. Herein, we report the synthesis of Co3O4 nanocube -3DrGO hybrid structure as a high-performance electrocatalyst for OER applications via a facile hydrothermal synthesis technique followed by heat treatment. The unique nanocube like structure offers more active edge sites which plays an important role in its catalytic performance. The hybrid structure exhibits an overpotential of 428 mV (vs RHE) and a small tafel slope of 96.92 mV dec-1 with 100% faradaic efficiency in 1 M NaOH alkaline electrolyte. The electrode needs an overpotential of 648 mV to afford a current density of 10 mA cm-2. This offers a low-cost electrocatalytic electrode for water splitting and rechargeable metal–air battery applications.

Figure 1
GaN Protection Layer on Si Photocathode for Photoelectrochemical Water Splitting
Authors: Zeng Guosong , Vanka Srinivas , Liu Guiji , Cooper Jason K. , Mi Zetian , Toma Francesca M.
Published: February 2020

As an earth-abundant narrow bandgap semiconductor material with mature manufacturing process, silicon has already been extensively used in photovoltaic industry. However, its low stability in aqueous conditions becomes an obstacle for its application in artificial photosynthesis. Thus, a great amount of efforts has been directed towards developing protection layer for Si-based photoelectrode. Deposition of metal oxides, such as TiO2, on Si have been reported to enhance its long-term stability. However, crystallinity and thickness of these metal oxides often limit the performance of Si-based photoelectrodes. On the contrary, MBE-grown GaN possesses extraordinarily chemical, thermal, and mechanical stabilities with low defect density and high crystallinity. These characteristics make GaN an appropriate candidate for Si photocathode protection. Our study shows that, the MBE-grown GaN on p-type Si can well protect the Si photocathode for more than 100 hrs. Various thicknesses of GaN were examined and showed similar photoelectrochemical performance. Our study reveals that the band alignment between Si and GaN ensures similarly efficient electron extraction at different GaN thicknesses. Interestingly, this behavior is in stark contrast to the well-known TiO2 protection coating. A self-healing effect was also observed during chronoamperometry test and the surface was characterized afterwards by XPS, pc-AFM and TEM. The results indicate that the surface was modified during solar water splitting, leading to more efficient charge carrier extraction and more stable surface.
Impact of Fe(III) on the Autocatalytic Processes of Corrosion of Stainless Steels in Concentrated Nitric Acid
Authors: Pellé Julien , Gwinner Benoit , Gruet Nathalie , Vivier Vincent
Published: February 2020

This study takes place in the industrial context of the spent nuclear fuel reprocessing plants, in which hot and concentrated nitric acid is used in the process to dissolve nuclear fuel. This imply a high oxidative solution, due to nitric acid but also to species resulting from the dissolution of the fuel and/or the equipment. Especially where there is stagnant solution in which different nitrogenous species can accumulate, causing the autocatalytic reduction reactions of nitric acid. These mechanisms can be responsible of the corrosion processes of the equipment. Then, in order to have resistant equipment to this acidic and oxidizing medium, stainless steels were chosen. The purpose of this work is to investigate the corrosion mechanisms of stainless steels in such aggressive medium. Particularly, it was established that the presence of Fe(III) (corrosion product) accelerates the corrosion of stainless steels, due to the rise of the cathodic reactions [1, 2]. Thus, this work was focused on the specific impact of Fe(III) on the corrosion processes, including autocatalytic reduction reactions of nitric acid. Indeed, it was not clear if this acceleration of the cathodic processes was induced by a direct reduction of Fe(III) to Fe(II) at the surface of the material or if it was an indirect impact of Fe(III) by a catalyse of the nitric acid reduction process (involving reduced species of nitric acid such as HNO2, NO2 and NO) (Figure 1). In order to investigate this point, we coupled stationary electrochemical techniques (chronoamperometry, steady-state polarisation curves) or dynamic electrochemical techniques (electrochemical impedance spectroscopy) with local analytical techniques (RAMAN microspectroscopy, Scanning ElectroChemical Microscope). These studies were completed with the analysis of the gaseous products of the reactions (NO2 and NO production) by mass and IR spectroscopies. It was shown that the direct reduction of Fe(III) to Fe(II) at the surface of stainless steel has a minor contribution to the corrosion. Thus, the role of Fe(III) is essentially related to its catalytic effect on the nitric acid reduction reaction (Figure 1). From the different measurements performed, the following mechanism of interaction of Fe(III) with the nitric acid reduction was proposed (Figure 1) and the kinetic constants of some elementary steps were determined.

[1] Fauvet, P., et al. (2008). "Corrosion mechanisms of austenitic stainless steels in nitric media used in reprocessing plants." Journal of Nuclear Materials 375(1): 52.

[2] Fauvet, P. (2012). Corrosion issues in nuclear fuel reprocessing plants. Nuclear corrosion science and engineering. D. Feron, Woodhead Publishing. 22: 679-728.

[3] Lange, R., Phénomènes de couplage acier 304L – platinoïdes dans les milieux de dissolution des combustibles usés. 2012, UNIVERSITÉ PIERRE ET MARIE CURIE. p. 174.

Figure 1
Investigation of a Novel Rhenium Disulfide Electrocatalyst By Sum Frequency Generation Vibrational Spectroscopy
Authors: Liu Qiliang , Lian Tianquan
Published: February 2020

The heterogeneous electrocatalysis is developing as a promising approach to overcome the energy regeneration issues around the world. It is well known for the enhancement of stability, selectivity, and productivity for the catalytic reaction, especially in the electrocatalytic reaction. By binding electrocatalytic molecules onto the metal or semiconductor electrode surface, CO2 reduction reaction or H2 evolution reaction can be more efficient. However, the behaviors of catalysts during heterogeneous electrocatalysis are always triggering people’s interest in understanding how interfacial electric field interacts with molecules. In this paper, a novel rhenium -based CO2 reduction electrocatalyst Re(SSbpy)(CO)3Cl was synthesized and attached to polycrystalline gold film electrode. By probing the symmetric CO stretching mode with potential dependent SFG vibrational spectroscopy, the Stark shifting rate of 7~8 cm-1/V under applied bias was revealed, indicating a weak correlation between symmetric CO stretching dipole and interfacial electric field. In addition, DFT calculation represented that this molecule tended to be adsorbed on the gold surface with nearly zero tilt angle with a great agreement to spectroscopic results.
Engineering on Ni-Co-S Bifunctional Electrocatalyst for Water-Splitting
Authors: Wu Jing
Published: February 2020

Efficient evolution of hydrogen and oxygen simultaneously with earth-abundant, highly active, and robust bifunctional electrocatalysts has been a significant concern for water splitting. Herein, non-noble metal based Ni-Co-S bifunctional catalysts with tunable stoichiometry and morphology were realized. The electronic structure engineering and subsequent morphological design synergistically contributed to significantly elevated electrocatalytical performance. Overpotentials η10 of 243 mV (vs.RHE) for OER and 80 mV for HER in 1M KOH solution, as well as Tafel slopes of 54.9 mV/dec for OER and 58.5mV/dec for HER were demonstrated together with prominent stability. In addition, DFT calculation was conducted to indicate the optimal electronic structure via visually mapped electron density difference of catalysts, and representatively verify that the enhanced OER activity of NiCo2S4 nanosheets is concerned with the Co top site on (110) surface. Moreover, the tandem bifunctional NiCo2S4 anode and cathode exhibited a required voltage down to 1.58V (J=10 mA/cm2) for simultaneous OER and HER, and no obvious performance decayed after 72 h. When integrated with a GaAs solar cell, such photo-assisted water splitting electrolyzer acquired a certificated solar-to-hydrogen efficiency up to 18.01%, further demonstrating the feasible engineering protocols as well as the promising potential of bifunctional NiCo2S4 for large-scale overall water splitting.[1, 2]

References

[1] H. Kim, K. Kang, et.al.,
Nat. Commun.
2015, 6, 8253.

[2] H. Wang, Y. Cui, et.al., Nat. Commun. 2015, 6, 7261.
Real-Time Observation of the Diffusion Mechanism Progression from Liquid to Solid-State of Transition Metal Complexes
Authors: Kim Tea-Yon , Wang Yujue , Raithel Austin , Hamann Thomas
Published: February 2020

Diffusion mechanisms vary in charge transport materials during the solidification from liquid to solid but mechanisms have only been deduced intuitively, without experimental evidence. However, these hypotheses have limited precision when performing mechanistic analysis of new emerging materials emerge. For example, transition metal complexes (TMCs) have shown a remarkable improvement in their properties when converted from liquid to solid-hole transport materials (HTMs) in mesoporous solar cells but it has been difficult to reveal what change in mechanism led to the advancement in HTMs. Herein we have successfully observed the change of diffusion mechanism for the TMCs, Cu(dmby)2
2+/+ and Co(bpy)3
3+/2+, during the solidification by the in-situ solidification analysis. The modified Dahms-Luff equation, which was partially substituted by the viscosity term, was used to evaluate the overall mechanism, and it was confirmed that the calculated self-exchange rate constant (k
ex) varies with phase and the viscosity-dependent value. Eventually, as the solidification progressed, the transport mechanism dominating Cu(dmby)2
2+/+ was changed from the ionic to the electrical diffusion, which led to the increase in the apparent diffusion coefficient (D
app), indicating a high conductivity and a high k
ex (8.7 x 108 M-1s-1) in the HTM. However, in the case of Co(bpy)3
3+/2+, the transport mechanism continued to be dominated by the ionic diffusion during the solidification progresses and the D
app was reduced due to the viscosity increase. This change in the diffusion mechanism, due to the solidification of the electrolyte, led to the reduction in the reorganization energy of TMCs calculated by Marcus Theory. This in turn could also affect the heterogeneous charge transfer reaction with the electrode, which may indicate the fundamental cause of the change in the performance in the devices. The results of this study provide an important milestone in establishing the charge transport mechanism for solid-state TMCs.
Understanding the Active Sites and Reaction Mechanism for Water Oxidation on Ruthenium Dioxide
Authors: Rao Reshma R , Shao-Horn Yang
Published: February 2020

Rutile Ruthenium Dioxide (RuO2) is a gold standard catalyst for water splitting in acidic solutions1-3. It can also undergo fast surface redox reactions in the electrochemically stable potential window of water, making it an ideal material for electrochemical capacitors that can charge and discharge in a much shorter time scale than batteries. However, there is a lack of fundamental understanding of the active sites and atomic scale processes occurring at the oxide-electrolyte interface upon interaction with water as previous work has been confined to the ultra high vacuum environment, and to the thermodynamically stable (110) surface4.

In this work, we use three different facets of RuO2, (110), (100) and (101) to demonstrate how changing the local environment of surface Ru and O atoms can enable tuning the electronic structure of the active site and alter its intrinsic oxygen evolution reaction (OER) activity. Using synchrotron based ambient pressure X-ray photoelectron spectroscopy and in situ surface diffraction on single crystal surfaces coupled with density functional theory calculations, we show that at 1.0 VRHE, water adsorbs molecularly or dissociatively on the coordinatively unsaturated site (CUS), depending on the surface orientation. This is followed by successive deprotonation occuring at potentials greater than 1.0 VRHE . At oxygen evolution potentials (1.5 VRHE), surface diffraction measurements reveal the presence of an –OO species on the CUS site for the (110) and (100) surface. Computation results show that this –OO group is stabilized by a neighboring –OH group suggesting that the final deprotonation step is rate-limiting. On the other hand, for the (101) surface that binds oxygen more weakly, a completely oxidized surface has been detected, implying a change in the rate-limiting step to the dissociation and deprotonation of the second water molecule on the oxidized surface. The mechanistic insight gained from in situ methods will be used to discuss the difference in OER activity and Tafel slope observed on the different RuO2 facets. Finally, the results obtained using single crystals will be extended to understanding the distinct redox peaks of RuO2 nanoparticles in the electrochemically stable potential window of water as well as the nature of intermediates prior to the evolution of oxygen. Thus, by using different experimental and theoretical techniques on model surfaces, this study identifies the active sites for oxygen electrocatalysis and demonstrates how catalyst surface structure can be altered to improve OER kinetics.

References:

[1] Trasatti S. Electrochimica Acta. 1984;29(11):1503-1512.

[2] Lee Y, Suntivich J, May KJ, Perry EE, Shao-Horn Y. The Journal of Physical Chemistry Letters. 2012;3(3):399-404.

[3] Stoerzinger KA, Qiao L, Biegalski MD, Shao-Horn Y. The Journal of Physical Chemistry Letters. 2014;5:1636-1641.

[4] Over H. Chemical Reviews. 2012;112(6):3356-3426.
Chemical and Morphological Origins of Improved Transport in Perfluoro Ionene Chain Extended Ionomers
Authors: Su Gregory M. , Cordova Isvar A. , Yandrasits Michael , Lindell Matthew , Feng Jun , Wang Cheng , Kusoglu Ahmet
Published: February 2020

The performance of proton-conducting ionomer membranes used in electrochemical applications such as fuel cells is complicated by an intricate interplay between chemistry and morphology that is challenging to characterize and control. Here, we report on a class of perfluoro ionene chain extended (PFICE) ionomers that contain either one (PFICE-2) or two (PFICE-3) bis(sulfonyl)imide groups on the side-chain in addition to a terminal sulfonic acid group. PFICE ionomers are promising materials, exhibiting greater water uptake and conductivity over a range of relative humidity values compared to prototypical perfluorinated sulfonic acid (PFSA) ionomers. Advanced in situ synchrotron characterization combined with simulations reveals insights into the connections between molecular structure and morphology that dictate performance. Energy-tunable X-rays with sensitivity to sulfur can decipher the unique bonding environment of different protogenic groups on the polymer side-chain. Guided by simulations, X-ray absorption spectroscopy can be sensitive to hydration level and configuration that dictates proton dissociation. In situ resonant X-ray scattering reveals that PFICE ionomers have a phase-separated morphology with enhanced short-range order that persists in both dry and hydrated state, allowing for improved transport pathways across hydration levels. Furthermore, side-chain chemistry and length can be used as a molecular design parameter to predict phase-separated domain spacing. The enhanced conductivity of PFICE ionomers is attributed to a unique side-chain chemistry and structure promoting hydrogen bonding configurations that facilitate proton dissociation at low water content in combination with a well-ordered phase-separated morphology that forms transport pathways. Overall, these results provide guidelines to design new ionomers with improved transport properties and demonstrate the value of in situ characterization methods such as resonant X-ray scattering and spectroscopy for unraveling the structural features in chemically-heterogeneous materials used in electrochemical systems.