bluuebunny/crossref_metadata_2025 huggingface dataset:
Cracking the Genetic Code of Nickel on the Performance of the High Energy Layered Cathode Materials
Authors: Lee Wontae , Lee Kyung Lok , Lee Eunkang , Muhammad Shoaib , Yu Ji-Sang , Yim Taeeun , Yoon Won-Sub
Published: February 2020

The latest trend in LiMO2 (M=Ni, Co, Mn) layered system is to increase the ratio of nickel element in order to obtain advanced cathode materials with higher capacity. However, there has not been a clear elucidation on the fundamental role of nickel element in the three-component layered system yet. Thus, the Co fixed LiNi0.5+xCo0.2Mn0.3-xO2 (x=0, 0.1, 0.2) layered materials were designed to unravel the role of Ni atom as a major contributor to the crystallographic and electrochemical nature of Ni-rich layered materials. The results, on the basis of synchrotron-based characterization techniques, present a decreasing trend of Ni2+ content in Li layer with increasing total Ni contents in the Co fixed LiNi0.5+xCo0.2Mn0.3-xO2 (x=0, 0.1, 0.2) layered materials unlike the previously reported trend, and it disabuses the misapprehension of cation mixing in Ni-rich cathode materials. Moreover, it is discovered that a c-axis parameter of layered system is not intimately related with the real lithium ion pathway. The lithium inter-slab space increases with growing level of nickel concentration even though the c-axis parameter decreases. To investigate the structural behavior of Co fixed cathode materials during charge/discharge (de-intercalation/intercalation) process, a synchrotron-based in situ XRD technique was used. The overall structure behavior is similar to each other; however, the degree of phase transition is different depending on the nickel content. The NCM721(x=0.2) cathode material exhibited a smooth phase transition having similar lattice parameter between H1 and H2 phase. For NCM523(x=0), however, the new emerged H2 phase started to be formed exhibiting large disparities of lattice parameter between H1 and H2 phase relatively to the higher nickel content materials. According to this trend, The NCM721 has recorded the highest lithium diffusion coefficient on the whole during the de-intercalation process, and then NCM622, NCM523 in this sequence. The NCM523 cathode material has higher Ni2+ content in the Li layer and narrower lithium inter-slab space compared to higher nickel content cathode material such as NCM622 which is even more Ni2+ content in the Li layer and narrower lithium inter-slab space than NCM721. Following this trend, the XRD patterns during the de-intercalation process also showed a distinctive trend. In relation to this, a higher nickel content material shows better electrochemical performance in terms of capacity and cycling behavior compared with lower ones.
Scaling Effects of the Synthesis of Lithium- and Manganese-Rich Cathode Materials Via Carbonate Co-Precipitation
Authors: Kenkel Alexander , Kloepsch Richard , Wang Jun , Li Jie
Published: February 2020

Li-rich cathode materials with the general formula Li1+x

M
1-x
O2 (M = Mn, Ni, Co; x <= 0.2) are very promising cathode materials for lithium ion batteries, particularly due to their significantly higher specific capacity (>200 mAh g-1) compared to state of the art cathode materials.[1] Popular members of the Li-rich family, like Li1.2Mn0.56Ni0.16Co0.08O2 [2] and the Co-free compound Li1.2Mn0.6Ni0.2O2 have already been structurally and electrochemically investigated, but mostly on laboratory scale. Thus, in order to obtain larger amounts of high-quality Li-rich cathode materials, the upscaling effects of the established co-precipitation synthesis route were thoroughly investigated in this work, specifically for the above mentioned stoichiometries. With regard to the upscaling process, the impact of the synthesis parameters (e.g. stirring speed and type, pH value, reaction time) on the resulting morphology of the precursor as well as that of the final oxide and consequently, its electrochemical performance was analyzed. For each material three differently sized batches were synthesized, one in a laboratory scale of 4 g and two larger batches up to 75 g.

For the Co-free materials a significant upscaling effect was observed (see Fig. 1): The faster stirring of the larger batches lead to larger, spherically shaped precursor particles. However, these large precursor particles form more inhomogeneous target materials upon calcination, which consequently resulted in an inferior electrochemical performance. The more homogeneous cathode particles of the small batches show very promising electrochemical properties with regard to both rate capability and capacity retention.

References:

[1] M.M.Thackeray, S.-H. Kang, C.S. Johnson, J.T. Vaughey, R. Benedek, S.A. Hackney, Journal of Materials Chemistry, 17 (2007) 3112-3125.

[2] J. Li, R. Klöpsch, S. Nowak, M. Kunze, M. Winter, S. Passerini, Journal of Power Sources, 196 (2011) 4821-4825.

Figure 1
Reaction Mechanism and Dynamics of Selenium As Cathode for High Energy Density Lithium-Ion Battery
Authors: Li Qianqian , Wu Jinsong , Liu Heguang , Dravid Vinayak
Published: February 2020

Selenium, with similar chemical properties as sulfur, has recently attracted much research attention as potential electrodes for high energy density lithium-ion batteries. Unlike sulfur cathode with poor cycling performance due to the instability of Li-S compounds formed in lithiation and delithiation, Se is promising in regards to improvement in the cycling stability. We have used in situ transmission electron microscopy (TEM) to investigate the reaction mechanism and dynamics in the lithiation and delithiation cycles. We observe that single crystalline structure of pristine selenium nanowire gradually transformed to a polycrystalline structure as lithium continue insertion without intermediate amorphous phase formed during the whole lithiation process. And Li2Se phase with a polycrystalline structure finally forms after full lithiation. Li-Se alloying reaction accompanies with dramatic volume expansion, including both elongation along axil direction and expansion in radial direction. High density of stress and strain occurs at reaction front region, and then these stresses and strains rapidly glide to unreacted region, and move out of the nanowire from the surface and edge eventually. This process efficiently drives large amount of lithium ions to move forward. For comparison, we studied also the structural evolutions in the sodiation and desodiation which may have great implications for the development of sodium-ion batteries. These observations and experiments not only can help to deeply understand the reaction mechanism and reaction process, but favor to design novel nanostructure of electrodes with excellent electrochemical performance.

This work was supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DEAC02-06CH11357, and the Initiative for Sustainability and Energy at Northwestern (ISEN). This work was also supported by the NUANCE Center, and made use of the EPIC facility (NUANCE Center-Northwestern University), which has received support from the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); and the State of Illinois, through the IIN.
First Principles Design of Hybrid Cathode Architectures Based on LiMn2O4 Spinel Oxides
Authors: Kim Soo , Aykol Muratahan , Wolverton Chris
Published: February 2020

LiMn2O4 (LMO) can deliver a reasonable discharge capacity of ~130 mAh g-1, where the three-dimensional lithium ions diffusion channel in the spinel structure allows a rapid de-/intercalation reaction. There are several drawbacks of the spinel LMO including a severe capacity fade during cycling due to a Jahn-Teller (JT) distortion and Mn2+ dissolution. This Mn dissolution presumably starts at the particle surface; and therefore, it is essential to completely understand of the surface structure and its stability. We have recently constructed the thermodynamic stability diagram of LMO using density functional calculations (DFT) to investigate how stability of bulk LMO and LMO surfaces correlate as a function of oxygen and lithium chemical potentials.1 We have also suggested that Li-excess environments and too high temperatures should be avoided upon synthesis to yield particles with less (001) LMO facet, i.e., the surface that is more prone to Mn dissolution.

   Furthermore, we have recently provided a novel strategy to suppress Mn dissolution and the JT distortion by investigating the spinel LMO (001) surface with a single layer of graphene using DFT.2 Our theoretical calculation in Ref. 2 suggests that the interaction between the graphene sheet and the LMO (001) surface suppresses the Mn3+ disproportionation reaction into Mn2+ and Mn4+. While all surface Mn atoms at the LMO (001) have an oxidation state of +3, we find that the (001) Mn atom that chemically bonds with graphene adopts an electron configuration that has a clear +4 character with an empty eg
band. By analyzing the (001) LMO surface Mn-O bond distance, we observe that the JT distortion is reduced as the oxidation state of surface Mn shifts to Mn4+ in the presence of the graphene sheet. A chemical bonding between graphene and LMO on the (001) surfaces provides an underlying mechanism that electronically modifies the LMO (001) surfaces, and subsequently stabilizes them against Mn3+ disproportionation reaction and the JT distortion by converting (001) surface Mn3+ to Mn4+. Our advanced first-principles computations shed lights on the development of alternative hybrid Mn-cathode architecture approaches that can overcome the key shortcomings in these cathode materials.

References

[1] S. Kim, M. Aykol, and C. Wolverton. Phys. Rev. B, 92, 115411.

[2] L. Jaber-Ansari, K. P. Puntambekar, S. Kim, M. Aykol, L. Luo, J. Wu, B. D. Myers, H. Iddir, J. T. Russell, S. J. Saldaña, R. Kumar, M. M. Thackeray, L. A. Curtiss, V. P. Dravid, C. Wolverton, and M. C. Hersam.
Adv. Energy. Mater.
5 (2015) 1500646

Acknowledgement

This computational research work was supported by Northwestern-Argonne Institute of Science and Engineering (NAISE) and the Dow Chemical Company.

Figure Caption: Hybrid Cathode Architectures: Graphene-stabilized LiMn2O4 (001) Li-terminated Surface.

Figure 1
The Nanode 3D Tin Anode for High Energy and High Rate
Authors: Moroz Stephanie , Wieser Manuel , Brown Melanie , Gamboa Kristine
Published: February 2020

The Nanode is a nanoporous conductive membrane that provides a three dimensional matrix as a low cost support for electrodes. It is fabricated using commodity raw materials and chemicals, and manufacturing processes are in development for production on a roll-to-roll line.

The Nanode is combined with tin and tin alloys to form high energy anodes for lithium ion batteries. A thin film of active material is applied to the extremely high surface area of the conductive substrate which acts as the current collector. This has been shown to achieve greater energy at higher discharge rates compared to graphite anodes. Testing has been performed from 1 to 10C discharge rates at 100% depth of discharge paired with commercial NCM cathodes.

In addition, the nanoporous structure accommodates the expansion of the thin film of tin within its pores, reducing the overall electrode expansion/contraction occurring on charge/discharge of the anode.

Altogether, the low cost production, high energy at high rate, and reduced expansion of this anode provide a beneficial combination of features for future lithium ion batteries.

The Nanode technology also shows promise for applications beyond traditional lithium ion batteries, using alternative battery chemistries. This is made possible by the Nanode’s complex yet versatile electrode structure supported by a flexible manufacturing process that allows for the deposition of a range of metallic thin films of different compositions. These applications hold the potential to improve the energy density of rechargeable batteries beyond the limits of the traditional foil/particle approach, and they could reduce the cost of energy storage.
Li4Ti5O12 on Graphene for Lithium Ion Batteries with High Rate Performance
Authors: Wen Lei , Liu Cheng-Ming , Huang Quan-guo , Luo Hong-Ze , Li Feng
Published: February 2020

Spinel Li4Ti5O12 has become an alternative anode material for graphite in lithium ion batteries for large scale electrical energy storage in terms of solving safety issues and improving battery life-time. In order to form a much more bonding between the LTO and current collector, which is beneficial for stable cycling and high rate performance, we introduce a wrinkled graphene between the electrode layer and aluminum current collector to improve the rate performance and cycling performance of Li4Ti5O12 electrode. The introduced wrinkled graphene layer provides larger contact area, lower contact resistance, stronger adhesion and better electrode stability of Li4Ti5O12 electrode. This excellent electrochemical performance and very simple preparation method makes LTO@G-Al electrodes suitable for high-rate lithium ion batteries.
Synthesis and Characterization of Complex Framework Material (CFM) Hosts for Li – S Battery
Authors: Wang Louis S. , Murugavel Shanthi Pavithra , Jampani Hanumantha Prashanth , Gattu Bharat , Datta Moni Kanchan , Velikokhatnyi Oleg I , Kumta Prashant N
Published: February 2020

Great demand for improvements in battery technology has recently been spurred by the rapidly growing personal electronics and electric vehicle industries. The search for high energy density batteries have reached a limit in lithium intercalation electrodes which have a theoretical capacity of ~250 mAh/g1. Lithium sulfur batteries are a promising alternative to intercalation chemistry batteries, as a sulfur cathode features a theoretical capacity of 1675 mAh/g2.

However, the development of lithium sulfur batteries has been impeded by two fundamental issues which are: the low conductivity of sulfur (~10-15 S/cm)3, and the dissolution of polysulfides formed during cycling4. While the conductivity issue can be mitigated by incorporating conductive carbon into the cathode, polysulfide dissolution has proven more challenging to address5
,
6. The formation and dissolution of polysulfides results in the loss of active material from the cathode which culminates in cell failure.

Previous attempts to prevent polysulfide dissolution by embedding sulfur into porous carbon structures have been moderately successful. However, the efficiency of these approaches is limited by a lack of control over porosity. To improve on these carbon structures, sulfur hosts with engineered structures and chemical properties should be developed.

In this work, lithium sulfur battery cathodes were created using complex framework materials as sulfur hosts. The cathodes were created by solution phase infiltration of sulfur into complex framework materials synthesized by microwave-assisted hydrothermal synthesis. the XRD spectrum and SEM image of one of the CFMs is shown in Figure 1. The cathodes demonstrated impressive electrochemical performance with an initial discharge capacity of ~1620 mAh/g which stabilized at 1100 mAh/g after 100 cycles.

Acknowledgement:

The authors acknowledge the financial support of DOE grant DE-EE 0006825, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM).

References:

1. F. Bidrawn, S. Lee, J. M. Vohs and R. J. Gorte, Journal of The Electrochemical Society, 2008, 155, B660-B665.

2. S. S. Zhang, Journal of Power Sources, 2013, 231, 153-162.

3. V. S. Kolosnitsyn and E. V. Karaseva, Russian Journal of Electrochemistry, 2008, 44, 506-509.

4. J.-W. Park, K. Ueno, N. Tachikawa, K. Dokko and M. Watanabe, The Journal of Physical Chemistry C, 2013, 117, 20531-20541.

5. S.-R. Chen, Y.-P. Zhai, G.-L. Xu, Y.-X. Jiang, D.-Y. Zhao, J.-T. Li, L. Huang and S.-G. Sun, Electrochimica Acta, 2011, 56, 9549-9555.

6. J. Jin, Z. Wen, G. Ma, Y. Lu and K. Rui, Solid State Ionics, 2014, 262, 170-173.

Figure 1
Silver Nanoparticle/Boron-Doped Graphene Nanoribbon Nanocomposite for Effective Surface Enhanced Raman Scattering
Authors: Li Wei Ting , Chiang Wei Hung
Published: February 2020

Surface-enhanced Raman scattering (SERS) provides high sensitivity and selectivity on molecule detection, making it attractive for biomedical and chemical detections. Generally there are two mechanisms to influence the SERS enhancement: electromagnetic mechanism (EM) created by the metals with surface plasmon resonance (SPR) property and chemical mechanism (CM) due to the charge transfer between the molecule and the substrate. The development of synthetic method to produce nanostructures with controllable EM and CM properties will lead to important advances on both fundamental study and innovative applications for SERS-based biomedical detections. Graphene nanoribbons (GNRs) represent a unique structure of carbon nanomaterials with controlled electronic properties by tuning their widths, making them can be potentially useful as the SERS-active substrate and used in other applications including energy, composites, biomedical and electronics.

Here we report a rational design to develop a SERS-active nanocomposite with improved EM and CM properties. Toward this goal, we prepared silver (Ag)/Boron-doped GNR (B-GNR) composites using a sequential reaction route. First we synthesized GNRs with averaged width around 4 to 5 nm by the chemical unzipping of singled-walled carbon nanotubes (SWCNTs). Additionally, the prepared GNRs were doped with B atoms by a controlled carbonthemic reaction under argon (Ar) flow at atmospheric pressure and the B dopant concentration was about 1.4 atomic percentage (atom%) according to the X-ray photoelectron spectroscopy (XPS) analysis. Ag NPs with 10 nm averaged size were decorated onto the B-GNRs surface through an atmospheric-pressure microplasma-assisted redox reaction. Detailed materials characterizations including transmission electron microscopy and UV-Vis spectroscopy show that Ag/B-GNR composites were successfully synthesized in our experiment. We further systematically studied the Raman response of the Ag/B-GNR composite using Rhodamine 6G (R6G) as the Raman probe molecules. The result indicates that the Ag/GNR composite shows superior SERS performance with low detection concentration of 10-12 M of R6G and high enhance factor (EF) of 1.9x1012. We furthermore systematically studied the CM enhancement via different probing molecules and substrates. Results show that SERS performance is strongly influenced by the charge transfer mechanism induced by the energy gap between the substrate Fermi level and the LUMO energy of probing molecules. Our study provide the conception to design the applicable SERS substrates.

Figure 1
A First Principle Study of Vanadium Decorated Graphene Oxide As Novel Hydrogen Storage Material
Authors: Kureshi Sahida , Tokarev Andrey , Cannon Mark , Quan Grace , Kjeang Erik
Published: February 2020

Transition metal functionalized graphene is good candidate for hydrogens storage material [1-3]. Transition metal atoms interact with carbon of substrate material through Dewar [4] and hydrogen molecules with Kubas [5] interaction and offer good binding energy. However due to higher cohesive energy of transition metals, synthesis of such material remains bottleneck. Boron-doping into graphene has been studied [6-8] to eliminate clustering of transition and alkali metal atoms. In this work, an alternate approach of using graphene oxide as base material is studied. Hydrogen adsorption in vanadium decorated graphene oxide is studied with density functional theory calculations based on generalized gradient approximation. The epoxyl and hydroxyl groups in graphene oxide can provide active sites for the binding of vanadium and help to mitigate the clustering problem. From the preliminary calculations, it is found that graphene oxide has very high binding energy of ~6.2 eV for vanadium, higher than the cohesive energy of vanadium (5.31 eV). Further, single vanadium atom can bind four H2 molecules with an average adsorption energy of -0.5 eV. Graphene oxide is easy to synthesis and based on the value of vanadium binding energy it is easy to decorate with vanadium. Thus, vanadium decorated graphene oxide is promising material for hydrogen storage material.

References:

Yildirim T, Ciraci S. Titanium-decorated carbon nanotubes as a potential high-capacity hydrogen storage medium. Physical review letters. 2005 May 5;94(17):175501.

Zhao Y, Kim YH, Dillon AC, Heben MJ, Zhang SB. Hydrogen storage in novel organometallic buckyballs. Physical review letters. 2005 Apr 22;94(15):155504.

Durgun E, Ciraci S, Yildirim T. Functionalization of carbon-based nanostructures with light transition-metal atoms for hydrogen storage. Physical Review B. 2008 Feb 4;77(8):085405.

Mingos DM. A historical perspective on Dewar's landmark contribution to organometallic chemistry. Journal of Organometallic Chemistry. 2001 Oct 15;635(1):1-8.

Kubas Gregory J. Molecular hydrogen complexes: coordination of a. sigma. bond to transition metals. Accounts of Chemical Research. 1988 Mar;21(3):120-8.

Park HL, Chung YC. Hydrogen storage in Al and Ti dispersed on graphene with boron substitution: First-principles calculations. Computational Materials Science. 2010 Oct 31;49(4): S297-301.

Beheshti E, Nojeh A, Servati P. A first-principles study of calcium-decorated, boron-doped graphene for high capacity hydrogen storage. Carbon. 2011 Apr 30;49(5):1561-7.

Tokarev A, Avdeenkov AV, Langmi H, Bessarabov DG. Modeling hydrogen storage in boron‐substituted graphene decorated with potassium metal atoms. International Journal of Energy Research. 2015 Mar 25;39(4):524-8.

Figure 1
(Invited) Fundamentals of Oxo-Functionalized Graphene and Graphene Oxide
Authors: Eigler Siegfried
Published: February 2020

The structure of graphene oxide is a matter of discussion since the first description around 1860, long before the structure of graphite was known. The confusion about the chemical structure can now be analyzed in many aspects.

We introduced oxo-functional graphene as a novel class of materials, which bears in contrast to conventional graphene oxide a hexagonal carbon lattice, a high surface purity and therefore on-plane functional groups in majority, as demonstrated by HRTEM micrographs.[1] Moreover oxo-G bears no relevant amounts of oxidative debris and thus, graphene oxide is considered as a one-component system.[2]. Oxo-G can be used to control the chemistry of surface functional groups and we identified endoperoxides as source of the toxicity of oxo-G, relevant for bio-applications.[3] Controlling the on-plane reactions is the basis for controlled chemistry of graphene oxide and we demonstrate the extention of the life-time of perovskite/PCBM solar cells.[4]

It allows increasing the performance of rationally designed graphene derivatives in applications, such as information storage or solar cells.

REFERENCES

[1] B. Butz, C. Dolle, C. E. Halbig, E. Spiecker and S. Eigler, Angew. Chem. Int. Ed., 2016, 55, 15771-15774.

[2] A. Naumov, F. Grote, M. Overgaard, A. Roth, C. E. Halbig, K. Norgaard, D. M. Guldi and S. Eigler, J. Am. Chem. Soc., 2016, 138, 11445-11448.

[3] H. Pieper, S. Chercheja, S. Eigler, C. E. Halbig, M. R. Filipovic and A. Mokhir, Angew. Chem. Int. Ed., 2016, 55, 405-407.

[4] H. Chen, Y. Hou, C. E. Halbig, S. Chen, H. Zhang, N. Li, F. Guo, X. Tang, N. Gasparini, I. Levchuk, S. Kahmann, C. O. Ramirez Quiroz, A. Osvet, S. Eigler and C. J. Brabec, J. Mater. Chem. A, 2016, 4, 11604-11610.
(Invited) Chemistry of Novel 2D Materials: Black Phosphorus and Antimonene
Authors: Abellán Gonzalo
Published: February 2020

Two-dimensional (2D) materials have attracted increasing interest in the last few years due to their unique morphology and properties and their use in a variety of applications, ranging from electronics to energy storage or catalysis, to name a few. Apart from various well-established 2D materials, such as graphene, h-BN, or MoS2, black phosphorus (BP) has received considerable attention over the last two years because its direct bandgap and his appealing properties for electronic and ultrafast optoelectronic applications. However, its lack of environmental stability severely limits its synthesis and processing.

We have recently demonstrated that high-quality, few-layer BP nanosheets, with controllable size and observable photoluminescence, can be produced in large quantities by liquid phase exfoliation under ambient conditions.1 Beyond this success, a more sophisticated chemical modification is highly desirable, like the molecular doping, that is an effective and flexible method towards modulating the electronic properties of 2D materials. Herein, we have developed a chemical route for the non-covalent functionalization of BP with different moieties, including electron-withdrawing organic molecules or tailor-made surfactants.2 Moreover we have extended these concepts towards a new 2D material: antimonene, creating stable suspensions in water and developing its non-covalent functionalization.3

1) D. Hanlon, C. Backes, E. Doherty, C. S. Cucinotta, N. C. Berner, C. Boland, K. Lee, A. Harvey, P. Lynch, Z. Gholamvand, S. F. Zhang, K. P. Wang, G. Moynihan, A. Pokle, Q. M. Ramasse, N. McEvoy, W. J. Blau, J. Wang, G. Abellan, F. Hauke, A. Hirsch, S. Sanvito, D. D. O’Regan, G. S. Duesberg, V. Nicolosi, J. N. Coleman, Nat. Commun. 2015, 6, 8563.

2) G. Abellán, V. Lloret, U. Mundloch, M. Marcia, C. Neiss, A. Görling, M. Varela, F. Hauke, A. Hirsch, Angew. Chem. In. Ed., 2016, 55 (47), 14557.

3) C. Gibaja, D. Rodriguez-San-Miguel, P. Ares, J. Gómez-Herrero, M. Varela, R. Gillen, J. Maultzsch, F. Hauke, A. Hirsch, G. Abellán, F. Zamora, Angew. Chem. In. Ed., 2016, 55 (46), 14345.
Graphene Nanoribbon Synthesis with a Fluorinated Molecular Precursor
Authors: Hayashi Hironobu , Yamaguchi Junichi , Jippo Hideyuki , Sato Shintaro , Yamada Hiroko
Published: February 2020

The surface-assisted reaction is a key process for graphene nanoribbons (GNRs) synthesis. So far, anthracene based compounds, as represented by 10,10’-dibromo-9,9’-bianthracene, are most-used molecular precursors for GNRs synthesis. However, even the simple anthracene based precursor molecules exhibit a variety of reactivity because the on-surface synthesis includes hierarchical reactions such as dehalogenation, polymerization, and cyclodehydrogenation. Considering that the reactivity of the small precursor molecules determines the final structure of GNRs, the key to success for synthesizing tailored GNRs is the deep understanding the relationship between the reactivity of the molecules and the geometry on the catalytic metal surface.

Here, we investigated the reactivity of a fluorinated precursor molecule during the GNR formation. The fluorine atoms were introduced at 2,3,6,7-positions of an anthracene sandwiched by 9-bromoanthracenes in order that the effect of fluorine substitution at the edge positions of polyanthrylene and GNRs would be investigated. Scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) indicate the formation of the edge-fluorinated polyanthrylenes. Interestingly, the following cyclodehydrogenation yields GNRs, dissociating the carbon-fluorine bonds at the edge positions of polyanthrylenes. Namely, the strong C-F bond survived during the polymerization step, but the following cyclodehydrogenation cleaved the C-F bond. Theoretical calculation implies that the structure of the intermediate state during the cyclodehydrogenation played an important role in the fluorine dissociation. Thus, the lessons from the dissociation of the strong C-F bond, which is believed as one of the strongest bonding in the solution chemistry, would provide the synthetic access to the proper design of precursor molecules for edge-functionalized GNRs.
(Invited) Controlling Solution Chemistry from Lab-Scale Spin Coating to Scalable Deposition for High-Performance Perovskite Solar Cells
Authors: Zhu Kai
Published: February 2020

Organic-Inorganic hybrid halide perovskites have recently emerged as a new class of light absorbers that have demonstrated a rapid progress and impressive efficiencies (>22%) for solar conversion applications. Despite the rapid progress demonstrated by these light absorbers, there is still a lack of understanding of some fundamental material/physical/chemical properties of these materials. There is also a significant processing gap between the lab-scale spin coating and scalable deposition methods toward future roll-to-roll manufacturing. The challenge results from the sensitivity of perovskite crystallization and film formation to the processing conditions, which depend strongly on the specific deposition method. In this presentation, I will present our recent studies toward a better understanding and control of perovskite nucleation, grain growth, and microstructure evolution using solution processing. The precursor chemistry and growth conditions are found to affect significantly the structural and electro-optical properties of perovskite thin films. We also find that the precursor ink chemistry (solvent, coordination chemistry) of perovskite is critical for scalable deposition; but this has largely been underexplored. We present a rational design of perovskite precursor film formation to achieve highly specular films using scalable deposition methods. Using these high quality perovskite films, we have achieved device efficiencies approaching the values obtained on small scale by spin coating. These findings make a significant advance towards commercialization of the perovskite photovoltaic technology. These results and others will be discussed.
Perovskite Solar Cells. Excited State Chemistry of Lead Halide Hybrid Perovskites
Authors: Kamat Prashant V , Mucunguzi Anselme , Hoffman Jacob , Yoon Seogjoon
Published: February 2020

With the emergence of highly efficient lead halide perovskites there is a need to understand the excited state behavior and charge separation events following photoexcitation. The excited state characterization using emission and transient absorption spectroscopy has allowed us to probe the charge recombination processes. Of particular interest are mixed halide lead perovskites (e.g.,CH3NH3PbI3-xBrx) which offer flexibility of tuning bandgap. Interestingly, they also undergo phase segregation to create Iodine-rich and Bromide- rich regions when subjected to visible irradiation. This intriguing aspect of halide ion movement in these mixed halide films can be tracked from the changes in the photoluminescence and absorption spectra. The photovoltaic performance of perovskite solar cells with varying degree of halide treatment will also be discussed.
(Invited) Push-Pull P-Extended porphyrins As Sensitizer for Dye-Sensitized Solar Cells
Authors: Wang Hong , Jinadasa Raja Gabadage , Hu Yi , Thomas Michael , D'Souza Francis , Yellappa Shivaraj
Published: February 2020

Significant progress has been made on dye-sensitized solar cells sensitized by push-pull porphyrins in recent years.1-3 Through installing push-pull groups at porphyrin meso-positions, exceptionally high power conversion efficiencies have been achieved.4, 5 In this presentation, we present the synthesis and characterization of a series of novel opp-dibenzoporphyrins, and their application as sensitizers for dye-sensitized solar cells. These porphyrin sensitizers are designed through installation of push (electron-donating) and pull (electron-withdrawing) groups at the porphyrin beta-positions. Significant push-pull effects were observed for these porphyrins. The effect of different conjugated spacers on the power conversion efficiency of these dyes was investigated. It was found that inclusion of ethynylphenyl bridge between the donating group and porphyrin core would segregate the frontier orbitals. Our data also show that conjugated bridges appear to play important roles in determining their power conversion efficiency. The electronic and optical properties of these pi-extended porphyrins were measured using UV-Vis spectroscopy, life-time and steady state fluorescence spectroscopy, and cyclic voltammetry. DFT calculations were also performed for these porphyrins.

Reference

1. T. Higashino and H. Imahori, Dalton Trans., 2015, 44, 448-463.

2. M. Urbani, M. Gratzel, M. K. Nazeeruddin and T. Torres, Chem. Rev., 2014, 114, 12330-12396.

3. L. L. Li and E. W. Diau, Chem. Soc. Rev., 2013, 42, 291-304.

4. A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M. Zakeeruddin and M. Grätzel, Science, 2011, 334, 629-634.

5. S. Mathew, A. Yella, P. Gao, R. Humphry-Baker, B. F. Curchod, N. Ashari-Astani, I. Tavernelli, U. Rothlisberger, M. K. Nazeeruddin and M. Gratzel, Nat. Chem., 2014, 6, 242-247.

Figure 1
Temperature-Dependent Hydrothermal Preparation of MoS2/Graphene Hybrid Electrocatalyst
Authors: Guo Xiaoru , Hou Yang , Ren Ren , Chen Junhong
Published: February 2020

Two-dimensional (2D) hybrid materials have been studied for use in photovoltaics, water splitting, sensors, batteries, and many other applications, which are prepared from popular 2D nanomaterials into heterojunctions or 3-dimensional (3D) frameworks. Benefiting from their unique 2D structures and tunable bandgaps, 2D hybrid materials can offer both a high surface area and a suitable work function. Molybdenum disulfide (MoS2)/graphene hybrid material has been proved as a high-performance and low-cost catalyst for energy applications, but its optimum preparation condition is yet to be determined.

This work focuses on the 3D structure of MoS2/graphene hybrid and primarily studies the crystallization condition and morphology change of MoS2 in MoS2/graphene hybrids by a temperature-varying hydrothermal method. Flower-like MoS2 nanoflakes have been successfully grown on graphene nanosheets by using the hydrothermal method at temperatures from 150 to 240 oC. The resulting hybrid material was characterized to understand its temperature-dependent crystallization process and its electrochemical performance in the dye-sensitized solar cell and the hydrogen evolution reaction. Through high-resolution scanning electron microscopy and high-resolution transmission electron microscopy, the 3D structures can be clearly observed and compared. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy are taken to identify the crystallization differences among different samples and understand temperature effects. The highest electrocatalytic efficiency for both the DSSC and the HER was obtained by preparing the MoS2/graphene hybrid at 180 oC, which benefits from both high reactivity of MoS2 1T phase and high conductivity of the hybrid structure. This research leads to a better understanding of temperature dependence of MoS2 crystallization and gives directions for better catalytic material design.
Supramolecular Metal Arraying in Porphyrin/Phthalocyanine Conjugates for Catalytic Applications
Authors: Tanaka Kentaro , Yamada Yasuyuki , Mihara Nozomi
Published: February 2020

Recently, we reported synthesis of porphyrin/phthalocyanine conjugates linked by fourfold rotaxane. In the conjugate, a porphyrin and a phthalocyanine formed a heterodimer in a cofacial fashion (Fig. 1a). [1] The conjugate is a promising platform for supramolecular catalysts based on dinuclear porphyrinoid complexes, because various metal ions to be a functional center are able to be arrayed in the conjugate regioselectively to afford homo- and hetero-dinuclear centers in the conjugate. [2,3] Moreover, these arrays were expanded to hetero-trinuclear arrays (Fig. 1b). [3-6]

In this paper, we will present regioselective metal arraying in the conjugate and the supramolecular catalytic functions (Fig. 2). One of the methods to prepare the hetero-dinuclear complexes was to use the difference of metalation rate between porphyrin and phthalocyanine. We found reaction conditions for porphyrin-selective Fe(II) or Ni(II) insertion and phthalocyanine-selective Mn(II) insertion. Subsequent metalation to another porphyrinoid in the conjugate gave a hetero-dinuclear complex. We used these multinuclear complexes in the conjugate as catalysts. The dinuclear iron complex exhibited good catalytic activity in electrochemical reduction of molecular oxygen to water. [7]

References:

1) Y. Yamada, M. Okamoto, K. Furukawa, T. Kato, and K. Tanaka., Angew. Chem. Int. Ed.,
51, 709 (2012,).

2) Y. Yamada, N. Mihara, and K. Tanaka., Dalton Trans.,
42, 15873 (2013).

3) N. Mihara, Y. Yamada, and K. Tanaka., submitted.

4) Y. Yamada, N. Mihara, S. Shibano, K. Sugimoto, and K. Tanaka., J. Am.Chem. Soc.,
135, 11505 (2013).

5) Y. Yamada, S. Akine, K. Sugimoto, and K. Tanaka, Chem. Euro. J., 22, 12371 (2016).

6) N. Mihara, Y. Yamada, S. Akine, K. Sugimoto, and K. Tanaka., submitted.

7) N. Mihara, Y. Yamada, and K. Tanaka., submitted.

Figure 1
(Invited) Materials Design By Atmospheric Pressure Plasmas for Solar Energy Harvesting
Authors: Mariotti Davide
Published: February 2020

Atmospheric pressure plasmas (APP) have demonstrated exceptional versatility to synthesize and modify a very wide range of materials with varying morphologies, sizes and compositions [1-3]. These include semiconducting, oxide and metal nanoparticles, nanostructured films and ultra-small quantum confined nanostructures. APPs have key features which would make the corresponding processes highly desirable for large scale manufacturing.

In recent years we have therefore focused our efforts in developing ad-hoc APP processes with in mind two main objectives. On one side we have developed processes that could be integrated in the fabrication of application devices so that we could demonstrate direct applicability of APPs to relevant device fabrication steps. In particular we have developed APP-based strategies for solar cell device fabrication [4]. At the same time we have tried to work bottom-up, whereby our materials synthesis approach was dictated by desired materials functionalities.

Here we will exemplify our efforts with a range of semiconducting nanoparticles and metal oxides to include Cu-, Zn-, Ni-, Mo- and Co-oxides. We will show different synthesis mechanisms and how specific properties such as bandgap, quantum confinement and plasmon resonance can be tailored guided by our materials needs. We will then demonstrate the materials functionalities within photovoltaic devices.

[1] Journal of Physics D: Applied Physics 43 (2010) 415402

[2] Chemical Physics Letters 478 (2009) 224

[3] Applied Physics Letters 104 (2014) 163103

[4] Plasma Process. Polym.
13 (2016) 70
(Invited) Plasma Assisted Oblique Angle Deposition of Transparent and Conductive in-Plane Anisotropic ITO Thin Films
Authors: Parra-Barranco Julian , Sanchez-Valencia Juan Ramon , Aparicio Francisco J. , Garcia-Garcia Francisco , Ferrer Francisco J. , Rico Victor , Lopez-Santos Carmen , Borras Ana , Gonzalez-Elipe Agustin R. , Barranco Angel
Published: February 2020

Glancing angle deposited (GLAD) oxide thin films are quite interesting materials due to the wide variety of nanostructures that can be obtained with this method. Most important properties of the oxide GLAD thin films rely in the possibility to tailor their nanostructure in the form of tilted columns and other more complex forms. This nanostructure is caused by geometrical shadowing effects during the thin film growth. Porous GLAD films have been used as hosts or templates to fabricate new nanocomposite materials and other complex optical nanostructures like photonic crystals, dye sensitized solar cells, optical sensors and microfluidic devices. [1-3] In this work we study the fabrication of transparent and conducting Indium tin oxide films (ITO) by a novel synthetic approach consisting in GLAD deposition assisted by a microwave ECR plasma. The ECR microwave discharges are fully compatible with the range of pressures required for the electron evaporation process utilized for the deposition of the ITO thin films. The objective of the plasma is to modify the growth mechanism of the GLAD process in order to control the columnar microstructure, porosity and the properties of the films [4]. As it will be shown, the GLAD ITO deposition assisted by the plasma discharge is a very effective process to develop in-plane anisotropy in the ITO films what determines the films properties.

[1] M. J. Brett et al. Science, 319 (2008) 1192.

[2] A. Barranco et al. Progress in Materials Science 76, (2016) 59-153.

[2] González-García et al, Nanotechnology 23 205701, 2012.

[3] Gonzalez-García et al. Energy. Environ. Sci. 4, 2011, 3426.

[4] J. Parra-Barranco et al. ACS Appl. Mater. Interf. 7, 2015, 10993.
(Invited) Plasma Deposition of Antibacterial Nano-Coatings on Polymeric Materials
Authors: Nikiforov Anton , Leys Christophe , Kuchakova Iryna , Vanneste Myriam , Heyse Pieter , De Vrieze Mike , Zille Andrea , Dinescu Gheorghe , Mitu Bogdana , Modic Martina , Cvelbar Uros
Published: February 2020

Non-woven textile materials with antimicrobial properties are of high demands for applications ranging from medical dressing to everyday cleaning products. We proposed a plasma assisted route to engineer polymer films and non-woven fabrics with antimicrobial nano-composite coatings. The project aims to optimize atmospheric pressure plasma deposition in order to engineer the coatings with high antibacterial activity and low cytotoxicity. Different methods of deposition are tested including radio-frequency plasma, direct current discharge in nitrogen as well barrier discharge in air with two methods of nano-particles incorporation: aerosol and impregnation. Nano-particles Ag, Cu and ZnO are tested as antimicrobial agents with average nano-particle size of about 50 nm. Nanoparticles are incorporated in between two layers of an organosilicon film with an impregnation process or alternatively through an aerosol injection step with averaged concentration of the nano-particles in the solution ranging in between 10 to 1000 mg/l. Incorporation is made in a “sandwich-like structure” where a top layer coating (barrier) of 5 - 50 nm thickness is used for precise control of metal ions release and a reservation layer of about 200 nm is used for NPs load. The effect of the barrier coating on the surface concentration of nano-particles is determined by XPS. It is shown that an increase of the thickness of the barrier layer from 5 to 25 nm leads to a decrease of Ag content from 0.24 to 0.08 at. %. Similar effect is found for nano-particles of Cu and ZnO. Antibacterial efficiency of the samples against P. aeruginosa ATCC 9027 and S. aureus M u50 bacteria shows that all treated samples exhibit higher antibacterial efficiency against S. aureus. The antibacterial efficiency of AgNPs and CuNPs is above 90% which is practically interesting for medical application while ZnONPs shows lower antibacterial efficiency. Cytotoxicity of the coatings and materials is investigated for different deposition conditions and analyzed in terms of possible medical applications.

This work is supported by the M.Era-Net project IWT 140812 “PlasmaTex”.
Copper Electrodeposition from a Water-Containing Choline Chloride-Based Deep Eutectic Solvent
Authors: Valverde Priscila , Green Todd , Roy Sudipta
Published: February 2020

Ionic liquids are increasingly being used to electrodeposit metals, alloys and semiconductor materials. The popularity of these solvents arises from their desirable characteristics such as large electrochemical windows, reasonable conductivities, and good environmental compatibility. An important class of ionic liquids are deep eutectic solvents (DESs). DESs have been shown to be stable under atmospheric conditions, are non-flammable and have low vapour pressures. DESs formulated from choline chloride (ChCl) hold special promise since they are readily available at a reasonable cost.

The focus of this study is on ‘ethaline’ prepared by mixing choline chloride with ethylene glycol in a 1:2 molar ratio. Although DESs have been used to electrodeposition, earlier studies have concentrated on systems with a low water content (< 0.5 wt%). This is in line with earlier studies using other ionic liquids, since water can reduce the electrochemical window. However, these DES systems are hygroscopic, and absorb water from the atmosphere unless special precautions are taken. Not only can water absorption have an adverse effect on the electrochemical window, it can also affect deposit composition and morphology. Conversely, other researchers have shown that water can protect against the anodic decomposition of the solvent itself and prevent the formation of chlorinated by-products.

Information about the impact of water content on metal electrodeposition from DESs is, however, relatively scarce. The objective of this study is to understand the influence of water on the morphology of copper electrodeposited from water-containing DESs. We first examined the effect of adding various concentrations of water (3 – 15 wt%) on the stability of the solution; in particular this was obtained from the polarisation behaviour of metal deposition. It was noted that water addition affected both the limiting current for copper deposition and the deposition potential. A second series of experiments were carried out to assess how much water is absorbed by the DES depending on the storage conditions. The water content in these experiments were determined using Karl Fischer titration and NIR spectroscopy. The effect of increasing water content on copper speciation was explored using UV-Vis spectroscopy.

Subsequently, Cu films were electroplated on a steel rotating disc substrate from electrolytes containing different weight percentages of water. The deposits were characterised using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). SEM images showed that the morphology of Cu deposits was also dependent on the water content of the DES. The relationship between the observed changes in electrochemical characteristics and deposit properties with increasing water content will be discussed.
Development of a Functional Reach Compliant Trivalent Chromium Electroplating Process
Authors: Hall Timothy D , Taylor E. J. , Inman Maria , Snyder Stephen , Xu Jing , Radhakrishnan Rajeswaran
Published: February 2020

Faraday Technology Inc. is a research, development and engineering firm developing electrochemical innovations based has pulse/pulse reverse electrolytic principles [1]. One of Faraday’s current activities is directed towards the development of an innovative functional REACH compliant chrome plating process based on a trivalent chromium electrolyte to replace hexavalent chromium plating. Hexavalent chromium plating has been used for many decades to provide hard, durable coatings with excellent wear and corrosion resistance properties. However, hexavalent chromium has come under increasing scrutiny due to the toxic nature of the bath, effects on the environment, and workers’ health. Faraday has demonstrated that the chrome coatings prepared using the FARADAYIC(R) Process have equivalent functional properties to the coatings produced with a hexavalent chromium bath. The data demonstrates equivalent or superior: 1) plating rate, 2) Knoop hardness, 3) current efficiency, 4) hydrogen embrittlement behavior, 5) adhesion, 6) corrosion resistance, 7) porosity, 8) thickness, 9) Taber Abrasion, Ball on Flat Reciprocating and Dithering wear resistance, and with no hexavalent chromium formation in the bath.

Therefore, this paper will discuss the 2013 EPA Green Chemistry Challenge Award winning work on the development of a REACH compliant functional trivalent chromium plating process from a single, simple-to-control trivalent-based electrolyte to replace hexavalent chromium plating.

Acknowledgements: This study is supported by the US Army (W911NF-11-2-0014) and private sources.

[1] E. J. Taylor “Adventures in Pulse/Pulse Reverse Electrolytic Processes: Explorations and Applications in Surface Finishing” J. Applied Surface Finsihing,
3(4), 178-189 (2008).