bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ X-Ray Nano-Tomography at ID16B: A Practical Guide to Battery Analysis
Authors: Vanpeene Victor , Martens Isaac , Drnec Jakub , Schulli Tobias , Capria Ennio , Villanova Julie
Published: July 2022

The past decade faced with rapid development of electric vehicles, portable electronic devices and green energy production, in which lithium-ion batteries (LiBs) technology plays a key role. In this context, extensive research has been made for increasing their energy density along with power density. This challenge requires pushing forward the resolution limits to probe degradation phenomena occurring at the active material level for a deeper understanding of the batter failure mechanism.

In this context, X-ray techniques have been intensively used to probe in details the morphological/chemical evolution along cycling of various battery materials. For instance, X-ray computed tomography brings valuable 3D information for material structural analysis at scale ranging from the micrometre to the nanometre. High flux and high coherent X-ray nano-beams provided by the synchrotron sources, combined with the fast acquisition obtained thanks to the new generation of cMOS detectors, make it possible to carry out in situ and operando measurements at the nano-scale to 3D monitor dynamic phenomena. These developments present a real interest for the energy storage applications.

This presentation will focus on the hard X-ray nano-tomography set-up developed at the ID16B beamline of the ESRF and its applications toward operando measurements applied to different case studies related to energy materials. This will be discussed as well in regards to the benefits and limitations brought by the extremely brilliant X-ray source EBS developed at the ESRF.
PEGDA with Metal-Organic Frameworks As Composite Electrolyte for All-Solid-State Lithium Batteries
Authors: He Zizhou , Fei Ling
Published: July 2022

The widely use of volatile and flammable traditional organic carbonate-based electrolytes in high-performance lithium-ion batteries (LIBs) is prone to cause safety hazards. Solid-state polymer electrolytes (SPE) have been developed to address the safety issues due to their numerous advantages, such as solvent-free, low flammability, wide electrochemical stability window, and good thermal and mechanical stability. However, the polymer tends to recrystallize at room temperature leading to insufficient ionic conductivity. Organic-matter-based fillers (e.g., metal-organic frameworks, covalent−organic frameworks, and lithiophilic polymers) have been found to increase the ionic conductivity of SPEs effectively by decreasing the crystallinity of polymer, synchronously to improve the mechanical property, thermal stability, and interfacial compatibility. Porous zeolitic imidazolate framework-8 (ZIF-8) has been used as fillers in this study. The ZIF-8 are integrated with the PEGDA matrix in this study, showing enhanced electrochemical and mechanical properties. Such performance enhancement is due to the composite solid-state electrolyte inherited the advantages of both polymer and fillers. The fillers not only inhibited the recrystallization of the polymer but also prevent the dendrite growth of the Li. The polymeric PEGDA enhanced the contact interface between the electrolyte and electrodes. Therefore, PEGDA-based SPEs with ZIF-8 is of great promise for all-solid-state lithium metal batteries.
(Digital Presentation) Effect of Electrolyte Additives on the Discharge Behavior and Performance of a WE43 Mg Alloy As Mg-Air Battery Anode
Authors: Peng Chih-Sheng , Chu Peng-Wei
Published: July 2022

Smartphones and electric cars have developed rapidly over the past ten years. Hence, high energy density storage devices are also getting increasing attention. Compared with commercial Li-ion batteries, Mg-air battery systems have the advantages of a high theoretical energy density (6800Wh/kg), natural abundance, environmental-friendliness, and low cost. However, Mg-air battery suffers from low anodic efficiency, discharge product accumulation, and sluggish reaction kinetics on both the anodes and cathodes. Adding additives to the electrolyte has been shown to increase the cell voltage and boost the anode efficiency. Nevertheless, the underlying mechanism of how electrolyte additives change the discharge behavior is still unclear. In this report, the discharge behavior and performance of a Mg-air battery with different electrolyte additives are investigated through a combination of electrochemical analysis, collection of the by-product hydrogen gas, and microscopic characterizations.

A WE43 Mg alloy was selected as the anode for primary Mg-air batteries due to its high activity in 3.5wt% NaCl solution. Various amounts of electrolyte additives, such as chelating agents, e.g. salicylate salts, and corrosion inhibitors, e.g. Na3PO4, were added to 3.5wt% NaCl solution together or separately. The discharge behavior and performance with different additives were analyzed by recording the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) before and after discharge, discharge voltage evolution, hydrogen evolved from the anodes, and cross-sectional observations of the alloy after discharge. The anodic efficiency loss contributed by the negative difference effect (NDE) and chunk effect (CE) were also quantified to study how different additives change the discharge behavior. The anode performance improvement and synergic effect of the electrolyte additives will be discussed.

Figure 1
An Electrochemical Ethylamine/Acetonitrile Redox Method for Ambient Hydrogen Storage
Authors: Wu Dezhen , Li Jialu , Yao Libo , Xie Rongxuan , Peng Zhenmeng
Published: July 2022

Hydrogen is an appealing energy carrier that can potentially replace conventional fossil fuels in the development of a clean, sustainable hydrogen economy, which would resolve environmental problems caused by the combustion of the non-renewable resources while also meeting the rising demand for energy. However, hydrogen storage has remained a major roadblock in the hydrogen economy development. As a matter of fact, the state-of-the-art methods fall short of the 2025 Department of Energy (DOE) onboard hydrogen storage target of 5.5 wt.% under 85 °C and 12 bars.

Herein we report a new, electrochemical ethylamine/acetonitrile redox method for efficient, high-capacity hydrogen storage under completely ambient conditions. The amine/nitrile redox couple is selected due to their moderate chemical polarity and relatively simple hydrogenation and dehydrogenation pathways, which would aid reaction activation and reduce the energy barrier. Electrochemical potential provides the driving force in CH3CH2NH2 dehydrogenation under ambient conditions, rather than high temperature and pressure that are typically required to thermally drive an endothermic process. We demonstrate an effective, complete cycle of CH3CN hydrogenation to CH3CH2NH2 for hydrogen uptake and CH3CH2NH2 dehydrogenation to CH3CN for hydrogen release at low overpotentials, using commercial Pt black catalyst in an electrochemical cell. The studied CH3CH2NH2/CH3CN system has a theoretical H2 storage capacity of 8.9 wt.%, well surpassing the 5.5 wt.% DOE target. This study offers a new, effective hydrogen storage strategy that can be extended to many other amine/nitrile redox systems and would help advance the hydrogen economy development.
(Invited) DNA Kirigami with Tripod-C60 Scalpel
Authors: Ray Ankita , Spencer Nicholas D. , Kuzuya Akinori , Yamakoshi Yoko
Published: July 2022

A tripod-C60 molecule was synthesized and attached onto a Au-coated AFM tip. Using the tripod skeleton of the molecule, tripod-C60 was immobilized onto the Au surface in a dispersed and stable manner, as observed by XPS and AFM imaging. Using an AFM tip functionalized with the tripod-C60, waffle-type DNA origami was scanned under visible light irradiation. Upon scanning, DNA damage was clearly observed by AFM imaging at the single molecule level. Control experiments in the absence of C60 (tripod only), in the dark, or in the presence of L-histidine or D2O confirmed that the observed DNA damage was induced by singlet oxygen (1O2) generated from C60 under photoirradiation.

References: (1) Ray, A.; Passiu, C.; Nasuda, M.; Ramakrishna, S. N.; Rossi, A.; Kuzuya, A.; Spencer, N. D.; Yamakoshi, Y. ACS Nano ASAP. (2) Ray, A.; Liosi, K.; Ramakrishna, S. N.; Spencer, N. D.; Kuzuya, A.; Yamakoshi, Y. J. Phys. Chem. Lett.
2020, 11, 7819–7826.

Figure 1
Zinc Passivation in Zinc-Slurries Operated Beyond the Zincate Solubility Limit
Authors: Fuchs David , Müller Christoph , Mahlendorf Falko , Hoster Harry
Published: July 2022

Recently, zinc-air batteries have received revived interest as one of the proposed post lithium-ion technologies. This revival is driven by the demand for safe and environmentally friendly energy storage solutions for fluctuating renewable energy. These energy storage systems need to address variable power, capacity and profitability requests. Zinc-air-flow batteries with high specific energy density, low-cost, highly available and eco-friendly active materials are suitable to fulfill these requirements. The use of a flow battery type with zinc-particles suspended in an alkaline solution (zinc-slurry) in addition to high performance oxygen-reduction electrodes enables the development of high-power zinc-air batteries. Usually, the energy density of zinc-air-flow cells is limited by the solubility of the oxidation products in the electrolyte. In our cell, the electrolyte is supersaturated with oxidation products, before finally ZnO precipitates from the electrolyte. The cell is therefore operated beyond zincate solubility limit, which allows higher specific capacities than reported in literature, even though the zincate solubility of the electrolyte is much lower than reported [1].

The flow cell has an active area of 100 cm² and incorporates a copper plate as current collector for the zinc-suspension electrode and an oxygen reduction electrode with gas-diffusion layer (supplied by Covestro). The zinc-slurry contains zinc-particles (supplied by Grillo) suspended in an alkaline solution (30 wt.-% KOH) and stabilized with polyacrylic acid.

One of the main limiting factors of the specific capacity of the zinc-slurry is passivation. While the passivation of stationary electrodes in flowing or quiescent electrolytes is fairly well understood, see e. g. [2], there is no literature on the passivation behaviour of zinc-slurry electrodes. In this study we determined the starting point of ZnO precipitation and the critical factor for the passivation of these anodes by analysing cell voltage, potential of the zinc electrode and the zincate concentration in the liquid phase of the zinc-slurry. Depending on parameters like current density and additive selection, it is possible to reach specific capacities of 287 mAh/gslurry or 574 mAh/gzinc.

Appleby, A.J. and M. Jacquier, The C.G.E. circulating zinc/air battery: A practical vehicle power source. Journal of Power Sources, 1976. 1(1): p. 17-34.

Bockelmann, M., et al., Electrochemical characterization and mathematical modeling of zinc passivation in alkaline solutions: A review. Electrochimica Acta, 2017. 237: p. 276-298.
The Advent of Aqueous >2.85V Zn-MnO2 Batteries: Uncovering Novel Mechanisms in This New High Voltage Chemistry
Authors: Yadav Gautam , Weiner Meir , Upreti Aditya , Huang Jinchao , Wei Xia , Lambert Timothy N. , Schorr Noah B. , Bell Nelson , Banerjee Sanjoy
Published: July 2022

Alkaline zinc (Zn)-manganese dioxide (MnO2) batteries are ubiquitous, safe, cheap and used in several applications that require only a single discharge. Its impact in the developing world has been significant where its affordability has helped consumers with low to medium economic background power several of their household devices and flashlights when grid reliability has been poor. Its single discharge is enough to deliver an energy density of ~400Wh/L. However, its promising characteristics are outweighed by its limited use in the next generation of green energy technologies because of the irreversibility of its active materials and its low nominal voltage of ~1.3V. The application of battery energy storage in these next generation of technologies like grid-storage, electric vehicles and personal electronics is extremely vital to decarbonize our future. Currently, expensive, toxic and flammable lithium-ion and lead acid batteries dominate these fields. If Zn-MnO2 batteries could be made rechargeable with an increase in its nominal voltage and capacity utilized, it could be serious contender to the dominant lithium-ion and lead acid batteries.

In this presentation, we report on an innovative approach where we solve the two aforementioned issues by redesigning the battery system to have two electrolytes that are decoupled from each other(1). The two electrolytes are aqueous-based, where the cathode and anode are immersed in mildly acidic solutions and alkaline solutions, respectively. Operating in decoupled electrolytes allows the chemistry to widen its potential window and access voltages of >2.85V, while also allowing the respective electrodes operate efficiently and reversibly in their respective electrolyte system. The neutralization of these electrolytes is prevented by gelation of the alkaline electrolyte, which removes the need of expensive ion-exchange membranes. As a demonstration of this concept, we have developed Zn-MnO2 batteries reaching voltages >2.85V that are able to access the theoretical capacity (617mAh/g) of MnO2. This translates to energy densities 2 to 3 times greater than the commercially available alkaline batteries that can be recharged multiple times at costs that are comparable to primary batteries (~$20-30/kWh).

G. Yadav et al., ACS Energy Lett. 2019, 4(9), 2144-2146.
Molecular and Cell-Level Engineering of Zinc-Based Aqueous Flow Batteries
Authors: Liu Nian
Published: July 2022

Among other flow batteries, zinc-based aqueous flow batteries (ZBAFB) have the advantages of 1) smaller amount of electrolyte, and 2) elimination of ion-exchange membrane by using complexing agents to phase-separate charged species (Br2 or I2). However, existing complexing agents are unsatisfactory, which leads to severe self-discharge. Moreover, flow batteries generally have low volumetric power density, limiting their wide applications. In this talk, I will show my lab's recent efforts on enhancing the performance of ZBAFB by designing novel complexing agents and innovating the cell form factors. I will also report our direct visualization of the halogen formation dynamics using in operando optical microscopy.
Understanding the Influence of Particle Morphology on the Capacitive Performance of Conductive Layered Metal-Organic Frameworks
Authors: Gittins James W. , Forse Alexander C.
Published: July 2022

Two-dimensional layered metal-organic frameworks (MOFs), characterised by their combined high intrinsic porosities and electrical conductivities, have emerged as one of the most promising electrode materials for next-generation energy storage devices, particularly supercapacitors. Several such MOFs have displayed encouraging performances in supercapacitors with a wide range of electrolytes, and have exhibited specific and areal capacitances on par with or exceeding state-of-the-art carbon materials.1-3 This has raised the prospect of using these materials in commercial devices, and their well-defined structures make them promising model electrode materials for supercapacitor structure-property investigations. However, layered MOFs can be synthesised with a range of particle morphologies, and hence 3D pore structures, as well as different degrees of particle agglomeration. Minimal work has been performed to understand how these factors impact the capacitive performances of these frameworks, and existing literature has struggled with small differences in observed morphology and low control over the samples.4 This has cast doubts over reported results, and has hindered both the development of MOF-based supercapacitors and their implementation as model electrodes.

In this work, a greater variation in particle morphology was obtained than observed in previous work on this topic. This was achieved by synthesising samples of the layered conductive MOF Cu3(HHTP)2, (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with different modulating agents, which influence the equilibrium determining the self-assembly process of a MOF and regulate the rate of framework growth. Using this approach, we present a detailed study into the influence of particle morphology and agglomeration on the capacitive performance of the layered MOF Cu3(HHTP)2 in symmetric supercapacitors with both organic and ionic liquid electrolytes. These studies reveal that ‘flake-like’ particle morphologies with very small length-to-width aspect ratios (<< 1) and little agglomeration are optimal for layered MOF supercapacitors. This sample displayed greater rate capabilities with organic electrolytes and significantly higher specific capacitances with ionic liquid electrolytes compared to ‘rod-like’ particles, with much larger length-to-width aspect ratios, and heavily agglomerated samples. These findings will pave the way for the next generation of supercapacitor devices using conductive layered MOF electrodes.

Figure 1
(Digital Presentation) Graphene Meets Ionic Liquids: Fermi Level Engineering via Electrostatic Forces
Authors: Velpula Gangamallaiah , Mali Kunal , De Feyter Steven
Published: July 2022

Graphene, a single layer of carbon atoms in a two-dimensional (2D) hexagonal lattice, showcases key properties suitable for electrode materials such as high specific surface area, good electrical and thermal conductivities.1 Ionic liquids (ILs) are a class of molten salts that are entirely composed of ions. These liquids possess exceptional properties appropriate for electrolytes, such as high electrochemical window, electrochemical stabilities and extremely low vapor pressure. Graphene-based 2D materials are promising candidates for a number of different energy applications. A particularly interesting one is in next generation supercapacitors, where graphene is being explored as an electrode material in combination with ionic liquids as electrolytes. Because the amount of energy that can be stored in such supercapacitors critically depends on the electrode − electrolyte interface, there is considerable interest in understanding the structure and properties of the graphene/IL interface. Here, we present the changes in the properties of graphene upon adsorption of ILs and ILs – organic solvent mixtures using a combination of experimental and theoretical tools. For example, Raman spectroscopy reveals that imidazolium tetrafluoroborate ILs (CnMIM BF4) cause n-type doping of graphene, and the magnitude of doping increases with increasing cation chain length despite the expected decrease in the density of surface-adsorbed ions (Fig 1). Molecular modeling simulations show that doping originates from the changes in the electrostatic potential at the graphene/IL interface. The findings described here represent an important step in developing a comprehensive understanding of the graphene/IL interface.2

References:

Geim, A. K.; Novoselov, K. S., Nature Materials, 6 (2007) 183

Velpula, G.; Phillipson, R.; Lian, J. X.; Cornil, D.; Walke, P.; Verguts, K.; Brems, S.; Uji-i, H.; Gendt, S.; Beljonne, D.; Lazzaroni, R.; Mali, K. S.; De Feyter, S, ACS Nano, 13 (2019) 351

Figure 1
Study of Cu, Co and Ru Nanoclusters on MoS2 to Predict Thin Film Morphology
Authors: Nies Cara-Lena , Nolan Michael
Published: July 2022

Interfaces of 2D materials with metals are of interest for a large variety of applications, including sensors, batteries, catalysis, electronics, and semi-conductor devices. Transition metal dichalcogenides (TMDs) and specifically MoS2 are some of the most widely studied 2D materials. A detailed understanding of the interactions of metals with 2D TMDs can give useful insights into possible applications for metal-TMD systems. However, the literature focuses mainly on comparing trends in single atom adsorption and studying nanoparticles on MoS2
monolayers.

In this work we aim to increase the understanding of metal-MoS2 interactions and metal nucleation on TMDs. We use density functional theory (DFT) to study the adsorption of small metal clusters with up to four atoms on MoS2
monolayers. Insights gained from this work allow us to understand the initial nucleation of metal thin films on TMDs as well as predict the likely morphology of the thin film as it grows.

The metals studied are Cu, Co and Ru, which are chosen for their range of applications, particularly in electronics. Metal-substrate interactions, preferred adsorption modes and stable nanocluster geometries are presented on pristine MoS2 and in the presence of the readily formed sulfur vacancy. The strength of interaction between the metals and MoS2 is in the order Co > Ru > Cu. Metal-substrate interactions are localised to the adsorption site; however we find that both Ru and Co can induce formation of sulfur vacancies through the formation of the corresponding metal sulfide.
(Invited) Graphene Oxide-Based Membranes: Viscoelastic Properties and Application to Broadband Microspeakers
Authors: Szkopek Thomas , Hu Kaiwen , Cardenas William , Huang Yi-Chi , Wei Huijing , Gaskell Robert-Eric , Martel Eli , Cerruti Marta
Published: July 2022

Graphene and graphene derivatives have attracted attention as materials for acoustic transduction [1-3]. Graphene oxide (GO) membranes and borate cross-linked graphene oxide (X-GO) membranes combine high stiffness, low mass density, and high loss coefficient. We show [4] that these mechanical properties are ideal for efficient, broadband, electro-acoustic transduction, where the acoustic diaphragm should be light, stiff, and internally damped. We present a quantitative comparison of the figure of merit, (E/ρ
3)1/2, where E is Young's modulus and ρ is the mass density, and the material performance index, tan δ (E/ρ
3)1/2, where tan δ is the loss coefficient. GO and X-GO exhibit high figures of merit, comparable to that of wood and exceeding that of aluminum and thermoplastics. The material performance indices of GO and X-GO exceed that of wood, thermoplastics, and aluminum. The latter are common diaphragm materials in acoustic transducers.

For acoustic applications, it is important to understand the frequency dependent viscoelastic response. The complex modulus G = G' + iG'' of GO and X-GO membranes was measured by dynamic mechanical analysis and analyzed by the application of the time-temperature superposition (TTS) principle of polymer rheology. We find that X-GO shows a more than 30% increase in storage modulus G’ over the frequency range of 1 to 10 kHz, exceeding 55 GPa at 10 kHz. There is a reduction in loss coefficient tan δ = G''/G' for X-GO of ≈30% over the same frequency range, reaching tan δ = 0.04 at 10 kHz, which is approximately one order of magnitude larger than that of aluminum.

A quantitative comparison of microspeaker performance was conducted at a fixed diaphragm mass m = 15-20 g and 14 mm x 8 mm size, including GO, X-GO, oak wood, polyethylene terephthalate (PET), aluminum, and titanium. Scanning laser measurements confirm pistonic operation of X-GO membranes. Microspeaker sound pressure level response was measured in both time and frequency domains. X-GO diaphragms exhibit 45% higher damping than aluminum membranes in microspeaker assemblies. Consequently, X-GO membranes enable the upshift of loudspeaker breakup frequency by 1/6 to 1/2 octave above speakers assembled with oak wood, PET, aluminum and titanium membranes. GO based materials are thus found to be an exceptional material for electro-acoustic transduction.

References:

[1] Q. Zhou, A. Zettl, Appl. Phys. Lett. 102, 223109 (2013).

[2] A. U. Khan, G. Zeltzer, G. Speyer, Z. K. Croft, Y. Guo, H. Nagar, V. Artel, A. Levi, C. Stern, D. Naveh, G. Liu, Adv. Mat. 33, 2004053 (2021).

[3] H. Tian, T.-L. Ren, D. Xie, Y.-F. Wang, C.-J. Zhou, T.-T. Feng, D. Fu, Y. Yang, P.-G. Peng, L.-G. Wang, L.-T. Liu, ACS Nano 5, 4878 (2011).

[4] K. Hu, R.E.Gaskell, W. Cardenas, H. Wei, Y.-C. Huang, M. Cerruti, T. Szkopek, Adv. Func. Mat. 2107167 (2021).

Figure 1
(Invited) Controlling Void Space in Crumpled Graphene for High Stability Silicon Anodes
Authors: She Zimin , Gad Mariam , Uceda Marianna , Pope Michael
Published: July 2022

Silicon anodes are thought to soon replace graphite in next-generation Li-ion batteries due to silicon’s high capacity (3590 mAh/g for the Li15Si4 alloy at room temperature), availability and natural abundance. However, lithiation of silicon causes a large volume expansion (~300%) which can cause pulverization of the primary silicon particles, cracking and delamination of the bulk electrode and the formation of an unstable solid-electrolyte interface which must rebuild upon each cycle. Some combination of these effects leads to rapid anode failure via electrical isolation of active material and/or electrolyte depletion. To mitigate these challenges, clusters of silicon nanoparticles can be wrapped with flexible 2D-materials like graphene which can potentially act as a dimensionally and electrochemically stable, permeable barrier layers. This can be achieved in a scalable way via spray drying of aqueous dispersions of graphene oxide and silicon. In this talk, I will describe recent work from our group which aims to introduce a controlled amount of void space within the graphene protected silicon structures with the aim of engineering zero-strain silicon/carbon anode particles. In the absence of void space control, capillary forces acting during the spray drying process tightly wrap graphene around silicon clusters leaving little room for volume expansion. In one case, void space is introduced via incorporation of sacrificial polystyrene nanoparticles within the core by co-spray drying silicon, polystyrene and graphene oxide. In a second case, we do not use a sacrificial material but, instead, incorporate a responsive, cross-linked hydrogel within the core which can be expanded upon hydration to increase the volume of the graphene shell. When dehydrated, the gel shrinks to generate the required void space and acts as a Li-ion conducting, elastic binder within the core. In both cases, I will describe the systematic evolution of the crumpled graphene microstructure and its impact on anode performance in both half-cells and full Li-ion batteries.
(Invited) Unusual Superconducting Behavior in an Ultrathin Weyl Semimetal
Authors: Rhodes Daniel , Jindal Apoorv , Saha Amartyajyoti , Li Zizhong , Watanabe Kenji , Taniguchi Takashi , Birol Turan , Fernandes Rafeal , Pasupathy Abhay
Published: July 2022

Two dimensional materials are layered materials that may be readily exfoliated down to a single atomic layer, presenting an opportunity to noninvasively, and efficiently, control electrical and magnetic ordering, as well as topology. In this talk, I discuss how topology emerges from the bulk, down to the monolayer and how the influence of an electrostatic gate allows us to identify a unique superconducting state in few-layer Td-MoTe2. In the bulk, MoTe2 is a type II Weyl semimetal with a superconducting transition temperature of 120 mK. First, I will discuss how in the clean limit the superconducting transition temperature is enhanced by a factor of 60x, as compared to bulk, in monolayer Td-MoTe2, while still retaining a low carrier density (~1013/cm2), and a density of states that is comparable to the bulk. I will show how the crystal structure factors into the behavior of the superconducting state under external in-plane magnetic fields and how this can be used to quantify of the spin-orbit coupling, an important factor for determining topology and realizing topological superconducting states. After discussion of the monolayer, I will show that this enhancement remains in bilayer MoTe2, despite the change in symmetry. Strangely, our results indicate that superconductivity in bilayer MoTe2 is much more tunable by an electrostatic gate than that of monolayer MoTe2. In addition, for monolayer the response to high in-plane magnetic fields is distinct from that of other 2D superconductors and reflects the canted spin texture of the electron pockets. In bilayer, there is a strong deviation from this behavior, and instead an anomalous anisotropic behavior is observed with in-plane magnetic fields. These findings have profound implications on 2D superconductivity, where previously strong spin-orbit effects were only considered in the case of out-of-plane spin textures and offer an avenue for future exploration in similarly structured materials.
Surface Functionalization of Two-Dimensional MXene Nanosheets to Tailor Sulfur-Host Architecture for Metal-Sulfur Batteries
Authors: Pai Rahul , Natu Varun , Sokol Maxim , Carey Michael , Barsoum Michel W. , Kalra Vibha
Published: July 2022

Practicality of lithium-sulfur batteries is severely hindered by the notorious polysulfide-shuttle phenomenon, leading to rapid capacity fade. This issue is aggravated with increase in sulfur loading, causing low-coulombic efficiency and cycle life. Herein, we present a facile strategy to combine hydrophobic sulfur and hydrophilic, conductive Ti3C2Tz-MXene via one-step surface functionalization using di(hydrogenated tallow) benzylmethyl ammonium chloride (DHT). The latter renders the Ti3C2Tz
surface hydrophobic, making it readily dispersible in sulfur dissolved in a carbon disulfide (CS2) solvent. By evaporating the solvent, we conformally coat the DHT-Ti3C2Tz (DMX) with sulfur. The developed composite, with higher available active area, enables effective trapping of lithium polysulfides (LiPs) on the electroactive sites within the cathode, leading to improvement in electrochemical performance at higher sulfur loadings. The DMX/S cathodes function with high sulfur loading of ∼10.7 mg·cm−2 and deliver a stable areal capacity of ∼7 mAh·cm−2 for 150 cycles in the standard ether electrolyte. Moreover, a DMX/S cathode in a pouch-cell configuration retains ∼770 mAh·g−1 after ∼200 cycles at 0.2C (85.5% retention). Postmortem spectroscopic studies elucidate the nature of the LiPs-MXene interaction and the effect of surface functionalization towards improved performance. To further demonstrate the applicability of such uniquely functionalized MXene sheets, we study them as a host to confine sulfur (S8) triggering a quasi-solid state redox mechanism enabling the use of commercialization-friendly carbonate electrolyte in metal-sulfur batteries. We demonstrate that the multilayer MXene structure provides tunable spacing for S8 confinement and its unique interlayer spacing prevents adverse polysulfide-carbonate reactions resulting in stable battery cycling.
(Invited, Digital Presentation) Cooperative Effects of Fe and Cu Sites in N-Doped Carbon Nanotubes on Oxygen Reduction Activity and Selectivity
Authors: Kato Masaru , Abe Daiki , Xie Siqi , Fujibayashi Natsuki , Yagi Ichizo
Published: July 2022

The oxygen reduction reaction (ORR) is a key reaction in polymer electrolyte fuel cells (PEFCs) and metal–air batteries. Although platinum group metal (PGM)-based ORR electrocatalysts have been widely used in state-of-the-art PEFCs, PGMs are rare and expensive. For future wide-spread applications of PEFCs, non-PGM electrocatalysts with high ORR activity and product selectivity to H2O must be developed. Natural catalysts of metalloenzymes including laccases and cytochrome c oxidases are known to catalyze the ORR and therefore encourage us to develop metalloenzyme-inspired electrocatalysts based on non-PGMs for the ORR because these metalloenzymes use iron and/or copper ions as active sites [1-3].

We develop non-PGM electrocatalysts of Cu- Fe- and N-doped carbon nanotubes, (Cu,Fe)-N-CNT, for the ORR, inspired by the heterometallic active site of cytochrome c oxidase [4]. The co-presence of Cu and Fe active sites increase the ORR activity and selectivity to H2O in acidic media, compared with monometallic Fe-N-CNT or Cu-N-CNT. Kinetic analysis revealed that the selective 4-electron reduction of O2 to H2O is dominant for (Cu,Fe)-N-CNT whereas the sequential (2+2)-electron reduction mainly proceeds for Fe-N-CNT or Cu-N-CNT, indicating that the ORR mechanism can be modulated by the co-presence of Cu and Fe active sites. We will discuss details on the ORR mechanistic insights based on spectroscopic data including in situ X-ray absorption spectroscopy and Mossbauer spectroscopy.

References

[1] M. Kato, I. Yagi, e-J. Surf. Sci. Nanotechnol., 18, 81 (2020).

[2] M. Kato, T. Murotani, I. Yagi, Chem. Lett., 45, 1213 (2016).

[3] M. Kato, M. Muto, N. Matsubara,Y. Uemura,Y. Wakisaka, T. Yoneuchi,D. Matsumura, T. Ishihara, T. Tokushima, S. Noro, S. Takakusagi, K. Asakura, I. Yagi, ACS Appl. Energy Mater., 1, 2358 (2018).

[4] M. Kato, N. Fujibayashi, D. Abe, N. Matsubara, S. Yasuda, I. Yagi, ACS Catal., 11, 2356 (2021).
(Invited) Conformations of Exciton Pairs Associated with Spin-Entanglement Transports during Singlet Fissions
Authors: Kobori Yasuhiro
Published: July 2022

Singlet fission (SF) is expected to exceed the Shockley–Queisser theoretical limit of efficiency of organic solar cells. Spin-entanglement in the triplet pair state via one singlet exciton is a promising phenomenon for several energy conversion applications including quantum information science. However, direct observation of the electron spin polarization by transports of entangled spin-states has not been demonstrated. Furthermore, vibronic mechanisms of the dissociation of the triplet excitons are poorly understood. In this study, time-resolved electron paramagnetic resonance has been utilized to observe the transportations of the singlet and quintet characters generating spin-correlated correlated triplet pair (SCTP) by probing the electron spin polarization (ESP) generated in thin films of 6,13-bis(triisopropylsilylethynyl)pentacene.[1] We have clearly demonstrated that the ESP detected in resonance field positions of the individual triplet excitons are dependent on morphology and on detection delay time after laser flash to cause SF. The ESPs were clearly explained by quantum superposition[1,2,3] of singlet-triplet-quintet wavefunctions via picosecond triplet-exciton dissociation as the electron spin polarization transfer from strongly exchange-coupled singlet TT states to the weakly-coupled SCTP via spin-spin dipolar couplings with preserving conformations of the excitons. Although the coherent superposition of the spin eigenstates was not directly detected, the present interpretation of the spin correlation of the separated T+T exciton pair may pave new avenues not only for elucidating the vibronic role on the de-coupling[2,3] between the two excitons but also for scalable quantum information processing using quick T+T dissociation via one-photon excitation.

References

Matsuda, S.; Oyama, S.; Kobori, Y. Sci.
2020,
11, 2934-2942.

Kobori, Y.; Fuki, M.; Nakamura, S.; Hasobe, T. Phys. Chem. B
2020,
124, 9411-9419.

Nakamura, S.; Sakai, H.; Nagashima, H.; Fuki, M.; Onishi, K.; Khan, R.; Kobori, Y.; Tkachenko, N. V.; Hasobe, T. Phys. Chem. C
2021,
125, 18287-18296.
Dynamic Excitons in Nitrile-Functionalized Ladder-Type Oligo(p-Phenylene)s By Pulse Radiolysis Coupled with Time-Resolved Infrared Spectroscopy
Authors: Yan Juchao , Grills David C. , Mani Tomoyasu
Published: July 2022

Research and development efforts toward organic solar cells (OSCs) for large-scale power generation have continued unabated throughout the world. In recent years, OSCs based on π-conjugated polymers and small molecules have received increasing interest due to favorable electronic properties, component versatility, and low production and installation costs. Despite the progress, many improvements are still needed prior to widespread commercialization, involving device efficiency, lifetime, and cost. Of these, increasing device efficiency, particularly power conversion efficiency (PCE), is the most challenging task. The currently achievable PCE, for example, is only 17.3%.1 The key to achieving high PCE is the search for new organic conjugated molecules that are capable of harvesting light, and transferring and transporting charges promptly and efficiently. This requires a full understanding of how electrons and holes are localized and delocalized in organic conjugated molecules.

Using time-resolved infrared (TRIR) detection combined with pulse radiolysis, Mani and co-workers2 have measured experimentally the degree of localization of an excess electron in a series of nitrile-functionalized oligofluorenes by the spectral shifts of nitrile vibrations. The nitrile vibrational bands in anions respond sensitively to the degree of electron delocalization (IR shifts) and the structural changes (IR linewidth). The electron is found to move back and forth within the oligomers, likely controlled by the movement of dihedral angles between monomer units.

Unlike the non-coplanarity of the fluorenyl-fluorenyl backbone in oligofluorenes, the rigid and planar structure of ladder-type, oligo(p-phenylene)s (Scheme 1)3 would facilitate π-electron delocalization and thus improve the multiphoton absorption response. Such a structure would also increase photoluminescence efficiency with enhanced thermal and photochemical stability. To investigate the coupling between charge distribution and vibrational motion and vibronic coupling, we incorporate nitrile group in each compound as the infrared reporter group.

In this talk, we report our molecular syntheses and characterizations of two of the title compounds (L3PCN and L4PCN, both neutral compounds and their radical anions) by TRIR followed by pulse radiolysis. Having no flexible dihedral angles, L3PCN and L4PCN exhibit sharper IR bands of the nitrile vibration than the oligofluorenes with the same number of benzene rings and some dihedral angles. Our results further demonstrate that the linewidth of the nitrile vibration, together with the IR shifts and intensities, reports on structural and accompanying electronic fluctuations,2 that is, on the dynamic excitons.

References

(1) Meng, L. X.; et al. Science 2018, 361, 1094.

(2) Mani, T.; et al. Journal of the American Chemical Society 2015, 137, 10979.

(3) Scherf, U.; et al. Makromolekulare Chemie-Rapid Communications 1991, 12, 489.

Figure 1
(Invited) Ultrafast Solar Energy Conversion with Earth-Abundant Complexes
Authors: Chabera Pavel , Lindh Linnea , Rosemann Nils , Hai Yen Tran Hoang , Warnmark Kenneth , Yartsev Arkady , Sundstrom Villy , Persson Petter
Published: July 2022

Transition-metal complexes are widely used as photosensitizers and photocatalysts, and in light-emitting devices.[1] We have studied ultrafast proceses in a variety of DSSC and photocatalytic aplications.[2,3] More recently we demonstrated the first iron complex [FeIII(btz)3]3+ exhibiting room temperature photoluminescence from a CT state and show that it has a 100 ps excited state CT lifetime which is unprecedented for any iron complex.[4] This was characterized as a rare low-spin FeIII
d5
complex with emission from a long-lived doublet ligand-to-metal charge transfer (2LMCT) state. Absence of intersystem crossing (ISC) in this complex avoids significant excited state energy losses as encountered in the prevailing class of d6
TM complexes of e.g. FeII and RuII. Furthermore, we have also shown [FeII(btz)3]2+ low-spin complex [5], a FeII analogue to [FeIII(btz)3]3+. It exhibits strong metal-to-ligand charge transfer (MLCT) absorption bands throughout the visible spectrum, and excitation of these bands gives rise to a 3MLCT state with a 528 ps excited state lifetime in CH3CN solution that is more than one order of magnitude longer compared to the MLCT lifetime of any previously reported FeII complex. Together, these results show that the FeII and FeIII oxidation states of the same Fe(btz)3 complex feature long lived MLCT and LMCT states, respectively. This demonstrates the versatility of iron N-heterocyclic carbene complexes as promising light-harvesters for a broad range of photophysical and photochemical applications, and on-going efforts for further improvements of the excited state dynamics of such systems will be outlined, including the very latest development of an iron compound [Fe(phtmeimb)2]+ with an excited state stable enough to emit light for 2 ns and able to engage in bimolecular electron transfer [6].

1 Ponseca, C. S., Jr.; Chabera, P.; Uhlig, J.; Persson, P.; Sundstrom, V. Ultrafast Electron Dynamics in Solar Energy Conversion.
Chem Rev
2017, 117 (16), 10940.

2 H. Imahori et al, Photoinduced Charge Carrier Dynamics of Zn−Porphyrin−TiO2 Electrodes: The Key Role of Charge Recombination for Solar Cell Performance,
J. Phys. Chem. A
2011, 115, 16, 3679-3690

3 M. Yamamoto et al, Visible light-driven water oxidation with a subporphyrin sensitizer and a water oxidation catalyst,
Chem. Commun.
2016,52, 13702-13705

4 Chabera, P. et al. A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence. Nature 2017, 543 (7647), 695.

5 Chabera, P. et al. Fe(II) Hexa N-Heterocyclic Carbene Complex with a 528 ps Metal-to-Ligand Charge-Transfer Excited-State Lifetime, J Phys Chem Lett 2018, 9, 459−463.

6 Kjær, K. S. et al. Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime. Science 2019, 363 (6424), 249-253.

Figure 1
(Invited) Kinetic Prediction of Reverse Intersystem Crossing in Thermally Activated Delayed Fluorescence Molecules
Authors: Aizawa Naoya
Published: July 2022

Reverse intersystem crossing (RISC), the endothermic spin-flip process of producing an emissive singlet exciton from a non-emissive triplet exciton, is of increasing interest for applications in organic electroluminescent materials, photocatalysts, and biomedical probes. Theoretical prediction of the rate constant of RISC (k
RISC) may enable an efficient priori screening of new materials in chemical spaces; yet, the understanding of its kinetics in vastly different structures is challenging. Here, we demonstrate a theoretical expression that reproduces experimental k
RISC ranging over five orders of magnitude in twenty different molecules. We show that the spin flip occurs across the singlet–triplet crossing seam involving a higher-lying triplet excited state where the semi-classical Marcus parabola is no longer valid.1 The present model also leads to a newly designed TADF molecule with high k
RISC of 108 s–1.2

1. N. Aizawa, Y. Harabuchi, S. Maeda, Y.-J. Pu, Nat. Commun.
11, 3909 (2020).

2. N. Aizawa, A. Matsumoto, T. Yasuda, Sci. Adv.
7, 5769 (2021).

Figure 1
(Invited) Photoabsorption and Excitation Energy Transfer in Fluorinated Non-Fullerene Acceptors for Organic Solar Cells
Authors: Muraoka Azusa
Published: July 2022

Recently, it was reported that OSCs based on non-fullerene acceptors have shown high photovoltaic performance with over 18% efficiency, being more than the power conversion efficiencies (PCEs) of 13% in OSCs based on fullerene. We considered theoretically the effects of fluorine atoms on the conversion efficiency of organic thin-film solar cells from the electronic analysis of donor/acceptor (D/A) complex interactions for NTz-Teh-FA and FNTz-Teh-FA using DFT. It was confirmed that it differs depending on the side-chain length, and it is necessary to consider the side-chain length. Because the longer the side-chain length, the lighter absorption and increased charge transfer. In the fluorinated acceptor, the polarity around the O atoms at both ends of the main chain was weakened, the twist angle of the molecular structure was reduced, and the light absorption at 600–700 nm was increased in the absorption spectrum. Therefore, it is considered that the fluorinated nonfullerene-type acceptor FNTz-Teh-FA, which has a long side chain, has the best light absorption and charge transfer. Excitation Energy Transfer (EET) calculations show that the Coulomb coupling contributes significantly. In addition, it was confirmed that the fluorinated complex had a higher EET. Therefore, it is considered that the charge separation efficiency is improved. Thus, it is considered that the short-circuit current density (JSC) is improved by improving the internal quantum efficiency (IQE), including the element of the charge separation efficiency.
(Invited, Digital Presentation) Properties of Defects That Determine the Charge Carrier Dynamics in Photocatalysts
Authors: Yamakata Akira , Kato Kosaku , Uemura Yohei , Asakura Kiyotaka
Published: July 2022

Defect engineering of photocatalysts has been intensively studied as a way to improve their activity. It is reported that introducing oxygen vacancies into TiO2 and SrTiO3 improve the activity of photocatalytic water splitting. On the other hand, the effects of oxygen vacancies on WO3 photocatalyst have not yet been elucidated sufficiently, though WO3 is one of the most appealing visible-light-responsive photocatalysts. Herein, we have investigated photocarrier dynamics in WO3 powder by using a transient absorption spectroscopy from mid-infrared to visible wavelength range. We found that electrons deeply trapped by defect states decayed within 1 ns, which is in contrast to the case of TiO2 and SrTiO3. The decay of the deeply trapped electrons is further accelerated by increasing oxygen vacancies through the reduction process. This result suggests that the deep trapping states associated with oxygen vacancies in WO3 work as a recombination center. On the other hand, long-life free/shallowly trapped electrons were increased when the WO3 powder was mildly reduced, whereas they decreased when it was reduced too heavily. These results indicate that shallow trapping sites in WO3 elongate photocarrier lifetime, but the effect of recombination acceleration by deep trapping sites becomes dominant when too much oxygen vacancies are introduced. Our study revealed the positive and negative aspects of defects in WO3, and highlighted the importance of appropriate defect control on improving the photocatalytic activity.
Ni-Catalyzed Plasmonic Oxygen Evolution at Near-Neutral Conditions
Authors: Murakoshi Kei
Published: July 2022

The oxygen evolution reaction is essential in the solar production of chemical fuels, green hydrogen. Plasmonic metal-semiconductor systems can be potentially used for the production. Hot electrons generated by localized surface plasmon resonance are rapidly injected into the semiconductor, and concentrated hot holes oxidize water on the catalysts for oxygen evolution. Using Ni-modified Au/TiO2, in situ electrochemical surface-enhanced Raman spectroscopy was performed over the pH range of 7–13. Significantly enhanced photocurrents at near-neutral conditions were generated with low-energy photons (1.58 eV). The results prove that nickel-based catalysts accelerated the four-electron multistep reaction via plasmon-assisted water oxidation.