bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Graphene Ion Blocking Layers for Robust Metal-Halide Perovskite Heterostructures
Authors: Blackburn Jeff , Hautzinger Matthew , Wieliczka Brian , Blum Volker , Luther Joey , Beard Matt C
Published: September 2023

Despite being only one atomic layer thick, a continuous monolayer of graphene should be completely impermeable to atoms and ions. As such, graphene monolayers could potentially be employed as ion blocking layers in numerous technologies where charge and/or energy transport across a key interface is desirable, but ionic or atomic transport is not. As a key example, the development of metal-halide perovskite/perovskite heterostructures is hindered by rapid interfacial halide diffusion leading to mixed alloys rather than sharp interfaces. This halide diffusion hinders the creation of tailored interfaces that funnel energy or charge in specified directions within energy technologies such as photovoltaic solar cells or light-emitting diodes. To circumvent this issue, we developed an ion-blocking layer consisting of single layer graphene (SLG) deposited between the metal-halide perovskite layers and demonstrate that it effectively blocks anion diffusion in perovskite/perovskite heterostructures. We study these interfaces with a suite of spectroscopy and elemental analysis tools to demonstrate that halides do not diffuse across the graphene-modified interface, whereas control samples without the SLG show rapid homogenization of the halides and loss of the sharp interface. The SLG has little electronic impact on the band alignment and optical properties of the individual semiconductors, as supported by density functional theory calculations, facilitating photoinduced energy transfer across the abrupt heterointerface and light-emitting diodes with no evidence of ion-diffusion during operation. Our results demonstrate that monolayer graphene can be used as an ion blocking layer in a variety of different heterostructures for advanced opto-electronic and electrochemical applications. Further, it establishes a route towards robust perovskite/perovskite heterostructures that are difficult to achieve by other means.
Size Effect of RuO2-Based 2D Conductive Binder
Authors: Takemura Yuta , Saito Ryota , Hermawan Angga , Muramatsu Keisuke , Sugimoto Wataru
Published: September 2023

In an electrode mixture MnO2 is one of the most well studied pseudocapacitive material for aqueous supercapacitors owing to the surface and near surface-confined redox processes. A large amount of conducting additive, generally 20-30 wt% acetylene black, needs to be added to achieve high-rate charge storage. Since the conducting additive does not contribute much to the specific capacitance, this leads to decrease in total energy density of the cell in terms of both mass and volume. Polymeric binders such as PTFE and PVdF are also necessary to fabricate rigid electrode with good contact. As an alternative to these typical conductive binders and polymer binders, we have studied the possibility of using RuO2 nanosheets as a novel inorganic binder with polymeric properties, high electronic conductivity and excellent pseudocapacitive properties. For example, by adding only 10-20 mol% of RuO2 nanosheets to particulate MnO2, a large synergetic effect is observed leading to a high utilization of MnO2 pseudocapacitance.[1] The optimized amount of RuO2 in the composite was 13 wt%, which is much lower than the amount generally used for conductive carbon additives despite the 10 times higher formula weight of RuO2 compared to carbon. In this work, we report the electrochemical properties of nanosheet composite electrodes composed of highly conductive RuO2 nanosheets (RuO2(ns)) and poorly conductive MnO2 nanosheets (MnO2(ns)) with various composition and nanosheet size.
The Effect of Anionic and Cationic Charge Carriers on the Supercapacitive Behavior of Graphene Nanoribbons
Authors: Heiba Asmaa R. , Abou Shahba Rabab M. , Dhmees Abdelghaffar S , Taher Fatma A , El Sawy Ehab
Published: September 2023

As worldwide energy consumption continues to increase, so too does the demand for improved energy storage technologies. Supercapacitors have attracted a lot of attention due to their quick charging/discharging rate, high power density, and long-term cycling stability in comparison to conventional batteries.1 Graphene nanoribbons (GNRs) with ultrathin two-dimensional structures and unique properties received a lot of attention recently as potential materials for electrochemical energy storage and specifically supercapacitors.2,3 GNRs maintain graphene’s unique lattice structure in one dimension and provide more open-edge structures compared to graphene, thus allowing faster ion diffusion, which makes GNRs highly promising for energy storage systems.2,3 GNRs have unique characteristics such as exceptional electrical conductivity, a highly modifiable surface area, strong chemical stability, low toxicity, great mechanical behavior, and the ability to tune properties for the desired application.

This presentation provides an overview of the production of GNRs from carbon nanotubes and their application in supercapacitors. The physical/chemical structure of GNRs was evaluated using XRD, TEM, FT-IR, Raman spectroscopy, and XPS. Since the selection of the cation and anion has been reported to have a dramatic effect on the specific capacitance of the studied materials,4 the supercapacitive behavior of GNR was thoroughly investigated in various media (H2SO4, KOH, K2SO4 ), using different loadings and different evaluation systems (three and two-electrode systems). GNRs, in all of the tested media, showed good stability (retained 95% of their capacitance over 10,000 cycles at a high current density of 10 A/g), a wide potential window (up to 1.7 V), and a relatively high capacitance (≈ 400-800 F/g). The best medium for GNRs highest supercapacitance in correlation with their surface chemical structure will be discussed.

References:

E. A. Worsley, S. Margadonna, and P. Bertoncello, Nanomaterials, 12, 3600 (2022).

Z. Liu et al., Advanced Functional Materials, 32, 2109543 (2022).

Twinkle et al., Materials Today: Proceedings, 50, 1511–1515 (2022).

B. Pal, S. Yang, S. Ramesh, V. Thangadurai, and R. Jose, Nanoscale Adv., 1, 3807–3835 (2019).
In-Operando Raman Study on the Use of 2D and Suboxide Titanium Host Materials for Lithium-Sulfur Batteries
Authors: Pereira Rhyz , Ruffino Anthony , Masiuk Stefan , Cardoza Neal A. , Badr Hussein , Barsoum Michel W. , Spanier Jonathan , Kalra Vibha
Published: September 2023

While Lithium-Sulfur (Li-S) batteries have promised high capacities and low-cost material inputs, their potential has yet to be realized due to inherent issues with sulfur cathodes. In particular the polysulfide shuttle effect and sulfur’s intrinsic insulating properties stand in the way of a commercial battery, the demands of which include high sulfur loading and high cycling stability. Engineering the sulfur cathode, via the use of promising new materials has been an avenue of research pursued in the hopes of mitigating the shuttle effect via polysulfide entrapment and introducing more conductive materials.

Of particular interest have been titanium oxide based materials which have shown polysulfide adsorption capabilities. However, the most common titanium oxide, anatase titanium (IV) oxide (TiO2) acts as an insulator, limiting its use in high sulfur loading batteries. Therefore, the use of more conductive titanium oxide materials is an attractive avenue of research. A previously reported freestanding titanium suboxide (TiO) carbon nanofiber cathode demonstrated excellent capacities (~790 mAh/g, ~2 mg/cm2). A rare lepidocrocite phase has also been observed via Raman spectroscopy in a newly discovered titanium carbide derived titanium oxide nanofilament (1D-NF). This material demonstrates properties that makes it attractive as a sulfur host material, having a high surface area of ~1700 m2/g, improved polysulfide reduction kinetics via the formation of polythionates, and polysulfide-cathode host interactions. The inclusion of these nanofilaments in sulfur cathodes yields capacities of ~800 mAh/g with ~1 mg/cm2 sulfur loading.

The proposed mechanism via which these titanium oxide based materials function has never been investigated in-operando, and herein we conduct an in-operando Raman study to understand the behavior of these materials. Principally we will investigate the Eg band whose vibration can be moderated by the interaction of terminal sulfur atoms acting as Lewis bases and titanium atoms acting as Lewis acids, due to their vacant valance electrons. This interaction has been observed via postmortem XPS. The use of in-operando Raman allows us to uniquely observe transient behavior of the host material as well as the impact of crystal structure on polysulfide host interactions.
Identifying Non-Stationarity in Non-Linear Harmonics of EIS Measurements of Li Batteries
Authors: Zabara Mohammed Ahmed , Katırcı Gökberk , Ülgüt Burak
Published: September 2023

Non-linear Harmonic Analysis is a technique used to investigate the distortions in Electrochemical Impedance Spectroscopy (EIS) measurements. The distortions are in both non-linear and non-stationary nature that appear as high order harmonics in the frequency domain. Differentiating the origin of the harmonics is important in understanding their nature and relating them to electrochemical phenomena. Here, we will show how the harmonics are in direct relation to the initial non-stationary response (initial transient) of the excited system [1]. We will show by both experimental measurements and simulations of dummy cell circuits, representing the electrochemical interface, that the initial transient exhibits high order harmonics that show the highest value at the characteristic frequency of the process [1]. We also extend the analysis to include more complex systems of primary Lithium batteries [2]. It is observed that the same non-stationary initial transient behavior is persistent in the time constants of the electrochemical processes. It is concluded that the capacitive components of the electrochemical processes are responsible for such non-stationary behavior in electrochemical systems [2].

[1] G. Katırcı, M. A. Zabara, and B. Ülgüt, “Methods—Unexpected Effects in Galvanostatic EIS of Randles’ Cells: Initial Transients and Harmonics Generated,” J Electrochem Soc, vol. 169, no. 3, p. 030527, Mar. 2022, doi: 10.1149/1945-7111/ac5ad7.

[2] M. A. Zabara, G. Katırcı, and B. Ülgüt, “Non-linear harmonics in EIS of batteries with lithium anodes: Proper controls and analysis,” Electrochim Acta, vol. 429, Oct. 2022, doi: 10.1016/j.electacta.2022.140969.
Two Dimensional V2O5 Nanosheets As an Advanced Cathode Material for Realizing Low-Cost Aqueous Aluminum Ion Battery
Authors: De Puja , Halder Joyanti , Priya Surbhi , Chandra Amreesh
Published: September 2023

Aluminum-ion batteries (AIBs) are rapidly gaining momentum for the next generation energy storage industry because of its various advantages. In this paper, interconnected sheets-like morphology of low cost V2O5 is being reported as a cathode material to improve the capacity, rate capability, and cycling stability of Al battery (AIB). Benefiting from the unique two-dimensional sheet morphology, the V2O5 cathode are able to deliver an initial discharge capacity of ~ 140 mAh g-1, at high current density of 0.5 A g-1, with an excellent capacity retention of 96 % after 1000 cycles at 1 A g-1, which is amongst the best cathode performances reported for aqueous AIBs. The high energy storage mechanism of V2O5 is based on the facile intercalation and deintercalation of the tri-valent Al ions from the electrolyte through the electrode material during discharging and charging processes, respectively. Notably, the smaller lattice expansion (~1.4 %) of V2O5, indicate the expansion and contraction of the crystal structure occur reversibly during the discharge-charge process. The stability of the material is established by analyzing the XRD patterns of the material after cycling. Such studies have remained ignored in AIBs till date.
Aluminum Alloys as Anodes for Aluminum Batteries
Authors: Bandiera Marco , Pavesi Arianna , Valota Giorgio , Abello Mary Angel , Trombetta Valentina , Bonfanti Andrea , Mancini Alessandro , Bertasi Federico
Published: September 2023

The development of batteries based on metals alternative to Lithium (e.g. Na, Mg, Zn, Al) requires the investigation of new electrodes and electrolytes. [1,2].

This is particularly true in the case of non-aqueous Aluminum batteries which typically include a pure (>99.8%) Aluminum anode which: a) suffer of poor cycling stability and low coulombic efficiency; b) is particularly subjected to dendrite growth; c) can undergo to corrosion phenomena upon cycling; and d) show a poor compatibility toward chloroaluminated electrolytes [3].

In this regard, the development of Aluminum alloys, alternative to pure Al anodes, is a challenging task which is barely investigated in the field of Aluminum ion batteries and requires experience in both battery electrochemistry and Aluminum metallurgy and casting.

In this scenario, the proposed work investigates the synthesis and characterization of ternary Aluminum, alloys comprising Si, Ti and B as alloying elements, as anodes for Al-ion batteries [4]. Deposition/stripping measurements, impedance spectroscopy, metallographic analysis, EDXS and XRD techniques unveil the complex interplay existing between the microstructures of the alloys and the obtained electrochemical performance. It is demonstrated that a remarkable improvement in the: a) oxidation/reduction currents and overvoltages; and b) interfacial stability with the electrolyte; can be obtained, with respect to a conventional Al anode. Results allow to demonstrate that the investigation of Aluminum alloys can be crucial for the development of future Aluminum batteries.

[1] F Bertasi, C Hettige, F Sepehr, X Bogle, G Pagot, K Vezzù, E Negro, S J Paddison, S G Greenbaum, M Vittadello, V Di Noto, ChemSusChem, 2015, 8 (18), 3069-3076

[2] F Bertasi, F Sepehr, G Pagot, SJ Paddison, V Di Noto, Advanced Functional Materials 2016, 26 (27), 4860-4865

[3] Y Zhang, S Liu, Y Ji, J Ma, H Yu, Advanced Materials 2018, 30 (38), 1706310

[4] Italian Patent Application n° 102022000024522
(Invited) Photoluminescence up-Conversion in CsPbBr3 Nanocrystals
Authors: Kuno Masaru
Published: September 2023

Photoluminescence up-conversion is a near ubiquitous process in colloidal semiconductor nanocrystals. Observed efficient up-conversion in high emission quantum yield CsPbBr3 nanocrystals suggest their possible use in optical refrigeration as well as light harvesting. We discuss efforts to understand the mechanism behind efficient up-conversion as well as studies into the identity of intermediate states responsible for the phenomenon. Here, photothermal measurements suggest real intermediate states deep in the gap that are responsible for efficient up-conversion.
Halide Ion Migration in 2D Metal Halide Perovskites
Authors: Mathew Preethi Susan , Kamat Prashant V
Published: September 2023

Two-dimensional (2D) halide perovskites have drawn attention for their unique optoelectronic properties. Interestingly, Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium and Dion-Jacobson 2D mixed-halide perovskite films with 1,4-phenylenedimethanammonium undergo halide segregation under irradiation. Anions become mobile under steady state irradiation to form I-rich and Br-rich domains. Upon ceasing illumination, film reverts to their original, mixed-halide compositions, establishing the reversibility of the phase segregation phenomenon. However, if films are in contact with dichloromethane, light irradiation causes the sequential expulsion of iodide and bromide and introduces irreversible changes to 2D films. The sequential disappearance of I- and Br- from pristine films (BA2Pb2Br4, and BA2Pb2I4) under photoirradiation, as observed from variances in expulsion rates, reflect differences in halide ion mobilities in these films. The impact of anion migration, leading to I- and Br- expulsion into solvents, within the context of 2D perovskite photostability will be discussed.
(Invited) Synthesis and Properties of Novel PL-Active 2D Lead-Free Double Perovskites
Authors: Wong Andrew Barnabas
Published: September 2023

In this work, novel two-dimensional lead-free double perovskites ((R)4MaMbMcX8, a+b+c=2) were synthesized to achieve novel compositional and dimensional tunability. Moreover, the samples were tuned to be PL-emissive under room temperature via a manganese alloying strategy. Bandgap and PL emission turnability were explored through halogen substitution (chlorine and iodine). An enhanced PL emission was observed for mixed halogen phases. Three emission pathways are possible to be investigated including band edge emission, emission stemmed from self-trapped excitons and the unique energy transfer process of alloyed Mn2+ ions, which will be discussed.
Non-Fullerene Acceptors for Organic Photovoltaics
Authors: Imahori Hiroshi
Published: September 2023

Non-fullerene acceptors (NFA) have attracted much attention in organic photovoltaics because of their excellent light-harvesting property and facile tuning of HOMO-LUMO levels. In particular, ITIC and Y6 type NFAs have exhibited very high power conversion efficiency exceeding 15%. In this talk I will give an overview of our initiatives on NFAs.

[1] T. Umeyama, K. Igarashi, D. Sasada, Y. Tamai, K. Ishida, T. Koganezawa, S. Ohtani, K. Tanaka, H. Ohkita, H. Imahori, Chem. Sci., 11, 3250-3257 (2020).

[2] T. Umeyama, K. Igarashi, D. Sasada, K. Ishida,T. Koganezawa, S. Ohtani, K. Tanaka, H. Imahori, ACS Appl.
Mater. Interfaces, 12, 39236-39244 (2020).

[3] T. Umeyama, K. Igarashi, Y. Tamai, T. Wada, T. Takeyama, D. Sasada, K. Ishida, T. Koganezawa, S. Ohtani, K. Tanaka, H. Ohkita, H. Imahori, Sus.
Energy Fuels, 5, 2028-2035 (2021).

[4] T. Umeyama, T. Wada, K. Igarashi, K. Kato, A. Yamakata, T. Takeyama, Y. Sakamoto, Y. Tamai, H. Ohkita, K. Ishida, T. Koganezawa, S. Ohtani, K. Tanaka, H. Imahori, ACS Appl. Energy Mater., 4, 14022-14033 (2021).

[5] S. Li, R. Nishikubo, T. Wada, T. Umeyama, H. Imahori, A. Saeki, Polymer J., in press.
(Invited) Development of Non-Fused Nonfullerene Acceptors Bearing Spiro-Substituted Structures and Application to Green-Light Wavelength-Selective Organic Solar Cells
Authors: Ie Yutaka
Published: September 2023

Organic solar cells (OSCs) have been extensively investigated as next-generation energy sources due to their potential for large-area fabrication, light weight, flexibility. The active layer of OSCs is composed of a blend of donors and acceptors, which form bulk heterojunction structures in the films. The development of A-D-A-type nonfullerene acceptors (NFAs) with large fused-ring donor structures have significantly accelerated OSC research. On the other hand, non-fused electron-accepting p-conjugated compounds have been investigated recently for application to NFAs. In this presentation, we focus on cyclopentene-annelated thiophene with spiro-substituted 2,7-bis(2-ethylhexyl)fluorene (FT) as a rigid and sterically bulky linker unit and develop a non-fused NFA containing FT units. We also focus on the development spiro-substituted NFAs with green-light wavelength-selective absorbance. The combination of these acceptors and poly(3-hexylthiophene) can produce green-light wavelength-selective OSCs for application in new greenhouse agrivoltaics.
(Invited) Machine Learning and Fast Experimental Screening-Assisted Development of Organic Solar Cell
Authors: Saeki Akinori
Published: September 2023

Non-fullerene, a small molecular electron acceptor, has substantially improved the power conversion efficiency of organic photovoltaics (OPVs).[1] However, the large structural freedom of π-conjugated polymers and molecules makes it difficult to be explored with limited resources. Machine learning, which is based on the rapidly growing artificial intelligence technology, is a high-throughput method to accelerate the speed of material design and process optimization; however, it suffers from limitations in terms of prediction accuracy, interpretability, data collection, and available data (particularly, experimental data). This recognition motivates the present review, which focuses on utilizing the experimental dataset for ML to efficiently aid OPV research. The author discusses the trends in ML-OPV publications, the NFA category, and the effects of data size and explanatory variables (fingerprints or Mordred descriptors) on the prediction accuracy and explainability, which broadens the scope of ML and would be useful for the development of next-generation solar cell materials.[2]

Despite the advance of ML, the predictive accuracy of ML currently remains insufficient for the design of OPV semiconductors that exhibit a complex connectivity between chemical structure and PCE. In this study, we examined the impact of data selection and the introduction of artificially generated failure data on ML predictions of NFA solar cells. The authors demonstrated that an ML model empowered by artificially generated failure data (~0% PCE by insoluble polymers based on an inappropriate choice of solubilizing side alkyl chains) led to improved predictions.[3] This approach was validated through the synthesis and characterization of twelve polymers (benzothiadiazole, thienothiophene, or tetrazine coupled with benzodithiophene; benzobisthiazole coupled with dioxo-benzodithiophene). Our work offers a facile approach to mitigate the difficulties of the ML-driven development of OPV materials that is also readily applicable to other material science fields.

Reference

[1] Kranthiraja, A. Saeki, Adv. Funct. Mater. 31 (2021) 2011168

[2] Miyake, A. Saeki, J. Phys. Chem. Lett. 12 (2021) 12391.

[3] Miyake, K. Kranthiraja, F. Ishiwari, A. Saeki, Chem. Mater. 34 (2022) 6912.
(Invited) Π-Extended Porphyrins: Fusion of Polycyclic Aromatic Hydrocarbons to Porphyrins
Authors: Wang Hong , Hu Yi , Moss Austen , Arvidson Jacob , Jang Youngwoo , Alsaleh Ajyal , D'Souza Francis
Published: September 2023

Largely π-extended structures represent one most fascinating yet very challenging frontiers in chemistry and materials science.1, 2 Incorporating both porphyrins and polycyclic aromatic hydrocarbons to obtain largely π-extended multichromophoric systems is especially attractive as the resulted largely π-extended systems are reminiscent of “nanographenes” doped with heteroatoms.3, 4 Due to limited availability of synthetic methods, only the simplest symmetrical π-extended porphyrins remain largely unexplored. The Wang group has been engaged in developing concise and versatile synthetic and functionalization methods for π-extended porphyrins. The availability of these methods offers easy access to many p-extended porphyrins with novel functionalities.5-7 In this talk, the synthesis, characterization, and the optical and photophysical properties of π-extended porphyrins fused with 5- and 6-membered rings including pentacene-, pentaquinone-, acenaphtho[1,2-b]pentacene- and 12H-benzo[f]benzo[4,5]imidazo[2,1-a]isoindole-fused porphyrins will be presented.

Figure 1
Greek Cross (+) Aggregate
Authors: Hariharan Mahesh
Published: September 2023

The independent discovery of dye aggregate by Jelley and Scheibe marked the beginning of a spectacular development in the field of aggregate photophysics.1 Subsequent research warranted an exceptional model for defining the exciton interactions in aggregates, proposed by Kasha and Davydov independently, which was later modified by incorporating the short-range excitonic coupling.2-3 Apart from the well-studied H- and J-aggregate, achieving the orthogonally cross-stacked assembly possessing null excitonic interactions remained elusive. The first crystalline evidence for the chromophoric Greek cross (+) assembly exhibiting monomer-like optical properties was reported in 2018.5 The emergent photophysical properties of the crafted Greek cross (+) architectures were explored using both experimental and computational techniques for understanding the aggregate properties beyond Kasha’s model.6-7 The manifestation of selective hole transfer coupling in the edge-to-edge arranged Greek cross (+) perylenediimide (PDI) dimer resulted in ultrafast dissociation of null exciton and evolution of the charge-separated state in a polar solvent, providing a way forward in the fundamental understanding of null aggregates.8

References

1 (a) Jelley, E. E.; Nature,
1936, 138, 1009– 1010; (b) Scheibe, G.; Angew. Chem.,
1937, 50, 212– 219; (c) Ramakrishnan, R.; Niyas, M. A.; Lijina, M. P.; Hariharan, M.; Acc. Chem. Res., 2019, 52, 3075−3086.

2 (a) Kasha, M.; Rawls, H. R.; El-Bayoumi, M.; Pure Appl. Chem., 1965, 11, 371–392; (b) Davydov, A. S.; Sov. Phys. Uspekhi; 1964, 7, 145– 178,

3 Hestand, N. J.; Spano, F. C.; J. Chem. Phys. 2015, 143, 244707.

4 Sebastian, E.; Philip, A. M.; Benny, A.; Hariharan, M.; Angew. Chem. Int. Ed.,
2018, 57,15696- 15701.

5 Lijina, M. P.; Benny, A.; Ramakrishnan, R.; Nair, N. G.; Hariharan, M.; J. Am. Chem. Soc.,
2020, 142, 17393-17402.

7 Benny, A.; Ramakrishnan, R.; Hariharan, M., Chem. Sci.,
2021, 12, 5064– 5072.

8 Sebastian, E.; Hariharan, M.; J. Am. Chem. Soc.,
2021, 143, 13769–13781; (b) Sebastian, E.; Hariharan, M.; ACS Energy Lett.,
2022
, 7, 696−711.

Figure 1
(Invited) Rational Design of Quantum Dot/Mediator Interfaces for Triplet Energy Transfer and Photon Upconversion
Authors: Lian Tianquan
Published: September 2023

Photon upconversion, where two or more low energy photons are converted into one high energy photon, shows great potential in bioimaging, catalysis and solar energy conversion. Photon upconversion has traditionally been realized with lanthanide-doped nanoparticles, or organic dye sensitized triplet-triplet annihilation (TTA) based upconversion platforms. In recent years, QD sensitized triplet-triplet annihilation based upconversion systems have achieved impressive upconversion quantum efficiency and demonstrated many unique advantages, including high photostability, large extinction coefficient, high spectral coverage and tunability, and low singlet-triplet energy gap. In this talk, we discuss our recent work in developing and understanding QD/mediator interface for efficient QD-sensitized photon upconversion. We summarize the main results of time-resolved spectroscopic studies of various factors affecting the rate of triplet energy transfer (TET) from the QD to the surface attached mediator (TET1) and from the mediator to the emitter in solution (TET2). To identify the key design rules, we compare three PbS sensitized upconversion systems using three mediator molecules with the same tetracene triplet acceptor at different distances from the QD. Our results show that the mediator triplet state is mostly formed by direct TET from quantum dot. With increasing distance between the mediator and PbS QD, the efficiency of the TET1 from the QD to the mediator decreases due to a decrease in the rate of this triplet energy transfer step, while the efficiency of the TET2 from the mediator to emitter increases due to a reduction in the QD induced mediator triplet state decay (via the external heavy atom effect). The rate constant of TET2 is three orders of magnitude slower than the diffusion limited value. We show that the effect of QD/mediator on the total unconversion efficiency measured under CW illumination conditions can be well accounted for by the independently determined efficiencies of TET1 and TET2 steps, providing important insight on the design and rational improvement of efficient photon upconversion systems. Ongoing detailed mechanistic studies of the TET1 process shows that both QD bright and dark exciton states contribute to the TET process and higher lying bridge states play significant role in enhancing TET from core/shell QDs.
(Invited) Coupling of Plasmonic Metal Nanostructures with Organic Molecules for Excitonic Radiation and Non-Radiation Processes
Authors: Wu Nianqiang
Published: September 2023

When plasmonic metal nanostructures are coupled with organic molecules, plasmon can transfer energy from the metal to the organic molecules, leading to exciton generation. In addition, plasmonic hot electrons can transfer from the metal to the adsorbate molecules, leading to chemical interface damping. Based on the above two transfer processes, photoluminescence, surface-enhanced Raman scattering and photocurrent of organic molecules can be enhanced by coupling of organic molecules with plasmonic metal nanostructure, which has implication in photodetection, sensing and solar energy conversion.
(Invited) Site-Selective Introduction of MnO2 Co-Catalyst to Gold Nanocubes for Enhanced Plasmonic Photocatalysis
Authors: Tatsuma Tetsu , Nishi Hiroyasu
Published: September 2023

Plasmon-induced charge separation (PICS) is known to take place at the interface between a nanoparticle exhibiting localized surface plasmon resonance (LSPR) and a semiconductor such as titanium oxide.1 PICS has been applied to photovoltaics, photocatalysis, and so on.2 For energy harvesting based on plasmonic photocatalysis, it is important to optimize geometrical arrangements of the plasmonic nanoparticles, semiconductor, and co-catalyst if any, to enhance the charge separation efficiency and minimize charge recombination probability.

Since LSPR confines light to a nanoscale region smaller than visible light wavelength, PICS allows one to fabricate plasmonic materials in nanoscale beyond the diffraction limit.3-7 We have reported fabrication of wide variety of plasmonic nanostructures via site-selective reactions such as oxidative dissolution of silver and oxidative deposition of lead oxide.

In the present work, gold nanocubes were adsorbed onto a thin film of titanium oxide to obtain a plasmonic photocatalyst. Then, lead oxide was deposited on the top or bottom part of the gold nanocube via the site-selective oxidation of lead ions based on PICS. Lead ions in the deposited lead oxide were replaced with manganese ions by galvanic replacement and the lead oxide was transformed to manganese oxide. The manganese oxide moieties on the gold nanocubes serve as co-catalyst of the plasmonic photocatalyst.

We examined photocatalytic currents for ethanol oxidation by PICS. As a result, the photocurrents were enhanced by introducing manganese oxide to the top part of the gold nanocubes. In marked contrast, the photocurrents were suppressed when the manganese oxide was introduced to the bottom part of the nanocubes. In the latter case, charge recombination occurs between the holes injected to manganese oxide and the electrons injected to titanium oxide. On the other hand, the charge recombination is suppressed in the former case, because manganese oxide is not directly contact with titanium oxide. Thus we found that the position of a co-catalyst greatly affect the activity of plasmonic photocatalysts.8

1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).

2. T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review].

3. I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012).

4. K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).

5. H. Nishi, M. Sakamoto, and T. Tatsuma, Chem. Commun., 54, 11741 (2018).

6. K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018).

7. T. Tatsuma and H. Nishi, Nanoscale Horiz., 5, 597 (2020) [review].

8. K. Kim, H. Nishi, and T. Tatsuma, J. Chem. Phys., 157, 111101 (2022).
(Invited) Ultrafast Charge Transfer Dynamics in WS2–Au Nanohybrid System Fabricated by Pulsed Laser Ablation in Liquid
Authors: Furube Akihiro , Sasaki Kohei , Kokufu Tatsuki , Katayama Tetsuro , Pankaj Koinkar
Published: September 2023

Nanosheet semiconductor materials have attracted much attention in recent years due to their unique optical, electronic, and chemical properties for various applications such as photodetectors, light emitters, photocatalysts, and biosensors. We have fabricated tungsten disulfide (WS2) nanostructures by pulsed laser ablation in liquid. We applied nanosecond and femtosecond lasers and found the latter to be suitable for nanosheet fabrication [1]. Visible light response was enhanced by attaching gold nanoparticles (AuNPs) onto WS2 nanosheets [2]. The charge transfer dynamics in the WS2-Au nanohybrid system was characterized using femtosecond diffuse reflectance spectroscopy. The nanosheet structure was found to reduce the bulk carrier property. Furthermore, modification with AuNPs was found to enhance the formation of carriers trapped deeply in the WS2 nanosheets. These findings will be useful for the design of future metal-nanosheet semiconductor hybrid systems.

Reference

Pankaj Koinkar, Kohei Sasaki, Tetsuro Katayama and Akihiro Furube, International Journal of Modern Physics B, 35, 2140007 (2021)

Tatsuki Kokufu, Daichi Nakayama, Tetsuro Katayama, Koinkar Pankaj, and Akihiro Furube, The 13th Asia-Pacific Conference on Near-Field Optics, OL30-A13 (2022)
Plasmon-Mediated Solar Steam Generation over Au@Cu7S4 Yolk@Shell Nanocrystals
Authors: Yang Shan-Jen , Hsu Yung-Jung
Published: September 2023

In recent years, solar steam generation has attracted extensive attention because it can address the shortage of water resources. Traditional techniques enabling solar steam generation are based on heating water under concentrated solar irradiation, suffering from low solar to heat conversion efficiency. By exploiting the heat localization effect from photothermal materials, the efficiency of solar steam generation can be significantly improved. Similarly, electromagnetic field confinement induced by plasmonic materials has also proven efficient for promoting solar steam generation. In this study, Au@Cu7S4 yolk@shell nanocrystals were prepared and employed as plasmonic mediums for superior solar steam generation. Here, Au was a typical plasmonic metal showing a plasmon resonance peak around 550 nm. Cu7S4, on the other hand, represented a self-doped plasmonic semiconductor capable of absorbing photons beyond 1000 nm. The combination of Au and Cu7S4 in Au@Cu7S4 nanocrystals allowed a broadband light absorption across the visible and near infrared regions. The superior solar steam generation over Au@Cu7S4 was attributed to the broadband light absorption and the enhanced solar to heat conversion efficiency rendered by the combined plasmonic effects of Au and Cu7S4.
Au@SnO2 Core@Shell Nanocrystals for Sustainable Environmental Purifications
Authors: Chang Huai En
Published: September 2023

The search for versatile catalysts for sustainable environmental purifications has been a challenging yet very important research topic especially in the post pandemic era. Core@shell nanocrystals composed of metal core and semiconductor shell have received significant attention as both photocatalysts and chemical catalysts for practical use in organic dyes degradation and bacterial disinfection. This work reports the synthesis of Au@SnO2 core@shell nanocrystals with controllable shell thicknesses. Under light illumination, Au@SnO2 can function as photocatalysts to decompose organic dyes (rhodamine B, RhB) and inactivate E. coli. Because of the band alignment between Au and SnO2, an enhanced photocatalytic activity was achieved on Au@SnO2. Time-resolved photoluminescence spectroscopic analysis was conducted to explore the influence of shell thickness on the interfacial charge dynamics of Au@SnO2 in order to establish the correlation with the resultant photocatalytic performance. On the other hand, the peroxidase mimics features of Au and SnO2 endowed Au@SnO2 with the capability of performing the disinfection of E. coli under darkness conditions. By combining the phtotocatalytic capacity with the peroxidase mimics features, Au@SnO2 demonstrated sustainable activity toward E. coli disinfection under both irradiation and darkness conditions.
(Invited) Semiconductor Heterostructures for Photocatalysis Applications
Authors: Hsu Yung-Jung
Published: September 2023

With the inherently high degree of complexity, heterostructures composed of two or more materials joined in unique architectures may exhibit superior synergetic properties that are difficult or impossible to acquire from their individual constituents [1-3]. For semiconductor heterostructures, the relative band alignment of the constituents promotes effective charge separation to bring them desirable properties for photocatalysis applications. Several representative works from our lab will be introduced to demonstrate the promising potentials of semiconductor nanoheterostructures.

References: (Times New Roman, 11pt)

[1] Chun-Wen Tsao, Mei-Jing Fang, Yung-Jung Hsu*, “Modulation of interfacial charge dynamics of semiconductor heterostructures for advanced photocatalytic applications”, Coordination Chemistry Reviews 2021, 438, 213876 (Invited Review).

[2] Mei-Jing Fang, Chun-Wen Tsao, Yung-Jung Hsu*, "Semiconductor Nanoheterostructures for Photoconversion Applications", Journal of Physics D: Applied Physics 2020, 53, 143001 (Invited Review).

[3] Yi-An Chen, Yu-Ting Wang, Hyun Sik Moon, Kijung Yong, Yung-Jung Hsu*, "Yolk-shell nanostructures: synthesis, photocatalysis and interfacial charge dynamics", RSC Advances 2021, 11, 12288-12305 (Invited Review; selected as themed collections of Photocatalysis).
(Invited) Creation of Active Water-Splitting Photocatalysts By Controlling Cocatalysts Using Atomically Precise Metal Nanoclusters
Authors: Negishi Yuichi
Published: September 2023

With global warming and the depletion of fossil resources, our fossil-fuel-dependent society is expected to shift to one that instead uses hydrogen (H2) as a clean and renewable energy. Water-splitting photocatalysts can produce H2 from water using sunlight, which are almost infinite on the earth. However, further improvements are indispensable to enable their practical application. To improve the efficiency of the photocatalytic water-splitting reaction, in addition to improving the semiconductor photocatalyst, it is extremely effective to improve the cocatalysts (loaded metal nanoclusters, NCs) that enable the reaction to proceed on the photocatalysts. We have thus attempted to strictly control metal NCs on photocatalysts by introducing the precise-control techniques of metal NCs established in the metal NC field into research on water-splitting photocatalysts. Specifically, the cocatalysts on the photocatalysts were controlled by adsorbing atomically precise metal NCs on the photocatalysts and then removing the protective ligands by calcination. This work has led to several findings on the electronic/geometrical structures of the loaded metal NCs, the correlation between the types of the loaded metal NCs and the water-splitting activity, and the methods for producing high water-splitting activity. We expect that the obtained knowledge will lead to clear design guidelines for the creation of practical water-splitting photocatalysts and thereby contribute to the construction of a hydrogen-energy society.

Figure 1
(Invited) Semiconductor Surface-Controlled Photocatalysis
Authors: Huang Michael H.
Published: September 2023

Photo-induced charge transfer has been found to depend strongly on the exposed semiconductor surfaces. For example, {110}-bound Cu2O rhombic dodecahedra show a high photocatalytic activity, but {100}-terminated Cu2O cubes are inactive. Photocatalytic behaviors of Cu2O-based semiconductor heterostructures, such as Cu2O-ZnO and Cu2O-ZnS composites, can both enhance and suppress photocatalytic activity depending on the contacting planes at the heterojunction. Interestingly, Cu2O photocatalytic activity can be greatly enhanced by functionalizing with conjugated molecules through surface band structure tuning, turning inert cubes to possess a superior photocatalytic activity. More recently, the photogenerated superoxide radicals can be used in some organic reactions, and the crystal surface is naturally linked to the product yields.
(Invited) In-Situ/Operando Monitoring of Mechanisms of Catalytic Reaction Using X-Rays
Authors: Lin Yan-Gu
Published: September 2023

Global climate warming and environment pollution have spurred scientists to develop new high-efficient and environmental-friendly energy technologies. Hydrogen plays a key role in deep decarbonization for realization of net-zero carbon dioxide emission by 2050. Presently, the most popular and economical commercial process for H2 production is steam–methane reforming, which uses fossil fuels as the raw material and produces comparable amounts of CO2 as the by–product. It is definitely an environmental unfriendly and a non–sustainable H2 production process, and development of green H2 production is in urgent need. Sunlight is a clean, renewable and abundant energy source on the earth. Its conversion to hydrogen has been considered an ideal solution to counter the depletion and environmental problems of fossil fuels. Hydrogen is an ideal fuel for fuel cell applications. Hydrogen has to be produced from renewable and carbon-free resources using nature energies such as sunlight if one thinks of clean energy and environmental issues. In this regard, a photoelectrochemical cell consisting of semiconductor photoelectrodes that can harvest light and use this energy directly for splitting water is a more promising way for hydrogen generation. Photocatalysis utilizes the energy delivered by light and enables chemical reactions that otherwise cannot take place. When used to power thermodynamically uphill reactions, photocatalysis offers a solution to large-scale solar energy storage. Despite over four decades of intense research, however, photocatalysis remains either too expensive or too inefficient or both. Poor understanding of the mechanisms behind the low performance is a key reason that limits the progress of this important field. To address this critical challenge, I will overview a number of the experimental studies that successfully revealed the catalytic reactions at solid/liquid interfaces in real time, e.g. electrochemical interface of photocatalysis and electrocatalysis. The experimental results demonstrate that the operando X-ray characterization provides the unique information for understanding the real reaction mechanism.
Hgn@ZnS Yolk@Shell Nanocrystals for Solar Hydrogen Production
Authors: Alvarado Cristhal , Hsu Yung-Jung
Published: September 2023

Design of metal/semiconductor heterostructures has become a topic of great interest in recent years due to the combined interaction between the two components that allows them to show synergistic properties and functionalities. Yolk@shell nanocrystals composed of metal and semiconductor components represent a new family of heterostructures. These structures comprise a core, mobile particle surrounded by a hollow, permeable shell, which can be employed as a robust nanoreactor for catalytic applications. In comparison with the similar counterpart, core@shell nanocrystals, yolk@shell nanocrystal have superior features, such as homogeneous reaction environment, accelerated mass transfer dynamics and incremental surface active sites. In this work, a novel hollow Au nanospheres (HGN)@ZnS yolk@shell nanocrystal have been prepared and employed as photocatalysts for hydrogen production. The samples were synthesized by conducting ion exchange reactions on HGN@Cu2O core@shell nanocrystal template, which involved a Kirkendall anion exchange process and a kinetically controlled cation exchange reaction. The microstructures, electronic interactions, band alignment and interfacial charge dynamics of the resultant HGN@ZnS were characterized. The effects of HGN as a charge separation enhancer and a plasmonic sensitizer on the photocatalytic performance of hydrogen production were explored. The results revealed the great promise of HGN@ZnS as highly efficient photocatalysts for solar hydrogen production.
MOF-Derived Carbons Modified CdSe Quantum Dots for Photocatalytic Hydrogen Production
Authors: Wang Chien-Yi , Wang Cheng-Yu , Hsu Yung-Jung
Published: September 2023

Metal-organic framework (MOF)-derived carbons have attracted great interest in recent years by virtue of their fascinating material properties, such as mesoporous structures, high electron conductivity and great chemical stability. By coupling the MOF-derived carbons with other functional materials, it is possible to tailor the resulting materials properties for expanding the application scenarios. Here, we have developed a low-temperature approach to the preparation of ZIF-67-derived carbon nanostructures (ZDCNT). Further coupling with CdSe quantum dots was conducted to enhance the photocatalytic performance toward solar hydrogen production. The electronic interactions between ZDCNT and CdSe were explored with time-resolved photoluminescence spectroscopy and in-situ X-ray absorption. A hydrogen production rate of 10.4 mmole g-1 hr-1 with a remarkable apparent quantum yield of 8.1 % at 300 nm can be achieved. Recycling tests further disclosed the high chemical stability for the ZDCNT modified CdSe, suggesting that the typical photocorrosion of CdSe can be resolved upon the modification with ZDCNT. This work delivers a new concept of photocatalyst paradigms by combining MOF-derived carbons with semiconductor.
Investigations of Charge Transfer Processes on Plasmonic Cathode Electrodes
Authors: Minamimoto Hiro , Tajiri Yuto , Sato Daiki , Murakoshi Kei , Mizuhata Minoru
Published: September 2023

The establishment of efficient light energy conversion system is an important issue in the field of photoelectrochemical region. For the realization of it, the wide-band semiconductor electrode could be the good candidate. However, semiconductor electrodes often have the limitation to the ultraviolet region because of their band gap energy. Because the sunlight energy mainly consists of visible light, the visible-light induced photoenergy conversion is a challenging issue. As the breakthrough for it, recently, the combination of the plasmonic metal nanostructures with wide semiconductor electrodes has been received much attention because of the addition of visible light response characters. Up to now, the various systems of the anodic reaction controls have been established. Recently, the cathode system which can control the reduction reactions at metal semiconductor interfaces have been reported via the introduction of plasmonic metal nanostructures into the p-type semiconductor electrodes. In our previous study, we have established the plasmonic photocathode by using the Ag nanostructures with the p-type GaP electrode [1]. In this system, it can be considered as the holes excited in the metal structures injected into the valence band of the p-type semiconductor and the remained electron are consumed in the hydrogen evolution reaction. In addition, we have observed the unique pH dependence on the hydrogen evolution which could not be observed on conventional metal electrodes. For understanding the unique reaction selectivity on the plasmonic cathode electrode, the detail understanding about both the charge transfer process and absolute electrochemical potential of generated electrons. In this study, we have attempted to obtain such information through the various chemical reactions using the various types of plasmonic structures. Through the various photoelectrochemical measurements, we have confirmed the changes in the electrochemical potential of excited electrons depending on the optical characters of plasmonic structures. The unique molecular selectivity was also observed. Our current research would provide the novel insight for the accurate design of the high efficient visible light conversion device.

[1] H. Minamimoto et al., Chem. Lett., 2020, 49, 806.