Recent Submissions

  • Chiral Helimagnetism and One-Dimensional Magnetic Solitons in a Cr-Intercalated Transition Metal Dichalcogenide

    Zhang, Chenhui; Zhang, Junwei; Liu, Chen; Zhang, Senfu; Yuan, Ye; Li, Peng; Wen, Yan; Jiang, Ze; Zhou, Bojian; Lei, Yongjiu; Zheng, Dongxing; Song, Chengkun; Hou, Zhipeng; Mi, Wenbo; Schwingenschlögl, Udo; Manchon, Aurélien; Qiu, Zi Qiang; Alshareef, Husam N.; Peng, Yong; Zhang, Xixiang (Advanced Materials, Wiley, 2021-07-24) [Article]
    Chiral magnets endowed with topological spin textures are expected to have promising applications in next-generation magnetic memories. In contrast to the well-studied 2D or 3D magnetic skyrmions, the authors report the discovery of 1D nontrivial magnetic solitons in a transition metal dichalcogenide 2H-TaS2 via precise intercalation of Cr elements. In the synthetic Cr1/3TaS2 (CTS) single crystal, the coupling of the strong spin–orbit interaction from TaS2 and the chiral arrangement of the magnetic Cr ions evoke a robust Dzyaloshinskii–Moriya interaction. A magnetic helix having a short spatial period of ≈25 nm is observed in CTS via Lorentz transmission electron microscopy. In a magnetic field perpendicular to the helical axis, the helical spin structure transforms into a chiral soliton lattice (CSL) with the spin structure evolution being consistent with the chiral sine-Gordon theory, which opens promising perspectives for the application of CSL to fast-speed nonvolatile magnetic memories. This work introduces a new paradigm to soliton physics and provides an effective strategy for seeking novel 2D magnets.
  • [Cu36H10(PET)24(PPh3)6Cl2] Reveals Surface Vacancy Defects in Ligand-Stabilized Metal Nanoclusters

    Dong, Chunwei; Huang, Renwu; Chen, Cailing; Chen, Jie; Nematulloev, Saidkhodzha; Guo, Xianrong; Ghosh, Atanu; Alamer, Badriah Jaber; Hedhili, Mohamed N.; Isimjan, Tayirjan T.; Han, Yu; Mohammed, Omar F.; Bakr, Osman (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-07-13) [Article]
    Precise identification and in-depth understanding of defects in nanomaterials can aid in rationally modulating defect-induced functionalities. However, few studies have explored vacancy defects in ligand-stabilized metal nanoclusters with well-defined structures, owing to the substantial challenge of synthesizing and isolating such defective metal nanoclusters. Herein, a novel defective copper hydride nanocluster, [Cu36H10(PET)24(PPh3)6Cl2] (Cu36; PET: phenylethanethiolate; PPh3: triphenylphosphine), is successfully synthesized at the gram scale via a simple one-pot reduction method. Structural analysis reveals that Cu36 is a distorted half cubic nanocluster, evolved from the perfect Nichol’s half cube. The two surface copper vacancies in Cu36 are found to be the principal imperfections, which result in some structural adjustments, including copper atom reconstruction near the vacancies as well as ligand modifications (e.g., substitution, migration, and exfoliation). Density functional theory calculations imply that the above-mentioned defects have a considerable influence on the electronic structure and properties. The modeling suggests that the formation of defective Cu36 rather than the perfect half cube is driven by the enlargement of the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the nanocluster. The structural evolution induced by the surface copper atom vacancies provides atomically precise insights into the defect-induced readjustment of the local structure and introduces new avenues for understanding the chemistry of defects in nanomaterials.
  • Oriented Halide Perovskite Nanostructures and Thin Films for Optoelectronics

    Chen, Jie; Zhou, Yang; Fu, Yongping; Pan, Jun; Mohammed, Omar F.; Bakr, Osman (Chemical Reviews, American Chemical Society (ACS), 2021-07-12) [Article]
    Oriented semiconductor nanostructures and thin films exhibit many advantageous properties, such as directional exciton transport, efficient charge transfer and separation, and optical anisotropy, and hence these nanostructures are highly promising for use in optoelectronics and photonics. The controlled growth of these structures can facilitate device integration to improve optoelectronic performance and benefit in-depth fundamental studies of the physical properties of these materials. Halide perovskites have emerged as a new family of promising and cost-effective semiconductor materials for next-generation high-power conversion efficiency photovoltaics and for versatile high-performance optoelectronics, such as light-emitting diodes, lasers, photodetectors, and high-energy radiation imaging and detectors. In this Review, we summarize the advances in the fabrication of halide perovskite nanostructures and thin films with controlled dimensionality and crystallographic orientation, along with their applications and performance characteristics in optoelectronics. We examine the growth methods, mechanisms, and fabrication strategies for several technologically relevant structures, including nanowires, nanoplates, nanostructure arrays, single-crystal thin films, and highly oriented thin films. We highlight and discuss the advantageous photophysical properties and remarkable performance characteristics of oriented nanostructures and thin films for optoelectronics. Finally, we survey the remaining challenges and provide a perspective regarding the opportunities for further progress in this field.
  • MXenes for Optoelectronic Devices

    Liu, Zhixiong; Alshareef, Husam N. (Advanced Electronic Materials, Wiley, 2021-07-08) [Article]
    MXenes have attracted increasing attention from the research community due to several unique properties that make them suitable for many applications. As a rapidly growing family of 2D transitional metal carbides and nitrides, they have demonstrated very promising properties in electrochemical devices. Recently, a few reports have emerged showing that MXenes have interesting optoelectronic properties. In this review, the fundamental properties of MXenes are discussed, especially those related to optoelectronic properties, and the recent reports on MXene-based optoelectronic applications including photovoltaic, plasmonic, photodetector, phototransistor, and light-emitting diode applications are reviewed. Last, and most importantly, a vision and a road map is articulated for the future research directions that make the most sense for this important class of materials.
  • Enhanced-Performance Self-Powered Solar-Blind UV-C Photodetector Based on n-ZnO Quantum Dots Functionalized by p-CuO Micro-pyramids

    Alwadai, Norah M.; Mitra, Somak; Hedhili, Mohamed N.; Alamoudi, Hadeel; Xin, Bin; Alaal, Naresh; Roqan, Iman S. (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-07-08) [Article]
    Smart solar-blind UV-C band photodetectors suffer from low responsivity in a self-powered mode. Here, we address this issue by fabricating a novel enhanced solar-blind UV-C photodetector array based on solution-processed n-ZnO quantum dots (QDs) functionalized by p-CuO micro-pyramids. Self-assembled catalyst-free p-CuO micro-pyramid arrays are fabricated on a pre-ablated Si substrate by pulsed laser deposition without a need for a catalyst layer or seeding, while the solution-processed n-ZnO QDs are synthesized by the femtosecond-laser ablation in liquid technique. The photodetector is fabricated by spray-coating ZnO QDs on a CuO micro-pyramid array. The photodetector performance is optimized via a p-n junction structure as both p-ZnO QDs and p-CuO micro-pyramid layers are characterized by wide band gap energies. Two photodetectors (with and without CuO micro-pyramids) are fabricated to show the role of p-CuO in enhancing the device performance. The n-ZnO QD/p-CuO micro-pyramid/Si photodetector is characterized by a superior photo-responsivity of ∼956 mA/W at 244 nm with a faster photoresponse (<80 ms) and 260 nm cut-off compared to ZnO QDs/Si photodetectors, confirming that the p-CuO micro-pyramids enhance the device performance. The self-powered photoresponse with a high photo-responsivity of ∼29 mA/W is demonstrated. These high-responsivity solar-bind UV-C photodetector arrays can be used for a wide range of applications.
  • Defining sulfonation limits of poly(ether-ether-ketone) for energy-efficient dehumidification

    Akhtar, Faheem; Abdulhamid, Mahmoud; Vovusha, Hakkim; Ng, Kim Choon; Schwingenschlögl, Udo; Szekely, Gyorgy (Journal of Materials Chemistry A, Royal Society of Chemistry (RSC), 2021-07-06) [Article]
    Dehumidification is a vital process in the cooling industry and has emerged as a promising tool for alleviating the effects of energy-intensive activities. Advanced engineering materials, which can be employed in dehumidification processes, have attracted considerable attention. However, the majority of commercial adsorbents suffer from low sorption performance in arid climates. In this work, sulfonated poly(ether-ether-ketones) (SPEEKs) were designed as desiccants for dehumidification processes. The in silico and experimental investigations at a molecular level enabled the development of desiccants exhibiting outstanding water uptake capacity of more than 300%, fast sorption uptake, and high transport rate. The sorption capacity of the prepared materials outperformed those of the previously reported desiccants. Membrane performance analyses demonstrated remarkably high water vapor permeability and selectivity; therefore, the desiccants developed herein showed potential for application in water vapor control and dehumidification processes in enclosed or confined spaces. Contrary to common assumptions, the correlation between the sulfonation degree and dehumidification performance showed a plateau after maximum curvature. The results of this study open new directions for tailoring energy-efficient materials for dehumidification processes.
  • Magnetic Tunnel Junction based Gradiometer for Detection of Cracks in Cement

    He, Guanyang; Zhang, Yiou; Hu, Yuebin; Zhang, Xixiang; Xiao, Gang (Sensors and Actuators A: Physical, Elsevier BV, 2021-07) [Article]
    Magnetic flux leakage (MFL) testing is a widely used technology for detecting structural defects in industry, where new magnetic sensors can provide an enhanced detectability. We have fabricated and developed vortex magnetic tunnel junctions (MTJs) into a new MFL probe, by designing a well-balanced magnetic gradiometer with a base length of 4 cm. Such gradiometer has exhibited a field detectability of 1.6 𝑛𝑇/√𝐻𝑧 at 1 kHz, and a superior common-mode rejection ratio (CMRR) of 82 dB. We have studied multiple configurations of crack detection in weakly magnetic cement by simulations, and provided corresponding experimental confirmations by this MFL probe. It has achieved a large standoff distance of 22 mm, which finds its applications in energy industry and other infrastructural systems.
  • Access to Ultrafast Surface and Interface Carrier Dynamics Simultaneously in Space and Time

    Zhao, Jianfeng; Nughays, Razan; Bakr, Osman; Mohammed, Omar F. (The Journal of Physical Chemistry C, American Chemical Society (ACS), 2021-06-29) [Article]
    Charge carrier dynamics at material surfaces and interfaces play a fundamental role in controlling the performance of photocatalytic reactions and photovoltaic devices; however, precise characterization of the surface dynamical properties of a material with nanometer (nm) and femtosecond (fs) spatial and temporal resolutions, respectively, is a precondition for profound understanding and is thus urgently needed. Many techniques have been developed to meet this demand, but barely any of them have simultaneous excellent surface sensitivity (depth resolution) and sufficient spatiotemporal resolutions, except for a one-of-a-kind second-generation scanning ultrafast electron microscope (S-UEM), which has been established and developed at KAUST to provide direct and controllable dynamical information about the ultrafast charge carrier dynamics and the localization of electrons and holes on the photoactive material surface and interfaces. In this feature article, the instrumentation, working principles, new capabilities, and unique applications of S-UEM in the ultrafast characterization of material surfaces and interfaces, including charge carrier injection, surface carrier diffusion, surface carrier trapping, and recombination, are systematically summarized and inspected. Future developments from both theoretical and experimental perspectives are also discussed.
  • Precise Sub-Angstrom Ion Separation Using Conjugated Microporous Polymer Membranes

    Zhou, Zongyao; Guo, Dong; Shinde, Digambar; Cao, Li; Li, Zhen; Li, Xiang; Lu, Dongwei; Lai, Zhiping (ACS Nano, American Chemical Society (ACS), 2021-06-29) [Article]
    Polymer membranes typically possess a broad pore-size distribution that leads to much lower selectivity in ion separation when compared to membranes made of crystalline porous materials; however, they are highly desirable because of their easy processability and low cost. Herein, we demonstrate the fabrication of ion-sieving membranes based on a polycarbazole-type conjugated microporous polymer using an easy to scale-up electropolymerization strategy. The membranes exhibited high uniform sub-nanometer pores and a precisely tunable membrane thickness, yielding a high ion-sieving performance with a sub-1 Å size precision. Both experimental results and molecular simulations suggested that the impressive ion-sieving performance of the CMP membranes originates from their uniform and narrow pore-size distribution.
  • 62-8: Invited Paper: High Color Gamut QDot ™ LCD Displays with Perovskite Quantum Dots: Devices Architecture, Performance and Reliability

    Sinatra, Lutfan; Lutfullin, Marat; Lentijo-Mozo, Sergio; Bakr, Osman (SID Symposium Digest of Technical Papers, Wiley, 2021-06-28) [Article]
    erovskite Quantum Dots (QDs) promise to deliver over 90% of Rec2020 color representation, the highest for RoHS compliant LCD displays. In this study, we strive to demonstrate the performance of LCD displays using QDot™ green emitting Perovskite QDs with various backlight architectures. Using different blue and red light sources, we fabricated four types of LCD display, which showed contrasting Rec2020 color gamut from 80 to 86 % and brightness from 1000 to 2000 nits. With these impressive metrics, Perovskite Quantum Dots paves the way for mass adoption of the technology in the display field.
  • Manipulation of hot carrier cooling dynamics in two-dimensional Dion–Jacobson hybrid perovskites via Rashba band splitting

    Yin, Jun; Naphade, Rounak; Maity, Partha; Gutierrez Arzaluz, Luis; Almalawi, Dhaifallah R.; Roqan, Iman S.; Bredas, Jean-Luc; Bakr, Osman; Mohammed, Omar F. (Nature Communications, Springer Science and Business Media LLC, 2021-06-28) [Article]
    AbstractHot-carrier cooling processes of perovskite materials are typically described by a single parabolic band model that includes the effects of carrier-phonon scattering, hot phonon bottleneck, and Auger heating. However, little is known (if anything) about the cooling processes in which the spin-degenerate parabolic band splits into two spin-polarized bands, i.e., the Rashba band splitting effect. Here, we investigated the hot-carrier cooling processes for two slightly different compositions of two-dimensional Dion–Jacobson hybrid perovskites, namely, (3AMP)PbI4 and (4AMP)PbI4 (3AMP = 3-(aminomethyl)piperidinium; 4AMP = 4-(aminomethyl)piperidinium), using a combination of ultrafast transient absorption spectroscopy and first-principles calculations. In (4AMP)PbI4, upon Rashba band splitting, the spin-dependent scattering of hot electrons is responsible for accelerating hot-carrier cooling at longer delays. Importantly, the hot-carrier cooling of (4AMP)PbI4 can be extended by manipulating the spin state of the hot carriers. Our findings suggest a new approach for prolonging hot-carrier cooling in hybrid perovskites, which is conducive to further improving the performance of hot-carrier-based optoelectronic and spintronic devices.
  • Cascade Electron Transfer Induces Slow Hot Carrier Relaxation in CsPbBr3 Asymmetric Quantum Wells

    Maity, Partha; Merdad, Noor A.; Yin, Jun; Lee, Kwangjae; Sinatra, Lutfan; Bakr, Osman; Mohammed, Omar F. (ACS Energy Letters, American Chemical Society (ACS), 2021-06-28) [Article]
    We report an engineering approach not only to delay hot carrier equilibrium but also to slow the cooling rate of CsPbBr3-based multiple quantum wells (MQWs), as evident from femtosecond transient absorption measurements and density functional theory calculations. Three energetically cascaded CsPbBr3 perovskite layers (stacked with thicknesses of 3, 7, and 20 nm for asymmetric MQWs and 20, 20, and 20 nm for symmetric MQWs) are separated by a 5 nm organic barrier of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. Time-resolved data demonstrate that the sequential hot-electron transfer between CsPbBr3 layers mediates the delayed hot carrier equilibrium in the asymmetric MQWs. Interestingly, the delayed hot carrier equilibrium is followed by a much slower relaxation in asymmetric MQWs (40 ps) than symmetric ones (3.2 ps), which could be attributed to the decoupling of a hot electron–hole originating from hot electron transfer. Our findings provide a promising approach for efficient hot carrier extraction in solar cells that exceed the Shockley–Queisser limit.
  • General synthesis of single-atom catalysts with high metal loading using graphene quantum dots

    Xia, Chuan; Qiu, Yunrui; Xia, Yang; Zhu, Peng; King, Graham; Zhang, Xiao; Wu, Zhenyu; Kim, Jung Yoon; Cullen, David A.; Zheng, Dongxing; Li, Peng; Shakouri, Mohsen; Heredia, Emilio; Cui, Peixin; Alshareef, Husam N.; Hu, Yongfeng; Wang, Haotian (Nature Chemistry, Springer Science and Business Media LLC, 2021-06-24) [Article]
    Transition-metal single-atom catalysts present extraordinary activity per metal atomic site, but suffer from low metal-atom densities (typically less than 5 wt% or 1 at.%), which limits their overall catalytic performance. Here we report a general method for the synthesis of single-atom catalysts with high transition-metal-atom loadings of up to 40 wt% or 3.8 at.%, representing several-fold improvements compared to benchmarks in the literature. Graphene quantum dots, later interweaved into a carbon matrix, were used as a support, providing numerous anchoring sites and thus facilitating the generation of high densities of transition-metal atoms with sufficient spacing between the metal atoms to avoid aggregation. A significant increase in activity in electrochemical CO<sub>2</sub> reduction (used as a representative reaction) was demonstrated on a Ni single-atom catalyst with increased Ni loading.
  • Significant Performance Improvement in n-Channel Organic Field-Effect Transistors with C 60 :C 70 Co-Crystals Induced by Poly(2-ethyl-2-oxazoline) Nanodots

    Nam, Sungho; Khim, Dongyoon; Martinez, Gerardo T.; Varambhia, Aakash; Nellist, Peter D.; Kim, Youngkyoo; Anthopoulos, Thomas D.; Bradley, Donal (Advanced Materials, Wiley, 2021-06-24) [Article]
    Solution-processed organic field-effect transistors (OFETs) have attracted great interest due to their potential as logic devices for bendable and flexible electronics. In relation to n-channel structures, soluble fullerene semiconductors have been widely studied. However, they have not yet met the essential requirements for commercialization, primarily because of low charge carrier mobility, immature large-scale fabrication processes, and insufficient long-term operational stability. Interfacial engineering of the carrier-injecting source/drain (S/D) electrodes has been proposed as an effective approach to improve charge injection, leading also to overall improved device characteristics. Here, it is demonstrated that a non-conjugated neutral dipolar polymer, poly(2-ethyl-2-oxazoline) (PEOz), formed as a nanodot structure on the S/D electrodes, enhances electron mobility in n-channel OFETs using a range of soluble fullerenes. Overall performance is especially notable for (C<sub>60</sub> -I<sub>h</sub> )[5,6]fullerene (C<sub>60</sub> ) and (C<sub>70</sub> -D<sub>5h(6)</sub> )[5,6]fullerene (C<sub>70</sub> ) blend films, with an increase from 0.1 to 2.1 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup> . The high relative mobility and eighteen-fold improvement are attributed not only to the anticipated reduction in S/D electrode work function but also to the beneficial effects of PEOz on the formation of a face-centered-cubic C<sub>60</sub> :C<sub>70</sub> co-crystal structure within the blend films.
  • Relation between Spherulitic Growth, Molecular Organization, and Charge Carrier Transport in Meniscus-Guided Coated Organic Semiconducting Films

    Zhang, Ke; Borkowski, Michal; Wucher, Philipp; Beaujuge, Pierre; Michels, Jasper J.; Blom, Paul. W. M.; Marszalek, Tomasz; Pisula, Wojciech (Advanced Electronic Materials, Wiley, 2021-06-23) [Article]
    Meniscus-guided coating (MGC) is an efficient and promising route to grow small molecule and polymer organic semiconductors (OSCs) into highly ordered and uniaxially orientated thin films for electronic applications. In this work, the impact of domain size and molecular order on the charge carrier transport in field-effect transistors for a molecular organic semiconductor 4-tolyl-bithiophenyl-diketopyrrolopyrrole (DPP(Th2Bn)2) is investigated. The spherulitic domain growth of DPP(Th2Bn)2 in thin films is controlled in the evaporative regime of zone-casting by varying the substrate velocity. The decrease of coating velocity leads to a lower nucleation density and larger domain size of DPP(Th2Bn)2. At sufficiently low velocity, the spherulitic domains first elongate and then uniaxially grow in the coating direction. Although at the same time the molecular order decreases due to higher film thickness, the charge carrier transport improves for larger domain size and reduced density of boundaries in the transistor channel. These results provide insight on the relation between domain growth, molecular organization, and charge carrier transport in zone-cast OSC thin films that are important for the upscaling of the technique for practical applications.
  • Ternary organic photodetectors based on pseudo-binaries nonfullerene-based acceptors

    Zhang, Tianyi; Moser, Maximilian; Scaccabarozzi, Alberto D.; Bristow, Helen; Jacoutot, Polina; Wadsworth, Andrew; Anthopoulos, Thomas D.; McCulloch, Iain; Gasparini, Nicola (Journal of Physics: Materials, IOP Publishing, 2021-06-16) [Article]
    The addition of a third component to a donor:acceptor blend is a powerful tool to enhance the power conversion efficiency of organic solar cells. Featuring a similar operating mechanism, organic photodetectors are also expected to benefit from this approach. Here, we fabricated ternary organic photodetectors, based on a polymer donor and two nonfullerene acceptors, resulting in a low dark current of 0.42 nA cm-2 at -2 V and a broadband specific detectivity of 1012 Jones. We found that exciton recombination in the binary blend is reduced in ternary devices due to the formation of a pseudo-binary microstructure with mixed donor-acceptor phases. With this approach a wide range of intermediate open-circuit voltages is accessible, without sacrificing light-to-current conversion. This results in ternary OPD with improved R values in the NIR. Moreover, morphology analyses reveal that ternary OPD devices showed improved microstructure ordering and consequentially higher charge carrier mobilities compared to the reference devices.
  • Concurrent cationic and anionic perovskite defect passivation enables 27.4% perovskite/silicon tandems with suppression of halide segregation

    Isikgor, Furkan Halis; Furlan, Francesco; Liu, Jiang; Ugur, Esma; Eswaran, Mathan Kumar; Subbiah, Anand Selvin; Yengel, Emre; de Bastiani, Michele; Harrison, George T.; Zhumagali, Shynggys; Howells, Calvyn Travis; Aydin, Erkan; Wang, Mingcong; Gasparini, Nicola; Allen, Thomas; Rehman, Atteq Ur; Van Kerschaver, Emmanuel; Baran, Derya; McCulloch, Iain; Anthopoulos, Thomas D.; Schwingenschlögl, Udo; Laquai, Frédéric; De Wolf, Stefaan (Joule, Elsevier BV, 2021-06-16) [Article]
    Stable and efficient perovskite/silicon tandem solar cells require defect passivation and suppression of light-induced phase segregation of the wide-band-gap perovskite. Here, we report how molecules containing both electron-rich and electron-poor moieties, such as phenformin hydrochloride (PhenHCl), can satisfy both requirements, independent of the perovskite’s surface chemical composition and its grain boundaries and interfaces. PhenHClpassivated wide-band-gap ( 1.68 eV) perovskite p-i-n single-junction solar cells deliver an open-circuit voltage (VOC) 100 mV higher than control devices, resulting in power conversion efficiencies (PCEs) up to 20.5%. These devices do not show any VOC losses after more than 3,000 h of thermal stress at 85C in a nitrogen ambient. Moreover, PhenHCl passivation improves the PCE of textured perovskite/silicon tandem solar cells from 25.4% to 27.4%. Our findings provide critical insights for improved passivation of metal halide perovskite surfaces and the fabrication of highly efficient and stable perovskite-based single-junction and tandem solar cells.
  • Molecular Doping Directed by a Neutral Radical

    Liu, Jian; van der Zee, Bas; Villava, Diego R.; Ye, Gang; Kahmann, Simon; Kamperman, Max; Dong, Jingjin; Qiu, Li; Portale, Giuseppe; Loi, Maria A.; Hummelen, Jan C.; Chiechi, Ryan C.; Baran, Derya; Koster, L. Jan Anton (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-06-16) [Article]
    Molecular doping makes possible tunable electronic properties of organic semiconductors, yet a lack of control of the doping process narrows its scope for advancing organic electronics. Here, we demonstrate that the molecular doping process can be improved by introducing a neutral radical molecule, namely nitroxyl radical (2,2,6,6-teramethylpiperidin-i-yl) oxyl (TEMPO). Fullerene derivatives are used as the host and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazoles (DMBI-H) as the n-type dopant. TEMPO can abstract a hydrogen atom from DMBI-H and transform the latter into a much stronger reducing agent DMBI•, which efficiently dopes the fullerene derivative to yield an electrical conductivity of 4.4 S cm–1. However, without TEMPO, the fullerene derivative is only weakly doped likely by a hydride transfer following by an inefficient electron transfer. This work unambiguously identifies the doping pathway in fullerene derivative/DMBI-H systems in the presence of TEMPO as the transfer of a hydrogen atom accompanied by electron transfer. In the absence of TEMPO, the doping process inevitably leads to the formation of less symmetrical hydrogenated fullerene derivative anions or radicals, which adversely affect the molecular packing. By adding TEMPO we can exclude the formation of such species and, thus, improve charge transport. In addition, a lower temperature is sufficient to meet an efficient doping process in the presence of TEMPO. Thereby, we provide an extra control of the doping process, enabling enhanced thermoelectric performance at a low processing temperature.
  • Sustained Solar-Powered Electrocatalytic H2 Production by Seawater Splitting Using Two-Dimensional Vanadium Disulfide

    Gnanasekar, Paulraj; Eswaran, Mathan Kumar; Palanichamy, Gayathri; Ng, Tien Khee; Schwingenschlögl, Udo; Ooi, Boon S.; Kulandaivel, Jeganathan (ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2021-06-15) [Article]
    Robust and stable electrodes made from earth-abundant materials have gained widespread interest in large-scale electrocatalytic water splitting toward hydrogen energy technologies. In this study, the vanadium disulfide (VS2)/amorphous carbon (AC) heterostructure was employed as an electrode for direct seawater splitting. Two-dimensional VS2 nanoparticles were deposited on AC with a high degree of uniformity via a well-optimized one-step chemical vapor deposition approach. The VS2/AC heterostructure electrode was found to possess rich active sulfur sites, near-zero Gibbs free energy, a large surface area, and exceptional charge transfer toward the electrolyte, resulting in enhanced hydrogen evolution reaction (HER) performance with a low onset potential and low overpotential of 11 and 61 mV (vs reversible hydrogen electrode (RHE)), respectively. The electrode also sustained robust stability throughout the 50 h of chronoamperometry studies under acidic electrolyte conditions. Interestingly, the VS2/AC electrocatalyst accomplished an exceptional HER performance under natural seawater conditions in the absence of an external electrolyte with an onset potential of 56 mV vs RHE and attained η200 at an overpotential of 0.53 V vs RHE. In spite of this, the heterostructure exhibited superior stability over 21 days at a high current density of 250 mA/cm2 under both indoor and solar-powered outdoor conditions. Overall, this VS2/AC heterostructure may open a new pathway toward direct seawater splitting for long-term, stable, large-scale hydrogen generation.
  • Energy Spotlight

    Dasgupta, Neil P.; Berry, Joseph J.; Bakr, Osman; Christopher, Phillip (ACS Energy Letters, American Chemical Society (ACS), 2021-06-11) [Article]
    Three papers recently published in ACS Energy Letters are featured in this month’s Energy Spotlight. These highlights include the design rules for optimizing Li metal morphology and composition through co-electrodeposition (highlighted by Neil P. Dasgupta), the use of aromatic formamidine variants to create a 2D/3D active layer for boosting the efficiency of 2D perovskite solar cells (highlighted by Joseph J. Berry and Osman M. Bakr), and inelastic neutron scattering to probe surface-bound hydrides during plasma-driven catalytic ammonia synthesis (highlighted by Phillip Christopher). We also encourage you to take a look at the latest Virtual Issue, Advances in Solid State Batteries, which will present key papers on this topic published in ACS Energy Letters. These and other papers included in this issue provide mechanistic insights into the energy conversion and storage processes.

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