Recent Submissions

  • Selectivity descriptors for the direct hydrogenation of CO2 to hydrocarbons during zeolite-mediated bifunctional catalysis

    Galilea, Adrian; Gong, Xuan; Caglayan, Mustafa; Nastase, Stefan-Adrian F.; Abou-Hamad, Edy; Gevers, Lieven; Cavallo, Luigi; Chowdhury, Abhishek Dutta; Gascon, Jorge (Nature Communications, Springer Science and Business Media LLC, 2021-10-08) [Article]
    AbstractCascade processes are gaining momentum in heterogeneous catalysis. The combination of several catalytic solids within one reactor has shown great promise for the one-step valorization of C1-feedstocks. The combination of metal-based catalysts and zeolites in the gas phase hydrogenation of CO2 leads to a large degree of product selectivity control, defined mainly by zeolites. However, a great deal of mechanistic understanding remains unclear: metal-based catalysts usually lead to complex product compositions that may result in unexpected zeolite reactivity. Here we present an in-depth multivariate analysis of the chemistry involved in eight different zeolite topologies when combined with a highly active Fe-based catalyst in the hydrogenation of CO2 to olefins, aromatics, and paraffins. Solid-state NMR spectroscopy and computational analysis demonstrate that the hybrid nature of the active zeolite catalyst and its preferred CO2-derived reaction intermediates (CO/ester/ketone/hydrocarbons, i.e., inorganic-organic supramolecular reactive centers), along with 10 MR-zeolite topology, act as descriptors governing the ultimate product selectivity.
  • Illuminating the Intrinsic Effect of Water Co-feeding on Methane Dehydroaromatization: A Comprehensive Study

    Caglayan, Mustafa; Paioni, Alessandra Lucini; Dereli, Busra; Shterk, Genrikh; Hita, Idoia; Abou-Hamad, Edy; Pustovarenko, Alexey; Emwas, Abdul-Hamid M.; Dikhtiarenko, Alla; Castaño, Pedro; Cavallo, Luigi; Baldus, Marc; Chowdhury, Abhishek Dutta; Gascon, Jorge (ACS Catalysis, American Chemical Society (ACS), 2021-09-07) [Article]
    Among all catalytic natural gas valorization processes, methane dehydroaromatization (MDA) still has a great potential to be utilized at an industrial level. Although the use of Mo/H-ZSM-5 as an MDA catalyst was first reported almost three decades ago, the process is yet to be industrialized, because of its inherent challenges. In order to improve the overall catalytic performance and lifetime, the co-feeding of water constitutes a promising option, because of its abundance and nontoxicity. Although water’s (limited) positive influence on catalyst lifetime has earlier been exhibited, the exact course of action (like mechanism or the water effect on active sites) is yet to be established. To bridge this knowledge gap, in this work, we have performed an in-depth investigation to elucidate the effects of water co-feeding over a well-dispersed Mo/H-ZSM-5 catalyst by using an array of advanced characterization techniques (nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetry–temperature-programmed oxidation/mass spectroscopy (TG-TPO/MS), scanning transmission electron microscopy (STEM), N2 physisorption, Raman spectroscopy, inductively coupled plasma–optical emission spectroscopy (ICP-OES)). Our results demonstrate that the addition of water results in the occurrence of steam reforming (of both coke and methane) in parallel to MDA. Moreover, the presence of water affects the reducibility of Mo sites, as corroborated with computational analysis to examine the state and locality of Mo sites under various water levels and transformation of the catalyst structure during deactivation. We anticipate that our comprehensive study of the structure–function relationship on Mo/H-ZSM-5 under humid MDA conditions will be beneficial for the development of future methane valorization technologies.
  • Molecular Engineering of Covalent Organic Framework Cathodes for Enhanced Zinc-Ion Batteries

    Wang, Wenxi; Kale, Vinayak Swamirao; Cao, Zhen; Lei, Yougjiu; Kandambeth, Sharath; Zou, Guodong; Zhu, Yunpei; Abou-Hamad, Edy; Shekhah, Osama; Cavallo, Luigi; Eddaoudi, Mohamed; Alshareef, Husam N. (Advanced Materials, Wiley, 2021-08-08) [Article]
    Covalent organic frameworks (COFs) are potentially promising electrode materials for electrochemical charge storage applications thanks to their pre-designable reticular chemistry with atomic precision, allowing precise control of pore size, redox-active functional moieties, and stable covalent frameworks. However, studies on the mechanistic and practical aspects of their zinc-ion storage behavior are still limited. In this study, a strategy to enhance the electrochemical performance of COF cathodes in zinc-ion batteries (ZIBs) by introducing the quinone group into 1,4,5,8,9,12-hexaazatriphenylene-based COFs is reported. Electrochemical characterization demonstrates that the introduction of the quinone groups in the COF significantly pushes up the Zn2+ storage capability against H+ and elevates the average (dis-)charge potential in aqueous ZIBs. Computational and experimental analysis further reveals the favorable redox-active sites that host Zn2+/H+ in COF electrodes and the root cause for the enhanced electrochemical performance. This work demonstrates that molecular engineering of the COF structure is an effective approach to achieve practical charge storage performance.
  • Characterization of Silica-Supported Tungsten Bis- and Tris-hydrides by Advanced Solid-State NMR

    Wackerow, Wiebke; Thiam, Zeynabou; Abou-Hamad, Edy; Almaksoud, Walid; Hedhili, Mohamed N.; Basset, Jean-Marie (The Journal of Physical Chemistry C, American Chemical Society (ACS), 2021-06-03) [Article]
    Tungsten-hydrides supported on oxide supports are unique catalysts regarding the direct transformation of ethylene to propylene, alkane metathesis, and the low-temperature hydrogenolysis of waxes to lower molecular paraffins. The number of hydrides coordinated to the tungsten center and their structure on the siliceous support with very high surface silica (KCC-1) is unknown. KCC-1(700) silica of extremely high surface area allows for a high tungsten metal loading of 14 wt %. We show here the full characterization of supported tungsten bis- and tris-hydrides, which, after reaction with N2O gas, yield well-defined tungsten bis- and tris-hydroxide species on KCC-1(700). The obtained tungsten-hydroxide species are perfectly suitable for a detailed NMR study. The obtained tungsten hydroxo complexes are proven to be a tungsten bis-hydroxo and tungsten tris-hydroxo species. This analysis supports the conclusion that supported tungsten-hydride complexes coexist on the support as bis-hydride and tris-hydride species. They are, respectively, in close proximity to the silicon bis-hydride and the silicon mono-hydride. This proximity is explained by the mechanism of the formation of tungsten-hydride on the silica surface.
  • Emergence of Room Temperature Magnetotransport Anomaly in Epitaxial Pt/γ′-Fe4N/MgO Heterostructures toward Noncollinear Spintronics

    Shi, Xiaohui; Jiang, Jiawei; Wang, Yadong; Hou, Zhipeng; Zhang, Qiang; Mi, Wenbo; Zhang, Xixiang (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-05-27) [Article]
    Noncollinear spin textures have attracted much attention due to their novel physical behaviors in heavy/ferromagnetic metal (HM/FM) systems. The transport anomaly, appearing as contrast humps in Hall resistivity curves, is the mark of noncollinear spin textures. Here, the epitaxial Pt/γ'-Fe<sub>4</sub>N bilayers with noncollinear spin textures were obtained by facing target sputtering. Large micromagnetic Dzyaloshinskii-Moriya interaction coefficient <i>D</i> of 2.90 mJ/m<sup>2</sup> appears in Pt/γ'-Fe<sub>4</sub>N/MgO systems, which is larger than 2.05 mJ/m<sup>2</sup> of Pt/Co/MgO systems with skyrmionic states. Moreover, at 300 K, magnetic bubble-like domains appear in Pt/γ'-Fe<sub>4</sub>N bilayers that just possess a 3 nm thick ferromagnetic layer instead of [HM/FM]<i><sub>n</sub></i> or [HM<sub>1</sub>/FM/HM<sub>2</sub>]<i><sub>n</sub></i> multilayers. Additionally, a room-temperature transport anomaly appears in Pt/γ'-Fe<sub>4</sub>N/MgO systems. The contrast humps of Pt(3 nm)/γ'-Fe<sub>4</sub>N(<i>t</i><sub>Fe<sub>4</sub>N</sub> ≤ 4 nm)/MgO heterostructures are not sharp due to the nonuniform distributions of the magnetic bubble-like domains with various sizes and irregular shapes, as observed by the magnetic force microscopy. The discovery of epitaxial Pt/γ'-Fe<sub>4</sub>N bilayers with noncollinear spin states is more crucial than that of polycrystalline or amorphous HM/FM systems for reducing ohmic heating, which provides a candidate for noncollinear spintronic applications.
  • Microscopy techniques applied to submicron characterization of oilfield produced water

    Medina, Sandra Constanza; Anjum, Dalaver H.; Behzad, Ali Reza; Vilagines, Regis D.; Tabatabai, S. Assiyeh Alizadeh; Leiknes, TorOve (Journal of Petroleum Science and Engineering, Elsevier BV, 2021-05-26) [Article]
    Produced water (PW) and formation water are complex mixtures of hydrocarbons and water produced at oil and gas upstream facilities. Submicron oil droplets represent a multitude of issues affecting the performance of downstream advanced water treatment processes, such as micro and ultra-filtration processes. Conventional de-oiling technologies do not efficiently remove submicron oil droplets in PW. An accurate characterization of submicron oil droplets and contaminants is required to improve PW treatment technology. In this study, a methodology for visualization and quantification of submicron oil droplets size distribution (DSD), using optical and electron microscopy techniques, was developed. Various microscopy techniques were evaluated, including epifluorescence microscopy (EpiFM), confocal laser scanning microscopy (CLSM), cryogenic scanning and transmission electron microscopy (cryo-SEM and cryo-TEM, respectively). Synthetic PW was used to improve and standardize the sample preparation and characterization methodology. The improved methodology was then tested with two PW samples from different oilfields in the Middle East region. Two methods were developed for the determination of DSD in oilfield PW samples. The first method is suitable for highly polydisperse PW samples with oil droplets larger than 250 nm. This method is based on using low-temperature agarose to immobilize the samples, avoiding coalescence, and allowing clear visualization of the oil droplets at high magnification in EpiFM. The second method is suitable for concentrated PW samples and oil droplets as small as 20 nm in size. This method is based on cryo-TEM with plunge freezing and without the use of agarose for sample immobilization. The agarose-immobilization technique was also applied for sample preparation in cryo-SEM. Cryo-SEM fixation by high-pressure freezing (HPF) preserved the morphology of oil droplets in synthetic oil-concentrated samples and allowed its visualization in a wide range of sizes from 50 nm up to 20 μm.
  • Highly Active Heterogeneous Catalyst for Ethylene Dimerization Prepared by Selectively Doping Ni on the Surface of a Zeolitic Imidazolate Framework

    Chen, Cailing; Alalouni, Mohammed R.; Dong, Xinglong; Cao, Zhen; Cheng, Qingpeng; Zheng, Lirong; Meng, Lingkun; Guan, Chao; Liu, L. M.; Abou-Hamad, Edy; Wang, Jianjian; Shi, Zhan; Huang, Kuo-Wei; Cavallo, Luigi; Han, Yu (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-04-28) [Article]
    The production of 1-butene by ethylene dimerization is an important chemical industrial process currently implemented using homogeneous catalysts. Here, we describe a highly active heterogeneous catalyst (Ni-ZIF-8) for ethylene dimerization, which consists of isolating Ni-active sites selectively located on the crystal surface of a zeolitic imidazolate framework. Ni-ZIF-8 can be easily prepared by a simple one-pot synthesis method in which site-specific anchoring of Ni is achieved spontaneously because of the incompatibility between the d<sup>8</sup> electronic configuration of Ni<sup>2+</sup> and the three-dimensional framework of ZIF-8. The full exposure and square-planar coordination of the Ni sites accounts for the high catalytic activity of Ni-ZIF-8. It exhibits an average ethylene turnover frequency greater than 1 000 000 h<sup>-1</sup> (1-butene selectivity >85%) at 35 °C and 50 bar, far exceeding the activities of previously reported heterogeneous catalysts and many homogeneous catalysts under similar conditions. Moreover, compared to molecular Ni complexes used as homogeneous catalysts for ethylene dimerization, Ni-ZIF-8 has significantly higher stability and shows constant activity during 4 h of continuous reaction. Isotopic labeling experiments indicate that ethylene dimerization over Ni-ZIF-8 follows the Cossee-Arlman mechanism, and detailed characterizations combined with density functional theory calculations rationalize this observed high activity.
  • Synthesis and Characterization of Iron-Doped TiO2 Nanoparticles Using Ferrocene from Flame Spray Pyrolysis

    Ismail, Mohamed; Hedhili, Mohamed N.; Anjum, Dalaver H.; Singaravelu, Venkatesh; Chung, Suk Ho (Catalysts, MDPI AG, 2021-03-29) [Article]
    Iron-doped titanium dioxide nanoparticles, with Fe/Ti atomic ratios from 0% to 10%, were synthesized by flame spray pyrolysis (FSP), employing a single-step method. Ferrocene, being nontoxic and readily soluble in liquid hydrocarbons, was used as the iron source, while titanium tetraisopropoxide (TTIP) was used as the precursor for TiO2. The general particle characterization and phase description were examined using ICP-OES, XRD, BET, and Raman spectroscopy, whereas the XPS technique was used to study the surface chemistry of the synthesized particles. For particle morphology, HRTEM with EELS and EDS analyses were used. Optical and magnetic properties were examined using UV–vis and SQUID, respectively. Iron doping to TiO2 nanoparticles promoted rutile phase formation, which was minor in the pure TiO2 particles. Iron-doped nanoparticles exhibited a uniform iron distribution within the particles. XPS and UV–vis results revealed that Fe2+ was dominant for lower iron content and Fe3+ was common for higher iron content and the iron-containing particles had a contracted band gap of ~1 eV lower than pure TiO2 particles with higher visible light absorption. SQUID results showed that doping TiO2 with Fe changed the material to be paramagnetic. The generated nanoparticles showed a catalytic effect for dye-degradation under visible light.
  • Engineering Band-Type Alignment in CsPbBr 3 Perovskite-Based Artificial Multiple Quantum Wells

    Lee, Kwangjae; Merdad, Noor A.; Maity, Partha; El Demellawi, Jehad K.; Lui, Zhixiong; Sinatra, Lutfan; Zhumekenov, Ayan A.; Hedhili, Mohamed N.; Min, Jung-Wook; Min, Jung-Hong; Gutierrez Arzaluz, Luis; Anjum, Dalaver H.; Wei, Nini; Ooi, Boon S.; Alshareef, Husam N.; Mohammed, Omar F.; Bakr, Osman (Advanced Materials, Wiley, 2021-03-24) [Article]
    Semiconductor heterostructures of multiple quantum wells (MQWs) have major applications in optoelectronics. However, for halide perovskites—the leading class of emerging semiconductors—building a variety of bandgap alignments (i.e., band-types) in MQWs is not yet realized owing to the limitations of the current set of used barrier materials. Here, artificial perovskite-based MQWs using 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole), tris-(8-hydroxyquinoline)aluminum, and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline as quantum barrier materials are introduced. The structures of three different five-stacked perovskite-based MQWs each exhibiting a different band offset with CsPbBr3 in the conduction and valence bands, resulting in a variety of MQW band alignments, i.e., type-I or type-II structures, are shown. Transient absorption spectroscopy reveals the disparity in charge carrier dynamics between type-I and type-II MQWs. Photodiodes of each type of perovskite artificial MQWs show entirely different carrier behaviors and photoresponse characteristics. Compared with bulk perovskite devices, type-II MQW photodiodes demonstrate a more than tenfold increase in the rectification ratio. The findings open new opportunities for producing halide-perovskite-based quantum devices by bandgap engineering using simple quantum barrier considerations.
  • Rapid fabrication of MOF-based mixed matrix membranes through digital light processing

    Pustovarenko, Alexey; Seoane, Beatriz; Abou-Hamad, Edy; King, Helen E.; Weckhuysen, Bert M.; Kapteijn, Freek; Gascon, Jorge (Materials Advances, Royal Society of Chemistry (RSC), 2021-03-09) [Article]
    3D printing, also known as additive manufacturing technology, has greatly expanded across multiple sectors of technology replacing classical manufacturing methods by combining processing speed and high precision. The scientific interest in this technology lies in the ability to create solid architectures with customized shapes and predetermined properties through the exploration of formulations enriched with multifunctional microporous additives such as metal-organic frameworks (MOFs). The concept of additive manufacturing involving advanced materials could be fruitfully adapted for MOF-based mixed matrix membrane fabrication to be used in gas separation applications. In this work, a digital light processing (DLP) approach for fast prototyping of MOF-based mixed matrix membranes (MOF-MMMs) with full control over the shape, size and thickness of the resulting composite using a conventionally available 3D printer has been explored. MOF-based printable inks have been formulated from a selection of commercially available acrylate oligomers and MIL-53(Al)-NH2 additive post-synthetically modified with methacrylic functionality. The formulations and resulting composites have been extensively characterized to demonstrate the suitability of the inks for DLP processing into free-standing MOF-based membranes. The MOF filler anchored to the polymeric matrix enhances the overall permeability at constant selectivity when applied for H2/CO2 separation. The obtained results confirm the applicability of the 3D DLP technology for fast prototyping of MOF-based MMMs and provide new opportunities for further development.
  • Highly efficient transverse-electric-dominant ultraviolet-C emitters employing GaN multiple quantum disks in AlN nanowire matrix

    Subedi, Ram Chandra; Min, Jung Wook; Mitra, Somak; Li, Kuang Hui; Ajia, Idris A.; Stegenburgs, Edgars; Anjum, Dalaver H.; Conroy, Michele; Moore, Kalani; Bangert, Ursel; Roqan, Iman S.; Ng, Tien Khee; Ooi, Boon S. (SPIE, 2021-03-05) [Conference Paper]
    Heavy reliance on extensively studied AlGaN based light emitting diodes (LEDs) to replace environmentally hazardous mercury based ultraviolet (UV) lamps is inevitable. However, external quantum efficiency (EQE) for AlGaN based deep UV emitters remains poor. Dislocation induced nonradiative recombination centers and poor electron-hole wavefunction overlap due to the large polarization field induced quantum confined stark effect (QCSE) in "Al"rich AlGaN are some of the key factors responsible for poor EQE. In addition, the transverse electric polarized light is extremely suppressed in "Al"-rich AlGaN quantum wells (QWs) because of the undesired crossing over among the light hole (LH), heavy hole (HH) and crystal-field split-off (SH) states. Here, optical and structural integrities of dislocation-free ultrathin GaN quantum disk (QDisk) (∼ 1.2 nm) embedded in AlN barrier (∼ 3 nm) grown employing plasma-assisted molecular beam epitaxy (PAMBE) are investigated considering it as a novel nanostructure to realize highly efficient TE polarized deep UV emitters. The structural and chemical integrities of thus grown QDisks are investigated by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). We, particularly, emphasize the polarization dependent photoluminescence (PL) study of the GaN Disks to accomplish almost purely TE polarized UV (∼ 260 nm) light. In addition, we observed significantly high internal quantum efficiency (IQE) of ∼ 80 %, which is attributed to the enhanced overlap of the electron-hole wavefunction in extremely quantum confined ultrathin GaN QDisks, thereby presenting GaN QDisks embedded in AlN nanowires as a practical pathway towards the efficient deep UV emitters.
  • The Importance of Thermal Treatment on Wet-Kneaded Silica–Magnesia Catalyst and Lebedev Ethanol-to-Butadiene Process

    Chung, Sang-Ho; Galilea, Adrian; Shoinkhorova, Tuiana; Mukhambetov, Ildar; Abou-Hamad, Edy; Telalovic, Selevedin; Gascon, Jorge; Ruiz-Martinez, Javier (Nanomaterials, MDPI AG, 2021-02-26) [Article]
    The Lebedev process, in which ethanol is catalytically converted into 1,3-butadiene, is an alternative process for the production of this commodity chemical. Silica–magnesia (SiO2–MgO) is a benchmark catalyst for the Lebedev process. Among the different preparation methods, the SiO2–MgO catalysts prepared by wet-kneading typically perform best owing to the surface magnesium silicates formed during wet-kneading. Although the thermal treatment is of pivotal importance as a last step in the catalyst preparation, the effect of the calcination temperature of the wet-kneaded SiO2–MgO on the Lebedev process has not been clarified yet. Here, we prepared and characterized in detail a series of wet-kneaded SiO2–MgO catalysts using varying calcination temperatures. We find that the thermal treatment largely influences the type of magnesium silicates, which have different catalytic properties. Our results suggest that the structurally ill-defined amorphous magnesium silicates and lizardite are responsible for the production of ethylene. Further, we argue that forsterite, which has been conventionally considered detrimental for the formation of ethylene, favors the formation of butadiene, especially when combined with stevensite.
  • One-step conversion of crude oil to light olefins using a multi-zone reactor

    Alabdullah, Mohammed A.; Rodriguez Gomez, Alberto; Shoinkhorova, Tuiana; Dikhtiarenko, Alla; Chowdhury, Abhishek Dutta; Hita, Idoia; Kulkarni, Shekhar Rajabhau; Vittenet, Jullian; Sarathy, Mani; Castaño, Pedro; Bendjeriou-Sedjerari, Anissa; Abou-Hamad, Edy; Zhang, Wen; Ali, Ola S.; Morales-Osorio, Isidoro; Xu, Wei; Gascon, Jorge (Nature Catalysis, Springer Nature, 2021-02-25) [Article]
    With the demand for gasoline and diesel expected to decline in the near future, crude-to-chemicals technologies have the potential to become the most important processes in the petrochemical industry. This trend has triggered intense research to maximize the production of light olefins and aromatics at the expense of fuels, which calls for disruptive processes able to transform crude oil to chemicals in an efficient and environmentally friendly way. Here we propose a catalytic reactor concept consisting of a multi-zone fluidized bed that is able to perform several refining steps in a single reactor vessel. This configuration allows for in situ catalyst stripping and regeneration, while the incorporation of silicon carbide in the catalyst confers it with improved physical, mechanical and heat-transport properties. As a result, this reactor–catalyst combination has shown stable conversion of untreated Arabian Light crude into light olefins with yields per pass of over 30 wt% with a minimum production of dry gas.
  • Ultra-thin dark amorphous TiOx hollow nanotubes for full spectrum solar energy harvesting and conversion‡

    Liu, Youhai; Song, Haomin; Bei, Zongmin; Zhou, Lyu; Zhao, Chao; Ooi, Boon S.; Gan, Qiaoqiang (Nano Energy, Elsevier BV, 2021-02-15) [Article]
    Dark titania (TiOx) have been widely used for solar energy harvesting and conversion applications due to its excellent light absorbing performance throughout the ultraviolet to near infrared wavelength band, low cost, and non-toxic nature. However, the synthesis methods of dark TiOx are usually complicated and time-consuming. Here we report a facile and rapid method to fabricate dark amorphous TiOx (am-TiOx) hollow nanotube arrays on nanoporous anodic alumina oxide (AAO) templates using atomic layer deposition. Systematic investigation was performed to demonstrate that Ti3+ and O- species in the am-TiOx ultra-thin films, as well as the spatial distribution of these am-TiOx ultra-thin films on the vertical side walls of AAO templates are two major mechanisms of the black color. Importantly, the film deposition took ~18 min only to produce the optimized ~4-nm-thick am-TiOx film. Representative applications were demonstrated using photocatalytic reduction of silver nitrate and photothermal solar vapor generation, revealing the potential of these ultra-thin dark am-TiOx/AAO structures for full spectrum solar energy harvesting and conversion.
  • Fresh insights into detonation nanodiamond aggregation: An X-ray photoelectron spectroscopy, thermogravimetric analysis, and nuclear magnetic resonance study

    Katsiev, Khabiboulakh; Solovyeva, Vera; Mahfouz, Remi; Abou-Hamad, Edy; Peng, Wei; Idriss, Hicham; Kirmani, Ahmad R. (Engineering Reports, Wiley, 2021-02-03) [Article]
    Detonation nanodiamonds (DNDs) are known to be produced in aggregated clusters of a few nanometer-sized primary crystalline particles embedded in an amorphous carbon matrix exhibiting high degree of polydispersity. A commonly accepted mechanism behind DND aggregation is the bridging of primary particles via oxygen containing functionalities. Here, we provide definitive spectroscopic evidence in favor of this working mechanism by carrying out systematic chemical compositional analysis on monodispersed DND aggregates of various sizes. Oxygen content is found to increase proportionally with the aggregate size confirming the role of oxygen containing functionalities as a cross-linker. Solid-state nuclear magnetic resonance data confirms these linkers to be of ether (COC) nature. Our results imply that oxygen content in DNDs can be independently tuned by varying the aggregate size, a knowledge which might benefit other applications, in addition. Next, we use this understanding to engineer the DND surfaces via an acid hydrolysis step to strip off these oxygen functionalities leading to size reduction of ca. 150 nm as-received DND aggregates to ca. 40 nm with >90% yields, without resorting to any other pre- or post-hydrolysis treatment such as surface functionalization or milling.
  • Ultrafast Energy Transfer Triggers Ionization Energy Offset Dependence of Quantum Efficiency in Low-bandgap Non-fullerene Acceptor Solar Cells

    Gorenflot, Julien; Laquai, Frédéric; Firdaus, Yuliar; De Castro, Catherine S. P.; Harrison, George; Khan, Jafar Iqbal; Markina, Anastasia; Balawi, Ahmed; Dela Peña, Top Archie; Liu, Wenlan; Liang, Ru-Ze; Sharma, Anirudh; Karuthedath, Safakath; Zhang, Weimin; Lin, Yuanbao; Alarousu, Erkki; Anjum, Dalaver H.; Beaujuge, Pierre; De Wolf, Stefaan; McCulloch, Iain; Anthopoulos, Thomas D.; Baran, Derya; Andrienko, Denis; Paleti, Sri Harish Kumar (Fundació Scito, 2021-01-25) [Presentation]
    In bulk heterojunction (BHJ) solar cells, the heterojunction interface between electron donor and acceptor drives the exciton-to-charge conversion, yet it also adds to energy and carrier losses. In principle, in low-bandgap non-fullerene acceptor (NFA) BHJs both electron affinity (EA) and ionization energy (IE) offsets should equally control the internal quantum efficiency (IQE). Allegedly, exciton-to-charge conversion is efficient even for close-to-zero offsets. Here, we rebut both notions and demonstrate that counterintuitively, the charge transfer from the exciton rather than the further charge separation is the limiting step controlled by the IE offset and secondly, that sizeable IE offsets are required to reach high exciton-to charge conversion efficiency. We find that efficient Förster Resonant Energy Transfer to the low bandgap acceptor precedes the charge transfer, which thus always occurs via hole transfer from the acceptor, hence the unimportance of the EA offset. We discuss the reasons for the threshold IE offset in terms of interface energetics and find that two physical parameters are sufficient to describe the evolution of the IQE with IE offset on a very large range of material systems. Our model also explain other experimental observations such as the difficulty of observing CT states emission and absorption in NFA based systems.
  • Charge-Storage Mechanism of Aluminum-Sulfur Batteries

    Smajic, Jasmin; Wee, Shianlin; Fernandes Simoes, Filipa R.; Hedhili, Mohamed N.; Wehbe, Nimer; Abou-Hamad, Edy; Da Costa, Pedro M. F. J. (ECS Meeting Abstracts, The Electrochemical Society, 2020-11-23) [Article]
    The electrochemical performance of aluminum-sulfur batteries is beset by poor stability and sluggish charge-storage properties. To address these issues, carbon allotropes have been used as electrode fillers, but successful outcomes remain inexplicably elusive. Here, a composite of sulfur and small diameter single-walled carbon nanotubes is synthesized and used as a cathode for reversible aluminum-sulfur batteries. The assembled electrode delivers a high capacity of 1024 mAh/g and effectively reduces the cell polarization by 37%. Moreover, the use of small-diameter SWCNT helps in lowering the electrolyte-to-sulfur ratio down to 17 μg/ml, an important step toward lean electrolyte conditions. Despite that, the capacity fade of the Al-S battery cannot be fully reversed. As we show, the consequence of the interaction between the electrolyte and S is the buildup of insoluble and poorly conductive discharge products, which inhibit charge diffusion and progressively deactivate the electrode, ultimately causing capacity decay. Overall, this works clarifies the carbon–sulfur–electrolyte interactions and their role in the underlying charge-storage mechanism of Al-S batteries.
  • Cyclized polyacrylonitrile anode for alkali metal ion batteries

    Zhang, Wenli; Sun, Minglei; Yin, Jian; Abou-Hamad, Edy; Schwingenschlögl, Udo; Da Costa, Pedro M. F. J.; Alshareef, Husam N. (Angewandte Chemie International Edition, Wiley, 2020-11-16) [Article]
    Alkali metal (Li, Na, and K) ion batteries are vital in portable and large-scale stationary energy storage. Recently, organic anodes have attracted increasing attention for alkali metal ion batteries due to their chemical diversity and potential high capacity. In this work, we discovered that cyclized polyacrylonitrile (cPAN) can serve as a superior anode for alkali metal ion batteries. Remarkably, upon activation cycling, as an anode of lithium-ion battery, cPAN exhibits a reversible capacity as high as 1238 mAh g-1 under a current density of 50 mA g-1. Based on electrochemical experiments and first-principles calculations, it is demonstrated that the hexagonal carbon ring, piperidine ring, and pyridine nitrogen in ladder cPAN are the main active sites for lithium-ion storage. In addition, we show that cPAN displays a unique potential-dependent solid electrolyte interphase formation from 0.1 to 0.01 V vs. Li/Li+. Furthermore, cPAN displays decent performance as an anode in SIBs and PIBs. The discovery of cPAN anode could pave the way for the future development of organic anodes for alkali metal ion batteries.
  • Active and stable Fe-based catalyst, mechanism, and key role of alkali promoters in ammonia synthesis

    Almaksoud, Walid; Rai, Rohit Kumar; Morlanes, Natalia Sanchez; Harb, Moussab; Ahmad, Rafia; Ould-Chikh, Samy; Anjum, Dalaver H.; Hedhili, Mohamed N.; Al-Sabban, Bedour E.; Albahily, Khalid; Cavallo, Luigi; Basset, Jean-Marie (Journal of Catalysis, Elsevier BV, 2020-11-13) [Article]
    Worldwide NH3 production reached 0.18 Gton in 2019, and 1-2 % of the global CO2 emissions are due to large-scale NH3 synthesis (1 billion tons of CO2 / year). A catalyst for ammonia synthesis has been obtained by pyrolysis of iron phthalocyanine (FePc) precursor under N2, followed by impregnation with alkali metals (Na, Li, K, and Cs) and H2 treatment. Characterization (XPS, XRD, HR-TEM, ICP-OES, TGA, CHNS analysis, and BET) revealed nano-sized core-shell structures formed during H2 treatment, with Fe in the core and promoters (“Cs2O” and “K2O”) with carbon on the shell. The alkali metals partially inhibit the methanation process of carbon. These Fe NPs were found to be very active and stable catalysts, as compared to the commercial iron-based catalyst KM1 (Haldor-Topsoe). Activities of promoted catalysts follow the order: K>Cs>Na∼Li, with more than 6% of NH3 at 400 °C and 7 MPa, and contact time (WHSV) of 12000 ml.g-1.h-1 with K. The apparent activation energy was found to be 31 kJ.mol-1 and 34 kJ.mol-1 for 3-K-FePc700 and 10-Cs-FePc700 suggesting the facile activation of N2 on the catalysts surface. DFT-based predicted atomic and electronic structures reveal a similarity in the partial charge distribution on surface Fe species with K or Cs. Surprisingly the main effect of alkali is related to the geometrical repartition of alkali, leading to a larger number of exposed iron atoms, active sites, in the case of K than Cs. The alkali (present as metal oxide) leaves at medium coverage of the surface some exposed Fe(0) for N2 non-dissociative chemisorption (end-on type). The free energy profile demonstrates that the thermodynamic stability of the reaction intermediates for nitrogen reduction reaction (NRR) increases with pressure indicating better feasibility of the reaction at higher pressures.
  • Intrinsic efficiency limits in low-bandgap non-fullerene acceptor organic solar cells

    Karuthedath, Safakath; Gorenflot, Julien; Firdaus, Yuliar; Chaturvedi, Neha; De Castro, Catherine S. P.; Harrison, George T.; Khan, Jafar Iqbal; Markina, Anastasia; Albalawi, Ahmed; Peña, Top Archie Dela; Liu, Wenlan; Liang, Ru-Ze; Sharma, Anirudh; Paleti, Sri Harish Kumar; Zhang, Weimin; Lin, Yuanbao; Alarousu, Erkki; Anjum, Dalaver H.; Beaujuge, Pierre; De Wolf, Stefaan; McCulloch, Iain; Anthopoulos, Thomas D.; Baran, Derya; Andrienko, Denis; Laquai, Frédéric (Nature Materials, Springer Nature, 2020-10-23) [Article]
    In bulk heterojunction (BHJ) organic solar cells (OSCs) both the electron affinity (EA) and ionization energy (IE) offsets at the donor–acceptor interface should equally control exciton dissociation. Here, we demonstrate that in low-bandgap non-fullerene acceptor (NFA) BHJs ultrafast donor-to-acceptor energy transfer precedes hole transfer from the acceptor to the donor and thus renders the EA offset virtually unimportant. Moreover, sizeable bulk IE offsets of about 0.5 eV are needed for efficient charge transfer and high internal quantum efficiencies, since energy level bending at the donor–NFA interface caused by the acceptors’ quadrupole moments prevents efficient exciton-to-charge-transfer state conversion at low IE offsets. The same bending, however, is the origin of the barrier-less charge transfer state to free charge conversion. Our results provide a comprehensive picture of the photophysics of NFA-based blends, and show that sizeable bulk IE offsets are essential to design efficient BHJ OSCs based on low-bandgap NFAs.

View more