| 1. |
- Bellani, Sebastiano, et al.
(författare)
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Graphene-Based Electrodes in a Vanadium Redox Flow Battery Produced by Rapid Low-Pressure Combined Gas Plasma Treatments
- 2021
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 33:11, s. 4106-4121
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Tidskriftsartikel (refereegranskat)abstract
- The development of high-power density vanadium redox flow batteries (VRFBs) with high energy efficiencies (EEs) is crucial for the widespread dissemination of this energy storage technology. In this work, we report the production of novel hierarchical carbonaceous nanomaterials for VRFB electrodes with high catalytic activity toward the vanadium redox reactions (VO2+/VO2+ and V2+/V3+). The electrode materials are produced through a rapid (minute timescale) low-pressure combined gas plasma treatment of graphite felts (GFs) in an inductively coupled radio frequency reactor. By systematically studying the effects of either pure gases (O-2 and N-2) or their combination at different gas plasma pressures, the electrodes are optimized to reduce their kinetic polarization for the VRFB redox reactions. To further enhance the catalytic surface area of the electrodes, single-/fewlayer graphene, produced by highly scalable wet-jet milling exfoliation of graphite, is incorporated into the GFs through an infiltration method in the presence of a polymeric binder. Depending on the thickness of the proton-exchange membrane (Nafion 115 or Nafion XL), our optimized VRFB configurations can efficiently operate within a wide range of charge/discharge current densities, exhibiting energy efficiencies up to 93.9%, 90.8%, 88.3%, 85.6%, 77.6%, and 69.5% at 25, 50, 75, 100, 200, and 300 mA cm(-2), respectively. Our technology is cost-competitive when compared to commercial ones (additional electrode costs < 100 (sic) m(-2)) and shows EEs rivalling the record-high values reported for efficient systems to date. Our work remarks on the importance to study modified plasma conditions or plasma methods alternative to those reported previously (e.g., atmospheric plasmas) to improve further the electrode performances of the current VRFB systems.
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| 2. |
- Beydaghi, Hossein, et al.
(författare)
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Functionalized metallic transition metal dichalcogenide (TaS2) for nanocomposite membranes in direct methanol fuel cells
- 2021
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 9:10, s. 6368-6381
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we designed a novel nanocomposite proton-exchange membrane (PEM) based on sulfonated poly(ether ether ketone) (SPEEK) and tantalum disulfide functionalized with terminal sulfonate groups (S-TaS2). The PEMs are prepared through a solution-casting method and exploited in direct methanol fuel cells (DMFCs). Two-dimensional S-TaS2 nanoflakes were prepared as a functional additive to produce the novel nanocomposite membrane for DMFCs due to their potential as a fuel barrier and an excellent proton conductor. To optimize the degree of sulfonation (DS) of SPEEK and the weight percentage (wt%) of S-TaS2 nanoflakes in PEMs, we used the central composite design of the response surface method. The optimum PEM was obtained for SPEEK DS of 1.9% and a weight fraction (wt%) of S-TaS2 nanoflakes of 70.2%. The optimized membrane shows a water uptake of 45.72%, a membrane swelling of 9.64%, a proton conductivity of 96.24 mS cm(-1), a methanol permeability of 2.66 x 10(-7) cm(2) s(-1), and a selectivity of 36.18 x 10(4) S s cm(-3). Moreover, SPEEK/S-TaS2 membranes show superior thermal and chemical stabilities compared to those of pristine SPEEK. The DMFC fabricated with the SPEEK/S-TaS2 membrane has reached the maximum power densities of 64.55 mW cm(-2) and 161.18 mW cm(-2) at 30 degrees C and 80 degrees C, respectively, which are similar to 78% higher than the values obtained with the pristine SPEEK membrane. Our results demonstrate that SPEEK/S-TaS2 membranes have a great potential for DMFC applications.
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| 3. |
- Chatzimanolis, Konstantinos, et al.
(författare)
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Inverted perovskite solar cells with enhanced lifetime and thermal stability enabled by a metallic tantalum disulfide buffer layer
- 2021
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry. - 2516-0230. ; 3:11, s. 3124-3135
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite solar cells (PSCs) have proved their potential for delivering high power conversion efficiencies (PCE) alongside low fabrication cost and high versatility. The stability and the PCE of PSCs can readily be improved by implementing engineering approaches that entail the incorporation of two-dimensional (2D) materials across the device's layered configuration. In this work, two-dimensional (2D) 6R-TaS2 flakes were exfoliated and incorporated as a buffer layer in inverted PSCs, enhancing the device's PCE, lifetime and thermal stability. A thin buffer layer of 6R-TaS2 flakes was formed on top of the electron transport layer to facilitate electron extraction, thus improving the overall device performance. The optimized devices reach a PCE of 18.45%, representing a 12% improvement compared to the reference cell. The lifetime stability measurements of the devices under ISOS-L2, ISOS-D1, ISOS-D1I and ISOS-D2I protocols revealed that the TaS2 buffer layer retards the intrinsic, thermally activated degradation processes of the PSCs. Notably, the devices retain more than the 80% of their initial PCE over 330 h under continuous 1 Sun illumination at 65 degrees C.
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| 4. |
- Najafi, Leyla, et al.
(författare)
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Hybrid Organic/Inorganic Photocathodes Based on WS2 Flakes as Hole Transporting Layer Material
- 2021
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Ingår i: Small Structures. - : John Wiley & Sons. - 2688-4062. ; 2:3
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Tidskriftsartikel (refereegranskat)abstract
- The efficient production of molecular hydrogen (H2) is a fundamental step toward an environmentally friendly economy. Photocathodes using organic bulk heterojunction (BHJ) films as light harvesters represent an attracting technology for low-cost photoelectrochemical water splitting. These photocathodes need charge transporting layers (CTLs) to efficiently separate and transport either holes or electrons toward the back-current collector and electrolyte, respectively. Therefore, it is pivotal to control the energy band edge levels and the work function (WF) of the CTLs to match the ones of the BHJ film, current collector, and electrolyte. Herein, the use of 2D p-doped WS2 flakes as hole transporting material for H2-evolving photocathodes based on the regioregular poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (rr-P3HT:PCBM) BHJ film is proposed. The WS2 flakes are produced through scalable liquid-phase exfoliation of the bulk crystal, whereas p-type chemical doping allows the tuning of the WS2 WF. This approach boosts the performances of the photocathodes, reaching photocurrent densities up to 4.14 mA cm−2 at 0 V versus reversible hydrogen electrode (RHE), an onset potential of 0.66 V versus RHE, and a ratiometric power-saved metric of 1.28% (under 1 sun illumination). To the best of the authors' knowledge, these performances represent the current record for 2D materials-based CTLs.
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| 5. |
- Zappia, Marilena, I, et al.
(författare)
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Two-Dimensional Gallium Sulfide Nanoflakes for UV-Selective Photoelectrochemical-type Photodetectors
- 2021
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:22, s. 11857-11866
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) transition-metal monochalcogenides have been recently predicted to be potential photo(electro)catalysts for water splitting and photoelectrochemical (PEC) reactions. Differently from the most established InSe, GaSe, GeSe, and many other monochalcogenides, bulk GaS has a large band gap of similar to 2.5 eV, which increases up to more than 3.0 eV with decreasing its thickness due to quantum confinement effects. Therefore, 2D GaS fills the void between 2D small-band-gap semiconductors and insulators, resulting of interest for the realization of van der Waals type-I heterojunctions in photocatalysis, as well as the development of UV light-emitting diodes, quantum wells, and other optoelectronic devices. Based on theoretical calculations of the electronic structure of GaS as a function of layer number reported in the literature, we experimentally demonstrate, for the first time, the PEC properties of liquid-phase exfoliated GaS nanoflakes. Our results indicate that solution-processed 2D GaS-based PEC-type photodetectors outperform the corresponding solid-state photodetectors. In fact, the 2D morphology of the GaS flakes intrinsically minimizes the distance between the photogenerated charges and the surface area at which the redox reactions occur, limiting electron-hole recombination losses. The latter are instead deleterious for standard solidstate configurations. Consequently, PEC-type 2D GaS photodetectors display a relevant UV-selective photoresponse. In particular, they attain responsivities of 1.8 mA W-1 in 1 M H2SO4 [at 0.8 V vs reversible hydrogen electrode (RHE)], 4.6 mA W-1 in 1 M Na2SO4 (at 0.9 V vs RHE), and 6.8 mA W--(1) in 1 M KOH (at 1.1. V vs RHE) under 275 nm illumination wavelength with an intensity of 1.3 mW cm(-2). Beyond the photodetector application, 2D GaS-based PEC-type devices may find application in tandem solar PEC cells in combination with other visible-sensitive low-band-gap materials, including transition-metal monochalcogenides recently established for PEC solar energy conversion applications.
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