| 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. |
- Palei, Milan, et al.
(författare)
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Photoluminescence enhancement and high accuracy patterning of lead halide perovskite single crystals by MeV ion beam irradiation
- 2020
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 8:29, s. 9923-9930
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Tidskriftsartikel (refereegranskat)abstract
- Focused ion beam (FIB) has recently been used to tune the optical properties of lead halide perovskites (LHPs), opening an interesting avenue for applications in optoelectronic devices. However, it has remained an open question to date whether FIB can be used to locally enhance the photoluminescence (PL) of LHPs. In this work we irradiate MAPbBr(3)(MA = methylammonium) single crystals with a high energy micron-sized ion probe of different ionic masses (3 MeV He+, 12.5 MeV Br5+, and 20 MeV I7+) and study the PL as a function of the damage induced by the ion beam. We find that at low damage levels the PL is enhanced about six times with respect to the pristine material, while increasing the damage level produces a progressive PL decrease, and, above a threshold, the PL is finally quenched below the value of the pristine crystal. We attribute this behavior to the interaction of free carriers with irradiation induced surface defects: at low damage levels the migration of carriers toward the bulk is inhibitedviatrapping-detrapping events at surface defects, allowing their radiative recombination near the surface; at higher damage, though, the probability for non-radiative recombination increases and gradually becomes dominant. We thus present a method to locally increase the PL of bulk LHP, which could be applied in a wide range of fields, such as highly sensitive ion beam detection or future optoelectronic device design.
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| 3. |
- 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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