| 1. |
- Najafi, Leyla, et al.
(författare)
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Microwave-Induced Structural Engineering and Pt Trapping in 6R-TaS2 for the Hydrogen Evolution Reaction
- 2020
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 16:50
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Tidskriftsartikel (refereegranskat)abstract
- The nanoengineering of the structure of transition metal dichalcogenides (TMDs) is widely pursued to develop viable catalysts for the hydrogen evolution reaction (HER) alternative to the precious metallic ones. Metallic group-5 TMDs have been demonstrated to be effective catalysts for the HER in acidic media, making affordable real proton exchange membrane water electrolysers. Their key-plus relies on the fact that both their basal planes and edges are catalytically active for the HER. In this work, the 6R phase of TaS2 is "rediscovered" and engineered. A liquid-phase microwave treatment is used to modify the structural properties of the 6R-TaS2 nanoflakes produced by liquid-phase exfoliation. The fragmentation of the nanoflakes and their evolution from monocrystalline to partly polycrystalline structures improve the HER-activity, lowering the overpotential at cathodic current of 10 mA cm(-2) from 0.377 to 0.119 V. Furthermore, 6R-TaS2 nanoflakes act as ideal support to firmly trap Pt species, which achieve a mass activity (MA) up 10 000 A g(Pt)(-1) at overpotential of 50 mV (20 000 A g(Pt)(-1) at overpotentials of 72 mV), representing a 20-fold increase of the MA of Pt measured for the Pt/C reference, and approaching the state-of-the-art of the Pt mass activity.
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| 2. |
- Najafi, Leyla, et al.
(författare)
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Topochemical Transformation of Two-Dimensional VSe2 into Metallic Nonlayered VO2 for Water Splitting Reactions in Acidic and Alkaline Media
- 2022
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 16:1, s. 351-367
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Tidskriftsartikel (refereegranskat)abstract
- The engineering of the structural and morphological properties of nanomaterials is a fundamental aspect to attain desired performance in energy storage/conversion systems and multifunctional composites. We report the synthesis of room temperature-stable metallic rutile VO2 (VO2 (R)) nanosheets by topochemically transforming liquid-phase exfoliated VSe2 in a reductive Ar-H2 atmosphere. The asproduced VO2 (R) represents an example of two-dimensional (2D) nonlayered materials, whose bulk counterparts do not have a layered structure composed by layers held together by van der Waals force or electrostatic forces between charged layers and counterbalancing ions amid them. By pretreating the VSe2 nanosheets by O-2 plasma, the resulting 2D VO2 (R) nanosheets exhibit a porous morphology that increases the material specific surface area while introducing defective sites. The assynthesized porous (holey)-VO2 (R) nanosheets are investigated as metallic catalysts for the water splitting reactions in both acidic and alkaline media, reaching a maximum mass activity of 972.3 A g(-1) at -0.300 V vs RHE for the hydrogen evolution reaction (HER) in 0.5 M H2SO4 (faradaic efficiency = 100%, overpotential for the HER at 10 mA cm(-2) = 0.184 V) and a mass activity (calculated for a non 100% faradaic efficiency) of 745.9 A g(-1) at +1.580 V vs RHE for the oxygen evolution reaction (OER) in 1 M KOH (overpotential for the OER at 10 mA cm(-2) = 0.209 V). By demonstrating proof-of-concept electrolyzers, our results show the possibility to synthesize special material phases through topochemical conversion of 2D materials for advanced energy-related applications.
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| 3. |
- Najafi, Leyla, et al.
(författare)
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Transition metal dichalcogenides as catalysts for the hydrogen evolution reaction : The emblematic case of "inert" ZrSe2 as catalyst for electrolyzers
- 2022
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Ingår i: Nano Select. - : Wiley-VCH Verlagsgesellschaft. - 2688-4011. ; 3:6, s. 1069-1081
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Tidskriftsartikel (refereegranskat)abstract
- The development of earth-abundant electrocatalysts (ECs) operating at high current densities in water splitting electrolyzers is pivotal for the widespread use of the current green hydrogen production plants. Transition metal dichalcogenides (TMDs) have emerged as promising alternatives to the most efficient noble metal ECs, leading to a wealth of research. Some strategies based on material nanostructuring and hybridization, introduction of defects and chemical/physical modifications appeared as universal approaches to provide catalytic properties to TMDs, regardless of the specific material. In this work, we show that even a theoretically poorly catalytic (and poorly studied) TMD, namely zirconium diselenide (ZrSe2), can act as an efficient EC for the hydrogen evolution reaction (HER) when exfoliated in the form of two-dimensional (2D) few-layer flakes. We critically show the difficulties of explaining the catalytic mechanisms of the resulting ECs in the presence of complex structural and chemical modifications, which are nevertheless evaluated extensively. By doing so, we also highlight the easiness of transforming 2D TMDs into effective HER-ECs. To strengthen our message in practical environments, we report ZrSe2-based acidic (proton exchange membrane [PEM]) and alkaline water electrolyzers operating at 400 mA cm–2 at a voltage of 1.88 and 1.92 V, respectively, thus competing with commercial technologies.
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