| 1. |
- Araujo, Rafael B., et al.
(författare)
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Predicting electrochemical properties and ionic diffusion in Na2+2xMn2-x(SO4)(3) : crafting a promising high voltage cathode material
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 4:2, s. 451-457
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Tidskriftsartikel (refereegranskat)abstract
- Sodium ion batteries have emerged as a good alternative to lithium based systems due to their low cost of production. In this scenario, the search for higher voltage, sodium cathodes results in a new promising alluaudite structure Na2+2xMn2-x(SO4)(3). The structural, electronic and Na diffusion properties along with defects have been reported in this investigation within the framework of density functional theory. A band gap of 3.61 eV has been computed and the average deintercalation potential is determined to be 4.11 V vs. Na/Na+. A low concentration of anti-site defects is predicted due to their high formation energy. The biggest issue for the ionic diffusion in the Na2+2xMn2-x(SO4)(3) crystal structure is revealed to be the effect of Mn vacancies increasing the activation energy of Na+ ions that hop along the [001] equilibrium positions. This effect leads to activation energies of almost the same high values for the ionic hop through the [010] direction characterizing a 2D like ionic diffusion mechanism in this system.
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| 2. |
- Banerjee, Amitava, et al.
(författare)
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Bromination-induced stability enhancement with a multivalley optical response signature in guanidinium [C(NH2)(3)](+)-based hybrid perovskite solar cells
- 2017
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 5:35, s. 18561-18568
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Tidskriftsartikel (refereegranskat)abstract
- Guanidinium lead iodide (GAPbI(3)) has been synthesized experimentally, but stability remains an issue, which can be modulated by the insertion of bromine (Br) into the system. We have performed a systematic theoretical investigation to see how bromination can tune the stability of GAPbI(3). The optical properties were also determined, and we have found formation enthalpy-based stability in the perovskite systems, which are active in the visible and IR region even after bromine insertion and additionally more active in the IR range with the transition from GAPbI(3) to GAPbBr(3). The spin orbit coupling effect is considered throughout the band structure calculations. The ensemble of the primary and secondary gaps in the half and fully brominated hybrid perovskites leads to the phenomenon of a multipeak response in the optical spectra, which can be subsequently attributed as multivalley optical response behaviour. This multivalley optical behaviour enables the brominated guanidinium-based hybrid perovskites to exhibit broad light harvesting abilities, and this can be perceived as an idea for natural multi-junction solar cells.
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| 3. |
- Dwibedi, Debasmita, et al.
(författare)
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Na2.44Mn1.79(SO4)(3) : a new member of the alluaudite family of insertion compounds for sodium ion batteries
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:36, s. 18564-18571
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Tidskriftsartikel (refereegranskat)abstract
- Sodium-ion batteries have been extensively pursued as economic alternatives to lithium-ion batteries. Investigating the polyanion chemistry, alluaudite structured Na2Fe2II(SO4)(3) has been recently discovered as a 3.8 V positive electrode material (Barpanda et al., Nature Commun., 5: 4358, 2014). Registering the highest ever Fe-III/Fe-II redox potential (vs. Na/Na+) and formidable energy density, it has opened up a new polyanion family for sodium batteries. Exploring the alluaudite family, here we report isotypical Na2+2xMn2-xII(SO4)(3) (x = 0.22) as a novel high-voltage cathode material for the first time. Following low-temperature (ca. 350 degrees C) solid-state synthesis, the structure of this new alluaudite compound has been solved adopting a monoclinic framework (s.g. C2/c) showing antiferromagnetic ordering at 3.4 K. Synergising experimental and ab initio DFT investigation, Na2+2xMn2-xII(SO4)(3) has been found to be a potential high-voltage (ca. 4.4 V) cathode material for sodium batteries.
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| 4. |
- Gupta, Divyani, et al.
(författare)
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High yield selective electrochemical conversion of N-2 to NH(3)via morphology controlled silver phosphate under ambient conditions
- 2022
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 10:38, s. 20616-20625
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Tidskriftsartikel (refereegranskat)abstract
- Development of a highly active catalyst for the synthesis of ammonia via the electrochemical dinitrogen reduction reaction (e-NRR) is an immense challenge. We report the modification of metallic Ag with inorganic phosphate to obtain Ag3PO4 as an effective electrocatalyst for the e-NRR in alkaline media under ambient conditions. The designed Ag3PO4 catalyst can effectually suppress the HER. The e-NRR activity was improved by fine-tuning the morphology by a template free one-pot synthesis. The synthesised Ag3PO4 having cuboidal morphology is shown to have superior activity and stability towards the e-NRR witnessed from a high faradaic efficiency of 26.67%, yield rate of 456.75 mu g h(-1) mg(cat)(-1) and TOF value of 0.46 h(-1) at a positive potential of 0 V vs. RHE in 0.1 M KOH. Careful examination of any N-contaminants present in catalyst/electrolyte/gas-feed is carried out by UV-vis spectroscopy and gas-purification methods prior to e-NRR measurements to eliminate any false NH3 production. Also, the true source of NH3 production is confirmed by means of N-15-isotope labelling experiments via(1)H-NMR spectroscopy.
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| 5. |
- Gupta, Divyani, et al.
(författare)
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Local electrocatalytic activity of PtRu supported on nitrogen-doped carbon nanotubes towards methanol oxidation by scanning electrochemical microscopy
- 2021
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 9:37, s. 21291-21301
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen-doped carbon nanotubes (NCNTs) were synthesized by treating HNO3-oxidized carbon nanotubes (CNTs) in an NH3 flow at different temperatures. PtRu nanoparticles were decorated over NCNTs. The PtRu catalysts were prepared by an impregnation-reduction method from metal chloride precursors with a total metal loading of about 10 wt%. The electrocatalytic activity with respect to methanol oxidation was studied using electrochemical and scanning electrochemical microscopy (SECM) measurements. Transmission electron microscopy revealed the spherical shape and narrow particle size distribution of the PtRu particles over NCNTs with average particle sizes of similar to 3-5 nm. A detailed X-ray photoelectron spectroscopy study was performed to quantitatively identify different nitrogen functional groups and to evaluate their role in the observed enhanced catalytic activity towards methanol oxidation. The determination of the local electrocatalytic activity of the proposed catalyst towards methanol oxidation and simultaneous evaluation of the intermediates produced during methanol oxidation were achieved using SECM. Density functional theory studies were performed to understand the adsorption sites of methanol and intermediates on different reactive sites and to investigate possible reaction mechanisms.
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| 6. |
- Gupta, Divyani, et al.
(författare)
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Self-powered NH3 synthesis by trifunctional Co2B-based high power density Zn-air batteries
- 2023
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 11:23, s. 12223-12235
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical production of NH3 by Zn-air batteries is a viable and economical approach to realize sustainable and competent energy conversion. We report the environment friendly, cost-effective, and energy efficient sonochemical synthesis of amorphous Co2B nanosheets for trifunctional electrocatalysis. The catalyst exhibits a high NH3 yield rate (2.98 mg h(-1) mg(cat.)(-1)), F.E (20.45%), and TOF of 0.74 h(-1) at -0.3 V vs. RHE, thereby unveiling an outstanding performance for the artificial ammonia synthesis. The reliable and true NH3 production is premediated by following rigorous protocol that involves the purification of gas supplies, elimination of N-contaminants, and quantification of NH3 by different methods, UV-Vis spectroscopy and N-15(2) isotope labelling experiments. More interestingly, DFT calculations on the Co2B catalyst surface shed light on the efficient NRR owing to the presence of Co active sites and possible HER suppression. The optimized Co2B catalyst shows outstanding oxygen bifunctional activity. When employed as an air-cathode for Zn-air batteries, it exhibited remarkable electrocatalytic activity delivering an open circuit potential of 1.45 V with a high power density of 500 mW cm(-2) and an energy density of 1078 W h kg(-1), which can perform NH3 generation with an overall NH3 production yield rate of 1.048 mg h(-1) mg(cat.)(-1).
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| 7. |
- Muduli, Subas Kumar, et al.
(författare)
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Evolution of hydrogen by few-layered black phosphorus under visible illumination
- 2017
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 5:47, s. 24874-24879
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Tidskriftsartikel (refereegranskat)abstract
- Recently, a new class of two-dimensional black phosphorus (BP) with a visible direct band gap is predicted as a potential candidate for photo-catalysis applications. Here, we present the first experimental evidence of hydrogen (H-2) evolution from aqueous solution by using BP (nanosheets and nanoparticles) under visible light illumination. Our experimental results describe that liquid phase exfoliated BP nanosheets and BP nanoparticles exhibit suitable energy level alignments for electron transfer and further proton reduction reactions in the solution under visible light illumination. Density functional theory (DFT) calculations predict that the H-2 evolution activity of bilayer BP is independent of edge or center positions, which is unique in BP as compared to those of other 2D materials.
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| 8. |
- Watcharatharapong, Teeraphat, et al.
(författare)
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Mapping Sodium Intercalation Mechanism, Electrochemical Properties and Structural Evolution in Non-stoichiometric Alluaudite Na2+2δFe2-δ(SO4)3 Cathode Materials
- 2019
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 7, s. 17446-17455
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Tidskriftsartikel (refereegranskat)abstract
- In the scientific advancement of future cathode materials, alluaudite sodium iron sulfate Na2+2δFe2−δ(SO4)3 (NxFyS) has emerged as one of the most promising candidates for sustainable sodium-ion batteries due to its high Fe2+/3+ redox potential (3.8 V vs.Na/Na+), low cost, and high rate capability. Usually, this material occurs in a non-stoichiometric form with partial Na+ substitutions on Fe sites, where δ is close to 0.25 (N2.5F1.75S) depending on the synthesis conditions. While many contemporary works have primarily been directed to study this non-stoichiometric compound, our previous theoretical prediction unveiled the possibility to synthesize stoichiometric alluaudite (N2F2S), which is expected to deliver higher specific capacity (∼120 mA h g−1) as compared to the non-stoichiometric derivatives. This provokes curiosity toward the non-stoichiometric effect on the electrochemical activities and sodium intercalation mechanism in alluaudite materials. In this work, we therefore perform rigorous first-principles calculations to study the structural evolution, electrochemical behavior, and voltage profile of NxFyS with y = 2, 1.75, and 1.5. We reveal the likelihood of two phase transitions after half desodiation process, whereas the probability is reduced with a higher degree of non-stoichiometry, suggesting improvement in the structural reversibility for N2.5F1.75S and N3F1.5S. The prediction of the voltage profiles shows the benefit of non-stoichiometry in enhancing the specific capacity and identifies the structural rearrangement of Fe2O10 dimers as the hidden reason behind the irreversible sharp peak experimentally observed in differential galvanostatic profiles.
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| 9. |
- Watcharatharapong, Teeraphat, et al.
(författare)
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Mapping the sodium intercalation mechanism, electrochemical properties and structural evolution in non-stoichiometric alluaudite Na2+2 delta Fe2-delta(SO4)(3) cathode materials
- 2019
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 7:29, s. 17446-17455
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Tidskriftsartikel (refereegranskat)abstract
- In the scientific advancement of future cathode materials, alluaudite sodium iron sulfate Na2+2 delta Fe2-delta(SO4)(3) (NxFyS) has emerged as one of the most promising candidates for sustainable sodium-ion batteries due to its high Fe2+/3+ redox potential (3.8 V vs. Na/Na+), low cost, and high rate capability. Usually, this material occurs in a non-stoichiometric form with partial Na+ substitutions on Fe sites, where delta is close to 0.25 (N2.5F1.75S) depending on the synthesis conditions. While many contemporary works have primarily been directed to study this non-stoichiometric compound, our previous theoretical prediction unveiled the possibility to synthesize stoichiometric alluaudite (N2F2S), which is expected to deliver higher specific capacity (similar to 120 mA h g(-1)) as compared to the non-stoichiometric derivatives. This provokes curiosity toward the non-stoichiometric effect on the electrochemical activities and sodium intercalation mechanism in alluaudite materials. In this work, we therefore perform rigorous first-principles calculations to study the structural evolution, electrochemical behavior, and voltage profile of NxFyS with y = 2, 1.75, and 1.5. We reveal the likelihood of two phase transitions after half desodiation process, whereas the probability is reduced with a higher degree of non-stoichiometry, suggesting improvement in the structural reversibility for N2.5F1.75S and N3F1.5S. The prediction of the voltage profiles shows the benefit of non-stoichiometry in enhancing the specific capacity and identifies the structural rearrangement of Fe2O10 dimers as the hidden reason behind the irreversible sharp peak experimentally observed in differential galvanostatic profiles.
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| 10. |
- Watcharatharapong, Teeraphat, et al.
(författare)
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Mechanistic study of Na-ion diffusion and small polaron formation in Krohnkite Na2Fe(SO4)(2)center dot 2H(2)O based cathode materials
- 2017
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488. ; 5:41, s. 21726-21739
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Tidskriftsartikel (refereegranskat)abstract
- Krohnkite-type Na2Fe(SO4)(2)center dot 2H(2)O mineral is a sustainable and promising polyanionic cathode that has been experimentally found to offer a high redox potential (3.25 V vs. Na/Na+) along with fast-ion diffusion and high reversibility. Owing to the structural complexity, Na+ diffusion was assumed to occur along a convoluted channel along the b-axis. However, theoretical work related to this material still appears missing to support that statement. In this work, DFT+U calculations have been performed with the primary aim to unveil the Na+ diffusion mechanism in this material. The electronic structure and charge transfer are also envisaged to reveal evidence of Fe2+/3+ redox reaction and a vital role of structural H2O. Based on formation energies of this material with varied Na concentration, a calculated voltage profile is determined to show two voltage plateaus at 4.81 and 3.51 V, corresponding to experimental results. Nudged elastic band calculation reveals that Na+ diffusion is primarily occuring in the [01 (1) over bar] direction with a moderate ionic mobility due to the structural distortion induced during migration, suggesting the possibility of defect-assisted diffusion. Intriguingly, the formation of small hole polarons is first observed, and could play a key role in the electronic conduction of this material.
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