Ni3N-coated Ni nanorod arrays for hydrogen and oxygen evolution in electrochemical water splitting. - In: ACS applied nano materials, ISSN 2574-0970, Bd. 3 (2020), 11, S. 10986-10995
Im Titel ist "3" tiefgestellt
Designing high efficiency non-noble metal catalysts for electrochemical hydrogen and oxygen evolution reactions (HER and OER) is a challenging and promising task. In the present work, a large-scale self-supported black nickel sheet composed of nickel nanorod arrays (B-Ni) was successfully fabricated via electroplating with a nanostructured Si template assisted strategy, and Ni3N coating layer was coated on the structured surface followed by a nitrogen plasma treatment with different treatment durations. The black color is due to the immensely enhanced light absorption through the surface nanostructures with high aspect ratio. The samples show promising catalytic performance when used as electrochemical catalysts for both HER and OER in alkaline electrolyte. Benefiting from the nanostructure and the Ni3N coating, B-Ni_N2_10 min exhibits low onset potentials of 1.560 and 0.165 V at a current density of 10 mA/cm2 for OER and HER, respectively. The calculated electrochemical surface area (ECSA) for B-Ni is 10 times higher than the pristine Ni sheet (P-Ni), while after nitrogen plasma treatment, the ECSA for B-Ni_N2_10 min is 21 times higher than that of the P-Ni. In addition, all the catalysts show good electrochemical stabilities. All the improvements for the electrochemical performances suggest that nanostructured nickel nitride could be a promising inexpensive catalyst system for both OER and HER processes.
https://doi.org/10.1021/acsanm.0c02222
Physics-based modeling and parameter identification for lithium ion batteries under high current discharge conditions. - In: Journal of the Electrochemical Society, ISSN 1945-7111, Volume 167 (2020), number 14, 140549
Extreme scenarios of high discharge current must be understood for better battery management system design. Physics-based modeling can give a better insight into the battery response but can be challenging due to the large number of parameters. In this work, an electrochemical pseudo-2D model is developed and used in the parameter identification and validated under high current discharge conditions. Commercial 18650 cells with maximum rated current of 20 A (13.3 C) are characterized with discharge rates up to 40 C under controlled thermal conditions. The proposed three-step parameter identification procedure starts with the open circuit voltage being used to estimate the equilibrium potentials. In a second step, kinetic parameters are identified under high current aided by a parameter sensitivity analysis and parameter optimization with an evolutionary algorithm. The third step is the verification by comparing simulation results with measurements resulting in root main square error under 89 mV for currents until 26.6 C. Limits of the model are explored in the 33.3 C case, where a parameter re-fit shows that polarization effects change for very high current.
https://doi.org/10.1149/1945-7111/abc726
Localized and programmable chemical vapor deposition using an electrically charged and guided molecular flux. - In: ACS nano, ISSN 1936-086X, Bd. 14 (2020), 10, S. 12885-12894
Chemical vapor deposition is a widely used material deposition technique. It commonly provides a uniform material flux to the substrate to cause uniform thin film growth. However, the ability to precisely adjust the local deposition rate would be highly preferable. This communication reports on a chemical vapor deposition method performed in a localized and programmable fashion by introducing an electrically charged and guided molecular flux. This allows for local adjustments of the deposition rate and three-dimensional shape by controlling the electric fields. Specifically, the precursor molecules are charged and then guided by arrays of electrodynamic funnels, which are created by a patterned dielectric layer, to predetermined deposition locations with a minimal spot size of 250 nm. Furthermore, nearest neighbor coupling is reported as a shaping method to cause the deposition of three-dimensional nanostructures. Additionally, the integration of individually addressable domain electrodes offers programmable charge dissipation to achieve an ON/OFF control. The described method is applicable to a wide variety of materials and precursors. Here, the localized and programmable deposition of three-dimensional copper oxide, chromium oxide, zinc oxide, and carbon nanowires is demonstrated.
https://doi.org/10.1021/acsnano.0c03726
Metal-insulator transition in crystalline V2O3 thin films probed at atomic-scale using emission Mössbauer spectroscopy. - In: Thin solid films, ISSN 1879-2731, Bd. 714 (2020), 138389
Im Titel sind "2" und "3" tiefgestellt
Microscopic understanding the metal-to-insulator transition (MIT) in strongly correlated materials is critical to the design and control of modern "beyond silicon" Mott nanodevices. In this work, the local MIT behaviors in single crystalline V2O3 thin films were probed on an atomic scale by online 57Fe emission Mössbauer spectroscopy (eMS) following dilute (<10^-3 at.%) implantation of 57Mn+ (T1/2 = 90 s). Both the epitaxial and the textured V2O3 thin films grown by direct current magnetron sputtering were studied. Three structural components were resolved and identified in the eMS spectra with parameters characteristic of Fe in the 2+ valence state, which are attributable to Fe in either lattice damage or structural defects and Fe in the intrinsic crystal structure of V2O3, respectively. The results prove that the oxygen vacancies are common in the V2O3 thin films. With co-existence of both the non-stoichiometry and epitaxial strain in the thin films, the epitaxial strain plays a dominant role in controlling the global MIT properties of the film. The atomic scale structural transition captured by the eMS affirms the early-stage dynamics of the MIT of V2O3 thin film reported previously. These results approve the feasibility to tune the electronic transport of the V2O3 thin films for the next-generation Mott nanodevices by the epitaxial strain via the sample growth parameters.
https://doi.org/10.1016/j.tsf.2020.138389
Investigation of epitaxial graphene via Raman spectroscopy: origins of phonon mode asymmetries and line width deviations. - In: Carbon, ISSN 1873-3891, Bd. 170 (2020), S. 666-676
In this work a comprehensive study is presented for the analysis of epitaxial graphene layers using Raman spectroscopy. A wide range of graphene types is covered, from defective/polycrystalline single layer graphene to multilayer graphene with low defect density. On this basis the influence of strain type, Fermi level and number of layers on the Raman spectrum of graphene is investigated. A detailed view on the 2D/G dispersion and the respective slopes of uniaxially and biaxially strained graphene is given and its implications on the asymmetry of the G peak analyzed. A linear dependency of the phonon mode asymmetry on uniaxial strain is presented in addition to the known Fermi level dependence. Additional impacts on the asymmetry are found to be arising from the defect density and transfer doping of adsorbates. The discovered transfer doping mechanism is contrary to pure phonon excitation through excitons and exhibits increasing asymmetry with increasing Fermi level. A new characteristic correlation between the 2D mode line width and the inverse I(D)/I(G) ratio is introduced that allows the determination of the strain type and layer number and explains the difference between Raman line widths of monolayer graphene on different substrates.
https://doi.org/10.1016/j.carbon.2020.07.016
Application of hydrosilane-free atmospheric pressure chemical vapor deposition of SiOx films in the manufacture of crystalline silicon solar cells. - In: Thin solid films, ISSN 1879-2731, Bd. 713 (2020), 138338
In this work we present SiOx films deposited in cost-effective laboratory scale three-dimensional printed atmospheric pressure chemical vapor deposition setup. As SiOx films are deposited at room temperature without complex vacuum systems, they can be a good candidate for the use in commercial c-Si solar cell production lines. The quality of the deposited films was investigated as to their integrity, conformity with various surfaces, and post-treatment resilience such as stability against etchants and annealing. Several applications of the SiOx film prepared with the atmospheric pressure chemical vapor deposition (APCVD) were discussed. In one application, the APCVD SiOx was utilized to effectively promote single-side texturing of Float Zone and Czochralski Si wafers by coating only one side with SiOx and subsequently annealing prior to texturing in an alkaline aqueous solution. Another application was to exploit the APCVD SiOx as a plating mask for silicon heterojunction solar cells. Two processing options prior to the oxide-film deposition were investigated: i) application of an Ag seed-layer, which promotes subsequent electroplating, and ii) printing of an organic grid, which, after stripping, creates openings in the SiOx that facilitate electroplating of the solar cell's electrode on the underlying transparent conducting oxide. In a different application, the APCVD SiOx films acted as protection against parasitic plating on the front side of passivated emitter and rear solar cells. The deposited films were characterized by ellipsometry, hemispherical reflectance measurements, scanning electron microscopy, energy dispersive X-ray spectroscopy and optical microscopy.
https://doi.org/10.1016/j.tsf.2020.138338
Polyimide@Ketjenblack composite: a porous organic cathode for fast rechargeable potassium-ion batteries. - In: Small, ISSN 1613-6829, Bd. 16 (2020), 38, 2002953, insges. 8 S.
Potassium-ion batteries (PIBs) configurated by organic electrodes have been identified as a promising alternative to lithium-ion batteries. Here, a porous organic PolyimideKetjenblack is demonstrated in PIBs as a cathode, which exhibits excellent performance with a large reversible capacity (143 mAh g^-1 at 100 mA g^-1), high rate capability (125 and 105 mAh g^-1 at 1000 and 5000 mA g^-1), and long cycling stability (76% capacity retention at 2000 mA g^-1 over 1000 cycles). The domination of fast capacitive-like reaction kinetics is verified, which benefits from the porous structure synthesized using in situ polymerization. Moreover, a renewable and low-cost full cell is demonstrated with superior rate behavior (106 mAh g^-1 at 3200 mA g^-1). This work proposes a strategy to design polymer electrodes for high-performance organic PIBs.
https://doi.org/10.1002/smll.202002953
Influence of thermal treatment on the magnetic properties and morphology of electrodeposited Fe-Co films. - In: Journal of magnetism and magnetic materials, ISSN 1873-4766, Bd. 513 (2020), 167204
Fe-Co films were prepared by electrodeposition from an electrolyte containing citric acid and annealed afterwards at different temperatures up to 700 ˚C. The grain sizes of the deposits increased from 11 nm to 30 nm with increasing annealing temperature, which lead to changes in magnetic properties of deposits. SQUID measurements indicate that there is a difference between the coercive force, Hc, of the as deposited samples (17 Oe) and the heat-treated samples (25-40 Oe) with a measurement error of 1-2 Oe. The remnant magnetization, Mr, decreased from 190 ± 12 emu/cm^3 for the as deposited to 75 ± 5 emu/cm^3 for the annealed samples, respectively. The saturation magnetization, Ms, seems not to be influenced strongly by the thermal treatment, with the only exception for the samples annealed at 500 ˚C. Thus, Ms has a slightly decreasing tendency from 1880 ± 90 emu/cm^3 for the as-deposited samples to 1780 ± 85 emu/cm^3 for samples annealed at 700 ˚C. The biggest value for Ms (2100 ± 105 emu/cm^3) was obtained if the samples were annealed at 500 ˚C. The thermal treatment generated cracks in the deposits. Interestingly, these cracks had a regular rectangular shape only if the deposits were annealed at 600 ˚C. The coercivity of the layers annealed at 600 ˚C was lower compared to layers annealed at the other temperatures. Magnetic force microscopy measurements indicated the magnetic domain distribution and the topography of the annealed deposits. The deposits showed the best soft magnetic properties if annealed between 500 and 600 ˚C.
https://doi.org/10.1016/j.jmmm.2020.167204
NiCo2O4Ni2P nanorods grown on nickel nanorod arrays as a bifunctional catalyst for efficient overall water splitting. - In: Materials today, ISSN 2468-6069, Bd. 17 (2020), 100490
The development of efficient and durable non-noble metal catalysts remains a challenge in electrocatalytic water splitting applications. To address this, a bifunctional catalyst involving hierarchical NiCo2O4Ni2P nanorods grown on nickel nanorod arrays (NiCo2O4@Ni2P/NAs) was designed and fabricated in this study for overall water splitting that provided high activity and acceptable stability. And if used as the cathode and anode in alkaline media, the NiCo2O4@Ni2P/NAs only required 1.58 V to achieve a current density of 10 mA cm^-2, which is superior to most reported catalysts and can be attributed to a unique core-shell structure and coexisting crystalline/amorphous Ni2P phases.
https://doi.org/10.1016/j.mtener.2020.100490
Molten iodide salt electrolyte for low-temperature low-cost sodium-based liquid metal battery. - In: Journal of power sources, ISSN 1873-2755, Bd. 475 (2020), 228674
Using low-melting-point electrolytes could overcome various key challenges of low-cost sodium-based liquid metal batteries (Na-LMBs), e.g. high rates of self-discharge and degradation of structural materials, by lowering their operating temperatures. Molten halide salts are considered promising electrolyte candidates for Na-LMBs due to their high stability and electrical conductivity. In this work, thermodynamic simulation via FactSageTM and thermal analysis via e.g. Differential Scanning Calorimeter (DSC) were carried out to explore the NaI-LiI-KI system, since it could be a promising electrolyte for Na-LMBs due to its low melting point and Na solubility. The results show that the eutectic NaI-LiI-KI performs as a pseudo-binary salt with a melting point of ˜290 ˚C. In this pseudo-binary salt, the solubility of NaI in the eutectic LiI-KI is ˜7 mol%. Using the eutectic NaI-LiI-KI electrolyte, Na-LMBs could be operated at < 350 ˚C. Moreover, the Na solubility and Na+ conductivity of the eutectic NaI-LiI-KI electrolyte, which are vital to the battery performance, were estimated by calculation based on the literature data. Additionally, its applicability and economy were also discussed based on cost pre-analysis of salt materials, salt treatment and structural materials regarding salt corrosivity.
https://doi.org/10.1016/j.jpowsour.2020.228674