Analysis of the physical and photoelectrochemical properties of c-Si(p)/a-SiC:H(p) photocathodes for solar water splitting. - In: Journal of physics, ISSN 1361-6463, Bd. 54 (2021), 19, 195101, S. 1-12
The photoelectrochemical (PEC) properties of sputtered aluminum doped hydrogenated amorphous silicon carbide thin films grown on p-type crystalline silicon substrates were investigated in 1 M solution under chopped light illumination. Optical and structural properties of the top absorber layer were systematically assessed after post-deposition isochronical annealing treatments. Samples exhibited a noticeable improvement of the opto-electronic properties after thermal treatments. In addition, an abrupt enhancement of the photocurrent was observed reaching a saturation value of 17 mA cm^-2 at -1.75 V vs. Ag/AgCl (3.5 M KCl). In this research we propose that this enhancement effect is associated to a charge transfer kinetic mechanism influenced by surface states and the p-type substrate. The latter most likely due to the space charge region extending beyond the absorber layer reaching the substrate. Current density-potential and electrochemical impedance spectroscopy measurements in dark revealed a reduction of the native layer at cathodic potentials higher than -1 V vs. Ag/AgCl (3.5 M KCl), which contributes to the high charge transfer kinetic of the system. We believe that these results will contribute to understand the substrate influence in the PEC performance of top absorber layers in multilayer structures for solar water splitting.
https://doi.org/10.1088/1361-6463/abdb69
InP and AlInP(001)(2 × 4) surface oxidation from density functional theory. - In: ACS omega, ISSN 2470-1343, Bd. 6 (2021), 9, S. 6297-6304
The atomic structure and electronic properties of the InP and Al0.5In0.5P(001) surfaces at the initial stages of oxidation are investigated via density functional theory. Thereby, we focus on the mixed-dimer (2 × 4) surfaces stable for cation-rich preparation conditions. For InP, the top In-P dimer is the most favored adsorption site, while it is the second-layer Al-Al dimer for AlInP. The energetically favored adsorption sites yield group III-O bond-related states in the energy region of the bulk band gap, which may act as recombination centers. Consistently, the In p state density around the conduction edge is found to be reduced upon oxidation.
https://doi.org/10.1021/acsomega.0c06019
Atomic force extrema induced by the bending of a CO-functionalized probe. - In: Nano letters, ISSN 1530-6992, Bd. 21 (2021), 5, S. 2318-2323
The control and observation of reactants forming a chemical bond at the single-molecule level is a long-standing challenge in quantum physics and chemistry. Using a single CO molecule adsorbed at the apex of an atomic force microscope tip together with a Cu(111) surface, bending of the molecular probe is induced by torques due to van der Waals attraction and Pauli repulsion. As a result, the vertical force between CO and Cu(111) exhibits a characteristic dip-hump evolution with the molecule-surface separation, which depends sensitively on the initial tilt angle the CO axis encloses with the surface normal. The experimental force data are reproduced by model calculations that consider the CO deflection in a harmonic potential and the molecular orientation in the Pauli repulsion term of the Lennard-Jones potential. The presented findings shed new light on vertical-force extrema that can occur in scanning probe experiments with functionalized tips.
https://doi.org/10.1021/acs.nanolett.1c00268
Deep learning with spatiotemporal attention-based LSTM for industrial soft sensor model development. - In: IEEE transactions on industrial electronics, Bd. 68 (2021), 5, S. 4404-4414
Industrial process data are naturally complex time series with high nonlinearities and dynamics. To model nonlinear dynamic processes, a long short-term memory (LSTM) network is very suitable for soft sensor model development. However, the original LSTM does not consider variable and sample relevance for quality prediction. In order to overcome this problem, a spatiotemporal attention-based LSTM network is proposed for soft sensor modeling, which can, not only identify important input variables that are related to the quality variable at each time step, but also adaptively discover quality-related hidden states across all time steps. By taking the spatiotemporal quality-relevant interactions into consideration, the prediction performance can be improved for the soft sensor model. The effectiveness and flexibility of the proposed model is demonstrated on an industrial hydrocracking process to predict the initial boiling points of heavy naphtha and aviation kerosene.
https://doi.org/10.1109/TIE.2020.2984443
Influence of tool geometry and process parameters on the properties of friction stir spot welded multiple (AA 5754 H111) aluminium sheets. - In: Materials, ISSN 1996-1944, Bd. 14 (2021), 5, 1157, insges. 23 S.
https://doi.org/10.3390/ma14051157
Contextual MEG and EEG source estimates using spatiotemporal LSTM networks. - In: Frontiers in neuroscience, ISSN 1662-453X, Bd. 15 (2021), 552666, S. 1-15
Most magneto- and electroencephalography (M/EEG) based source estimation techniques derive their estimates sample wise, independently across time. However, neuronal assemblies are intricately interconnected, constraining the temporal evolution of neural activity that is detected by MEG and EEG; the observed neural currents must thus be highly context dependent. Here, we use a network of Long Short-Term Memory (LSTM) cells where the input is a sequence of past source estimates and the output is a prediction of the following estimate. This prediction is then used to correct the estimate. In this study, we applied this technique on noise-normalized minimum norm estimates (MNE). Because the correction is found by using past activity (context), we call this implementation Contextual MNE (CMNE), although this technique can be used in conjunction with any source estimation method. We test CMNE on simulated epileptiform activity and recorded auditory steady state response (ASSR) data, showing that the CMNE estimates exhibit a higher degree of spatial fidelity than the unfiltered estimates in the tested cases.
https://doi.org/10.3389/fnins.2021.552666
Magnetic behavior in commercial iron-silicon alloys controlled by the dislocation dynamics at temperatures below 420 K. - In: Journal of alloys and compounds, ISSN 1873-4669, Bd. 856 (2021), 157934
A decrease of the temperature dependent coercive forces up to around 370 K is discovered in iron silicon alloys, both in quenched samples and in samples which were previously thermally treated to achieve the highest magnetic quality. Alloys of composition Fe-6 wt.% Si and Fe-3 wt.% Si are studied. This reduction in the coercive force is controlled by an increase in the mobility of the domain walls due to the increase in the dislocation's mobility enhanced by the movement of vacancies. It is worthwhile to mention that this reduction in coercive force is only present at these slightly elevated temperatures which are markedly smaller than the usual annealing temperatures for heat treatment of iron silicon alloys while it disappears again at room temperature. Neutron thermodiffraction, magnetic hysteresis loops tracer and mechanical spectroscopy are used as experimental techniques.
https://doi.org/10.1016/j.jallcom.2020.157934
Biomass-derived highly dispersed Co/Co9S8 nanoparticles encapsulated in S, N-co-doped hierarchically porous carbon as an efficient catalyst for hybrid Na-CO2 batteries. - In: Materials today, ISSN 2468-6069, Bd. 19 (2021), 100594, insges. 12 S.
Im Titel sind "9", "8" und "2" tiefgestellt
Na-CO2 batteries are prospective in energy storage and CO2 recycling applications; development of a high-efficiency, low-cost electrocatalyst to promote CO2 reduction and carbonate decomposition is extremely vital for practical Na-CO2 batteries. Herein, a highly efficient cathode catalyst for rechargeable hybrid Na-CO2 batteries is successfully synthesized by encapsulating highly dispersed Co/Co9S8 nanoparticles into carbon skeletons, consisting of biomass-derived S, N-co-doped hierarchically porous carbon (Co/Co9S8SNHC). The conductive and hierarchically porous framework structure of the Co/Co9S8@SNHC can not only accelerate electron transport, electrolyte infiltration, and CO2 diffusion but also can inhibit overgrowth and agglomeration of Co/Co9S8 nanoparticles and expose numerous high density of active sites, as well as offer sufficient space to store discharge products. Benefiting from the synergistic effect among S and N dopants, carbon defects, and Co/Co9S8 nanoparticles in robust porous carbon structure, the hybrid Na-CO2 batteries displayed a low charge overpotential (only ˜0.32 V) at 0.2 mA/cm2 and repeatedly charged and discharged over 200 cycles at 0.1 mA/cm2. Besides, an ultrahigh areal capacity of ˜18.9 mAh/cm2 was obtained at 0.5 mA/cm2, the highest value to date for Na-CO2 batteries. Meanwhile, the hybrid Na-CO2 battery charging from Na2CO3@C catalytic cathode demonstrated the high catalytic activity of biomass-derived S,N-co-doped hierarchically porous carbon (Co/Co9S8@SNHC) for CO2 reduction and carbonate decomposition. Given this finding, this work might open up a potential avenue for the reasonable design of low-cost and highly efficient catalysts for advanced metal-CO2 batteries systems.
https://doi.org/10.1016/j.mtener.2020.100594
Efficient and inexpensive MPCVD method to synthesize Co3O4/MoS2 heterogeneous composite materials with high stability for supercapacitors. - In: Journal of materials research and technology, ISSN 2214-0697, Bd. 10 (2021), S. 953-959
Large-sized metal oxide particles have the potential to constitute cheap, high-performance, and high-stability supercapacitor electrode materials. Herein, the marketable large-sized Co3O4 particles (˜6 [my]m) as the starting raw material, inexpensive Co3O4/MoS2 core-shell heterogeneous composites have been one-step fabricated via an improvised MPCVD system modified by a domestic microwave oven. After that, the surface morphology, composition structure, and valence state of elements were analyzed to the confirmed successful synthesis of MoS2 on the surface of Co3O4. Besides, the performance was tested by cyclic voltammetry and galvanostatic charge-discharge method. The results show that the synergistic effect of Co3O4 core and MoS2 shell can effectively improve the material's electrochemical performance. The specific capacitance of Co3O4/MoS2 composite can reach 337 F g^-1 with a current density of 0.5 A g^-1, which is six times more than the raw Co3O4 powder. Furthermore, it could maintain 93.6% of the initial specific capacitance after 2000 charges and discharges. Finally, the mechanism of material performance improvement is proposed.
https://doi.org/10.1016/j.jmrt.2020.12.101
Anti-corrosive siloxane coatings for improved long-term performance of supercapacitors with an aqueous electrolyte. - In: Electrochimica acta, ISSN 1873-3859, Bd. 372 (2021), 137840, S. 1-15
This paper reports on the impact that the corrosion of the stainless steel current collectors has on the performance fade of a symmetric, carbon/carbon electrochemical capacitor, operating with an aqueous electrolyte (1M Na2SO4). The results obtained by applying electrochemical ageing protocols (voltage-holding tests) confirm that the current collector of the positive electrode undergoes tremendous degradation during 200 h in the charged state. To prevent the detrimental impact of the corrosion, a hydrophobic siloxane coating has been successfully applied. In the case of siloxane-protected current collectors that are subjected to identical ageing protocols, no significant deterioration in the electrochemical capacitor performance was observed. The siloxane coating reduces the electrochemical corrosion rate of 316L stainless steel significantly, as the potentiodynamic polarization tests and the electrochemical impedance spectroscopy results show. The presence of the coating is demonstrated by the water contact angle measurements, atomic force microscopy and energy-dispersive X-ray spectroscopy analysis.
https://doi.org/10.1016/j.electacta.2021.137840