ABSTRACT
The search for highly efficient and inexpensive electrocatalysts is crucial to the advancement of environmentally friendly and sustainable energy sources. Here, adopting a one-step hydrothermal method, we have effectively fabricated a self-supported multi-metal molybdenum-based oxide (FeCoNi-MoO4) on nickel foam (NF). In addition to changing the catalyst's microstructure, the introducing of Fe and Co, enhanced its active center count, improved its electronic structure, and in turn reduced the difficulty for high-valence Ni and Fe species to form, which accelerates the oxygen evolution reaction (OER) kinetics by promoting the development of the actual active materials, NiOOH and FeOOH. FeCoNi-MoO4 has outstanding OER performance, requiring just 204 mV overpotentials at 10 mA cm-2 and 271 mV at 100 mA cm-2. Its exceptional OER kinetics at both low and high currents are indicated by a Tafel slope of 50.6 mV dec-1, which is attributed to the combined effect of its multi-metal composition and a higher number of active sites. Moreover, the FeCoNi-MoO4 electrode was operated continuously for over 48 h. Furthermore, the density functional theory (DFT) results demonstrated that the introducing of Fe and Co, which quickens the rate of electron transfer during the electrocatalytic process, improves the ability of oxygen intermediate species to adsorb, and ultimately lowers the overpotential, is responsible for the increased electrocatalytic activity of FeCoNi-MoO4. This work offers hope for further developments in the sector by proposing an efficient approach for creating multi-active electrocatalysts that are stable, economical, and efficient.
ABSTRACT
Traditional calibration technology has been widely used in measurement and monitoring; however, there are limitations of poor calibration accuracy, which can not meet the accuracy requirements in some scenarios. About this problem, we proposed a grey wolf optimization algorithm based on levy flight and mutation mechanism to solve camera internal parameters in this paper. The algorithm is based on the actual nonlinear model, which takes the minimum average value of reprojection error as the objective function. The grey wolf position is randomly generated within a given range. Then, the grey wolf optimization algorithm based on levy flight and mutation mechanism is used to iteratively calculate the optimal position, which is the internal parameters of cameras. The two groups of experimental data were performed to verify the algorithm. The result shows better effectiveness and calibration accuracy of the proposed algorithm compared with other optimization methods.
Subject(s)
Algorithms , Calibration , MutationABSTRACT
Currently, the oxygen evolution reaction (OER) is constrained by complex four-electron transport, thus it is difficult to understand the catalytic mechanism. In this work, the electronic properties and catalytic performance of M1M2/NC (M = Mn, Fe, Co, Ni, Cu and Zn, random combination in pairs) is studied by density functional theory, the calculated results show that the overpotential of FeCu/NC is 0.88 V, which is used as the optimal catalyst to further study the OER reaction mechanism. Combined with the volcano map and the d-band center position, the low overpotential of FeCu/NC is because it has a more suitable position of d-band center -1.806 eV than other materials. Moreover, the calculation results show that the density of states (DOS) of iron-containing materials is stronger than that of other materials near the Fermi level, which can promote the catalytic reaction. In addition, O∗OH and O∗H, O∗H and O∗ linearly related theoretical equations are proposed, respectively. Furthermore, the analysis of the catalytic mechanism shows that the formation of the catalytic rate-determining step is affected by the movement of the d-band center, the distance of the transition state adsorption and the electric field.
Subject(s)
Graphite , Adsorption , Catalysis , Electronics , OxygenABSTRACT
Platinum oxide supported on a Lewis acid niobium oxide (Nb2O5) support has been used for various heterogeneous and homogeneous catalysts. In this work, we used urea as a precipitating agent to obtain crystallized Nb2O5 with high surface area via a hydrothermal route. Nb2O5-supported Pt catalysts were subsequently synthesized via an incipient wetness impregnation approach. Multiple characterizations including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nitrogen adsorption/desorption confirmed the identical structural and textural properties of the Nb2O5 support before and after the impregnation process. Furthermore, the X-ray absorption fine structure technique (XAFS) results with related data analysis indicate that the platinum species in the fresh and H2-pretreated samples were in the form of single atoms or ultrafine clusters. In addition, the decrease in coordination number (CN) of the first-shell Pt-O bond, as well as the formation of Pt-Pt contribution with very low CN, after H2-pretreatment was verified, which corresponds to the decrease of oxidation state for Pt species on the surface of supports. Thus, the ultrafine-clustered metallic Pt species are considered to be more active than the oxidized Pt single ions. The current results will be of great significance in controllable synthesis of active Pt-based catalysts for other catalytic oxidation reactions.
ABSTRACT
The morphology of catalyst is a very important factor influencing the photocatalytic activity of the catalyst. Owing to its scientific and technological importance, controllable preparation of photocatalysts with different morphologies has been studied. In this work, BiOIO3/g-C3N4 heterojunction composites are synthesized using hydrothermal method and the composites with different morphologies are fabricated by adjusting the amount of NaOH in precursor solutions to control the growth of BiOIO3 crystal plane. The physicochemical properties of BiOIO3/g-C3N4 heterojunction composites were investigated by XRD, XPS, FTIR, SEM, TEM, HRTEM, BET, UV-vis DRS and PL characterization. The effect of the BiOIO3 morphology on the photocatalytic efficiency of BiOIO3/g-C3N4 heterojunction composites was evaluated by photocatalytic removal of gas-phase Hg0 under visible light irradiation. When the morphology of BiOIO3 is regular square-like, BiOIO3/g-C3N4 has the optimal removal efficiency 92.6% of Hg0. Finally, electron-hole migration path and photocatalytic mechanism of catalysts are proposed.
ABSTRACT
Tagged Magnetic Resonance Imaging (MRI) is a noninvasive technique for examining myocardial function and deformation. Tagged MRI can also be used in quasi-static MR elastography to acquire strain maps of other biological soft tissues. Harmonic phase (HARP) provides automatic and rapid analysis of tagged MR images for the quantification and visualization of myocardial strain. We propose a new artifact reduction method in strain maps. Image intensity of the DC component is estimated and subtracted from spatial modulation of magnetization (SPAMM) tagged MR images. DC peak interference in harmonic phase extraction is greatly reduced after DC component subtraction. The proposed method is validated using both simulated and MR acquired tagged images. Strain maps are obtained with better accuracy and smoothness after DC component subtraction.
ABSTRACT
In this paper, we proposed a new method for analyzing the image formation of a prism. The prism was considered as a single optical system composed of some planes. By analyzing each plane individually and then combining them together, we derived a transformation matrix which can express the relationship between an object point and its image by the refraction of a prism. We also explained how to use this matrix for epipolar geometry and three-dimensional point reconstruction. Our method is based on optical geometry and could be used in a multiocular prism. Experimentation results are presented to prove the accuracy of our method is better than former researchers' and is comparable with that of the multicamera stereovision system.
