Hydrogen (H2) production from direct seawater electrolysis is an economically appealing yet fundamentally and technically challenging approach to harvest clean energy. The current seawater electrolysis technology is significantly hindered by the poor stability and low selectivity of the oxygen evolution reaction (OER) due to the competition with chlorine evolution reaction in practical application. Herein, iron and phosphor dual‐doped nickel selenide nanoporous films (Fe,P‐NiSe2 NFs) are rationally designed as bifunctional catalysts for high‐efficiency direct seawater electrolysis. The doping of Fe cation increases the selectivity and Faraday efficiency (FE) of the OER. While the doping of P anions improves the electronic conductivity and prevents the dissolution of selenide by forming a passivation layer containing P–O species. The Fe‐dopant is identified as the primary active site for the hydrogen evolution reaction, and meanwhile, stimulates the adjacent Ni atoms as active centers for the OER. The experimental analyses and theoretical calculations provide an insightful understanding of the roles of dual‐dopants in boosting seawater electrolysis. As a result, a current density of 0.8 A cm−2 is archived at 1.8 V with high OER selectivity and long‐term stability for over 200 h, which surpasses the benchmarking platinum‐group‐metals‐free electrolyzers.

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The structural, thermal, electrical and mechanical properties of fully dense B 4 C ceramics, sintered using Spark Plasma Sintering (SPS), were studied and compared to the properties of B 4 C ceramics previously published in the literature. New results on B 4 C's mechanical responses were obtained by nanoindentation and ring-on-ring biaxial strength testing. The findings contribute to a more complete knowledge of the properties of B 4 C ceramics, an important material in many industrial applications.Materials 2020, 13, 1612 2 of 21 bonds, the intericosahedral bonds and the highly delocalized intraicosahedral sp2 bonds [5]; and their localization and delocalization, iconicity and covalent character along with the electron density determine the properties of B 4 C [15][16][17][18][19]. Group theory predicts 5A 1g + 2A 1u + 2A 2g + 6A 2u + 7E g + 8E u representation for the normal modes of lattice dynamics of R3m rhombohedral B 4 C, where the 12 modes of A 1g and Eg symmetry are Raman active, the 14 modes of A 2u and E u symmetry are Infrared (IR) active and the A 1u and the A 2g modes are optically inactive. When the zero-frequency modes are removed, the number of IR active modes become 12 [20]. If carbon atoms are introduced into the icosahedron, a higher number of vibrational modes can be expected in the collected spectra [5].It was reported that B 4 C exhibits a strong anisotropy of the elastic constants, meaning that elastic moduli are orientation dependent [21]. It was found that the Young's modulus of B 5.6 C single crystal has a maximum E max = 522 GPa along the [111] direction and a minimum Emin = 64 GPa and a maximum shear modulus Gmax = 233 GPa along the [201] direction and Gmin = 165 GPa in the [112] direction [5]. The elastic moduli of isotropic polycrystalline B 4 C have a dependence on the stoichiometry of the B or C atoms [22][23][24][25][26]. While B 4 C exhibits high elastic moduli, determined by the atomic bonding in the compound, the extremely rigid framework arising from the covalently bonded icosahedra and chain units leads to their refractory nature and extreme hardness [27]. B 4 C shows good flexure strength, which is dependent on external factors, such as processing conditions, size of the samples tested, grain size, porosity, presence of defects and so forth. Because B 4 C ceramic is relatively brittle, it shows a strong flaw sensitivity, where defects play a detrimental role and often are responsible for premature failure. Therefore, there has been a significant effort to improve the compaction technologies to provide enhancement in sintering, with the majority of the techniques used for densification of B 4 C being pressureless sintering [28][29][30][31][32], hot pressing [33][34][35][36], hot isostatic pressing [37], direct current sintering [38][39][40][41][42], high pressure sintering in multi-anvil apparatus [43] and contactless flash sintering [44] techniques. Currently, the most accepted and well developed processing technique for densification of B 4 C is the direct current sinterin...

An increase of testing frequency to reduce the testing time could affect the fatigue behavior of metallic materials. The current paper investigates the effect of testing frequency on the high and very high cycle fatigue behavior of AA2024, Ti-6Al-4V, and Inconel 718 alloys tested at 20, 90, and 1000 Hz. To quantify the effect of testing frequency a two-parameter Weibull distribution and Basquin’s equation were utilized as well as the threshold stress intensity factor range was determined. Fatigue crack initiation sites were evaluated on the fracture surface with respect to different testing frequencies. The results showed that changes in the testing frequency significantly influence the mechanical response of the Ti-6Al-4V alloy, while no substantial impact on the fatigue properties of AA2024 and Inconel 718 alloys was identified. The findings of the study contribute to a more complete knowledge of the frequency sensitivity of the alloys and provide valuable insights for the design and evaluation of materials used in high-frequency applications.