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The anode of a proton exchange membrane electrolysis cell (PEMEC) has a complex two-phase flow. Excessive gas concentrations tend to build up on the catalyst layer (CL) surface and inside the porous transport layers (PTLs), inhibiting electrolytic reactions from occurring. Therefore, efficient bubble management methods are required. In this paper, the principle of actions and the effect of mechanical vibration and water velocity as methods of bubble management are investigated. PEMEC bubble kinetic and two-phase flow performance were investigated using high-speed optical imaging at different amplitudes, frequencies and water velocities, and the results were correlated with electrochemical performance. The results show that the vertical sinusoidal vibration can cause cyclic compression of the PTL by the ribs, which promote the discharge of the blocked gas into the flow channel. This effect can be enhanced by increasing the amplitude of the vibration. During vibration, the inertia of the water causes the large bubbles to break up into smaller bubbles and can generate longitudinal shear forces that can promote the bubbles to detach and move. Increasing the frequency can enhance this effect by shortening the period of the action. However, the vertical sinusoidal vibration does not promote the discharge of air bubbles from the flow channel out of the cell, in which the thrust and lateral shear provided by water flow is necessary. Increasing the water velocity can also generate more bubble flow. The combination of vibration and high water velocity can significantly reduce the gas concentration in the cell. Polarization data shows a 7.2% reduction in cell polarization under the experimental conditions (80 mL/min, 1.5 mm, 150 Hz) compared to the normal state. The results of this study can provide theoretical basis and experimental data for the study of bubble management methods, optimization of working conditions and improvement of operating efficiency of PEMEC. • Mechanical vibration and water velocity for bubble management in PEM electrolysis cell were studied. • The overflow of bubbles into the flow channel is facilitated by increasing the amplitude. • By increasing the frequency, bubble breakage, detachment and movement are facilitated. • Increased water velocity reduces bubble volume and facilitates gas discharge from the cell. [ABSTRACT FROM AUTHOR]

• The HSCF limit of the TC11 alloy increased by 10.26% after USRP treatment. • The USRP treatment increased the dislocation density, decreased the β phase content and introduced CRS field, which improved the crack initiation and propagation resistance. • The HSCF limit of the TC11 alloy increased by 47.44% after PEO treatment. • Barrier layer inhibits damage caused by chloride to the substrate and hydrogen permeation. • The HSCF resistance of samples treated with USRP + PEO higher than that of the samples treated with USRP and PEO alone. The effects of the ultrasonic surface rolling process (USRP), plasma electrolytic oxidation (PEO), and their combined treatment (USRP + PEO) on the hot salt corrosion fatigue (HSCF) behavior of TC11 alloy are comparatively studied. The mechanism of improving the HSCF performance of TC11 alloy through the above surface strengthening techniques is revealed by analyzing the surface integrity and microstructure of the modified layer. The results show that the TC11 alloy exhibits high HSCF sensitivity, and fatigue limit reduces by 27.78 % under the condition of 0.1 mg/cm2 solid NaCl deposition at 500 °C compared to the sample without salt deposition. The mechanism of HSCF is that corrosion pits promote the initiation of fatigue cracks by causing local stress concentration on the sample's surface. Meanwhile, hydrogen and hydride generated by hot salt corrosion also promote fatigue crack propagation. Compared with the base material (BM) sample under the condition of 0.1 mg/cm2 NaCl deposition, the HSCF limit increases by 10.26 % by USRP treatment. This is due to the combination of an increase in dislocation density, a decrease of β-phase content, and the introduction of compressive residual stress (CRS), improving the high-temperature fatigue resistance, corrosion resistance, and hydrogen damage resistance of TC11 alloy. PEO treatment increases HSCF resistance of TC11 alloy, and the HSCF limit increases by 47.44 % compared with the BM sample. This is mainly because the dense barrier layer (DBL) could effectively inhibit erosion by the chloride medium and inhibit hydrogen damage, which significantly improve the crack initiation resistance. The HSCF limit of the TC11 alloy further increases by 64.10 % by the USRP + PEO treatment, and the effect of improving the HSCF resistance is better than that of USRP or PEO treatment alone. This is attributed to the fact that USRP pretreatment increases the alloy's erosion resistance to a corrosive medium by increasing the thickness of the DBL. Meanwhile, the synergistic effect of stable CRS and gradient nanostructure introduced by USRP significantly increases the crack initiation and propagation resistance of HSCF for TC11 alloys. [ABSTRACT FROM AUTHOR]

• The fretting fatigue of gradient nanostructured GH4169 was significantly improved at high temperature. • Compressive residual stress plays a leading factor in improving fretting fatigue resistance at high temperature. • Compressive residual stress of gradient nanostructured GH4169 was much more stable than that of non-gradient nanostructured alloy. • The mechanism of fretting fatigue of gradient nanostructured GH4169 at high temperature was revealed. • The mechanism of stability of compressive residual stress was revealed. In this study, a gradient nanostructured GH4169 superalloy was prepared by ultrasonic surface rolling process (USRP), and the fretting fatigue resistance was investigated at elevated temperatures. After USRP, a high density of deformation twins, stacking faults and dislocations as well as precipitates were observed in the surface of the gradient nanostructured GH4169 superalloy when examined using transmission electron microscopy. Factor separation analysis was carried out to determine the leading factor for the improvement of the fretting fatigue properties of GH4169 at elevated temperatures, and the compressive residual stress was found to be the leading factor. The mechanism was determined to be dislocation movement that can be pinned by deformation twins, stacking faults and precipitates and, thus, is able to stabilize the compressive residual stress at elevated temperatures. As a result, the USRP-treated GH4169 with gradient nanostructure was found to have the highest fretting fatigue resistance at elevated temperatures. [ABSTRACT FROM AUTHOR]

• The fatigue life decreases greatly with the increase of salt deposition. • The HSCF sensitivity of the TC11 alloy at 500 °C was further increased by PHSC. • Combined effect of cyclic stress and salt broken the protective layer of TiO 2. • Local stress concentration of pits accelerated the initiation of fatigue cracks. • Hydrogen and the hydride phase promoted fatigue crack propagation. Pre-hot salt corrosion (PHSC) tests is the samples with 0.1, 0.5, 1 and 4 mg/cm2 salt coating are corroded at 500 °C for 100 h. The hot salt corrosion fatigue (HSCF) tests were conducted on PHSC specimens at a stress ratio, a maximum stress amplitudes and temperature of −1, 450 MPa and 500 °C, respectively. The effect of PHSC on HSCF behavior of TC11 alloy at 500 °C was studied by deposition of solid NaCl. The HSCF sensitivity of the TC11 alloy at 500 °C was further increased by PHSC, and increased gradually with the increase in solid NaCl content. When the salt content exceeded 1 mg/cm2, the HSCF life was reduced by more than 99% compared with the samples without salt coating. The mechanism of HSCF was that the local stress concentration of the corrosion pits accelerated the initiation of fatigue cracks, hydrogen and the hydride phase promoted fatigue crack propagation. The PHSC process promoted the formation of corrosion pits, and accelerated the infiltration of hydrogen into the matrix and hydride formation, so the fatigue resistance of pre hot salt corrosion samples was reduced further. A greater NaCl deposition resulted in more severe surface corrosion damage of the titanium alloy, a stronger coupling of corrosion factors and alternating load in the HSCF process, and a greater reduction in fatigue resistance. [ABSTRACT FROM AUTHOR]

Efficient and cost-effective removal of radioactive iodine anions from contaminated water has become a crucial task and a great challenge for waste treatment and environmental remediation. Herein, we present hexadecylpyridinium chloride monohydrate modified bentonite (HDPy-bent) for the efficient and selective removal of iodine anions (I− and IO 3 −) from contaminated water. Batch experiments showed that HDPy-bent could remove more than 95% of I− and IO 3 − within 10 min, and had maximum I− and IO 3 − adsorption capacities of 80.0 and 50.2 mg/g, respectively. Competitive experiments indicated that HDPy-bent exhibited excellent I− and IO 3 − selectivity in the excessive presence of common concomitant anions including PO 4 3−, SO 4 2−, HCO 3 −, NO 3 −, Cl− (maximum mole ratio of anions vs iodine anions was ∼50,000). An anion exchange mechanism was proposed for the selective adsorption of iodine anions. Optimal adsorption structure of HDPy+/I− (IO 3 −) at atomic level and driving forces of the I− (IO 3 −) adsorption were calculated by density functional theory (DFT) simulations. Moreover, the good durability and reusability of the HDPy-bent has been demonstrated with 5 adsorption-desorption cycles. Dynamic column experiment also demonstrated that HDPy-bent exhibited excellent removal and fractional recovery capabilities towards I− and IO 3 − from simulated groundwater and environmental water samples. In conclusion, this work presents a promising adsorbent material for the decontamination of radioactive iodine anions from wastewater on a large scale. [Display omitted] • HDPy-bent showed excellent adsorption abilities for iodide and iodate. • Anions exchange mechanism was confirmed by batch experiments and DFT simulations. • The pyridine N was the intrinsic active site of the modified bentonite. • HDPy-bent was efficient for removing radioiodine anions from wastewater. [ABSTRACT FROM AUTHOR]