Development of anion exchange membranes with good dimension, chemical stability, high conductivity and long life-time simultaneously is still a challenge for practical application of anion exchange ...membrane fuel cells. Herein, a mechanically and chemically stable poly(styrene-b-(ethylene-co-butylene)-b-styrene) triblock copolymer based crosslinked membranes are designed, prepared and characterized. N,N,N′,N′-tetramethyl-1,6-hexanediamine is introduced into the membranes as the crosslinker and functional reagent, which exhibits the significant improvement in water uptake (less than 7%), swelling ratio (8–5%, greatly smaller than uncrosslinked membranes) and tensile strength (higher than 18MPa). The hydroxide conductivity (14.9mScm−1 at 30°C) of the obtained membrane is obtained due to hydrophilic/hydrophobic microphase separation formed between the structure of crosslinking and quaternary ammonium groups. It demonstrates that incorporating stable crosslinking structure to polymer backbone greatly improves the chemical stability under Fenton and alkaline long-term tests. Furthermore, the peak power density of an H2/O2 single fuel cells reaches high peak power density of 416mWcm−2 at 0.514V. Based on these outstanding properties, the developed crosslinked membranes will be a promising candidate material for anion exchange membrane fuel cells.
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•The crosslinked triblock SEBS based AEMs were prepared with a facile method.•TMHDA was used as both crosslinker and functional reagent.•The AEMs show good dimension stability and low swelling ratio.•The crosslinked AEMs exhibit good oxidative stability and alkaline stability.•A peak power density of 416mWcm−2 was obtained in AEMFC.
SUMMARY
Focal mechanism solutions and their predicted stress pattern can be used to investigate tectonic deformation in seismically active zones and contribute to understanding and constraining the ...kinematic patterns of the outward growth and uplift of the Tibetan Plateau. Herein, we determined the focal mechanisms of 398 earthquakes in Northeast Tibet recorded by the China National Seismic Network (CNSN) by using the cut-and-paste method. The results show that the earthquakes predominately exhibited thrust and strike-slip faulting mechanisms with very few normal events. We then combined the derived focal mechanisms with global centroid moment tensor (GCMT) catalogue solutions and previously published solutions to predict the regional distribution of the stress field through a damped linear inversion. The inversion results show that most of region is dominated by a thrust faulting regime. From the southern East Kunlun fault in the west to the northern Qilian Mountains along the Altyn Tagh fault (ATF), the maximum compression axis rotates slightly clockwise; farther to the south of the Haiyuan fault in the east, there is an evident clockwise rotation of the maximum compression axis, especially at the eastern end of the Haiyuan fault. In the Qilian Mountains, the axis of the compressive stress orientation approximately trends NE–SW, which does not markedly differ from the direction of India–Eurasia convergence, emphasizing the importance of the compressive stress in reflecting the remote effects of this continental collision. The overall spatial pattern of the principal stress axes is closely consistent with the GPS-derived horizontal surface velocity. A comparison of the stress and strain rate fields demonstrated that the orientations of the crustal stress axes and the surface strain axes were almost identical, which indicates that a diffuse model is more suitable for describing the tectonic characteristics of Northeast Tibet. Additionally, the compressive stress orientation rotated to ENE–WSW in the northern Qilian Mountains along the ATF and to ENE–WSW or E–W along the eastern part of the Haiyuan fault and its adjacent area to the south, highlighting the occurrence of strain partitioning along large left-lateral strike-slip faults or the lateral variation of crustal strength across these faults. Combining geodetic, geological and seismological results, we suggest that a hybrid model incorporating both the diffuse model associated with shortening and thickening of the upper crust and the asthenospheric flow model accounting for the low-velocity zone in the middle-lower crust may reflect the primary mode of crustal deformation in Northeast Tibet.
A 9-cell proton exchange membrane (PEM) water electrolysis stack is developed and tested for 7800 h. The average degradation rate of 35.5 μV h−1 per cell is measured. The 4th MEA of the stack is ...offline investigated and characterized. The electrochemical impedance spectroscopy (EIS) shows that the charge transfer resistance and ionic resistance of the cell both increase. The linear sweep scan (LSV) shows the hydrogen crossover rate of the membrane has slight increase. The electron probe X-ray microanalyze (EPMA) illustrates further that Ca, Cu and Fe elements distribute in the membrane and catalyst layers of the catalyst-coated membranes (CCMs). The cations occupy the ion exchange sites of the Nafion polymer electrolyte in the catalyst layers and membrane, which results in the increase in the anode and the cathode overpotentials. The metallic impurities originate mainly from the feed water and the components of the electrolysis unit. Fortunately, the degradation was reversible and can be almost recovered to the initial performance by using 0.5 M H2SO4. This indicates the performance degradation of the stack running 7800 h is mainly caused by a recoverable contamination.
•Degradation of electrolysis stack after running 7800 h is investigated.•Cations occupied ion exchange sites of membrane and the catalyst layers.•Cations impurities cause the increase in ohmic resistance and charge transfer resistance.•The hydrogen crossover rate of the MEA slightly increased after 7800 h operation.•Cell performance is almost completely recovered after dilute sulfur acid treatment.
Metal oxide semi-conductors are widely applied in various fields due to their low cost, easy processing, and good compatibility with microelectronic technology. In this study, ternary ...α-Fe2O3/TiO2/Ti3C2Tx nanocomposites were prepared via simple hydrothermal and annealing treatments. The composition, morphology, and crystal structure of the samples were studied using XPS, SEM, EDS, XRD, and multiple other testing methods. The gas-sensing measurement results suggest that the response value (34.66) of the F/M-3 sensor is 3.5 times higher than the pure α-Fe2O3 sensor (9.78) around 100 ppm acetone at 220°C, with a rapid response and recovery time (10/7 s). Furthermore, the sensors have an ultra-low detection limit (0.1 ppm acetone), excellent selectivity, and long-term stability. The improved sensitivity of the composites is mainly attributed to their excellent metal conductivity, the unique two-dimensional layered structure of Ti3C2Tx, and the heterojunction formed between the nanocomposite materials. This research paves a new route for the preparation of MXene derivatives and metal oxide nanocomposites.
Nanostructured ultrathin catalyst layer based on open-walled PtCo bimetallic nanotube arrays has been designed and constructed through a hydrothermal and physical vapor deposition method for proton ...exchange membrane fuel cells (PEMFCs). The open-walled PtCo bimetallic NTAs with a diameter ca. 100nm were directly aligned with proton exchange membrane, forming an ultrathin catalyst layer with a thickness ca. 300nm. The incorporation of Co in Pt is realized by a facile thermal annealing method, endowing the catalyst layer with improved activity. During the purification of catalyst-coated-membrane (CCM) electrode, the sealed off PtCo nanotubes cracked into open-walled nanotubes, making both the interior and exterior surfaces exposed to the surroundings. The catalyst layer is binder-free and beneficial for exposing catalytic active sites, enhancing mass transport during the operation of PEMFCs. Serving as cathode, a maximum power density of 14.38kWgPt−1 was achieved with a cathodic Pt loading of 52.7μgcm−2, which is 1.7 fold higher than the conventional CCM. Accelerated degradation test (ADT) manifests that the prepared nanostrucutred ultrathin catalyst layer is more stable than the conventional CCM. The proposed catalyst layer structure and also its preparation method hold great potential for PEMFCs and other applications.
Nanostructured ultrathin catalyst layer based on open-walled PtCo bimetallic nanotube arrays has been designed and constructed for fuel cells. The concept is realized by hydrothermal synthesis and physical vapor deposition method. Beneficial from its structural advantages, a power density of 17.02kWgPt−1 (anode) and 14.38kW gPt−1 (cathode) has been achieved. And the advanced catalyst layer presented enhanced durability over the conventional catalyst layer. Display omitted
•A nanostructured ultrathin catalyst layer (NUCL) has been constructed for PEMFCs.•The NUCL is based on open walled Co-doped Pt nanotube arrays (NTAs).•The Co-doped Pt NTAs is prepared from a template-assisted deposition and etching strategy.•Single cell test manifests that NUCL has a pronounced catalyst utilization and durability.
The Chuan-Dian Rhombus Block is the main channel for materials escaping southeastward from the Tibetan Plateau. Verifying the extent of the lower crustal flow and its impact on the lithospheric ...deformation, isostatic state, and seismicity in the Chuan-Dian Rhombus Block is of vital importance. Based on data from the China Seismic Experimental Site, the current study analyzes the rheological structure of the eastern boundary of the Chuan-Dian Rhombus Block (i.e., the Xianshuihe–Xiaojiang Fault System). The results reveal a low-viscosity zone of 1020 Pa∙s, with a thickness of approximately 20 km in the middle–lower crust beneath the Xianshuihe fault. The low-viscosity zone extends southward and gradually thins until it basically disappears at the Xiaojiang fault. Our results indicate that the extent of the lower crustal flow is restricted in the Xianshuihe fault and the northernmost part of the Anninghe–Zemuhe fault and does not extend to the Xiaojiang fault. The crust of the Xianshuihe fault is notably thickened and in an isostatic disequilibrium state. The Xiaojiang fault maintains a relatively thick seismogenic layer and isostatic equilibrium.
•A 20-km-thick low-viscosity zone is revealed beneath Xianshuihe fault.•Xianshuihe fault features a low rheological strength and nonisostasy.•Low viscosity in mantle beneath Xiaojiang fault is due to deep material migration.•Lower crustal flow concentrates in Xianshuihe and Anninghe–Zemuhe faults.
Platinum dispersity on the carbon support is first shown as a factor of local oxygen transport resistance in this work, while its impact on PEMFC performance is also analyzed. The dispersity of ...platinum is defined as the distribution density of Pt particles on the surface of carbon supports. In order to exclude the influence of catalyst layer thickness, different platinum dispersity cathode catalyst layers are prepared by mechanical mixing Pt/C with different mass ratios, different Pt loadings with the same amount of Pt and carbon in the MEAs to keep the thickness of catalyst layers consistent. Initial fuel cell performance is much higher with lower Pt dispersity. Oxygen transport resistance is measured through limiting current density method, and the total oxygen transport resistance Rtotal, Fick diffusion resistance RF, and local oxygen transport resistance R are calculated. All of them increase at higher Pt dispersity. Platinum dispersity shows obvious influence both on performance and oxygen transport resistance. Thus, increasing the ratio of platinum particles distributed at the surface of carbon supports and the density of platinum particles on carbon supports can be effective ways to solve the problem of performance loss with low Pt loading at high current densities.
•Explore an important factor of local oxygen transport resistance – Pt dispersity.•Investigate the influence of Pt dispersity on MEA performance.•Verify the great influence of water film on local oxygen transport resistance.
Bimetallic platinum-copper (Pt-Cu) alloy nanowires have emerged as a novel class of fuel cell electrocatalysts for oxygen reduction reaction (ORR) due to their intrinsic high catalytic activity and ...durability, but preparing such electrocatalysts with clean surface via facile method is still a challenge. Herein, PtCu alloy with nanowire networks (NWNs) structure is obtained by a simple modified polyol method accompanied with a salt-mediated self-assembly process in a water/ethylene glycol (EG) mixing media. The formation mechanism of PtCu NWNs including the morphological evolution and the relevant experimental parameters has been investigated systematically. We propose that a micro-interface in H2O-EG media formed with the assistance of disodium dihydrogen pyrophosphate (Na
2
H
2
P
2
O
7
) and its unique nature of coordinating with Pt
2+
or Cu
2+
play critical roles in the formation of NWNs. When tested as ORR catalyst, the PtCu
NWNs
/C exhibits much higher activity and durability than that of Pt
NWNs
/C and commercial Pt/C, even exceeding the target of DOE in 2020. The excellent performance of PtCu
NWNs
/C could be attributed to the unique structure of NWNs with 2.4 nm ultrathin wavy nanowires and plentiful surface defects and the modified electronic effect caused by alloying with Cu atoms.
We processed the data recorded by 32 continuous GPS stations from the Crustal Movement Observation Network of China and combined them with published GPS observations in a common geodetic reference ...frame to better depict the ongoing crustal velocities and deformation field of Northeast Tibet. The derived velocity field indicates that the deformation of Northeast Tibet is characterized mainly by crustal shortening coupled with the eastward extrusion of crustal material and clockwise block rotation. We further used the GPS velocity field to evaluate the strain rate tensors by the method of Sandwell and Wessel (2016). The strain rate field shows an obvious transition of the contraction rate from NE-SW to NEE-SWW, and a decrease in the maximum shear strain rate from west to east was observed along the East Kunlun fault and Haiyuan fault, indicating that the block rotation and lateral extrusion therein may be partitioned by NE-SW-oriented compression to some extent. The inhomogeneity of the rotation strain rate implies that Northeast Tibet does not behave like a single rigid block but instead resembles a left-lateral shear zone, supporting the hypothesis that the northward transfer of motion along the East Kunlun fault may play a significant role in the deformation style of this area. The dilatation rate verified that most of Northeast Tibet experiences crustal thickening, which coincides with the average uplift rate of ~1 mm/y revealed by GPS velocities and channel steepness indices. We also estimated the geodetic moment rates and compared them with the seismic moment rates estimated using the truncated Gutenberg-Richter earthquake distribution. The ratio of the seismic strain rate to the geodetic strain rate in the regions near the Altyn Tagh fault, the Qaidam Basin adjoining the Qilian Mountains, the Haiyuan fault and the central part of the East Kunlun fault are near unity, indicating that the deformation in these areas is dominated by seismic release and may represent fully coupled seismogenic zones. The occurrence of large earthquakes in the past (estimated magnitudes M ≥ 6) coupled with a high geodetic deformation rate in these regions could indicate overdue M ≥ 6 earthquakes. However, other factors, including the occurrence of creep and the long recurrence time of Mw ≥ 8.0 earthquakes, should be taken into consideration along the Haiyuan fault. By contrast, in other regions, including the southern and eastern parts of the Haiyuan fault, along the Elashan fault, and the northern Qilian Mountains, the geodetic moment rate is higher than the seismic moment rate by a factor between 3 and 9. We propose that this phenomenon is related to the undersampling of long-term earthquake rates within the seismic catalogue, long-term aseismic crustal deformation, or a combination of these factors. Our study has implications for better comprehending the current seismotectonic pattern of Northeast Tibet.
•A new GPS kinematics picture of Northeast Tibet was portrayed.•Northeast Tibet resembles a left-lateral shear zone, not a rigid block.•Block rotation and lateral extrusion be partitioned by NE-SW compression.•Most of the seismogenic zones were distributed in the boundary faults.
This study focuses on the M greater than or equal to 6.7 earthquakes that have occurred since 1816 on the Xianshuihe fault zone in southwest China. The interseismic Coulomb stress accumulation and ...the Coulomb stress changes caused by coseismic dislocation and postseismic viscoelastic relaxation of the previous shocks were computed for different periods on the relevant fault segments. Based on these results, we analyzed the relationship between time-adjacent strong shocks and the Coulomb stress evolution before every earthquake. The analysis suggests that strong earthquakes mostly occurred in the Coulomb stress enhancement region caused by coseismic dislocation and postseismic viscoelastic relaxation of the last earthquake. Considering the Coulomb stress evolution at the fault planes of the epicentral area before earthquakes, we found that the Coulomb stress accumulation caused by the interseismic tectonic loading was dominant for most strong earthquakes. For some other earthquakes the stress changes caused by coseismic dislocation and postseismic viscoelastic relaxation of surrounding earthquakes were very significant, which may be equivalent to the effect of interseismic tectonic loading lasting hundreds of years. Based on the time-dependent probabilistic risk model and the Dieterich (1994) model, we estimate the background seismic activity and the future earthquake probability for different fault segments, using long term seismic activity and strong earthquake recurrence cycles. It is shown that the Bamei, Selaha, and Kangding segments of the Xianshuihe fault zone have high earthquake probability, and are likely to have strong earthquakes. If energy is accumulated up to the year 2050, the magnitude of an event on these three segments could reach M sub(w) 7.2, M sub(w) 7.0, and M sub(w) 7.1 respectively, while if the S7 and S8 cascades rupture, the event on these segments could reach a magnitude of up to M sub(w) 7.2.
