混联机器人搅拌摩擦焊接系统集成研究

机器人搅拌摩擦焊设备因具有焊接适应性强、易于实现空间全位置焊接、自动化程度高、生产效率高等技术特点,近年来得到了越来越多地应用.针对空间曲线焊缝搅拌摩擦焊接需求,开展了五轴混联型机器人搅拌摩擦焊接系统研究.该系统由搅拌摩擦焊接机器人子系统、液压主轴子系统、传感与控制子系统和中央控制单元组成,能够实现复杂构件的空间曲面焊...     

Surface modification of graphitic carbon nitride nanoparticles with B,O and S doping/carbon vacancy for efficient dehydrogenation of sodium borohydride in methanol

Herein, the surface properties of graphitic carbon nitride (GCN) with sulphur(S), boron (B) and oxygen (O) dopants were improved. The heteroatom-doped metal-free GCN exhibited both rich surface functional groups and a carbon defect structure. These metal-free catalysts were used to obtain hydrogen (H₂) from the sodium borohydride (SB) methanolysis for the first time. Compared to GCN, S, B, and O doped GCN catalyst obtained showed a 2.2-fold improvement in H₂ production. HGR value obtained with B, O and S doped GCN (10 mg) via SB of 2.5% was 9166 ml min ⁻¹g⁻¹. XPS, SEM-EDX, TEM, FTIR, and XRD analyses were used for the structural properties of catalysts. The activation energy (Ea) for B, O and S doped GCN was 28.89 kJ mol⁻¹.     

Prediction of TC11 single-track geometry in laser metal deposition based on back propagation neural network and random forest

Laser metal deposition process usually involves the nonlinear interaction of multiple factors, such as process parameters and ambient temperature. In this study, random forest (RF) and multilayer back propagation neural network (BPNN) algorithms were employed to investigate the coupling relationship between process parameters and single-track geometry in laser metal deposition for TC11 alloy. With laser power, scanning speed, and powder feeding rate as inputs and track width and height as outputs, 30 different groups of experimental results were adopted as training groups. Their geometries were also predicted. The maximum relative errors of track width and height predictions based on BPNN model were 0.007 % and 0.029 %, respectively, which were lower than those based on RF model. Then, the two models were used to predict the geometry under four new sets of process parameters. Experimental results showed that the maximum error of BPNN model is lower than that of RF model. BPNN model also showed potential to improve cladding quality and efficiency.

     

Tailoring the p-Band Center of N?S Pair for Accelerating High-Performance Lithium–Oxygen Battery

The local coordination environment of catalytical moieties directly determines the performance of electrochemical energy storage and conversion devices, such as Li–O₂ batteries (LOBs) cathode. However, understanding how the coordinative structure affects the performance, especially for non-metal system, is still insufficient. Herein, a strategy that introduces S-anion to tailor the electronic structure of nitrogen–carbon catalyst (SNC) is proposed to improve the LOBs performance. This study unveils that the introduced S-anion effectively manipulates the p-band center of pyridinic-N moiety, substantially reducing the battery overpotential by accelerating the generation and decomposition of intermediate products Li_1–3O₄. The lower adsorption energy of discharging product Li₂O₂ on N S pair accounts for the long-term cyclic stability by exposing the high active area under operation condition. This work demonstrates an encouraging strategy to enhance LOBs performance by modulating the p-band center on non-metal active sites.     

Universal Source-Template Route to Metal Selenides Implanting on 3D Carbon Nanoarchitecture: Cu2−xSe@3D-CN with Se?C Bonding for Advanced Na Storage

The development of high-performance sodium ion batteries (SIBs) is heavily relied on the exploration of the appropriate electrode material for Na⁺ storage, which ought to feature merits of high capacity, easy-to-handle synthesis, high conductivity, expedite mass transportation, and stable structure upon charging–discharging cycle. Herein, a universal source-template method is reported to synthesize a variety of transition metal (e.g., V, Sb, W, Zn, Fe, Co, Ni, and Cu) selenides implanting on N doped 3D carbon nanoarchitecture hybrids (M_mSe_n@3D-CN) with powerful Se C bonding rivet. Benefiting from the superior architecture and potent Se C bonding between Cu_2−xSe and N-doped 3D carbon (3D-CN), the Cu_2−xSe@3D-CN nanohybrids, as anode of SIBs, show high capacity, high-rate capability, and long-cycle durability, which can deliver a reversible capacity of as high as 386 mAh g⁻¹, retain 219 mAh g⁻¹ even at 10 A g⁻¹, and run durably over thousands of charging–discharging cycles. The Cu_2−xSe@3D-CN as anode is also evaluated by developing a full SIB by coupling with the Na₃V₂(PO₄)₃ cathode, which can deliver high energy density and show excellent stability, shedding light on its potential in practical application.     

Melamine-phytic acid derived supramolecular synthesis of g-C3N4 for enhanced solar hydrogen evolution

It is an effective approach to regulate the structure of photocatalysts by introducing the heteroatoms into the lattice for extended light absorption and enhanced charge separation. In this work, the P atoms were introduced to substitute the corner C atoms of g-C₃N₄ by calcinating the melamine-phytic acid derived supramolecular with high-density phosphate groups, which is synthesized by hydrothermal method. The intermediate state produced by the introduction of P atoms leads to the enhanced light absorption of P–CN_(7.2g-IP6) with a negative shifted conduction band position, which benefits the photocatalytic hydrogen reaction kinetically. Moreover, the electron transferred from P atom to the surrounding N atoms results in the positively charged P center, which could act as Lewis acid site. Such formed Lewis acid site at positively charged P center together with the Lewis base sites, such as amine or imine groups in P–CN, makes it easier to separate photogenerated charges, thus enabling the P–CN_(7.2g-IP6) to exhibit an enhanced photocatalytic hydrogen rate of 2.743 mmol·g⁻¹·h⁻¹, which is about 6.77 times that of pristine g-C₃N₄ (0.405 mmol·g⁻¹·h⁻¹). This work provides an alternative approach to regulating the structure of photocatalysts.     

Synergistically Tailoring the Electronic Structure and Ion Diffusion of Atomically Thin Co(OH)2 Nanosheets Enable Fast Pseudocapacitive Sodium Ion Storage

The fast-growing development for high-capacity anodes is undermined by their unsatisfactory rate performance and cycling stability stemming from sluggish ion-migration speed, poor electronic conductivity, and mechanical degradation induced by the stress accumulation, which greatly hamper practical applications of Na-ion batteries. Here, a combined experimental and theoretical study on atomic-thickness (0.6 nm) Co(OH)₂ nanosheet with surface defects (2D-Co(OH)₂@D NSs) and large interplanar spacing (0.465 nm) is presented, in which fast ion/electron transport is permitted to boost battery reactions. The mechanical degradation on cycling can be well buffered via tailoring mesopores across the Co(OH)₂ nanosheet and an elastic solid–electrolyte interface is established by modulating the electronic structure of the Co(OH)₂ surface. The 2D-Co(OH)₂@D NSs exhibit high rate-capacity (>228 mAh g⁻¹ at 20 A g⁻¹) and superior cyclic stability with negligible decay during 1300 cycles. This study will shed light on the development of electrode materials at atomic-level design for high-power and long-lived performance.     

In situ induced growth strategy of Co2P nanocrystals encapsulated into stable 3D carbon network as a bifunctional electrocatalyst for Zn-air battery

Rational design of inexpensive and robust carbon-based bifunctional catalysts is of considerable interest for practical application of rechargeable Zn-air battery (ZAB) technology. Herein, a facile in-situ induced growth strategy is developed to construct Co₂P nanocrystals encapsulated into a stable 3D carbon nanotube-modified graphene network (Co₂P@NPCNG). Specifically, cobalt tetranitrophthalocyanine (CoPc(NO₂)₄) is employed not only as the coupling agent to form and complex Co₂P nanocrystals with graphene, but also as the inducer to catalyze the graphitization of melamine to grow the uniform Co₂P nanocrystal-encapsulated CNTs on graphene in situ. Encouragingly, the as-synthesized Co₂P@NPCNG exhibits favorable bifunctional oxygen electrocatalytic activity, fast reaction kinetics and excellent stability. Impressively, both liquid ZAB and all-solid-state ZABs used Co₂P@NPCNG as air-cathode catalysts display considerable open-circuit voltage, charge-discharge property and long lifetime. Significantly, density functional theory (DFT) calculations demonstrate that the superior properties of Co₂P@NPCNG originate to the synergetic contributions between the stable configuration of 3D conductive carbon network and high metallic density of Co₂P. This work may provide feasible and facile avenues to strategically construct high-efficient 3D carbon-based bifunctional electrocatalysts for portable and even wearable devices.     

Performance superiority of an arc-shaped polymer electrolyte membrane fuel cell over a straight one

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a promising electricity-producing technology but needs further improvement to become economically viable. Oxygen transfer to reaction zone is known as one of the main PEMFC performance-limiting factors. Accordingly, various recent studies have been focused on fuel cell design to improve oxygen transfer. The present study numerically investigates the influences of converting a straight (or planar) PEMFC to a bent (arc-shaped) one. The idea of PEMFC bending originates from the fact that it can create a velocity component perpendicular to gas diffusion layer (GDL) and exert centrifugal force on channel gas flow towards the GDL; thereby, enhancing oxygen transfer. The results indicate that PEMFC bending can enhance performance up to about 8.33% for the examined operating conditions. It is also observed that PEMFC bending impact factor generally increases with operating pressure, stoichiometry ratio and bending angle, but decreases with operating voltage.     

Reactivating the Dead Lithium by Redox Shuttle to Promote the Efficient Utilization of Lithium for Anode Free Lithium Metal Batteries

Anode free lithium metal batteries (AFLMBs), as a kind of novel battery configuration with zero excess lithium, can improve the energy density to the limit compared with lithium metal batteries and effectively ensure the safety. However, the lifespan of AFLMBs is a tricky problem because there is no extra lithium source to compensate for the irreversible loss of active lithium, which is mainly caused by the continuous decomposition of electrolyte and the formation of dead lithium. Herein, a redox shuttle additive, which can be oxidized in the cathode and reduced in the electrolyte reversibly, is introduced to improve the lithium utilization and lifespan of AFLMBs by reactivating the dead lithium. During the charging process, the redox shuttle additive can be oxidized on the cathode surface and serve as electron acceptor toward dead lithium. The electrically isolated dead lithium in the electrolyte can be re-activated into active lithium ions when captured by oxidized redox shuttle additive.As a result, electrolyte with redox shuttle achieves average higher coulombic efficiency of 99.13% than electrolyte without redox shuttle (97.71%). In addition, the AFLMB with redox shuttle exhibits improved cycling performance with extended lifespan.