Amorphous-crystalline cobalt-molybdenum bimetallic phosphide heterostructured nanosheets as Janus electrocatalyst for efficient water splitting

Efficient and sustainable Janus catalysts toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are highly desirable for future hydrogen production via water electrolysis. Herein we report an active Janus electrocatalyst of amorphous-crystalline cobalt-molybdenum bimetallic phosphide heterostructured nanosheets on nickel foam (CoMoP/CoP/NF) for efficient electrolysis of alkaline water. As-reported CoMoP/CoP/NF consists of amorphous bimetal phosphide nanosheets doped with crystalline CoMoP/CoP heterostructured nanoparticles on NF. It can efficiently catalyze both HER (η = 127 mV@100 mA cm^?2) and OER (η = 308 mV@100 mA cm^?2) in alkaline electrolyte with long-term durability. Serving as anode and cathode of water electrolyzer, CoMoP/CoP/NF generates electrolytic current of 10, 50 and 100 mA cm^?2 at low voltage of 1.50, 1.59, and 1.67 V, respectively.     

In situ growth of three-dimensional graphene coatings on arbitrary-shaped micro/nano materials and its mechanism studies

In the past decade, there have been great advances in the controllable growth of two-dimensional (2D) graphene sheets. However, the preparation of 3D structured graphene such as graphene coatings on arbitrary-shaped micro/nano materials still remains a formidable challenge. Herein, we have proposed a general strategy for the in situ growth of 3D graphene coatings on the micro/nano particles with arbitrary shapes. Inspired by the CVD growth mechanism of 2D graphene sheets on the bulk metal substrates, we have in situ constructed a nanometer-thick catalytic interface on the micro/nano particle surface by introducing a trace amount of transition metal salts and solid carbon sources with strictly-controlled content and ratio. Growth of 3D graphene coatings is accomplished through a solid-state reaction. Under the catalysis of the in situ formed catalytic interface consisting of highly-ordered metal nanoislands, the nano-thick amorphous carbon layer which arousing from the pyrolysis of carbon sources can be effectively transformed into a continuous and uniform graphene coating throughout the material surface based on a “dissolution–precipitation” mechanism. 3D graphene coatings have been successfully grown on lithium iron phosphate, silver, copper and silicon particles. The growth mechanism of the 3D graphene coatings has been studied in detail and a growth model is also proposed.     

Hydrogen from wet air and sunlight in a tandem photoelectrochemical cell

A solid-state photoelectrochemical (SSPEC) cell is an attractive approach for solar water splitting, especially when it comes to monolithic device design. In a SSPEC cell the electrodes distance is minimized, while the use of polymer-based membranes alleviates the need for liquid electrolytes, and at the same time they can separate the anode from the cathode. In this work, we have made and tested, firstly, a SSPEC cell with a Pt/C electrocatalyst as the cathode electrode, under purely gaseous conditions. The anode was supplied with air of 80% relative humidity (RH) and the cathode with argon. Secondly, we replaced the Pt/C cathode with a photocathode consisting of 2D photocatalytic g-C₃N₄, which was placed in tandem with the photoanode (tandem-SSPEC). The tandem configuration showed a three-fold enhancement in the obtained photovoltage and a steady-state photocurrent density. The mechanism of operation is discussed in view of recent advances in surface proton conduction in absorbed water layers. The presented SSPEC cell is based on earth-abundant materials and provides a way towards systems of artificial photosynthesis, especially for areas where water sources are scarce and electrical grid infrastructure is limited or nonexistent. The only requirements to make hydrogen are humidity and sunlight.     

Development of a small DMFC bipolar plate stack for portable applications

The direct methanol fuel cell (DMFC) is regarded as a promising candidate in portable electronic power applications. Bipolar plate stacks were systematically studied by controlling the operating conditions, and by adjusting the stack structure design parameters, to develop more commercial DMFCs. The findings indicate that the peak power of the stack is influenced more strongly by the flow rate of air than by that of the methanol solution. Notably, the stack performance remains constant even as the channel depth is decreased from 1.0 to 0.6 mm, without loss of the performance in each cell. Furthermore, the specific power density of the stack was increased greatly from ∼60 to ∼100 W l⁻¹ for stacks of 10 and 18 cells, respectively. The current status of the work indicates that the power output of an 18-cell short stack reaches 33 W in air at 70 °C. The outer dimensions of this 18-cell short stack are only 80 mm × 80 mm × 51 mm, which are suitable for practical applications in 10–20 W DMFC portable systems.     

Microstructure and mechanical behaviour of semi-solid die-casting AZ91D magnesium alloy

Microstructures and mechanical properties of an AZ91D magnesium alloy prepared with semi-solid die-casting (SSDC) were characterized in as-cast conditions. The SSDC alloy exhibits a unique microstructure featuring primary α-Mg globules uniformly distributed in the matrix of fine secondary α-Mg grains and β-Mg₁₇Al₁₂ intermetallic. High ultimate tensile strength and elongation have been achieved before fracture. Observations on the vertical-section microstructure of the fractured sample by scanning electron microscopy (SEM) show that the crack mainly originated from the brittle fracture of the eutectic phase causes the interface decohesion of the ductile Mg phase, making fracture a rather critical event. Before that, the deformation of ductile α-Mg phase in the matrix as well as the “pulling out” of primary α-Mg phase combines to provide the SSDC alloy a certain strain.     

热变形对汽车用Al-Sc-Zr合金高温流变形行为的影响及本构方程的建立

在Gleeble-3000D热模拟机上对Al-0.2Sc-0.04Zr铝合金开展了热变形实验,系统地研究该合金变形参数在0.001~5 s-1和440~600 ℃下的高温流变行为。研究结果表明:在低应变速率和较高的温度下,DRX的发生较为完全。同时,在较低温度（T≤520 ℃）下变形,主要软化机制为动态回复;在较高温度（T>520 ℃）下变形,软化机制转变为动态再结晶,且获得了较为完全的动态再结晶组织;在高温（T≥600 ℃）下变形,晶粒出现明显的长大。分析应力指数（n）和变形激活能（Q）,二者均随变形温度的升高而增加。采用双曲正弦模型,建立了适合Al-0.2Sc-0.04Zr合金的本构方程,可很好地预测峰值应力,为工业化生产提供理论依据。      

Online stiffness estimation for robotic tasks with force observers

In this paper we propose an online stiffness estimation technique for robotic tasks based only on force data, therefore, not requiring contact position information. This allows estimations to be obtained in robotic tasks involving interactions with unstructured and unknown environments where geometrical data is unavailable or unreliable. Our technique – the Candidate Observer Based Algorithm (COBA) – uses two force observers, configured with different candidate stiffnesses, to estimate online the actual target object stiffness. COBA is embedded in a force control architecture with computed torque in the task space. The theoretical presentation of the algorithm, as well as simulation tests and experimental results with a lightweight robot arm are also presented.     

高性能混凝土外加剂对水泥砂浆力学性能的影响

采用混合水平正交表研究了新型外加剂对砂浆强度的影响.通过掺加不同因子及水平数的新型外加剂成型了16组水泥砂浆试件,测试了3 d和28 d龄期的强度,采用正交设计中的方差分析、试验误差等方法分析表明,高性能混凝土外加剂并不是性能最好的外加剂,不减少用水量的情况下,用高性能混凝土外加剂替代同等质量水泥后,外加剂对强度的影响并不是显著因素.掺量较少的情况下,对混凝土强度的提高不明显,掺量过大,会造成缓凝.掺加聚羧酸减水剂提高强度,高性能混凝土外加剂和减水剂之间存在交互作用.     

Bimodal plate structures induced by pulsed laser in duplex-phase Zr alloy

A duplex-phase Zr-2.5Nb alloy was treated by pulsed laser, followed by careful microstructural characterization using field emission gun scanning electron microscope and attached electron backscatter diffraction. Beneath the modification zones with common uniform α-plate structures(UPS), a layer of unreported bimodal α-plate structures(BPS) featured by coarse(submicron)plates forming multiple cores surrounded by dense fine(nanoscale) plates was found. Presence of such BPS is attributed to non-equilibrium thermodynamic conditions induced by the pulsed laser treatments. Limited diffusion of Nb due to the short pulse during laser heating allows β phases with distinctly different Nb contents to be presented: Nb-enriched prior β films and Nb-depleted β phases, transforming into the fine and the coarse plates during cooling, respectively. Orientation analyses show that both types of plates in the BPS are aroused essentially from a single β orientation, suggesting epitaxial growth of the Nb-depletedβ phases from the preexisting β films.     

Multi-objective robust design optimization of a novel negative Poisson’s ratio bumper system

Negative Poisson’s ratio (NPR) structure has outstanding performances in lightweight and energy absorption, and it can be widely applied in automotive industries. By combining the front anti-collision beam, crash box and NPR structure, a novel NPR bumper system for improving the crashworthiness is first proposed in the work. The performances of the NPR bumper system are detailed studied by comparing to traditional bumper system and aluminum foam filled bumper system. To achieve the rapid design while considering perturbation induced by parameter uncertainties, a multi-objective robust design optimization method of the NPR bumper system is also proposed. The parametric model of the bumper system is constructed by combining the full parametric model of the traditional bumper system and the parametric model of the NPR structure. Optimal Latin hypercube sampling technique and dual response surface method are combined to construct the surrogate models. The multi-objective robust optimization results of the NPR bumper system are then obtained by applying the multi-objective particle swarm optimization algorithm and six sigma criteria. The results yielded from the optimizations indicate that the energy absorption capacity is improved significantly by the NPR bumper system and its performances are further optimized efficiently by the multi-objective robust design optimization method.