Efficient and stable PtFe alloy catalyst for electrocatalytic methanol oxidation with high resistance to CO

Direct methanol fuel cells(DMFC) are widely considered to be an ideal green energy conversion device but their widespread applications are limited by the high price of the Pt-based catalysts and the instability in terms of surface CO toxicity in long-term operation.Herein,the PtFe alloy nanoparticles(NPs) with small particle size(~4.12 nm) supported on carbon black catalysts with different Pt/Fe atomic ratios(Pt_(1)Fe_(2)/C,Pt_(3)Fe_(4)/C,Pt_(1)Fe_(1)/C,and Pt_(2)Fe_(1)/C) are successfully prepared for enhanced anti-CO poisoning during methanol oxidation reaction(MOR).The optimal atomic ratio of Pt/Fe for the MOR is 1:2,and the mass activity of Pt_(1)Fe_(2)/C(5.40 A mg_(Pt)^(-1)) is 13.5 times higher than that of conventional commercial Pt/C(Pt/C-JM)(0.40 A mg_(Pt)^(-1)).The introduction of Fe into the Pt lattice forms the PtFe alloy phase,and the electron density of Pt is reduced after forming the PtFe alloy.In-situ Fourier transform infrared results indicate that the addition of oxyphilic metal Fe has reduced the adsorption of reactant molecules on Pt during the MOR.The doping of Fe atoms helps to desorb toxic intermediates and regenerate Pt active sites,promoting the cleavage of C-O bonds with good selectivity of CO_(2)(58.1%).Moreover,the Pt_(1)Fe_(2)/C catalyst exhibits higher CO tolerance,methanol electrooxidation activity,and long-term stability than other Pt_(x)Fe_(y)/C catalysts.

Underwater Laser Welding/Cladding for High-performance Repair of Marine Metal Materials:A Review

With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must be performed in underwater environments.The underwater laser welding/cladding technique is a promising and advanced technique which could be widely applied to the maintenance of the damaged equipment.The present review paper aims to present a critical analysis and engineering overview of the underwater laser welding/cladding technique.First,we elaborated recent advances and key issues of drainage nozzles all over the world.Next,we presented the underwater laser processing and microstructural-mechanical behavior of repaired marine materials.Then,the newly developed powder-feeding based and wire-feeding based underwater laser direct metal deposition techniques were reviewed.The differences between the convection,conduction,and the metallurgical kinetics in the melt pools during underwater laser direct metal deposition and in-air laser direct metal deposition were illustrated.After that,several challenges that need to be overcame to achieve the full potential of the underwater laser welding/cladding technique are proposed.Finally,suggestions for future directions to aid the development of underwater laser welding/cladding technology and underwater metallurgical theory are provided.The present review will not only enrich the knowledge in the underwater repair technology,but also provide important guidance for the potential applications of the technology on the marine engineering.

Underwater laser directed energy deposition of NV E690 steel

Powder-based laser direct metal deposition(DMD),one of the directed energy deposition,was applied in air andunderwater to repair pre-machined NV E690 steel plates.Systematic investigations on the effects of underwaterenvironment and ambient pressures(0.01–0.35 MPa)on the microstructure evolution,phase transformation,andmechanical properties were conducted.The water quenching effect refined the grain size and increased thedislocation density and lath martensite content.The theoretical models of the underwater pressurized nitridingprocess and the precipitation kinetics of(Ti,V)N particles were established.Moreover,the microstructure evolution and the mechanical properties of other underwater DMD repaired samples did not show obvious relationwith the underwater ambient pressures.This investigation not only provides a candidate for the underwaterrestoration technique but also bridges marine engineering and emerging DMD technology.

Flexible thermochromic fabrics enabling dynamic colored display

Color-changeable fbers can provide diverse functions for intelligent wearable devices such as novel information displays and human-machine interfaces when woven into fabric.This work develops a low-cost,efective,and scalable strategy to produce thermochromic fbers by wet spinning.Through a combination of diferent thermochromic microcapsules,fexible fbers with abundant and reversible color changes are obtained.These color changes can be clearly observed by the naked eye.It is also found that the fbers exhibit excellent color-changing stability even after 8000 thermal cycles.Moreover,the thermochromic fbers can be fabricated on a large scale and easily woven or implanted into various fabrics with good mechanical performance.Driven by their good mechanical and physical characteristics,applications of thermochromic fbers in dynamic colored display are demonstrated.Dynamic quick response(QR)code display and recognition are successfully realized with thermochromic fabrics.This work well confrms the potential applications of thermochromic fbers in smart textiles,wearable devices,fexible displays,and human-machine interfaces.

Robust sliding mode control of general time-varying delay stochastic systems with structural uncertainties

This paper presents a new robust sliding mode control （SMC） method with well-developed theoretical proof for general uncertain time-varying delay stochastic systems with structural uncertainties and the Brownian noise （Wiener process）. The key features of the proposed method are to apply singular value decomposition （SVD） to all structural uncertainties and to introduce adjustable parameters for control design along with the SMC method. It leads to a less-conservative condition for robust stability and a new robust controller for the general uncertain stochastic systems via linear matrix inequality （LMI） forms. The system states are able to reach the SMC switching surface as guaranteed in probability 1. Furthermore, it is theoretically proved that the proposed method with the SVD and adjustable parameters is less conservatism than the method without the SVD. The paper is mainly to provide all strict theoretical proofs for the method and results.