Investigation on electrochemical behavior and surface conductivity of titanium carbide modified Ti bipolar plate of PEMFC

The titanium carbide (TiC) modified layer is prepared by plasma surface modification technology on the surface of Ti plate (TA1) to meet the performance requirements of bipolar plate of PEMFC. The microstructure characterization confirms that a compact and defectless TiC modified layer is formed on the surface of Ti bipolar plate. The corrosion current density of TiC modified plate in simulated PEMFC environment is reduced by approximately an order of magnitude and the self-corrosion potential is significantly improved compared with bare Ti plate. The interfacial contact resistance (ICR) of TiC modified plate (7.5 mΩ cm², under loading pressure of 140 N) is evidently lower than bare Ti plate (98.1 mΩ cm²). Even after potentiostatic polarization, the ICR of TiC modified plate still remains at satisfactory values. Furthermore, the contact angle of TiC modified plate reaches a higher value of 112°, which is beneficial to the water discharge of PEMFC.     

Biocompatible nanofilm coating by magneto-luminous polymerization of methane

Coating is uniquely feasible means to impart biocompatibility to artificial materials to be used in biology and medicine, because a totally different surface-state could be created. However, it is necessary to understand factors that control “biocompatibility” first. The examination of molecular level factors involved in interfacial interaction revealed that the best surface-state for biocompatibility should contain no chemical functional group. Such a surface-state cannot be created by conventional chemical means, and application of conventional coating could be used in rather limited cases only. Magneto-luminous polymerization of methane yields nanofilm of amorphous carbon, which seems to be the closest to the ideal non-interacting surface. Fundamental factors involved in interactions of polymer surface with surrounding medium, and mechanisms how magneto-luminous polymerization coating yields amorphous carbon nanofilm, which has the least interfacial interaction capability, are described in this paper.     

Dark current and photovoltage models on the formation of depletion region in C60/NPB organic heterojunctions

We establish quantitative models on the formation of depletion regions in organic photodiodes (OPD) based on fullerene/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (C₆₀/NPB) heterojunctions. The models describe the relation of dark current and open-circuit voltage to the deposited thickness of C₆₀ or NPB. Interfacial electronic structures, such as built-in potential, the charge density, the minimized thicknesses of completely developed depletion regions and the energy level bending on each side of the heterojunction were derived from the fitting model. Also, we observed a shift of depletion region from NPB to C₆₀ due to the relative change of charge density under illumination. The device performance proved the reasonability of the models. This paper provides a universally applicable method to probe the interfacial information of organic semiconductors.     

Fabrication of antennae-like nanoheterostructure attached by porphyrin for increased photocatalytic hydrogen generation and electron transfer mechanism

In order to obtain a highly efficient photocatalyst for hydrogen evolution, an excellent photo active molecule, tetra (p-carboxylphenyl) porphyrin (TCPP) was introduced and orientedly attached on an antennae-like Cu₂O/NiO heterostructure. Subsequently, heterogeneous Cu₂O/NiO/TCPP nanocomposites were achieved. Assembly mechanism of the nanocomposites was investigated in detail. The results showed that, by coordination interaction and hydrogen bond, TCPP molecules can be strongly assembled onto the NiO-riveted Cu₂O. Because of strong interaction among Cu₂O, NiO and TCPP, and the enhanced light absorption, quick transfer of more photo-generated electrons can be achieved. Furthermore, the nanocomposite displayed a higher photocatalytic activity compared with other contrast materials (Cu₂O/NiO/NiTCPP, Cu₂O/NiO, Cu₂O et al.). It was attributed to the improved separation of charges as well as light absorption, which was originated from the well-matched band structure and special heterogeneous interface. This study will open up new perspectives for the fabrication and application of heterojunction photocatalysts.     

A density functional theory study of CO2 hydrogenation to methanol over Pd/TiO2 catalyst: The role of interfacial site

The interface between metal and support has a very significant influence on the activity and selectivity of the CO₂ hydrogenation to methanol, but there is still lack of investigation in understanding its role in the reaction process. In the current work, the synthesis of methanol through CO₂ hydrogenation on a model Pd/TiO₂ catalyst was studied based on the periodic density functional theory calculation, and the reaction mechanism and active sites were revealed after examining the possible routes. The charge density difference and Millikan charge analysis demonstrate that CO₂ adsorbed at the interfacial site is activated due to obtaining charge from the catalyst, and it is transformed into chemisorbed CO₂^δ−. It is found that interface is the active site for the subsequent hydrogenation process of CO₂ while metal Pd provides an active site to the dissociation of H₂. Moreover, there is a metal-support interaction, where the formed H at the Pd particles reacts with the CO₂ and intermediates adsorbed at interface by the spillover, and the methanol is produced on the support surface. In addition, the RWGS + CO-Hydro route is determined to be the dominant pathway for methanol synthesis, and CO hydrogenation to HCO is the rate-determining step.     

Flame retardant synergy between interfacial and bulk carbonation in glass fiber reinforced polypropylene

Glass fiber reinforced polypropylene (GF-PP) composites have high flammability on account of wick effect which leads to accelerated flow of the polymer melt along the glass fibers (GF) surface to the flame zone. In this study, dipentaerythritol (DPER), a charring agent, was adsorbed on the GF surface through the hydrogen bond between silane coupling agent and DPER. DPER has a synergistic effect with the intumescent flame retardants (IFR) added in the composites, which can induce interfacial carbonization on the surface of GF, thus transforming the intrinsic smooth GF surface into roughness one. In this way, the negative effect of the wick effect in flame retardancy is weakened. Moreover, the char residues remained on the surface of GF can bring an improved adhesion between GF and char residues formed in the resin so that a more stable barrier char layer is formed. The PP composites with 20 wt% modified glass fiber (M-GF) and 30 wt% IFR can achieve the UL-94V-0, and its limiting oxygen index (LOI) value increased from 16.5% to 29.5%. Simultaneously, the heat release rate (HRR), total heat release (THR) and total smoke release (TSR) decreased significantly, and the peak of heat release rate (PHRR) reduced 60.6% compared with GF-PP.     

Validation of two-phase CFD models for propellant tank self-pressurization: Crossing fluid types,scales, and gravity levels

This paper examines our computational ability to capture the transport and phase change phenomena that govern cryogenic storage tank pressurization and underscores our strengths and weaknesses in this area in terms of three computational-experimental validation case studies. In the first study, 1g pressurization of a simulant low-boiling point fluid in a small scale transparent tank is considered in the context of the Zero-Boil-Off Tank (ZBOT) Experiment to showcase the relatively strong capability that we have developed in modelling the coupling between the convective transport and stratification in the bulk phases with the interfacial evaporative and condensing heat and mass transfer that ultimately control self-pressurization in the storage tank. Here, we show that computational predictions exhibit excellent temporal and spatial fidelity under the moderate Ra number – high Bo number convective-phase distribution regimes. In the second example, we focus on 1g pressurization and pressure control of the large-scale K-site liquid hydrogen tank experiment where we show that by crossing fluid types and physical scales, we enter into high Bo number – high Ra number flow regimes that challenge our ability to predict turbulent heat and mass transfer and their impact on the tank pressurization correctly, especially, in the vapor domain. In the final example, we examine pressurization results from the small scale simulant fluid Tank Pressure Control Experiment (TCPE) performed in microgravity to underscore the fact that in crossing into a low Ra number – low Bo number regime in microgravity, the temporal evolution of the phase front as affected by the time-dependent residual gravity and impulse accelerations becomes an important consideration. In this case detailed acceleration data are needed to predict the correct rate of tank self-pressurization.     

Influence of hard segment content and nature on polyurethane/multiwalled carbon nanotube composites

Knowledge of how polyurethanes, PU, complexity affects their derived multiwalled carbon nanotube, MWCNT, composites could shed important clues for preparing future tailored PU/MWCNT elastic, strong and electrically conductive composites. In this regard, hard segment content and nature, along with MWCNT functionalisation, are believed to have great influence on both nanoscale PU/MWCNT self assembling mechanisms and on final composites properties. In this work the effect of PU hard segment content into composites was analysed. According to the results, a preferential interaction of nanotubes with polyurethanes hard segments can be assumed although nanotubes introduction hindered both soft and hard segments crystallisation. In all cases carbon nanotubes percolative network formation seemed to be crucial for obtaining significant reinforcement, being observed at this stage, a reduction of ductility, phenomena which is related to an increase on hard domains interconnections by MWCNT. The hard to soft segment ratio into PU plays a crucial role on determining the stress transfer to MWCNT. In addition, PU hard domains nature has important effect on nanotubes reinforcing character, this fact being related to the different PU intrinsic morphologies as well as different PU-MWCNT interactions.     

Mechanical properties and strengthening mechanism of SiCf/SiC mini-composites modified by SiC nanowires

The effects of the SiC nanowires (SiCNWs) and PyC interface layers on the mechanical and anti-oxidation properties of SiC fiber (SiC_f)/SiC composites were investigated. To achieve this, the PyC layer was coated on the SiC_f using a chemical vapour infiltration (CVI) method. Then, SiCNWs were successfully coated on the surface of SiC_f/PyC using the electrophoretic deposition method. Finally, a thin PyC layer was coated on the surface of SiC_f/PyC/SiCNWs. Three mini-composites, SiC_f/PyC/SiC, SiC_f/PyC/SiCNWs/SiC, and SiC_f/PyC/SiCNWs/PyC/SiC, were fabricated using the typical precursor infiltration and pyrolysis method. The morphologies of the samples were examined using scanning electron microscopy and energy dispersive X-ray spectrometry. Tensile and single-fibre push-out tests were carried out to investigate the mechanical performance and interfacial shear strength of the composites before and after oxidization at 1200 °C. The results revealed that the SiC_f/PyC/SiCNWs/SiC composites showed the best mechanical and anti-oxidation performance among all the composites investigated. The strengthening and toughening is mainly achieved by SiCNWs optimization of the interfacial bonding strength of the composite and its own nano-toughening. On the basis of the results, the effects of SiCNWs on the oxidation process and retardation mechanism of the SiC_f/SiC mini-composites were investigated.     

Phase-field simulation of tip splitting in dendritic growth of Fe-C alloy

Two types of dendrite tip splitting including dendrite orientation transition and twinned-like dendrites in Fe-C alloys were investigated by phase-field method.In equiaxed growth, the possible dendrite growth directions and the effect of supersaturation on tip splitting were discussed;the dendrite orien-tation transition was observed, and it was found that the orientation regions of anisotropy parameters were reduced from three to two with increasing the supersaturation, which was due to the effect of interfacial anisotropy controlled by the solute in front of S/L interface changing with the increase of supersaturation.In directional solidification, it was found that the twinned-like dendrites were formed with the fixed anisotropy couples and no seaweed dendrites were observed;these were concluded from the results of competition between process anisotropy and inherent anisotropy.The formation process of twinned-like dendrite was investigated by tip splitting phenomenon, which was related to the chan-ges of dendrite tips growth velocity.Then, the critical speed of tips splitting and solute concentration of twinned-like dendrites were investigated, and a new type of microsegregation in Fe-C alloys was proposed to supplement the dendrite growth theories.