Numerical study of microscopic particle arrangement of suspension flow in a narrow channel for the estimation of macroscopic rheological properties

In a narrow channel, the apparent relative viscosity of a suspension with finite-size particles is strongly dependent on its microscopic particle arrangement. Relative viscosity increases when suspended particles flow near the channel wall; thus, a suspension in a narrow channel does not always exhibit the same rheological properties even if the concentration is the same. In this study, we focus on the inertia and concentration of particles in a narrow channel and consider their effects on the microscopic particle arrangement and macroscopic suspension rheology. Two-dimensional pressure-driven suspension flow simulations were performed using a two-way coupling scheme, and normalized particle density distribution (PDD) were implemented to consider their particle arrangements. The results demonstrated that the velocity profiles for the particle suspension were changed by the Reynolds number and particle concentration because of the interactions between particles according to the power-law index. These changes affected the particle equilibrium positions in the channel, and the subsequent changes in solvent layer thickness caused changes in the macroscopic apparent viscosity. The behavior of microscopic particles played important roles in determining macroscopic rheology. Thus, we have confirmed that a normalized PDD can be used to estimate and assess the macroscopic rheology of a suspension.     

Bimetallic platinum–ruthenium nanoparticles immobilized on reduced graphene oxide-TiO2 (RGO-TiO2) support for ethanol electro oxidation in acidic media

The present work addresses the potentialities of Pt–Ru nanoparticles deposited on a graphene oxide (RGO) and TiO₂ composite support towards electrochemical oxidation of ethanol in acidic media relevant for fuel cell applications. To immobilize platinum–ruthenium bimetallic nanoparticles on to an RGO-TiO₂ nanohybrid support a simple solution-phase chemical reduction method is utilized. An examination using electron microscopy and energy dispersive X-ray spectroscopy (EDS) indicated that Pt–Ru particles of 4–8 nm in diameter are dispersed on RGO-TiO₂ composite support. The corresponding Pt–Ru/RGO-TiO₂ nanocomposite electrocatalyst was studied for the electrochemical oxidation of ethanol in acidic media. Compared to the commercial Pt–Ru/C and Pt/C catalysts, Pt–Ru/RGO-TiO₂ nanocomposite yields higher mass-specific activity of about 1.4 and 3.2 times, respectively towards ethanol oxidation reaction (EOR). The synergistic boosting provided by RGO-TiO₂ composite support and Pt–Ru ensemble together contributed to the observed higher EOR activity and stability to Pt–Ru/RGO-TiO₂ nanocomposite compared with other in-house synthesized Pt–Ru/RGO, Pt/RGO and commercial Pt–Ru/C and Pt/C electrocatalysts. Further optimization of RGO-TiO₂ composite support provides opportunity to deposit many other types of metallic nanoparticles onto it for fuel cell electrocatalysis applications.     

A review of thin film electrolytes fabricated by physical vapor deposition for solid oxide fuel cells

The ohmic resistance in solid oxide fuel cells (SOFCs) mainly comes from the electrolyte, which can be reduced by developing novel electrolyte materials with higher ionic conductivity and/or fabricating thin-film electrolytes. Among various kinds of thin-film fabrication technology, the physical vapor deposition (PVD) method can reduce the electrolyte thickness to a few micrometers and mitigate the issues associated with high-temperature sintering, which is necessary for wet ceramic methods. This review summarizes recent development progress in thin-film electrolytes fabricated by the PVD method, especially pulsed laser deposition (PLD) and magnetron sputtering. At first, the importance of the substrate surface morphology for the quality of the film is emphasized. After that, the fabrication of thin-film doped-zirconia and doped-ceria electrolytes is presented, then we provide a brief summary of the works on other types of electrolytes prepared by PVD. Finally, we have come to the summary and made perspectives.     

One-step to prepare high-performance gas diffusion layer (GDL) with three different functional layers for proton exchange membrane fuel cells (PEMFCs)

Gas diffusion layer (GDL) is one of the most important components of fuel cells. In order to improve the fuel cell performance, GDL has developed from single layer to dual layers, and then to multiple layers. However, dual or multi layers in GDL are usually prepared by layer-by-layer methods, which cost too much time, energy, and resources. In this work, we successfully developed a facile one-step method to prepare a GDL with three functional layers by utilizing the different sedimentation rates and filtration rates of short carbon fiber (CF) and carbon nanotube (CNT). The treatment temperature for this GDL is much lower than that of traditional method. The thickness of the GDL can be effectively controlled from as thin as 50 μm to more than 200 μm by simply adjusting the content of CF. The GDL with high flexibility is suitable to develop high performance flexible electronics. The fuel cell with the GDL has the maximum power density 1021 mW cm^?2, which shows 19% improvement comparing to the conventional one. Therefore, this work breaks the traditional concept that GDL for fuel cells only can be prepared by very complex and high-cost procedure.     

The role of microbial electrogenesis in regulating methane and nitrous oxide emissions from constructed wetland-microbial fuel cell

This study assesses a sustainable solution to greenhouse gases (GHGs) mitigation using constructed wetland-microbial fuel cells (CW-MFC). Roots of wetland plant Acorus Calamus L. are placed in biological anode to better enable anode microorganisms to obtain rhizosphere secretion for power improvement. Three selected cathode materials have a large difference in GHG emissions, and among them, carbon fiber felt (CFF) shows the lowest emissions of methane and nitrous oxide, which are 0.77 ± 0.04 mg/(m²·h) and 130.78 ± 13.08 μg/(m²·h), respectively. The CFF CW-MFC achieves the maximum power density of 2.99 W/m³. As the influent pH value is adjusted from acidic to alkaline, the GHGs emissions are reduced. The addition of Ni inhibits GHGs emission but decreases the electricity, the power density is reduced to 1.09 W/m³, and the methane and nitrous oxide emission fluxes decline to 0.20 ± 0.04 mg/(m²·h) and 15.49 ± 1.86 μg/(m²·h), respectively. Low C/N ratio reduces methane emission, while high C/N ratio effectively inhibits nitrous oxide emission. At the influent pH 8 and C/N = 5:1, the methane emission flux is approximately 10.60 ± 0.27 mg/(m²·h), and the nitrous oxide emission flux is only 10.90 ± 1.10 μg/(m²·h). Based on the above experimental results by controlling variable factors, it is proposed that CW-MFC offers an environment-friendly solution to regulate GHG emissions.     

Nonsimilar solution of a boundary layer flow of a Reiner–Philippoff fluid with nonlinear thermal convection

The thermodynamics modeling of a Reiner–Philippoff-type fluid is essential because it is a complex fluid with three distinct probable modifications. This fluid model can be modified to describe a shear-thinning, Newtonian, or shear-thickening fluid under varied viscoelastic conditions. This study constructs a mathematical model that describes a boundary layer flow of a Reiner–Philippoff fluid with nonlinear radiative heat flux and temperature- and concentration-induced buoyancy force. The dynamical model follows the usual conservation laws and is reduced through a nonsimilar group of transformations. The resulting equations are solved using a spectral-based local linearization method, and the accuracy of the numerical results is validated through the grid dependence and convergence tests. Detailed analyses of the effects of specific thermophysical parameters are presented through tables and graphs. The study reveals, among other results, that the buoyancy force, solute and thermal expansion coefficients, and thermal radiation increase the overall wall drag, heat, and mass fluxes. Furthermore, the study shows that amplifying the space and temperature-dependent heat source parameters allows fluid particles to lose their cohesive force and, consequently, maximize flow and heat transfer.     

Sintering behavior of BaCe0.7Zr0.1Y0.2O3-δ electrolyte at 1150 °C with the utilization of CuO and Bi2O3 as sintering aids and its electrical performance

BaCe_0.7Zr_0.1Y_0.2O_3-δ (BCZY) is one of the promising electrolytic candidate for solid oxide fuel cell (SOFC) due to its good proton conductivity and better stability. Herein, the effect of dual sintering aids such as CuO-Bi₂O₃ upon the sinterability at low temperature, improved electrochemical properties, and thermo-chemical changes about proton-conducting BaCe_0.7Zr_0.1Y_0.2O_3-δ electrolyte were investigated in detail. FESEM micrographs and shrinkage curves revealed significant improvement in sinterability and densifications of BCZY electrolyte. The dense pellets were sintered with CuO-Bi₂O₃ (2–3 mol %) as sintering aids at a temperature of 1150 °C for 5 h. The perfectly uniform distribution of sintering aids increased the linear shrinkage of BCZY from 5% till 19–21%. The crystallite size and grain growth within the structure was enhanced due to the formation of the melting phase of Bi₂O₃ and Cu²⁺ incorporation in the perovskite structure. The elevated and improved electrochemical measurement for BCZY with 2 mol% of CuO-Bi₂O₃ as sintering aid categorized it well suited for solid oxide fuel cells.     

Investigation of La0.6Sr0.4Co1-xNixO3-δ (x=0, 0.2, 0.4, 0.6, 0.8) catalysts on solid oxide fuel cells anode for biogas dry reforming

The introduction of catalyst on anode of solid oxide fuel cell (SOFC) has been an effective way to alleviate the carbon deposition when utilizing biogas as the fuel. A series of La_0.6Sr_0.4Co_1-xNi_xO_3-δ (x = 0, 0.2, 0.4, 0.6, 0.8) oxides are synthesized by sol-gel method and used as catalysts precursors for biogas dry reforming. The phase structure of La_0.6Sr_0.4Co_1-xNi_xO_3-δ oxides before and after reduction are characterized by X-ray diffraction (XRD). The texture properties, carbon deposition, CH₄ and CO₂ conversion rate of La_0.6Sr_0.4Co_1-xNi_xO_3-δ catalysts are evaluated and compared. The peak power density of 739 mW cm^?2 is obtained by a commercial SOFC with La_0.6Sr_0.4Co_0.4Ni_0.6O_3-δ catalyst at 850 °C when using a mixture of CH₄: CO₂ = 2:1 as fuel. This shows a great improvement from the cell without catalyst for internal dry reforming, which is attributed to the formation of NiCo alloy active species after reduction in H₂ atmosphere. The results indicate the benefits of inhibiting the carbon deposition on Ni-based anode through introducing the La_0.6Sr_0.4Co_0.4Ni_0.6O_3-δ catalyst precursor. Additionally, the dry reforming technology will also help to convert part of the exhaust heat into chemical energy and improve the efficiency of SOFC system with biogas fuel.     

Antibacterial activity of V- doped rod-like MgO crystals decorated with nanoflake layer

In present study, we report a V doping fabrication method for obtaining rod-like MgO crystals decorated with a nanoflake layer. This novel structure has only been minimally reported in literature. Pure MgO and Mg₂V₂O₇–MgO composite materials were obtained by precipitation and impregnation methods, with vanadium added concentrations of 0–9%. The influence of V doping on crystal structure and particle morphology of MgO was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis demonstrated that MgO has a cubic structure, while X-ray photoelectron spectroscopy (XPS) revealed that V⁵⁺ exists on the surface of MgO. The specific surface areas and pore sizes of MgO composites were calculated by BET and BJH analysis. These techniques revealed that specific surface area and pore size of MgO increased due to vanadium doping. The antibacterial effects of Mg₂V₂O₇–MgO composite materials against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were assessed using a bacterial killing/colony-forming unit (CFU) assay and bacteriostatic ring method. Our results demonstrate that V doping dramatically improved antimicrobial properties of MgO, with 7 mol% doping inducing the best antibacterial activity. The antibacterial mechanisms of Mg₂V₂O₇–MgO composite material were also proposed.     

Understanding on the hydrogen detection of plasma sprayed tin oxide/tungsten oxide (SnO2/WO3) sensor

The plasma spray technique was well proven in producing metal oxide based gas sensors in the last two decades using different powder feedstocks. However, limited research was made to fabricate hydrogen gas sensor from tin oxide layer coated over tungsten oxide layer. This paper attempts to interpret the hydrogen gas sensing performances of plasma sprayed coating derived by depositing tin oxide layer over tungsten oxide (SnO₂/WO₃) layer. Plasma sprayed SnO₂/WO₃ sensor showed maximum response of 90% at 150 °C in contrast to stand-alone WO₃ (89% at 350 °C) and stand-alone SnO₂ (89% at 250 °C). The lower operating temperature of SnO₂/WO₃ sensor without compromising gas response was attributed to the WO₃–SnO₂ hetero-junction. SnO₂/WO₃ sensor showed selective sensing towards hydrogen with respect to carbon monoxide and methane gases. This sensor also possessed repeatable characteristics after 39 days from the initial measurement. In a nut-shell, plasma spayed SnO₂/WO₃ sensor showed stability of base resistance, repeatability after successive response and recovery cycles, selective sensing towards 500 ppm H₂ with significant magnitude of gas response of 90%, response time of 35 s and recovery time of 269 s at a temperature of 150 °C.