Fabrication Process Simulation of a PEM Fuel Cell Catalyst Layer and Its Microscopic Structure Characteristics

The catalyst layers (CLs) in proton exchange membrane fuel cells (PEMFCs) are porous composites of complex microstructures of the building blocks, i.e., Pt nano-particles, carbonaceous substrates and Nafion ionomers. It is important to understand the factors that control the microstructure formation in the fabrication process. A coarse-grained molecular dynamics (CG-MD) method is employed to investigate the fabrication process of CLs, which depends on the type and amount of components and also the type of the dispersion medium (ethylene glycol, isopropanol or hexanol) used during ink preparation of the catalyst-coated membranes (CCMs). The dynamical behaviors of all the components are outlined and analyzed following the fabrication steps. In addition, the Pt nano-particle size distribution is evaluated and compared with the labor testing. Furthermore, the primary pore size distributions in the final formations of three cases are shown and compared with the experiments. The sizes of the reconstructed agglomerates are also considered on the effect of solvent polarity. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.064203jes] All rights reserved

Effect of Stress on Creep Behavior of Single Crystal Alloy IC6SX at 980°C

Ni3Al-based single crystal alloy IC6SX was prepared by seed crystal method. The effect of different stress conditions on creep behavior of this alloy at 980°C was investigated. The results showed that the creep life of this alloy at 980°C decreased significantly with the increase of stress. When the stress increased from 180 MPa to 230 MPa, the creep life dropped from 245.5 h to 69.3 h, and the steady-state creep rate increased slightly but not significantly. Meanwhile, the morphology of γ′ phase and dislocation after creep were studied. The results showed that with the increase of stress, the density of dislocations in the γ′ phase increased gradually, the strength of this alloy decreased gradually, so the creep life decreased significantly. The Y-NiMo phase resolved from the γ phase decreased gradually as the creep life decreased. The creep experiment of the alloy was carried out at 980°C. Due to the higher temperature, the diffusion of atoms in this alloy became faster. Deformation was not only caused by the slippage of dislocations in the crystal but also by the diffusion of atoms. Therefore, the creep mechanism of single crystal alloy IC6SX at this temperature is a mixed mechanism of dislocation glide and diffusion

Additional file 1 of Development of a multiple cross displacement amplification combined with nanoparticles-based biosensor assay for rapid and sensitive detection of Streptococcus pyogenes

Additional file 1

Bimetal Zeolitic Imidazolite Framework-Derived Iron‑, Cobalt- and Nitrogen-Codoped Carbon Nanopolyhedra Electrocatalyst for Efficient Oxygen Reduction

Replacing precious metal electrocatalysts with high-performance and low-cost nonprecious metal electrocatalysts (NPMCs) is crucial for the commercialization of fuel cell technologies. Herein, we present a novel and facile route for synthesis of iron-, cobalt-, and nitrogen-codoped carbon nanopolyhedra electrocatalysts (Fe,Co,N-CNP) by one-step pyrolysis of a new type of Fe/Co bimetal zeolitic imidazolate framework (Fe,Co-ZIF) crystals that were self-assembled by oxygen-free solvothermal reaction of Fe²⁺ and Co²⁺ with 2-methylimidazole. During the pyrolysis process, the Fe²⁺ ions in Fe,Co-ZIF not only effectively inhibit the aggregation of Co nanoparticles but also increase the specific surface area (SSA) and N content of the resultant electrocatalysts. The optimized Fe,Co,N-CNP(0.3) (Fe/Co molar ratio of 0.3 in Fe,Co-ZIF) electrocatalyst exhibited a highly promising activity for oxygen reduction reaction (ORR) with a positive half-wave potential (<i>E</i>_1/2) of 0.875 V (29 mV higher than that of the commercial Pt/C), excellent methanol tolerance, and electrochemical stability in the alkaline electrolyte. Also, Fe,Co,N-CNP(0.3) presents comparable ORR catalytic activity as Pt/C in the acidic electrolyte with <i>E</i>_1/2 of 0.764 V and superior methanol tolerance and electrochemical stability. The outstanding ORR performance of Fe,Co,N-CNP(0.3) is ascribed to the synergistic contribution of homogeneous Fe, Co, and N codoping structure, high SSA, and hierarchically porous structure for rapid mass transport. This novel and rational methodology for controlled synthesis of ZIFs-derived nitrogen-doped porous carbon nanopolyhedras offers new prospects in developing highly efficient NPMCs for ORR

Hydrothermal Synthesis of Highly Dispersed Co₃O₄ Nanoparticles on Biomass-Derived Nitrogen-Doped Hierarchically Porous Carbon Networks as an Efficient Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions

Developing high-performance bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of vital importance in energy storage and conversion systems. Herein, we demonstrate a facile hydrothermal synthesis of highly dispersed Co₃O₄ nanoparticles (NPs) anchored on cattle-bone-derived nitrogen-doped hierarchically porous carbon (NHPC) networks as an efficient ORR/OER bifunctional electrocatalyst. The as-prepared Co₃O₄/NHPC exhibits a remarkable catalytic activity toward both ORR (outperforming the commercial Pt/C) and OER (comparable with the commercial RuO₂ catalyst) in alkaline electrolyte. The superior bifunctional catalytic activity can be ascribed to the large specific surface area (1070 m² g^–1), the well-defined hierarchically porous structure, and the high content of nitrogen doping (4.93 wt %), which synergistically contribute to the homogeneous dispersion of Co₃O₄ NPs and the enhanced mass transport capability. Moreover, the primary Zn–air battery using the Co₃O₄/NHPC cathode demonstrates a superior performance with an open-circuit potential of 1.39 V, a specific capacity of 795 mA h g_Zn^–1 (at 2 mA cm^–2), and a peak power density of 80 mW cm^–2. This work delivers a new insight into the design and synthesis of high-performance bifunctional nonprecious metal electrocatalysts for Zn–air battery and other electrochemical devices

One-Step Conversion from Core–Shell Metal–Organic Framework Materials to Cobalt and Nitrogen Codoped Carbon Nanopolyhedra with Hierarchically Porous Structure for Highly Efficient Oxygen Reduction

Rational design of porous structure is an effective way to fabricate the nonprecious metal electrocatalysts (NPMCs) toward oxygen reduction reaction (ORR) with high activity comparable or even superior to Pt-based electrocatalysts. Herein, we demonstrate a facile synthetic route to fabricate cobalt and nitrogen codoped carbon nanopolyhedra with hierarchically porous structure (Co,N-HCNP) by one-step carbonization of core–shell structured ZIF-8@ZIF-67 crystals. The resultant Co,N-HCNP electrocatalyst possesses a unique hierarchically micro/mesoporous structure with internal micropores and external mesopores, of which sufficient exposure and accessibility of ORR active sites can be achieved due to the large specific surface area and efficient transport pathway. More importantly, the existence of ZIF-8 core in the core–shell structured ZIF-8@ZIF-67 can promote the homogeneous pyrolysis of ZIF-67 shell, leading to a uniform distribution of Co–N_<i>x</i> active sites for Co,N-HCNP. As a result, the well-designed Co,N-HCNP electrocatalyst exhibits remarkable ORR activity with a high onset potential comparable to the commercial Pt/C, a half-wave potential of 0.855 V (9 mV more positive than that of Pt/C), and a kinetic current density of 63.84 mA cm^–2 at 0.8 V (2.3-fold enhancement compared with that of Pt/C) in alkaline electrolyte. Furthermore, the Co,N-HCNP electrocatalyst also presents outstanding electrochemical durability and methanol tolerance in comparison with Pt/C. The unique hierarchically porous structure of Co,N-HCNP achieved in this work provides a new insight into the design and synthesis of nanoarchitecture with targeted pore structure and opens a new avenue for the synthesis of highly efficient NPMCs for ORR

Nitrogen and Phosphorus Codoped Mesoporous Carbon Derived from Polypyrrole as Superior Metal-Free Electrocatalyst toward the Oxygen Reduction Reaction

To replace high-cost platinum group metal (PGM) electrocatalysts for oxygen reduction reaction (ORR) that is the crucial cathode reaction in fuel cell technology and metal–air battery, the development of low-cost and high-efficiency non-PGM catalysts for ORR has attracted much attention during the past decades. As one of the promising candidates, N-doped carbon is highly desirable for its strong designability and outstanding catalytic activity and stability. In this work, a facile and rational strategy is demonstrated for preparation of N,P-codoped mesoporous carbon (N,P-MC) for ORR by the direct pyrolysis treatment of polypyrrole with phytic acid as P-dopant and polystyrene sphere as template. The resultant N,P-MC exhibits a mesoporous structure with the optimized ORR active sites originating from the N,P-codoping. Owing to these features, N,P-MC exhibits excellent ORR activity, remarkable electrochemical stability, and superior methanol tolerance, comparable or even better than that of commercial Pt/C catalyst. The origin of enhanced ORR performance can be attributed to both the increased active sites and the mesoporous structure, which is expected to guide the future preparation of more capable carbon-based electrocatalysts for oxygen reduction and other electrocatalytic application

Construction of an alternative NADPH regeneration pathway improves ethanol production in Saccharomyces cerevisiae with xylose metabolic pathway

Full conversion of glucose and xylose from lignocellulosic hydrolysates is required for obtaining a high ethanol yield. However, glucose and xylose share flux in the pentose phosphate pathway (PPP) and glycolysis pathway (EMP), with glucose having a competitive advantage in the shared metabolic pathways. In this work, we knocked down ZWF1 to preclude glucose from entering the PPP. This reduced the [NADPH] level and disturbed growth on both glucose or xylose, confirming that the oxidative PPP, which begins with Zwf1p and ultimately leads to CO2 production, is the primary source of NADPH in both glucose and xylose. Upon glucose depletion, gluconeogenesis is necessary to generate glucose-6-phosphate, the substrate of Zwf1p. We re-established the NADPH regeneration pathway by replacing the endogenous NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene TDH3 with heterogenous NADP + -GAPDH genes GDH, gapB, and GDP1. Among the resulting strains, the strain BZP1 (zwf1Δ, tdh3::GDP1) exhibited a similar xylose consumption rate before glucose depletion, but a 1.6-fold increased xylose consumption rate following glucose depletion compared to the original strain BSGX001, and the ethanol yield for total consumed sugars of BZP1 was 13.5% higher than BSGX001. This suggested that using the EMP instead of PPP to generate NADPH reduces the wasteful metabolic cycle and excess CO2 release from oxidative PPP. Furthermore, we used a copper-repressing promoter to modulate the expression of ZWF1 and optimize the timing of turning off the ZWF1, therefore, to determine the competitive equilibrium between glucose-xylose co-metabolism. This strategy allowed fast growth in the early stage of fermentation and low waste in the following stages of fermentation