Abstract Compared with the relatively simple monometallic and bimetallic oxide catalytic systems, polymetallic catalysts have attracted much attention in recent years. CuO–(Y 2 O 3 ) (1− x )/2 (CeO 2 ) x ( x = 0, 0.2, 0.4, 0.6, 0.8, and 1) polymetallic catalyst for hydrogen production by methanol steam reforming(MSR) was prepared by sol–gel method and characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, X‐ray photoelectron spectroscopy (XPS), and Specific surface area and pore size analyser(BET) techniques. XRD results show that the diffraction peaks of CuO–(Y 2 O 3 ) 0.4 (CeO 2 ) 0.2 are sharp and intense, indicating that it is highly crystalline. SEM results show that the pore structure of catalyst becomes loose with the increase of Ce doping amount, and the catalyst particles become more uniform in size and more loose in shape. The BET results show that compared with other catalysts, CuO–(Y 2 O 3 ) 0.4 (CeO 2 ) 0.2 catalyst has larger specific surface area, which improves the catalytic performance. XPS results showed that CuO–(Y 2 O 3 ) 0.4 (CeO 2 ) 0.2 still had catalytic activity after reduction treatment. The results of MSR showed that the doping amount of cerium and the reaction conditions affected the catalytic performance of the catalyst. Ce doping promoted the synergistic effect of Cu and Y, and the hydrogen production of CuO–(Y 2 O 3 ) 0.4 (CeO 2 ) 0.2 was the highest (about 6.74 × 10 −3 mol/min/g cat ). Ce doping leads to the change of CO/CO 2 selectivity in gas products. The CO selectivity of CuO–(Y 2 O 3 ) 0.4 (CeO 2 ) 0.2 catalyst is only 2% under the catalytic conditions of 400°C, W/M 4:1, and LHSV 20 h −1 , which shows good catalytic activity.
To deal with the air pollution and global warming caused by marine industry due to the use of fossil fuels, the application of proton exchange membrane fuel cells has received a lot of attentions in marine industry. However, the cationic contaminants from marine atmosphere have adverse effects on the performance of fuel cells. The mainly reason is the destruction of the ability of the proton exchange membrane to transfer protons by cationic contaminants. To understand the effects of marine cationic contaminants on the transport performance of the membrane, an all-atom model of cations (Na + , K + , Ca 2+ and Mg 2+ ) contaminated Nafion 117 membrane is established in this study, and classical molecular dynamics simulations are performed. The diffusion coefficients of cations, water molecules and hydronium ions are calculated using mean square displacements and Einstein's diffusion law. As expected, the diffusion coefficients of water molecules and hydronium ions are quite smaller than the simulation results without the presence of cationic contaminants. Radial distribution functions and relative concentrations are analyzed to study the interactions between cations and sulfonic groups. It was found that the diffusion coefficient is negatively related to the interaction degree between particles and sulfonic groups.
The present study reports on the synthesis of two-dimensional (2D) ceria and graphene quantum dots (CeO2-δ-GQD) composites and their functional properties. Composites were prepared by a simple liquid phase deposition (LPD) method followed by a thermal treatment in air at 250 and 400 °C. The structural and optical properties of composites were investigated by X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), High-Resolution Transmission Electron Microscopy (HR-TEM), Raman spectroscopy, Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-Vis and photoluminescence (PL). The composites consist of crystalline CeO2-δ regions of about 1.8–2.9 nm in size, coexisting with highly disordered GQDs areas. The CeO2-δ-GQD composites experience gradual dehydration and oxidation of carbon processes during thermal treatment, influencing the CeO2 crystal size, Ce3+/Ce4+ ratio, and O vacancies presence. These effects allow for the control of some of the composite functional properties. Specifically, the CeO2-GQD250 composites exhibit a low recombination rate of charge carriers due to the synergistic interaction between the components and low presence of Ce3+. In contrast, the CeO2-GQD400 composites show a high Eg of 3.8 eV (Eg ∼3.2 eV for CeO2NPs) associated with a CeO2 quantum size effect and extremely low fraction of GQDs.
The arrangement of catalytic layers inside the reactor is an important factor that affects the efficiency of methane steam reforming to produce hydrogen, and the traditional continuous catalytic layer structure is limited by the heat and mass transfer, resulting in unbalanced heat distribution inside the reactor and poor reaction performance. In order to improve the performance of methane reforming and balance the internal temperature of the reactor, different catalytic layers were designed based on 2D numerical simulation, and different numbers of discrete catalytic layers were modeled to compare the heat and mass transfer, methane conversion rate and hydrogen yield between the walls and inside the reactor. The results show that the increase in the number of catalyst gaps improves the temperature gradient inside the reactor, reduces the average cold point temperature difference inside the reactor by up to 7.2%, maintains a better thermal balance inside the reactor, improves the reaction rate inside the reactor, and the methane conversion rate and hydrogen yield after the reaction have been improved by 28.46% and 12.7% respectively.
Proton exchange membrane fuel cells (PEMFCs) are considered a promising energy source in the field of transport and distributed power generation. Fundamental research into their key components is needed to improve PEMFC performance and accelerate commercialization. Binder addition and compression induced by assembly pressure can significantly change the microstructure of the gas diffusion layer and affect mass transport. A two-dimensional multicomponent lattice Boltzmann (LB) model considering the cathode electrochemical reaction was developed, and a GDL was reconstructed numerically and considering a binder structure. The effects of the binder and compression on mass transport and electrochemical performance within the GDL were investigated. The results showed that an increase in binder volume fraction led to more chain-like structures and closed pores that were unfavorable for mass transport. Compression increased the mass transfer resistance of the GDL in the region under the rib, leading to a decrease in oxygen concentration and local current density.
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