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Highly dispersed NiMo@rGO nanocomposite catalysts fabricated by a two-step hydrothermal method for hydrogen evolution

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International Journal of Minerals,Metallurgy and Materials 2023年第12期30卷 2432-2440页

作者： Duanhao Cao Xiaofeng Ma Yipeng Zhang La Ta Yakun Yang Chao Xu Feng Ye Jianguo Liu School of Energy Power and Mechanical Engineering North China Electric Power UniversityBeijing 102206China

Exploring and designing a high-performance non-noble metal catalyst for hydrogen evolution reaction(HER)are crucial for the large-scale application of H2 by water electrolysis.Here,novel catalysts with NiMo nanoparticles decorated on reduced graphene oxide(NiMo@r GO)synthesized by a two-step hydrothermal method were reported.Physical characterization results showed that the prepared NiMo@r GO-1 had an irregular lamellar structure,and the NiMo nanoparticles were uniformly dispersed on the rGO.NiMo@rGO-1 exhibited outstanding HER performance in an alkaline environment and required only 93 and 180 mV overpotential for HER in 1.0 M KOH solution to obtain current densities of-10 and-50 mA·cm^(-2),respectively.Stability tests showed that NiMo@rGO-1 had a certain operating stability for32 h.Under the same condition,the performance of NiMo@rGO-1 can be comparable with that of commercial Pt/C catalysts at high current density.The synergistic effect between NiMo particles and lamellate graphene can remarkably promote charge transfer in electrocatalytic reactions.As a result,NiMo@rGO-1 presented the advantages of high intrinsic activity,large specific surface area,and small electrical impedance.The lamellar graphene played a role in dispersion to prevent the aggregation of nanoparticles.The prepared NiMo@rGO-1 can be used in anion exchange membrane water electrolysis to produce hydrogen.This study provides a simple preparation method for efficient and low-cost water electrolysis to produce hydrogen in the future.

关键词： hydrogen evolution reaction NiMo nanocomposite reduced graphene oxide synergistic effect

Conductive and tribological properties of TiN-Ag composite coatings under grease lubrication

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Friction 2021年第4期9卷 774-788页

作者： Feihu LIN Yanqiu XIA Xin FENG School of Energy Power and Mechanical Engineering North China

TiN-Ag composite coatings were prepared by pulsed bias arc ion plating.X-ray diffraction(XRD)and energy dispersive X-ray spectroscopy(EDS)were applied to analyze the compositions of the coatings.Tribological properties of the coatings were studied using an MFT-R4000 ball-on-disk friction tester in the presence of lubricating greases containing multilayer graphene.Scanning electron microscopy(SEM),Raman spectroscopy,and X-ray photoelectron spectroscopy(XPS)were used to analyze the worn surface compositions of the lubricating films.The results show that with the decrease in Ag in the film,hardness increased but electrical conductivity decreased.The coating with 10 at%Ag content shows the best friction-reducing and anti-wear properties,which can be attributed to the moderate content of Ag embedded in the TiN crystal gap that enhanced the grain bonding force to improve the anti-wear and self-lubricating ability.Graphene can be adsorbed on the coating as a solid lubricant.

关键词： silver tribology contact resistance lubricating grease

Computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at various loads

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Particuology 2022年第6期20卷 105-116页

作者： Jian Chang Zhijian Zhou Xinrui Ma Jinshuo Liu school of energy Power and Mechanical EngineeringNorth China Electric Power UniversityBeijing 102206China

This work presents a computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads(630,440 and 300 MW;relative loads of 100%,70%and 48%)to clarify the effect of load change on the furnace processes.A computational fluids dynamics model was established;the flow field,temperature profile,species concentration and NOx emissions were predicted numerically;and the influence of burner tilt angles was evaluated.Simulation results indicate that a decrease in boiler load decreases the gas velocity,attenuates the airflow rotations,and increases the tangent circle size.The high-temperature zone and flame moved toward the side walls.Such behaviors impair air-fuel mixing,heat transfer and steady combustion in the furnace.In terms of species concentrations,a decrease in boiler load increased the O2 content,decreased the CO content,and decreased the char burnout rates only slightly.A change in boiler load from 630 to 440 and 300 MW increased the NOx emissions from 202 to 234 and 247 mg/m^(3),respectively.Burner tilt angles are important in coal combustion and NOx emissions.A burner angle of-15°favors heat transfer and low NOx emissions(<185 mg/m^(3))for the current tangentially fired boiler.

关键词： Combustion NOx emission Tangentially fired boiler Variable load operation Computational fluids dynamics

A review on 3d transition metal dilute magnetic REIn_(3) intermetallic compounds

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Chinese Physics B 2022年第3期31卷 76-83页

作者：郭新鹏郭永权殷林瀚何强 School of Energy Power and Mechanical Engineering North China Electric Power UniversityBeijing 102206China

The dilute magnetic intermetallic compound(DMIC) is an extended study of the dilute magnetic semiconductor. The giant magnetic effect and room temperature ferromagnetism are induced by doping minor 3d transition metal into REIn_(3) intermetallic compound. Owing to the metallic processability, the REIn_(3)-based DMIC might have the potential application as magnetoelectric device. In this review, the structural stability, magnetic and electric transport properties of REIn_(3-x)T_(x)(RE = rare earth;T = Co, Mn, Fe;x = 0–0.3) have been systematically summarized and analyzed.

关键词： dilute magnetic intermetallic compounds phase transition magnetic properties magnetic transport

energy-Saving Optimization Study on 700°C Double Reheat Advanced Ultra-Supercritical Coal-Fired power Generation System

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Journal of Thermal Science 2023年第1期32卷 30-43页

作者： WANG Jing DUAN Liqiang YANG Jinfu YANG Ming JING Yutian TIAN Liguo School of Energy Power and Mechanical Engineering North China Electric Power University Institute of engineering Thermophysics Chinese Academy of Sciences

700°C double reheat advanced ultra-supercritical power generation technology is one of the most important development directions for the efficient and clean utilization of coal. To solve the great exergy loss problem caused by the high superheat degrees of regenerative steam extractions in 700°C double reheat advanced ultra-supercritical power generation system, two optimization systems are proposed in this paper. System 1 is integrated with the back pressure extraction steam turbine, and system 2 is simultaneously integrated with both the outside steam cooler and back pressure extraction steam turbine. The system performance models are built by the Ebsilon Professional software. The performances of optimized systems are analyzed by the unit consumption method. The off-design performances of optimization systems are analyzed. The results show that: the standard power generation coal consumption rates of optimization systems 1 and 2 are decreased by 1.88 g·(kW·h)–1, 2.97 g·(kW ·h)–1compared with that of the 700°C reference system; the average superheat degrees of regenerative steam extractions of optimized systems 1 and 2 are decreased by 122.2°C, 140.7°C(100% turbine heat acceptance condition), respectively. The comparison results also show that the performance of the optimized system 2 is better than those of the optimized system 1 and the 700°C reference system. The power generation standard coal consumption rate and the power generation efficiency of the optimized system 2 are about 232.08 g·(kW ·h)–1and 52.96%(100% turbine heat acceptance condition), respectively.

关键词： 700 °C advanced ultra-supercritical (A-USC) double reheat cycle extraction steam superheat degree unit consumption method system optimization

Numerical Investigation on the Effects of Design Parameters and Operating Conditions on the Electrochemical Performance of Proton Exchange Membrane Water Electrolysis

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Journal of Thermal Science 2023年第6期32卷 1989-2007页

作者： HASSAN Alamir H. WANG Xueye LIAO Zhirong Xu Chao Key Laboratory of power Station energy Transfer Conversion and System of MOE School of EnergyPower and Mechanical EngineeringNorth China Electric Power UniversityBeijing102206China mechanical power engineering Department Faculty of Engineering-MattariaHelwan UniversityCairo11718Egypt

Proton exchange membrane electrolysis cell(PEMEC)is one of the most promising methods to produce hydrogen at high purity and low power consumption.In this study,a three-dimensional non-isothermal model is used to simulate the cell performance of a typical PEMEC based on computational fluid dynamics(CFD)with the finite element method.Then,the model is used to investigate the distributions of current density,species concentration,and temperature at the membrane/catalyst(MEM/CL)interface.Also,the effects of operating conditions and design parameters on the polarization curve,specific electrical energy demand,and electrical cell efficiency are studied.The results show that the maximum distribution of current density,hydrogen concentration,oxygen concentration,and temperature occur beneath the core ribs and increase towards the channel outlet,while the maximum water concentration distribution happens under the channel and decreases towards the channel exit direction.The increase in gas diffusion layer(GDL)thickness reduces the uneven distribution of the contour at the MEM/CL interface.It is also found that increasing the operating temperature from 323 K to 363 K reduces the cell voltage and specific energy demand.The hydrogen ion diffusion degrades with increasing the cathode pressure,which increases the specific energy demand and reduces the electrical cell efficiency.Furthermore,increasing the thickness of the GDL and membrane rises the specific energy demand and lowers the electrical efficiency,but increasing GDL porosity reduces the specific electrical energy demand and improves the electrical cell efficiency;thus using a thin membrane and GDL is recommended.

关键词： hydrogen production proton exchange membrane water electrolysis gas diffusion layer cell efficiency

Physics of cavitation near particles

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Journal of Hydrodynamics 2024年第1期36卷 102-118页

作者： Jia-xin Yu Xiao-yu Wang Jun-wei Shen Jin-sen Hu Xiang-qing Zhang Da-qing He Yu-ning Zhang Key Laboratory of power Station energy Transfer Conversion and System(Ministry of Education) School of Energy Power and Mechanical EngineeringNorth China Electric Power UniversityBeijing102206China

The combined effect of cavitation and silt abrasion presents a great challenge and threat to secure the operation and the efficiency of hydraulic machineries working in sediment-laden fluid.The present paper critically reviews the current research progress on the interaction mechanisms of the bubbles and the particles.Firstly,the analytical models including boundary treatment methods for predicting the jet dynamics of the bubble collapse near particles are demonstrated.Secondly,the bubble collapsing dynamics,jet dynamics and shock wave characteristics near particles are revealed both experimentally and numerically.Finally,the bubble-particle-wall system is investigated with a focus on microjets.

关键词： Cavitation bubble particle jet shock wave

A novel preheating method for the Li-ion battery using supercooled phase change materials

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Science China(Technological Sciences) 2023年第1期66卷 193-203页

作者： FANG XuanYi NONG XinLu LIAO ZhiRong XU Chao Key Laboratory of power Station energy Transfer Conversion and System of Ministry of Education School of EnergyPower and Mechanical EngineeringNorth China Electric Power UniversityBeijing 102206China

The Li-ion battery is widely used in power tools, energy storage systems, and electric vehicles. In reality, battery thermal management is essential to control the battery temperature within a specific temperature range. Although research has shown that preheating the battery at low temperatures on cold days can improve output performance significantly, few efforts have been made to study the preheating method in-depth. As a result, this research proposes two preheating designs for cylindrical batteries with supercooled phase change materials: Single-and dual-phase change material(PCM) designs. A mathematical model is developed to analyze the effect of the PCM layer’s height, thickness, and mass on the preheating effect for seven candidate PCMs with high supercooling degrees. Furthermore, the economic efficiency of the single-PCM design with different PCMs is compared. In addition, the optimal ratio of the PCMs’ height for the dual-PCM design is investigated. Eventually, the improvement of the battery’s output performance is discussed. The results reveal that the proposed designs can effectively preheat the battery with a temperature rise higher than 10°C. The single-PCM design using Li NO3·3H2O shows the best preheating ability, while CH3COONa·3H2O is the most economical. Although the dual-PCM design cannot outperform the single-PCM design, it can preheat the battery twice and show better flexibility. Compared with the battery without preheating, a 26650-format battery with the single-PCM design can prolong the operating time by 38.8 min and save the electric quantity by 2.1 A h;while they are by 42.8 min and 2.3 A h with the dual-PCM design.

关键词： preheating method Li-ion battery phase change material supercooling

Experimental Study on the Molten Salt at Micron Scale during the Melting Process

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Journal of Thermal Science 2024年第1期33卷 70-85页

作者： TIAN Ziqian LIAO Zhirong XU Chao FANG Yongzhe JIANG Kaijun YUAN Mengdi Key Laboratory of power Station energy Transfer Conversion and System Ministry of Education of ChinaSchool of Energy Power and Mechanical EngineeringNorth China Electric Power UniversityBeijing 102206China

The investigation of the melting behaviors of the molten salt at micron scale during the melting process is critical for explaining the solid-liquid phase transition mechanism.In this paper,a novel experimental system and analysis method were proposed to study the melting process with three heating rates in the range of1-10℃/min of the solar salt at micron scale.The solid-liquid boundary morphology and phase transition kinetics of molten salt particles were focused on.Meanwhile,the correlations between liquid fraction,temperature and time under different heating rates were studied.The solid-liquid boundary morphology was depicted by the visualized experimental set-up,and the instantaneous liquid volume fraction during the non-isothermal phase transition was obtained.Then,the correlation between temperature and liquid volume fraction was proposed to reveal the evolution of the solid-liquid boundary with temperature at different heating rates.Furthermore,the non-isothermal phase transition kinetic equation was established by introducing a constant parameter(V_(a,b)),and more kinetic parameters such as 1g V_(a,b) and-lg V_(a,b)/b were studied.The results showed that the exponent b is not sensitive to the heating rate with a range of 3-5 for solar salt particles.However,the heating rate influences the value of V_(a,b) and presents a positive relationship.Besides,the non-isothermal phase transition kinetic equations at different heating rates in the range of 1-10℃/min can be quickly predicted by the proposed improved experimental test method.This study could fill the research insufficiency and provide significant guidance for future research on the solid-liquid transition mechanism of molten salts at micron scale.

关键词： molten salt non-isothermal phase transition solid-liquid boundary morphology liquid volume fraction micron scale melting process