Review of the Configuration and Transient Stability of Large-scale Renewable Energy Generation through Hybrid DC Transmission

Based on the complementary advantages of Line Commutated Converter(LCC)and Modular Multilevel Converter(MMC)in power grid applications,there are two types of hybrid DC system topologies:one is the parallel connection of LCC converter stations and MMC converter stations,and the other is the series connection of LCC and MMC converter stations within a single station.The hybrid DC transmission system faces broad application prospects and development potential in large-scale clean energy integration across regions and the construction of a new power system dominated by new energy sources in China.This paper first analyzes the system forms and topological characteristics of hybrid DC transmission,introducing the forms and topological characteristics of converter-level hybrid DC transmission systems and system-level hybrid DC transmission systems.Next,it analyzes the operating characteristics of LCC and MMC inverter-level hybrid DC transmission systems,provides insights into the transient stability of hybrid DC transmission systems,and typical fault ride-through control strategies.Finally,it summarizes the networking characteristics of the LCC-MMC series within the converter station hybrid DC transmission system,studies the transient characteristics and fault ridethrough control strategies under different fault types for the LCC-MMC series in the receiving-end converter station,and investigates the transient characteristics and fault ride-through control strategies under different fault types for the LCC-MMC series in the sending-end converter station.

Utlra-fast hydrolysis performance of MgH_(2) catalyzed by Ti-Zr-Fe-Mn-Cr-V high-entropy alloys

Hydrogen energy is one of the ideal energy alternatives and the upstream of the hydrogen industry chain is hydrogen production,which can be achieved via the reaction of inorganic materials with water,known as hydrolysis.Among inorganic materials,the high hydrogen capacity for hydrolysis of MgH_(2)(15.2 wt%)makes it a promising material for hydrogen production via hydrolysis.However,the dense Mg(OH)_(2) passivation layer will block the reaction between MgH_(2) and the solution,resulting in low hydrogen yield and sluggish hydrolysis kinetics.In this work,the hydrogenyield and hydrogen generation rate of MgH_(2) are considerably enhanced by adding Ti-Zr-Fe-Mn-Cr-V high-entropy alloys(HEAs) for the first time.In particular.the MgH_(2)-3 wt% TiZrFe_(1.5)MnCrV_(0.5)(labelled as MgH_(2)-3 wt% Fe_(1.5)) composite releases 1526.70 mL/g H_(2) within 5 min at 40℃,and the final hydrolysis conversion rate reaches 95.62% within 10 min.The mean hydrogen generation rate of the MgH_(2)-3 wt% Fe_(1.5) composite is 289.16 mL/g/min,which is 2.38 times faster than that of pure MgH_(2).Meanwhile,the activation energy of the MgH_(2)-3 wt% Fe_(1.5) composite is calculated to be 12.53 kJ/mol. The density functional theory(DFT) calculation reveals that the addition of HEAs weakens the Mg-H bonds and accelerates the electron transfer between MgH_(2) and HEAs,Combined with the cocktail effect of HEAs as well as the formation of more interfaces and micro protocells,the hydrolysis performance of MgH_(2) is considerably improved.This work provides an appealing prospect for real-time hydrogen supply and offers a new effective strategy for improving the hydrolysis performance of MgH_(2).

Local tetragonal distortion of Pt alloy catalysts for enhanced oxygen reduction reaction efficiency

Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and catalytic performance is still lacking.Herein,we present a synthetic strategy that uses transition-metal oxide-assisted thermal diffusion.PtCo/C catalysts with localized tetragonal distortion were obtained by controlling the thermal diffusion process of transition-metal elements.This localized structural distortion induced a significant strain effect on the nanoparticle surface,which further shortened the length of the Pt-Pt bond,improved the electronic state of the Pt surface,and enhanced the performance of the catalyst.PtCo/C catalysts with special short-range structures achieved excellent mass activity(2.27 Amg_(Pt)^(-1))and specific activity(3.34 A cm^(-2)).In addition,the localized tetragonal distortion-induced surface compression of the Pt skin improved the stability of the catalyst.The mass activity decreased by only 13% after 30,000 cycles.Enhanced catalyst activity and excellent durability have also been demonstrated in the proton exchange membrane fuel cell configuration.This study provides valuable insights into the development of advanced Pt-based nanocatalysts and paves the way for reducing noble-metal loading and increasing the catalytic activity and catalyst stability.

Key technology and application of AB_(2) hydrogen storage alloy in fuel cell hydrogen supply system

At present,there is limited research on the application of fuel cell power generation system technology using solid hydrogen storage materials,especially in hydrogen-assisted two-wheelers.Considering the disadvantages of low hydrogen storage capacity and poor kinetics of hydrogen storage materials,our primary focus is to achieve smooth hydrogen ab-/desorption over a wide temperature range to meet the requirements of fuel cells and their integrated power generation systems.In this paper,the Ti_(0.9)Zr_(0.1)Mn_(1.45)V_(0.4)Fe_(0.15) hydrogen storage alloy was successfully prepared by arc melting.The maximum hydrogen storage capacity reaches 1.89 wt% at 318 K.The alloy has the capability to absorb 90% of hydrogen storage capacity within 50 s at 7 MPa and release 90% of hydrogen within 220 s.Comsol Multiphysics 6.0 software was used to simulate the hydrogen ab-/desorption processes of the tank.The flow rate of cooling water during hydrogen absorption varied in a gradient of(0.02 t x)m s^(-1)(x=0,0.02,0.04,0.06,0.08,0.1,0.12).Cooling water flow rate is positively correlated with the hydrogen absorption rate but negatively correlated with the cost.When the cooling rate is 0.06 m s^(-1),both simulation and experimentation have shown that the hydrogen storage tank is capable of steady hydrogen desorption for over 6 h at a flow rate of 2 L min^(-1).Based on the above conclusions,we have successfully developed a hydrogen-assisted two-wheeler with a range of 80 km and achieved regional demonstration operations in Changzhou and Shaoguan.This paper highlights the achievements of our team in the technological development of fuel cell power generation systems using solid hydrogen storage materials as hydrogen storage carriers and their application in twowheelers in recent years.

Discovering Cathodic Biocompatibility for Aqueous Zn–MnO_(2) Battery:An Integrating Biomass Carbon Strategy

Developing high-performance aqueous Zn-ion batteries from sustainable biomass becomes increasingly vital for large-scale energy storage in the foreseeable future.Therefore,γ-MnO_(2) uniformly loaded on N-doped carbon derived from grapefruit peel is successfully fabricated in this work,and particularly the composite cathode with carbon carrier quality percentage of 20 wt%delivers the specific capacity of 391.2 mAh g^(−1)at 0.1 A g^(−1),outstanding cyclic stability of 92.17%after 3000 cycles at 5 A g^(−1),and remarkable energy density of 553.12 Wh kg^(−1) together with superior coulombic efficiency of~100%.Additionally,the cathodic biosafety is further explored specifically through in vitro cell toxicity experiments,which verifies its tremendous potential in the application of clinical medicine.Besides,Zinc ion energy storage mechanism of the cathode is mainly discussed from the aspects of Jahn–Teller effect and Mn domains distribution combined with theoretical analysis and experimental data.Thus,a novel perspective of the conversion from biomass waste to biocompatible Mn-based cathode is successfully developed.

Energy Planning of Beijing Towards Low-carbon,Clean and Efficient Development in 2035

Energy transition towards clean,efficient energy supply has been a common sense of the government and public in China.However,lacking reasonable planning will lead to undisciplined development,resource waste,and excessive investment.In this context,this paper investigates potential pathways of Beijing energy transition towards a high-level low-carbon,clean and efficient energy system in 2035 with an extended energysocpe model.Firstly,based on available data,future energy demands are predicted by a newly proposed hybrid forecasting method,which combines the traditional regression model,grey model,and support vector machine model with an entropy-based weighted factor.Secondly,the superstructure-based optimization model is employed to investigate the system configuration and operation strategy of the future Beijing energy system.Finally,the uncertainty impact of electricity price,natural gas price,hydrogen price,and the capital expenditures of electrolyzer and steam methane reforming for hydrogen applications are studied.The forecasting results show that all walks of life will witness a continuously increasing energy demand in multiple sectors of Beijing towards 2035.The planning results suggest that the imported electricity and natural gas will dominate the energy supply of Beijing in 2035 with a contribution of 86%of the energy resources consumption of 384 TWh.Moreover,the energy system presents a high end-use electrification level of 65%and high penetration of efficient technologies,which supply 119 TWh via combined heat and power,26 TWh via heat pump and 95 TWh via district heating network.The energy use of various sectors of energy resources,technologies and end-use are closely related.Hydrogen will have an increased penetration in the private mobility sector,but the locally generated hydrogen is mainly from steam methane reforming technology.

Economic analysis of hydrogen production from China’s province-level power grid considering carbon emissions

Hydrogen energy contributes to China’s carbon peaking and carbon neutralization by serving as an important energy carrier.However,the calculation of the cost of hydrogen production by the power grid ignores the current cost of carbon emissions.To measure the cost of hydrogen-production projects in various provinces more comprehensively and accurately,this study incorporates the carbon-emission cost into the traditional levelized cost of hydrogen model.An analysis of the energy structure of the power supply is conducted in each province of China to calculate carbon-emission costs,which are then subjected to a sensitivity test.Based on the results,the carbon-emission costs for hydrogen in each province are between 0.198 and 1.307 CNY/kg,and the levelized cost of hydrogen based on carbon-emission costs varies from 24.813 to 48.020 CNY/kg;in addition,carbon-emission costs range from 0.61%to 3.4%of the total costs.The results also show that the levelized cost of hydrogen considering carbon-emission costs in the Shanghai municipality specifically is most sensitive to the carbon-emission price,changing by 0.131 CNY/kg for every 10%fluctuation in the carbon-emission price.

Aligne d nanofib ers incorporate d composite solid electrolyte for high-sensitivity oxygen sensing at medium temperatures

otentiometric oxygen sensors have been widely used in internal combustion engines,industrial boilers,and metallurgical heat treatment furnaces.However,traditional oxygen sensors based on yttria-stabilized zirconia(YSZ)electrolyte can only be operated at elevated temperatures(>750℃)due to their rela-tively low ionic conductivity.In this study,we present a highly efficient micro-oxygen sensor that can be operated at a temperature as low as 300℃.This micro-oxygen sensor incorporates a composite solid electrolyte,i.e.,well-aligned gadolinium-doped cerium oxide(CGO)nanofibers embedded within a YSZ matrix(YSZ/CGO_(f)).The arrays of CGO nanofibers in the YSZ matrix are parallel to the conduction direc-tion,providing rapid conducting channels for oxygen ions.Benefitting from this design,the composite electrolyte leads to a conductivity of four times higher than that of traditional YSZ solid electrolytes at low temperatures.This enhancement in conductivity is attributed to the presence of a defective interfacial region between CGO_(f)and YSZ,which promotes the mobility of oxygen ions.The strategy of constructing fast ionic conduction in the composite electrolyte by using well-aligned nanofibers may be considered for the design and optimization of other micro/nano-devices including sensors,batteries,and fuel cells.

Efficient nanocatalysis of Ni/Sc_(2)O_(3)@FLG for magnesium hydrolysis of hydrogen generation

Magnesium is one of the most promising candidates of light metal materials for hydrogen production by hydrolysis due to its efficient and economical properties.Various modification methods have been investigated to improve the hydrolytic properties of Mg.However,the direction of the design of efficient catalysts is unclear and needs to be guided by a richer catalytic mechanism of hydrolysis.In this work,a simple approach was used to synthesize Few Layer Graphene(FLG)-loaded ultra-fine highly dispersed Ni/Sc_(2)O_(3)nanocatalyst,which achieves impressive catalytic hydrolysis results.Here,the addition of 4 wt%Ni/Sc_(2)O_(3)@FLG catalyst allows Mg to produce 833 mL g^(-1)of H_(2) in 20 s at 30°C.There is an initial hydrogen release rate as high as 5942 mL g^(-1)min^(-1),a final hydrogen yield of 859 mL g^(-1)(99.13%),and almost complete conversion of Mg to Mg(OH)_(2).Furthermore,surprisingly,even with only 0.2 wt%catalysts added,Mg still has an initial hydrogen generation rate of 3627 mL g^(-1)min^(-1),which is over 20 times faster than that of Mg.It also produces 690 mL g^(-1)of H_(2) in 30 s at 30°C.Hydrolysis kinetic curves and microscopic morphology tests show that FLG could shape and hold Mg into thin sheets,giving them an ultra-high hydrolysis rate and conversion rate.The formation of micro-galvanic cells between Ni and Mg accelerates the electrochemical corrosion of Mg and greatly enhances electron transfer during hydrolysis.This work provides a new strategy for the preparation of efficient nanocatalysts,which is expected to make“Mg-efficient catalyst”the most ideal light metal-based material for hydrogen production by hydrolysis.

A highly efficient hydrolysis of MgH_(2)catalyzed by NiCo@C bimetallic synergistic effect

MgH_(2)has a high theoretical hydrogen production capacity and mild conditions for hydrogen production by hydrolysis,so it is suitable as an ideal hydrogen source for fuel cells.However,with the progress of the hydrolysis reaction,MgH_(2)is impeded from reacting further by the continuous deposition of magnesium hydroxide on its surface,resulting in low hydrogen yield and slow reaction kinetics.In the present work,a highly efficient NiCo bimetallic synergistic catalysis is developed to improve the hydrolysis performance of MgH_(2).The MgH_(2)-8 wt%NiCo@C composite ball-milled for 5 h achieves nearly 100%hydrogen desorp-tion efficiency within 15 min in 0.05 mol L^(-1)MgCl_(2)solution.Because the interaction between Ni and Co on the surface of MgH_(2)can form a channel for rapid hydrogen evolution,which hinders the continuous formation of the Mg(OH)_(2)passivation layer and promotes the hydrolysis reaction of MgH_(2).This is very important for the implementation of MgH_(2)hydrolysis to produce hydrogen in the future.

Integration of multi-physics and machine learning-based surrogate modelling approaches for multi-objective optimization of deformed GDL of PEM fuel cells

The development of artificial intelligence(AI)greatly boosts scientific and engineering innovation.As one of the promising candidates for transiting the carbon intensive economy to zero emission future,proton exchange membrane(PEM)fuel cells has aroused extensive attentions.The gas diffusion layer(GDL)strongly affects the water and heat management during PEM fuel cells operation,therefore multi-variable optimization,including thickness,porosity,conductivity,channel/rib widths and compression ratio,is essential for the improved cell performance.However,traditional experiment-based optimization is time consuming and economically unaffordable.To break down the obstacles to rapidly optimize GDLs,physics-based simulation and machine-learning-based surrogate modelling are integrated to build a sophisticated M 5 model,in which multi-physics and multi-phase flow simulation,machine-learning-based surrogate modelling,multi-variable and multi-objects optimization are included.Two machine learning methodologies,namely response surface methodol-ogy(RSM)and artificial neural network(ANN)are compared.The M 5 model is proved to be effective and efficient for GDL optimization.After optimization,the current density and standard deviation of oxygen dis-tribution at 0.4 V are improved by 20.8%and 74.6%,respectively.Pareto front is obtained to trade off the cell performance and homogeneity of oxygen distribution,e.g.,20.5%higher current density is achieved when sacrificing the standard deviation of oxygen distribution by 26.0%.

Niobium fluoride-modified hydrogen evolution reaction of magnesium borohydride diammoniate

Metal borohydride ammoniates have become one of the most promising hydrogen storage materials due to their ultrahigh capacities.However,their application is still restricted by the high temperature of hydrogen desorption and the release of ammonia.Here,to promote the dehydrogenation evolution and suppress the ammonia release,different amounts of NbF 5 were introduced into Mg(BH4)2·2NH3.Compared to the pure Mg(BH_(4))_(2)·2NH_(3),the Mg(BH_(4))_(2)·2NH_(3)-NbF_(5) composites exhibit lower onset dehydriding temperatures(53–57℃)and higher dehydriding capacities(5.6 wt.%–8.2 wt.%)at below 200℃,with the complete suppression of ammonia.In addition,7.4 wt.%H_(2) could be released from Mg(BH_(4))_(2)·2NH_(3)–5 mol%NbF5 composite at 200℃ within 20 min and the apparent activation energy is calculated to be 60.28 kJ mol^(-1),which is much lower than that of pure Mg(BH_(4))_(2)·2NH_(3)(92.04 kJ mol^(-1)).Mg(BH_(4))_(2)·2NH_(3) should mechanochemically react with NbF5,forming dual-metal(Mg,Nb)borohydride ammoniate and spherical MgF2.The introduction of electronegative Nb cation results in-situ formation of(Mg,Nb)borohydride ammoniate towards a lower dehydrogenation temperature and a higher hydrogen release purity.The increased phase boundaries among the Mg(BH_(4))_(2)·2NH_(3),dual-metal(Mg,Nb)borohydride ammoniate,and MgF2 phases further facilitate the hydrogen diffusion during the dehydrogenation of the composites.

Graphene-Supported Sc_(2)O_(3)/TiO_(2) for Superior Catalysis on Hydrogen Sorption Kinetics of MgH_(2)

Complex metal oxide catalysts greatly accelerate the hydrogen sorption rates in the magnesium hydride system.In this study,the graphene-supported Sc_(2)O_(3)/TiO_(2) catalyst is synthesized by means of a simple method,and a surprisingly synergetic effect of the Sc_(2)O_(3)-TiO_(2) cocatalyst on the hydrogen storage performance of MgH_(2) is observed.The MgH_(2)-Sc_(2)O_(3)/TiO_(2)@Gn composite starts to release hydrogen at 140°C and reaches the peak dehydrogenation temperature at 239.9°C.It absorbs 6.55 wt%of H_(2) in 1 min and desorbs 5.71 wt%of H_(2) in 10 min at 300°C,showing excellent hydrogen absorption and desorption performance.Furthermore,with the decrease of the grain size and changes in the structure,the activity of the catalyst is greatly improved.The low-valent titanium and scandium and oxygen vacancies formed in the process of dehydrogenation facilitate hydrogen diffusion and electron transfer,and further improve the kinetic performance of the Mg/MgH_(2)-Sc_(2)O_(3)/TiO_(2)@Gn system.This study aims to provide insights into studying complex metal oxides as catalysts to improve hydrogen storage performance,and shed light on other catalysis-related research.

Application of Machine Learning in Optimizing Proton Exchange Membrane Fuel Cells: A Review

Proton exchange membrane fuel cells (PEMFCs) as energy conversion devices for hydrogen energy are crucial for achieving an eco-friendly society, but their cost and performance are still not satisfactory for large-scale commercialization. Multiple physical and chemical coupling processes occur simultaneously at different scales in PEMFCs. Hence, previous studies only focused on the optimization of different components in such a complex system separately. In addition, the traditional trial-and-error method is very inefficient for achieving the performance breakthrough goal. Machine learning (ML) is a tool from the data science field. Trained based on datasets built from experimental records or theoretical simulation models, ML models can mine patterns that are difficult to draw intuitively. ML models can greatly reduce the cost of experimental attempts by predicting the target output. Serving as surrogate models, the ML approach could also greatly reduce the computational cost of numerical simulations such as first-principle or multiphysics simulations. Related reports are currently trending, and ML has been proven able to speed up tasks in this field, such as predicting active electrocatalysts, optimizing membrane electrode assembly (MEA), designing efficient flow channels, and providing stack operation strategies. Therefore, this paper reviews the applications and contributions of ML aiming at optimizing PEMFC performance regarding its potential to bring a research paradigm revolution. In addition to introducing and summarizing information for newcomers who are interested in this emerging cross-cutting field, we also look forward to and propose several directions for future development.

Nanocrystalline High Entropy Alloys with Ultrafast Kinetics and High Storage Capacity for Large-Scale Room-Temperature-Applicable Hydrogen Storage

High-entropy alloys(HEAs)are a promising solution for large-scale hydrogen storage(H-storage)and are therefore receiving increasing attention from the materials science community.In this study,we systematically investigated the microstructures and H-storage properties of V_(35)Ti_(35)Cr_(10) Fe_(10)M_(10)(M=Mn,Co,Sc,or Ni)HEAs prepared by arcmelting.The cast HEAs were found to be nanocrystalline.The crystal lattice parameters and hydrogen absorption energies of the alloys were calculated using density functional theory(DFT)calculations.The alloys can be fully activated in just one cycle of hydrogen absorption/desorption under mild conditions,after which they reach hydrogen absorption saturation in approximately 100 s at ambient temperature.The hydrogenation kinetics of the HEAs are approximately five times higher than that of conventional solid-solution alloys with a body-centered cubic(BCC)structure.By performing in-situ hydriding differential scanning calorimetry in combination with DFT calculations,we revealed that the alloys are more susceptible to hydrogenation than traditional BCC structural alloys.The H-storage capacity of V_(35)Ti_(35)Cr_(10) Fe_(10)M_(10) alloys at ambient temperature was higher than that of HEAs reported in the literature.Quasi-in-situ X-ray diffraction characterization of the HEAs’hydrogenation revealed a phase transition process from a BCC to facecentered cubic,passing through a pseudo-BCC structure.Our work introduces a new perspective for designing alloys with ultrafast hydrogen absorption kinetics and high capacity for large-scale,room-temperature-applicable H-storage.

Ultrathin zirconium-porphyrin based nanobelts as photo-coupled electrocatalysis for CH_(4) oxidation to CO

The development of novel and effective methods for the activation of methane is fascinating,which offers a promising potential for the sustainable development of chemical industry and the mitigation of greenhouse effect.Here we successfully synthesize two-dimensional(2D)Zr/5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin(TCPP)ultrathin nanobelts(UNBs)as a high efficiency catalyst for methane(CH_(4))oxidation to carbon monoxide(CO).The Co-UNBs show well photo-coupled electrocatalytic performances for CH4 activation(CO production rates are 0.171 and 8.416 mmol·g−1·h−1 under dark/visible light,respectively).Density functional theory(DFT)calculations were performed to illustrate the mechanism of photoelectrocatalytic process and the high efficiency oxidation of CH4 to CO.Based on the ultrathin structure and highly efficient catalytic properties,this work provides a prospecting avenue for the design and synthesis of methane oxidation catalyst.