Ameliorating the re/dehydrogenation behaviour of MgH2 by zinc titanate addition

Magnesium hydride(MgH_(2))is the most feasible and effective solid-state hydrogen storage material,which has excellent reversibility but initiates decomposing at high temperatures and has slow kinetics performance.Here,zinc titanate(Zn_(2)TiO_(4))synthesised by the solid-state method was used as an additive to lower the initial temperature for dehydrogenation and enhance the re/dehydrogenation behaviour of MgH_(2).With the presence of Zn_(2)TiO_(4),the starting temperature for the dehydrogenation of MgH_(2)was remarkably lowered to around 290℃–305℃.In addition,within 300 s,the MgH_(2)–Zn_(2)TiO_(4)sample absorbed 5.0 wt.%of H_(2)and 2.2–3.6 wt.%H_(2)was liberated from the composite sample in 30 min,which is faster by 22–36 times than as-milled MgH_(2).The activation energy of the MgH_(2)for the dehydrogenation process was also downshifted to 105.5 k J/mol with the addition of Zn_(2)TiO_(4)indicating a decrease of 22%than as-milled MgH_(2).The superior behaviour of MgH_(2)was due to the formation of Mg Zn_(2),MgO and MgTiO_(3),which are responsible for ameliorating the re/dehydrogenation behaviour of MgH_(2).These findings provide a new understanding of the hydrogen storage behaviour of the catalysed-MgH_(2)system.

Deactivation mechanism for water splitting:Recent advances

Hydrogen(H_(2)) has been regarded as a promising alternative to fossil-fuel energy.Green H_(2) produced via water electrolysis(WE)powered by renewable energy could achieve a zero-carbon footprint.Considerable attention has been focused on developing highly active catalysts to facilitate the reaction kinetics and improve the energy efficiency of WE.However,the stability of the electrocatalysts hampers the commercial viability of WE.Few studies have elucidated the origin of catalyst degradation.In this review,we first discuss the WE mechanism,including anodic oxygen evolution reaction(OER)and cathodic hydrogen evolution reaction(HER).Then,we provide strategies used to enhance the stability of electrocatalysts.After that,the deactivation mechanisms of the typical commercialized HER and OER catalysts,including Pt,Ni,RuO_(2),and IrO_(2),are summarized.Finally,the influence of fluctuating energy on catalyst degradation is highlighted and in situ characterization methodologies for understanding the dynamic deactivation processes are described.

Amine-functionalized mesoporous UiO-66 aerogel for CO_(2) adsorption

A mesoporous UiO-66-NH_(2) aerogel is prepared via a straightforward sol-gel method without using any binders or mechanical pressures, in which the amine groups are directly introduced into the matrix by using 2-aminoterephthalic acid. The novel UiO-66-NH_(2) aerogel also exhibits high specific surface area and mesopore-dominated structure, implying its highly potential use in CO_(2) adsorption. For ulteriorly investigating the effect of amine loading on the CO_(2) adsorption ability, a series of UiO-66-NH_(2) aerogel with different amino content is fabricated by changing the ligand/metal molar ratio. When the molar ratio is 1.45, the CO_(2) adsorption capacity reaches the optimum value of 2.13 mmol·g^(-1) at 25 ℃ and 0.1 MPa, which is 12.2% higher than that of pure UiO-66 aerogel. Additionally, UiO-66-NH_(2)-1.45 aerogel also has noticeable CO_(2) selectivity against N_(2) and CH_(4) as well as good regeneration stability. Such results imply that it has good application prospect in the field of CO_(2) adsorption, and also contains the potential to be applied in catalysis, separation and other fields.

Recent advances in catalytic systems for CO_(2) conversion to substitute natural gas(SNG):Perspective and challenges

It has been well established that carbon dioxide(CO_(2))is one of the main greenhouse gasses and a leading driver of climate change.The chemical conversion of CO_(2) to substitute natural gas(SNG)in the presence of renewable hydrogen is one of the most promising solutions by a well-known process called CO_(2) methanation.There have been comprehensive efforts in developing effective and efficient CO_(2) methanation catalytic systems.However,the choice of competitive and stable catalysts is still a monumental obstruction and a great challenge towards the commercialization and industrialization of CO_(2) methanation.It is necessary to emphasize the critical understandings of intrinsic and extrinsic interactions of catalyst components(active metal,support,promoter,etc.)for enhanced catalytic performance and stability during CO_(2) methanation.This study reviews the up-to-date developments on CO_(2) methanation catalysts and the optimal synergistic relationship between active metals,support,and promoters during the catalytic activity.The existing catalysts and their novel properties for enhanced CO_(2) methanation were elucidated using the state-of-the-art experimental and theoretical techniques.The selection of an appropriate synthesis method,catalytic activity for CO_(2) methanation,deactivation of the catalysts,and reaction mechanisms studies,have been explicitly compared and explained.Therefore,future efforts should be directed towards the sustainable developments of catalytic configurations for successful industrial applications of CO_(2) utilization to SNG using CO_(2) methanation.

Isomerization of linear C5–C7 over Pt loaded on protonated fibrous silica@Y zeolite（Pt/HSi@Y）

A novel fibrous silica Y zeolite (HSi@Y) loaded with Pt has been studied based on its ability to produce protonic acid sites originating from molecular hydrogen. The Pt/HSi@Y was prepared using seed assisted crystallization followed by protonation and Pt-loading. The product formed had a spherical morphology with bicontinuous lamellar with a diameter in the range of 500-700 nm. The catalytic activity of the Pt/HSi@Y has been assessed based on light linear alkane (C5-C7) isomerization in a micro-catalytic pulse reactor at 423-623 K. A pyridine IR study confirmed that the introduction of fibrous silica on Y zeolite increased the Lewis acid sites corresponding with the formation of extra-framework Al which led to the generation of more protonic acid sites. A hydrogen adsorbed IR study showed that the protonic acid sites which act as active sites in the isomerization were formed via dissociative-adsorption of molecular hydrogen releasing electrons to the nearby Lewis acid sites. Thus, it is suggested that the presence of Pt and HSi@Y with a high number of Lewis acid as well as weak Bronsted acid sites improved the activity and stability in C5, C6 and C7 isomerization via hydrogen spill-over mechanism.

Mo doped Ru-based cluster to promote alkaline hydrogen evolution with ultra-low Ru loading

Green hydrogen energy developed through electrochemistry is one of the solutions to current energy problems.The less noble metal ruthenium(Ru)plays an important role in alkaline electrocatalytic hydrogen evolution reaction(HER)as an effective electrocatalyst.Nevertheless,the high cost(>110 RMB per gram)hinders the large-scale application of Ru in industrial hydrogen production.Moreover,the strong adsorption of OH*in-termediates over Ru limits the electrocatalytic performance in alkaline HER.Here,we report the Mo-doped Ru nanocluster embedded on N-doped carbon framework(RuMo/NC)as alkaline HER catalyst,which shows excellent catalytic performance with an overpotential of 24.2 mV to reach 10 mA cm-2 with only 0.4 wt%o of Ru,much lower than that of most reported Ru-based catalysts.DFT calculations reveal the introduction of Mo has improved the activity by alleviating the poisoning effect of OH*over Ru in HER.Through fully utilizing Ru in the catalyst,this work marks a step forward in the development of Ru-based catalysts in alkaline HER.

Catalytic steam reforming of tar for enhancing hydrogen production from biomass gasification:a review

Presently,the global search for alternative renewable energy sources is rising due to the depletion of fossil fuel and rising greenhouse gas(GHG)emissions.Among alternatives,hydrogen(H2)produced from biomass gasification is considered a green energy sector,due to its environmentally friendly,sustainable,and renewable characteristics.However,tar formation along with syngas is a severe impediment to biomass conversion efficiency,which results in process-related problems.Typically,tar consists of various hydrocarbons(HCs),which are also sources for syngas.Hence,catalytic steam reforming is an effective technique to address tar formation and improve H2 production from biomass gasification.Of the various classes in existence,supported metal catalysts are considered the most promising.This paper focuses on the current researching status,prospects,and challenges of steam reforming of gasified biomass tar.Besides,it includes recent developments in tar compositional analysis,supported metal catalysts,along with the reactions and process conditions for catalytic steam reforming.Moreover,it discusses alternatives such as dry and autothermal reforming of tar.

Operating conditions combination analysis method of optimal water management state for PEM fuel cell

The water content of proton exchange membrane fuel cells(PEMFCs)affects the transport of reactants and the conductivity of the membrane.Effective water management measures can improve the performance and extend the lifespan of the fuel cell.The water management state of the stack is influenced by various external operating conditions,and optimizing the combination of these conditions can improve the water management state within the stack.Considering that the stack's internal resistance can reflect its water management state,this study first establishes an internal resistance-operating condition model that considers the coupling effect of temperature and humidity to determine the variation trend of total resistance and stack humidity with single-factor operating conditions.Subsequently,the water management state optimization method based on the ANN-HGPSO algorithm is proposed,which not only quantitatively evaluates the influence weights of different operating conditions on the stack's internal resistance but also efficiently and accurately obtains the optimal combination of five operating conditions:working temperature,anode gas pressure,cathode gas pressure,anode gas humidity,and cathode gas humidity to achieve the optimal water management state in the stack,within the entire range of current densities.Finally,the response surface experimental results of the stack also validate the effectiveness and accuracy of the ANN-HGPSO algorithm.The method mentioned in this article can provide effective strategies for efficient water management and output performance optimization control of PEMFC stacks.

Tellurium intervened Fe-N codoped carbon for improved oxygen reduction reaction and high-performance Zn-air batteries

Pyrolysis-acquired iron and nitrogen codoped carbon(Fe-N-C)has been comprehensively investigated for its promising oxygen reduction reaction(ORR)catalytic performance and structural complexity.The modification of non-metal elements with larger atomic radius and the corresponding intrinsic microstructure-property relations are rarely reported.In this study,tellurium(Te)intervened Fe-N-C was prepared by micelles-induced polymerization with Te nanowires as an in-situ intervening agent.The out-plane bonding of Te with Fe induced the increase of both N content and proportion of pyridinic N on the material surface,thus improving the ORR catalytic performance.The assembled Zn-air battery demonstrated a maximum power density of 250 mW/cm^(2)and excellent rate capability under various discharge current densities,which was much better than the Pt/C.Overall,the current work demonstrates a novel Te/Fe-N-C material and reveals an original Te intervened Fe-N-C strategy and N reconfiguration mechanism,which is of great significance for the design of key materials in energy-related fields.