Liquid organic hydrogen carriers

The development of efficient hydrogen storage materials is one of the biggest technical challenges for the coming ＂hydrogen economy＂. The liquid organic hydrogen carriers （LOHCs） with high hydrogen contents, reversibilities and moderate dehydrogenation kinetics have been considered as an alternative option supplementing the extensively investigated inorganic hydride systems. In this review, LOHCs for long distance H2 transport and for onboard application will be discussed with the focuses of the design and development of LOHCs and their hydrogenation ＆ dehydrogenation catalyses.

Recent progress in electrochemical synthesis of carbon-free hydrogen carrier ammonia and ammonia fuel cells:A review

Ammonia(NH3)is a cornerstone widely used in the modern agriculture and industry,the annual global production gradually increases to almost 200 million tons.Nearly 80%of the produced NH3 is used in the fertilizer industry and is essential for the development of global agriculture and consequently for maintaining population growth.Furthermore,NH3 can power hydrogen(H2)fueled devices,such as H2 fuel cells(FC),to use the interconversion between chemical energy and electric energy of nitrogen(N2)cycle,which can effectively alleviate the intermittent problems of renewable energy.However,the problems faced by NH3 in storage and release still restrict its development.Herein,this review introduces the latest research and development of electrochemical NH3 synthesis and direct NH3 FC,as well as outlines the technical challenges,possible improvement measures and development perspectives.N2 reduction reaction(NRR)and nitrate reduction reaction(NO3RR)are two potential approaches for electrochemical NH3 synthesis.However,the existing research foundation still faces challenges in achieving high selectivity and efficiency.Direct NH3 FC are easy to transport and are expected to be widely used in mobile energy consuming equipment,but also limited by the lack of highly active and stable NH3 oxidation electrocatalysts.The perspectives of ammonia fuel cells as an alternative green energy are discussed.

Dimethyl ether as circular hydrogen carrier:Catalytic aspects of hydrogenation/dehydrogenation steps

The intermittent nature of renewable resources requires for most applications the development of efficient and cost-effective technologies for steady supply of electrical energy.The storage of energy in the form of hydrogen chemically bound within organic molecules(rather than physically as compressed gas or cooled liquid)represents an alternative approach that is attracting great research interest.Compared to other liquid organic hydrogen carriers(LOHCs),dimethyl ether(DME)appears to have the largest potential impact on society,especially if inserted in technological chains of CO_(2) sequestration and utilization,so to determine an effective mitigation of environmental issues,without any net effect on the carbon footprint.Specifically,the steps of H2 storage and H2 release can take place in two coupled chemical processes,constituted by the exothermic synthesis of DME via CO_(2) hydrogenation and the endothermic steam reforming of DME,respectively.Herein,the latest advances in the development of heterogeneous bifunctional and hybrid catalysts for the direct hydrogenation of CO_(2) to DME are thoroughly reviewed,with special emphasis on thermodynamics,catalyst design and process feasibility.Despite many aspects behind the mechanism of DME synthesis from H2-CO_(2) streams are still to be uncovered,the recent progress in the research on H2 release by DME steam reforming is increasing the interest for effectively closing this binary H2 loop,in view of future green deals and sustainable research developments.

Ammonia as a carbon-free hydrogen carrier for fuel cells: a perspective

Driven by the growing need to decarbonize,hydrogen energy is considered a potential alternative to fossil fuels.However,due to the problems associated with energy storage and transportation for portable applications,the scalable utilization of hydrogen is not fully developed.In this perspective,the potential of utilizing ammonia as a hydrogen carrier for on-site power generation via ammonia decomposition is systematically discussed.Firstly,an analysis of the chemical properties of ammonia and the limitations of this product for hydrogen production are presented.Secondly,some existing worldwide industrial projects that present the current development status are summarized.Then,recent advances in target engineering of efficient catalysts via various strategies are provided.Finally,different types of structured reactors to date for ammonia decomposition are explored.This perspective aims to shed light on the potential of ammonia as a promising alternative to traditional hydrogen storage methods and highlights the challenges and opportunities that lie ahead in this exciting field of research.

Fast hydrogenation kinetics of acridine as a candidate of liquid organic hydrogen carrier family with high capacity

Hydrogen has been deemed as one of the most efficient energy carriers for a broad variety of industrial applications[1,2].Large-scale,low-cost hydrogen production,safe storage and delivery represent a tremendous technological challenge and have become a subject of intense research and development activities in the past few decades[3–5].

Hydrogen storage by liquid organic hydrogen carriers:Catalyst,renewable carrier,and technology--A review

Hydrogen has attracted widespread attention as a carbon-neutral energy source,but developing efficient and safe hydrogen storage technologies remains a huge challenge.Recently,liquid organic hydrogen carriers(LOHCs)technology has shown great potential for efficient and stable hydrogen storage and transport.This technology allows for safe and economical large-scale transoceanic transportation and long-cycle hydrogen storage.In particular,traditional organic hydrogen storage liquids are derived from nonrenewable fossil fuels through costly refining procedures,resulting in unavoidable environmental contamination.Biomass holds great promise for the preparation of LOHCs due to its unique carbon-balance properties and feasibility to manufacture aromatic and nitrogen-doped compounds.According to recent studies,almost 100%conversion and 92% yield of benzene could be obtained through advanced biomass conversion technologies,showing great potential in preparing biomass-based LOHCs.Overall,the present LOHCs systems and their unique applications are introduced in this review,and the technical paths are summarized.Furthermore,this paper provides an outlook on the future development of LOHCs technology,focusing on biomass-derived aromatic and N-doped compounds and their applications in hydrogen storage.

Nonstoichiometric Yttrium Hydride–Promoted Reversible Hydrogen Storage in a Liquid Organic Hydrogen Carrier

N-Ethylcarbazole(NEC)is one of the most promising liquid organic hydrogen carriers(LOHCs),but its application is limited by sluggish kinetics due to lack of high-efficiency,low-cost catalysts.This work reports a cobalt(Co)-based catalyst promoted by nonstoichiometric yttrium hydride(YH_(3−x))to achieve high-efficiency,reversible hydrogen storage in NEC,with>5.5 wt%reversible hydrogen storage capacity could be achieved below 473 K,and with good kinetics.The YH_(3−x)-promoted Co-based catalyst is the first non-noble metal catalyst with high activity for NEC hydrogenation and 12H-NEC dehydrogenation reactions.A mechanistic study suggests that YH_(3−x)facilitates the reversible hydrogen transfer both in the hydrogenation and the dehydrogenation reactions.The nonstoichiometric YH_(3−x)contained both lattice H and H vacancies with tunable H chemical potential serve as the H donor and H acceptor for reversible hydrogen transfer.Our results support the practical application of LOHCs and inspire new approaches for the utilization of conventional metal hydrides to promote versatile H transfer reactions.

Rare Earth Elements(La,Ce,Pr)Modified Co/NC Catalyst for Efficient and Stable Ammonia Decomposition to Hydrogen Production

Co/NC catalysts modified with rare earth elements(La,Ce,Pr)were prepared by pyrolysis of rare earth elements doped ZIF-67.The experimental results show that the modification of rare earth elements significantly improves the ammonia decomposition activity and stability of the Co/NC catalyst.The La-Co/NC catalyst can achieve an 82.3%ammonia decomposition and 18.4 mmol hydrogen production rate at 550℃with a GHSV of 20000 cm^(3)·h^(-1).Furthermore,no obvious performance degradation is observed after 72 hours of reaction for all rare earth elements modified catalysts.It is shown that the modification of rare earth elements significantly improves the surface alkalinity and surface chemical state of the catalyst,and thus improves the ammonia decomposition activity of the catalyst.A new type of high-performance ammonia decomposition Co-based catalyst is proposed,and the promoting effect of rare earth elements on the activity of ammonia decomposition is revealed.

Bimetallic Ru-Ni/TiO2 catalysts for hydrogenation of N-ethylcarbazole:Role of TiO2 crystal structure

Hydrogenation of N-ethylcarbazole(NEC),the hydrogen lean form of a liquid organic hydrogen carrier,on TiO2 supported Ru-Ni bimetallic catalysts is investigated.Crystal structure of TiO2 plays a critical role on the hydrogenation activity and selectivity towards fully hydrogenated product.Ru/anatase catalyst exhibits higher selectivity but lower reactivity compared to Ru/rutile catalyst.Ni addition significantly promotes the performance of Ru/anatase catalyst while causes severe performance deterioration of Ru/rutile catalyst.Commercial P25,a mixture of anatase and rutile phases in approximate ratio A/R1/4,is found to be the best TiO2 support for NEC hydrogenation.Ru/P25 catalyst outperforms both Ru/rutile and Ru/anatase and its activity can be further slightly improved by Ni addition.The unexpected synergism between the two different TiO2 phases for Ru based NEC hydrogenation catalysts is related to metal-support interaction and Ru-Ni interaction.

Challenges and opportunities for using formate to store, transport, and use hydrogen

In this perspective article,the synthesis and thermodynamic properties of aqueous solutions of formate salts(FS,HCO2-)are described in relationship to the concept of H2carriers.The physiochemical properties of solid FS,aqueous formate solutions,and aqueous bicarbonate solutions set the limitations for storage capacity,deliverable capacity,and usable H2capacity of these H2carriers,respectively.These parameters will help in the design of systems that use H2carriers for storage and transport of H2for fuel cell power applications.FS,as well as admixtures with formic acid(FA,H2CO2),have potential to address the goals outlined in the U.S.Department of Energy’s H2@scale initiative to store in chemical bonds a significant quantity of energy(hundreds of megawatts)obtained from large scale renewable resources.

A study on hydrogen uptake and release of a eutectic mixture of biphenyl and diphenyl ether

Hydrogen storage in Liquid Organic Hydrogen Carrier(LOHC)systems is appealing for the safe storage and distribution of excess renewable energy via existing gasoline infrastructures to end-users.We present the eutectic mixture of biphenyl and diphenyl ether of its first use as a LOHC material.The material is hydrogenated with 99%selectivity without the cleavage of C–O bond,with commercial heterogeneous catalysts,which is confirmed by nuclear magnetic spectroscopy and gas chromatography-mass spectrometry.Equilibrium concentration,dehydrogenation enthalpy,and thermo-neutral temperature are calculated using a density functional theory.The results indicate that O-atom-containing material exhibits more favorable dehydrogenation thermodynamics than that of the hydrocarbon analogue.The H2-rich material contains6.8 wt%of gravimetric hydrogen storage capacity.A preliminary study of catalytic dehydrogenation on a continuous reactor is presented to demonstrate a reversibility of this material.

有机液体储氢载体催化脱氢技术研究进展

绿氢(可再生能源制氢)的开发及利用是推动能源绿色转型和实现“双碳”目标的重点发展方向之一.然而,大规模绿氢的安全储运技术仍需进一步完善.以环烷烃/芳烃为主的有机液体储氢载体(LOHCs)体系因其高储氢密度、安全高效、运输方便等优势成为绿氢长距离大规模输送的关键技术.相比于工艺成熟的芳烃加氢技术,富氢LOHCs(环烷烃)脱氢技术开发的难度较大,是近年来研究的热点.本文系统综述了环己烷(CH)、甲基环己烷(MCH)、十氢萘(DHN)和全氢二苄基甲苯(H18-DBT)4类典型富氢LOHCs脱氢技术的研究进展.基于目前的研究结果,阐述了单环烷烃(CH、MCH)和多环烷烃(DHN、H18-DBT)的脱氢反应路径和机理,重点从活性组分和载体两方面总结了脱氢催化剂的设计思路、构效关系和研究进展,详细分析了基于不同模型的富氢LOHCs脱氢动力学,探讨了4类典型脱氢反应装置的优缺点.总体来讲,环烷烃作为LOHCs距离工业化应用还有一段距离,继续完善环烷烃脱氢动力学和脱氢机理、提高Pt系催化剂的催化活性和稳定性、开发具有实际应用意义的非贵金属催化剂以及优化反应器结构成为未来环烷烃脱氢技术研究需要聚焦的难点.

有序介孔炭负载Pt-MoO_(x)催化剂的制备及其催化甲基环己烷脱氢性能

以有序介孔炭(CMK-3)作为载体,采用原子层沉积技术制备出催化剂y Pt CMK-3及MoO_(x)助剂调控催化剂y Pt-z MoO_(x)CMK-3(y、z分别为Pt和MoO_(x)的沉积循环次数),研究了沉积循环次数对Pt金属分散度和催化剂甲基环己烷脱氢性能的影响。结果表明,适中的Pt分散度和适量原子级分散的MoO_(x)助剂能显著提升Pt基催化剂的性能。与10Pt CMK-3相比,10Pt-1MoO_(x)CMK-3催化剂上的脱氢速率(单位时间内单位质量Pt产生H_(2)的物质的量)从79.02 mol(g·h)提高至97.88 mol(g·h),甲基环己烷转化率由71%提高到91%。MoO_(x)助剂加入对Pt颗粒分散度影响较小,主要提高了Pt表面电子密度,降低了催化剂的起活温度。此外,MoO_(x)助剂还通过氢溢流促进H_(2)在催化剂表面的脱附,从而提高H_(2)产率。

Ba promoter effect on cobalt-catalyzed ammonia decomposition kinetics: A theoretical analysis

Ammonia decomposition is a key reaction in the context of hydrogen storage, transport, and release. This study combines density functional theory(DFT) calculations with microkinetic modeling to address the promotion mechanism of Ba species for ammonia decomposition on Co catalysts. The modified adsorption properties of Co upon the addition of metallic Ba or BaO suggest that the promoters play a role in alleviating the competitive adsorption of H. Calculating the full reaction pathway of ammonia decomposition shows that limiting the investigation to the N–N association step, as done previously, overlooks the effect of the promoter on the energy barriers of the NHxdehydrogenation steps. Challenges of modeling the ammonia decomposition reaction are addressed by understanding that the NH_(2) intermediate is stabilized on the step sites rather than the terrace sites. When the effect of H-coverage on the adsorption of NH_(3) is not considered in the microkinetic simulations, the results conflict with the experiments.However, accounting for the effect of H-coverage, as performed here, shows that BaO-doped Co has higher rates than pristine Co and Ba-doped Co at the reaction temperature of 723.15 K. When H is adsorbed on the Ba-doped Co, the adsorption of ammonia becomes significantly endergonic, which makes the rates relatively slow. The superiority of the BaO-promoted catalyst is attributed to a lower energy for the transition state of the rate-determining step, coupled with a reduced impact of the hydrogen coverage on weakening the ammonia adsorption. The kinetic analysis of the influence of Ba and BaO on the Co surface shows that BaO-doped Co aligns more closely with experimental observations than Badoped Co. This implies that Ba on the Co surface is likely to be in an oxide form under reaction conditions.Understanding the kinetics of the ammonia decomposition reaction provides a foundation for developing highly effective catalysts to accelerate the industrial utilization of ammonia as a sustainable hydrogen carrier.

电内加热Pt/NPC催化剂高效催化甲基环己烷脱氢反应研究

高效储氢技术研发是实现氢能规模化应用的关键。甲基环己烷(MCH)作为理想的有机液体储氢介质,具有质量储氢密度高、储运安全方便等优势,但其脱氢过程仍存在反应温度高、效率低等难题,开发高效脱氢催化剂并引入有效的过程强化是解决上述问题的关键。以不同焙烧温度得到的氮掺杂多孔碳(NPC)作为载体,通过浸渍法制备了系列NPC负载Pt的催化剂(Pt/NPC),在新型电内加热(IEH)模式下,研究了其对MCH脱氢反应性能的影响规律。研究结果表明,随着NPC焙烧温度的升高,Pt^(2+)占比先增加后减少,并在550℃达到最大值。在MCH脱氢反应中,Pt^(2+)占比与反应速率呈近似线性正相关。在优化的Pt/NPC催化剂上,IEH模式下的释氢速率约为传统外加热(CEH)模式的3倍。组合温度测量、反应热与传热计算、性能评价和原位红外表征结果阐明了IEH模式下高的加热速率与传热速率,以及增强的MCH吸附是提升催化性能的重要原因。本研究可为新型电内加热反应方式及与之相匹配高效催化剂的设计研发提供指导。

用于常温氢氧复合的新型Pt/疏水改性陶瓷催化剂

常温氢氧复合反应由于安全性高且能耗低,在核工业除氚、消氢等领域有重要应用,其得以实现的关键为制得性能优异的疏水催化剂。为获得稳定性优且兼具高催化活性的疏水催化剂,本研究制备了新型Pt/疏水改性陶瓷催化剂。陶瓷载体通过构筑CeO2表面粗糙结构,结合涂覆低表面能十三氟辛基三甲氧基硅烷(PFOTMS)进行疏水改性,而后经浸渍-气相还原制得疏水催化剂。结果表明,与常规仅涂覆低表面能材料对陶瓷载体进行疏水改性相比,新型疏水结构的构筑不仅可使疏水催化剂获得更优的疏水性,还可进一步提升催化剂的催化活性及稳定性。制得的新型Pt/疏水改性陶瓷催化剂在480 min反应时长内,氢氧复合效率可维持在99.5%。

有机液体储氢技术催化脱氢过程强化研究进展

氢能是实现化石能源清洁高效利用和支撑可再生能源大规模发展的理想互联媒介,然而氢的储运是制约氢能规模化应用的关键技术瓶颈。有机氢化物(LOHC)储氢技术具有成本低、储氢密度大、安全稳定等优势,可匹配现有化石能源输运架构,有望在大规模、长距离和分布式的氢储运场景中发挥重要作用。但是,在LOHC储氢循环中,相对于发展较为成熟的加氢技术,LOHC脱氢过程效率低、稳定性差,是制约该技术发展的关键。基于此,本文综述了LOHC储氢技术催化脱氢过程强化的研究进展和发展趋势,概述了LOHC储氢基本概念和催化脱氢反应基本原理,从催化过程强化、产物分离强化、能量效率强化等方面总结了脱氢过程强化策略,通过对比不同技术手段的特点,分析了LOHC储氢技术催化脱氢过程目前亟需解决的难题,即开发高效的脱氢催化剂、提高催化脱氢过程的传热传质效率以及降低脱氢过程能耗,这对LOHC储氢技术的实际应用具有重要的参考和借鉴意义。

基于反应器设计的有机液态储氢载体脱氢反应强化研究进展

有机液态储氢载体(liquid organic hydrogen carriers,LOHC)技术是一种应用前景广阔的液态储氢技术,但LOHC脱氢过程中动力学缓慢等问题制约了该技术发展,基于动力学和传热传质强化的反应器设计是必然选择。本文分析了有机液态储氢载体脱氢反应动力学性能强化机制,指出催化剂表面高反应物浓度和高温是高反应速率的关键,且需减少副产物和催化剂失活。提出了传热强化、传质强化策略,以固定床反应器为例介绍了强化传热的目标和措施,指出了强化传质应提高外扩散速率并避免内扩散的影响。简述了多种类型LOHC“气液固”三相反应器的研究进展及其强化策略,最后总结了这些反应器的特点并提出了可能的新型反应器设计方向。可为针对有机液态储氢材料脱氢过程的新型反应器开发提供理论思路和参考依据。

工业副产气化学链回收氢气技术研究进展

我国的工业副产气年产量巨大,是一种重要的制氢资源。由于其高杂质含量,回收其中的H_(2)需要采用复杂的工艺且成本较高,导致副产气的利用率低。相比传统方法,化学链制氢技术只需两步或三步即可制得H_(2),为工业副产气转化为高纯H_(2)提供了一条很有前景的途径。本文针对工业副产气化学链制氢技术的研究进展,讨论了工业副产气化学链制氢工艺的技术优势,总结了不同还原气对化学链制氢过程的影响。在化学链制氢反应过程中,H_(2)的反应活性优于CO,而CH_(4)的反应过程复杂,反应温度对不同气体的反应特性影响较为显著,杂质气体N_(2)和CO_(2)会对制氢过程产生不利影响。针对载氧体,高活性和稳定性载氧体是研究的重点,设计复合型载氧体、掺杂异价元素和负载离子导体等方法是改善载氧体反应性能的重要途径。总的来讲,化学链制氢技术取得了较快的进展,也为其他化学链反应研究提供了借鉴。

助剂对ZnFe_(2)O_(4)氧载体化学链制氢反应性能的影响

采用溶胶-凝胶法制备不同助剂掺杂改性的ZnFe_(2)O_(4)氧载体,探究不同助剂(Sr、Ce、La和Al)对其性能的影响。化学链制氢实验在固定床反应器中进行,结果表明:添加助剂能有效提高氧载体的性能,单位质量氧载体H_(2)产量从高到低依次为La>Sr>Al>Ce,La改性的ZnFe_(2)O_(4)氧载体反应活性最高。结合X射线衍射、H_(2)-程序升温还原、吸附比表面测试法等表征手段和化学链制氢实验对掺杂助剂La的氧载体物理化学性质作进一步分析,考察不同掺杂质量分数对氧载体反应性能的影响。结果表明:添加质量分数为12%La助剂的ZnFe_(2)O_(4)在化学链制氢反应中单位H_(2)产量最高;La助剂的加入提高了氧载体的比表面积,促进氧空位的形成,加快晶格氧的迁移速率,有利于化学链制氢反应。