Exploration of the oxygen transport behavior in non-precious metal catalyst-based cathode catalyst layer for proton exchange membrane fuel cells

High cost has undoubtedly become the biggest obstacle to the commercialization of proton exchange membrane fuel cells(PEMFCs),in which Pt-based catalysts employed in the cathodic catalyst layer(CCL)account for the major portion of the cost.Although nonprecious metal catalysts(NPMCs)show appreciable activity and stability in the oxygen reduction reaction(ORR),the performance of fuel cells based on NPMCs remains unsatisfactory compared to those using Pt-based CCL.Therefore,most studies on NPMC-based fuel cells focus on developing highly active catalysts rather than facilitating oxygen transport.In this work,the oxygen transport behavior in CCLs based on highly active Fe-N-C catalysts is comprehensively explored through the elaborate design of two types of membrane electrode structures,one containing low-Pt-based CCL and NPMCbased dummy catalyst layer(DCL)and the other containing only the NPMC-based CCL.Using Zn-N-C based DCLs of different thickness,the bulk oxygen transport resistance at the unit thickness in NPMC-based CCL was quantified via the limiting current method combined with linear fitting analysis.Then,the local and bulk resistances in NPMC-based CCLs were quantified via the limiting current method and scanning electron microscopy,respectively.Results show that the ratios of local and bulk oxygen transport resistances in NPMCbased CCL are 80%and 20%,respectively,and that an enhancement of local oxygen transport is critical to greatly improve the performance of NPMC-based PEMFCs.Furthermore,the activity of active sites per unit in NPMCbased CCLs was determined to be lower than that in the Pt-based CCL,thus explaining worse cell performance of NPMC-based membrane electrode assemblys(MEAs).It is believed that the development of NPMC-based PEMFCs should proceed not only through the design of catalysts with higher activity but also through the improvement of oxygen transport in the CCL.

Progress on Platinum-Based Catalyst Layer Materials for H_(2)-PEMFC

The constant increase in energy demand and related environmental issues have made fuel cells an attractive technology as an alternative to conventional energy technologies.Like any technology,fuel cells face drawbacks that scientific society has been focused on to improve and optimize the overall technology.Thus,the cost is the main inhibitor for this technology due to the significantly high cost of the materials used in catalyst layers.The current discussion mainly focuses on the fundamental electrochemical half-cell reaction of hydrogen oxidation reaction(HOR)and oxygen reduction reaction(ORR)that are taking place in the catalyst layers consisting of Platinum-based and Platinum-non noble metals.For this purpose,studies from the literature are presented and analyzed by highlighting and comparing the variations on the catalytic activity within the experimental catalyst layers and the conventional ones.Furthermore,an economic analysis of the main platinum group metals(PGMs)such as Platinum,Palladium and Ruthenium is introduced by presenting the economic trends for the last decade.

Recent advances in carbon-supported non-precious metal singleatom catalysts for energy conversion electrocatalysis

Non-precious metal single-atom catalysts(NPM-SACs)with unique electronic structures and coordination environments have gained much attention in electrocatalysis owing to their low cost,high atomic utilization,and high performance.NPM-SACs on carbon support(NPM-SACs/CS)are promising because of the carbon substrate with a large surface area,excellent electrical conductivity,and high chemical stability.This review provides an overview of recent developments in NPM-SACs/CS for the electrocatalytic field.First,the state-of-the-art synthesis methods and advanced characterization techniques of NPM-SACs/CS are discussed in detail.Then,the structural adjustment strategy of NPM-SACs/CS for optimizing electrocatalytic performance is introduced concisely.Furthermore,we provide a comprehensive summary of recent advances in developing NPM-SACs/CS for important electrochemical reactions,including carbon dioxide reduction reaction,hydrogen evolution reaction,oxygen evolution reaction,oxygen reduction reaction,and nitrogen reduction reaction.In the end,the existing challenges and future opportunities of NPM-SACs/CS in the electrocatalytic field are highlighted.

Hydroxylated metal–organic-layer nanocages anchoring single atomic cobalt sites for robust photocatalytic CO_(2) reduction

Assembly of two-dimensional(2D)metal–organic layers(MOLs)based on the hard and soft acid–base theorem represents an exquisite strategy for the construction of photocatalytic platforms in virtue of the highly exposed active sites,much improved mass transport,and greatly elevated stability.Herein,nanocages composed of MOLs are produced for the first time through a cosolvent approach utilizing zirconium-based UiO-66-(OH)2 as the structural precursor.To endow the catalytic activity for CO_(2) conversion,single atomic Co^(2+)sites are appended to the Zr-oxo nodes of the MOL cages,demonstrating a remarkable CO yield of 7.74 mmol·g^(-1)·h^(-1) and operational stability of 97.1%product retention after five repeated cycles.Such an outstanding photocatalytic performance is mainly attributed to the unique nanocage morphology comprising enormous 2D nanosheets for augmented Co^(2+)exposure and the abundant surface hydroxyl groups for local CO_(2) enrichment.This work underlines the tailoring of both metal–organic framework(MOF)morphology and functionality to boost the turnover rate of photocatalytic CO_(2) reduction reaction(CO_(2)RR).

Role of local coordination in bimetallic sites for oxygen reduction: A theoretical analysis

Understanding of the oxygen reduction reaction(ORR)mechanism for single atom catalysts is pivotal for the rational design of non-precious metal cathode materials and the commercialization of fuel cells.Herein,a series of non-precious metal electrocatalysts based on nitrogen-doped bimetallic(Fe and Co)carbide were modeled by density functional theory calculations to predict the corresponding reaction pathways.The study elucidated prior oxygen adsorption on the Fe atom in the dual site and the modifier role of Co atoms to tune the electronic structures of Fe.The reaction activity was highly correlated with the bimetallic center and the coordination environment of the adjacent nitrogen.Interestingly,the preadsorption of*OH resulted in the apparent change of metal atoms'electronic states with the d-band center shifting toward the Fermi level,thereby boosting reaction activity.The result should help promote the fundamental understanding of active sites in ORR catalysts and provide an effective approach to the design of highly efficient ORR catalysts on an atomic scale.

Enhanced confinement synthesis of atomically dispersed Fe-N-C catalyst from resin polymer for oxygen reduction

Due to larger atom utilization,unique electronic properties and unsaturated coordination,atomically dispersed non-precious metal catalysts with outstanding performances have received great attention in electrocatalysis.Considering the challenge of serious aggregation,rational synthesis of an atomic catalyst with good dispersion of atoms is paramount to the development of these catalysts.Herein,we report an enhanced confinement strategy to synthesize a catalyst comprised of atomically dispersed Fe supported on porous nitrogen-doped graphitic carbon from the novel and more cross-linkable Melamine-Glyoxal Resin.Densified isolated grid trapping,excessive melamine restricting,and nitrogen anchoring are strongly combined to ensure the final atomic-level dispersion of metal atoms.Experimental studies revealed enhanced kinetics of the obtained catalyst towards oxygen reduction reaction(ORR).This catalytic activity originates from the highly active surface with atomically dispersed iron sites as well as the multi-level three-dimensional structure with fast mass and electron transfer.The enhanced confinement strategy endows the resin-derived atomic catalyst with a great prospect to develop for commercialization in future.

A non-precious metal catalyst for oxygen reduction prepared by heat-treating a mechanical mixture of carbon black,melamine and cobalt chloride

A non-precious metal catalyst CoMe]C for the oxygen reduction reaction is prepared by heat-treating a mechanical mixture of carbon black, melamine and cobalt chloride at 600 under nitrogen atmosphere for 2 h. The catalytic activity of CoMe/C is characterized by the electrochemical linear sweep voltammetry technique. The onset reduction potential of the catalyst is 0.55 V （vs. SCE） at a scanning rate of 5 mV/s in 0.5 mol/L H2SO4 solution. The formation of the ORR activity sites of CoMe/C is facilitated by metallic β- cobalt.

Catalytic applications of single-atom metal-anchored hydroxides:Recent advances and perspective

Developing isolated single atomic noble metal catalysts is one of the most effective methods to maximize noble metal atom utilization efficiency and enhance catalytic performances.Layered double hydroxides(LDHs)are two-dimensional nanoarchitectures in which M^(3+) and M^(2+) sites are atomically isolated due to static repulsions,providing special anchoring sites for single noble metal atoms and enabling the tuning of catalytic activity.Herein,a comprehensive review of the advances in LDHs supported single-atom catalysts(M/LDH SACs)is presented,focusing on the synthetic strategies,structure characterization,and application of M/LDH SACs in energy devices.Strong electronic coupling between single atomic noble metal atoms and corresponding anchoring sites of LDHs determines not only the catalytic activity of M/LDH SACs but also the stability during catalytic reactions.Furthermore,a perspective is proposed to highlight the challenges and opportunities for understanding the reaction mechanism and development of highly efficient M/LDH SACs.

Reduced formation of peroxide and radical species stabilises iron-based hybrid catalysts in polymer electrolyte membrane fuel cells

The incorporation of Pt into an iron-nitrogen-carbon(Fe NC)catalyst for the oxygen reduction reaction(ORR)was recently shown to enhance catalyst stability without Pt directly contributing to the ORR activity.However,the mechanistic origin of this stabilisation remained obscure.It is established herein with rotating ring disc experiments that the side product,H_(2)O_(2),which is known to damage FeNC catalysts,is suppressed by the presence of Pt.The formation of reactive oxygen species is additionally inhibited,independent of intrinsic H_(2)O_(2) formation,as determined by electron paramagnetic resonance.Transmission electron microscopy identifies an oxidised Fe-rich layer covering the Pt particles,thus explaining the inactivity of the latter towards the ORR.These insights develop understanding of Fe NC degradation mechanisms during ORR catalysis,and crucially establish the required properties of a precious metal free protective catalyst to improve Fe NC stability in acidic media.

The effect of temperature on ionic liquid modified Fe-N-C catalysts for alkaline oxygen reduction reaction

Modifying solid catalysts with an ionic liquid layer is an effective approach for boosting the performance of both Pt-based and non-precious metal catalysts toward the oxygen reduction reaction. While most studies operated at room temperature it remains unclear whether the IL-associated boosting effect can be maintained at elevated temperature, which is of high relevance for practical applications in low temperature fuel cells. Herein, Fe-N-C catalysts were modified by introducing small amounts of hydrophobic ionic liquid, resulting in boosted electrocatalytic activity towards the alkaline oxygen reduction reaction at room temperature. It is demonstrated that the boosting effect can be maintained and even strengthened when increasing the electrolyte temperature up to 70℃. These findings show for the first time that the incorporation of ionic liquid is a suited method to obtain advanced noble metal-free electrocatalysts that can be applied at operating temperature condition.

Mg-Al层状双金属氧化物催化臭氧降解阿特拉津的性能研究

采用水热沉淀-煅烧法在煅烧温度为400℃和Mg与Al物质的量比为3时制得Mg_(3)Al-400复合材料,通过SEM、FT-IR和XPS等分析Mg_(3)Al-400复合材料的形貌结构和理化组成,考察运行参数对其催化臭氧降解阿特拉津(ATZ)的影响。结果表明:Mg_(3)Al-400具有优异的催化臭氧降解ATZ性能,当其投加量为350 mg/L,ATZ质量浓度为5 mg/L,溶液初始pH值为6时,反应3 min后ATZ的去除率高达99%。此外,Mg_(3)Al-400在5次循环后仍具有较好的稳定性。自由基抑制试验表明·O_(2)-和·OH对ATZ的降解起到关键作用。对降解过程和反应机理分析可知,表面Mg—OH是其发挥催化作用的活性位点。

Metal-mediated Layer-by-layer Films of Multi-metalloporphyrin Arrays:a Novel Switchable Catalyst System

1 Results Metalloporphyrins as one kind of effective catalysts have received considerable attention in the past two decades,because of their selective oxidation of hydrocarbons and other organic compound under mild conditions.Great efforts have been made to oxidize or epoxidize the hydrocarbons and cycloparaffin with the oxidants such as PhIO,H2O2 catalyzed by the metalloporphyrins.However,the metalloporphyrins are normally dissolved in the reaction solution or immobilized on silica or other porous supp...

汽车尾气净化催化剂金属载体表面预处理的研究

金属载体催化剂在汽车尾气净化领域具有明显应用前景,但金属载体与活性涂层的牢固结合以及金属的高温抗氧化性能是急需解决的问题。本文通过表面预处理在FeCrAl合金箔片表面生成Al2O3过渡层,使γ-Al2O3活性涂层与FeCrAl箔良好结合,并采用SEM、EDS、XPS、XRD、超声振落及热冲击的方法研究了预处理后FeCrAl箔的表面结构、活性涂层的性能及与FeCrAl箔的结合。结果表明,经过预处理的FeCrAl箔对活性涂层的一次负载率>11%;在500℃和900℃下,涂层的比表面积分别为166.0m2/g和71.05m2/g;在59kHz,30min超声波作用下,涂层脱落率为1.5%～2.5%;800℃至室温热冲击涂层损失率为0.1449%。该Al2O3过渡层有可能使金属载体与活性涂层间的结合问题得到解决。

负载贵金属的层柱分子筛的芳烃加氢饱和性能

负载贵金属的层柱分子筛的芳烃加氢饱和性能刘维桥阎富山孙桂大达志坚闵恩泽（抚顺石油学院材料科学与技术研究所，抚顺１１３００１）（石油化工科学研究院，北京１０００８３）关键词层柱粘土，芳烃，加氢饱和，贵金属催化剂芳烃加氢饱和是石油化工领域的一个重要精制过...

磷酸锆类层柱催化剂的制备、表征及其催化甲醇氧化羰基化反应性能

以层 状 α磷酸 锆为插层 主体，采 用高温 固相 离子 交换 插层 法制 备了 Ｃｕ２ ＋ ， Ｋ ＋ 柱 撑 的磷酸锆类 层柱催化 剂，并用 Ｘ Ｒ Ｄ， Ｉ Ｒ 和 Ｔ Ｇ 等方 法对 其进 行了 表征 ． 结 果 表明 ，金 属离 子柱 撑 的 α磷酸锆 类层柱催 化剂的 层间距由 原来的０ ７６ ｎ ｍ 扩 撑至０８１ ｎ ｍ ， 结 晶度 有所 下降 ． 通 过甲 醇氧化羰基 化液相法 制备碳 酸二甲酯 反应，考 察了磷 酸锆 类层 柱催 化剂 的催 化性 能． 在一 定的 反 应条件下，甲 醇转化 率可达１６ ７ ％ ， 碳酸 二甲酯选 择性可达 ５７ ％ ， 而 且催化 剂用 量少， 结构 稳定， 对设备腐蚀

Ru-ZnO气敏材料的敏感特性研究

采用化学沉淀法合成了纯ＺｎＯ微细粉，用浸渍法合成了Ｒｕ－ＺｎＯ气敏材料及Ａｌ２Ｏ３基催化剂。采用静态配气法测试了ＺｎＯ单层膜及双层膜旁热式气敏元件的敏感特性。实验结果表明，Ｒｕ的掺杂可提高ＺｎＯ的气体灵敏度，催化剂涂层的施加可改善Ｒｕ－ＺｎＯ对汽油、乙醇、丁烷的气敏选择性。

原子层沉积方法在设计制备高效电催化剂中的应用（英文）

人类对不可再生化石能源的依赖导致了全球范围内的能源危机和环境污染.电化学能源转换技术由于具有清洁、高效、原料来源广泛及可再生等优点而受到广泛关注.电催化剂能加快反应动力学,提高目标产物选择性,在电化学能源转换技术中起着至关重要的作用.目前, Pt是多数重要的电化学反应(如电解水、氧还原以及一些小分子醇类和酸类的氧化反应)中使用最多和最有效的催化剂之一.然而Pt催化剂面临着价格昂贵、易中毒、易流失等问题,使其在大规模工业化应用中受到限制.为了提高Pt催化剂的利用率和稳定性,研究人员进行了大量工作.例如,制备尺寸小的Pt纳米颗粒,增加单位质量Pt表面积和Pt利用率;在Pt催化剂中加入Ru或Pd等其它金属,促进醇类和酸类氧化反应中间产物的氧化,减缓Pt中毒;选用抗腐蚀性能好的载体,增加Pt与载体间相互作用,从而抑制Pt颗粒在高电位、高湿度、高酸碱度电化学工作环境中的脱落和聚集.尽管如此,利用传统的方法仍然很难精确调控电催化剂的组成、尺寸和纳米结构,无法最大程度提高贵金属Pt的利用效率.原子层沉积(ALD)技术可在原子尺度控制物质生长,既能在多孔、复杂基体上沉积尺度均一的纳米薄膜或颗粒,也能精确调控、构筑各类纳米结构.本文总结了近年来利用ALD技术制备高性能电催化剂的代表性研究进展.文章首先介绍了ALD反应机理、载体表面官能团对ALD生长的促进作用以及ALD制备方法对催化剂金属-载体相互作用的影响等基本原理和知识.总结了利用ALD技术制备高活性Pt催化剂的各种方法,包括制备超细纳米颗粒,纳米线、纳米薄膜、纳米管,纳米3D结构等不同形貌Pt催化剂等.介绍并探讨了利用ALD构筑纳米陷阱、包覆超薄多孔碳膜/氧化物膜、选择性修饰载体等提高Pt催化剂稳定性的策略.文章还介绍了如何通过调节ALD反应温度、前驱体种类,以及利用选择性沉积等方法,精确调控双贵金属电催化剂中金属的比例、尺寸、结构等以提高催化剂性能,并重点阐述了双金属核壳催化剂的制备方法.此外,文章还概述了ALD方法制备非贵金属催化剂的研究进展.最后,文章总结了ALD技术在设计、制备电催化剂领域的优势和不足,展望了ALD在该领域的发展和应用前景,为设计、制备高性能电催化剂提供了参考.

快速界面法制备FeOOH@CoNi-LDH@NF用于高效析氧

以六水合硝酸钴、六水合硝酸镍、尿素和氟化铵为原料,采用水热法在镍网上原位构筑层状双金属氢氧化物(LDH)(CoNi-LDH@NF),然后采用快速界面法在硝酸钠和六水合氯化铁的100℃溶液中对其进行刻蚀制备了FeOOH@CoNi-LDH@NF。利用XRD、SEM、XPS和TEM对FeOOH@Co Ni-LDH@NF进行了形貌表征和物相分析,并在1 mol/L KOH电解液中进行了电催化析氧性能测试。结果表明,异质界面明显的粗糙纳米棒结构极大地增多了FeOOH@CoNi-LDH@NF的有效活性位点数,提升了对中间物质的转换速率。驱动100m A/cm;的电流密度仅需291 mV过电势,Tafel斜率为48 mV/dec;该电极具有至少100 h的耐久性,展示出优异的碱性析氧性能。

贵金属粒子催化刻蚀制备硅太阳能电池减反射层研究进展

贵金属纳米粒子催化性能的研究已成为当前新材料及能源科学研究领域的热点之一。最近,在用贵金属粒子作为催化剂,辅助刻蚀硅衬底制作太阳能电池减反射层方面开展了大量的研究工作。综述了近年来贵金属粒子催化刻蚀硅制备减反射层的研究进展,分析了贵金属粒子的催化机理和减反射层制作的影响因素,展望了贵金属粒子催化刻蚀薄膜太阳能电池硅衬底研究的发展趋势。

Pd、Pt及其双金属催化剂的表面特性和催化活性

发现由ESCA技术测得的Pd-Pt/Al_2O_3催化剂的表相Pt原子浓度低于体相浓度,Pd/Pt比低者其表相Pd原子浓度高于体相浓度,EPMA测定结果表明,表相Pd和Pt原子浓度均高于体相浓度。经CO处理后其表相Pd原子浓度降低,而Pt原子浓度却有所增高,可见Pt原子向催化剂表相的富集作用更为明显。从吸附的CO红外光谱也可证明,金属向催化剂表相的富集作用以CO在Pd-Pt/Al_2O_3上与Pt的键合能力比与Pd的键合能力强。H_2的低温和中温TPD峰面积与催化剂的Pd/Pt比和除H_2活性有着密切关系。