SnO2-TiO2薄膜载体对Au-Pt纳米颗粒电化学性能的影响

采用真空镀膜法在玻碳(GC)电极表面修饰SnO2-TiO2薄膜, 在SnO2-TiO2/GC复合电极表面组装Au-Pt双金属纳米颗粒, 制得Au-Pt/SnO2-TiO2/GC复合电极. 通过循环伏安法(CV)研究了SnO2-TiO2薄膜载体对Au-Pt双金属纳米颗粒电化学性能的影响; 采用扫描电镜(SEM)及X射线光电子能谱(XPS)对Au-Pt在SnO2-TiO2薄膜沉积的形貌及结构进行了表征. 研究结果表明, 10 nm的Au-Pt双金属纳米颗粒均匀地组装于SnO2-TiO2薄膜表面; SnO2-TiO2薄膜载体改善了复合电极抗CO中毒能力; Au-Pt双金属合金的形成提高了Pt 对甲醇氧化的电催化能力, SnO2-TiO2薄膜载体又使Pt纳米粒子d空轨道增多, 提高了Au-Pt双金属纳米颗粒的稳定性和催化性能.     

Preparation of polyaniline–tin dioxide composites and their application in methanol electro-oxidation

Polyaniline–tin dioxide (PANI-SnO₂) composites were prepared by chemical polymerization method, and characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. Due to the good stability in diluted acidic solution, PANI-SnO₂ composites were selected as the catalyst support and second catalyst for methanol electro-oxidation. The electrocatalytic properties of the PANI-SnO₂ supported Pt catalyst (Pt/PANI-SnO₂) for methanol oxidation have been investigated by cyclic voltammetry, chronoamperometry, and chronopotentiometry. Under the same loading mass of Pt, the Pt/PANI-SnO₂ catalyst shows higher electrocatalytic activity towards methanol electro-oxidation than Pt/SnO₂ catalyst.     

硼掺杂碳化硅负载Pt催化剂的甲醇电催化氧化性能

以硼掺杂碳化硅(B0.1SiC)为载体,采用循环伏安法在B0.1SiC载体上电沉积Pt纳米粒子制备了Pt/B0.1SiC催化剂。利用X射线光电子能谱、X射线衍射、氮气吸附-脱附、扫描电镜及透射电镜等测试方法对催化剂的晶型、表面性质及形貌进行了表征。结果表明,硼原子掺杂进入SiC晶格并取代了Si位点,使B0.1SiC载体的导电性增强;Pt纳米粒子均匀地分布在B0.1SiC载体上,平均粒径为2.7 nm。与相同条件下制备的Pt/SiC催化剂相比,Pt/B0.1SiC具有较大的电化学活性表面积、更高的甲醇催化氧化活性和稳定性。     

以多聚甲醛为还原剂制备新型阳极Pt/CMK-3催化剂

 以多聚甲醛为还原剂,采用液相还原法制备了Pt/CMK-3直接甲醇燃料电池(DMFC)阳极催化剂,并采用透射电镜和X射线衍射技术对其进行了表征. 结果表明,有序介孔碳CMK-3具有规整的二维有序孔道结构,为DMFC中电子和燃料的传输提供了方便的路径,同时它较大的比表面积使得Pt纳米粒子很好地分散在其表面; Pt/CMK-3催化剂中Pt粒子的平均粒径为2.8 nm, 小于E-TEK公司的商品化Pt/XC-72和以甲醇为还原剂制备的Pt/C-M催化剂,并且粒径分布范围窄,结晶度低. 察了Pt/CMK-3催化剂对甲醇的电催化氧化性能,发现Pt/CMK-3催化剂对甲醇氧化的电催化性能优于Pt/XC-72和Pt/C-M催化剂.     

Physical and electrochemical characterizations of microwave-assisted polyol preparation of carbon-supported PtRu nanoparticles

PtRu nanoparticles supported on Vulcan XC-72 carbon and carbon nanotubes were prepared by a microwave-assisted polyol process. The catalysts were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The PtRu nanoparticles, which were uniformly dispersed on carbon, were 2-6 nm in diameter. All PtRu/C catalysts prepared as such displayed the characteristic diffraction peaks of a Pt face-centered cubic structure, excepting that the 2theta values were shifted to slightly higher values. XPS analysis revealed that the catalysts contained mostly Pt(0) and Ru(0), with traces of Pt(II), Pt(IV), and Ru(IV). The electro-oxidation of methanol was studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. It was found that both PtRu/C catalysts had high and more durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a direct methanol fuel cell single stack test cell using the Vulcan-carbon-supported PtRu alloy as the anode catalyst showed high power density.     

炭黑负载Pt-Fe双金属催化剂对甲醇的电催化氧化性能

采用浸渍还原法制备了炭黑负载Pt及Pt-Fe双金属催化剂,通过X光衍射、扫描电镜及X射线光电子能谱对催化剂进行了表征.利用循环伏安法和计时电流法研究了溶液pH值和Pt/Fe原子比对Pt-Fe/C催化剂的甲醇电催化氧化活性与稳定性的影响.结果显示,当溶液pH值为9.0,Pt/Fe原子比为1∶1时,所得Pt-Fe/C催化剂对甲醇的电催化氧化活性与稳定性明显优于Pt/C催化剂.Fe的引入不仅提高了Pt粒子的分散与电化学活性表面积,而且有利于富Pt表面的形成,从而提高了Pt的有效利用率与催化性能.     

聚乙酰苯胺修饰碳纳米管载铂催化剂对甲醇电催化氧化

以原位化学聚合的聚乙酰苯胺/多壁碳纳米管(PAANI-MWCNTs)复合纳米材料作为载体,采用硼氢化钠还原法将Pt纳米粒子担载到PAANI-MWCNTs复合纳米材料表面,制备了Pt/PAANI-MWCNTs复合纳米催化剂.样品的结构和形貌用紫外-可见(UV-Vis)光谱、拉曼光谱、扫描电镜(SEM)、透射电镜(TEM)和X射线衍射(XRD)进行了表征.结果表明,聚乙酰苯胺与碳纳米管之间存在较强的π-π相互作用,使其能牢固地吸附于多壁碳纳米管表面,对碳纳米管的结构完整性和导电性有一定的改善作用.同时,金属Pt纳米颗粒较为均匀地分散在PAANI-MWCNTs表面,粒径分布范围较窄.采用循环伏安法和计时电流法在酸性溶液中研究了Pt/PAANI-MWCNTs催化剂对甲醇的电催化氧化活性,结果表明Pt/PAANI-MWCNTs复合纳米催化剂比用混酸处理的碳纳米管载铂催化剂对甲醇呈现出更高的电催化氧化活性和更好的抗中毒能力及稳定性.     

原子层沉积制备掺氮碳膜修饰的 Pt/CNTs 实现甲醇高效电催化氧化

甲醇燃料电池作为一种清洁、高效的能源转化形式广受关注. 贵金属 Pt 是甲醇燃料电池阳极催化剂不可缺少的活性组分, 但 Pt 价格昂贵, 易与 CO 等中间体强相互作用而中毒失活, 从而限制了甲醇燃料电池的广泛应用. 因此, 如何提高Pt 的利用率成为一个关键问题. 研究表明, 在碳材料载体中掺杂氮元素, 改变了载体本身的表面结构和电子性质, 有利于Pt 颗粒的成核和生长, 可获得尺寸小、分布均匀的 Pt 纳米颗粒, 能显著提升催化反应活性和 Pt 利用率. 然而, 传统的氮掺杂方法需要在高温、高压及氨气条件下进行, 增加了催化剂制备难度和成本.原子层沉积技术是逐层超薄沉积技术, 能够在原子级别精确控制膜的厚度, 既可制备尺度均一、高度可控的纳米粒子,也能实现材料表面的可控超薄修饰. 本课题组利用原子层沉积技术优势, 首先在碳纳米管表面沉积了直径 2 nm 左右的 Pt纳米颗粒, 然后在 Pt 纳米颗粒外表面超薄修饰聚酰亚胺膜, 通过后处理得到多孔掺氮碳膜修饰的 Pt/CNTs 催化剂. 碳膜的厚度可简单通过调控聚酰亚胺膜的沉积厚度来控制. 结果表明, 适当厚度的碳膜修饰 Pt/CNTs 催化剂可显著提升其甲醇电氧化性能, 电流密度可达商业 20% Pt/C 的 2.7 倍, 催化剂稳定性也显著改善. 然而碳膜修饰过厚会导致催化剂活性降低.通过计算催化剂电化学活性表面积发现, 超薄修饰碳膜后催化剂活性表面积有所降低, 这是由于碳膜的覆盖导致表面 Pt原子数减少. 修饰前后催化剂颗粒尺度变化不大, 推测催化剂活性的提高与形成了有利于催化反应的 Pt-碳膜界面有关.然而, 当碳膜修饰层过厚时, 会导致反应物分子难以扩散到 Pt 颗粒表面, 使催化剂活性降低. 预吸附单层 CO 溶出实验结果表明, 多孔掺氮碳膜超薄修饰 Pt/CNTs 催化剂后, CO 氧化峰的起始电位和峰值电位都向低电位处偏移, 这表明 Pt 表面吸附的 CO 在较低电位下即可被氧化, CO 更容易从 Pt 表面移除, 从而提高了催化剂的抗 CO 毒化能力. X 射线光电子能谱实验结果进一步表明, 经多孔掺氮碳膜修饰后, Pt 的 4f 电子向高结合能处偏移, 表明 Pt 原子周围的电子密度减小, 从而弱化了 Pt 对 CO 吸附的σ-π键反馈作用, 即减弱了 Pt 原子对 CO 的吸附, 这是导致掺氮碳膜修饰后催化剂活性及稳定性都大幅提高的原因.     

一步法制备纳米铂/石墨烯及电催化甲醇的交流阻抗和扩散系数测定

采用绿色还原剂抗坏血酸,一步法制备纳米铂/石墨烯。对其进行X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)形貌结构表征,铂纳米粒子均匀分散于纳米石墨烯片层褶皱间,有效减少了团聚现象。运用循环伏安法(CV)和计时电流法(CA)研究纳米铂/石墨烯对甲醇电催化氧化活性和稳定性,通过交流阻抗(EIS)定量测定,发现铂/石墨烯比铂具有更优异的电荷传输性能,电荷转移阻抗下降了34.8%。计时电量法(CC)测定得到甲醇在铂/石墨烯电极的表面扩散系数为1.42×10~(-9) cm~2·s~(-1)。与铂纳米粒子相比,纳米铂/石墨烯对甲醇电催化氧化具有更高的活性和稳定性,显著提高电极催化活性表面积和电荷传输及转移性能。     

一步法制备还原态氧化石墨烯载铂纳米粒子及其对甲醇氧化的电催化性能

以天然石墨为原料,采用改进的Hummers法制备氧化石墨.然后采用简单的一步化学还原法在乙二醇(EG)中同时还原氧化石墨烯(GO)和H₂PtCl₆制备高分散的铂/还原态氧化石墨烯(Pt/RGO)催化剂.采用傅里叶变换红外(FTIR)光谱、X射线衍射(XRD)和透射电子显微镜(TEM)对催化剂的微结构、组成和形貌进行表征.结果表明, GO已被还原成RGO, Pt纳米粒子均匀分散在RGO表面,粒径约为2.3 nm.采用循环伏安法和计时电流法评价催化剂对甲醇氧化的电催化性能,测试结果表明, Pt/RGO催化剂对甲醇氧化的电催化活性和稳定性与Pt/C和Pt/CNT相比有了很大提高.另外其对甲醇电催化氧化的循环伏安图中正扫峰电流密度(I_f)和反扫峰电流密度(I_b)的比值高达1.3,分别是Pt/C和Pt/CNT催化剂的2.2和1.9倍,表明Pt/RGO催化剂具有高的抗甲醇氧化中间体CO_ad的中毒能力.     

双牺牲模板法制备一维管状Pt-Mn3O4-C复合物及其优越的甲醇电催化氧化性能

通过双牺牲模板法合成了以一维管状Mn₃O₄-C为催化剂载体的新型Pt 基电催化剂. 催化剂的表面形貌、晶体结构及其组成分别采用透射电镜、X射线衍射仪、能量散射X射线光谱进行表征. 通过循环伏安法对Pt-Mn₃O₄-C复合物的电化学性能进行了测试. 结果表明平均粒径为1.8 nm的Pt 纳米颗粒均匀分散在管式Mn₃O₄-C载体上, 与商业的E-TEK Pt/C 催化剂(20% (w, 质量分数) Pt)相比, Pt-Mn₃O₄-C对甲醇氧化有更好的电催化活性和更高的稳定性. Pt 纳米粒子在Mn₃O₄-C上的均匀分散及Pt 和Mn₃O₄的协同催化效应使得Pt-Mn₃O₄-C具有优异的性能.     

Electrodeposition and electrocatalytic properties of platinum nanoparticles on multi-walled carbon nanotubes: effect of the deposition conditions

Platinum (Pt) nanoparticles were electrochemically deposited on multi-walled carbon nanotubes (MWCNTs) through a three-step process, including an electrochemical treatment of MWCNT, electro-oxidation of PtCl₄ ²⁻ to Pt(IV) complex, and an electro-conversion of Pt(0) on MWCNT. The effect of formation conditions for Pt(IV) complexes on the Pt nanoparticals transformed was investigated. The structure and elemental composition of the resulting Pt/MWCNT electrode were characterized by transmission electron micrograph (TEM) and energy dispersive X-ray spectroscopy (EDX). The electrocatalytic properties of the resulting Pt/MWCNT electrode for methanol oxidation have been investigated. The high electrocatalytic activity and good stability of Pt/MWCNT electrode may be attributed to the high dispersion of platinum nanoparticles and the particular properties of the MWCNT supports.     

多孔聚乙酰苯胺纳米纤维载铂催化剂对甲醇的电催化氧化

采用简单的化学氧化聚合法制备了新型多孔结构的聚乙酰苯胺纳米纤维(np-PAANI), 并以此为载体在络合剂的存在下合成了Pt纳米微粒修饰的np-PAANI复合物膜电极C/np-PAANI/Pt. 样品的形貌和结构通过扫描电镜(SEM)、透射电镜(TEM)和X射线衍射(XRD)进行了表征. 在0.5 mol·L-1 CH3OH+0.5 mol·L-1 H2SO4混合溶液中考察了C/np-PAANI/Pt催化剂对甲醇的电催化氧化性能. 结果表明, 以np-PAANI负载的Pt催化剂对甲醇的电催化氧化活性和稳定性都比普通PAANI结构及石墨粉负载的Pt催化剂好很多.     

Combinatorial optimization of ternary Pt alloy catalysts for the electrooxidation of methanol

We report the combinatorial and high-throughput optimization of improved ternary Pt alloy electrocatalysts for the oxidation of methanol for use in direct methanol fuel cell (DMFC) anodes. Following up on the discovery of a ternary Pt20Co60Ru20 catalyst with significantly improved electrocatalytic activity for methanol oxidation over standard Pt-Ru catalysts, we optimize the electrocatalytic activity of this composition using a closely sampled Pt-Co-Ru "optimization library". We also screen for compositional and structural stability using high-throughput methods. Composition-activity maps confirmed improved activity in compositional neighborhood of the Pt20Co60Ru20 catalyst. Activity trends of Pt-Ru binary alloys were in excellent agreement with fundamental surface electrochemical studies. Structural and compositional catalyst stability was probed using X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). Combination of the stability-composition and activity-composition maps resulted in "consensus maps" pointing to a new optimized ternary alloy electrocatalyst for methanol electrooxidation with an overall composition of Pt18Co62Ru20.     

In situ synthesis of Pt/carbon nanofiber nanocomposites with enhanced electrocatalytic activity toward methanol oxidation

Pt/carbon nanofiber (Pt/CNF) nanocomposites were facilely synthesized by the reduction of hexachloroplatinic acid (H(2)PtCl(6)) using formic acid (HCOOH) in aqueous solution containing electrospun carbon nanofibers at room temperature. The obtained Pt/CNF nanocomposites were characterized by TEM and EDX. The Pt nanoparticles could in situ grow on the surface of CNFs with small particle size, high loading density, and uniform dispersion by adjusting the concentration of H(2)PtCl(6) precursor. The electrocatalytic activities of the Pt/CNF nanocomposites were also studied. These Pt/CNF nanocomposites exhibited higher electrocatalytic activity toward methanol oxidation reaction compared with commercial E-TEK Pt/C catalyst. The results presented may offer a new approach to facilely synthesize direct methanol fuel cells (DMFCs) catalyst with enhanced electrocatalytic activity and low cost.     

A simple one-step preparation of high utilization AuPt nanoparticles supported on MWCNTs for methanol oxidation in alkaline medium

A simple one-step preparation of gold–platinum electrocatalysts supported on multi-walled carbon nanotubes (MWCNTs) with high utilization is reported. A low Pt loading series of bimetallic AuPt/MWCNTs catalysts were prepared by the improved ethylene glycol reduction method, and then they were compared in terms of the electrocatalytic activity for methanol oxidation using cyclic voltammetry (CV) and chronoamperometry in alkaline solutions. The structure of AuPt/MWCNTs was characterized by the transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The results showed high Pt utilization, uniform AuPt nanoparticles size and good electrocatalytic activity for methanol electro-oxidation. The effect of Au/Pt mass ratio on electrocatalytic activity was also investigated by CV and chronoamperometry. The highest peak current density, lowest onset potential and best anti-poisoning effect for methanol electro-oxidation appeared at the Au/Pt/MWCNTs mass ratio of 2:4:32.     

Electro-deposition of platinum nanoparticles on 4-mercaptobenzene-functionalized multi-walled carbon nanotubes

A new method to electro-deposit platinum nanoparticles on the surface of multi-walled carbon nanotubes (MWNTs) functionalized with 4-mercaptobenzene has been described. X-ray photoelectron spectroscopy results reveal that 4-mercaptobenzene was attached to the surface of MWNTs. Transmission electron microscope and X-ray diffraction analysis confirm that platinum nanoparticles were highly dispersed on the surface of MWNTs, and the average size of the platinum particle is 4.2 nm. The electrocatalytic properties of the Pt/MWNT composite electrode for methanol oxidation were investigated by cyclic voltammetry, and the results show that the fabricated composites exhibit high catalytic activity and good long-term stability. The study provides a feasible approach to fabricate Pt/MWNT composite electrode for direct methanol fuel cell.     

纳米三氧化钨修饰碳纳米管载铂催化剂对甲醇氧化的电催化性能

采用表面修饰技术将碳纳米管(CNT)表面羧基化, 通过羧基将钨离子基团修饰到碳纳米管的外表面, 再通过高温焙烧处理将钨离子基团氧化成WO₃, 成功合成了纳米WO₃/CNT复合物, 进一步还原Pt 的前驱体而得到Pt-WO₃/CNT复合催化剂. 采用X射线粉末衍射(XRD)和透射电镜(TEM)对样品的形貌和晶型结构进行了表征, 结果表明, Pt纳米粒子为面心立方晶体结构, 均匀地分布在WO₃修饰的碳纳米管表面. 采用循环伏安(CV)和计时电流法研究了在酸性溶液中Pt-WO₃/CNT催化剂对甲醇的电催化氧化活性, 结果表明WO₃修饰的碳纳米管载铂催化剂比用混酸处理的碳纳米管载铂催化剂对甲醇呈现出更高的电催化氧化活性和更好的稳定性.     

Pt/TiO2纳米纤维的制备及其对甲醇的电催化氧化活性

采用静电纺丝技术结合还原浸渍法制备了Pt/TiO₂纳米纤维电催化剂, 通过X射线衍射(XRD)分析、扫描电镜(SEM)、透射电镜(TEM)和X射线能谱(EDS)等测试手段对样品的晶相、形貌、微结构和化学组成进行了表征. 测试结果表明, TiO₂纳米纤维为锐钛矿和金红石组成的混晶, Pt 纳米颗粒均匀地分布于TiO₂纳米纤维的表面, 且Pt 颗粒大小较均一, 平均粒径为4.0 nm, Pt/TiO₂纳米纤维中Pt 的质量分数约为20%. 采用三电极体系的循环伏安和计时电流电化学分析方法研究了样品在酸性溶液中对甲醇的电催化氧化活性, 结果表明, 与负载相同质量分数Pt 的Pt/P25 和商业Pt/C 催化剂相比较, Pt/TiO₂纳米纤维催化剂对甲醇呈现出较高的电催化氧化活性和更好的稳定性.     

分级结构氮掺杂碳纳米笼担载的铂基高效甲醇氧化电催化剂

高性能低成本的担载型铂基催化剂是直接甲醇燃料电池(DMFC)实用化过程中的一大挑战.利用高比表面积、高稳定性、容易负载金属的载体实现 Pt颗粒的高度分散,既可提高催化剂的催化性能,又可提高 Pt的利用率以降低成本,是担载型 Pt基催化剂实用化的有效途径.碳材料是一种常用的催化剂载体,近年来我们课题组发展了一种高性能的碳纳米笼材料,并可通过异原子掺杂调变其表面性能,提高其活性和负载能力.我们采用原位氧化镁模板法制备氮掺杂碳纳米笼：以具有多级结构的碱式碳酸镁作为氧化镁模板的前体,吡啶为碳源和氮源,经高温热解沉积,在原位形成的氧化镁模板表面形成氮掺杂的石墨化碳纳米薄层;经稀盐酸浸泡并洗涤,获得高纯度的氮掺杂碳纳米笼.氮掺杂碳纳米笼具有分等级的微纳米结构、高导电性、高比表面积和可调变的孔结构,结合表面氮原子的锚钉作用,氮掺杂碳纳米笼有望成为电化学催化剂 Pt的优良载体.
　　在前期研究基础上,本文探索多级结构氮掺杂碳纳米笼(hNCNC)作为新型载体负载 Pt的能力,并评价所构建的负载型催化剂 Pt/hNCNC的电催化性能.通过简便的微波辅助多元醇还原法,将氯铂酸还原成 Pt纳米粒子负载于 hNCNC的表面.为了揭示氮掺杂的效应,我们对比研究了具有相似分级结构但无掺杂的碳纳米笼(hCNC)以及商业化活性炭(Val-can XC-72)作为载体的情况.经热重(TG)和 X射线光电子能谱(XPS)分析,三种催化剂 Pt/hNCNC、Pt/hCNC和 Pt/XC-72的负载量均接近理论负载量(23.1 wt%),都主要以金属态存在.然而,扫描电子显微镜(SEM)和透射电子显微镜(TEM)结果表明, Pt/hNCNC的 Pt分散状态优于 Pt/hCNC,更远优于 Pt/XC-72. Pt/hNCNC的平均 Pt粒径最小,仅约3.3 nm.这种良好的分散状态主要得益于氮原子掺杂,高负电性的氮原子改变了局域的表面极性,有利于 Pt颗粒的成核,也有利于固定 Pt颗粒.
　　由于 hNCNC对 Pt的优异分散能力, Pt/hNCNC表现出高的电化学活性面积.氢吸附和一氧化碳溶出伏安曲线表明, Pt/hNCNC的电化学活性面积高于 Pt/hCNC和 Pt/XC-72,这与显微观察和 X射线衍射(XRD)结果相吻合. Pt/hNCNC展现出优异的甲醇电催化氧化活性和高稳定性,其催化电流明显高于 Pt/hCNC和 Pt/XC-72,电流衰减亦慢于 Pt/hCNC和 Pt/XC-72. hNCNC的分级微纳米结构有利于孔内传质和电子输运,从而提高反应速度. hNCNC的氮掺杂有利于 Pt在载体表面的分散,增强了载体-金属相互作用,提高了电化学活性面积和催化活性.为了进一步考察 hNCNC对 Pt的负载能力,本文还考察了高负载量 Pt/hNCNC的性能.在负载量高达60 wt%时, Pt/hNCNC中的 Pt颗粒仍无明显聚集,其甲醇氧化电流增加了30%,可以有效提高 DMFC的输出电流密度.
　　综上可见, hNCNC可以有效分散并稳定 Pt颗粒,从而提高电化学活性面积和甲醇电催化氧化活性,优于未掺杂的碳纳米笼和传统碳材料,展示了 hNCNC高分散 Pt颗粒用作 DMFC的高效阳极催化剂的重要前景,也表明 hNCNC有望成为应用广泛的新型载体.