Pt纳米催化剂在质子交换膜燃料电池催化层中的尺寸效应研究

以XC-72碳黑为载体, H2[PtCl6]为前驱体, 采用浸渍还原法并结合后续高温处理, 制备出不同尺寸Pt颗粒(3～8 nm)的Pt/C催化剂. 在基于质子交换膜燃料电池(PEMFC)单电池的电化学电解池中, 对实际PEMFC催化层中燃料电池反应的Pt催化剂尺寸效应进行了研究. 结果表明, 在PEMFC催化层环境中, Pt/C纳米催化剂对氢氧化和氧还原反应均有显著的粒度尺寸效应. 随着Pt粒度减小, 氢氧化和氧还原反应的表面积活性均降低.     

A Nanoporous PdCo Alloy as a Highly Active Electrocatalyst for the Oxygen‐Reduction Reaction and Formic Acid Electrooxidation

A nanoporous (NP) PdCo alloy with uniform structure size and controllable bimetallic ratio was fabricated simply by one‐step mild dealloying of a PdCoAl precursor alloy. The as‐made alloy consists of a nanoscaled bicontinuous network skeleton with interconnected hollow channels that extend in all three dimensions. With a narrow ligament size distribution around 5 nm, the NP PdCo alloy exhibits much higher electrocatalytic activity towards the oxygen‐reduction reaction (ORR) with enhanced specific and mass activities relative to NP Pd and commercial Pt/C catalysts. A long‐term stability test demonstrated that NP PdCo has comparable catalytic durability with less loss of ORR activity and electrochemical surface area than Pt/C. The NP PdCo alloy also shows dramatically enhanced catalytic activity towards formic acid electrooxidation relative to NP Pd and Pd/C catalysts. The as‐made NP PdCo holds great application potential as a promising cathode as well as an anode electrocatalyst in fuel cells with the advantages of superior catalytic performance and easy preparation.     

通过调控晶体结构提高氧气还原反应电催化活性:MPt金属间相纳米晶（英文）

燃料电池的正极主要发生氧还原反应(ORR),但是该反应的动力学速率较慢,需要催化剂来降低反应的过电势.目前商用的催化剂是碳载铂纳米粒子催化剂,但是铂高昂的价格严重阻碍了燃料电池的大规模商业化.近年来的理论和实验研究表明,过渡金属(M)与铂(Pt)形成的纳米晶合金(MPt)能够作为有效的ORR催化剂,同时由于引入价格低廉的过渡金属,催化剂成本有所降低.然而,即使合金化的催化剂具有良好的初始催化性能,但是在燃料电池的实际操作环境,即高电压、高温和酸性条件,长时间运行之后,过渡金属很容易被腐蚀流失,从而留下表面配位数较低的铂原子,而这些铂原子对ORR反应几乎没有催化作用,导致催化剂逐渐失活,燃料电池的输出功率逐渐降低.最近一些研究表明,铂基催化剂在一定条件下,例如加热,能够发生固态相变,形成结构有序的即金属间纳米晶(iNCs).与无序排列的合金相比,这种有序的MPt能够调控表面铂原子与含氧中间体的结合能,可以进一步提高ORR活性;同时,由于在金属间纳米晶中铂原子与过渡金属原子具有很强的相互作用,过渡金属在酸性溶液中也不容易被腐蚀,从而大大提高了催化剂的稳定性.本综述以FePt,CoPt和PbPt为例,总结了它们的相变规律和条件,同时关注它们的合成-结构-性能的构效关系,突出金属间结构在提高活性和稳定性方面的优势.最后,为了进一步提高MPt金属间纳米晶的活性,我们提出一些可能的方向和观点,包括:(1)在实现无序-相变的同时实现形貌调控来提高催化剂活性;(2)关注尺寸效应,尽可能减小MPt金属间纳米晶的尺寸,提高铂的利用率,从而提高催化剂活性;(3)关注材料的有序程度,尽可能提高材料的有序度,充分发挥金属间纳米晶对于氧还原反应的优势     

Efficient fuel cell catalysts emerging from organometallic chemistry

During the last few decades organometallic methodologies have generated a number of highly effective electrocatalyst systems based on mono‐ and bimetallic nanosparticles having controlled size, composition and structure. In this microreview we summarize our results in fuel cell catalyst preparation applying triorganohydroborate chemistry, ‘reductive particle stabilization’ using organoaluminum compounds, and the controlled decomposition of organometallic complexes. The advantages of organometallic catalyst preparation pathways are exemplified with Ru? Pt nanoparticles@C as promising anode catalysts to be used in direct methanol oxidation fuel cells (DMFC) or in polymer electrolyte fuel cells (PEMFC) running with CO‐contaminated H₂ as the feed. Recent findings with highly efficient PtCo₃@C fuel cell catalysts applied for the oxygen reduction reaction (ORR) and with the effect of Se‐doping on Ru@C ORR catalysts clearly demonstrate the benefits of organometallic catalyst synthesis. Copyright © 2010 John Wiley & Sons, Ltd.     

Accelerating the oxygen reduction reaction via a bioinspired carbon‐supported zinc electrocatalyst

Oxygen utilization in electrochemical energy generation systems requires to overcome the slow kinetics of oxygen reduction reaction (ORR). Herein, we have outstretched an efficient strategy in order for developing a bioinspired Zn (N₄)/sulfur/graphitic carbon composite (Zn‐S‐Gc) with an effective performance for the ORR at low temperature. The catalyst composite was created by attaching the Zn (N₄) centers in the form of zinc phthalocyanine on the sulfur‐linked graphitic carbon surface. The most positive ORR onset potential of about 1.00 V versus a reversible hydrogen electrode (RHE) was obtained due to the unique structure of a new catalyst in KOH solution (pH = 13) at low temperature (T = 298 K). The catalyst was evaluated using the rotating‐disk electrode method in the potential range of ?0.02–1.18 V versus RHE. The number of transferred electrons as one of the most important parameters (n > 3.70) is almost constant in a wide range of low overpotentials (0.1–0.6 V), which indicates a more efficient four‐electron pathway from O₂ to H₂O on the catalyst surface. The estimated Tafel slope in an appropriate range is about ≈ ?133.3 mV/dec at a low current density and E_1/2 of the electrocatalyst displays a negative shift of only 11 mV after 10,000 cycles. The mean size of the catalyst centers is on the nanoscale (<50 nm).     

Tungsten Nitride‐Cobalt Anchored in N‐Doped Ordered Porous Carbon as an Efficient Oxygen Reduction Reaction Electrocatalyst

We prepared a non‐precious‐metal tungsten nitride‐cobalt (WN‐Co) electrocatalyst anchored in nitrogen‐doped ordered porous carbon (NOPC) through an in situ method. The WN‐Co/NOPC electrocatalyst possesses good oxygen reduction reaction (ORR) capability in alkaline media, including a high onset potential of −132 mV, a dominant four‐electron process, and a superior stability (onset potential and limiting current density were almost unchanged after 5000 cycles in 0.1 m KOH). The improved ORR performance was comparable to that of WN/NOPC and Co/NOPC with regard to three aspects: the even dispersion and uniform size of electrocatalyst particles provide more reactive sites; the nitrogen doping, high specific surface area and highly ordered mesoporous channel of catalyst support (NOPC) are conducive to the infiltration of the electrolyte; the existence of WN reinvests the catalyst with good stability, and the anchored configuration of WN and Co in the NOPC will prevent the particles from agglomerating after a long‐term cycle, thereby improving the stability of the catalyst particles.     

Hollow-Structure Pt-Ni Nanoparticle Electrocatalysts for Oxygen Reduction Reaction

An electrocatalyst with high oxygen reduction reaction (ORR) activity and high stability during start–stop operation is necessary. In this paper, hollow-structure Pt-Ni electrocatalysts are investigated as ORR catalysts. After synthesis via sacrificial SiO₂ template method, the electrocatalyst exhibits much higher specific activity (1.88 mA/cm²) than a commercial Pt/C catalyst. The mass activity (0.49 A/mg) is 7 times higher than the commercial Pt/C catalyst. The kinetics of the ORR is evaluated using Tafel and K-L plots. It also exhibits a higher durability than commercial Pt/C catalyst during accelerated durability test (ADT). Moreover, the electrocatalyst shows good resistance against accelerated durability test for start–stop, the specific activity and mass activity drops 34.6% and 40.8%, respectively, far better than the commercial catalyst.     

碳纳米管负载金属卟啉电催化剂制备及其催化活性

采用微波合成法制备了多壁碳纳米管负载钴卟啉(CoTMPP/MWNT)电催化剂,利用透射电子显微镜对催化剂微观结构进行了表征,并通过旋转圆盘和旋转环盘技术对电催化剂的氧还原活性进行了评价.结果表明,与有机回流合成法制备的催化剂相比,微波法合成的CoTMPP/MWNT催化剂具有更好的氧还原性能,半波电位正向移动110mV;与多孔碳为载体的CoTMPP/BP2000催化剂相比,多壁碳纳米管为载体的CoTMPP/MWNT电催化剂的起始电位高10mV,还原电流损失低21%,表现出更好的氧还原活性和稳定性.在CoTMPP/MWNT电催化剂表面进行的氧还原过程中电子转移数为3·6,H2O2生成量为18%.MWNT独特的电子特性、强抗腐蚀能力及其与活性钴离子之间的相互作用有助于改善催化剂的氧化还原性能.     

Covalent Grafting of Carbon Nanotubes with a Biomimetic Heme Model Compound To Enhance Oxygen Reduction Reactions

The oxygen reduction reaction (ORR) is one of the most important reactions in both life processes and energy conversion systems. The replacement of noble‐metal Pt‐based ORR electrocatalysts by nonprecious‐metal catalysts is crucial for the large‐scale commercialization of automotive fuel cells. Inspired by the mechanisms of dioxygen activation by metalloenzymes, herein we report a structurally well‐defined, bio‐inspired ORR catalyst that consists of a biomimetic model compound—an axial imidazole‐coordinated porphyrin—covalently attached to multiwalled carbon nanotubes. Without pyrolysis, this bio‐inspired electrocatalyst demonstrates superior ORR activity and stability compared to those of the state‐of‐the‐art Pt/C catalyst in both acidic and alkaline solutions, thus making it a promising alternative as an ORR electrocatalyst for application in fuel‐cell technology.     

Co3O4/聚吡咯/石墨烯碱性溶液中电化学还原氧

燃料电池具有较高的能量密度和发电效率,以清洁能源为原料,零污染排放,是一种具有发展前景的能量储存和转化装置.阴极氧还原反应(ORR)在燃料电池中起着关键作用.ORR广泛采用贵金属铂基催化剂,但是它们价格昂贵,电子动力学转移速率慢,碱性条件下易团聚,这些亟需解决的问题阻碍了燃料电池商业化进程.近期,一些非贵金属催化剂被广泛研究,例如氮掺杂碳材料、Fe/N/C和Co/N/C材料等,它们有可能在未来替代铂基催化剂.我们的目标是合成新型高催化活性的Co/N/C及其衍生非贵金属材料,用于ORR催化反应.由于石墨烯具有独特的形貌、较大的比表面积和良好的导电性,其表面含有功能化的官能团,所以我们选择石墨烯作为碳载体.首先,用改性休克尔方法合成了氧化石墨烯(GO),为了提高其催化活性,采用聚吡咯作为氮源对其进行了氮掺杂,制备了聚吡咯/氧化石墨烯(Ppy/GO).通过ORR催化性能测试发现,GO对ORR具有一定的催化活性,它的起始电位和阴极电流电位分别为–0.31 V vs SCE和–0.38 V vs SCE;Ppy/GO的起始电位和阴极电流电位分别为–0.20 V vs SCE和–0.38 V vs SCE,氮掺杂对GO的催化活性有所提高.采用水热法沉积氧化钴合成了Co3O4/聚吡咯/氧化石墨烯(Co3O4/Ppy/GO).其形貌为Co3O4分散在氮掺杂GO表面.在KOH电解质(0.1 mol/L)中测试,Co3O4/Ppy/GO的起始电位和阴极电流电位分别为–0.20 V和–0.38 V vs SCE.经过800℃高温煅烧处理后,Co3O4/Ppy/GO-800的催化活性明显提高,起始电位和阴极电流电位分别达到–0.10 V和–0.18 V vs SCE.ORR电子转移数为3.4,接近于4电子反应途径.Co3O4/Ppy/GO对ORR的催化活性及4电子催化选择性较高,可能是由于纳米形态的Co3O4和Ppy/GO之间具有较强的表面作用力,聚吡咯掺杂的氧化石墨烯具有较强的电子储存及释放能力.综上,我们通过水热法制备了钴、氮共掺杂的GO,并研究了其对ORR的催化活性和电子转移选择性.结果表明Co3O4/Ppy/GO是一种高效的非贵金属电催化剂,在碱性电解质中具有很高的ORR催化活性,在燃料电池阴极催化剂方面很有前景.     

石墨化氮化碳负载Cu纳米颗粒用作高效氧还原电催化剂

高活性低成本氧还原反应(ORR)电催化剂是燃料电池和金属/空气电池等可再生能源技术的关键组成部分.在离子液体[(C16mim)2CuCl4]和质子化的石墨化氮化碳(g-CN)的存在下,采用简易的水热反应制备了Cu/g-CN电催化剂用于ORR.与纯的g-CN相比,所制Cu/g-CN表现出高的ORR催化活性:起始电势正移99 mV,为2倍动力学电流密度.另外,Cu/g-CN还表现出比商用Pt/C(HiSPECTM 3000,20%)催化剂更好的稳定性和甲醇容忍性.因此,该催化剂作为廉价的高效ORR电催化剂有望应用于燃料电池中.     

Preparation and Catalytic Activity of Carbon Nanotube-Supported Metalloporphyrin Electrocatalyst

The multiwalled carbon nanotube-supported CoTMPP (CoTMPP/MWNT) electrocatalyst was prepared by the microwave synthesis method, and its microstructure was characterized using transmission electron microscopy. The electrocatalytic performance of CoTMPP/MWNT for oxygen reduction reaction (ORR) was evaluated by rotating disc electrode and rotating ring disc electrode technique. Compared with the CoTMPP/MWNT electrocatalyst prepared by the traditional organic reflux method, the one prepared by the microwave synthesis method showed better performance for ORR, and the half-wave potential exhibited a positive shift of 110 mV. Compared with CoTMPP/BP2000, the CoTMPP/MWNT electrocatalyst showed a 10 mV higher on-set potential and a 21% lower reduction current loss in ORR, indicating that the CoTMPP/MWNT electrocatalyst had higher catalytic activity and better stability than CoTMPP/BP2000. The number of exchanged electrons during ORR and the yield of peroxide were 3.6 and 18%, respectively. The high corrosion resistance and unique electronic property of MWNT, and the interaction between MWNT and active metal ions can efficiently improve the electrocatalytic performance of the CoTMPP/MWNT catalyst.     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-hydroxy-imidamide-functionalized graphene: an efficient metal-free electrocatalyst for oxygen reduction

Metal-free electrocatalysts for oxygen reduction reaction (ORR) are key to the development of efficient, durable, and low-cost alternatives to noble-metal-based electrocatalysts in fuel cell cathodes. In recent years, many efforts are directed to the metal-free catalyst based on heteroatom-doped graphene. In this work, we demonstrate that the graphene surface can be converted into the catalyst for the oxygen reduction by chemical functionalization. In this context, we first synthesized malononitrile-functionalized graphene oxide. Amidoximation of nitrile group and reduction in graphene oxide were then carried out by hydroxylamine in one step. The electrochemical behavior of functionalized graphene-modified electrode for the reduction in oxygen was studied. The results showed that the electrocatalyst fabricated by this method exhibited striking catalytic activities in alkaline solution. In alkaline solution, this catalyst showed a competitive activity to the commercial Pt catalyst via four-electron transfer pathway with better ORR selectivity and stability. In addition, this metal-free electrocatalyst exhibited tolerance to methanol crossover effect. Based on its outstanding performance, this functionalized graphene electrocatalyst showed the promising prospect of a metal-free catalyst for fuel cell with much lower cost than currently used Pt/C catalyst.     

基于超重力技术开展Co-N-CNTs催化剂制备及其氧还原性能的研究

开发高效的非贵金属氧还原(ORR)催化剂是促进燃料电池商业化进程的关键。本研究利用超重力技术制备了一种优良的非贵金属ORR催化剂Co-N-CNTs。物理表征表明,通过超重力技术可以使作为活性位点的金属Co纳米颗粒均匀分布在Co-N-CNTs催化剂表面,X射线光电子能谱(XPS)揭示Co-N-CNTs催化剂中的N元素不仅可以和碳纳米管(CNTs)中的C元素形成吡咯氮和石墨氮,还可以形成具有更高氧还原活性的吡啶氮结构。电化学测试结果表明,通过超重力技术制备的Co-N-CNTs催化剂的起始电位和半波电位与商业Pt/C催化剂相当;而且,Co-N-CNTs催化剂展现出优良的抗甲醇性能。     

Tungsten carbide nanocrystal promoted Pt/C electrocatalysts for oxygen reduction

Tungsten carbide nanocrystals on carbon (W2C/C) and tungsten carbide nanocrystals and Pt on carbon (Pt-W2C/C) composite electrocatalysts were prepared by the intermittent microwave heating (IMH) method and tested for the electroreduction of oxygen in the acidic media for the first time. The results revealed that the tungsten carbide nanocrystal promoted Pt/C electrocatalyst was very active for ORR with the onset potential of 1.0 V vs SHE at ambient temperature that is over 100 mV more positive compared with that of traditional Pt/C electrocatalyst. The kinetic parameters were determined. The exchange current densities at both high and low overpotential regions are two orders higher for ORR on Pt-W2C/C than that on Pt/C, showing a synergetic effect to improve the activity for ORR. The novel electrocatalysts show a poisoning resistant property toward methanol.     

Single-wall carbon nanotubes supported platinum nanoparticles with improved electrocatalytic activity for oxygen reduction reaction

Significant enhancement in the electrocatalytic activity of Pt particles toward oxygen reduction reaction (ORR) has been achieved by depositing them on a single wall carbon nanotubes (SWCNT) support. Compared to a commercial Pt/carbon black catalyst, Pt/SWCNT films cast on a rotating disk electrode exhibit a lower onset potential and a higher electron-transfer rate constant for oxygen reduction. Improved stability of the SWCNT support is also confirmed from the minimal change in the oxygen reduction current during repeated cycling over a period of 36 h. These studies open up ways to utilize SWCNT/Pt electrocatalyst as a cathode in the proton-exchange-membrane-based hydrogen and methanol fuel cells.     

快速微波法制备掺氮石墨烯用于碱性氧还原电催化剂

采用微波法在氨气气氛下快速加热石墨烯（G）制备了含氮量在4.05 wt%-5.47 wt%的掺氮石墨烯（NG）. 将上述的掺氮石墨烯用作碱性电解质条件下的氧还原电催化剂,起始还原电势为0.17 V（vs SHE）,接近商用碳载铂催化剂的0.21 V（vs SHE）. 采用透射电子显微镜、拉曼光谱和X射线光电子能谱研究了掺氮石墨烯的形貌、结构和掺杂氮原子的键合方式. 结果发现,掺氮石墨烯的氧还原起始电位随着石墨氮原子含量的提高而上升,说明石墨类型的氮含量是影响其氧还原催化活性的关键因素. 实验结果表明,微波法快速制备的掺氮石墨烯在碱性条件下表现出较高的氧还原催化活性,具有作为碱性燃料电池阴极催化剂的潜力.     

Bio‐inspired iron/sulfur/graphene nanocomposite and its use in the catalysis of the oxygen reduction reaction at room temperature in alkaline media on a glassy carbon electrode

This work demonstrates the performance of a bio‐inspired iron/sulfur/graphene nanocomposite as a non‐platinum electrocatalyst for the oxygen reduction reaction (ORR) in an alkaline medium. The catalyst shows the most positive ORR onset potential (1.1 V vs. RHE) according to its unique structure in the alkaline medium (KOH solution, pH = 13) at low temperature (T = 298 K). The catalyst is evaluated by the rotating‐disk electrode (RDE) method under various rotating speeds (0–2,000 rpm) in the potential range ?0.02–1.18 V vs. a rechargeable hydrogen electrode (RHE). The number of transferred electrons, as one of the most important parameters, is almost constant over a wide range of potentials (0.1–0.8 V), which indicates a more efficient four‐electron pathway from O₂ to H₂O on the FePc‐S‐Gr surface. The mean size of catalyst centers are in the nanoscale (<10 nm). The estimated Tafel slope in the appropriate range is about ?110 mV per decade at low current density, and E_1/2 of FePc‐S‐Gr displays a negative shift of only 7.1 mV after 10,000 cycles.     

Pt/WO_3/C nanocomposite with parallel WO_3 nanorods as cathode catalyst for proton exchange membrane fuel cells

Pt/WO3/C nanocomposites with parallel WO3 nanorods were synthesized and applied as the cathode catalyst for proton exchange membrane fuel cells(PEMFCs). Electrochemical results and single cell tests show that an enhanced activity for the oxygen reduction reaction(ORR) is obtained for the Pt/WO3/C catalyst compared with Pt/C. The higher catalytic activity might be ascribed to the improved Pt dispersion with smaller particle sizes. The Pt/WO3/C catalyst also exhibits a good electrochemical stability under potential cycling. Thus, the Pt/WO3/C catalyst can be used as a potential PEMFC cathode catalyst.     

Iron Carbide Nanoparticles Encapsulated in Mesoporous Fe‐N‐Doped Carbon Nanofibers for Efficient Electrocatalysis

Exploring low‐cost and high‐performance nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) in fuel cells and metal–air batteries is crucial for the commercialization of these energy conversion and storage devices. Here we report a novel NPMC consisting of Fe₃C nanoparticles encapsulated in mesoporous Fe‐N‐doped carbon nanofibers, which is synthesized by a cost‐effective method using carbonaceous nanofibers, pyrrole, and FeCl₃ as precursors. The electrocatalyst exhibits outstanding ORR activity (onset potential of ?0.02 V and half‐wave potential of ?0.140 V) closely comparable to the state‐of‐the‐art Pt/C catalyst in alkaline media, and good ORR activity in acidic media, which is among the highest reported activities of NPMCs.