氧还原电化学催化剂研究的最新进展（英文）

燃料电池可以在接近室温条件下将氢或烃类中蕴含的巨大化学能通过电化学途径直接转化为清洁、稳定、可持续的电能,因而被视为极有前景的、能够满足日益增长的世界能源需求的终极解决方案之一.在一个典型的氢燃料电池中,氢在正极氧化而氧在负极还原,从动力学角度说,氧还原反应(ORR)比氢氧化反应进行的慢得多.无论是在酸性还是碱性条件下,氧的还原都可以一个四电子过程或是两个双电子过程进行,当然在酸性和碱性环境中反应的机理不同.铂一直是最有效的ORR催化剂,但受到价格昂贵、稳定性差和易中毒等因素的制约,目前非铂催化剂成为越来越引人瞩目的发展方向.本综述试图从分子催化剂、金属纳米材料催化剂、金属氧化物催化剂和新兴的二维材料催化剂等方面,选取近十年来最能代表ORR电化学催化剂方面成就的例子分析其优缺点,并为今后该领域的研究提供一些有益的思路.典型的分子催化剂是卟啉类化合物,当这种四齿的N4配体与过渡金属特别是铁、钴络合时,往往显示出良好的ORR催化性能,多数情况下其中的过渡金属中心、配体和碳支撑体系共同组成催化剂的活性中心.在另一些报道中,邻菲罗啉或是连吡啶型N_2化合物也可以作为配体使用.第四和第五副族的很多金属形成的不同价态的氧化物都具有氧还原活性,比如MnO_x,CoO_x,TiO_x,ZrO_x,IrO_x等.金属氧化物表现出易于修饰,不容易团聚和抗腐蚀等诸多优点,而其良好的ORR性能与表面的缺陷密切相关,因此钙钛矿型氧化物ABO_x也引起人们的广泛关注,人们可以通过调节氧化物的晶型、尺寸和组成来获得更好的催化性能.近年来随着液相合成技术的发展,人们可以制备出理想形状和尺寸的单分散纳米粒子,然后通过旋涂、自组装等手段将其修饰到合适的电极上以获得增强性能的ORR催化剂.通过形状与尺寸调控,或组合成其它复杂的纳米结构,都有可能提高催化活性或是稳定性,因此有关纳米催化剂的研究日趋增多.在此基础上,考虑到石墨烯的可修饰性和良好的电化学性能,纳米材料复合石墨烯所形成的二维或三维结构也可提供很好的氧还原催化性能,而MoS_2代替石墨烯作为支撑物所构成的二维催化剂也是值得注意的研究方向.综上所述,尽管现有的非铂催化剂仍难以完全满足商业化的要求,设计理念和合成方法的快速发展有望在不远的将来解决这一难题.而设计合成可控尺寸、形状、组成和表面形貌的纳米催化剂在很大程度上将加速这一进程.     

石墨烯衍生物负载的纳米催化剂用于氧还原反应

综述了用于燃料电池中氧还原反应(ORR)的石墨烯衍生物负载的各种纳米催化剂的最新进展。介绍了用于表征石墨烯基电催化剂的常规电化学技术以及石墨烯基电催化剂最新的研究进展。负载于还原氧化石墨烯(RGO)上的Pt催化剂的电化学活性和稳定性均得到显著提高。其它贵金属催化剂,如Pd, Au和Ag也表现出较高的催化活性。当以RGO或少层石墨烯为载体时, Pd催化剂的稳定性提高。讨论了氧化石墨烯负载Au或Ag催化剂的合成方法。另外,以N4螯合络合物形式存在的非贵过渡金属可降低氧的电化学性能。 Fe和Co是可替代的廉价ORR催化剂。在大多数情况下,这些催化剂稳定性和耐受性的问题均可得到解决,但其整体性能还很难超越Pt/C催化剂。     

石墨烯量子点负载银纳米粒子制备及氧还原电催化活性

银基氧还原电催化剂具有较高的电催化活性且价格相对低廉,因而受到广泛关注. 本文采用简单、预先合成的石墨烯量子点作为载体和还原剂,制得了负载于石墨烯量子点、且无保护剂和表面活性剂的表面洁净银纳米粒子（Ag NPs/GQDs）. 电化学研究表明,Ag NPs/GQDs复合电催化剂的氧还原有较高的电催化活性,氧在碱性溶液中可经4电子途径还原为水. 与商业铂碳电极（Pt/C）相比,AgNPs/GQDs电极具有高催化电流密度、良好稳定性和极佳抗甲醇性能. 该银纳米粒子对开发高性能和低成本的非铂氧还原电催化剂有潜在的应用前景.     

基于内嵌钴/氮掺杂多孔碳三维石墨烯笼的抗团聚高效氧还原电催化剂

氧还原反应是决定燃料电池、金属-空气电池等多种新型清洁能源存储与转化技术之性能与应用的关键反应. 铂及其合金是目前催化活性最好的氧还原反应催化剂,但其高昂的成本限制了规模化应用. 在小尺寸效应作用下,微纳米结构催化剂颗粒在电极制备与电化学反应过程中的团聚限制了催化剂本征催化活性的充分发挥. 本文基于喷雾热解技术,发展了一种基于内嵌钴/氮掺杂多孔碳三维石墨烯笼的高活性、抗团聚非贵金属氧还原反应催化剂. 此结构中,金属有机骨架化合物ZIF-67衍生的钴/氮掺杂多孔碳纳米结构是催化氧还原反应的活性中心,包覆其外的三维石墨烯笼不仅可在钴/氮掺杂碳纳米结构之间构建连续的三维载流子传导网络,且可高效抑制其在催化剂制备与电化学反应过程中的团聚与活性损失. 在碱性电解液中,此类非贵金属催化剂表现出可与铂基催化剂媲美的氧还原反应活性和优异的稳定性.     

石墨烯衍生物负载的纳米催化剂用于氧还原反应（英文）

综述了用于燃料电池中氧还原反应(ORR)的石墨烯衍生物负载的各种纳米催化剂的最新进展.介绍了用于表征石墨烯基电催化剂的常规电化学技术以及石墨烯基电催化剂最新的研究进展.负载于还原氧化石墨烯(RGO)上的Pt催化剂的电化学活性和稳定性均得到显著提高.其它贵金属催化剂,如Pd,Au和Ag也表现出较高的催化活性.当以RGO或少层石墨烯为载体时,Pd催化剂的稳定性提高.讨论了氧化石墨烯负载Au或Ag催化剂的合成方法.另外,以N4螯合络合物形式存在的非贵过渡金属可降低氧的电化学性能.Fe和Co是可替代的廉价ORR催化剂.在大多数情况下,这些催化剂稳定性和耐受性的问题均可得到解决,但其整体性能还很难超越Pt/C催化剂.     

通过铁掺杂和造孔提高氮掺杂石墨烯/碳纳米管复合物电催化氧还原性能的研究（英文）

氧还原反应催化剂的性能直接影响着能源转换和存储器件如燃料电池和金属-空气电池的性能. 开发低成本、高性能的非铂族金属氧还原催化剂对于这类器件的实际应用和商业化十分重要,因此备受关注. 氮掺杂的石墨烯/碳纳米管复合物同时具备碳纳米管的良好导电性能和有利于传质的三维网络结构优点,以及氮掺杂石墨烯的高活性优点,因此有望发展为这类可替代铂族催化剂的氧还原电催化剂之一,但目前其催化性能还需进一步提高. 本文研究发现通过在氮掺杂石墨烯/碳纳米管复合物的过程中引入铁元素可以有效提高催化剂的氧还原活性,并且发现通过在热处理和氮掺杂过程中加入二氧化硅纳米颗粒及随后除去二氧化硅,可以在氮掺杂的石墨烯/碳纳米管复合物材料中有效地形成多孔结构. 这种多孔结构的形成不仅可以在复合物中引入更多的高活性催化位点,而且有利于暴露更多的催化活性位并促进氧还原反应中的传质过程. 结合碳纳米管、石墨烯和多孔结构的三者优点,所制备的多孔氮掺杂碳材料表现出优异的电催化氧还原性能. 进一步的实验表明,这类材料还表现出优异的抗甲醇中毒能力和良好的稳定性,因此在性能改进后有望用于燃料电池等能量转换与存储器件.     

碳载氧化锰表面氧还原反应路径研究(英文)

氧还原反应(ORR)是一个复杂的过程,尤其在碱性电解液中,炭载型催化剂表面的ORR路径尤为复杂,因为碳本身可以催化ORR以二电子转移过程发生,产生过氧化氢,继而过氧化氢或者发生化学分解生成氧气(HODR),或者发生电化学还原生成OH(HORR).本文详细研究了ORR在常用氧化锰催化剂表面的反应路径.通过比较HODR和HORR的转换频率发现,尽管利用旋转环盘电极方法得到的表观电子转移数接近4,真实的ORR主要是2电子过程,反应生成的过氧化氢继而大部分发生化学分解生成氧气.该结果有助于理解碱性电解质中炭载型过渡金属氧化物电催化剂对ORR的催化行为.     

金属/金属氧化物纳米粒子在不对称氢化和氢转移反应中的应用研究进展

近年来,金属/金属氧化物纳米粒子催化的不对称氢化和氢转移反应已经成为催化领域的前沿和研究热点之一. 金属/金属氧化物纳米粒子的催化模式类似于“纳米反应器”,底物可以通过有机包覆层扩散至催化中心,局部的高催化剂浓度通常可以极大地提高催化反应转换数（TON）和转化频率（TOF）. 在以纳米金属为催化活性中心方面,Orito纳米铂体系获得最多的关注,科学家们从手性修饰剂的结构改造、催化剂载体的选择、不同的反应介质、纳米催化剂的形貌和催化反应机理等方面开展了较为系统的研究,并取得重要进展. 此外,纳米钯、铑、钌、铱和铁等金属纳米催化剂也在烯烃、酮和亚胺等化合物的不对称氢化和氢转移反应中表现出良好的催化性能,特别是纳米铱和铁催化剂已获得95%以上的对映选择性. 在金属/金氧化物纳米粒子为催化剂载体方面,其催化不对称氢化及氢转移反应的效率及对映选择性可与均相催化剂相媲美,同时还解决了均相催化剂难于回收再循环的缺陷. 本文简要介绍了近年来手性金属纳米催化剂在不对称氢化和氢转移反应领域的研究进展,讨论了相关反应的催化机理,并对该领域仍存在的问题和未来的发展方向进行了展望.     

纳米材料电催化进展——电催化剂表面结构调控与性能

电催化剂的结构决定其性能.从微观层面研究表面结构与催化性能之间的内在联系和规律是设计和研制高活性、高稳定性、高选择性电催化剂的基础.本文以本研究组关于氢和氧的吸脱附、乙二醇氧化和CO2还原的研究结果为主,综述了电催化剂表面结构和性能调控方面的研究进展.给出面心立方晶体不同晶带上铂单晶电极的循环伏安特征,电催化性能和规律,在此基础上创建的金属纳米晶体表面结构控制和生长的电化学方法,以及对具有开放结构、高催化活性和高稳定性的Pt和Fe纳米晶催化剂的形状和表面结构控制合成.     

热处理温度对Pt3Co二元金属催化剂氧还原性能影响及泛函密度理论研究

制备低成本、高活性、高稳定性的铂（Pt）基氧还原反应（ORR）催化剂是质子交换燃料电池（PEMFC）大规模商业化应用的关键。以钴（Co）等非贵金属与Pt掺杂制备二元合金PtM催化剂不仅可以减少Pt用量,还可以获得高于Pt金属催化剂的ORR催化活性和稳定性。本研究使用浸渍还原法制备碳载铂钴ORR催化剂,通过控制热处理还原温度来控制纳米颗粒的结构、晶相、尺寸等,从而改善催化剂的ORR性能。XRD、TEM和电化学分析结果综合表明,热处理温度对纳米颗粒合金度和平均粒径有显著的影响,平均粒径和合金度随着热处理温度升高而增大。通过控制热处理温度可以获得粒径与合金度之间的最优值从而提高催化剂氧还原活性,实验表明,800℃是低粒径和高合金度的平衡点,在所有制备的催化剂中有最高的质量活性(0.41 A/mg_Pt)和稳定性。进一步的密度泛函理论（DFT）计算表明高合金度的Pt₃Co结构表面可以降低速控步反应势垒,提高ORR活性。     

Metal–Organic Frameworks Based Electrocatalysts for the Oxygen Reduction Reaction

In view of the clean and sustainable energy, metal–organic frameworks (MOFs) based materials, including pristine MOFs, MOF composites, and their derivatives are emerging as unique electrocatalysts for oxygen reduction reaction (ORR). Thanks to their tunable compositions and diverse structures, efficient MOF-based materials provide new opportunities to accelerate the sluggish ORR at the cathode in fuel cells and metal–air batteries. This Minireview first provides some introduction of ORR and MOFs, followed by the classification of MOF-based electrocatalysts towards ORR. Recent breakthroughs in engineering MOF-based ORR electrocatalysts are highlighted with an emphasis on synthesis strategy, component, morphology, structure, electrocatalytic performance, and reaction mechanism. Finally, some current challenges and future perspectives for MOF-based ORR electrocatalysts are also discussed.     

Unravelling the Structure of Electrocatalytically Active Fe–N Complexes in Carbon for the Oxygen Reduction Reaction

Non‐precious Fe/N co‐modified carbon electrocatalysts have attracted great attention due to their high activity and stability in oxygen reduction reaction (ORR). Compared to iron‐free N‐doped carbon electrocatalysts, Fe/N‐modified electrocatalysts show four‐electron selectivity with better activity in acid electrolytes. This is believed relevant to the unique Fe–N complexes, however, the Fe–N structure remains unknown. We used o,m,p‐phenylenediamine as nitrogen precursors to tailor the Fe–N structures in heterogeneous electrocatalysts which contain FeS and Fe₃C phases. The electrocatalysts have been operated for 5000 cycles with a small 39 mV shift in half‐wave potential. By combining advanced electron microscopy and Mössbauer spectroscopy, we have identified the electrocatalytically active Fe–N₆ complexes (FeN₆, [Fe^III(porphyrin)(pyridine)₂]). We expect the understanding of the FeN₆ structure will pave the way towards new advanced Fe–N based electrocatalysts.     

Metal–Organic Frameworks Based Electrocatalysts for the Oxygen Reduction Reaction

In view of the clean and sustainable energy, metal–organic frameworks (MOFs) based materials, including pristine MOFs, MOF composites, and their derivatives are emerging as unique electrocatalysts for oxygen reduction reaction (ORR). Thanks to their tunable compositions and diverse structures, efficient MOF‐based materials provide new opportunities to accelerate the sluggish ORR at the cathode in fuel cells and metal–air batteries. This Minireview first provides some introduction of ORR and MOFs, followed by the classification of MOF‐based electrocatalysts towards ORR. Recent breakthroughs in engineering MOF‐based ORR electrocatalysts are highlighted with an emphasis on synthesis strategy, component, morphology, structure, electrocatalytic performance, and reaction mechanism. Finally, some current challenges and future perspectives for MOF‐based ORR electrocatalysts are also discussed.     

Nitrogen and Oxygen Co-Doping Assisted Synthesis of Highly Dispersed Pd Nanoparticles on Hollow Carbon Spheres as Efficient Electrocatalysts for Oxygen Reduction Reaction

Electrochemical reduction of O₂ (oxygen reduction reaction; ORR) provides an opportunity to achieve the commercial application of clean energy, but it remains challenging, so the rational design of inexpensive and efficient electrocatalysts is required. Palladium-based electrocatalysts have emerged as a class of the most promising candidates for the ORR, which could accelerate O₂ adsorption, dissociation, and electron transfer. However, the metal Pd atoms tend to aggregate into nanoparticles, driven by the tendency of the metal surface free energy to decrease, which significantly reduces the atom utilization efficiency and the catalytic performance. Herein, a facile double solvent impregnation method is developed for the synthesis of highly dispersed Pd nanoparticles supported on hollow carbon spheres (Pd-HCS), which could act as efficient electrocatalysts for the ORR in basic solution. Systematic investigation reveals that the nitrogen-containing and oxygen-containing functional groups (especially −COOH groups) are essential for achieving the homogenous dispersion of Pd nanoparticles. Significantly, the optimized Pd-HCS electrocatalyst with homogeneously dispersed Pd nanoparticles and Pd−N sites delivers high electrocatalytic activity for the ORR and excellent stability, without significant decay in onset potential and half-potential and good resistance to methanol crossover. This work offers a new route for the rational design of efficient ORR electrocatalysts toward advanced materials and emerging applications.     

Recent development of efficient electrocatalysts derived from porous organic polymers for oxygen reduction reaction

Porous organic polymers (POPs) have recently emerged as promising candidates for catalyzing oxygen reduction reaction (ORR). Compared to conventional Pt-based ORR catalysts, these newly developed porous materials, including both non-precious metal based catalysts and metal-free catalysts, are more sustainable and cost-effective. Their porous structures and large surface areas facilitate mass and electron transport and boost the ORR kinetics. This mini-review will give a brief summary of recent development of POPs as electrocatalysts for the ORR. Some design principles, different POP structures, key factors for their ORR catalytic performance, and outlook of POP materials will be discussed.     

Carbon/titanium oxide supported bimetallic platinum/iridium nanocomposites as bifunctional electrocatalysts for lithium-air batteries

Platinum (Pt) and iridium (Ir) catalysts are well known to strongly enhance the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics, respectively. Pt–Ir-based bimetallic compounds along with carbon-supported titanium oxides (C–TiO₂) have been synthesized for the application as electrocatalysts in lithium oxygen batteries. Transition metal oxide-based bimetallic nanocomposites (Pt–Ir/C–TiO₂) were prepared by an incipient wetness impregnation technique. The as-prepared electrocatalysts were composed of a well-dispersed homogenous alloy of nanoparticles as confirmed by X-ray diffraction patterns and Fourier transform scanning electron microscopy analyses. The electrochemical characterizations reveal that the Pt–Ir/C–TiO₂ electrocatalysts were bifunctional with high activity for both ORR and OER. When applied as an air cathode catalyst in lithium-air batteries, the electrocatalyst improved the battery performance in terms of capacity, reversibility, and cycle life compared to that of cathodes without any catalysts.     

In-situ self-templated preparation of porous core-shell Fe1-xS@N,S co-doped carbon architecture for highly efficient oxygen reduction reaction

Transition metal compound(TMC)/carbon hybrids,as prospering electrocatalyst,have attracted great attention in the field of oxygen reduction reaction(ORR).Their morphology,structure and composition often play a crucial role in determining the ORR performance.In this work,we for the first time report the successful fabrication of porous core-shell Fe_1-xS@N,S co-doped carbon(Fe_1-xS@NSC-t,t represents etching time)by a novel in-situ self-template induced strategy using Fe3O4 nanospheres and pyrrole as sacrificial self-template.The post-polymerization of pyrrole can be accomplished by the Fe³⁺released through the etching of Fe₃O₄ by HCl acid.Thus,the etching time has a significant effect on the morphology,structure,composition a nd ORR performance of Fe_1-xS@NSC-t.Based on the cha racterizations,we find Fe_1-xS@NSC-24 can realize effective and balanced combination of Fe_1-xS and NSC,possessing porous core-shell architecture,optimized structure defect,specific surface area and doped heteroatoms configurations(especially for pyridinic N,graphitic N and Fe-N structure).These features thus lead to outstanding catalytic activity and cycling stability towards ORR.Our work provides a good guidance on the design of TMC/carbon-based electrodes with unique stable morphology and optimized structure and composition.     

Co/N-doped carbon nanotube arrays grown on 2D MOFs-derived matrix for boosting the oxygen reduction reaction in alkaline and acidic media

The development of high-performance and cost-effective electrocatalysts towards oxygen reduction reaction(ORR) is of significant importance,but still challenging for the practical applications in related energy systems.ORR process typically suffers from sluggish kinetics,the exploration of ORR electrocatalyst thus requires elaborate design.Herein,an effective strategy is developed for growing Co/N-doped carbon nanotube arrays on 2D MOFs-derived matrix via the pyrolysis of Co/Zn metalorganic-framework(MOF) nanosheets.The Co/Zn-MOF nanosheets serve as both the self-template for the 2D carbonized framework morphology and C/N source for the in-situ growth of 1D N-doped carbon nanotubes.The constructed hie rarchical architecture effectively integrates the OD/1D Co nanoparticle/Ndoped carbon nanotube interface and 1D(nanotubes)/2D(nanosheets) junction into frameworks with highly exposed active surface,enhanced mass-transport kinetics and electrical conductivity.As a result,the designed composite exhibits superior ORR activity and durability in alkaline media as compared to commercial Pt/C.Particularly,it shows promising ORR performance with a half-wave potential of 0.78 V versus reversible hydrogen electrode and negligible activity attenuation after 5000 potential cycles in acidic electrolyte.The designed strategy can be extended to construct other MOFs-derived carbon matrixes with diverse hierarchical structures and provide an efficient avenue for searching highperformance electrocatalysts.     

A Chemical Dealloying Approach for Pt Surface-enriched Pt3Co Alloy Nanoparticles as Oxygen Reduction Reaction Electrocatalysts

Pt-based alloys are the optimal electrocatalysts for oxygen reduction reaction(ORR) currently. Dealloying of Pt-based alloys has shown to be an effective approach to improving ORR activity. Electrochemical dealloying is controllable for morphology by changing electrochemical parameters but is difficult to scale up due to complex operation and energy consumption. Chemical dealloying is suitable for a large scale but it is not easy to control the morphology because highly corrosive acids(HNO₃ or H₂SO₄) are commonly used. In this work, a facile chemical dealloying method for Pt₃Co/C has been employed to synthesize elec-trocatalysts for ORR using weak acids and buffer solutions of different pH, which could slow down the dissolution rate for Co atoms and increase the diffusion time for Pt atoms to improve ORR activity. It can be observed that the mass activities(MA) of the Pt₃Co/C alloy after dealloying with H₃PO₄ and NaH₂PO₄/Na₂HPO₄ buffer solution of pH=6 are close to that after electrochemical dealloying process, and are more than two times that of commercial Pt/C. In addition, Pt₃Co/C after dealloying with a buffer solution of pH=6 only showed a slight degradation in the half-wave potential and electrochemical surface area(ECSA) after stability test for 5000 cycles, which is more stable than commercial Pt/C. It shows that by controlling pH of the solvent, the ORR activity can be further increased. This facile approach provides a new strategy to control morphology of Pt-based electrocatalysts by chemical dealloying, which can contribute to promising application for cathodic electrocatalysts design of proton exchange membrane fuel cells (PEMFCs).     

N,S-Co-Doped Porous Carbon Nanofiber Films Derived from Fullerenes (C60) as Efficient Electrocatalysts for Oxygen Reduction and a Zn–Air Battery

The development of highly efficient metal-free electrocatalysts for the oxygen reduction reaction (ORR) has attracted great attention for the creation of electrochemical energy devices. In this study, one-dimensional (1 D) fullerene nanofibers prepared from liquid–liquid interfacial precipitation are first fabricated into fullerene-derived carbon nanofiber films (FCNFs) through a simple filtration procedure. Then, pyrolysis of the FCNFs in the presence of ammonia and sulfur produces N- and S-co-doped porous carbon nanofiber films (N,S-PCNFs). As excellent metal-free electrocatalysts for the ORR, N,S-PCNFs exhibit remarkable catalytic activity, superior stability, and excellent methanol tolerance in both alkaline and acidic solution. Such a high ORR performance benefits from the robust porous nanofiber network structure with high concentrations of active N- and S- groups and abundant defects. Notably, upon practical use of N,S-PCNFs as catalysts in Zn-air batteries, a high power density and a large operating voltage are achieved, with a performance comparable to that of the commercial Pt/C catalyst. This work presents a facile strategy for the creation of a new class of energy nanomaterials based on fullerenes, demonstrating their practical uses in electrocatalytic ORR processes and Zn-air batteries.