热处理碳载Fe-三聚氰胺及Fe-g-C3N4催化剂的氧还原催化性能

分别以三聚氰胺和三聚氰胺的聚合物为配体, 采用浸渍法合成了两种氧还原反应(ORR)催化剂Fe-N/C(1)和Fe-N/C(2). 通过X射线衍射光谱(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和电化学测试对催化剂的成分、形貌和电催化性能进行了表征. 结果表明, 以三聚氰胺聚合物为配体制备的Fe-N/C具有更高的ORR催化活性. 在高温热处理过程中, 催化剂表面能形成更多的石墨N活性点, 是其ORR性能提高的重要原因.     

吡啶掺杂碳载钴酞菁催化氧还原的电化学性能及在燃料电池中的应用

以碳黑(Vulcan XC-72R)为载体, 吡啶(Py)和钴酞菁(CoPc)为催化剂前驱体, 经溶剂分散法制备了Py掺杂碳负载纳米钴酞菁复合催化剂(Py-CoPc/C). 通过扫描电镜-能谱分析(SEM-EDS)、X射线光电子能谱(XPS)分析和X射线衍射(XRD)分析技术对催化剂的组成和微观结构进行了表征, 并运用线性扫描循环伏安法(LSV)和旋转圆盘电极(RDE)技术考察了不同Py掺杂含量对碳载钴酞菁(CoPc/C)催化氧还原反应(ORR)活性的影响及稳定性. 结果显示: Py掺杂可以明显改善CoPc/C 对ORR的电催化性能, 其中掺杂20%Py下所制备的20%Py-20%CoPc/C 催化剂对ORR表现出最佳的催化活性, 以其制备的气体扩散电极在O₂气氛饱和的0.1 mol·L^-1 KOH 电解质溶液中, 0.2 V (相对于标准氢电极)即可产生明显的氧还原电流, 半波电位为-0.03 V. 相比于40%Py/C 和未掺杂的40%CoPc/C, 20%Py-20%CoPc/C催化剂的半波电位分别正移了160 和15 mV. 进一步运用RDE理论研究表明, 在Py-CoPc/C 电极上ORR的电子转移总数为2.38, 高于CoPc/C电极上的电子转移总数1.96, 从而使ORR的选择性明显提高. SEM-EDS和XRD分析表明Py掺杂提高了CoPc/C催化剂的分散性和N含量, 更利于O₂的吸附. XPS分析表明: 吡啶结构的N与石墨结构的N均存在于Py-CoPc/C 催化剂中,与催化剂表面的Co离子配位可能是促使ORR活性提高的原因. 最后以20%Py-20%CoPc/C制备了膜电极组装(MEA)电极, 应用于H₂/O₂ 燃料电池单电池发电, 室温下获得最大发电功率密度为21 mW·cm^-2, 相对于CoPc/C提高至2.4倍.     

High performance Fe and N-codoped graphene quantum dot supported Pd3Co catalyst with synergistically improved oxygen reduction activity and great methanol tolerance

Designing high-performance and durable non-platinum catalysts as oxygen reduction reaction (ORR) catalysts is still a major barrier of fuel cell commercialization. In this work, simple hydrothermal and impregnation routes were applied to prepare non-platinum Pd-Co bimetallic nano-catalysts such as Fe-N doped graphene quantum dot (Fe-N-GQD) supported Pd₃Co (Pd₃Co/Fe-N-GQD 10 wt%), carbon supported Pd₃Co/C (10 wt%), graphene quantum dot supported Pd₃Co/C (10 wt%). The synthesized catalysts were physico-chemically characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electronmicroscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical investigation was carried out in three electrode half-cell system to evaluate the catalyst activity for oxygen reduction reaction (ORR), the tolerance to methanol crossover and durability. In comparison to commercial Pt/C (ETEK, 20 wt%), the Pd₃Co/Fe-N-GQD with lower weight percentage catalyst (∼10 wt%) displayed comparable electrocatalytic activity toward ORR with even higher methanol-tolerance capability and durability. The fabricated Pd₃Co/Fe-N-GQD with (10 wt %) metal loading exhibited only 20% lower activity than Pt/C (ETEK, 20 wt%) toward ORR. Nevertheless the durability study of the catalyst in acidic media showed that the Pd₃Co/Fe-N-GQD preserve 40% of its activity while Pt/C (ETEK, 20 wt%) exhibited only 20% of its initial catalytic activity for ORR. Moreover the activity loss in the presence of methanol (0.1 M) was obtained for Pt/C (ETEK, 20 wt%) and Pd₃Co/Fe-N-GQD 35% and 14%, respectively. To investigate the role of catalyst support, catalytic activities of Pd₃Co/Fe-N-GQD, Pd₃Co/C, Pd₃Co/GQD and Pd/Fe-N-GQD were compared. The results demonstrated superior catalytic activity of Pd₃Co/Fe-N-GQD which could be related to the cocatalytic role of Fe-N-GQD due to the presence numerous of active sites exposed to the reactants.     

Synthesis of dual-doped non-precious metal electrocatalysts and their electrocatalytic activity for oxygen reduction reaction

The pyrolyzed carbon supported ferrum polypyrrole(Fe-N/C) catalysts are synthesized with or without selected dopants, p-toluenesulfonic acid(TsOH), by a facile thermal annealing approach at desired temperature for optimizing their activity for the oxygen reduction reaction(ORR) in O2-saturated 0.1 mol/L KOH solution. The electrochemical techniques such as cyclic voltammetry(CV) and rotating disk electrode(RDE) are employed with the Koutecky-Levich theory to quantitatively obtain the ORR kinetic constants and the reaction mechanisms. It is found that catalysts doped with TsOH show significantly improved ORR activity relative to the TsOH-free one. The average electron transfer numbers for the catalyzed ORR are determined to be 3.899 and 3.098, respectively, for the catalysts with and without TsOH-doping. The heat-treatment is found to be a necessary step for catalyst activity improvement, and the catalyst pyrolyzed at 600℃ gives the best ORR activity. An onset potential and the potential at the current density of-1.5 mA/cm2 for TsOH-doped catalyst after pyrolysis are 30 mV and 170 mV, which are more positive than those without pyrolized. Furthermore, the catalyst doped with TsOH shows higher tolerance to methanol compared with commercial Pt/C catalyst in 0.1 mol/L KOH. To understand this TsOH doping and pyrolyzed effect, X-ray diffraction(XRD), scanning electron microscope(SEM) and X-ray photoelectron spectroscopy(XPS) are used to characterize these catalysts in terms of their structure and composition. XPS results indicate that the pyrrolic-N groups are the most active sites, a finding that is supported by the correspondence between changes in pyridinic-N content and ORR activity that occur with changing temperature. Sulfur species are also structurally bound to carbon in the forms of C–Sn–C, an additional beneficial factor for the ORR.     

Mn-N-C催化剂的制备及其在碱性介质中对氧还原反应的电催化性能

选用壳聚糖(CS)为原料制备了壳聚糖水杨醛席夫碱锰配合物(Mn-CS-sal)。将Mn-CS-sal配合物负载于石墨碳上得到碳载配合物(Mn-CS-sal/C),后经高温热处理得到Mn-N-C目标催化剂(Mn-N-C-t,t=200、400、600、800、1 000℃)。采用FT-IR、XRD、XPS和电化学等方法对催化剂的组成和结构进行了表征,对其在氧还原反应中的电催化性能进行了研究。结果表明,所得到的Mn-N-C催化剂对氧还原反应(ORR)具有很好的催化作用,但以600℃热处理制备的催化剂其活性最好。催化剂中Mn-N-C结构是催化ORR的活性位。采用循环伏安法获得了Mn-N-C-t催化ORR的动力学参数,即总的转移电子数n和电子传递系数αnα;具有最佳活性的Mn-N-C-600催化剂的总转移电子数为3.63,说明在此条件下,Mn-N-C-600催化ORR主要以4e转移途径为主,由此提出了可能的氧还原反应的机理。     

改性炭黑-LaMnO3复合材料的制备及其共价复合效应对氧还原性能的影响

以VulcanXC-72炭黑为载体,通过对炭载体石墨化处理和表面化学修饰,将其与化学沉淀法制备的纳米级LaMnO₃颗粒共混,再经特定温度下煅烧,制备出改性炭黑-LaMnO₃复合材料.X射线光电子能谱和热重分析表明,当煅烧温度在300℃时,炭载体与LaMnO₃纳米颗粒之间形成了大量C-O-M（M=La,Mn）化学键.扫描电子显微镜和高分辨透射电子显微镜分析发现,纯相LaMnO₃纳米颗粒主要呈现短棒、三支棒或竹节棒的形貌特征,炭载体则为具有完整石墨层的空心球结构,LaMnO₃均匀分散在炭载体上.在25℃,1mol/LNaOH溶液中的电化学测试结果表明,成分比（LaMnO₃：C）为2：3的复合材料具有很高的氧还原电催化活性,氧还原反应电子数为3.81,中间产物H₂O₂产率为9.5%,其活性接近商业Pt/C催化剂（E-TEK）.高的氧还原电催化活性主要归因于LaMnO₃纳米颗粒与炭载体之间形成了大量共价键.     

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.     

Fe-N-modified multi-walled carbon nanotubes for oxygen reduction reaction in acid

We report a facile synthesis of Fe-N-C catalysts based on the surface functionalization of multi-walled carbon nanotubes (MWCNTs), which show high activity and stability for oxygen reduction reaction (ORR) in acid. Fe-N-MWCNT catalysts, whose ORR mass activities could vary by 3-4 times depending on the choice of Fe precursors, were found to have considerably higher ORR mass activity and higher stability than N-modified MWCNTs (N-MWCNTs). The Fe-N-MWCNT catalyst with a dominant Fe-N(x) moiety (with x ≈ 4) and a surface Fe/C ratio of ～0.004 exhibits the highest ORR mass activity in acid (～0.7 mA mg(-1)(Fe-N-MWCNT) at 0.8 V vs. RHE), where the lower mass activity of other Fe-N-MWCNT catalysts can be attributed to lower Fe/C ratios and Fe-N(x) moieties (with x smaller than 4) as revealed from X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Moreover, the enhanced stability of Fe-N-MWCNTs in comparison to N-MWCNTs can be attributed to less H(2)O(2) production during ORR as determined from rotating ring disk electrode (RRDE) measurements, and higher activity for H(2)O(2) electro-reduction by rotating disk electrode (RDE) measurements. The large surface Fe/C ratio and Fe-N(x) moiety corresponding to high ORR activity and stability of Fe-N-MWCNTs demonstrate that surface functionalization can be very helpful to graft active catalytic sites onto carbon nanostructures, and to provide insights into the ORR mechanism of non-noble metal catalysts (NNMCs) for proton exchange membrane fuel cells (PEMFCs).     

Biomass derived Fe-N/C catalyst for efficiently catalyzing oxygen reduction reaction in both alkaline and neutral pH conditions

Fe-N/C is a promising oxygen reduction reaction (ORR) catalyst to substitute the current widely used precious metal platinum. Cost-effectively fabricating the Fe-N/C material with high catalytic activity and getting in-depth insight into the responsible catalytic site are of great significance. In this work, we proposed to use biomass, tea leaves waste, as the precursor to prepare ORR catalyst. By adding 5% FeCl₃ (wt%) into tea precursor, the pyrolysis product (i.e., 5%Fe-N/C) exhibited an excellent four-electron ORR activity, whose onset potential was only 10 mV lower than that of commercial Pt/C. The limiting current density of 5%Fe-N/C (5.75 mA/cm²) was even higher than Pt/C (5.44 mA/cm²). Compared with other biomass or metal organic frameworks derived catalysts, 5%Fe-N/C showed similar ORR activity. Also, both the methanol tolerance and material stability performances of as-prepared 5%Fe-N/C catalyst were superior to that of Pt/C. X-ray adsorption fine structure characterization revealed that the FeN₄O₂ might be the possible catalytic site. An appropriate amount of iron chloride addition not only facilitated catalytic site formation, but also enhanced material conductivity and reaction kinetics. The results of this work may be useful for the Fe based transition metal ORR catalyst design and application.     

Hollow PtFe Alloy Nanoparticles Derived from Pt-Fe3O4 Dimers through a Silica-Protection Reduction Strategy as Efficient Oxygen Reduction Electrocatalysts

The development of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) is critical for the large-scale production of fuel cells. Platinum (Pt) nanoparticle catalysts show excellent performance for ORR, though the high cost of Pt is a limiting factor that directly impacts fuel cell production costs. Alloying Pt with other transition metals is an effective strategy to reduce Pt utilization whilst maintaining good ORR performance. In this work, novel hollow PtFe alloy catalysts were successfully synthesized by high-temperature pyrolysis of SiO₂-coated Pt-Fe₃O₄ nanoparticle dimers supported on carbon at 900 °C, followed by SiO₂ shell removal and partial dealloying of the PtFe nanoparticles formed using HF. The obtained hollow PtFe nanoparticle catalysts (denoted herein as PtFe-900) showed a 2.3-fold enhancement in ORR mass activity compared to PtFe nanoparticles synthesized without SiO₂ protection, and a remarkable 7.8-fold enhancement relative to a commercial Pt/C catalyst. Further, after 10 000 potential cycles, the ORR mass activity of PtFe-900 remained very high (90.9 % of the initial mass activity). The outstanding ORR performance of PtFe-900 can be attributed to the modification of Pt lattice and electronic structure by alloying with Fe at high temperature under the protection of the SiO₂ coating. This work guides the development of improved, highly dispersed Pt-based alloy nanoparticle catalysts for ORR and fuel cell applications.     

Fe-N/C-TsOH催化剂应用碱性介质催化氧还原的电催化活性

通过溶剂分散热处理方法制备了一种吡咯和对甲苯磺酸(TsOH)共同修饰的碳载非贵金属复合催化剂(Fe-N/C-TsOH),并采用扫描电子显微镜(SEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)对催化剂的形貌和组成成分进行表征. 借助循环伏安法(CV)和旋转圆盘技术研究了TsOH对催化剂在0.1 mol·L^-1 KOH介质中催化氧还原性能的影响. 结果表明：TsOH的存在对催化剂催化氧还原反应(ORR)的活性影响很大. 以其制备的气体扩散电极在碱性电解质溶液中催化氧还原过程时转移的电子数为3.899,远比不含TsOH修饰的催化剂催化氧还原的电子数(3.098)高. 此外,研究发现600 ℃热处理过的Fe-N/C-TsOH催化剂表现出最佳的氧还原催化性能. 相比未经热处理过的Fe-N/C-TsOH催化剂,起峰电位和-1.5 mA·cm^-2电流密度对应的电压分别向正方向移动30 和170 mV. XPS研究结果表明吡咯氮是催化剂主要活性中心,提供氧还原活性位,而TsOH加入形成的C―S_n―C和―SO_n―有利于催化剂催化氧还原活性的提高,从而使该催化剂对氧还原表现出很好的电催化性能和选择性.     

Single‐Atom Cr−N4 Sites Designed for Durable Oxygen Reduction Catalysis in Acid Media

Single‐atom catalysts (SACs) are attracting widespread interest for the catalytic oxygen reduction reaction (ORR), with Fe?N_x SACs exhibiting the most promising activity. However, Fe‐based catalysts suffer serious stability issues as a result of oxidative corrosion through the Fenton reaction. Herein, using a metal‐organic framework as an anchoring matrix, we for the first time obtained pyrolyzed Cr/N/C SACs for the ORR, where the atomically dispersed Cr is confirmed to have a Cr?N₄ coordination structure. The Cr/N/C catalyst exhibits excellent ORR activity with an optimal half‐wave potential of 0.773 V versus RHE. More excitingly, the Fenton reaction is substantially reduced and, thus, the final catalysts show superb stability. The innovative and robust active site for the ORR opens a new possibility to circumvent the stability issue of the non‐noble metal ORR catalysts.     

One-step synthesis of carbon-supported Pd–Pt alloy electrocatalysts for methanol tolerant oxygen reduction

A facile, one-step reduction route was developed to synthesize Pd-rich carbon-supported Pd–Pt alloy electrocatalysts of different Pd/Pt atomic ratios. As-prepared Pd–Pt/C catalysts exhibit a single phase fcc structure and an expansion lattice parameter. Comparison of the oxygen reduction reaction (ORR) on the Pd–Pt/C alloy catalysts indicates that the Pd₃Pt₁/C bimetallic catalyst exhibits the highest ORR activity among all the Pd–Pt alloy catalysts and shows a comparative ORR activity with the commercial Pt/C catalyst. Moreover, all the Pd–Pt alloy catalysts exhibited much higher methanol tolerance during the ORR than the commercial Pt/C catalyst. High methanol tolerance of the Pd–Pt alloy catalysts could be attributed to the weak adsorption of methanol induced by the composition effect, to the presence of Pd atoms and to the formation of Pd-based alloys.     

CNx-modified Fe3O4 as Pt nanoparticle support for the oxygen reduction reaction

A novel electrocatalyst support material, nitrogen-doped carbon (CN_x)-modified Fe₃O₄ (Fe₃O₄-CN_x), was synthesized through carbonizing a polypyrrole-Fe₃O₄ hybridized precursor. Subsequently, Fe₃O₄-CN_x-supported Pt (Pt/Fe₃O₄-CN_x) nanocomposites were prepared by reducing Pt precursor in ethylene glycol solution and evaluated for the oxygen reduction reaction (ORR). The Pt/Fe₃O₄-CN_x catalysts were characterized by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrocatalytic activity and stability of the as-prepared electrocatalysts toward ORR were studied by cyclic voltammetry and steady-state polarization measurements. The results showed that Pt/Fe₃O₄-CN_x catalysts exhibited superior catalytic performance for ORR to the conventional Pt/C and Pt/C-CN_x catalysts.     

ZIF67衍生硫化钴/多孔碳复合催化剂的制备及其电催化性能

采用离子交换法与热处理相结合的方法,以ZIF67为前驱体,硫代乙酰胺为硫源,制备出硫化钴/多孔碳(CoS/C)复合催化材料,并探讨了硫化时间对复合催化剂的形貌、结构及其氧还原(ORR)性能的影响。采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)、N2吸附-脱附测定仪、X射线光电子能谱分析(XPS)、拉曼光谱仪(Raman)和旋转圆盘电极(RDE)技术表征催化剂的物理特征和电催化性能。研究结果显示,在碱性条件下该复合催化剂具有与20%(w/w)的商业Pt/C催化剂相媲美的ORR活性,其半波电位仅比Pt/C催化剂低31 mV。随着硫化时间的增加,硫化钴颗粒逐渐增大,催化剂中碳材料的无序程度出现先减小后增大的趋势。在硫化时间为10 min时,复合催化剂在0.1 mol·L-1KOH中表现出良好的电催化活性,且在ORR过程中复合催化剂的平均转移电子数可达到3.72,接近于4,说明氧气在该催化剂表面发生的是四电子转移过程。     

Synthesis and study of catalysts of electrochemical oxygen reduction reaction based on polymer complexes of nickel and cobalt with Schiff bases

The article presents the results of studies of new nanosize catalysts of electrochemical oxygen reduction reaction (ORR) obtained using the method of thermal decomposition of polymer complexes of nickel and cobalt with tetradentate (N₂O₂) Schiff bases. The catalysts are characterized using the methods of thermogravimetry, electrochemical quartz microgravimetry, scanning electron microscopy with X-ray microanalysis, XPS. The ORR process on electrodes modified by the above catalysts was studied using the voltammetry and rotating disk electrode techniques. The obtained catalysts manifested high specific activity per initial polymer mass (more than 600 mA/mg).     

新型钴-聚吡咯-碳载Pt燃料电池催化剂的制备与表征

采用脉冲微波辅助化学还原法制备了钴-聚吡咯-碳(Co-PPy-C)载Pt催化剂(Pt/Co-PPy-C),其中Pt的总质量占20%.利用透射电镜(TEM)、光电子射线能谱分析(XPS)和X射线衍射(XRD)研究了催化剂的结构,用循环伏安(CV)、线性扫描伏安(LSV)等方法考察了其电化学活性及氧还原反应(ORR)动力学特性及耐久性.Pt/Co-PPy-C电催化剂的金属颗粒直径约1.8 nm,略小于商用催化剂Pt/C(JM)颗粒尺寸(约2.5 nm);催化剂在载体上分散均匀,粒径分布范围较窄.Pt/Co-PPy-C的电化学活性比表面积(ECSA)(75.1 m2·g-1)高于商用催化剂的ECSA(51.3 m2·g-1).XPS测试表明,自制催化剂表面的Pt主要以零价形式存在.而XRD结果显示,自制催化剂中Pt(111)峰最强,Pt主要为面心立方晶格.Pt/Co-PPy-C具有与Pt/C(JM)相同的半波电位;在0.9 V下,Pt/Co-PPy-C的比活性(1.21 mA·cm-2)高于商用催化剂的比活性(1.04 mA·cm-2),表现出更好的ORR催化活性.动力学性能测试表明催化剂的ORR反应以四电子路线进行.CV测试1000圈后,Pt/Co-PPy-C和Pt/C(JM)的ECSA分别衰减了13.0%和24.0%,可见自制催化剂的耐久性高于商用Pt/C(JM),在质子交换膜燃料电池(PEMFC)领域有一定的应用前景.     

A Universal and Facile Way for the Development of Superior Bifunctional Electrocatalysts for Oxygen Reduction and Evolution Reactions Utilizing the Synergistic Effect

Increasing energy demands have stimulated intense research activities on reversible electrochemical conversion and storage systems with high efficiency, low cost, and environmental benignity. It is highly challenging but desirable to develop efficient bifunctional catalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). A universal and facile method for the development of bifunctional electrocatalysts with outstanding electrocatalytic activity for both the ORR and OER in alkaline medium is reported. A mixture of Pt/C catalyst with superior ORR activity and a perovskite oxide based catalyst with outstanding OER activity was employed in appropriate ratios, and prepared by simple ultrasonic mixing. Nanosized platinum particles with a wide range of platinum to oxide mass ratios was realized easily in this way. The as‐formed Pt/C–oxide composites showed better ORR activity than a single Pt/C catalyst and better OER activity than a single oxide to bring about much improved bifunctionality (ΔE is only ≈0.8 V for Pt/C–BSCF; BSCF=Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ), due to the synergistic effect. The electronic transfer mechanism and the rate‐determining step and spillover mechanism were two possible origins of such a synergistic effect. Additionally, the phenomenon was found to be universal, although the best performance could be reached at different platinum to oxide mass ratios for different oxide catalysts. This work thus provides an innovative strategy for the development of new bifunctional electrocatalysts with wide application potentials in high‐energy and efficient electrochemical energy storage and conversion.     

Carbon-supported Pd-Co as cathode catalyst for APEMFCs and validation by DFT

Carbon supported PdCo catalysts in varying atomic ratios of Pd to Co, namely 1 : 1, 2 : 1 and 3 : 1, were prepared. The oxygen reduction reaction (ORR) was studied on commercial carbon-supported Pd and carbon-supported PdCo nanocatalysts in aqueous 0.1 M KOH solution with and without methanol. The structure, dispersion, electrochemical characterization and surface area of PdCo/C were determined by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Cyclic Voltammetry (CV), respectively. The electrochemical activity for ORR was evaluated from Linear Sweep Voltammograms (LSV) obtained using a rotating ring disk electrode. The catalysts were evaluated for their electrocatalytic activity towards oxygen reduction reaction (ORR) in Alkaline Polymer Electrolyte Membrane Fuel Cells (APEMFCs). PdCo(3 : 1)/C gives higher performance (85 mW cm(-2)) than PdCo(1 : 1)/C, PdCo(2 : 1)/C and Pd/C. The maximum electrocatalytic activity for ORR in the presence of methanol was observed for PdCo(3 : 1)/C. First principles calculations within the framework of density functional theory were performed to understand the origin of its catalytic activity based on the energy of adsorption of an O(2) molecule on the cluster, structural variation and charge transfer mechanism.     

Efficient Oxygen Reduction Reaction (ORR) Catalysts Based on Single Iron Atoms Dispersed on a Hierarchically Structured Porous Carbon Framework

Single Fe atoms dispersed on hierarchically structured porous carbon (SA‐Fe‐HPC) frameworks are prepared by pyrolysis of unsubstituted phthalocyanine/iron phthalocyanine complexes confined within micropores of the porous carbon support. The single‐atom Fe catalysts have a well‐defined atomic dispersion of Fe atoms coordinated by N ligands on the 3D hierarchically porous carbon support. These SA‐Fe‐HPC catalysts are comparable to the commercial Pt/C electrode even in acidic electrolytes for oxygen reduction reaction (ORR) in terms of the ORR activity (E_1/2=0.81 V), but have better long‐term electrochemical stability (7 mV negative shift after 3000 potential cycles) and fuel selectivity. In alkaline media, the SA‐Fe‐HPC catalysts outperform the commercial Pt/C electrode in ORR activity (E_1/2=0.89 V), fuel selectivity, and long‐term stability (1 mV negative shift after 3000 potential cycles). Thus, these nSA‐Fe‐HPCs are promising non‐platinum‐group metal ORR catalysts for fuel‐cell technologies.