The Direct Electron Transfer of Iron‐containing Metal Organic Frameworks (Mil‐100) and Its Catalysis for the Oxygen Reduction Reaction in Room‐Temperature Alkaline Media on a Glass Carbon Electrode

The most common electrocatalysts for the oxygen reduction reaction (ORR) are platinum‐based ones. This work demonstrates the performance of iron‐containing metal organic frameworks (MOFs) as non‐platinum‐based nano‐electrocatalysts for ORR in an alkaline medium. As a new non‐platinum catalyst to achieve the active sites for the ORR, Mil‐100 (Fe) nanoparticles were used in aqueous KOH by the rotating‐disk electrode method. The main objectives of this study are the investigations on the electron transfer number (n ), Tafel slope, and catalytic performance. The particles size of the obtained powders is in the nanoscale range (approximately 25 nm). The electron transfer number for the ORR on the surface of iron‐containing catalyst is approximately 4, and the Tafel slope of diffusion‐corrected kinetic current density is ~50.7 mV per decade at low overpotential. This work might extend a new non‐precious‐metal catalyst structure for ORR for use in low‐temperature fuel cells.     

Single‐Atom Iron Catalysts on Overhang‐Eave Carbon Cages for High‐Performance Oxygen Reduction Reaction

Single‐atom catalysts have drawn great attention, especially in electrocatalysis. However, most of previous works focus on the enhanced catalytic properties via improving metal loading. Engineering morphologies of catalysts to facilitate mass transport through catalyst layers, thus increasing the utilization of each active site, is regarded as an appealing way for enhanced performance. Herein, we design an overhang‐eave structure decorated with isolated single‐atom iron sites via a silica‐mediated MOF‐templated approach for oxygen reduction reaction (ORR) catalysis. This catalyst demonstrates superior ORR performance in both alkaline and acidic electrolytes, comparable to the state‐of‐the‐art Pt/C catalyst and superior to most precious‐metal‐free catalysts reported to date. This activity originates from its edge‐rich structure, having more three‐phase boundaries with enhanced mass transport of reactants to accessible single‐atom iron sites (increasing the utilization of active sites), which verifies the practicability of such a synthetic approach.     

Soft‐Templating Synthesis of N‐Doped Mesoporous Carbon Nanospheres for Enhanced Oxygen Reduction Reaction

The development of ordered mesoporous carbon materials with controllable structures and improved physicochemical properties by doping heteroatoms such as nitrogen into the carbon framework has attracted a lot of attention, especially in relation to energy storage and conversion. Herein, a series of nitrogen‐doped mesoporous carbon spheres (NMCs) was synthesized via a facile dual soft‐templating procedure by tuning the nitrogen content and carbonization temperature. Various physical and (electro)chemical properties of the NMCs have been comprehensively investigated to pave the way for a feasible design of nitrogen‐containing porous carbon materials. The optimized sample showed a favorable electrocatalytic activity as evidenced by a high kinetic current and positive onset potential for oxygen reduction reaction (ORR) due to its large surface area, high pore volume, good conductivity, and high nitrogen content, which make it a highly efficient ORR metal‐free catalyst in alkaline solutions.     

Ir-skinned Ir-Cu Nanoparticles with Enhanced Activity for Oxygen Reduction Reaction

The development of methanol-tolerate oxygen reduction reaction(ORR) electrocatalysts is of special significance to direct methanol fuel cells system. Iridium is known for its better methanol tolerance than platinum and able to survive in harsh acidic environment. However, its activity is relatively low and thus the approach to improve Ir's ORR is desired. Herein, bimetallic Ir-Cu nanoparticles(NPs) with controllable Ir/Cu compositions(ca. 1:2 to 4:1, atomic ratio) are synthesized via a galvanic replacement-based chemical method. The as-synthesized Ir-Cu NPs are investigated as ORR catalysts after electrochemically leaching out the surface Cu and forming Ir-skinned structures. Around 2- to 3-fold enhancement in the intrinsic activity has been observed in these Ir-skinned Ir-Cu catalysts compared to Ir counterpart. The approach is demonstrated to be a promising way to prepare efficient Ir ORR catalysts and lower catalyst cost.     

N‐Doped Carbon Aerogel Derived from a Metal–Organic Framework Foam as an Efficient Electrocatalyst for Oxygen Reduction

Metal–organic frameworks (MOFs) are promising alternative precursors for the fabrication of heteroatom‐doped carbon materials for energy storage and conversion. However, the direct pyrolysis of bulk MOFs usually gives microporous carbonaceous materials, which significantly hinder the mass transportation and the accessibility of active sites. Herein, N‐doped carbon aerogels with hierarchical micro‐, meso‐, and macropores were fabricated through one‐step pyrolysis of zeolitic imidazolate framework‐8/carboxymethylcellulose composite gel. Owing to the hierarchical porosity, high specific surface area, favorable conductivity, excellent thermal and chemical stability, the as‐prepared N‐doped carbon aerogel exhibits excellent oxygen reduction reaction (ORR) activity, long‐term durability, and good methanol tolerance in alkaline medium. This work thus provides a new way to fabricate new types of MOF‐derived carbon aerogels for various applications.     

Single-Atom Iron Catalysts on Overhang-Eave Carbon Cages for High-Performance Oxygen Reduction Reaction

Single-atom catalysts have drawn great attention, especially in electrocatalysis. However, most of previous works focus on the enhanced catalytic properties via improving metal loading. Engineering morphologies of catalysts to facilitate mass transport through catalyst layers, thus increasing the utilization of each active site, is regarded as an appealing way for enhanced performance. Herein, we design an overhang-eave structure decorated with isolated single-atom iron sites via a silica-mediated MOF-templated approach for oxygen reduction reaction (ORR) catalysis. This catalyst demonstrates superior ORR performance in both alkaline and acidic electrolytes, comparable to the state-of-the-art Pt/C catalyst and superior to most precious-metal-free catalysts reported to date. This activity originates from its edge-rich structure, having more three-phase boundaries with enhanced mass transport of reactants to accessible single-atom iron sites (increasing the utilization of active sites), which verifies the practicability of such a synthetic approach.     

A Template‐Free Method for Preparation of Cobalt Nanoparticles Embedded in N‐Doped Carbon Nanofibers with a Hierarchical Pore Structure for Oxygen Reduction

Designing and preparing porous materials without using any templates is a challenge. Herein, single‐nozzle electrospinning technology coupled with post pyrolysis is applied to prepare cobalt nanoparticles embedded in N‐doped carbon nanofibers with a hierarchical pore structure (HP‐Co‐NCNFs). The resultant HP‐Co‐NCNFs have lengths up to several millimeters with an average diameter of 200 nm and possess abundant micro/meso/macropores on both the surface and within the fibers. Such a microstructure endows the surface area as high as 115 m² g^?1. When used as an electrocatalyst for the oxygen reduction reaction (ORR), the HP‐Co‐NCNFs exhibit outstanding electrochemical performance in terms of activity, methanol tolerance, and durability. The hierarchically porous structure and high surface area can effectively decrease the mass transport resistance and increase the exposed ORR active sites. The sufficient amount of exposed ORR active sites along with accessible transport channel and enhanced electrical conductivity may be responsible for the good electrocatalytic performance.     

Pig Bone Derived Hierarchical Porous Carbon‐Supported Platinum Nanoparticles with Superior Electrocatalytic Activity Towards Oxygen Reduction Reaction

Hierarchical porous carbon (HPC) with nitrogen doped three dimension open macropore structure was prepared from pig bone, and applied for the support material for platinum nanoparticle (Pt NP) electrocatalyst. Compared with carbon black supported Pt NP electrocatalysts, the Pt/HPC exhibited larger electrochemical active surface area and enhanced catalytic properties for the oxygen reduction reaction (ORR) in terms of on‐set potential, current density, mass activity and stability. The superior catalytic activity is mainly attributed to the high surface area, hierarchical porous structures and the nitrogen‐doped surface properties of the HPC, indicating it is a promising support material for the ORR electrocatalysts.     

Enhanced Electrocatalytic Performance of Anthraquinonemonosulfonate‐Doped Polypyrrole Composite: Electroanalysis for the Specific Roles of Anthraquinone Derivative and Polypyrrole Layer on Oxygen Reduction Reaction

To analyze the specific roles of anthraquinone‐2‐sulfonate (AQS) and polypyrrole (PPy) layer on oxygen reduction reaction (ORR), the electrocatalytic reduction of oxygen was investigated on the AQS/PPy composite modified graphite electrode. Results show that the enhanced electrocatalytic performance is attributed to the excellent electrocatalytic activity of the immobilized AQS functional groups to mediate two‐electron reduction of O₂ to H₂O₂. The PPy layer may not participate in ORR, but it can further catalyze the two‐electron reduction of H₂O₂ to produce H₂O in the potential range more negative than that the two‐electron reduction of oxygen proceeds efficiently on the AQS sites.     

Electrochemical Preparation of N‐Doped Cobalt Oxide Nanoparticles with High Electrocatalytic Activity for the Oxygen‐Reduction Reaction

Nitrogen‐doped CoO (N‐CoO) nanoparticles with high electrocatalytic activity for the oxygen‐reduction reaction (ORR) were fabricated by electrochemical reduction of CoCl₂ in acetonitrile solution at cathodic potentials. The initially generated, highly reactive nitrogen‐doped Co nanoparticles were readily oxidized to N‐CoO nanoparticles in air. In contrast to their N‐free counterparts (CoO or Co₃O₄), N‐CoO nanoparticles with a N content of about 4.6 % exhibit remarkable ORR electrocatalytic activity, stability, and immunity to methanol crossover in an alkaline medium. The Co?N_x active sites in the CoO nanoparticles are held responsible for the high ORR activity. This work opens a new path for the preparation of nitrogen‐doped transition metal oxide nanomaterials, which are promising electrocatalysts for fuel cells.     

Iodine‐Doped Cobalt Phthalocyanine Supported on Multiwalled Carbon Nanotubes for Electrocatalysis of Oxygen Reduction Reaction

4‐(4,6‐Diaminopyrimidin‐2‐ylthio) phthalocyaninatocobalt(II) (CoPyPc) was iodine doped, and its electrocatalytic properties explored. Physical characterization techniques such as UV‐vis, X‐ray photoelectron, electron paramagnetic resonance and infra‐red spectroscopy were used. Cyclic voltammetry, electrochemical impedance spectroscopy and rotating disk electrode were used for electrochemical characterization of electrodes modified with the prepared phthalocyanine and its nanocomposites. The electrocatalytic effect of a new iodine‐doped cobalt phthalocyanine derivative supported on multiwalled carbon nanotubes was then investigated towards oxygen reduction reaction. The electrocatalytic activity of the iodine‐doped cobalt phthalocyanine was found to be superior in terms of current over the undoped phthalocyanine nanocomposite.     

杂原子掺碳材料氧还原催化剂研究进展

开发替代Pt类高活性、低成本的非贵金属燃料电池阴极氧还原催化剂是实现燃料电池商业化的必由之路. 研发催化活性高,稳定性好,价格便宜的非贵金属催化剂是当务之急. 碳纳米材料,尤其杂原子掺杂的碳纳米材料有其独特的结构和催化性能而备受瞩目. 本文结合作者课题组的研究工作,综述了近年杂原子掺杂碳纳米材料催化剂燃料电池阴极氧电催化还原方面的研究进展.     

Au@Pt纳米粒子催化O2还原反应的电化学研究

以100 nm的Au粒子为核,抗坏血酸为还原剂,H2PtCl6·6H2O为前驱体,合成了Pt包Au核壳结构纳米粒子( Au@ Pt)及其修饰的玻碳(GC)电极(Au@ Pt/GC).采用旋转圆盘电极等常规电化学方法,比较了Au@ Pt/GC和商用碳载铂(Pt/C)修饰的玻碳电极(Pt/C/GC)催化O2还原反应活性及耐甲醇性能,发现Au@ Pt纳米粒子在铂用量很低的情况下,其催化O2还原反应活性仍与商用Pt/C相当,而且还具有优良的耐甲醇性能;其催化O2还原反应机理按O2直接还原成H2O的四电子历程进行.     

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.     

Optimal Configuration of N‐Doped Carbon Defects in 2D Turbostratic Carbon Nanomesh for Advanced Oxygen Reduction Electrocatalysis

The charge redistribution strategy driven by heteroatom doping or defect engineering has been developed as an efficient method to endow inert carbon with significant oxygen reduction reaction (ORR) activity. The synergetic effect between the two approaches is thus expected to be more effective for manipulating the charge distribution of carbon materials for exceptional ORR performance. Herein we report a novel molecular design strategy to achieve a 2D porous turbostratic carbon nanomesh with abundant N‐doped carbon defects (NDC). The molecular level integration of aromatic rings as the carbon source and urea units as the N source and sacrificial template into the novel precursor of polyurea (PU) promises the formation of abundant carbon edge defects and N doping sites. A special active site—a carbon edge defect doped with a graphitic valley N atom—was revealed to be responsible for the exceptional ORR performance of NDC material.     

Porous‐Organic‐Framework‐Templated Nitrogen‐Rich Porous Carbon as a More Proficient Electrocatalyst than Pt/C for the Electrochemical Reduction of Oxygen

Porous nitrogen‐rich carbon (POF‐C‐1000) that was synthesized by using a porous organic framework (POF) as a self‐sacrificing host template in a nanocasting process possessed a high degree of graphitization in an ordered structural arrangement with large domains and well‐ordered arrays of carbon sheets. POF‐C‐1000 exhibits favorable electrocatalytic activity for the oxygen‐reduction reaction (ORR) with a clear positive shift of about 40 mV in the onset potential compared to that of a traditional, commercially available Pt/C catalyst. In addition, irrespective of its moderate surface area (785 m² g^?1), POF‐C‐1000 showed a reasonable H₂ adsorption of 1.6 wt % (77 K) and a CO₂ uptake of 3.5 mmol g^?1 (273 K).     

生物质基碳材料作为氧还原反应催化剂的研究进展

燃料电池作为一种清洁能源有很大的发展前景,其阴极氧还原反应多采用铂基催化剂,但由于贵金属铂的储量稀少、价格昂贵等原因,严重阻碍了燃料电池的商业化进程。寻找高活性、高稳定性的新材料来替代阴极铂基催化剂成为燃料电池大规模商业化亟待解决的关键问题之一。研究表明,以生物质为原料的碳材料有望成为商业铂基氧还原催化剂的一种理想替代品。本文综述了这方面的研究进展,并且展望了未来的发展趋势。     

Zeolitic Imidazolate Framework (ZIF)‐Derived,Hollow‐Core,Nitrogen‐Doped Carbon Nanostructures for Oxygen‐Reduction Reactions in PEFCs

The facile synthesis of a porous carbon material that is doped with iron‐coordinated nitrogen active sites (FeNC‐70) is demonstrated by following an inexpensive synthetic pathway with a zeolitic imidazolate framework (ZIF‐70) as a template. To emphasize the possibility of tuning the porosity and surface area of the resulting carbon materials based on the structure of the parent ZIF, two other ZIFs, that is, ZIF‐68 and ZIF‐69, are also synthesized. The resulting active carbon material that is derived from ZIF‐70, that is, FeNC‐70, exhibits the highest BET surface area of 262 m² g^?1 compared to the active carbon materials that are derived from ZIF‐68 and ZIF‐69. The HR‐TEM images of FeNC‐70 show that the carbon particles have a bimodal structure that is composed of a spherical macroscopic pore (about 200 nm) and a mesoporous shell. X‐ray photoelectron spectroscopy (XPS) reveals the presence of Fe‐N‐C moieties, which are the primary active sites for the oxygen‐reduction reaction (ORR). Quantitative estimation by using EDAX analysis reveals a nitrogen content of 14.5 wt. %, along with trace amounts of iron (0.1 wt. %), in the active FeNC‐70 catalyst. This active porous carbon material, which is enriched with Fe‐N‐C moieties, reduces the oxygen molecule with an onset potential at 0.80 V versus NHE through a pathway that involves 3.3–3.8 e^? under acidic conditions, which is much closer to the favored 4 e^? pathway for the ORR. The onset potential of FeNC‐70 is significantly higher than those of its counterparts (FeNC‐68 and FeNC‐69) and of other reported systems. The FeNC‐based systems also exhibit much‐higher tolerance towards MeOH oxidation and electrochemical stability during an accelerated durability test (ADT). Electrochemical analysis and structural characterizations predict that the active sites for the ORR are most likely to be the in situ generated N? FeN₂₊₂/C moieties, which are distributed along the carbon framework.