纳米碳纤维载铂作为质子交换膜燃料电池阳极催化剂

采用化学还原法合成了微结构不同的纳米碳纤维(板式、鱼骨式、管式)载铂催化剂(分别记为Pt/p-CNF、Pt/f-CNF、Pt/t-CNF). 通过高分辨透射电镜(HRTEM)和X射线衍射(XRD)等分析技术对催化剂的微观结构进行了表征, 并利用循环伏安(CV)法分析了催化剂的电化学比表面积(ESA). 在此基础上, 制备了膜电极(MEA), 通过单电池测试了催化剂的电催化性能. 结果表明: 铂纳米粒子在不同的纳米碳载体上表现出不同的粒径, 在板式、鱼骨式和管式纳米碳纤维上的铂纳米粒子平均粒径分别为2.4、2.7和2.8 nm. 板式纳米碳纤维载铂催化剂作单电池阳极时表现出良好的电催化性能, 其对应的最高功率密度可达0.569 W·cm^-2, 高于鱼骨式纳米碳纤维载铂催化剂和管式纳米碳纤维载铂催化剂对应的最高功率密度(分别为0.550和0.496 W·cm^-2). 同时, 也制备了碳黑(Pt/XC-72)载铂催化剂. 相比于Pt/XC-72, 纳米碳纤维载体上的铂纳米颗粒有较小的粒径、较好的分散和较高的催化活性, 说明纳米碳纤维是质子交换膜燃料电池(PEMFCs)催化剂的良好载体.     

纳米碳纤维的表面性质和微结构对氧还原催化活性的影响

采用超声处理的方法分别对管式纳米碳纤维(t-CNF)和鱼骨式纳米碳纤维(f-CNF)进行了表面化学处理. XPS结果表明, 在混酸(浓硫酸+浓硝酸)和氨水中进行超声化学处理可以在CNF表面分别引入含氧官能团和含氮官能团. 电化学测试结果表明, 2种不同微结构CNF的氧还原催化活性都遵循相同的趋势, 即CNF-P相似文献   

Ir–V nanoparticles supported on microstructure controlled carbon nanofibers as electrocatalyst for oxygen reduction reaction

Ir–V nanoparticles supported on microstructure controlled carbon nanofibers (CNFs) or on carbon black, Vulcan XC-72 (XC-72), have been synthesized via chemical reduction, and the oxygen reduction reaction (ORR) properties of catalysts are investigated in this paper. The physico-chemical properties are characterized by high resolution transmission electron microscope (HRTEM), N₂ physisorption and electrochemical analysis. HRTEM results show that the metal nanoparticles are separated on carbon support with well-controlled particle size, dispersity, and composition uniformity. Moreover, the metal nanoparticles on CNFs have a smaller size than those on XC-72. Cyclic voltammetric analysis reveals that Ir–V/CNFs exhibits a higher ORR activity than Ir–V/XC-72, and this may be associated with the smaller metal nanoparticles and the stronger metal-support interaction of Ir–V/CNFs. Linear sweep voltammetric analysis at different rotation rates proves that ORR on the Ir–V/CNFs electrode is a 4e^? process.     

Electrochemical Detection of Hydrazine Based on Electrospun Palladium Nanoparticle/Carbon Nanofibers

In this work, we developed an electrochemical method for the detection of hydrazine based on palladium nanoparticle/carbon nanofibers (Pd/CNFs). Pd/CNFs were prepared by electrospinning technique and subsequent thermal treatments. The electrocatalytic behaviors of Pd/CNFs modified glassy carbon electrode (Pd/CNF‐GCE) for hydrazine oxidation were evaluated by cyclic voltammetry (CV), an obvious and well‐defined oxidation peak appeared at ?0.32 V (vs. Ag/AgCl). The mechanism of the oxidation of hydrazine at Pd/CNF‐GCE was also studied, which demonstrated an irreversible diffusion‐controlled electrode process and a four‐electron transfer involved in the overall reaction. Furthermore, the wide linear range, low detection limit, good reproducibility and excellent storage stability were obtained utilizing differential pulse voltammetry (DPV).     

Properties of Pd–Ag/C catalysts in the reaction of selective hydrogenation of acetylene

Samples of Pd/C and Pd–Ag/C, where C represents carbon nanofibers (CNFs), are synthesized by methane decomposition on a Ni–Cu–Fe/Al₂O₃ catalyst. The properties of Pd/CNF are studied in the reaction of selective hydrogenation of acetylene into ethylene. It is found that the activity of the catalyst in hydrogenation reaction increases, while selectivity decreases considerably when the palladium content rises. The obtained dependences are caused by the features of palladium’s interaction with the carbon support. At a low Pd content (up to 0.04 wt %) in the catalyst, the metal is inserted into the interlayer space of graphite and the catalytic activity is zero. It is established by EXAFS that the main share of palladium in catalysts of 0.05–0.1 wt % Pd/CNF constitutes the metal in the atomically dispersed state. The coordination environment of palladium atoms consists of carbon atoms. An increase in the palladium content in a Pd/CNF catalyst up to 0.3 wt % leads to the formation of highly dispersed (0.8–1 nm) Pd particles. The Pd/CNF samples where palladium is mainly in the atomically dispersed state exhibit the highest selectivity in the acetylene hydrogenation reaction. The addition of silver to a 0.1 wt % Pd/CNF catalyst initially probably leads to the formation of Pd–Ag clusters and then to alloyed Pd–Ag particles. An increase in the silver content in the catalyst above 0.3% causes the enlargement of the alloyed particles and the palladium atoms are blocked by a silver layer, which considerably decreases the catalytic activity in the selective hydrogenation of acetylene.     

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.     

Factors controlling the energetics of the oxygen reduction reaction on the Pd-Co electro-catalysts: insight from first principles

We report here results of our density functional theory based computational studies of the electronic structure of the Pd-Co alloy electrocatalysts and energetics of the oxygen reduction reaction (ORR) on their surfaces. The calculations have been performed for the (111) surfaces of pure Pd, Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) alloys, as well as of the surface segregated Pd/Pd(0.75)Co(0.25) alloy. We find the hybridization of dPd and dCo electronic states to be the main factor controlling the electrocatalytic properties of Pd/Pd(0.75)Co(0.25). Namely the dPd-dCo hybridization causes low energy shift of the surface Pd d-band with respect to that for Pd(111). This shift weakens chemical bonds between the ORR intermediates and the Pd/Pd(0.75)Co(0.25) surface, which is favorable for the reaction. Non-segregated Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) surfaces are found to be too reactive for ORR due to bonding of the intermediates to the surface Co atoms. Analysis of the ORR free energy diagrams, built for the Pd and Pd/Pd(0.75)Co(0.25), shows that the co-adsorption of the ORR intermediates and water changes the ORR energetics significantly and makes ORR more favorable. We find the onset ORR potential estimated for the configurations with the O-OH and OH-OH co-adsorption to be in very good agreement with experiment. The relevance of this finding to the real reaction environment is discussed.     

Fe–N/C nanofiber electrocatalysts with improved activity and stability for oxygen reduction in alkaline and acid solutions

Fe–N/C nanofiber (Fe–N/CNF) electrocatalysts were prepared by impregnating electrospun polyacrylonitrile nanofibers with iron nitrate (Fe(NO₃)₃) solution and subsequent heat treatment, exhibiting improved activity and stability during oxygen reduction reaction (ORR) both in 0.1 M KOH (pH?=?13) and 0.5 M H₂SO₄ (pH?=?0) electrolyte solutions. Higher treatment temperature and NH₃ atmosphere were preferred by the Fe–N/CNF catalysts, and especially the concentration of Fe(NO₃)₃ solution exerted great effects on the surface morphology, structure, and thus electrocatalytic performance of the catalysts. The Fe–N/CNFs prepared using 0.5 wt% Fe(NO₃)₃ solution showed relatively higher ORR activity in alkaline and acid solutions and better stability especially in 0.5 M H₂SO₄ solution than the catalyst without Fe, probably because Fe could promote the graphitization of the polymer-converted carbon species, enhancing the resistance to electrochemical oxidation and thus the stability of the Fe–N/CNF catalysts.     

部分氧化碳化硅提高钯催化氧还原反应性能

燃料电池具有能量转换效率高的优点,是能量转换与储存的高效器件之一.目前,燃料电池阴极氧还原反应(ORR)动力学缓慢,并且催化ORR大量使用铂碳(Pt/C)催化剂,由于Pt储量少,价格高,载体碳材料易发生碳蚀导致催化剂稳定性降低,限制了其进一步商业化应用.钯(Pd)与Pt为同族元素,具有相似的电子结构和化学性质,其储量是...     

Influence of nitrogen doping on oxygen reduction electrocatalysis at carbon nanofiber electrodes

Nondoped and nitrogen-doped (N-doped) carbon nanofiber (CNF) electrodes were prepared via a floating catalyst chemical vapor deposition (CVD) method using precursors consisting of ferrocene and either xylene or pyridine to control the nitrogen content. Structural and compositional differences between the nondoped and N-doped varieties were assessed using TEM, BET, Raman, TGA, and XPS. Electrochemical methods were used to study the influence of nitrogen doping on the oxygen reduction reaction (ORR). The N-doped CNF electrodes demonstrate significant catalytic activity toward oxygen reduction in aqueous KNO(3) solutions at neutral to basic pH. Electrochemical data are presented which indicate that the ORR proceeds by the peroxide pathway via two successive two-electron reductions. However, for N-doped CNF electrodes, the reduction process can be treated as a catalytic regenerative process where the intermediate hydroperoxide (HO(2)(-)) is chemically decomposed to regenerate oxygen, 2HO(2)(-) <==> O(2) + 2OH(-). The proposed electrocatalysis mechanisms for ORR at both nondoped and N-doped varieties are supported by electrochemical simulations and by measured difference in hydroperoxide decomposition rate constants. Remarkably, approximately 100 fold enhancement for hydroperoxide decomposition is observed for N-doped CNFs, with rates comparable to the best known peroxide decomposition catalysts. Collectively the data indicate that exposed edge plane defects and nitrogen doping are important factors for influencing adsorption of reactive intermediates (i.e., superoxide, hydroperoxide) and for enhancing electrocatalysis for the ORR at nanostructured carbon electrodes.     

Co1-xS-MnS@CNTs/CNFs的制备及其氧还原电催化性能

氧还原反应是燃料电池中重要的阴极反应,但由于动力学迟缓等问题导致其效率低.碳基材料具有导电性高、稳定性好、比表面积大等优点,常被应用于电催化氧还原反应.然而其在电催化氧还原反应中效率较低,对碳基材料进行Co、Mn掺杂有望提高其氧还原效率.本文采用静电纺丝技术制备出含有Co,Mn双金属的碳纳米纤维,经热解和硫化后碳纳米纤...     

Ruthenium Nanoparticles on Nano‐Level‐Controlled Carbon Supports as Highly Effective Catalysts for Arene Hydrogenation

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with [Ru₃(CO)₁₂] in toluene heated at reflux provided the corresponding CNF‐supported ruthenium nanoparticles, Ru/CNFs (Ru content=1.1–3.8 wt %). TEM studies of these Ru/CNFs revealed that size‐controlled Ru nanoparticles (2–4 nm) exist on the CNFs, and that their location was dependent on the surface nanostructures of the CNFs: on the edge of the graphite layers (CNF‐P), in the tubes and on the surface (CNF‐T), and between the layers and on the edge (CNF‐H). Among these Ru/CNFs, Ru/CNF‐P showed excellent catalytic activity towards hydrogenation of toluene with high reproducibility; the reaction proceeded without leaching of the Ru species, and the catalyst was reusable. The total turnover number of the five recycling experiments for toluene hydrogenation reached over 180 000 (mol toluene) (mol Ru)^?1. Ru/CNF‐P was also effective for the hydrogenation of functionalized benzene derivatives and pyridine. Hydrogenolysis of benzylic C? O and C? N bonds has not yet been observed. Use of poly(ethylene glycol)s (PEGs) as a solvent made possible the biphasic catalytic hydrogenation of toluene. After the reaction, the methylcyclohexane formed was separated by decantation without contamination of the ruthenium species and PEG. The insoluble PEG phase containing all of the Ru/CNF was recoverable and reusable as the catalyst without loss of activity.     

Chemoselective Hydrogenation of Functionalized Nitroarenes and Imines by Using Carbon Nanofiber‐Supported Iridium Nanoparticles

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with Ir₄(CO)₁₂ in mesitylene at 165 °C provided the corresponding CNF‐supported iridium nanoparticles, Ir/CNFs (Ir content=2.3–2.6 wt. %). Transmission electron microscopy (TEM) studies of these Ir/CNF samples revealed that size‐controlled Ir nanoparticles (average particle size of 1.1–1.5 nm) existed on the CNFs. Among the three Ir/CNF samples, Ir/CNF‐T showed an excellent catalytic activity and chemoselectivity towards hydrogenation of functionalized nitroarenes and imines; the corresponding aniline derivatives were obtained with high turnover numbers at ambient temperature under 10 atm of H₂, and the catalyst is reusable. Ir/CNF‐T was also effective for the reductive N‐alkylation of anilines with carbonyl compounds.     

Carbon‐Supported Divacancy‐Anchored Platinum Single‐Atom Electrocatalysts with Superhigh Pt Utilization for the Oxygen Reduction Reaction

Maximizing the platinum utilization in electrocatalysts toward oxygen reduction reaction (ORR) is very desirable for large‐scale sustainable application of Pt in energy systems. A cost‐effective carbon‐supported carbon‐defect‐anchored platinum single‐atom electrocatalysts (Pt₁/C) with remarkable ORR performance is reported. An acidic H₂/O₂ single cell with Pt₁/C as cathode delivers a maximum power density of 520 mW cm^?2 at 80 °C, corresponding to a superhigh platinum utilization of 0.09 g_Pt kW^?1. Further physical characterization and density functional theory computations reveal that single Pt atoms anchored stably by four carbon atoms in carbon divacancies (Pt‐C₄) are the main active centers for the observed high ORR performance.     

Silica-Derived Nanostructured Electrode Materials for ORR,OER, HER,CO2RR Electrocatalysis,and Energy Storage Applications: A Review**

Silica-derived nanostructured catalysts (SDNCs) are a class of materials synthesized using nanocasting and templating techniques, which involve the sacrificial removal of a silica template to generate highly porous nanostructured materials. The surface of these nanostructures is functionalized with a variety of electrocatalytically active metal and non-metal atoms. SDNCs have attracted considerable attention due to their unique physicochemical properties, tunable electronic configuration, and microstructure. These properties make them highly efficient catalysts and promising electrode materials for next generation electrocatalysis, energy conversion, and energy storage technologies. The continued development of SDNCs is likely to lead to new and improved electrocatalysts and electrode materials. This review article provides a comprehensive overview of the recent advances in the development of SDNCs for electrocatalysis and energy storage applications. It analyzes 337,061 research articles published in the Web of Science (WoS) database up to December 2022 using the keywords “silica”, “electrocatalysts”, “ORR”, “OER”, “HER”, “HOR”, “CO₂RR”, “batteries”, and “supercapacitors”. The review discusses the application of SDNCs for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂RR), supercapacitors, lithium-ion batteries, and thermal energy storage applications. It concludes by discussing the advantages and limitations of SDNCs for energy applications.     

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.     

Oxygen Reduction Reaction in a Droplet on Graphite: Direct Evidence that the Edge Is More Active than the Basal Plane

Carbon‐based metal‐free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium have been extensively investigated with the aim of replacing the commercially available, but precious platinum‐based catalysts. For the proper design of carbon‐based metal‐free electrocatalysts for the ORR, it would be interesting to identify the active sites of the electrocatalyst. The ORR was now studied with an air‐saturated electrolyte solution droplet (diameter ca. 15 μm), which was deposited at a specified position either on the edge or on the basal plane of highly oriented pyrolytic graphite. Electrochemical measurements suggest that the edge carbon atoms are more active than the basal‐plane ones for the ORR. This provides a direct way to identify the active sites of carbon materials for the ORR. Ball‐milled graphite and carbon nanotubes with more exposed edges were also prepared and showed significantly enhanced ORR activity. DFT calculations elucidated the mechanism by which the charged edge carbon atoms result in the higher ORR activity.     

Synthesis of Pd-Pt bimetallic nanocrystals with a concave structure through a bromide-induced galvanic replacement reaction

This article describes a systematic study of the galvanic replacement reaction between PtCl(6)(2-) ions and Pd nanocrystals with different shapes, including cubes, cuboctahedrons, and octahedrons. It was found that Br(-) ions played an important role in initiating, facilitating, and directing the replacement reaction. The presence of Br(-) ions led to the selective initiation of galvanic replacement from the {100} facets of Pd nanocrystals, likely due to the preferential adsorption of Br(-) ions on this crystallographic plane. The site-selective galvanic replacement resulted in the formation of Pd-Pt bimetallic nanocrystals with a concave structure owing to simultaneous dissolution of Pd atoms from the {100} facets and deposition of the resultant Pt atoms on the {111} facets. The Pd-Pt concave nanocubes with different weight percentages of Pt at 3.4, 10.4, 19.9, and 34.4 were also evaluated as electrocatalysts for the oxygen reduction reaction (ORR). Significantly, the sample with a 3.4 wt.% of Pt exhibited the largest specific electrochemical surface area and was found to be four times as active as the commercial Pt/C catalyst for the ORR in terms of equivalent Pt mass.     

Facile Synthesis of AuPd Nanochain Networks on Carbon Supports and Their Application as Electrocatalysts for Oxygen Reduction Reaction

The present work reports the facile synthesis and characterization of carbon‐supported porous Pd shell coated Au nanochain networks (AuPdNNs/C). By using Co nanoframes as sacrificial templates, AuPdNNs/C series have been prepared by a two‐step galvanic replacement reaction (GRR) technique. In the first step, the Au metal precursor, HAuCl₄, reacts spontaneously with the formed Co nanoframes through the GRR, resulting in Au nanochain networks (AuNNs). The second GRR is performed with various concentrations of Pd precursor (0.1, 1, and 10 mM PdCl₂), resulting in AuPdNNs/C. The synthesized AuPdNNs/C series are investigated as electrocatalysts for oxygen reduction reaction (ORR) in alkaline solution. The physical properties of the AuPdNNs/C catalysts are characterized by scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), UV‐vis absorption spectroscopy, and cyclic voltammetry (CV). Rotating disk electrode (RDE) voltammetric studies show that the Au_0.8Pd_0.2NNs/C (prepared using 1 mM PdCl₂) has the highest ORR activity among all the AuPdNNs/C series, which is comparable to commercial Pt catalyst (E‐TEK). The ORR activity of AuPdNNs/C is presumably due to the enhanced Pd surface area and high porosity of Pd nanoshells.     

Electrochemistry of perfluorinated fullerenes: the case of three isomers of C60F36

1-Naphthol has been used as an in situ fluorescent probe to characterize the surface physicochemical properties of carbon nanofibers (CNFs). The fluorescence of 1-naphthol adsorbed on untreated CNFs originates from the ¹L_b state and its peaks are shifted by the polarity of the surrounding media, indicating that there is a relatively non-polar area on the CNF surface. 1-Naphthol interacting with oxidized sites on the surface of nitric acid-treated CNFs exhibited an ion-pair fluorescence. This shows that there are some functional groups, interacting with 1-naphthol, on the treated CNF surface. The surface physicochemical properties of the CNFs can be characterized by this fluorescent probe.