配合物的形成对金属离子氧化还原性影响的讨论

正在水溶液中,Fe~(3+)可把I~-氧化成I_2,但I_2又可把铁(Ⅱ)氰配离子Fe(CN)_6~(4-)氧化成铁(Ⅲ)氰配离子Fe(CN)_6~(3-);同样地,Co~(3+)可把H_2O氧化成O_2,但O_2又可把钴(Ⅱ)氨配离子[Co(NH_3)_6~(2+)]氧化成钴(Ⅲ)氨配离子[Co(NH_3)_6~(3+)];对于钴氰配离子,甚至氧化性极弱的H_2O也可把钴(Ⅱ)氰配离子[Co(CN)_6~(4-)]氧化成钴(Ⅲ)氰配离子[Co(CN)_6~(3-)]     

离子交换膜的电子显微镜研究

透射电子显微镜可用于鉴识阳离子交换膜内部结构非均相性程度和“阳膜”内部的离子性基团的分布。对含氟离子膜(Nafion,MRF)和早已熟悉的聚苯乙烯磺酸膜(AMEC-322和 PE-PSSA)进行了研究,超薄片的电镜图象揭示了 Nafion 膜和 MRF-4MB 膜内许多细小、均匀分布的离子基团浓集点的均相本质。但在聚苯乙烯磺酸膜(AMEC-322,PE-PSSA)中,这些基团的分布是非均相的,这是与这些膜的聚合物基体非均相性本质相一致的。     

偶氮基双核钴配合物的合成、结构及光学性质

室温下,通过调控反应体系的pH值,构筑了一例新的基于5-偶氮四唑水杨酸(H3ASA)的钴配合物[Co2(HASA)2(H2 O)6],并借助X-射线单晶衍射解析其晶体结构.结果显示,该配合物为单斜晶系,P21/c空间群,每个不对称单元由两个Co(Ⅱ)离子、两个HASA2-配体以及6个配位水分子组成.晶体结构中,中心离子...     

核壳结构钴基催化剂的制备及费托合成性能

利用热分解法制备了高分散度球形四氧化三钴(Co3O4)粒子,以其作为核心,采用聚乙烯吡咯烷酮(PVP)作为两亲试剂,在碱性条件下,以十六烷基三甲基溴化铵(CTAB)为模板、正硅酸乙酯(TEOS)为硅源,制备了硅基材料均匀包裹的核壳结构钴基催化剂(Co3O4@MCM-41)。XRD,N2吸脱附曲线与BJH孔径分布与TEM等表征结果显示,钴核仍保持Co3O4晶相且被硅壳完全包覆,硅壳属于MCM-41类型介孔材料。与普通初湿浸渍法制备的催化剂Co3O4/MCM-41相比,催化剂Co3O4@MCM-41易于还原、活性相稳定,并可在较低的甲烷选择性下,高选择性地催化合成气生成中间馏分油(C5～C18)。相关表征与理论分析结果表明,这与其独特的结构有关。     

聚吡咯修饰Nafion膜直接甲醇燃料电池的性能

用FeCl3化学氧化法制备了PPy/Nafion改性膜,采用浸渍-还原法在PPy/Nafion阴极侧上沉积Co金属,制得Co-PPy/Nafion电解质膜。采用TG、CV及交流阻抗谱测试了Nafion膜及改性膜的热稳定性,质子电导性和甲醇渗透性能,结果表明:PPy/Nafion及Co-PPy/Nafion改性膜具有更好的热稳定性和抗甲醇渗透性。分别以Co-PPy/Nafion改性膜、PPy/Nafion改性膜和纯Nafion膜为电解质膜,PtRu/C为阳极催化剂,Pt/C为阴极催化剂组装DMFC并考察其性能。实验结果表明:Co-PPy/Nafion改性膜组装单电池在高浓度甲醇及大电流密度的测试条件下,表现出更优异的电池性能。     

Co基费托合成催化剂载体的研究进展

综述了近年来钴(Co)基催化剂载体在费托合成反应中的研究进展.重点评述了柱撑蒙脱土、新型介孔分子筛等载体对钴基催化剂活性和选择性等方面的影响,概述了Co/Al_2O_3催化剂在费托合成反应中的催化机理,对今后Co基费托合成催化剂的研究提出了一点建议.     

钴离子掺杂聚苯胺/石墨烯复合材料的制备及电化学性能研究

采用一锅化学氧化聚合掺杂法制备了钴离子掺杂聚苯胺/石墨烯(PGC)复合材料,优化了Co2+与苯胺(An)的摩尔比,研究了与石墨烯(RGO)的复合对钴离子掺杂聚苯胺(Co2+-PANI)微观结构、形貌及电化学性能的影响,通过红外光谱(FT-IR)、扫描电镜(SEM)、X射线能谱(EDS)对PGC复合材料的结构和形貌进行了...     

稀土-钴簇合物为前体的催化剂制备及其费-托反应性能测试

费–托(F-T)合成是由煤炭、天然气或生物质等原料加工生成合成气(CO和H2),再经过催化剂的催化作用转化为高品质液态燃料的合成方法,这项技术不仅可以有效地减少大气污染,而且为替代石油资源提供了新的途径。因此,研制开发低甲烷、高液态烃选择性的钴基催化剂显得尤为重要。本文以γ-Al2O3为载体,(CO)6Co2HCCCOOH、Co3(CO)9CCOOH和Yb4O{(CO)9Co3CCOO}4为前体,按照Co5%(质量分数)的负载量制备了一系列钴基催化剂。用X-射线衍射、程序升温还原、比表面测试等技术考察了钴基催化剂的结构和还原性能,分析了不同前体对F-T反应性能的影响。结果表明,不同钴前体所制备的催化剂,钴物种的分散度和还原度有很大的差别。其中,含稀土的钴羰基簇合物为前体的催化剂,具有较小的晶粒度和比较好的分散度,较小的钴晶粒对液态烃的选择性有利。其相应的Co/Al2O3催化剂的费-托活性由大到小依次为:Yb4O{(CO)9Co3CCOO}4,(CO)6Co2HCCCOOH,Co3(CO)9CCOOH+Yb4O{(CO)9Co3CCOO}4,Co3(CO)9CCOOH。     

UH004-Nafion复合质子交换膜研究

将Nafion溶液与溶剂的混合液涂覆在UH004纳滤膜上,制成Nafion/UH004复合膜用于全钒液流电池(VRB)中。该复合膜涂覆的Nafion溶液为400μL,测试其H/V离子选择性系数和电池性,结果均优于UH004。     

离子交换膜在电解法制造碳酸钾中的应用研究

采用添加KHCO_3的阴极液循环法,由KCl水溶液的离子膜电解,一次得到K_2CO_3.试验中对Nafion膜的导电度进行了测定,探讨了碱金属阳离子在离子膜中的行为.对各种离子在Nafion膜中的移动速度进行了测定,表明影响电流效率的主要因素是OH~-离子的反向渗透.由于CO_3~(2-)在离子膜中的移动速度很小,所以在制取高浓度K_2CO_3时仍可获得90%以上的电流效率.通过控制添加的KHCO_3的量,可以得到KHCO_3及Cl~-含量极低的高纯度K_2CO_3.     

Electrocatalytic reduction of dioxygen at glassy carbon electrodes modified with polypyrrole/anthraquinonedisulphonate composite film in various pH solutions

Functionalized polypyrrole (PPy) film with anthraquinonedisulphonate (AQDS) incorporated as dopant was prepared by anodic polymerization of pyrrole (Py) at a glassy carbon electrode from aqueous solution. The electrochemical behavior of AQDS in PPy matrix and the electrocatalytic reduction of dioxygen on the resulting composite film were investigated in various pH solutions. The formal potential of AQDS and the reduction potential of dioxygen both exhibit pH dependence. In all pH solutions employed, the electrocatalytic reduction of dioxygen at the PPy/AQDS composite film establishes a pathway of irreversible two-electron reduction to form hydrogen peroxide. The pH 6.0 buffer solution is a more suitable medium for the reduction of dioxygen, where the PPy/AQDS composite film showed a more efficient electrocatalytic performance. It was found that AQDS is an effective mediator for the reduction of dioxygen and the reduced AQ is responsible for the enhanced catalytic activity. The catalytic current is under mixed kinetic-diffusion control. The number of electrons transferred and kinetic parameters of dioxygen reduction were determined using cyclic voltammetry, rotating disk voltammetry and Tafel polarization technique.     

Electrocatalytic reduction of dioxygen by cobalt porphyrin-modified glassy carbon electrode with single-walled carbon nanotubes and nafion in aqueous solutions

Cobalt porphyrin (CoP)-modified glassy carbon electrode (GCE) with single-walled carbon nanotubes (SWNTs) and Nafion demonstrated a higher electrocatalytic activity for the reduction of dioxygen in 0.1 M H₂SO₄ solution. Cyclic and hydrodynamic voltammetry at the CoP-SWNTs/GCE-modified electrodes in O₂-saturated aqueous solutions was used to study the electrocatalytic pathway. Compared with the CoP/GCE-modified electrodes, the reduction potential of dioxygen at the CoP-SWNTs/GCE-modified electrodes was shifted to the positive direction and the limiting current was greatly increased. Especially, the Co(TMPP)-SWNTs/GCE-modified electrode was catalyzed effectively by the 4e⁻ reduction of dioxygen to water, because hydrodynamic voltammetry revealed the transference of approximately four electrons for dioxygen reduction and the minimal generation of hydrogen peroxide in the process of dioxygen reduction.     

Electrocatalytic reduction of dioxygen on hemin based carbon paste electrode

A hemin-modified carbon paste electrode was constructed by a simple, rapid and effective method. The electrochemical behaviour of the modified electrode was characterized by cyclic voltammetry. The modified electrode obtained was very stable and exhibited electrocatalytic response for the reduction of oxygen. The possible mechanism for the catalytic reduction of dioxygen is discussed. The dioxygen is reduced via a one-step reduction accompanying four electrons and four protons transfer at pH 7–11.     

Electrocatalytic reduction of oxygen at glassy carbon electrode modified by polypyrrole/anthraquinones composite film in various pH media

The electrocatalytic reduction of dioxygen by one mono and four dihydroxy derivatives of 9,10-anthraquinone (AQ) incorporated in polypyrrole (PPy) matrix on glassy carbon electrode has been investigated. The electrochemical behaviour of the modified electrodes was examined in various pH media and both the formal potential of anthraquinones and reduction potential of dioxygen exhibited pH dependence. AQ and PPy composite film showed excellent electrocatalytic performance for the reduction of O₂ to H₂O₂. pH 6.0 was chosen as the most suitable medium to study the electrocatalysis by comparing the peak potential of oxygen reduction and enhancement in peak current for oxygen reduction. The diffusion coefficient values of AQ at the modified electrodes and the number of electrons involved in AQ reduction were evaluated by chronoamperometric and chronocoulometric techniques, respectively. In addition, hydrodynamic voltammetric studies showed the involvement of two electrons in O₂ reduction. The mass specific activity of AQ used, the diffusion coefficient of oxygen and the heterogeneous rate constants for the oxygen reduction at the surface of modified electrodes were also determined by rotating disk voltammetry.     

Electrocatalytic reduction of dioxygen at a modified glassy carbon electrode based on Nafion-dispersed single-walled carbon nanotubes and cobalt–porphyrin with palladium nanoparticles in acidic media

Cathodic dioxygen (O₂) reduction was performed at a modified glassy carbon electrode (GCE) by single-walled carbon nanotubes (SWCNT)/Nafion^® (NF) film with cobalt (II) tetra (2-amino-phenyl) porphyrin (CoTAPP) and palladium (Pd) nanoparticles incorporated and employed as doping agents. Both the electrochemical behavior of SWCNT with a P(CoTAPP)–Pd nanoparticle matrix and the electrocatalytic reduction of O₂ were investigated using transmission electron microscopy (TEM), cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) techniques in 0.1 mol l⁻¹ H₂SO₄ aqueous solutions. The electrocatalytic reduction of O₂ at the SWCNT/NF/P(CoTAPP)–Pd composite film established a pathway of four-electron transfer reductions into H₂O. Hydrodynamic voltammetry revealed that the modified electrode was catalyzed effectively by the four-electron transferred reduction of dioxygen into H₂O with minimal generation of H₂O₂. The SWCNT/NF/P(CoTAPP)–Pd composite film showed a highly efficient electrocatalytic performance. P(CoTAPP)–Pd was an effective mediator for the reduction of dioxygen and was responsible for the enhanced catalytic activity.     

Electrochemical reduction of dioxygen on a thioglycolic acid-capped CdTe quantum dots modified glassy carbon electrode

A novel modified electrode was constructed by immobilizing thioglycolic acid-capped CdTe quantum dots (QDs) on a glassy carbon electrode (GCE) using Nafion ionomers. The results obtained by electrochemical impedance spectroscopy, cyclic voltammetry, and rotating disk electrode using the modified QDs?CNafion/GCE in a 0.20?M phosphate buffer of pH 7.0 revealed that the QDs act as effective mediators for the electrocatalytic reduction of dioxygen.     

Novel electrocatalyst for the oxygen reduction reaction in acidic media using electrochemically activated iron 2,6-bis(imino)-pyridyl complexes

Electrochemically activated materials produced from iron 2,6-bis(imino)-pyridyl complexes were deposited onto a glassy carbon electrode from an acetonitrile solution containing 0.1 mol dm⁻³ tetrabutylammonium perchlorate and 0.002 mol dm⁻³ monomeric iron chelate by successively scanning the potential between −0.6 and 0.8 V vs. the Ag/Ag⁺ reference electrode (RE). The electrocatalytic activity of the resultant material to the reduction of dioxygen molecules in aqueous sulfuric acid solution was studied by hydrodynamic voltammetry. It is found that although the material can dissolve in sulfuric acid solution, it is re-deposited on the electrode surface during cathodic polarization. The re-deposited material can efficiently catalyse the electrochemical reduction of molecular dioxygen through different pathways depending upon the structure of the ligands. The material produced from the iron chelate with 2,4,6-trimethylphenyl substituents allows only a two-electron reduction of dioxygen molecules, while the reduction of dioxygen on the material produced from the iron chelate with 2,6-biisopropylphenyl substituents follows the four-electron pathway to produce water. The latter material shows good stability and unusually high mass activity towards the oxygen reduction reaction in the acidic medium. Although the onset potential is quite low (−0.2 V vs. SCE), the material is a prospective candidate in power sources, oxygen sensors and some chemical processes. It is suggested that the active center for oxygen reduction is determined by the structure of the activated material.     

Bioelectrocatalytic mediatorless dioxygen reduction at carbon ceramic electrodes modified with bilirubin oxidase

Carbon ceramic electrodes were prepared by sol-gel processing of a hydrophobic precursor - methyltrimethoxysilane (MTMOS) - together with dispersed graphite microparticles according to a literature procedure. Bilirubin oxidase (BOx) was adsorbed on this electrode from buffer solution and this process was followed by atomic force microscopy (AFM). The electrodes exhibited efficient mediatorless electrocatalytic activity towards dioxygen reduction. The activity depends on the time of adsorption of the enzyme and the pH. The electrode remains active in neutral solution. The bioelectrocatalytic activity is further increased when a fraction of the carbon microparticles is replaced by sulfonated carbon nanoparticles (CNPs). This additive enhances the electrical communication between the enzyme and the electronic conductor. At pH 7 the carbon ceramic electrode modified with bilirubin oxidase retains ca. half of its highest activity. The role of the modified nanoparticles is confirmed by experiments in which a film embedded in a hydrophobic silicate matrix also exhibited efficient mediatorless biocatalytic dioxygen reduction. Scanning electrochemical microscopy (SECM) of the studied electrodes indicated a rather even distribution of the catalytic activity over the electrode surface.     

Preparation and activity of mono- or bi-metallic nanoparticles for electrocatalytic reactions

Improvement of Pt activity for electrocatalytic reactions is possible by modifying Pt nanoparticles with other metals able to activate water. Selected examples are discussed with the electrooxidations of methanol and ethanol or the electroreduction of dioxygen. Nanoparticles electrodes of Pt-Ru (for methanol oxidation), of Pt-Sn (for ethanol oxidation) or of Pt-Cr (for oxygen reduction) supported on carbon powder can be prepared from colloidal precursors. This kind of preparation allows varying the composition and/or the structure of the electrode. The formulation of improved electrodes can be obtained after complete study of the reaction mechanism by “in situ” spectroscopic experiment.     

Co (II) porphyrin adsorbed on SiO2/SnO2/phosphate prepared by the sol-gel method: Application in electroreduction of dissolved dioxygen

This paper describes the immobilization procedure of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21-H,23-H-porphyrin ion on SiO₂/SnO₂/phosphate, obtained by the sol-gel processing method. P 2p X-ray photoelectron and the ³¹P MAS NMR spectra revealed that dihydrogen phosphate is the species present on the surface. The porphyrin was adsorbed on the surface of the modified material and furthermore metallized in situ with Co (II) ion. The porphyrin metallation process was followed with UV-vis spectroscopy by inspecting the Q bands of the free and metallated porphyrin. The free porphyrin presented four Q bands associated to a D_2h local symmetry and the metallated one, two bands related to a D_4h local symmetry. The amount of electroactive species adsorbed on the material was estimated by integrating the area under the peak of Co (II) → Co (I) reduction by using the pulse differential voltammetric technique. The amount of the metallated porphyrin was 2.3 × 10⁻¹⁰ mol cm⁻². A carbon paste electrode of the modified material containing metallated porphyrin was used to study the electrocatalytic reduction of dissolved dioxygen by means of cyclic voltammetry, chronoamperometry and linear sweeping voltammetry. The modified electrode was very stable and exhibited the electrocatalytic reduction of dissolved dioxygen at −180 mV versus SCE by a two-electron mechanism, producing hydrogen peroxide at pH 5.4. The electroactive species was strongly retained on the material surface, presumably inside the pores of the material, since in a test of various oxidation-reduction cycles no significant decrease of the current densities was detected, indicating that it was not leached off during the experiment.