NaOH溶液中碱浓度、氧气压力以及温度对Pt电极上氧气还原反应的影响

设计制作一种新型耐压电化学池并采用循环伏安(CV)和线性扫描伏安(LSV)技术系统研究了碱浓度、氧气压力以及温度对NaOH溶液中氧气还原反应(ORR)的影响.研究结果表明,碱浓度、氧气压力和温度对ORR动力学和热力学都有很大的影响.随着碱浓度增大,ORR过程逐渐由2电子(生成HO2-)转为1电子(生成O2-)反应,并且由于氧气溶解度减小和体系粘度增大ORR过程受到很大抑制.增大压力可以明显增加氧气溶解度,从而从动力学上促进ORR过程;同时计算得到了氧气在不同浓度NaOH溶液中的亨利系数.随着介质温度升高,由于氧气反应活性增强、扩散系数增大和溶解度减小的共同作用,表现出在给定浓度下存在一最佳温度使得ORR峰电流达到最大.     

水热条件下坡缕石在NaOH溶液中的行为及结构变化

分别用1,2和3 mol·L^-1的NaOH溶液,在不同的温度条件下对坡缕石进行了侵蚀实验。对反应后的固相产物进行了XRD和SEM分析,对浸出液中的金属阳离子进行了原子吸收光谱分析。讨论了反应温度和碱溶液浓度对碱溶后产物的影响。XRD和SEM结果表明,c_NaOH≤2 mol·L^-1时,坡缕石经碱溶液侵蚀后,可以生成蒙脱石和方沸石,其中反应温度的升高有利于方沸石的形成,碱溶液浓度的升高有利于蒙脱石的形成。当碱溶液浓度达到3 mol·L^-1,反应温度为200 ℃时,最终产物为SiO₂。浸出液的定量分析结果显示,坡缕石与碱溶液的反应过程中,Na⁺对八面体阳离子的置换具有选择性,置换顺序为：Al³⁺＞Fe³⁺(Fe²⁺)＞Mg²⁺。     

阿德福韦酯糖精共晶形成的热力学

测定不同温度下阿德福韦酯(AD)在系列浓度糖精(SAC)乙醇溶液中的溶解度及AD在恒温下系列浓度糖精水溶液中的溶解度, 研究AD-SAC共晶形成的热力学, 得到了共晶的溶度积(K_sp)、络合常数(K₁₁)及反应自由能(ΔG⁰)等热力学参数, 建立了不同温度下的AD-SAC-乙醇三相图. 结果表明: 在乙醇中, 温度对K_sp和K₁₁有极显著性影响(P<0.01), 随着温度的降低, K_sp逐渐减小, K₁₁增大, 共晶的溶解为吸热过程, 共晶的形成为吸热的自发过程, 温度的下降有利于增加AD与SAC在乙醇中的络合效应. AD在SAC水溶液中的溶解度随SAC浓度的升高呈现三阶段特征, 先线性增长至平台区后再倒数下降.     

碱性介质中二(高碘酸根)合铜(Ⅲ)酸根氧化乙二醇独丁醚的反应动力学及机理

在25℃～40℃区间用分光光度法在碱性介质中研究了二(高碘酸根)合铜(Ⅲ)酸根配离子(DPC)氧化乙二醇独丁醚(EGB)的反应动力学。结果表明:反应对DPC为一级,对EGB是1< n_ap< 2(n_ap代表表观反应级数);在保持准一级条件([EGB]₀ 》[Cu(Ⅲ)]₀)下,表观速率常数,k_obs,在弱碱性介质中,随[OH^-]增大而减小,在较强碱性介质中随[OH^-]增大而增大,随着[IO₄^-]增加而减小;无盐效应。提出了含有自由基过程的反应机理,由假设的两种同时进行的反应机理推出的速率方程能很好的解释全部实验现象,进一步求得速控步的速率常数和活化参数。     

属离子与卟啉的嵌入反应动力学研究(Ⅷ)meso-四对羟基苯卟啉与铜(Ⅱ)在DMF中的配位反应

在35.0±0.1℃、离子强度0.1(0.1mol·L^-1NaClO₄)条件下,研究了在N,N'-二甲基甲酰胺溶液中meso-四对羟基苯卟啉与CuⅡ的配位反应动力学。根据在此体系中CuCl₂的缔合状态,溶液氢离子浓度对反应速率的影响,得到铜Ⅱ卟啉生成反应的动力学方程,测量了该反应的活化参量。结果表明反应遵循缔合离解机理,活性中间体的离解是反应的决速步骤。     

Dawson型磷钨杂多阴离子P2W18O626-的电化学性质和对O2还原的电催化作用

用循环伏安、交流伏安和交流阻抗法对Dawson型磷钨杂多阴离子P₂W₁₈O₆₂^6-的电化学性质进行了详细研究, 循环伏安结果显示, P₂W₁₈O₆₂^6-在pH 2.52的0.1 mol·L^-1 Na₂SO₄+NaHSO₄溶液中有两对可逆的单电子还原-氧化波和两对可逆的双电子还原-氧化波. 单电子波的峰电位和电流与溶液的pH无关, 双电子波的峰电位则随溶液pH的增加而负移, 峰电流降低, 表明双电子电极过程有H⁺参与, 其数目为2. 交流阻抗谱表明P₂W₁₈O₆₂^6-的电极过程完全受扩散控制, 实验测定其扩散系数(D_O)为2.5×10^-6 cm²·s^-1. 循环伏安结果表明P₂W₁₈O₆₂^6-的第III对波对O₂还原为H₂O₂具有显著的电催化作用, 催化效率约达300%. 将P₂W₁₈O₆₂^6-应用于PW₁₁O₃₉Fe(III)(H₂O)^4-构成的类电-芬顿过程, 使该过程对硝基苯的降解效率显著提高.     

NO2-对乳酸-丙酮-BrO3--Mn2+-H2SO4化学振荡反应的影响

研究NO₂^-对乳酸-丙酮-BrO₃^--Mn²⁺-H₂SO₄化学振荡反应的影响时发现,NO₂^-对振荡反应的诱导期t_in、周期t_p有显著的影响。NO₂^-的浓度C_NO2^-与诱导期倒数的对数ln(1/t_in)、NO₂^-浓度的对数lnC_NO2^-与周期的对数lnt_p均有良好的线性关系,线性范围为7.46×10^-5～2.99×10^-3mol·L^-1。在此浓度范围内,NO₃^-无影响,是一重现性好,灵敏度高,操作简单的NO₂^-动力学分析测试体系。获得诱导期、周期的表观活化参数E_in、E_p分别为56.82kJ·mol^-1、64.51kJ·mol^-1。结合被动采样法,测得室外大气中NO₂日平均浓度值为1.59×10^-9mol·L^-1,最后对NO₂^-共存时的振荡反应诱导期机理进行了初步探讨。     

HCF(X~1A’)+SO2反应的动力学研究

用激光光解-激光诱导荧光方法研究了室温下(T＝293 K) HCF(X^~1A^’)自由基与SO₂分子的反应动力学. 实验中HCF(X^~1A^’)自由基是由213 nm激光光解HCFBr₂产生的, 用激光诱导荧光(LIF)检测HCF(X^~1A^’)自由基的相对浓度随着反应时间的变化, 得到此反应的二级反应速率常数为: k＝(1.81±0.15)×10^－12 cm³•molecule^－1•s^－1, 体系总压为1862 Pa. 高精度理论计算表明, HCF(X^~1A^’)和SO₂分子反应的机理是典型的加成-消除反应. 我们运用RRKM-TST理论计算了此二级反应速率常数的温度效应和压力效应, 计算结果和室温下测定的二级反应速率常数符合得较好.     

取代基对有机金属铼化合物中分子内α-氢转移反应势垒的影响

使用B3LYP方法研究了有机铼化合物R³R⁵(NHR⁴)Re(＝CHR¹)(＝NR²)中分子内α-氢转移反应, 探讨了不同取代基对α-氢转移反应势垒的影响. 研究发现, 可以通过改变取代基来影响过渡金属Re有机化合物中的α-氢转移反应. R¹位置的取代基为Me或CMe₃时, 可以较大程度降低α-氢转移反应的势垒. R²为H时, α-氢转移反应势垒最低. R³和R⁵位置为SiH₃时的反应势垒最低. R⁴为CMe₃时, α-氢转移反应势垒最低. 研究结果还表明, 取代基对于反应势垒的影响有加和性.     

二(过碘酸根)合铜(Ⅲ)酸根离子氧化二乙醇胺的反应动力学及机理

在25～40℃区间用分光光度法在碱性介质中研究了二(过碘酸根)合铜(Ⅲ)酸根配离子(DPC)氧化二乙醇胺(DEA)的反应动力学。结果表明,反应对DPC为一级,对二乙醇胺是1.7～1.9级。准一级速率常数k_obs随［OH^-］增大而增大,随［IO^-₄］ex(外加的IO^-₄离子浓度)的增加而减小,也随［KNO₃］增大而减小,有负盐效应。在氮气保护下,反应体系能引发丙烯腈聚合。提出了含有自由基过程的反应机理。经此导出的速率方程圆满地解释了全部实验事实,并计算出速控步骤的速率常数及相应的活化参数。     

硼、氮掺杂的二硫化钼用于氧还原电催化研究

对于碱性燃料电池的阴极反应,开发具有优异催化性能的新型催化剂至关重要.本工作采用一种简单的热解方法合成了硼、氮掺杂的二硫化钼(B,N-MoS2)材料并将其应用于氧还原(ORR)电催化分析.通过循环伏安法(CV)与线性扫描伏安法(LSV)等电化学分析方法,采用旋转盘电极(RDE)与旋转环盘电极(RRDE)等技术测试了该材...     

Sodalite‐type Cu‐based Three‐dimensional Metal–Organic Framework for Efficient Oxygen Reduction Reaction

Inspired by copper‐based oxygen reduction biocatalysts, we have studied the electrocatalytic behavior of a Cu‐based MOF (Cu‐BTT) for oxygen reduction reaction (ORR) in alkaline medium. This catalyst reduces the oxygen at the onset (E_onset) and half‐wave potential (E^1/2) of 0. 940 V and 0.778 V, respectively. The high halfway potential supports the good activity of Cu‐BTT MOF. The high ORR catalytic activity can be interpreted by the presence of nitrogen‐rich ligand (tetrazole) and the generation of nascent copper(I) during the reaction. In addition to the excellent activity, Cu‐BTT MOF showed exceptional stability too, which was confirmed through chronoamperometry study, where current was unchanged up to 12 h. Further, the 4‐electrons transfer of ORR kinetics was confirmed by hydrodynamic voltammetry. The oxygen active center namely copper(I) generation during ORR has been understood by the reduction peak in cyclic voltammetry as well in the XPS analysis.     

The electrochemical behavior of PtRu- and Pt-modified zeolite X in alkaline solution

Zeolite NaX was modified by Pt and Pt/Ru nanodispersed metallic clusters. The procedure of impregnation with acetylacetonate salt/acetone solution was applied. Scanning electron microscope analysis confirmed partial zeolite framework destruction. According to energy dispersive X-ray analysis, Pt/Ru ratio in sample was about 1. Electrochemical behavior of PtRu- and Pt-modified zeolites was investigated in alkaline solutions, 5 mM NaOH?+?1 M Na₂SO₄ and 0.1 M NaOH. The shape of cyclic voltammograms of 13XPtRu electrode, recorded in slightly alkaline solution, was greatly affected by the presence of hydrogen that remained in the sample after synthetic procedure. Oxygen reduction reaction (ORR) was investigated in an O₂-saturated aqueous 0.1-M NaOH solution. The obtained Tafel slopes indicated ORR mechanism that involves one-electron discharge-determining step. According to Koutecky–Levich slope, the oxygen reduction reaction followed 4e^? mechanism on both 13XPtRu and 13XPt electrode. The onset of ORR on 13XPtRu electrode was shifted toward more positive potentials in comparison to 13XPt electrode.     

Oxygen reduction on rotating porous cylinder of modified reticulated vitreous carbon

A rotating cylinder porous electrode (RCPE) of reticulated vitreous carbon (RVC) matrix was used for oxygen reduction reaction (ORR) in H₂SO₄ solutions. Cyclic voltammetry and hydrodynamic voltammetric techniques were used for electrochemical characterization of the ORR. Cyclic voltammograms in stationary solutions showed better performance of the anodically oxidized RVC (for periods of 1 and 5 min) for the ORR than the untreated RVC in which the first scan (ORR) after the surface treatment was of no utility, and the second scan was presented here. The hydrodynamic voltammograms obtained at the treated RCPE gave well-defined limiting current plateau with positively shifted onset potential as compared with the untreated (plain) RVC electrode. The analysis of the limiting current data on RCPE and the determination of a limiting current enhancement factor α enabled us to quantify the enhancement extent exerted by the anodic oxidation treatment. An enhancement factor of up to ∼3 was obtained at the RCPE electrode anodically oxidized for 5 min. It was found that the α slightly decreased with the rotation speed depending on the extent of anodic oxidation of RVC. This was attributed to the different mode of mass transfer (diffusion) to the interior of the micropores with different microstructure resulting from different extent of anodic oxidation. X-ray photoelectron spectroscopic and scanning electron microscopic measurements helped us to characterize the anodically oxidized RVC surface.     

克拉霉素的电化学反应机理研究与应用

应用线性扫描伏安法、循环伏安法、常规脉冲伏安法等电化学手段并结合紫外吸收光谱研究了药物克拉霉素(clarithromycin, CAM)在pH 1.8～9.2 Britton-Robinson缓冲溶液和0.05 mol•L^－1 NaOH溶液中的电化学行为. 在所研究的pH范围, CAM分别产生P₁, P₂, P₃, P₄四个还原波, 其中P₁, P₂, P₄三个波均为其药效活性基团C-9位羰基的还原所产生. 实验结果表明: 在pH 1.8～5.7的B-R缓冲溶液条件下所获得的P₁波为两电子不可逆弱吸附还原波; 在6.0＜pH＜9.2的B-R缓冲溶液中, CAM产生P₂和P₃两个波, 其中P₂为两电子不可逆还原波, P₃为催化氢波. 在0.05 mol• L^－1 NaOH溶液中, CAM产生的P₄波是一个单电子的不可逆吸附还原波. 根据P₄波的峰电流i_P与CAM浓度的线性关系, 建立了CAM含量测定的新方法.     

The electrochemical reduction reaction of dissolved oxygen on Q235 carbon steel in alkaline solution containing chloride ions

Cyclic voltammetry, electrochemical impedance spectroscopy, and rotating disk electrode voltammetry have been used to study the effect of chloride ions on the dissolved oxygen reduction reaction (ORR) on Q235 carbon steel electrode in a 0.02 M calcium hydroxide (Ca(OH)₂) solutions imitating the liquid phase in concrete pores. The results indicate that the cathodic process on Q235 carbon steel electrode in oxygen-saturated 0.02 M Ca(OH)₂ with different concentrations of chloride ions contain three reactions except hydrogen evolution: dissolved oxygen reduction, the reduction of Fe(III) to Fe(II), and then the reduction of Fe(II) to Fe. The peak potential of ORR shifts to the positive direction as the chloride ion concentration increases. The oxygen molecule adsorption can be inhibited by the chloride ion adsorption, and the rate of ORR decreases as the concentration of chloride ions increases. The mechanism of ORR is changed from 2e⁻ and 4e⁻ reactions, occurring simultaneously, to quietly 4e⁻ reaction with the increasing chloride ion concentration.     

Effect of lithium ions on oxygen reduction in ionic liquid-based electrolytes

The effect of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) on the oxygen redox reaction (ORR) in several pyrrolidinium-based ionic liquids (ILs) is investigated by cyclic voltammetry. The results are compared to those found with LiTFSI-tetraglyme and LiTFSI-1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidone solutions. The effect of the addition of tris(pentafluorophenyl) borane (TPFPB) to IL-LiTFSI solutions is also investigated. The results demonstrate that the presence of 0.1 M Li⁺ renders the ORR similar in the investigated ILs, lowers the reduction voltammetric currents and makes ORR electrochemically irreversible. The addition of TPFPB to IL-TFSI solutions favours the solubility of oxygen-based products of Li⁺ and should positively affect the performance of IL-based lithium-air batteries.     

Oxygen reduction reaction on carbon-supported palladium nanocubes in alkaline media

Carbon-supported Pd nanocubes with the size of 30, 10 and 7 nm were prepared and their electrocatalytic activity towards the oxygen reduction reaction (ORR) in alkaline solution was studied. For comparison carbon-supported spherical Pd nanoparticles and commercial Pd/C catalyst were used. The catalysts were characterised by transmission electron microscopy, electro-oxidation of carbon monoxide and cyclic voltammetry and the ORR activity was evaluated using the rotating disk electrode method. The ORR on all studied Pd/C catalysts proceeded via four-electron pathway where the rate-limiting step was the transfer of the first electron to O₂ molecule. The specific activity of Pd nanocubes was more than two times higher than that of spherical Pd nanoparticles and increased with increasing the particle size.     

Electrocatalysis of Cyclic Voltammetrically Prepared Co‐MnO2 Composite towards Oxygen Reduction Reaction (ORR)

For the first time, cobalt particles were electrodeposited on the surface of manganese oxides by cyclic voltammetry (CV) from an aqueous solution of 0.1 M Na₂SO₄ containing 5 mM CoSO₄, and then the samples obtained were characterized by scanning electron microscopy (SEM) and energy dispersive X‐ray analysis (EDAX), respectively. And then, the as‐prepared Co/MnO₂‐coated graphite electrode was employed to the oxygen reduction reaction (ORR). Interestingly, the reduction peak potential of ORR on a Co/MnO₂‐modified graphite electrode was positively shifted for about 100 mV as compared with that on a MnO₂‐modified graphite electrode, indicating that the electrocatalysis of Co/MnO₂ composite towards ORR is superior to that of pure MnO₂.     

Electrocatalytic Reduction of Oxygen at Anthraquinonedisulfonate/Polypyrrole Composite Film Modified Electrodes and Its Application to the Electrochemical Oxidation of Azo Dye

We report here the electrocatalytic reduction of oxygen on thin anthraquindisulfonate (AQDS)/poplypyrrole (PPy) composite film modified electrodes and its application to the electrooxidation of azo dye‐amaranth. The polymer‐coated cathode exhibited good electrocatalytic activity towards oxygen reduction reaction (ORR), and allowed the formation of strong oxidant hydroxyl radical (^.OH) in the medium via Electro‐Fenton's reaction between cathodically generated H₂O₂ and added or regenerated Fe²⁺. The electrochemical behaviors of ORR in various pH solutions were described using cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometric (CA) techniques. The effect of solution pH on amaranth mineralization by the Fe²⁺/H₂O₂ and Fe³⁺/H₂O₂ electrooxidation systems was studied. In addition, the long‐term electrocatalytic activity and stability of the AQDS/PPy composite film during multiple experimental runs were also examined electrochemically.