碳载钴酞菁催化剂的制备及其氧还原催化性能研究

研究了一种通过固相加热一步合成碳载钴酞菁复合催化剂(CoPc/C)的制备方法.通过XRD,IR对制备的催化剂进行了表征.结果显示,得到的产物为CoPc/C,平均粒径30nm.利用极化曲线和交流阻抗等电化学方法测试了其在碱性介质中对氧还原的催化性能.该催化剂在碱性介质中(6mol·L-1KOH)空气气氛下,氧还原的初始电位达到0V,电极电位为-0.10V vs·Hg/HgO时电流密度达到100mA·cm-2,有显著的氧还原电催化效果.对实验得到的极化曲线及交流阻抗数据进行拟合处理及计算,获得相关动力学参数.     

多壁纳米碳管空气电极的交流阻抗研究

研究了多壁纳米碳管、活性炭和石墨等空气电极的交流阻抗特性.结果表明,纳米碳管空气电极的阻抗谱由两个半圆组成,高频区半圆对应欧姆极化阻抗,低频区半圆对应电化学极化阻抗.催化剂Pt以纳米颗粒的形式沉积在碳管的外表面,明显减小了电极的欧姆阻抗和电化学极化阻抗,提高了氧还原反应的电催化活性.活性炭电极除存在电化学阻抗外,还存在薄液膜扩散阻抗(Nernst扩散),石墨电极形成的薄液膜反应区域较小,电极反应呈Warburg扩散阻抗特征,相应的电催化活性较低.采用交流阻抗等效电路分析方法,对拟合的动力学数据进行了解释.     

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.     

双核双金属酞菁(FeCoPc_2)阴极催化直接硼氢化物燃料电池

研制一种无膜型直接硼氢化物燃料电池(DBFC).循环伏安测试发现FeCoPc2在碱性溶液中对氧还原具有催化作用.稳态极化曲线表明,由于FeCoPc2结构具有较强的共轭效应以及Fe、Co在催化中的协同作用使它比FePc、CoPc具有更强的氧还原能力,并获得了110mW/cm2的功率密度.恒电流放电测试表明该燃料电池性能具有良好的稳定性.     

碳载钴酞菁催化剂的一步法制备及其在碱性条件下对氧的电催化还原

通过固相加热,一步合成了以VulcanXC-72(碳黑)为载体的碳载钴酞菁(CoPc/C)复合催化剂,其可用作空气电极的氧还原催化剂。通过X射线衍射、红外光谱等测试技术对催化剂进行了表征。利用极化曲线和交流阻抗(EIS)方法测试了其在碱性介质(6mol/LKOH)中对氧还原的催化性能。结果显示,得到的产物为CoPc/C复合物,平均粒径30nm。以磷酸处理的碳黑为载体,在600℃下制备的CoPc/C复合催化剂表现出最佳的催化活性。以其制备的电极在空气气氛下-0.03V(Hg/HgO)电位时即可产生明显氧还原电流,-0.2V时电流密度达90×10-3A/cm2。     

温度对尖晶石LiMn2O4中锂离子嵌脱过程的影响

运用电化学阻抗谱研究了商品化尖晶石LiMn₂O₄电极在1 mol/L LiPF₆-EC(碳酸乙烯酯):DEC(碳酸二乙酯)电解液中―10～30 ℃范围内的阻抗谱特征、固体电解质相界面(SEI)膜阻抗、电子电阻和电荷传递电阻等随温度的变化. 研究结果表明, 尖晶石LiMn₂O₄电极的阻抗谱特征与温度有关, 随温度的升高, 与活性材料电子电导率相关的半圆和与SEI膜相关的半圆会发生重叠而成为一个半圆. 通过选取适当的等效电路拟合了实验所得的电化学阻抗谱数据, 测得尖晶石LiMn₂O₄电极在1 mol/L LiPF₆-EC:DEC 电解液中, 锂离子迁移通过SEI膜的离子跳跃能垒平均值为15.49 kJ/mol; 电子电导率的热激活化能平均值为24.21 kJ/mol; 嵌入反应活化能平均值为53.07 kJ/mol.     

镍纳米线电极的交流阻抗研究

用交流阻抗法研究了一种新型电极－镍纳米线电极在碱性溶液中的电化学行为,给出了相应的等效电路和拟合效果。实验结果表明,外加电位对电极表面化学反应速度和类型有显著影响。在外加电位不高时,Ni（Ⅱ）氧化成Ni(Ⅲ)的电化学过程随着电位的升高而明显加速;当外加电位高于0．40V以后,电极表面同时发生电化学析氧反应。相同条件下,镍纳米线电极的表面电化学反应速度远远高于镍块体电极。     

双酚A在硼掺杂金刚石薄膜电极上的电化学行为研究

硼掺杂金刚石(BDD)薄膜电极是用于废水处理的理想电极材料。利用循环伏安法和电化学阻抗谱研究了环境激素双酚A(BPA)在BDD电极上的电化学行为,分析在电极/溶液界面上的电化学过程及相关的电极动力学参数。研究发现BPA在电极上的直接电化学氧化过程为不可逆过程,氧化峰电势在1.4 V左右。电极/溶液界面的双电层结构可以用一个电容与一个电阻并联的等效电路来进行拟合,当极化电位从0.5 V增加至2.0 V时,电荷转移电阻Rct由7.043×104Ω·cm2降至1.366×103Ω·cm2,下降了80.60%,表明提高电极电位可明显降低电催化反应的电阻,有利于电催化氧化反应的进行,可提高电催化反应速率。     

尖晶石LiMn2O4中锂离子嵌入脱出过程的电化学阻抗谱研究

运用电化学阻抗谱(EIS)研究了尖晶石LiMn2O4电极的首次充放电过程. 发现EIS谱高频区域拉长压扁的半圆是由两个半圆相互重叠而成的, 分别归属于与锂离子通过固体电解质相界面膜(SEI膜)的迁移和与尖晶石LiMn2O4材料的电子电导率相关的特征. 通过选取适当的等效电路, 对实验所得的电化学阻抗谱数据进行拟合, 获得尖晶石LiMn2O4电极首次充放电过程中SEI膜电阻、电子电阻和电荷传递电阻等随电极极化电位变化的规律. 根据研究结果提出了嵌锂物理机制模型.     

贮氢电极的电化学研究（Ⅱ）—贮氢电极的交流阻抗研究

用交流阻抗的方法对贮氢电极进行了研究。实验表明，贮氢电极的交流阻抗图由两个半圆组成，高频区半圆对应于电化学反应，低频区半圆对应于氢原子在贮氢合金表面的吸附过程。低频区的半圆受电极活化次数和放电深度的影响。活化次数越多、放电时间越长、低频区半圆越小。提出了贮氢电极的等效电路图，对这些实验结果作出了解释。     

A comparative DFT study of oxygen reduction reaction on mononuclear and binuclear cobalt and iron phthalocyanines

The oxygen reduction reaction (ORR) catalyzed by mononuclear and planar binuclear cobalt (CoPc) and iron phthalocyanine (FePc) catalysts is investigated in detail by density functional theory (DFT) methods. The calculation results indicate that the ORR activity of Fe-based Pcs is much higher than that of Co-based Pcs, which is due to the fact that the former could catalyze 4e^- ORRs, while the latter could catalyze only 2e^- ORRs from O₂ to H₂O₂. The original high activities of Fe-based Pcs could be attributed to their high energy level of the highest occupied molecular orbital (HOMO), which could lead to the stronger adsorption energy between catalysts and ORR species. Nevertheless, the HOMO of Co-based Pcs is the ring orbital, not the 3d Co orbital, thereby inhibiting the electron transfer from metal to adsorbates. Furthermore, compared with mononuclear FePc, the planar binuclear FePc has more stable structure in acidic medium and more suitable adsorption energy of ORR species, making it a promising non-precious electrocatalyst for ORR.     

Pt/C催化剂氧还原反应的交流阻抗动态研究

本文通过RDE和EIS联合技术、等效电路模型,研究了酸性体系中商业Pt/C催化剂ORR行为. 研究发现Pt/C动态界面包括两个彼此独立的过程：1）Pt表面原有PtO还原至Pt过程,2）ORR促进新PtO形成过程,为催化材料稳定性及活化性提供了关键依据;并发现动态界面促进多孔电极重构以及与传输匹配过程.在高过电位下,ORR的高反应速率可通过增加催化材料憎水性予以改善. 上述研究结果可对ORR的直流电化学研究进行有效补充,并提供建模基础.     

Electrocatalytic activity of carbon-supported metallophthalocyanine catalysts toward oxygen reduction reaction in alkaline solution

Carbon-supported metallophthalocyanine catalysts, composed of a transition central metal M (M = Co, Mn, Ni, Fe) in the phthalocyanine ring, were synthesized in this work. As cathodic reaction in a fuel cell, the oxygen reduction reaction (ORR) was investigated in alkaline medium with linear scanning voltammetry at the surface of these electrocatalysts deposited onto a rotating disk electrode (RDE). It was found that the number of electrons transferred depended on the nature of the metallic cation in the catalyst. Evidences provided with Koutecky-Levich approach showed that iron phthalocyanine (FePc) exhibited the better electrocatalytic ability toward the ORR with four electrons exchanged and low activation overpotential. Among these different as-prepared materials, MnPc and FePc led to a four-electron pathway, while CoPc and NiPc proceeded by a two-electron route. The latter reaction process was also determined with a rotating ring-disk electrode (RRDE), which allowed the determination of hydrogen peroxide formed as O₂ reduction intermediate in a small amount, i.e., less than 1.2 %.     

Ambient temperature oxygen sensors based on fluoride solid electrolyte: the roles of the constituents in the sensing electrode mixtures containing phthalocyanines

The short-circuit-current response properties of ambient temperature oxygen sensors of the type, Ag|Ag(6)I(4)WO(4)|PbSnF(4)(PSF)| sensing electrode (SE), O(2); SE: mixtures of Pt-black/Pc's/PSF, carbon/Pc's/PSF, Pc's/PSF, Pt-black/PSF, carbon/PSF (phthalocyanines, Pc's: FePc, CoPc, CuPc, H(2)Pc) have been examined to elucidate the roles of the incorporated Pc's, Pt-black and carbon. FePc and CoPc act as the catalyst for the SE-reaction involving the two-electron reduction of oxygen, whereas CuPc and H(2)Pc have not such a catalytic action. The difference is related to the types of the first oxidation of Pc's, i.e. the central metal oxidation and the ligand oxidation. In addition, the sensitivity (S) and 90% response time (t(90)) depend on the oxidation potentials. FePc is the best of the Pc's used here in terms of t(90) (i.e. 40 s for the SE-mixtures of Pt-black/FePc/PSF and carbon/FePc/PSF). Although Pt-black acts as the catalyst, it tends to give rise to hysteresis, drifts and slow response. The undesirable effects are lessened by incorporating Pc's. For the Pt-black/FePc/PSF sensor, the response properties are almost dominated by the incorporated FePc and hence are comparable to those of the C/FePc/PSF sensors. This indicates that Pt-black can be substituted by carbon materials. The incorporated carbon has no such catalytic action. The role is to make the SE-mixtures more electronically conductive, resulting in the improvement of S and t(90).     

Does CO poison Fe-based catalysts for ORR?

Catalysts for the oxygen reduction reaction (ORR) were prepared on carbon black (C) using Fe^IIphthalocyanine (FePc) and Cl–Fe^IIItetramethoxyphenylporphyrin (ClFeTMPP), as Fe precursors with and without a pyrolysis step at 800 °C. CO poisoning of the ORR catalytic sites for all these Fe/N/C electrocatalysts was attempted at pH 1 and 13, but to no avail, even if an iron ion is known to occupy the center of the active sites in at least the unpyrolyzed FePc/C or ClFeTMPP/C. The exact nature of the active center of these Fe-based heat-treated catalysts may still be a subject of debate but, in light of the absence of CO poisoning for unpyrolyzed FePc/C and ClFeTMPP/C, resistance to CO poisoning by the heat-treated catalysts cannot be used as evidence that the active center of their catalytic site is devoid of iron.     

Electronic Configuration Regulation by N-Doped MXenes Boosting Electrocatalytic Performance of Cobalt Phthalocyanine

The precise control of electronic configurations of catalytic sites via molecular engineering is significantly desirable for boosting electrocatalytic activity. We reported a new-type composite electrocatalyst with cobalt phthalocyanine supported on N-doped MXene nanosheets (N-MXene/CoPc) through a self-assembly process. Beneficial from the joint action of N sites participation and axial coordination, N-MXene/CoPc exhibits a high ORR activity with positive onset potential (E_onset=0.98 V vs. RHE) and half-wave potential (E_1/2=0.863 V), which is superior over the pristine CoPc (E_1/2=0.72 V) and the composite with undoped MXene as support (MXene/CoPc, E_1/2=0.771 V). Additionally, N-MXene/CoPc exhibits an excellent durability with only 8.5 % attenuation after 25000 s of continuous i-t test, while a more obvious decay 18.6 % for 20 wt.% Pt/C. This work not merely reported a robust ORR catalyst, but more provides a reasonable design strategy for nonnoble-metal catalysts through catalyst-support interactions.     

金属酞菁与高价金属盐或氧化物在乙苯液相催化氧化反应中的协同效应

金属络合物催化饱和烷烃的选择性催化氧化一直是有机合成中具有挑战性的课题之一.饱和烷烃的催化氧化可采用各种氧源,如PhIO、H2O2、有机过氧化物或次氯酸盐等[1,2],然而采用分子氧为氧源对烃类化合物进行选择性催化氧化一直是人们致力于解决的目标.利用分子氧为氧源实现饱和烷烃的选择性催化氧化大致可分为两条路线:(1)在共还原剂(H2,醛,抗坏血酸)存在下利用原位产生的氧化剂的催化氧化[3,4];(2)金属卟啉[5]、杂多酸[6]及其它催化剂对饱和烷烃的直接催化氧化.路线(1)需要消耗大量的共还原剂,实际上是对分子氧的间接利用,不具有明显的实…     

Biaxially-Strained Phthalocyanine at Polyoxometalate@Carbon Nanotube Heterostructure Boosts Oxygen Reduction Catalysis

Iron phthalocyanine (FePc) with unique FeN₄ site has attracted increasing interests as a promising non-precious catalyst. However, the plane symmetric structure endows FePc with undesired catalytic performance toward the oxygen reduction reaction (ORR). Here, we report a novel one-dimensional heterostructured ORR catalyst by coupling FePc at polyoxometalate-encapsulated carbon nanotubes (FePc-{PW₁₂}@NTs) using host-guest chemistry. The encapsulation of polyoxometalates can induce a local tensile strain of single-walled NTs to strengthen the interactions with FePc. Both the strain and curvature effects of {PW₁₂}@NT scaffold tune the geometric structure and electronic localization of FeN₄ centers to enhance the ORR catalytic performance. As expected, such a heterostructured FePc-{PW₁₂}@NT electrocatalyst exhibits prominent durability, methanol tolerance, and ORR activity with a high half-wave potential of 0.90 V and a low Tafel slope of 30.9 mV dec⁻¹ in alkaline medium. Besides, the assembled zinc-air battery demonstrates an ultrahigh power density of 280 mW cm⁻², excellent charge/discharge ability and long-term stability over 500 h, outperforming that of the commercial Pt/C+IrO₂ cathode. This study offers a new strategy to design novel heterostructured catalysts and opens a new avenue to regulate the electrocatalytic performance of phthalocyanine molecules.