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Pt基一维纳米材料的可控合成及其电催化研究
论文作者:童鞋论文网  论文来源:www.txlunwenw.com  发布时间:2019/9/3 9:49:05  

摘要:以甲醇为燃料的质子交换膜燃料电池(即直接甲醇燃料电池,DMFC)由于其高能量转换效率、高功率密度以及环境友好等特点,有望应用于汽车和便携式电子设备等设备的下一代动力源。然而,为了确保足够的能量效率和功率输出,DMFC的阴阳极电化学反应仍需使用大量贵金属铂催化。自然界中铂资源有限,售价昂贵,铂材料在催化活性和耐久性上的不足极大地制约了DMFC的商业应用。因此,迫切需要设计开发新型的Pt基催化剂,以期大幅提升Pt在阳极甲醇电氧化(MOR)和阴极氧气电还原(ORR)上的活性、耐久性和原子经济性。

本文设计制备了两种一维Pt基纳米电催化剂,即铂碲铜合金纳米管(PtTeCu NT)和铂铜合金纳米带(PtCu NB)。此外,以乙酸为催化剂,制备了一个共轭共价有机框架聚合物(TQ-BTA-COF)作为铂催化剂的载体。使用高分辨透射电镜(HRTEM)、场发射扫描电镜(FESEM)、电感耦合等离子体光谱发射仪(ICP-AES)、X射线粉末衍射(XRD)和X射线光电子能谱(XPS)等对所制备的电催化剂进行了结构和物性表征;使用循环伏安(CV)、线性扫描循环伏安(LSV)和加速衰减实验(ADT)等对电催化剂进行电化学研究。取得的主要研究结果如下:

(1) 首先,通过水热反应合成了碲纳米线(Te NW),在乙二醇中以Te NW为牺牲模板,水合肼为还原剂及随后的化学修饰处理,成功合成了PtTeCu NT,并对其进行了结构、物性和和电化学性能研究。结果显示,热处理温度为150 ℃时得到的PtTeCu NT催化剂(PtTeCu-150)在酸性介质中显示了高的ORR活性和优秀的稳定性,其质量比活性达到141.9 A g-1约为商业化催化剂Pt/C-JM的3倍,其面积比活性达到6.58 A m-2,约为Pt/C-JM的6~7倍。

(2) 其次,在无任何模板分子或表面活性剂的条件下,以氯铂酸钠为铂源,氯化铜为铜源,酸化的XC-72R炭黑为载体,通过一锅法制备得到PtCu NB,对制备反应使用的溶剂对PtCu NB的电催化性能的影响进行了详细研究。结果显示,在六个醇溶剂中,在甲醇中制备的PtCu NB催化剂显示了最高的电催化性能。

(3) 最后,以六羰基酮和四氨苯为反应物,DMF或DMSO为溶剂,乙酸为催化剂,经由水热反应合成了TQ-BTA-COF,并研究了合成反应中溶剂对其电化学性能的影响。研究显示,由于电活性的吡嗪单元基团的存在,TQ-BTA-COF显示出一定的氧化还原活性。在DMF中合成的TQ-BTA-COF的氧化还原可逆性优于在DMSO中得到的TQ-BTA-COF的可逆性。进一步将TQ-BTA-COF与石墨烯复合得到TQ-BTA-COF/Gr复合物,并以TQ-BTA-COF/Gr复合物为载体,制备了纳米铂簇负载的TQ-BTA-COF/Gr (Pt/TQ-BTA-COF/Gr),初步考察了其对ORR的电催化性能。

Direct methanol fuel cell (DMFC), as one of the proton exchange membrane fuel cell, uses methanol as fuel. DMFCs can be applied to next-generation powers for automobiles and portable electronic devices due to their high energy conversion efficiency, high power density and low environmental pollution. However, in order to ensure sufficient energy efficiency and output power, the electrochemical reaction within the anode and cathode of DMFC still requires to be catalysized using high-load noble metal platinum. Platinum resources in nature are scarce and its price is very expensive. Poor activity and durability of platinum catalysts greatly restricts the commercial application of DMFC. Therefore, it is urgent to design and develop a novel Pt-based alloy catalyst to greatly improve the activity, durability and atomic economy of Pt in methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR).

In this dissertation, two Pt-based one-dimensional nanoelectrocatalysts, namely platinum-tellurium-copper nanotubes (PtTeCu NTs) and platinum-copper nanobelts(PtCu NBs), were synthesized. Further, a conjugated covalent organic framework compound (TQ-BTA-COF) was prepared using acetic acid as a catalyst. Which acts as a carrier for platinum nanoelectrocatalysts. The structure and physical properties of the prepared catalyst were characterized by high resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), inductively coupled plasma optical emission spectrometry (ICP-AES), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The prepared catalyst was also electrochemically characterized using cyclic voltammetry (CV), linear sweep cyclic voltammetry (LSV), and accelerated decay experiments (ADT).The main results are as follows:

(1) Firstly, the Te nanowires were prepared by hydrothermal method. Then the PtTeCu nanotubes were synthesized in ethylene glycol by using Te nanowires as sacrificial templates, hydrazine hydrate as reducing agents and subsequent chemical modification. The PtTeCu NTs catalysts were studied by physical properties and electrochemical properties. The experimental results indicate that the PtTeCu NT catalyst obtained at a heat treatment temperature of 150 °C (PtTeCu-150) shows high ORR activity and excellent catalytic stability in an acidic medium. Its mass specific activity is 141.87 A g-1, which is about 3 times that of Pt/C-JM. And its area specific activity is 6.58 A m-2, which is about 6 to 7 times that of Pt/C-JM.

(2) Secondly, PtCu NBs were achieved by a simple one-pot method without any template molecules or surfactant using chloroplatinate sodium as the platinum source, copper chloride as the copper source and acidified carbon black as the support, respectively. The effect of the solvent used in the preparation reaction on the ORR performance of the PtCu NB catalyst was investigated in detail. The experimental results show that among the various solvents used, the PtCu NB catalyst obtained with methanol as the solvent showed the highest mass specific activity and area specific activity.

(3) Finally, the TQ-BTA-COF was synthesized by hydrothermal method using hexacarbonyl ketone and 1,2,4,5-tetraaminobenzene as the raw materials, DMSO or DMF as the solvents and acetic acid as the catalyst, respectively. Electrochemical studies have shown that TQ-BTA-COF polymers have electroactive pyrazine unit groups. The effect of solvent on the electrochemical performance of TQ-BTA-COF in the synthesis reaction was investigated. Then TQ-BTA-COF was combined with graphene to obtain TQ-BTA-COF/Gr composite. In addition, the electrocatalyst (Pt/TQ-BTA-COF/Gr) was prepared by loading the nano-platinum cluster on the TQ-BTA-COF/Gr composite, its electrocatalytic performance of ORR was preliminarily investigated.

关键词:直接甲醇燃料电池;Pt基合金催化剂;氧还原反应;甲醇氧化反应;共价有机框架聚合物

direct methanol fuel cell; Pt-based alloy catalyst; oxygen reduction reaction; methanol oxidation reaction; covalent organic framework polymer

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