基于高稳定性核壳材料的燃料电池阴极催化剂研究

发布时间：2018-03-08 04:25

本文选题：直接醇类燃料电池　切入点：氧还原反应　出处：《燕山大学》2014年博士论文　论文类型：学位论文

【摘要】：作为一种环保高效的新能源技术，直接醇类燃料电池（DMFC）具有启动和工作温度低、比功率高、比能量高、工作电流大等特点，是目前最接近大规模商业化的燃料电池。DMFC中电极催化剂是该电池装置的核心部件之一，关系到DMFC的工作效率、使用寿命、制备成本等。炭黑负载铂基催化剂（Pt/C）是应用最为广泛的DMFC电极催化剂。但Pt/C的稳定性较差，特别是在DMFC阴极的高氧气浓度、高电势的环境中，Pt/C比较容易失去活性。这无疑缩短了DMFC的使用寿命。此外，铂是一种贵金属，它的使用增加了DMFC的制造成本。使用高稳定载体材料可以有效提高铂基催化剂的稳定性，而制备高稳定性的非铂催化剂取代铂基催化剂是降低DMFC制造成本的有效途径。本文以高稳定的纳米金刚石（nanodiamond ND）和纳米碳化硅（nano-SiC）为基础材料，，制备新型核壳材料，并将之用于制备高稳定的DMFC阴极铂基以及非铂催化剂。具体内容如下： 1）在高于10-2Pa的真空环境中，对ND和nano-SiC进行1300-1600C的热处理，可以使二者表面石墨化，形成表面石墨烯层覆盖的ND（ND@G）和碳化硅(SiC@G)。因为有高稳定性的ND和nano-SiC为核，同时又有高导电性的石墨烯壳层，所以ND@G和SiC@G同时兼具了高稳定性和较好的导电性。以二者为载体，制备铂催化剂（Pt/ND@G和Pt/SiC@G）能够避免因为载体材料被腐蚀氧化而导致的催化剂失活。通过在0.5mol/L的硫酸（H2SO4）溶液中进行加速老化试验(ADT)，可以发现在Pt载量相同时，Pt/ND@G和Pt/SiC@G表现出了远高于Pt/C的稳定性，同时还具有相近甚至略好于Pt/C的阴极氧还原反应（oxygen reduction reaction, ORR）催化活性。 2）利用浓氢氟酸与浓硝酸的混合溶液（体积比1:2），对nano-SiC进行选择性刻蚀处理，在其表面形成富含含氧官能团的无定型碳层(SiC@O-G)。含氧官能团能够为纳米铂颗粒提供形核点，进而增加载体与纳米铂颗粒之间的结合力。这使得纳米铂颗粒的迁移团聚被遏制，加之高稳定SiC为核心的支撑作用，SiC@O-G负载的铂基催化剂的ADT测试结果也明显优于Pt/C。 3）以ND为原料，分别制备了核壳结构的非铂催化剂——表层为氮掺杂或铁、氮共掺的石墨烯，核心为ND的N-ND@G和Fe-N-ND@G。首先对ND@G进行氧化，再将其与三聚氰胺混合，在N2氛中进行热处理可以获得N-ND@G；而在ND表面负载纳米Fe(OH)3颗粒，将其与三聚氰胺混合，在N2气氛下保温850C热处理3小时，ND在Fe催化剂作用下表面石墨化的同时实现Fe、N掺杂，获得Fe-N-ND@G。通过电化学实验，可以发现N-ND@G和Fe-N-ND@G在碱性条件下，对ORR具有较高的催化活性。在-0.2V（vs. Hg/HgO）高电势区域，N-ND@G和Fe-N-ND@G催化的ORR反应电子数分别达到3.7和3.9，为近四电子反应。其中N-ND@G催化ORR的LSV曲线的半波电位值为-0.12V（vs. Hg/HgO），与载量为20wt%的Pt/C（半波电位-0.052V vs. Hg/HgO）相比仅相差68mV。吡咯型N、吡啶型N和石墨型N间的协同作用是使N-ND@G具有较高ORR催化活性的主要因素。Fe-N-ND@G的催化ORR的LSV曲线的半波电位值为-0.097V（vs. Hg/HgO），对ORR催化活性要高于N-ND@G，更加接近Pt/C催化剂，这说明Fe与N共掺进一步提高了ORR催化活性。而且N-ND@G和Fe-N-ND@G都具有极高的稳定性，是极具潜力的非铂催化剂。
[Abstract]:As a kind of environmental protection, new energy technology, direct methanol fuel cell (DMFC) has a start and low working temperature, high specific power, high specific energy, working characteristic of the large current, is the electrode catalyst of fuel cell.DMFC is the most close to the large-scale commercial application is one of the core components of the battery device, related to DMFC the work efficiency, service life, cost of preparation. The platinum based catalysts supported on carbon black (Pt/C) is the most widely used DMFC electrode catalyst. But the stability of Pt/C is poor, especially in the high oxygen concentration of DMFC cathode, high potential environment, Pt/C is easy to lose activity. This will reduce the DMFC service life. In addition, platinum is a precious metal, its use has increased the production cost of the DMFC.
The use of high stable carrier material can effectively improve the stability of platinum based catalysts, and non platinum catalysts with high stability to replace platinum based catalysts is an effective way to reduce the manufacturing cost of DMFC. The high stability of nano diamond (nanodiamond ND) and nanometer silicon carbide (nano-SiC) as basic material, preparation of novel core-shell materials. And used the DMFC cathode platinum based preparation of high stable and non platinum catalyst. The specific contents are as follows:
1) in a vacuum environment is higher than that of 10-2Pa, ND and 1300-1600C on heat treatment of nano-SiC, can make the two graphite surface, formed on the surface of graphene layer covered ND (ND@G) and silicon carbide (SiC@G). Because of the high stability of ND and nano-SiC as the core, and has the high conductivity of graphene shell electric, so ND@G and SiC@G are both high stability and good conductivity. In two as the carrier, the preparation of platinum catalysts (Pt/ND@G and Pt/SiC@G) can avoid the catalyst carrier material is caused by corrosion oxidation inactivation. The sulfur acid 0.5mol/L (H2SO4) solution for accelerated aging test (ADT), can be found in the same Pt load, Pt/ND@G and Pt/SiC@G showed stability is much higher than that of Pt/C, but also has similar or even slightly better than the cathodic oxygen reduction reaction of Pt/C (oxygen reduction reaction, ORR) catalytic activity.
2) using a mixed solution of concentrated hydrofluoric acid and nitric acid (volume ratio 1:2), nano-SiC selective etching process, the formation of amorphous carbon layer rich in oxygen-containing functional groups on the surface (SiC@O-G). Oxygen containing functional groups can provide nucleation sites for platinum nanoparticles, and further increasing the binding force between the body and the loading of platinum nanoparticles this makes the migration of particles. The platinum nanoparticles agglomeration were checked, and support the role of high stable SiC as the core, the ADT test results of platinum based catalysts supported on SiC@O-G is obviously superior to that of Pt/C.
3) using ND as the raw material were prepared by the non - platinum catalyst surface core-shell structure for nitrogen doped graphene or iron, nitrogen doped, ND N-ND@G and Fe-N-ND@G. as the core of the first oxidation of ND@G, and then mixed with melamine, heat treatment in N2 atmosphere of N-ND@G can be obtained; while on the surface of ND nano Fe (OH) 3 particles with the mixture of melamine, under N2 atmosphere heat preservation heat treatment of 850C for 3 hours, at the same time, the realization of Fe, ND in Fe under the effect of catalyst surface graphitization of N doped Fe-N-ND@G. by electrochemical experiments, can be found in N-ND@ G and Fe-N-ND@G in alkaline condition. The high catalytic activity of ORR. -0.2V (vs. Hg/HgO) in the high potential region, ORR reaction catalyzed by Fe-N-ND@G and N-ND@G electron number reached 3.7 and 3.9, nearly four electron reaction. The half wave potential of LSV curve of N-ND@G catalyzed by ORR as the value of the -0.12V (vs. Hg/HgO), and Load is 20wt% (Pt/C -0.052V vs. Hg/HgO half wave potential) compared to a difference of only 68mV. pyrrole type N, synergistic effect of pyridine type N and type N graphite is the half wave potential of LSV curve of ORR.Fe-N-ND@G catalytic main factors in the N-ND@G has a high catalytic activity of ORR the value of -0.097V (vs. Hg/HgO), the the catalytic activity of ORR is higher than N-ND@G, more close to the Pt/C catalyst, which shows that Fe and N Co doped to further improve the catalytic activity of ORR. And has high stability of N-ND@G and Fe-N-ND@G, is a non platinum catalyst potential.

【学位授予单位】：燕山大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：O643.36;TM911.4

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