磁控溅射法制备铂及铂钴电催化剂的研究

发布时间：2018-04-10 02:09

  本文选题：质子交换膜燃料电池　切入点：磁控溅射　出处：《南京大学》2017年硕士论文

【摘要】：现如今,Pt/C催化剂依旧是质子交换膜燃料电池中应用最为普遍的催化剂,但由于Pt资源储量有限、价格昂贵,因而增加了燃料电池的成本。为了推动燃料电池商业化的进程,必须改进催化剂的制作方法或改变催化剂的结构,来提高Pt的利用率、降低催化剂中Pt的载量。目前,Pt/C催化剂的制作方法主要有浸渍法、胶体法和微乳液法等,但这些方法的步骤都较为繁琐,将催化剂分散在扩散层或质子交换膜上时,也易导致分散不均,而且单用Pt作为催化剂,存在活性较低且易中毒的问题。磁控溅射法是一种操作较为简便的物理方法,在低压氩气氛围中,磁场与电场交互作用下,氩离子撞击靶材,使溅射粒子均匀分散在基底上,提高了催化剂的均匀性,间接降低了催化层的厚度。本论文利用磁控溅射的方法,首先将还原氧化石墨烯层覆盖的碳纸作为基底,在其表面直流溅射Pt,利用还原氧化石墨烯的高致密性阻止Pt的掉落,从而提高Pt的利用率;其次将扩散层作为基底,在其表面分别直流溅射Pt、双靶共溅射Pt与Co,利用Co对Pt活性的激发,从而降低Pt的载量。具体研究工作如下:首先,我们将氧化石墨悬浊液涂布在碳纸上,在氢氩混合气体氛围中进行热还原后,将铂用直流溅射法沉积在还原氧化石墨烯上,制备出一种结构优化的气体扩散电极。我们考察了氧化石墨溶液浓度及还原温度对还原氧化石墨烯的覆盖率及还原程度的影响,并研究了溅射时气体流量及厚度对气体扩散电极的形貌及性能的影响。结果表明,浓度为1 mg·ml-1的氧化石墨溶液,具有最佳的覆盖率,而且还原温度越高,还原氧化石墨烯中氧含量越少,氧化石墨还原程度越高;随着溅射厚度的增加,Pt薄膜表面会出现明显的凸起和沟壑形貌,气体流量30 scm,厚度为10 nm的Pt膜具有最佳的单电池功率密度175.6 mW·cm-2,最高的电化学活性面积65.4 m2·g-1。从上述结果发现,还原氧化石墨烯能够有效阻挡Pt落入碳纸中;Pt薄膜表面的凸起形貌有利于提高Pt的活性面积,适当的气体流量与厚度能够使其达到峰值,使催化剂发挥出最佳的催化活性。为了降低催化剂中Pt的用量,我们首先将Pt用直流溅射法直接溅射在扩散层上,调整溅射厚度,测试其作为阴极气体扩散电极的质子交换膜燃料电池极化曲线。结果表明,单溅射铂而不使用碳载体,电池性能依旧表现良好。在溅射厚度80 nm时,铂载量0.20 mg·cm-2,最大功率密度可达691.7 mW·cm-2。然后,我们采用双靶共溅的方法,将Pt用直流溅射、Co用射频溅射,同时分散在扩散层上,在氢氩混合气中进行热处理后,测试其单电池性能。结果表明,同样厚度的催化层,双靶共溅射Pt与Co与单一直流溅射Pt的单电池性能相差并不明显。从上述结果发现,高温处理,使Co与Pt形成合金结构,Co的加入,提高了 Pt的催化活性,在性能得以保持的前提下,Pt载量得到明显下降。
[Abstract]:Today Pt- / C catalyst is still the most widely used catalyst in proton exchange membrane fuel cell (PEMFC), but the cost of fuel cell is increased because of the limited Pt resource and high price.In order to promote the commercialization of fuel cells, it is necessary to improve the preparation method of the catalyst or to change the structure of the catalyst to increase the utilization of Pt and reduce the Pt loading in the catalyst.At present, the preparation methods of Pt- / C catalyst are mainly impregnation, colloid and microemulsion methods, but the steps of these methods are complicated, when the catalyst is dispersed on the diffusion layer or the proton exchange membrane, it is also easy to lead to uneven dispersion.Moreover, using Pt as catalyst alone has the problem of low activity and easy poisoning.The magnetron sputtering method is a simple physical method. Under the interaction of magnetic field and electric field in low pressure argon atmosphere, argon ions impact on the target, which makes the sputtering particles dispersed uniformly on the substrate and improves the uniformity of the catalyst.The thickness of the catalyst layer is reduced indirectly.In this paper, the carbon paper coated with reduced graphene layer was first used as the substrate by magnetron sputtering, and the Pt was deposited on the surface by DC sputtering. The high density of reduced graphene was used to prevent the Pt from falling and the utilization rate of Pt was improved.Secondly, the diffusion layer was used as the substrate, and the Pt and Coon were co-sputtering on the surface of the diffusion layer respectively. The Pt activity was excited by Co, thus the loading of Pt was reduced.The specific research work is as follows: firstly, we coated graphite oxide suspension on carbon paper, then deposited platinum on reduced graphene by direct current sputtering after thermal reduction in the mixed gas atmosphere of hydrogen and argon.A gas diffusion electrode with optimized structure was prepared.The effects of the concentration of graphite oxide solution and reduction temperature on the coverage and reduction degree of reduced graphene were investigated. The effects of gas flow rate and thickness on the morphology and properties of gas diffusion electrode during sputtering were studied.The results showed that the graphite oxide solution with concentration of 1 mg ml-1 had the best coverage, and the higher the reduction temperature, the less the oxygen content in the reduced graphene and the higher the degree of reduction of graphite oxide.With the increase of sputtering thickness, the surface of Pt thin film has obvious protruding and gully morphology. The Pt film with the gas flow rate of 30 scm, the thickness of 10 nm Pt film has the best single cell power density of 175.6 MW cm-2, and the highest electrochemical active area is 65.4 m2 g-1.From the above results, it is found that the reduced graphene oxide can effectively block Pt from falling into carbon paper and the protruding morphology of Pt film surface is beneficial to increase the active area of Pt, and the proper gas flow rate and thickness can make it reach its peak value.The catalyst has the best catalytic activity.In order to reduce the amount of Pt in the catalyst, we first directly sputtering Pt onto the diffusion layer by DC sputtering, adjusting the sputtering thickness, and measuring the polarization curve of PEMFC as cathode gas diffusion electrode.The results show that the performance of the battery is still good without carbon carrier.When the sputtering thickness is 80 nm, the platinum loading is 0.20 mg / cm ~ (-2) and the maximum power density is 691.7 MW / cm ~ (-2).Then, by using the method of double target co-splashing, the single cell performance was tested after the Pt was sputtered by DC sputtering with RF sputtering and dispersed on the diffusion layer after heat treatment in the mixture of hydrogen and argon.The results show that there is no significant difference in the performance of Pt and Co with single DC sputtering Pt with the same thickness of catalyst layer.From the above results, it is found that the addition of Co into Pt alloy structure after high temperature treatment improves the catalytic activity of Pt, and decreases the Pt load obviously under the condition of keeping the performance of Pt.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM911.4
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本文编号：1729179