【作者】 黄磊；

【导师】 沈培康；

【作者基本信息】 广西大学 ， 材料物理与化学， 2019， 硕士

【摘要】 铂(Pt)是质子交换膜燃料电池(PEMFCs)中不可缺少的材料,然而有限的储量和过度的消耗严重制约了 Pt基催化剂的可持续发展和广泛应用。与汽油动力汽车相比,目前PEMFCs存在的最主要问题是Pt基催化剂的高成本。因此,只有当Pt基催化剂的成本被有效降低时,PEMFCs才能在未来的新能源汽车市场上更具竞争力。为了应对这些挑战,我们致力于减少Pt的消耗,降低催化剂的成本,改善催化剂的性能。大量的工作已经表明,提高催化性能并且减少Pt消耗最有效的方法,就是通过引入其他的金属元素与Pt进行合金化处理,并且通过调控合成出高原子利用率和开放结构的合金催化剂。本研究主要是通过将Pt与Cu、Ni、Co等过渡金属元素进行合金化处理得到更为高效的合金纳米材料。此外,催化剂的形貌也会对其性能产生很大影响,我们通过制备结构更为开放,更高Pt原子利用率的异形结构纳米材料,从而来提高催化剂的催化活性和稳定性。为了提高Pt基催化剂对甲醇氧化反应(MOR)的催化性能,降低Pt的消耗,我们采用改进的溶剂热法一步合成了径向Pt-Co纳米枝晶(ND)。值得注意的是,通过调节CTAC的量和反应时间,径向Pt-Co ND能够很好的被控制。与此同时,由于其拥有富Pt的表面,大量的第一级纳米枝晶和紧密相连的二级纳米枝晶,径向Pt-Co ND拥有大量的尖端区域,这将促进催化过程中的电子传输和离子交换,提高催化剂的催化性能。此外,与商业Pt/C相比,在甲醇氧化反应中,径向Pt-Co ND具有更高的催化性能和稳定性。这项研究为制备高性能的合金纳米枝晶材料提供了更多的可能。通过采用改进的溶剂热法和独特的二次腐蚀方法,我们合成了 Pt-Cu-Ni菱形十二面体纳米框架(NF)。作为Pt-Cu-Ni纳米框架的中间产物,Pt-Cu-Ni实心固体纳米晶体可以通过调节反应时间和Ni前驱体的量来很好地控制。基于Pt-Cu纳米框架的形成机制,我们在这里研究了三元纳米框架的生长机理和形态演变过程。纳米晶体的形态、原子比和平均粒径的变化已经证明了 Pt-Cu-Ni纳米晶体的形态演化过程。与后续的蚀刻步骤相比,Pt-Cu-Ni实心纳米晶体(SD)的生长机制在整个过程中也是至关重要的。形状可调的纳米框架催化剂在氧还原反应(ORR)中表现出优越的催化性能,Pt-Cu-Ni纳米框架催化剂在0.9 V时显示出0.86 mg-1Pt的质量活性,这是商业Pt/C催化剂的6倍。值得注意的是,与大多数催化剂相比,Pt-Cu-Ni纳米框架催化剂具有更正的起始电位。更重要的是,改进的溶剂热法和二次蚀刻的合成方法为纳米框架催化剂的发展和应用开启了一个新的方法。为了降低催化剂的成本和Pt的消耗,提出了一种简便的电化学置换制备方法,并且可以通过强还原剂和表面活性剂容易地控制纳米结构。通过改变N2的引入,成功地合成了两种不同的Pt-Co球体,Pt-Co核壳球(CSS)和Pt-Co中空合金球(HAS)。有趣的是,Pt-Co CSS具有富含Pt的壳,其具有7个原子层厚度,这促进了 Pt原子的有效利用。Pt-Co HAS具有高度开放的结构和单一合金相。对于MOR来说,Pt-Co CSS和Pt-Co HAS表现出增强的催化性能。与商业的Pt/C催化剂相比,Pt-Co CSSs催化剂的质量活性提高了 4倍,稳定性更好。更重要的是,目前的工作为批量制备Pt基催化剂和合成壳纳米结构打开了大门。更多还原

【Abstract】 Platinum(Pt)is an indispensable material in proton exchange membrane fuel cells(PEMFCs).However,the limited storage and excessive consumption severely restrict the sustainable development and wide application of Pt-based catalysts.Compared with gasoline-powered vehicles,the most important problem in the current PEMFCs is the high cost of Pt-based catalysts.Therefore,only when the cost of Pt-based catalysts is effectively reduced,PEMFCs can be more competitive in the future new energy vehicle market.In order to meet these challenges,we are committed to reducing the consumption of Pt,reducing the cost of the catalyst and improving the catalytic performance of the catalyst.Numerous studies have shown that the most effective way to improve the catalytic performance of the catalyst and reduce the Pt consumption is to alloy the Pt by introducing other metal elements,and to synthesize an alloy catalyst with high atomic utilization and open structure.This study mainly improves the catalytic activity and stability of the catalyst by alloying Pt with Cu,Ni,Co and other transition metal elements to obtain more efficient alloy nanomaterials.In addition,the morphology of the catalyst will also have a great impact on its performance.We prepare nanomaterials with more open structure and higher Pt atomic utilization rate.In order to improve the catalytic performance of the Pt-based catalysts for methanol oxidation reaction(MOR)and reduce the consumption of Pt,we have synthesized radial Pt-Co nanodendrites in one step by modified solvothermal method.It is worth noting that the radial Pt-Co ND can be well controlled by adjusting the amount of CTAC and reaction time.At the same time,radial Pt-Co nanodendrites possess the Pt-rich surface,and lots of tip regions which will promote electron transfer and mass exchange in catalytic processes,because their large number of first-order nanodendrites and closely connected secondary nanodendrites.In addition,radial Pt-Co nanodendrites have higher catalytic performance and stability in methanol oxidation than commercial Pt/C.This study provides more possibilities for the preparation of higher performance alloy nanodendrities catalyst materials.We have synthesized Pt-Cu-Ni rhombohedral dodecahedral framework(NF)by using improved solvothermal method and unique secondary etching method.As an intermediate product of the Pt-Cu-Ni nanoframe,Pt-Cu-Ni solid state nanocrystals can be well controlled by adjusting the reaction time and the amount of Ni precursor.Based on the formation mechanism of Pt-Cu nanoframes,we studied the growth mechanism and morphological evolution of ternary nanoframes.The morphology,atomic ratio and average particle size of nanocrystals have demonstrated the morphological evolution of Pt-Cu-Ni nanocrystals.The growth mechanism of Pt-Cu-Ni solid nanocrystals(SD)is also critical throughout the process compared to subsequent etching steps.The shape-tunable nanoframe catalyst exhibits superior catalytic performance in the oxygen reduction reaction(ORR).The Pt-Cu-Ni nanoframe catalyst exhibits a mass activity of 0.86 mg-1Pt at 0.9 V,which is 6 times higher than that of commercial Pt/C catalyst.It is worth noting that the Pt-Cu-Ni nanoframe catalyst has a more positive onset potential than most catalysts.More importantly,the improved solvothermal and secondary etching methods open the door to the development and application of nanoframe catalysts.To reduce the cost of the catalyst and the consumption of Pt,a facile electrochemical displacement preparation method has been proposed,and the nanostructures can be easily controlled by a strong reducing agent and a surfactant.Two distinct Pt-Co spheres,Pt-Co core-shell spheres(CSSs)and Pt-Co hollow alloy spheres(HASs)are successfully synthesized by changing the introduction of N2.Interestingly,the Pt-Co CSSs possess a Pt-rich shell with 7 atomic layer thickness,which promotes the efficient utilization of Pt atoms.Pt-Co HASs have a highly open structure and a single alloy phase.For MOR,the Pt-Co CSSs and Pt-Co HASs exhibit enhanced catalytic performances.Compared with commercial Pt/C catalyst,the mass activity of Pt-Co CSSs catalyst is increased by 4 times and have better stability.More importantly,the current work opens a door to batch preparation of Pt-based catalysts and synthesis of shell nanostructures.更多还原