PtAu合金纳米线合成及对甲酸的电氧化性能

发布时间：2018-06-21 23:59

本文选题：PtAu合金 + 纳米线　；参考：《湖南大学》2015年硕士论文

【摘要】：纳米材料用于直接甲酸燃料电池(DFAFC)的阳极氧化已经研究了近十年,并正在成为便携式电源系统的研究的一个重要领域。与直接甲醇燃料电池(DMFC)相比,甲酸通过Nafion膜具有较小的交叉通量在DFAFC可以允许使用高度浓缩燃料溶液或更薄的膜。而甲醇容易透过Nafion膜使电池性能下降。甲酸是在室温下一种液体物质,并且是安全的食品添加剂。自2002年以来,Pt基催化剂被广泛的用作DFAFC阳极催化剂。要实现甲酸燃料电池的商业化需要进一步解决CO“毒化”和Pt负载量的问题。Pt基催化剂中加入第二种金属,如Pt/Ru, Pt/Pd, Pt/Au已经被研究作为DFAFC阳极催化剂的替代品。Au在DFAFCs环境中的高度稳定性使其成为铂合金的首选金属元素,引入Au有利于提高Pt催化剂对甲酸电催化氧化的活性。化学还原法,阳极氧化铝沉积法制得的纳米线若作为甲酸燃料电池的阳极还需要进一步的修饰,过程繁琐。直接电沉积组装纳米线是利用交流电场的作用在溶液中直接沉积纳米线的一种新方法。溶液中金属离子在电场作用下迁移还原并入晶格,形成密集、连续而且高晶的合金纳米线。这样得到的纳米线以金属键结合,热力学上稳定、结构上确定、性能上特殊,克服了由纳米粒子直接组装形成的纳米线机械稳定性差的缺陷,也省却了预先制备纳米粒子的过程,制得的纳米线可以直接用作甲酸催化氧化的阳极。本文将采用直接电沉积自组装法制备了PtAu合金纳米线。通过改变交流电参数和电沉积液组成,在金微电极上沉积组装形貌和成分可控的PtAu合金纳米线。通过SEM,TEM,EDS,XRD等方法对纳米线形貌,成分和结构进行表征。研究交流电沉积工艺参数对合成PtAu合金纳米线的影响；将不同成分的PtAu合金纳米线用于甲酸的阳极电氧化,研究合成的合金纳米线催化剂活性和稳定性,确定最优的成分比。研究获得如下结论：(1)电沉积液中添加剂的种类直接影响纳米线的分枝程度和成分范围。在电沉积液中添加0.5 mo1.dm-3的H3B 03作为添加剂能够稳定沉积液,增加沉积液的导电性进而调节沉积速率得到枝状合金纳米线。加入NH4Cl溶液,在相同条件下合成的纳米线分枝数目相对减少。加入NH3·H2O形成新的络合物,铂的还原速率降低,合金中Pt成分降低,表面结构不平整。(2)改变氯铂酸和氯金酸的浓度,可以调节PtAu合金纳米线中原子百分比。电沉积液的浓度浓度越大,得到的纳米线直径越大。Pt的成分越多形成的纳米线更光滑(3)交流电沉积时,电压和频率是直接电沉积的关键因素。电压阈值能够为金属离子的还原提供动力。在13mmol·dm-3 H2PtCl6·6H2O,0.2 mmol·dm-3 HAuCl4·4H2O和0.5 mol·dm-3 H3BO3的电沉积液中,采用正弦交流电信号一步直接电沉积PtAu合金纳米线,当保持沉积频率为20 MHz不变,低电压下得到粗糙的合金纳米线,电压为16-18 Vpp范围内可以得到结构明确,线条清楚的PtAu合金枝状纳米线。(4)电压和频率为枝状纳米线的产生提供足够的过电位。保持高电压16 Vpp不变,在1-20MHz频率范围内,随着频率的增加,离子还原速率和纳米线生长速率越快,纳米线的直径变小,PtAu合金纳米线侧分枝越明显。PtAu合金纳米线中Pt原子分数增加。(5)纳米线沿着电场的方向生长,在场强大的区域更容易发生枝状生长,而场强较小区域易形成一维纳米线结构。PtAu合金枝状纳米线的生长机理直接电沉积自组装理论来解释,枝晶的形成是扩散限制过程的典型产物。(6)通过对Au、Pt单金属纳米线及PtAu合金纳米线的XRD谱图分析,与Au、Pt单金属X衍射图谱对比,PtAu合金纳米线峰位置落于Au、Pt单金属之间,没有出现单金属特征峰。TEM和FFT结果显示合金纳米线是一种单相的合金结构。结果表明在PtAu纳米线结构中Au和Pt两种金属是合金化的。(7)将制得的Au、Pt单金属纳米线及Pt35Au65.Pt79Au21合金纳米线在0.5 mol·dm-3 HCOOH和0.5 mol·dm-3 H2SO4的混合溶液中进行循环伏安扫描,可知Pt35Au65、Pt79Au21氧化峰电流密度是Pt单金属纳米线的3和1.6倍,Pt35Au65纳米线氧化电位最负。在不同扫速下得到的氧化峰电流与扫描速率的平方根成线性关系,说明反应在电极表面是控制扩散的过程。
[Abstract]:The anodizing of nanomaterials for direct formic acid fuel cells (DFAFC) has been studied for nearly ten years and is becoming an important field in the research of portable power systems. Compared with direct methanol fuel cells (DMFC), formic acid has a small cross pass through the Nafion membrane and can allow the use of highly concentrated fuel solution at DFAFC. A thinner film. And methanol is easy to reduce the battery performance through the Nafion membrane. Formic acid is a liquid substance at room temperature and is a safe food additive. Since 2002, the Pt based catalyst has been widely used as a DFAFC anode catalyst. To commercialize formic acid fuel cells, the CO "poison" and Pt load need to be further solved. Problem.Pt based catalyst, adding second metals, such as Pt/Ru, Pt/Pd, Pt/Au, has been studied as a substitute for DFAFC anode catalyst,.Au in DFAFCs environment, the high stability made it become the preferred metal element of platinum alloy. The introduction of Au to improve the activity of the Pt catalyst to the electrocatalytic oxidation of METHIC acid. Chemical reduction method, Yang Jiyang The nanowires, as the anode of formic acid fuel cells, need to be further modified and the process is complicated. The direct electrodeposition of nanowires is a new method of direct deposition of nanowires in solution using the action of AC electric field. The metal ions in the solution are transferred to the lattice under the action of the electric field, and the concentration is formed. Continuous and high crystalline alloy nanowires. The obtained nanowires are bonded by metal bonds, thermodynamically stable, structurally determined, and special in performance, overcoming the defects of poor mechanical stability of nanowires directly assembled by nanoparticles, and the process of preparing nanoparticles in advance. The nanowires can be directly used as armour. PtAu alloy nanowires were prepared by the direct electrodeposition self assembly method. By altering the alternating current parameters and the composition of the electrodepositing fluid, the PtAu alloy nanowires, which were assembled on the gold microelectrodes, were deposited on the microelectrodes. The morphology, composition and structure of the nanowires were characterized by SEM, TEM, EDS, XRD and other methods. The effect of AC deposition process parameters on the synthesis of PtAu alloy nanowires was investigated. The PtAu alloy nanowires with different components were used for the anodic oxidation of formic acid. The activity and stability of the synthesized alloy nanowire catalysts were studied and the optimal composition ratio was determined. The following conclusions were obtained: (1) the types of additives in the electrodeposition effusion were directly affected by the types of additives. The branching degree and composition range of the rice line. Adding 0.5 mo1.dm-3 H3B 03 to the electrodepositing fluid can stabilize the deposition fluid as an additive, increase the conductivity of the deposition fluid and adjust the deposition rate to get the dendrite nanowires. The number of branched nanowires synthesized by adding NH4Cl solution is relatively reduced. The formation of NH3. H2O is formed. The reduction rate of platinum is reduced, the composition of Pt in the alloy decreases and the surface structure is uneven. (2) the change of the concentration of chloro platinum acid and chlorauric acid can adjust the percentage of atoms in the PtAu alloy nanowires. The greater the concentration of the electrodepositing liquid, the greater the diameter of the nanowires, the more the nanowires form more smooth (3) alternating current (.Pt). Voltage and frequency are the key factors for direct electrodeposition. The voltage threshold can provide power for the reduction of metal ions. In the 13mmol. Dm-3 H2PtCl6. 6H2O, 0.2 mmol, dm-3 HAuCl4 4H2O and 0.5 mol dm-3 H3BO3, the sinusoidal alternating current signal is used to direct the direct deposition of the nanowires of the PtAu alloy when the deposition frequency is kept. The rate is 20 MHz constant, the coarse alloy nanowires are obtained at low voltage and the voltage is 16-18 Vpp in the range. The PtAu alloy branch nanowires with clear structure and clear lines. (4) voltage and frequency provide sufficient overpotential for the generation of branched nanowires. Keep high voltage 16 Vpp unchanged and increase with frequency within the range of 1-20MHz frequency. Adding, the faster the ion reduction rate and the nanowire growth rate, the smaller the diameter of the nanowires, the more obvious the Pt atom fraction of the.PtAu alloy nanowires increased in the side branch of the PtAu alloy nanowires. (5) the nanowires grow along the electric field, and the presence of the field is easier to occur in the field, and the field strength is easier to form a Wiener line structure than the area. The growth mechanism of.PtAu alloy branched nanowires is explained by direct electrodeposition theory. The formation of dendrites is a typical product of the diffusion limiting process. (6) by analyzing the XRD spectra of Au, Pt single metal nanowires and PtAu alloy nanowires, the peak position of PtAu alloy nanowires falls on Au, Pt single metal, compared with Au, Pt single metal X diffraction patterns. No single metal peak.TEM and FFT results show that the alloy nanowires are a single phase alloy structure. The results show that the two metals of Au and Pt are alloyed in the PtAu nanowire structure. (7) the mixed Au, Pt single metal nanowires and Pt35Au65.Pt79Au21 alloy nanowires are mixed in the 0.5 mol dm-3 HCOOH and 0.5 mol. The cyclic voltammetry in the combined solution shows that the peak current density of Pt35Au65, Pt79Au21 oxidation is 3 and 1.6 times of the Pt nanowires, and the oxidation potential of the Pt35Au65 nanowires is the most negative. The peak current of oxidation at different speeds is linear with the square root of the scanning rate, indicating that the reaction is the process of controlling the diffusion on the surface of the electrode.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O643.36

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