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  本文選題：PtAu合金 + 納米線��； 參考：《湖南大學(xué)》2015年碩士論文

【摘要】：納米材料用于直接甲酸燃料電池(DFAFC)的陽極氧化已經(jīng)研究了近十年,并正在成為便攜式電源系統(tǒng)的研究的一個重要領(lǐng)域。與直接甲醇燃料電池(DMFC)相比,甲酸通過Nafion膜具有較小的交叉通量在DFAFC可以允許使用高度濃縮燃料溶液或更薄的膜。而甲醇容易透過Nafion膜使電池性能下降。甲酸是在室溫下一種液體物質(zhì),并且是安全的食品添加劑。自2002年以來,Pt基催化劑被廣泛的用作DFAFC陽極催化劑。要實現(xiàn)甲酸燃料電池的商業(yè)化需要進(jìn)一步解決CO“毒化”和Pt負(fù)載量的問題。Pt基催化劑中加入第二種金屬,如Pt/Ru, Pt/Pd, Pt/Au已經(jīng)被研究作為DFAFC陽極催化劑的替代品。Au在DFAFCs環(huán)境中的高度穩(wěn)定性使其成為鉑合金的首選金屬元素,引入Au有利于提高Pt催化劑對甲酸電催化氧化的活性�；瘜W(xué)還原法,陽極氧化鋁沉積法制得的納米線若作為甲酸燃料電池的陽極還需要進(jìn)一步的修飾,過程繁瑣。直接電沉積組裝納米線是利用交流電場的作用在溶液中直接沉積納米線的一種新方法。溶液中金屬離子在電場作用下遷移還原并入晶格,形成密集、連續(xù)而且高晶的合金納米線。這樣得到的納米線以金屬鍵結(jié)合,熱力學(xué)上穩(wěn)定、結(jié)構(gòu)上確定、性能上特殊,克服了由納米粒子直接組裝形成的納米線機(jī)械穩(wěn)定性差的缺陷,也省卻了預(yù)先制備納米粒子的過程,制得的納米線可以直接用作甲酸催化氧化的陽極。本文將采用直接電沉積自組裝法制備了PtAu合金納米線。通過改變交流電參數(shù)和電沉積液組成,在金微電極上沉積組裝形貌和成分可控的PtAu合金納米線。通過SEM,TEM,EDS,XRD等方法對納米線形貌,成分和結(jié)構(gòu)進(jìn)行表征。研究交流電沉積工藝參數(shù)對合成PtAu合金納米線的影響；將不同成分的PtAu合金納米線用于甲酸的陽極電氧化,研究合成的合金納米線催化劑活性和穩(wěn)定性,確定最優(yōu)的成分比。研究獲得如下結(jié)論：(1)電沉積液中添加劑的種類直接影響納米線的分枝程度和成分范圍。在電沉積液中添加0.5 mo1.dm-3的H3B 03作為添加劑能夠穩(wěn)定沉積液,增加沉積液的導(dǎo)電性進(jìn)而調(diào)節(jié)沉積速率得到枝狀合金納米線。加入NH4Cl溶液,在相同條件下合成的納米線分枝數(shù)目相對減少。加入NH3·H2O形成新的絡(luò)合物,鉑的還原速率降低,合金中Pt成分降低,表面結(jié)構(gòu)不平整。(2)改變氯鉑酸和氯金酸的濃度,可以調(diào)節(jié)PtAu合金納米線中原子百分比。電沉積液的濃度濃度越大,得到的納米線直徑越大。Pt的成分越多形成的納米線更光滑(3)交流電沉積時,電壓和頻率是直接電沉積的關(guān)鍵因素。電壓閾值能夠為金屬離子的還原提供動力。在13mmol·dm-3 H2PtCl6·6H2O,0.2 mmol·dm-3 HAuCl4·4H2O和0.5 mol·dm-3 H3BO3的電沉積液中,采用正弦交流電信號一步直接電沉積PtAu合金納米線,當(dāng)保持沉積頻率為20 MHz不變,低電壓下得到粗糙的合金納米線,電壓為16-18 Vpp范圍內(nèi)可以得到結(jié)構(gòu)明確,線條清楚的PtAu合金枝狀納米線。(4)電壓和頻率為枝狀納米線的產(chǎn)生提供足夠的過電位。保持高電壓16 Vpp不變,在1-20MHz頻率范圍內(nèi),隨著頻率的增加,離子還原速率和納米線生長速率越快,納米線的直徑變小,PtAu合金納米線側(cè)分枝越明顯。PtAu合金納米線中Pt原子分?jǐn)?shù)增加。(5)納米線沿著電場的方向生長,在場強(qiáng)大的區(qū)域更容易發(fā)生枝狀生長,而場強(qiáng)較小區(qū)域易形成一維納米線結(jié)構(gòu)。PtAu合金枝狀納米線的生長機(jī)理直接電沉積自組裝理論來解釋,枝晶的形成是擴(kuò)散限制過程的典型產(chǎn)物。(6)通過對Au、Pt單金屬納米線及PtAu合金納米線的XRD譜圖分析,與Au、Pt單金屬X衍射圖譜對比,PtAu合金納米線峰位置落于Au、Pt單金屬之間,沒有出現(xiàn)單金屬特征峰。TEM和FFT結(jié)果顯示合金納米線是一種單相的合金結(jié)構(gòu)。結(jié)果表明在PtAu納米線結(jié)構(gòu)中Au和Pt兩種金屬是合金化的。(7)將制得的Au、Pt單金屬納米線及Pt35Au65.Pt79Au21合金納米線在0.5 mol·dm-3 HCOOH和0.5 mol·dm-3 H2SO4的混合溶液中進(jìn)行循環(huán)伏安掃描,可知Pt35Au65、Pt79Au21氧化峰電流密度是Pt單金屬納米線的3和1.6倍,Pt35Au65納米線氧化電位最負(fù)。在不同掃速下得到的氧化峰電流與掃描速率的平方根成線性關(guān)系,說明反應(yīng)在電極表面是控制擴(kuò)散的過程。
[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.
【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TB383.1;O643.36

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本文編號：2050611