【摘要】：鈀材料廣泛用于氫同位素儲(chǔ)存和分離、催化和傳感等領(lǐng)域.傳統(tǒng)的負(fù)載鈀催化材料具有優(yōu)異的乙醇和甲醇等電化學(xué)催化氧化性能.除此之外,負(fù)載鈀催化材料還具有優(yōu)異的甲烷催化燃燒性能.然而,很多研究顯示負(fù)載鈀催化材料存在很多不足,例如在工程應(yīng)用過程中不穩(wěn)定,納米顆粒會(huì)發(fā)生聚集和長大,進(jìn)而引起材料性能急劇下降等.不同于鈀片、海綿鈀粉末和負(fù)載鈀催化材料,多孔鈀具有三維連通的孔隙結(jié)構(gòu),可避免團(tuán)聚現(xiàn)象的發(fā)生.同時(shí),多孔鈀還具有一些特殊的物理化學(xué)性能.研究表明,梯度孔隙結(jié)構(gòu)是一種高效的電化學(xué)催化結(jié)構(gòu).因而近年來很多研究者都致力于探索具有高孔隙率和梯度孔隙結(jié)構(gòu)多孔鈀塊材的制備方法.已有的研究包括造孔劑法和模板法等,但上述方法制得的多孔鈀塊材均存在比表面積低或難以獲得塊體材料缺點(diǎn).我們研究組發(fā)展了一種制備兼具高孔隙率和梯度孔隙結(jié)構(gòu)的多孔鈀塊材的新方法.即通過以一定粒度的NaCl顆粒作為造孔劑放電等離子燒結(jié)制備PdAl合金復(fù)合塊材,然后通過去離子水溶解獲得多孔PdAl合金,最后經(jīng)過在鹽酸溶液中去合金化得到具有數(shù)十微米的宏觀大孔和約10納米的納米孔等梯度孔隙結(jié)構(gòu)的多孔鈀塊材.當(dāng)造孔劑添加量為20 vol.%,制得了孔隙率高達(dá)88%且完整的多孔鈀塊材.對(duì)該多孔鈀塊材的力學(xué)性能進(jìn)行了測(cè)試,其壓縮強(qiáng)度為0.5 MPa.對(duì)該塊材進(jìn)行氮吸附測(cè)試,測(cè)試結(jié)果顯示其比表面積達(dá)到54 m~2/g.我們進(jìn)一步對(duì)該多孔鈀塊材的乙醇電化學(xué)催化氧化性能進(jìn)行了研究.對(duì)不同掃描速度下多孔鈀塊材在KOH(1 mol/L)+乙醇(0.8 mol/L)溶液中電催化活性進(jìn)行分析.隨著掃描速率從10 mV/s提高到50 mV/s,正掃描峰電流密度也逐漸提高,且峰電位向正電位方向移動(dòng).對(duì)峰電流密度和掃描速率的平方根進(jìn)行擬合,發(fā)現(xiàn)它們之間存在明顯的線性關(guān)系,表明該電催化氧化行為是一個(gè)受擴(kuò)散控制的過程.隨著溶液中乙醇濃度不斷增加,正掃描方向乙醇氧化峰的峰電流呈現(xiàn)出先增大后減小的趨勢(shì).這是因?yàn)橐掖蓟土u基在鈀表面的競(jìng)爭(zhēng)性吸附造成的.當(dāng)乙醇濃度較高時(shí),乙醇基會(huì)占據(jù)鈀表面大量的活性位,從而阻礙和抑制羥基的吸附.此時(shí),羥基在鈀表面的吸附成為電氧化反應(yīng)的控制因素.因此,只有選擇合適的乙醇濃度,才能更好地發(fā)揮材料的電催化性能.當(dāng)乙醇濃度為2 mol/L時(shí),峰電流最大,達(dá)到120 mA/cm~2,表明多孔鈀塊材具有優(yōu)異的電催化性能,這與該材料的梯度孔隙結(jié)構(gòu)、高比表面積和高孔隙率密切相關(guān).進(jìn)一步對(duì)多孔鈀塊材的催化穩(wěn)定性進(jìn)行研究.該多孔鈀塊材顯示出了優(yōu)異的催化穩(wěn)定性,當(dāng)經(jīng)過50次循環(huán)后,乙醇氧化峰的峰電流僅下降到~110 mA/cm~2.
[Abstract]:Palladium materials are widely used in hydrogen isotope storage and separation, catalysis and sensing. The traditional supported palladium catalysts have excellent electrochemical catalytic oxidation properties such as ethanol and methanol. In addition, PD-supported catalytic materials also have excellent catalytic combustion performance of methane. However, many studies have shown that PD-supported catalysts have many shortcomings, such as instability in engineering applications, aggregation and growth of nano-particles, resulting in a sharp decline in the properties of materials, and so on. Unlike palladium sheet, sponge palladium powder and supported palladium catalyst, porous palladium has three-dimensional connected pore structure, which can avoid agglomeration. At the same time, porous palladium also has some special physical and chemical properties. The results show that the gradient pore structure is an efficient electrochemical catalytic structure. In recent years, many researchers have devoted themselves to exploring the preparation methods of porous palladium block with high porosity and gradient pore structure. The previous studies include pore-forming agent method and template method, but the porous palladium block prepared by the above-mentioned method has the disadvantage of low specific surface area or difficult to obtain bulk material. Our team has developed a new method for preparing porous palladium block with both high porosity and gradient pore structure. The composite block of NaCl alloy was prepared by spark plasma sintering with certain particle size of PdAl particles as pore-forming agent, and then the porous PdAl alloy was obtained by dissolving it with deionized water. After de-alloying in hydrochloric acid solution, porous palladium block with macropores of dozens of microns and nano-pores of about 10 nm was obtained. When the amount of pore-forming agent was 20 vol.%, the porous palladium block with 88% porosity was prepared. The mechanical properties of the porous palladium block were tested and the compressive strength was 0.5 MPa.. The results of nitrogen adsorption test showed that the specific surface area of the bulk material was 54 mg ~ 2 mg 路m ~ (- 1) 路h ~ (- 1). The electrochemical catalytic oxidation of ethanol in the porous palladium block was further studied. The electrocatalytic activity of porous palladium block in KOH (1 mol/L) ethanol (0.8 mol/L) solution at different scanning rates was analyzed. With the increase of scanning rate from 10 mV/s to 50 mV/s, the peak current density increases gradually, and the peak potential moves to the direction of positive potential. By fitting the square root of the peak current density and scanning rate, it is found that there is an obvious linear relationship between them, which indicates that the electrocatalytic oxidation is a diffusion controlled process. With the increase of ethanol concentration in the solution, the peak current of ethanol oxidation peak in the positive scanning direction increases first and then decreases. This is due to the competitive adsorption of ethanol and hydroxyl groups on the surface of palladium. When the concentration of ethanol is high, ethanol group occupies a large number of active sites on the surface of palladium, thus hindering and inhibiting the adsorption of hydroxyl groups. At this time, the adsorption of hydroxyl on the surface of palladium becomes the control factor of the electrooxidation reaction. Therefore, only when the appropriate ethanol concentration is selected, the electrocatalytic properties of the materials can be brought into play better. When ethanol concentration was 2 mol/L, the peak current reached 120 mA/cm~2, indicating that the porous palladium block had excellent electrocatalytic properties, which was closely related to the gradient pore structure, high specific surface area and high porosity of the material. The catalytic stability of porous palladium block was further studied. The porous palladium block showed excellent catalytic stability. After 50 cycles, the peak current of ethanol oxidation peak only decreased to ~ 110 mA/cm~2..
【作者單位】： 成都大學(xué)機(jī)械工程學(xué)院;四川大學(xué)材料科學(xué)與工程學(xué)院;澳大利亞莫納什大學(xué)化學(xué)學(xué)院理學(xué)院;
【基金】：supported by the National Natural Science Foundation of China(11572057) the School Foundation of Chengdu University(2080516030)~~
【分類號(hào)】：O643.36;O646

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