兼具高孔隙率和梯度孔隙结构的多孔钯块材的制备、表征及其电化学性能研究（英文）
发布时间：2019-04-29 12:10
【摘要】：钯材料广泛用于氢同位素储存和分离、催化和传感等领域.传统的负载钯催化材料具有优异的乙醇和甲醇等电化学催化氧化性能.除此之外,负载钯催化材料还具有优异的甲烷催化燃烧性能.然而,很多研究显示负载钯催化材料存在很多不足,例如在工程应用过程中不稳定,纳米颗粒会发生聚集和长大,进而引起材料性能急剧下降等.不同于钯片、海绵钯粉末和负载钯催化材料,多孔钯具有三维连通的孔隙结构,可避免团聚现象的发生.同时,多孔钯还具有一些特殊的物理化学性能.研究表明,梯度孔隙结构是一种高效的电化学催化结构.因而近年来很多研究者都致力于探索具有高孔隙率和梯度孔隙结构多孔钯块材的制备方法.已有的研究包括造孔剂法和模板法等,但上述方法制得的多孔钯块材均存在比表面积低或难以获得块体材料缺点.我们研究组发展了一种制备兼具高孔隙率和梯度孔隙结构的多孔钯块材的新方法.即通过以一定粒度的NaCl颗粒作为造孔剂放电等离子烧结制备PdAl合金复合块材,然后通过去离子水溶解获得多孔PdAl合金,最后经过在盐酸溶液中去合金化得到具有数十微米的宏观大孔和约10纳米的纳米孔等梯度孔隙结构的多孔钯块材.当造孔剂添加量为20 vol.%,制得了孔隙率高达88%且完整的多孔钯块材.对该多孔钯块材的力学性能进行了测试,其压缩强度为0.5 MPa.对该块材进行氮吸附测试,测试结果显示其比表面积达到54 m~2/g.我们进一步对该多孔钯块材的乙醇电化学催化氧化性能进行了研究.对不同扫描速度下多孔钯块材在KOH(1 mol/L)+乙醇(0.8 mol/L)溶液中电催化活性进行分析.随着扫描速率从10 mV/s提高到50 mV/s,正扫描峰电流密度也逐渐提高,且峰电位向正电位方向移动.对峰电流密度和扫描速率的平方根进行拟合,发现它们之间存在明显的线性关系,表明该电催化氧化行为是一个受扩散控制的过程.随着溶液中乙醇浓度不断增加,正扫描方向乙醇氧化峰的峰电流呈现出先增大后减小的趋势.这是因为乙醇基和羟基在钯表面的竞争性吸附造成的.当乙醇浓度较高时,乙醇基会占据钯表面大量的活性位,从而阻碍和抑制羟基的吸附.此时,羟基在钯表面的吸附成为电氧化反应的控制因素.因此,只有选择合适的乙醇浓度,才能更好地发挥材料的电催化性能.当乙醇浓度为2 mol/L时,峰电流最大,达到120 mA/cm~2,表明多孔钯块材具有优异的电催化性能,这与该材料的梯度孔隙结构、高比表面积和高孔隙率密切相关.进一步对多孔钯块材的催化稳定性进行研究.该多孔钯块材显示出了优异的催化稳定性,当经过50次循环后,乙醇氧化峰的峰电流仅下降到~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..
【作者单位】： 成都大学机械工程学院;四川大学材料科学与工程学院;澳大利亚莫纳什大学化学学院理学院;
【基金】：supported by the National Natural Science Foundation of China(11572057) the School Foundation of Chengdu University(2080516030)~~
【分类号】：O643.36;O646
[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..
【作者单位】： 成都大学机械工程学院;四川大学材料科学与工程学院;澳大利亚莫纳什大学化学学院理学院;
【基金】：supported by the National Natural Science Foundation of China(11572057) the School Foundation of Chengdu University(2080516030)~~
【分类号】：O643.36;O646
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