论文部分内容阅读
本文采用“一锅法”将氧化石墨烯(GO)、炭黑(C)和钯离子用NaBH4共还原,制备了石墨烯-炭黑二元载体(Gr-C)负载的钯催化剂(20%Pd/Gr-C),用于催化甲酸的电氧化反应.电化学测试结果表明,前驱体GO和C的质量比为3:7的Pd/Gr_(0.3)C_(0.7)催化剂催化活性最好,它的峰电流密度(102.14 mA mgPd~(-1))约为Pd/C催化剂(34.40 mA mgPd~(-1))的3倍,为钯/石墨烯催化剂(Pd/Gr,38.50 mA mgPd~(-1))的2.6倍.甲酸在Pd/Gr_(0.3)C_(0.7)催化剂电极直接氧化时的峰电位比Pd/C催化剂的峰电位负移约120mV,比Pd/Gr催化剂的峰电位负移约70 mV.采用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、拉曼光谱、电感耦合等离子发射光谱(ICP-AES)等手段对催化剂进行了表征.从SEM图像可以观察到,球形的炭黑团簇聚集在具有褶皱的石墨烯面上,形成了炭黑团簇/石墨烯三维立体结构,有效地抑制了相邻石墨烯层在范德华力作用下的吸引聚集和堆叠造成的石墨烯表面积减小,减小了单层石墨烯叠合成为多层石墨所造成的导电性损失,避免了相邻石墨烯片叠合形成封闭空间,有助于反应物和产物分子的运动.载体的三维结构使反应物分子更容易到达钯纳米粒子,有利于催化性能的提高.XPS结果也证实了二元Gr-C载体对Pd催化的促进作用.Pd/Gr_(0.3)C_(0.7)催化剂的Pd 3d5/2峰发生了右移,表明Pd 3d电子结合能正移,Pd 3d电子云密度降低.具有较低的3d电子云密度的Pd不易与甲酸氧化过程中吸附的中间体(COOH)ads结合,钯催化剂上(COOH)ads表面覆盖率降低,从而使甲酸更容易直接脱氢氧化生成CO_2,有利于甲酸通过直接途径进行电化学氧化.与Pd/C,Pd/Gr相比,Pd/Gr_(0.3)C_(0.7)催化剂对甲酸电氧化有最好的催化活性.Pd/Gr_(0.3)C_(0.7)催化剂优异的催化活性可归因于其内在的三维纳米结构:炭黑团簇有效地抑制了石墨烯纳米片的聚集,保持了其大的比表面积和高导电性,促进了反应物和产物分子的运动.此外,Pd纳米粒子与二元载体之间的强相互作用降低了Pd的3d电子云密度,使甲酸氧化主要经直接途径进行.本文证实了钯金属和石墨烯-炭黑二元载体之间的强相互作用,提供了简单和高性价比的方法以提高钯基催化剂的活性,有利于工业化的应用
In this paper, graphene-carbon black binary supports (Gr-C) supported palladium catalysts were prepared by co-reduction of graphene oxide (GO), carbon black (C) and palladium ions with NaBH4 using "one- 20% Pd / Gr-C) was used to catalyze the electrooxidation of formic acid.The results of electrochemical tests showed that the catalytic activity of Pd / Gr_ (0.3) C_ (0.7) The best peak current densities (102.14 mA mgPd -1) were about three times that of Pd / C catalyst (34.40 mA mgPd -1) and were palladium / graphene catalysts (Pd / Gr, 38.50 (mg · dm ^ (-1)), and the peak potential of formic acid at Pd / Gr_ (0.3) C_ (0.7) was lower than that of Pd / C by about 120mV, The peak potentials were negative-shifted by about 70 mV.The structures of the samples were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and inductively coupled plasma atomic emission spectrometry ICP-AES) were used to characterize the catalyst.From the SEM images, it can be observed that the spherical carbon black clusters accumulate on the graphene surface with the folds, forming the three-dimensional structure of carbon black clusters / graphene effectively Adjacent graphene is suppressed The graphene surface area caused by the attraction, aggregation and stacking by the van der Waals forces is reduced, which reduces the conductivity loss caused by the monolayer graphene superimposition as the multi-layer graphite, and avoids the overlapping of adjacent graphene sheets to form a closed Space to facilitate the movement of reactants and product molecules.The three-dimensional structure of the carrier makes the reactant molecules reach the palladium nanoparticles more easily, which is beneficial to the improvement of the catalytic performance.XPS results also confirm that the binary Gr-C supports Pd-catalyzed Pd 3d5 / 2 peak of Pd / Gr_ (0.3) C_ (0.7) catalyst shifted to the right, indicating that Pd 3d electron binding energy can move forward and Pd 3d electron cloud density decrease with a lower 3d electron cloud density Pd is not easy to combine with the adsorbed intermediates (COOH) ads in the formic acid oxidation, the surface coverage of the (COOH) ads on the palladium catalyst is reduced, so that the formic acid is easier to be directly dehydrogenated to form CO 2, which facilitates the formic acid to be directly electrochemically Oxidation.The Pd / Gr_ (0.3) C_ (0.7) catalyst has the best catalytic activity for formic acid oxidation compared with Pd / C and Pd / Gr.The excellent catalytic activity of Pd / Can be attributed to its inherent three-dimensional nanostructures: carbon black clusters effectively suppressed The aggregation of graphene nanosheets keeps its large specific surface area and high conductivity and promotes the movement of reactants and product molecules.In addition, the strong interaction between Pd nanoparticles and binary carriers reduces the 3d of Pd Electron cloud density, the Formic acid oxidation is mainly carried out by direct route.This paper confirms the strong interaction between palladium metal and graphene-carbon black binary carrier, provides a simple and cost-effective method to improve the activity of palladium-based catalyst, Is conducive to industrial applications