Combinations of graphene (Gr) and carbon black (C) were employed as binary carbon supports to fabricate Pd-based electrocatalysts via one-pot co-reduction with Pd2+. The electrocatalytic perfor-mance of the resulting Pd/Gr-C catalysts during the electrooxidation of formic acid was assessed. A Pd/Gr0.3C0.7 (Gr oxide:C = 3:7, based on the precursor mass ratio) electrocatalyst exhibited better catalytic performance than both Pd/C and Pd/Gr catalysts. The current density generated by the Pd/Gr0.3C0.7 catalyst was as high as 102.14 mA mgPd-1, a value that is approximately 3 times that obtained from the Pd/C (34.40 mA mgPd-1) and 2.6 times that of the Pd/Gr material (38.50 mA mgPd-1). The anodic peak potential of the Pd/Gr0.3C0.7 was 120 mV more negative than that of the Pd/C and 70 mV more negative than that of the Pd/Gr. Scanning electron microscopy images indi-cated that the spherical C particles accumulated on the wrinkled graphene surfaces to form C clus-ter/Gr hybrids having three-dimensional nanostructures. X-ray photoelectron spectroscopy data confirmed the interaction between the Pd metal and the binary Gr-C support. The Pd/Gr0.3C0.7 also exhibited high stability, and so is a promising candidate for the fabrication of anodes for direct for-mic acid fuel cells. This work demonstrates a simple and cost-effective method for improving the performance of Pd-based electrocatalysts, which should have potential industrial applications.%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/Gr0.3C0.7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/Gr0.3C0.7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120 mV,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/Gr0.3C0.7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CO2,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/Gr0.3C0.7催化剂对甲酸电氧化有最好的催化活性.Pd/Gr0.3C0.7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.
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