Pd-Sb/C复合纳米催化剂对甲酸电催化氧化的性能研究

Preparation and Characterization of Carbon Supported Pd-Sb Composite Nanocatalysts for Formic Acid Electrooxidation

以柠檬酸三钠为稳定剂,硼氢化钠为还原剂,制备了碳载型的Pd-Sb复合纳米催化剂(Pd-Sb/C),通过调制不同Pd:Sb摩尔比研究了其对甲酸电催化性能的影响.TEM结果表明,合成的纳米颗粒粒径较小且均匀分散在碳载体表面.XRD和XPS测试表明,Pd-Sb/C中少量的单质态Sb(0)高度分散在Pd颗粒中或表面,形成合金化程度较低的Pd Sb合金.电化学测试表明,当Pd:Sb=20:1时,合成的催化剂对甲酸的催化效能最佳.与合成的Pd/C和商业Pd/C相比,Pd-Sb/C(20:1)的电流密度分别是Pd/C的2.6倍、商业Pd/C的4.2倍.Pd-Sb/C的整体催化性能得到改善主要归因于适量的单质态Sb(0)引入到Pd中,诱导产生电子效应和"双功能"效应,一方面减小Pd与CO毒性物种之间的吸附作用,另一方面促使Pd表面吸附的CO快速氧化,提高了Pd-Sb/C催化剂的抗CO中毒能力,使得Pd-Sb/C催化剂的整体催化性能得到改善.

Palladium is considered as an efficient anode catalyst with high catalytic activity for electrooxidation of formic acid. To further improve the catalytic activity and stability, alloying or surface modification with Sb is an effective way. In this work, the well dispersed carbon supported Pd-Sb composite nanocatalysts （Pd-Sb/C） were synthesized by traditional impregnation reduction method with trisodium citrate as the complexing agent, sodium borohydride as the reducing agent. The morphologies of Pd-Sb/C and the effects of molar ratio of Pd to Sb on the electrocatalytic properties of Pd-Sb/C for HCOOH electrooxidation were studied. The XRD and XPS analyses on the as-prepared Pd-Sb/C catalyst revealed that Sb（0） was presented on the Pd surface, and the im- mature alloying of Pd with Sb was achieved. Cyclic voltammetryic and chronoamperometric studies indicated a volcano-shaped re- lationship between Sb content and electrocatalytic activity with an optimum molar ratio of Pd：Sb=20：1. Compared with the com- mercial Pd/C catalyst, the Pd-Sb/C （20：1） presented the highest electrocatalytic activity and best stability. This enhancement may be attributed to the electronic effect and bi-functional effect induced by addition of Sb onto Pd surface, resulting in a weaker adsorption and accelerated oxidative removal of CO poison formed during HCOOH electrooxidation.