几种商业催化剂电氧化二甲醚的催化性能研究

通过循环伏安法研究了三种商业催化剂--40%Pt/C, 20%Pt-10%Ru/C(Johnson Matthey)和 20%PtRu/C, Pt:Ru =1:1(E-TEK)在酸性介质中对二甲醚电氧化的催化性能,比较了不同商业催化剂的催化活性.实验发现,在Pt担载量为0.1 mg/cm2和25 ℃时,JM-两种催化剂的催化活性都高于E-TEK的,且JM-PtRu/C二元催化剂对二甲醚电氧化的活性又比JM-Pt/C高.这一结果表明了Ru的加入能一定程度上提高催化剂的活性和抗中毒能力.当温度由25 ℃升高到70 ℃,JM-PtRu/C对二甲醚电氧化的起始氧化和氧化峰电位分别负移160 mV和200 mV、氧化峰电流密度提高了0.63倍;而JM-Pt/C的分别仅负移80 mV和96 mV、氧化峰电流密度却提高了2.77倍.这表明了Ru 的加入提高了催化剂的抗中毒能力、催化活性和以二甲醚为燃料的电池输出电压.同时升高温度使得Pt对CO的吸附能力下降,可提高其电池的输出电流.进一步实验还表明了二甲醚的吸附是一个弱吸附,其吸附步骤是氧化的限制过程,而且Ru的加入一定程度上也抑制了二甲醚的吸附,即Pt和Ru的比应有一个优化值.实验还发现了这三种催化剂在50 ℃下电催化氧化二甲醚后,电极的电化学表面积均有增大的现象.本文的研究结果将为进一步探索新的直接二甲醚燃料电池阳极催化剂提供了一定的指导意义和基础数据.

Studies on electrocatalysis of three types of commercialised catalysts to dimethyl-ether oxidation

The electrooxidation of dimethyl ether (DME) on commercialised Pt/C and PtRu/C catalysts from Johnson Matthey (JM) and E-TEK in acid solution were investigated by the traditional electrochemistry method. The experimental results showed that catalysts from JM had better electrocatalytic activity and higher tolerance to the poisonous species for electrooxidation of DME at a loading of 0.1mg/cm2 and 25 ℃, and the JM's PtRu/C had the best performance and that showed that the addition of a second metal Ru enhanced the tolerance of Pt to the poisonous species of CO. When the reaction temperature was raised from 25 ℃ to 70 ℃, the onset and peak potentials of the DME electrooxidation shifted negatively 160 mV and 200 mV, respectively, the peak current density increased more than 0.63 times, while those values from JM's Pt/C only had negative shifts of 80 mV and 96 mV, respectively, but the current density increased more than 2.77 times. The above results showed that the introduction of Ru not only gave the best catalytic activity and lowest adsorption to CO species, but also would give better output of the cell potential. Raising the reaction temperatures will make ions move fast and weak the adsorption of CO to Pt and could increase the output of the cell current density. The E-TEK's PtRu/C showed the lowest electrocatalytic activity to DME oxidation. The experimental results also indicated that the adsorption of DME is likely to be rate determined step in the DME oxidation process and was suppressed with the addition of second metal Ru. So it is essential to optimize the atomic ratio of Pt and Ru. The results will be very helpful to find out new catalysts for DME oxidation and DME fuel cells.