由于燃料电池催化剂的电催化活性与Pt颗粒尺寸、催化剂载体、辅助催化剂的关系仍不清楚。为此,本文采用FESEM、 XRD、 BET、 TEM和CV等方法,以存在Pt纳米颗粒、 CN_x纳米线、 TiO₂辅助催化剂的多成分复杂结构Pt/TiO₂-CN_x体系为研究对象,进行了TiO₂锐钛矿(A)/金红石(R)相含量对Pt电催化剂电化学活性面积的研究。结果表明,TiO₂在700 ^oC ~ 900 ^oC热处理过程中发生锐钛矿-金红石相变,同时伴随着两相晶粒尺寸的长大,锐钛矿相在900 ^oC时完全转化为金红石相。TEM结果表明超细小Pt纳米颗粒成功负载在TiO₂-CN_x载体表面,粒径尺寸范围为1.8 ~ 2.8 nm。TiO₂ (A)/(R)相含量对TiO₂-CN_x载体的BET比表面积和Pt/TiO₂-CN_x催化剂真实“有效的”电化学活性面积(ECSA)都存在“火山形”效应。当金红石相含量为25%时,TiO₂(25%R)-CN_x载体和Pt/TiO₂(25%R)-CN_x催化剂具有最大的比表面积和最多的电化学活性位点。原因推测可能是随着金红石相含量的增加,当金红石含量为25%时Pt纳米颗粒和TiO₂(25%R)-CN_x载体之间存在强烈的金属-载体相互作用,可以锚定超细小Pt纳米颗粒,导致Pt/TiO₂(25%R)-CN_x催化剂具有最高的ECSA。因此,Pt/TiO₂(25%R)-CN_x较适宜做燃料电池的催化剂。

The relationship between the electrochemical activity of fuel cell catalysts and Pt particle size, as well as the catalyst support and co-catalyst is still unclear. In this work, FESEM, XRD, BET, TEM and CV techniques were adopted to investigate the effects of TiO₂ anatase (A)/rutile (R) phases content on the electrochemical activity of Pt electrocatalyst. The results showed that the anatase-rutile phase transformation occurred during the heat treatment of TiO₂ at 700 ~ 900 ^oC accompanied by the growth of two-phase crystalline size, and anatase was completely transformed into rutile at 900 ^oC. TEM results revealed that the ultrafine Pt electrocatalysts with the particle size of 1.8 ~ 2.8 nm were successfully prepared over the TiO₂-CN_x supports. The content of TiO₂ (A)/(R) phases had a “volcano-type” effect on both the BET surface area of TiO₂-CN_x supports and the real “effective” electrochemical active surface area (ECSA) of Pt/TiO₂-CN_x catalysts. When the rutile content was 25%, the TiO₂(25%R)-CN_x support and Pt/TiO₂(25%R)-CN_x catalyst had the largest specific surface area and the most electrochemical active sites, respectively. It is speculated that raising the rutile content, there might be a strong metal-support interaction between Pt nanoparticles and TiO₂(25%R)-CN_x support with the rutile content of 25%, which could anchor the ultrafine Pt nanoparticles, resulting in the highest ECSA of Pt/TiO₂(25%R)-CN_x catalyst. Therefore, the Pt/TiO₂(25%R)-CN_x became more suitable as a catalyst for fuel cells.