关键词: 催化剂, TiO₂, 锐钛矿, 金红石, 电化学活性面积

Abstract:

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.

Key words: catalyst, TiO₂, anatase, rutile, electrochemical active surface area