甲酸在铂上电氧化的吸附中间物和机理的研究

根据pH对(甲酸+甲酸钠)/Pt体系的循环伏安图的图形和峰电位。甲酸/Pt和一氘代甲酸(DCOOH)/Pt循环伏安图的对比,以及in situ甲酸预吸附的实验,表明甲酸是通过O—H键的断裂而在铂表面上发生解离吸附,生成中间物HCOO_(2d)。在铂表面上,HCOO_(2d)可呈多种吸附态。甲酸的正常电氧化(即不考虑强吸附中间物的形成和氧化)是按反应序列(3)进行的。

STUDY ON INTERMEDIATES AND MECHANISM FOR OXIDATION OF FORMIC ACID ON PLATINUM ANODE

(1) The effect of pH on the cyclic voltammogram of platinum in HClO_4 containing HCOOH and HCOONa mixture was observed. The results show that the shape of the cyclic voltammogram of platinum is similar in all cases, but the peak potentials decrease with the increase of pH (see Fig.2). In addition, the oxidation peak for cathodic sweep consists of two sub-oxidation peaks which overlap each other and their current curves are coadjacent(see Fig.4).(2) The experiment suggested by Razaq and Pletcher for the comparison between the rates of the electrooxidation of HCOOH and DCOOH on platinum was repeated. The results are coincident essentially, that is, there is a noticeable isotopic effect (see Fig.5).(3) The experiment of pre-adsorption of formic acid in situ shown in the PTS in Fig.6 was programmed. It appears that the peak current for the first oxidation peak in i-E profile in creases after pre-adsorption, but decreases with the increase of pre-adsorbed time.(4) According to the facts mentioned above, we suggest that a dissociative adsorption of formic acid on platinum surface takes place by cleaving a O—H bond, and an adsorbed intermediate HCOO_(ad) which behaves as the multiple adsorbed states is formed. The ordinary oxidation of formic acid (i.e. making on mention of formation and oxidation for the strongly adsorbed intermedites) on platinum anode proceeds via the reaction sequence(3).