碳材料电化学腐蚀的质谱-电化学循环伏安(MSCV)法的研究: I. 溶液pH值对不同 碳材料的影响

用MSCV法研究了活性炭及乙炔黑在pH1-12范围内的电氧化,两种炭的φ~s、η~s与pH的关系(φ~s及η~s是CO~2开始析出的电位及超电位)以及I~M、φ~I与pH的关系(I~M、φ~I分别为给定电位下的质谱强度及给定I~M下的电位)均为一折点在的pH～7的折线。这暗示酸、碱介质中有不同的氧化机理。pH>7时,η~s及Tafel斜率b均较pH<7时的大。似可推断在酸性介质中形成CO~2所需的氧原子来自水分子放电,其活性明显大于来自碱性溶液中OH^-放电产生的氧原子。因而在酸性介质中炭氧化为CO~2较碱性介质中易于进行。两种炭之间氧化活性亦有明显区别。活性炭的φ~s比φⅲ(O~2/H~2O)负400-600mV;乙炔黑的φ~s则接近或正于φⅲ(O~2/H~2O)。前者的I~M及b均后者大。乙炔黑较低的氧化活性可归因于其较高的有序性结构。

MSCV studies of carbon electrooxidation: I. Influences of pH on different carbon materials

The electrooxidation of active carbon and acetylene black was studied using MSCV (Mass Spectroscopic Cyclic Voltammetry) technique over pH 1-12. For both active carbon and acetylene black the pH dependences of φ~s and η ~s (the onset potential and overpotential of CO~2 formation), I~M (the mass intensity of CO~2 at a given potential) and φ ~I (the potential at a given mass intensity) are all broken lines deflecting near pH 7. These phenomena imply that the mechanism of carbon oxidation is different in acidic and basic media. Both η~s and Tafel slope b in the range of pH>7 were found higher than that in pH<7. Based on these observations it is postulated that in acidic media the O atom needed for CO~2 formation comes from the discharge of H~2O molecules and the oxidation of carbon to CO~2 is easier than in basic media where the O atom comes from the discharge of OH^-. There were also distinct differences between active carbon and acetylene black. φ~s was found 400-600mV lower than φⅲ (O~2/H~2O) for active carbon but close to or higher than φⅲ (O~2/H~2O0 for acetylene black. At the same time, I~M and b of the former were higher than the latter. The lower oxidation activity of acetylene black is attributed to its more highly ordered structure.