Study of the Nature of Formic Acid Adsorbates on Rough Pt and its Interaction with CO
Xia Xinhua((波恩大学物理化学所,Wegelerstrabe 12, D 253115 Bonn, Germany)
Iwasita T.((波恩大学物理化学所,Wegelerstrabe 12, D 253115 Bonn, Germany)
- 1997年第3卷 
应用现场红外反射光谱（ＦＴＩＲ）和微分电化学质谱（ｄｉｆｆｅｒｅｎｔｉａｌｅｌｅｃｔｒｏｃｈｅｍｉｃａｌｍａｓｓｓｐｅｃｔｒｏｍｅｔｅｒ，ＤＥＭＳ）研究了甲酸在多孔Ｐｔ上吸附质的性质．伏安结果显示了甲酸在多孔Ｐｔ上吸附质的氧化与吸附电位和吸附时间有关．在线质谱结果表明从甲酸吸附质氧化成二氧化碳所需要的电子数（ｎｅ）与吸附电位无关．显然地ｎｅ＝２．２说明了甲酸吸附质是由ＣＯ和ＣＯＨ组成，而不是只有单一的ＣＯ或者ＣＯＨ．另一方面，在１２６２ｃｍ－１和２０４８ｃｍ－１出现的现场红外光谱带证实了甲酸在多孔Ｐｔ上的吸附质中存在ＣＯ和ＣＯＨ表面物质．此外，用ＤＥＭＳ技术和碳－１３同位素标的甲酸作探针研究了甲酸吸附质和ＣＯ的相互作用．结果表明溶液中的甲酸不能取代先吸附的ＣＯ，而溶液中的ＣＯ可以与７５％先吸附的甲酸吸附质发生交换．The nature of formic acid adsorbates formed on porous platinum electrode has been studied by in situ infrared reflectance spectroscopic (FTIR) and differential electrochemical mass spectroscopic (DEMS) techniques. By carefully avoiding the contamination of the environment( i.e ., air) voltammetric experiments show that the oxidation of formic acid adsorbates depends on both adsorption potential and adsorption time. The online DEMS results show furthermore that the number of electrons necessary for the formation of one molecule of CO 2 from adsorbed formic acid is independent of the adsorption potential. Its value of 2.2 demonstrates that the composition of formic acid adsorbates is a mixture of CO and COH, but not CO or COH alone. The existence of these two species has been clearly proved by in situ FTIR experiments on electrodeposited platinum with a roughness factor of 11. The bands at 1 262 cm -1 , 1 840 cm -1 , and in the frequency range of 2 048 to 2 060 cm -1 are due to the surface adsorbed COH, bridge and linearly bound CO ad , respectively. In addition, the interaction between formic acid adsorbates and CO has been investigated by using DEMS via isotopic labelled 13 C formic acid as a probe as well. These experiments show that the surface species previously fromed from CO and formic acid cannot be exchanged by formic acid in solution. whereas about 75 percent of the firstly formed formic acid adsorbates can be replaced by bulk CO.