jp055949s_si_001.pdf (23.1 kB)
Structure Sensitivity of Methanol Electrooxidation Pathways on Platinum: An On-Line Electrochemical Mass Spectrometry Study
journal contribution
posted on 2006-05-25, 00:00 authored by Tom H. M. Housmans, Ad H. Wonders, Marc T. M. KoperBy monitoring the mass fractions of CO2 (m/z 44) and methylformate (m/z 60, formed from CH3OH + HCOOH)
with on-line electrochemical mass spectrometry (OLEMS), the selectivity and structure sensitivity of the
methanol oxidation pathways were investigated on the basal planesPt(111), Pt(110), and Pt(100)and the
stepped Pt electrodesPt(554) and Pt(553)in sulfuric and perchloric acid electrolytes. The maximum reactivity
of the MeOH oxidation reaction on Pt(111), Pt(110), and Pt(100) increases in the order Pt(111) < Pt(110) <
Pt(100). Mass spectrometry results indicate that the direct oxidation pathway through soluble intermediates
plays a pronounced role on Pt(110) and Pt(111), while, on Pt(100), the indirect pathway through adsorbed
carbon monoxide is predominant. In 0.5 M H2SO4, introducing steps in the (111) plane increases the total
reaction rate, while the relative importance of the direct pathway decreases considerably. In 0.5 M HClO4,
however, introducing steps increases both the total reaction rate and the selectivity toward the direct oxidation
pathway. Anion (sulfate) adsorption on (111) leads to a more prominent role of the direct pathway, but, on
all the other surfaces, (bi)sulfate seems to block the formation of soluble intermediates. For both electrolytes,
increasing the step density results in more methylformate being formed relative to the amount of CO2 detected,
indicating that the [110] steps themselves catalyze the direct oxidation pathway. A detailed reaction scheme
for the methanol oxidation mechanism is suggested based on the literature and the results obtained here.