Surface science studies of model fuel cell electrocatalysts

The oxidation of small organic molecules: A survey of recent fuel cell related research

Pyridinium and its substituted derivatives are effective and stable homogeneous electrocatalysts for the aqueous multiple-electron, multiple-proton reduction of carbon dioxide to products such as formic acid, formaldehyde, and methanol. Importantly, high faradaic yields for methanol have been observed in both electrochemical and photoelectrochemical systems at low reaction overpotentials. Herein, we report the detailed mechanism of pyridinium-catalyzed CO2 reduction to methanol. At metal electrodes, formic acid and formaldehyde were observed to be intermediate products along the pathway to the 6e−-reduced product of methanol, with the pyridinium radical playing a role in the reduction of both intermediate products. It has previously been thought that metal-derived multielectron transfer was necessary to achieve highly reduced products such as methanol. Surprisingly, this simple organic molecule is found to be capable of reducing many different chemical species en route to methanol through six sequential e...

Using a one-electron shuttle for the multielectron reduction of CO2 to methanol: kinetic, mechanistic, and structural insights.

The oxidation of formic acid on thin, epitaxially-grown Pd overlayers on Au and Pt single crystal electrodes was studied as a function of overlayer thickness ranging from submonolayer coverages up to the equivalent of 10 monolayers. The results were compared with those for massive Pd single crystal surfaces. The electrocatalytic properties of the Pd overlayers were found to depend markedly on their thickness and on their crystallographic orientation. Pd(100) showed the highest catalytic activity of all three low-index faces, and Pd films on Pt(hkl), even when two or three layers thick, generally exhibited a much higher activity than Pd films on Au(hkl) or massive Pd(hkl). In all cases a high resistivity of the Pd surfaces against poisoning by CO was observed, which makes Pd an interesting alternative to the often quickly deactivated Pt as catalyst for organic fuel cell reactions.

Formic Acid Oxidation on Ultrathin Pd Films on Au(hkl) and Pt(hkl) Electrodes

An FTIR and quadrupole mass spectroscopic study of CO adsorption and oxidation with 16O2 and 18O2 on copper supported on ZnO and TiO2 is presented. The experimental results indicate that CO is adsorbed on the metallic particles dispersed on both oxides on two kinds of sites, on the normal terrace sites and on sites at the borderline of the particles. Moreover, on titania, a band at 2126 cm-1, assigned to CO adsorbed on isolated Cu atoms and/or on two-dimensional small clusters, is detected. A frequency shift of the bands of CO adsorbed on the metallic particles observed in the CO−O2 coadsorption experiments and the occurrence of a scrambling reaction between CO and 18O2 reveal that on all these samples, there are metallic sites which are able to adsorb at the same time oxygen atoms and carbon monoxide. Carbon dioxide and carbonate-like species are formed:  the asymmetric stretching frequencies of CO2 and the quadrupole mass spectroscopic analysis reveal that with 18O2, different isotopic molecular CO2's a...

C. Lamy

Papers

A study by electrochemically modulated infrared reflectance spectroscopy of the electrosorption of formic acid at a platinum electrode

Infrared study of adsorbed species on electrodes: Adsorption of carbon monoxide on Pt, Rh and Au