The electrooxidation of formic acid and methanol

A large body of work has been published and recently reviewed on spectroscopic evidence of the adsorption and transformation of formic acid on Pt and Pt alloy surfaces according to reactions (34) and (35) [130,131]. Pt was found to interact weakly up to a potential of 0.2 V/RHE. Above this electrode potential, both reaction pathways were found to be present. Reaction (34) was estabhshed as the dominant process with reaction (35) being the site-blocking side reaction. On Ru, however, formic acid reacted distinctly differently. Here formic acid decomposition into surface COads was found to be very pronounced even at very low electrode potentials. 

Bulk Pt alloys for the electrooxidation of formic acid have been less frequently studied compared to underpotential deposition (upd) modified Pt surfaces. The Pt50Ru5o surface was again found to be one of the most active Pt-Ru surfaces. Underpotentially deposited metals, such as Bi, Se, Sb, were studied as reaction modifiers for Pt surfaces and provided significant electrocatalytic activity increases. Electronic factors (ligand effects) rather than bifunctional effects were held responsible for these activity modifications, because the metal coverages that caused the activity gains were extremely small. 

The electrooxidation of methanol has attracted tremendous attention over the last decades due to its potential use as the anode reaction in direct methanol fuel cells (DMFCs). A large body of literature exists and has been periodically reviewed [130,131,156], [173-199]. Unlike for formic acid, a generally accepted consensus on the specific mechanistic pathways of methanol electrooxidation is still elusive. 

Spectroscopic evidence, in particular DEMS [130], strongly suggests that adsorbed CO is not just forming in a parallel poisoning pathway, but that it constitutes a mechanistic intermediate, at least at low to medium electrode potentials of 0.2- 

In this chapter, we have described modern electrochemical surface science and catalysis and shown fundamental correlations between the structure, bonding, composition and electrocatalytic reactivity at the interface. 

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