Abstract
The electro-oxidation of CO on Pt surface is not only fundamentally important in electrochemistry, but also practically important in residential fuel cells for avoiding the poisoning of Pt catalysts by CO. We carried out cyclic voltammetry on Pt(111), (110), (100), (10 10 9), (10 9 8), (10 2 1), (432), and (431) single-crystal surfaces using a three compartment cell to understand the activity and durability towards the electro-oxidation of CO saturated in 0.1 M HClO4. During the potential cycles between 0.07 and 0.95 V vs. the reversible hydrogen electrode, the current for the electro-oxidation of CO at potentials lower than 0.5 V disappeared, accompanied by surface reconstruction. Among the electrodes, the Pt(100) electrode showed the lowest onset potential of 0.29 V, but the activity abruptly disappeared after one potential cycle; the active sites were extremely unstable. In order to investigate the processes of the deactivation, potential-step measurements were also conducted on Pt(111) in a CO-saturated solution. Repeated cycles of the formations of Pt oxides at a high potential and Pt carbonyl species at a low potential on the surface were proposed as the deactivation process.
Highlights
The electrochemical oxidation of CO, on the Pt surface, is one of the most fundamental and most studied electrochemical reactions [1,2,3]
Many papers have been devoted to the oxidation of a pre-adsorbed monolayer of CO, often referred to as CO stripping, which usually occurs at a relatively high potential, in the 0.7 to 1.0 V range, vs. the reversible hydrogen electrode (RHE), within a narrow potential range, far from the equilibrium potential for the reaction
By examining cyclic voltammograms (CVs) in N2 -saturated HClO4 before and after the potential cycling in the CO-saturated solution, we propose the surface reconstruction on all the Pt electrodes
Summary
The electrochemical oxidation (electro-oxidation) of CO, on the Pt surface, is one of the most fundamental and most studied electrochemical reactions [1,2,3]. Many papers have been devoted to the oxidation of a pre-adsorbed monolayer of CO, often referred to as CO stripping, which usually occurs at a relatively high potential, in the 0.7 to 1.0 V range, vs the reversible hydrogen electrode (RHE), within a narrow potential range, far from the equilibrium potential for the reaction,. A current can often be observed in the lower potential region, from 0.3 to 0.5 V vs RHE, depending both on the characteristics of the Pt surface and to some extent on the potential at which CO was initially adsorbed. This current has been referred to as “pre-peak,” “pre-wave,” “pre-oxidation”, or “pre-ignition” current. With the use of an electrolyte solution saturated with CO (bulk CO), the current can flow steadily, since CO is being supplied continuously from the solution, in contrast to the case of pre-adsorbed CO, which is only a monolayer of CO adsorbed on the surface
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