Correlation between CO Oxidation and H Adsorption/Desorption on Pt Surfaces in a Wide pH Range: The Role of Alkali Cations

Abstract

It is well‐known that hydrogen adsorption/desorption on Pt open surfaces sites (110 and 100) shows a dependence on the pH below a pure Nernstian shift. Also, it is recognized that the oxidation of CO (and organic molecules) on Pt open surface electrodes occurs at more negative potentials in alkaline media than in acidic solutions. In contrast, both electrochemical processes develop a pure Nernstian behavior at the close‐packed Pt(111) over the whole pH range. The current work employs experimental results of hydrogen desorption and carbon monoxide oxidation on Pt electrodes with different surface orientations over a wide pH range to reveal that the unusual Nernstian behavior observed at open surface sites is linked to an electrochemical process for both reactions, owing to the fact that similar absolute values are detected. Furthermore, the nature and concentration of alkali cations appear to play an important role in the mutual electrochemical process.

Well‐Defined Platinum Surfaces for the Ethanol Oxidation Reaction

“…Furthermore, anions and cations play an important role in electrocatalysis at low and high pH, respectively . Sulfate and phosphate species adsorb stronger on Pt surfaces than perchlorate species and therefore higher catalytic activity toward the EOR in perchloric acid solution is observed.…”

“…Sulfate and phosphate species adsorb stronger on Pt surfaces than perchlorate species and therefore higher catalytic activity toward the EOR in perchloric acid solution is observed. On the other hand, at high pH metal cation species change the adsorption potential of hydroxide species at open surface, which are necessary to oxidize and remove the main catalyst poison (CO) from the catalyst surface . The role of alkali cations (Li + , Na + , K + , Cs + , and Be 2+ ) on the oxidative stripping of carbon monoxide from stepped Pt single‐crystal electrodes in alkaline media has been reported .…”

“…[22] Furthermore, anions and cations play an important role in electrocatalysis at low and high pH, respectively. [23,24] Sulfate and phosphate species adsorb stronger on Pt surfaces than perchlorate species and therefore higher catalytic activity toward the EOR in perchloric acid solution is observed. On the other hand, at high pH metal cation species change the adsorption potential of hydroxide species at open surface, which are necessary to oxidize and remove the main catalyst poison (CO) from the catalyst surface.…”

“…On the other hand, at high pH metal cation species change the adsorption potential of hydroxide species at open surface, which are necessary to oxidize and remove the main catalyst poison (CO) from the catalyst surface. [23,24] The role of alkali cations (Li + , Na + , K + , Cs + , and Be 2 + ) on the oxidative stripping of carbon monoxide from stepped Pt single-crystal electrodes in alkaline media has been reported. [25] Main results suggested that Li + and Be 2 + cations markedly affect the adsorption of OH (at both on steps and on terraces) and thereby have a significant promoting effect on the CO oxidation reaction.…”

Methanol Oxidation on Graphenic-Supported Platinum Catalysts

“…Interestingly, Pt/rGO-TT and Pt/C develops inflection points at short times at the same potential range (0.65 ≤ E ≤ 0.75), where the onset potential for the CO removal ( Figure 5) and the pre-peak at the potentiodynamic experiments in presence of methanol is observed ( Figure 6). This result suggests a change of rate-determining step (RDS), which may be attributed to an enhancement of the water dissociation reaction (i.e., OH ad formation) necessary to remove CO from the catalyst surface [34,35]. Additionally, it is observed that at E ≥ 0.85 V (anodic peak during the positive sweep potential, Figure 6), the current decay is faster at Pt/rGO-TT and Pt/C, which is related to the low performance of Pt oxide surface toward the MOR [36].…”