The role of sodium surface species on electrochemical promotion of catalysis in a Pt/YSZ system: The case of ethylene oxidation

• Sodium added on Pt/YSZ system affects catalytic and electrocatalytic properties.
• Proposed model considers work-function changes by promoter species independently.
• High Na coverage causes interaction among promoter species and reaction components.
• Reaction changes from electrophilic to volcano and electrophobic at high Na coverage.

The role of sodium addition as foreign (impurity) species on the electrochemical promotion of ethylene oxidation in a Pt/YSZ system was investigated. It was found that the presence of sodium surface species on the catalyst surface can significantly affect its catalytic and electrocatalytic properties, but there is no clear evidence at this stage that such species are necessary for the observation of EPOC. Under negative polarisation, low coverage sodium was found to have a pronounced effect on the electrochemical promotion of ethylene oxidation as an electronic promoter. The reaction changed behaviour from electrophilic at low sodium coverage (0.11%) and low to intermediate oxygen partial pressure (pO2 ⩽ 3.0 kPa) to electrophobic at high sodium coverage (65%) and under high oxygen partial pressures (pO2 = 8.0 kPa). In between the two sets of conditions, the reaction showed volcano-type behaviour depending on the coverage of sodium and gas-phase oxygen partial pressure.

The role of sodium, as an ex situ added surface species, on the electrochemical promotion of ethylene oxidation in a Pt/YSZ system was investigated. It was found that the presence of sodium on the catalyst surface can significantly affect its catalytic and electrocatalytic properties; moreover, experimental results indicated an interaction between the two promoting species (sodium and oxygen ions) especially at high sodium coverage (above 50%).Figure optionsDownload high-quality image (153 K)Download as PowerPoint slide