THE INFLUENCE OF TEMPERATURE ON THE KINETICS AND MECHANISM OF REDUCED CO2 ELECTROOXIDATION ON ELECTRODISPERSED PT IN 0.5-M H2SO4 AND 1-M H3PO4

The kinetics of reduced CO2 electrooxidation on electrodispersed Pt have been investigated in 0.5 M H2SO4 and 1 M H3PO4 in the 2-80°C range by voltammetric and potentiostatic methods. Kinetic data can be interpreted through a complex reaction pathway involving two different reduced CO2 adsorbates. The reaction mechanism advanced earlier at 25°C is valid as a first approach for interpreting the reaction in the entire temperature range and in different electrolytes. The influence of temperature and potential sweep rate on the kinetic response of the system shows that an interconversion process involving the different CO2 adsorbates should be considered in the reaction mechanism. The interconversion process can explain the voltammetric peak multiplicity change with v and T. The apparent activation energy (80±15 kJ mol-1) is the same for the electrooxidation of both reduced CO2 adsorbates. This figure can be interpreted in terms of a modification of clathrate-type CO2 adsorbates into an intermediate which immediately decomposes electrochemically into H+, H2O and CO2. The influence of CO2 adsorbates on the H-atom electrosorption/electrodesorption reactions is also discussed. © 1990.