Surface processes and kinetics of CO2reduction on Pt(100) electrodes of different surface structure in sulfuric acid solutions

Abstract

The reduction of CO₂ on a Pt(100) electrode in CO₂ saturated 0.5 M H₂SO₄ solutions was studied by in situ FTIR reflection spectroscopy and a programmed potential step technique. Different surface structures of Pt(100) electrode were prepared by different treatments including fast potential cycling (200 V s⁻¹) for a known time. The Pt(100) surface was characterized by a parameter γ that designates the relative amplitude of the current peak of hydrogen adsorption on (100) sites distributed on the one-dimensional surface domains to that on the two-dimensional surface domains. The in situ FTIR spectroscopic results demonstrated that the reduction of CO₂ on the Pt(100) dominated by two-dimensional surface domains produced only bridge-bonded CO (CO_B) species, which give rise to IR absorption near 1840 cm⁻¹. However both bridge- and linear-bonded CO (CO_L, yielding IR absorption at around 2010 cm⁻¹) species are found for CO₂ reduction on the Pt(100) dominated by one–dimensional surface domains. The small intensity of the CO_L and CO_B bands indicates that coverage by reduced CO₂ species (r-CO₂, or CO_L and CO_B species) is low. The cyclic voltammetric (CV) studies confirmed quantitatively the in situ FTIRS results, and revealed that the r-CO₂ species adsorb preferentially on (100) sites distributed on the two-dimensional surface domains. The initial rate of CO₂ reduction υ_i, i.e., the rate of CO₂ reduction on a clean Pt(100) surface, has been determined quantitatively from studies using a programmed potential step technique. It has been demonstrated that the maximum values of υ_i (υ_i^m) measured on Pt(100) electrodes with different surface structures all appeared at − 0.19 V. From analysis of the relationship between υ_i^m and γ we have determined that the υ_i^m of CO₂ reduction on (100) sites distributed on the two-dimensional surface domains is 0.53 × 10⁻¹¹ mol cm⁻² s⁻¹ and that on (100) sites distributed on the one-dimensional surface domains is approximately 2.66 × 10⁻¹¹ mol cm⁻² s⁻¹. Based on in situ FTIRS and electrochemical studies a migration process of the r-CO₂ from the one-dimensional surface domains to the two-dimensional surface domains has been proposed to be involved in CO₂ reduction. The present study has thrown new light on the electrocatalytic activity of different surface structures of a Pt(100) electrode and the surface processes and kinetics of CO₂ reduction.