Surface processes and kinetics of CO2 reduction 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 (COB) species, which give rise to IR absorption near 1840 cm−1. However both bridge- and linear-bonded CO (COL, 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 COL and COB bands indicates that coverage by reduced CO2 species (r-CO2, or COL and COB 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 υi, 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 υi (υim) measured on Pt(100) electrodes with different surface structures all appeared at − 0.19 V. From analysis of the relationship between υim and γ we have determined that the υim 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.